EP0868976A2 - Procédé et dispositif de polissage pour le polissage à grande vitesse avec un plateau abrasif rotatif - Google Patents

Procédé et dispositif de polissage pour le polissage à grande vitesse avec un plateau abrasif rotatif Download PDF

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Publication number
EP0868976A2
EP0868976A2 EP98301690A EP98301690A EP0868976A2 EP 0868976 A2 EP0868976 A2 EP 0868976A2 EP 98301690 A EP98301690 A EP 98301690A EP 98301690 A EP98301690 A EP 98301690A EP 0868976 A2 EP0868976 A2 EP 0868976A2
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EP
European Patent Office
Prior art keywords
platen
abrasive
sheet
work piece
lapped
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP98301690A
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German (de)
English (en)
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EP0868976A3 (fr
Inventor
Wayne O. Duescher
Gary A. Staus
Mark J. Luedtke
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Keltech Engineering Inc
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Keltech Engineering Inc
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Publication date
Application filed by Keltech Engineering Inc filed Critical Keltech Engineering Inc
Publication of EP0868976A2 publication Critical patent/EP0868976A2/fr
Publication of EP0868976A3 publication Critical patent/EP0868976A3/fr
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces

Definitions

  • the present invention relates to lapping, polishing, finishing or smoothing of surfaces with apparatus and processes which use abrasive sheeting.
  • the present invention relates to such processes and apparatus which use removable or replaceable abrasive sheeting which operates at high surface speeds and secures the abrasive sheeting to a platen on a flexible shaft which platen moves the sheeting at those high speeds.
  • the lapping system is capable of extremely smooth surface finishing at high speeds.
  • Lapping and polishing are performed in many fields and industries. Metal and parts polishing is the most obvious field, but smoothing of surfaces is extensively used in lens manufacture, semiconductive wafer manufacture, gem polishing, preparation of supports for optical elements, providing surfaces which can be joined or seamed and the like. The smoothness and reproducibility of the processes and apparatus used to create the needed levels of smoothness are critical to the success of products.
  • U.S. Patent No. 5,584,746 (Tanaka) describes a method of polishing semiconductor wafers and apparatus therefor. The import of Tanaka is the physical control placed over the wafer as it is being polished. The wafer is secured by a vacuum system on a wafer mounting plate.
  • the relative flexibility of the wafer is discussed as a method of controlling uniformity of the wafer surface as is the uniformity of the vacuum applied through the wafer support.
  • the polishing of the wafer surface is accomplished by typical means including a polishing pad which is mounted on a polishing surface (turntable). It is suggested that the pad should not be subject to plastic deformation and may be preferably selected from a group comprising close cell foam (e.g., polyurethane), polyurethane impregnated polyester non-woven fabric and the like, which are known materials in the art. No specific means of securing the polishing pad to the support surface is described in Tanaka. No specific speeds of rotation for the operation of the process are shown in the examples.
  • U.S. Patent No. 5,317,836 (Hasegawa) describes an apparatus for polishing chamfers of a wafer.
  • Hasegawa describes that in the manufacture of wafer materials from single crystal ingots such as silicon, the wafer is produced by a combination or selection of processes including slicing, chamfering, lapping, etching, buffing, annealing and polishing. It is noted that chipping and/or incomplete surface polishing are a problem in such ingot conversion to wafers.
  • Hasegawa describes the use of a rotary cylindrical buff formed with at least one annulargroove in its side describing a circle normal to the axis of the cylindrical buff and a wafer holder capable of holding and turning the wafer about an axis.
  • the improvement is described as including at least the ability of the cylindrical buff being adapted to freely shift axially, that the annular groove has a width substantially greater than the thickness of the wafer, and that the apparatus further comprises a means for axially biasing the cylindrical buff. No specific speeds of rotation for the operation of the process are shown in the examples.
  • U.S. Patent No. 5,007,209 (Saito) describes an optical fiber connector polishing apparatus and method. Saito describes a method and apparatus for polishing optical fiber connectors with high accuracy. Saito indicates that the polishing is accomplished by using an elastic polishing board rotating at high speed, but no specific speed of rotation or method of attachment of the polishing board is described. Positioning pins and other controls are provided in the system to accurately align the swing fulcrum arm carrying the polishing material.
  • U.S. Patent No. 4,085,549 describes a lens polishing machine comprising a lap tool holder and lens blank holder including independent means to provide linear and rotary movement between a lens blank and lap tool.
  • the machine is described as useful for high speed grinding and polishing.
  • the polishing element is gimbal mounted on its lower extreme in a spherical bearing to allow a lens blank holder to follow the contour of the lens during the polishing process.
  • the movement between the rotary drive and linear drive mechanisms independent of each other provides a balanced and low vibration operation. No specific speeds of rotation are recited and the abrasion is provided by a slurry.
  • U.S. Patent No. 4,612,733 (Lee) describes a very high speed lap with a positive lift effect.
  • the apparatus and method comprises a rotary lapping system which uses a liquid slurry of abrasive particles.
  • the diameters of the particles are shown to be from about 1.5 to 5 micrometers, but may be outside this range.
  • the system is described as producing positive lift by presenting leading edge surfaces with a positive angle of attack in the liquid abrasive slurry, the leading edge surfaces generating a positive lift through hydrodynamic interaction with the slurry.
  • Each of the positive lift tools presents a grinding surface to said workpiece when it is rotated in the slurry.
  • U.S. Patent No. 4,709,508 (Junker) describes a method and apparatus for high speed profile grinding of rotatably clamped rotation symmetrical workpieces. Rather than the grinding element contacting the surface to be ground with a grinding surface which is rotating within a plane, the edge of the grinding element (e.g., at the circumference of a disk rather than on its face) is brought against the surface to be ground.
  • U.S. Patent No. 5,197,228 describes methods and apparatus for grinding metal parts, especially with devices having a cooperative workpiece holder and a tool holder which form a grinding station.
  • the grinder table is reciprocally moveable along an axis which is at right angle to the axis of travel of the workpiece.
  • the grinder table may also be equipped for controlled simultaneous movement along two axes.
  • a microprocessor is designed to send and receive signals to or from all of the moving parts of the grinding machine for moving the workpiece table towards or away from the grinding bit.
  • U.S. Patent No. 4,194,324 describes a carrier for semiconductive wafers during polishing steps in their manufacture.
  • An annular flange is present to receive pressure loading from the polishing machine during the wafer polishing operation.
  • the holder of the polishing machine includes the ability to apply a vacuum to the carrier to maintain the carrier selectively on the polishing machine.
  • the arrangement on the equipment allows release of the vacuum during polishing and enables simple intentional removal of the carrier.
  • Cam follower-slot arrangements permit tilting of the mounting head.
  • U.S. Patent No. 5,576,754 describes a sheet holding device for an arcuate surface with vacuum retention.
  • the sheet and device are described as useful for internal drum plotters in imaging equipment. Vacuum pressure is applied to imaging film to keep it securely positioned within the arcuate focal plane of the imaging equipment.
  • U.S. Patent No. 5,563,683 describes a substrate holder for vacuum mounting a substrate.
  • the holder is provided with two kinds of grooves or clearances in the supporting surface. Circular support faces with multiple grooves and/or a plurality of pins to support the work are shown.
  • the device is generally described to be useful as a holder, with such particular uses as in the manufacture of semiconductors and the support of photosensitive substrate being shown.
  • U.S. Patent No. 4,943,148 describes a silicon wafer holder with at least one access port providing access to the underside of the wafer with vacuum pressure.
  • U.S. Patent No. 4,707,012 also describes a method of applying vacuum holding forces to a semiconductor wafer during manufacture in an improved manner.
  • U.S. Patent No. 4,620,738 shows the use of a vacuum pickup system for semiconductor wafers. The wafers are placed into or removed from holders by the vacuum pickup.
  • U.S. Patent No. 5,414,491 describes a vacuum holder for sheet materials comprising a plurality of arrays of vacuum channels including a plurality of vacuum plenums. Flow sensors are provided so that the system can indicate the presence and/or size of the sheets being held. Specifically described are common types of imaging materials using sheets of plain paper, photographic paper and photographic film.
  • U.S. Patent No. 5,374,021 describes a vacuum holding system which is particularly useful as a vacuum table for holding articles.
  • the holding table is particularly described with respect to the manufacture of printed circuit boards.
  • Controlled passageways are provided which are supposed to control the application of reduced pressure and to reduce the application of the vacuum when vacuum support is not required.
  • U.S. Patent No. 5,324,012 describes a holding apparatus for holding an article such as a semiconductor wafer. At least a portion of the holder contacting the wafer comprises a sintered ceramic containing certain conductive materials. The use of conductive materials and fewer pores reduces the occurrence and deposition of fine particles during use. The benefits of the materials are said to be in contributions to the cleanability of the surface, insurance of mechanical strength, reduction of weight and increased dimensional stability.
  • U.S. Patent No. 5,029,555 describes a holding apparatus and method for supporting wafers during a vacuum deposition process.
  • the apparatus is an improved system for the angled exposure of at least one surface portion of a substrate supported on a surface holder to an emission of a source impinging obliquely on the surface portion.
  • the device moves the surface holder to improve the uniformity of the emission received on the surface portion.
  • Wheel mechanisms are coupled together to provide maintenance capability for predetermined positions of the surface.
  • the substrate holder is moved while its orientation to the source is carefully controlled.
  • U.S. Patent Nos. 4,483,703 and 4,511,387 describe vacuum holders used to shape glass. Frames are shown with slidable members moving a deformable vacuum holder between a shaping station and a mold retraction station. Pistons drive movable elements, such as the vacuum holder, on a supporting frame.
  • U.S. Patent No. 4,851,749 describes a motor driven mechanical positioner capable of moving an arm to any one of about 840 discrete angular positions.
  • An infrared light emitting device acts with a phototransistor to control the appropriate angular position.
  • Sensing devices also act on interdependent speed controls so as to increase the accuracy of the positioning of the arm.
  • U.S. Patent No. 5.180,955 describes a positioning apparatus comprising an electromechanical system which provides controlled X-Y motion with high acceleration, high maximum speeds, and high accuracy, particularly for positioning an end-effector at predetermined locations.
  • a high speed mini-positioner is provided comprising a positioning linkage having a changeable parallelogram structure and a base structure.
  • a main benefit of the system is the fact that the bars and bearings of the positioner are symmetrical about the X-Y plane passing through the linkage height. The symmetry means that all actuator forces and all inertial reaction forces act in vectors lying in the plane of symmetry.
  • U.S. Patent No. 5,547,330 describes an ergonomic three axis positioner.
  • the positioner is intended to move an article along three mutually perpendicular axes through a system of interconnected slides and slide joints.
  • Rack and pinions are also used to independently move the slides.
  • the device is suggested for use in the visual inspection of work, particularly in the semiconductor industry.
  • U.S. Patent No. 4,219,972 describes a control apparatus for a grinding machine.
  • a revolution speeds changing means is provided which can selectively effect changes at high speeds when grinding and changes at low speeds when dressing the article.
  • U.S. Patent No. Re. 30,601 describes an apparatus and method particularly effective in the positioning of a semiconductor wafer in a preferred plane with respect to a photomask. Sensors regularly monitor the position of the wafer and a reference plane. A photoalignment system is provided in which a wafer is not physically touched by any portion of the photoalignment tool, thereby avoiding any contamination.
  • Lapping or polishing at high speeds with fine abrasive particles offer significant advantages in the speed of lapping, savings of time in lapping, and smoothness in the finished articles.
  • Materials, processes, apparatus and specific features integrated into the lapping processes and apparatus of the present invention can provide a unique lapping effect with regard to both the quality (smoothness and uniformity of the produced surface) and efficiency of the system.
  • the present invention relates to a new field of lapping technology with its own unique complexities due to the combination of high rotational speeds on the abrasive platen and the use of sheets of abrasive material rather than slurries. The combination of these two aspects creates dynamics and forces which have not been addressed by previous lapping systems and requires an entirely new background of engineering to address the problems.
  • One process of the present invention for lapping a surface comprises:
  • One preferred lapper system for practicing the present invention comprises:
  • Sequence of steps B comprising: a) providing a work piece to be lapped, having at least one surface to be lapped, which can be adjusted to a position parallel to said at least one surface of b) where
  • Another preferred aspect of the lapper system of the invention comprises:
  • Another preferred lapper platen system according to the present invention comprises:
  • Another aspect is a preferred process within the scope of the invention which comprises:
  • a very important process aspect of the present invention includes the initial positioning and contacting of the workpiece and the abrasive sheet material as in a process for initiating contact between a workpiece to be ground and an abrasive surface comprising abrasive sheeting on a rotatable platen, the process comprising:
  • pressure is applied between the work piece and the abrasive sheet by a flexible joint or engagement or gimbal supporting the work piece.
  • the pressure applied between the workpiece and the rotating platen may be from 0.1 psi to 100 psi, preferably from 0.1 to 25 psi, more preferably from 0.1 or 0.5 to 5 psi.
  • a particular improved process of the invention may be considered to comprise a process for lapping a surface comprising:
  • the plateau defines an annular shape on said front face, and more particularly where the sheet of abrasive material comprises a circular sheet or annular sheet of material.
  • the sheet of abrasive material most preferably comprises an annular shape in which a central open portion is at least three times the radial dimension as the width of said annular sheet.
  • a reduced gas pressure may be applied against said back surface of said sheet between said sheet and said platen through vents which are present at least or only on said flat surface of said plateau, the reduced pressure securing the sheet against rotational movement relative to the rotatable platen.
  • a preferred abrasive sheet comprises an annular distribution of abrasive material on a backing material, with a center area of said sheet being a self-supporting structure which passes across said center area, contacting inner edges of said annular distribution of abrasive material.
  • the central area may be free of abrasive material, such as where said abrasive sheet comprises a continuous substrate with a central area having no abrasive on said backing material, and an annular zone of said backing material surrounding said central area having abrasive material on a surface overlaying said plateau and facing away from said platen, or where said abrasive sheet comprises an annular zone and said central area, said central area being bonded to said annular zone, having less height than said annular zone when said sheet is lying flat, and there being a seam or bond between said annular zone and said central area.
  • abrasive material such as where said abrasive sheet comprises a continuous substrate with a central area having no abrasive on said backing material, and an annular zone of said backing material surrounding said central area having abrasive material on a surface overlaying said plateau and facing away from said platen, or where said abrasive sheet comprises an annular zone and said central area, said central area being bonded to said annular zone, having
  • a preferred lapper platen system according to the present invention may comprise:
  • Movement and control of movement of the workpiece holder can be extremely important in the performance of the present invention.
  • the control of the movement is best effected by the use of support systems for the workpiece which allow smooth motion of the workpiece, especially by air pressure, hydraulic pressure, linear electric motors and the like.
  • Another improved process for lapping a surface comprises: using a lapper system comprising:
  • a safety box system is also included within the lapping system which may include a means for introducing a first amount of liquid onto said abrasive surface of said platen at a location before contact between a work piece held on said work piece holder and said abrasive surface on said platen;
  • the second amount of water is larger than the first amount, the first amount providing a function as a lubricant, coolant, or the like, and the second amount assisting in washing away residue from the work piece and/or the abrasive sheet.
  • the means for directing air against the abrasive surface of the platen assisting in the rapid removal of the liquid and the solid matter carried with it.
  • a work piece holder may be used which has a control element thereon which allows for independent movement and alignment of said work piece holder along three perpendicular axes so that a work piece on said work piece holder can be adjusted and oriented towards parallelity with said platen so that a work piece can be lapped;
  • Rotating of said platen is done at a rotational velocity sufficient to generate a surface speed of at least 4,000 surface feet per minute (or even more than 20,000 surface feet per minute), which, depending upon the diameter of the rotating abrasive may be at an angular speed of at least 500 revolutions per minute (which with a 15.2 cm or 6 inch diameter platen and abrasive sheet, equates to over 700 surface feet per minute at the periphery of the abrasive surface), or even more than 3,000 revolutions per minute (which with a 15.2 cm diameter abrasive sheet equates to over 4200 surface feet per minute and with a 30.4 cm or 12 inch abrasive sheet equates to over 8400 surface feet per minute) and contacting said abrasive material with said work piece.
  • the process of the present invention allows the boundary layer of any liquid (e.g., coolant or lubricant) applied to the working surface of the abrasive sheet to be controlled to improve the uniformity of the lapped surface.
  • Figure 1 is a perspective view of a lapping apparatus according to the present invention.
  • Figure 2 is a perspective view of a lapping platen for supporting abrasive sheets according to the present invention.
  • Figure 3 is a cross-section of a lapping system according to the present invention.
  • Figure 4 is a perspective view of an apparatus for applying liquid to the surface of a lapping platen according to the present invention.
  • Figure 5 is a side view of a platen with raised peripheral edge portions.
  • Figure 6 is a perspective view of a platen with raised peripheral edge portions.
  • Figure 7 is a cutaway view of a platen with raised peripheral edge portions.
  • Figure 8 is a cutaway view of a different configuration of a platen with raised peripheral edge portions.
  • Figure 9 is a cutaway view of a platen with a pivot connection to a rotary shaft.
  • Figure 10 is a perspective view of a single Bellview spring washer.
  • Figure 11 is a cutaway view of a platen with a pivot control mechanism within a shaft.
  • Figure 12 is a perspective view of an annular platen with a beveled edge.
  • Figure 13 is an edge view of a platen with a beveled edge and a workpiece being lapped in a linear manner by said platen.
  • Figure 14 is an edge view of a workpiece and a platen.
  • Figures 15 are overhead views of abrasive platens with segments of abrasive sheets thereon.
  • Figure 16 shows a workpiece holder with a vertical vibration damping element on it.
  • Figure 17 shows a platen with abrasive sheeting thereon with special surface features to improve performance.
  • Figure 18 shows a workpiece holder with various orientations of gimbals to reduce tilting torque on the workpiece holder under high speed lapping.
  • Figure 19 shows an overhead view of a platen and multiple part workpiece holder according to one aspect of the present invention.
  • Figure 20 shows cross-sections of platens of an earlier but workable form (a) of the present invention, and two improved configurations (b) and (c) according to the present invention.
  • Apparatus and methods are needed for super high speed lapping at greater than 500 rpm, greater than 1500 rpm, higher than 2000 rpm, and even speeds of 2500, 3000 rpm and greater, equating to surface speeds at the periphery of the abrasive sheet of from about 500 to more than 25,000 surface feet per minute (sfpm, or sfm), depending upon the diameter of the platen and sheet as well as the angular speed.
  • these higher speeds should be useable with finer and harder pre-made abrasive materials without the use of liquid abrasive slurries.
  • a lapping apparatus comprises at least the following elements:
  • One process practiced in the present invention is a process for lapping a surface comprising:
  • Still another process according to the present invention includes a process for initiating contact between a workpiece to be ground and an abrasive surface comprising abrasive sheeting on a rotatable plate, said process comprising:
  • This process may effect mechanical alignment of said workpiece and/or said workpiece holder to promote parallelity between a surface of said workpiece to be ground and said abrasive surface after step c) but before step e).
  • the process may also have said controlling forces providing a contact force between 0.1 and 10 pounds per square inch between a surface of said workpiece to be ground and said rotating platen during lapping of said workpiece while said abrasive sheet is moving with at least 1,500 surface feet per minute while in contact with said workpiece.
  • the process may also have the workpiece holder supported by a pivot joint and said workpiece holder pivoting upon contact between said workpiece and said abrasive surface to hold a surface of said workpiece to be lapped in a more parallel orientation with said abrasive surface.
  • the protective walls that, rather than merely having four essentially vertical walls intercept material which is expelled from the work area by the rotational forces from the rotating platen (and often a rotating workpiece holder in conjunction with a rotating platen), the surfaces (the walls) which are intersected by the plane formed by the contact points between the platen and the workpiece are angled (hereinafter referred to as the intersection plane), sloped or curved so that impacting expelled material is deflected downward from the point of contact by the angle of impact.
  • This guard wall or enclosure is neither a trivial matter nor a system which is relevant to traditional lapping.
  • much lower rotational speeds such as 200 revolutions per minute and/or smaller diameters (producing lower surface speeds, e.g., less than 300 surface feet per minute) allow materials such as detritus, used slurry, cooling liquid and the like the flow or stream off the surface at speeds which are comparable to the rotational speeds of the platen.
  • the dynamics, problems, and failure of the system are unique and require differ considerations.
  • This event is unique to combination of the abrasive sheet and the high platen speed of rotation. Neither the abrasive sheeting alone nor high speed rotation (with slurry or powder) creates the forces effecting this explosive event.
  • the guard system is therefore uniquely necessary with the combined system of the present invention.
  • a process for lapping a surface according to this invention is also described wherein a back surface of the workpiece is pivotally connected to a rotating joint which is in turn connected to a shaft which rotates said workpiece, and said workpiece is allowed to pivot around said pivot joint as contact is made between said abrasive surface and said work piece so that said surface to be lapped becomes more parallel towards said platen after said contact as compared to before said contact.
  • the process for lapping a surface according to the present invention may also comprise an underlying process of:
  • One particular advantage of one optional alternative of the present invention is the ability of the apparatus to use preformed sheets of abrasive materials at high speeds, and to rapidly and cleanly replace the sheets without significant delays.
  • the apparatus During lapping and polishing processes, it is often necessary to change the abrasive medium at various stages.
  • the individual sheets were secured to the chuck or rotating face by an adhesive.
  • the adhesive may have been precoated on the backside of the abrasive sheet or applied as coating to the rotating support surface or the backside of the sheet immediately before use. This adhesive coating adds another parameter or variable which must be controlled in attempts to precisely lap surfaces.
  • some adhesives remain liquid or pliable (e.g., pressure-sensitive adhesives) and the centrifugal forces produced in high speed rotational abrasion can cause the adhesive to shift, flow or shear, altering the thickness of the adhesive layer even while the process is being performed.
  • One optional, but highly preferred aspect of the present invention therefore is to support a sheet having at least one abrasive workface and a backside on a rotatable support by vacuum forces, and to perform the abrading process with the vacuum forces maintaining at least part, if not all of the contact between the support and the backside of the sheet.
  • Adhesive supplemental forces may be particularly used to advantage where the adhesive contacts or adheres the abrasive sheet and the rotatable platen in a region which will not place the abrasive sheet into contact with the workpiece.
  • references described above do not describe rotational speeds in excess of 1500, 2000, 2500 or even 3000 rpm, or expressed in other units, with surface speeds at the periphery of the rotatable lapping platen of at least 550, at least 1,000, more preferably at least 1500 or at least 2,000 sfpm, still more preferably at least 2,500 or 3,000 sfpm, again still more preferably at least 3,500 or 4,000 sfpm, and most preferably at least 8,000 or 10,000 or even 12,000 and more sfpm. Furthermore, it is usually the abrasive segment of the apparatus and process of that prior art which is being rotated (although as shown in U.S.
  • the abrasive sheets comprise sheets of exposed abrasive grit as either a self-supporting sheet or film material or an adhered layer on a support sheet.
  • the sheets may have any type of abrasive material or surfacing on the face which is to contact the workpiece.
  • the preferred sheets are sheet abrasive material manufactured and sold by Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, and comprises either a polymeric backing sheet with high Mohs hardness abrasive particulates on a coated layer or a self supporting sheet of such high Mohs hardness abrasive particulates.
  • Preferred abrasive material comprises diamond particles or particles comprising small diamond particles supported in a binding matrix (other than any adhesive matrix forming the self-supporting layer or adhering the particles to a support).
  • the sheets may comprise a single layer of material (e.g., a binder with abrasive grit therein or sintered abrasive grit without any other binder) or multiple layers of materials.
  • Such multiple layers could comprise one or more supporting layers, intermediate layers (e.g., primer layers, vibrational damping layers, electrically conductive or antistatic layers, magnetic layers, printed layers, sealer or barrier layers to prevent migration of materials between other layers), and an abrasive outer layer.
  • the single layer, at least one layer in the combination of layers, or the interaction of the combination of layers must be able to support a vacuum against the back surface.
  • the back surface (of the abrasive sheet) itself is non-porous or low porosity. This is desirable as too much porosity would prevent the sheet from being held against the rotatable support surface.
  • the sheet does not have to be completely non-porous, although this is the preferred method of making the sheets used in the present invention, especially when combined with the vacuum draw-down of the abrasive sheets.
  • the back surface should not have such a degree of topography which would allow free air flow along the back surface when it is being held against a surface by a pressure of at least 8, 9, 10, 11 or at least 12 lb/in 2 . If there were raised channels, ridges or the like which would allow air flow from the center of the sheet to its outer edges, the pressure would not consistently support the sheet as air would more readily leak out from the region between the support surface and the backside of the abrasive sheet. That construction would be useful, but less preferred in the practice of the present invention.
  • the abrasive material may be any known abrasive material, depending upon the ultimate needs in the process for grinding, polishing or lapping a particular finished article.
  • the abrasive particulate or raised particulate areas may comprise any solid, hard, material such as silica, titania, alumina, Carborundum, boron nitride, homogeneous inorganic oxides (such as metal oxides) or blends of inorganic oxides, diamonds (natural or synthetic), or any other material which is harder than the solid surface to be polished, ground or lapped.
  • the abrasive surface may be abrasive particles bound in a binder, either partially embedded, superficially bound to the surface, or initially embedded so that the binder must initially wear away to expose the particles.
  • the abrasive surface may be a replicated surface structure of a pure abrasive material, an etched abrasive surface, molded surface or the like.
  • the abrasive surface may also be deposited islands of abrasive material, with either physicalprocesses used to place the abrasive (e.g., vapor deposition, screened application of powders which are fused, powder arrays which are electrostatically deposited and bonded to the surface, impact embedding of the particles) or chemical processes (e.g., electrochemical deposition, chemical deposition at seeded sites) to form the particles in a random or ordered manner.
  • the preferred material is an abrasive sheeting manufactured by Minnesota Mining and Manufacturing Co., known as Diamond Abrasive Disks (3M). These sheets are quite effective for the high speed, fine finish lapping processes and apparatus of the present invention.
  • Also useful in the practice of the present invention are diamond particles contained in a metal matrix on a sheet of plastic backing material (e.g., 3M Metal BondTM Abrasive).
  • 3M Metal BondTM Abrasive The only modification of the sheets which is essential for making them completely compatible with the present invention is having the sheet converted (cut) to fit the abrasion platen.
  • the sheets may be cut into, for example, circular shapes, with or without positioning holes or a centering hole in the sheet.
  • This abrasive sheet material has been able to provide an improvement at high speed lapping which was not recognized at lower speed lapping, where the problem was not notice and/or was not as significant.
  • the 3M Metal BondTM Abrasive has islands of the abrasive material, as opposed to having a continuous matrix of binder with the abrasive particles therein. The islands therefore allow swarf, debris and liquid to pass between the islands (driven by centrifugal forces) and away from the contact area between the abrasive sheet and the workpiece.
  • Figure 1 shows a perspective of a basic lapping apparatus 2 according to the present invention.
  • the apparatus 2 usually comprises at least a main support frame 4 with a vibration absorbing surface 6 which may be a single layer 6 as shown in Figure 1 or multiple layers (not shown).
  • the composition of the layer may be thick metal, layered metal, composite, coated metal, and the like.
  • Two thick sheets of metal (not shown) is preferred, with one sheet fixed to the main frame 4 and the other sheet fixed to the frame top 8 at the arms 12 or which is removably attached to the first layer (not shown).
  • There is also conveniently a frame top 8 which may be removably or permanently attached to the main frame 4 .
  • An electrical enclosure 10 is shown over the vibration absorbing surface 6 .
  • a supporting frame 14 is shown for a workpiece spindle 16 .
  • a computer 18 is also shown in the lapping apparatus 2 to provide controls over the operation.
  • the abrasive sheet (not shown) support platen 20 is located at a position on the vibration damping surface 6 over which the workpiece spindle 16 may be positioned.
  • Various positioning systems (later shown) which operate to keep the alignment of the workpiece spindle 16 and the abrasion support platen 20 can be preferred part of the apparatus 2 .
  • An abrasion platen drive motor 22 can be seen underneath the vibration damping surface 6 .
  • the size of the apparatus 2 is somewhat dependent upon the needs for the user.
  • the length 24 of the base of the main frame 24 may be, for example, between about 3 to 8 feet (0.9 to 2.42m), the width of the main frame may be, for example, between 1.5 feet and 4 feet (0.45 to 1.22m), and the height of the main frame may be, for example, between 1.5 feet and 4 feet (0.45 to 1.22m). Greater variations in the dimensions are of course possible, but the preferred dimensions are within this range, and especially between 4.5 feet and 5.5 feet (1.64 and 2.0m) in length and 2 to 3 feet (0.68 and 0.91m) in width and height.
  • a heavy construction is preferred, with at least 0.6cm thick steel plate in the arms 12, 30, 32, 34, 38, 40 , etc. (collectively referred to as the arms 12 .
  • the arms 12 may be hollow with sheet metal of that thickness or larger, or may be solid.
  • the dimensions of the arms 12 may be, for example, from 2 to twelve inches (5 to 31 cm) a side (assuming a square). This fairly massive composition will keep vibration to a minimum.
  • a four wall box 19 is shown surrounding the platen 20 above its flat surface (e.g., the plane of rotation of the surface).
  • a curved lip 21 is shown at the top of the four wall box 19 to prevent ricochet of exploded pieces and to deflect them down within the box 19 , possibly to a collection area (not shown).
  • FIG. 2 shows an abrasive platen 50 useful in the practice of the present invention.
  • a wide range of diameters is useful for such abrasive platens 50 .
  • Typical diameters are from 7.5 to 50 cm, more preferably from 7.5 to 40 cm in diameter.
  • the abrasive platens 50 of the invention are provided with a sufficient number of ports or holes (not numbered) to enable a vacuum to be distributed against the backside of an abrasive sheet (not shown).
  • three circular distributions of such holes 52, 54, 56 are shown distributed as a series of holes 58 .
  • the holes 58 are a convenient, exemplary distribution, but are not essential to the practice of the present invention.
  • Vacuum access to the backside of an abrasive sheet may be provided in many different types of distribution.
  • the distributions do not even have to be symmetrical, but should be reasonably distributed so that sections of an abrasive pad will not lift from the platen 50 during high speed rotation while other areas are secure.
  • a circular distribution is convenient as the abrasive sheets generally used tend to be circular to fit with the circular motion of rotation and the usually circular shape of the platen 50 . Other shapes may be selected, but they would tend to be prone to greater eccentricities in their motion and therefore would be less desirable.
  • the circular set 52 of holes 58 nearer the center of the top surface 66 of the platen 50 help to secure the center portion of an abrasive pad to the platen 50 .
  • the circular distributions 54 and 56 tend to secure an abrasive pad to the surface 66 of the platen 50 along a radius 60 .
  • the number and spacing of holes on the platen surface 66 are designed to secure an abrasive sheet without the holes (e.g., 58 ) being so large as to deform the sheet into the contours (not shown) of the holes.
  • Holes on the surface are preferably less than 5 mm in diameter, more preferably less than 4 mm, still more preferably less than 3.5 or less than 3.0 mm, and most preferably greater than 0.5 mm and less than 3 mm.
  • the minimum size and number is determined by that number and size which will support a vacuum against the backside of an abrasive sheet. A minimum size of about 0.2 mm is a reasonable starting point for commercial design. Smaller holes would clog too easily from materials produced during operation of the apparatus. More preferred would be diameters of at least 0.5 mm, more preferably at least 0.7, still more preferably at least 1.0 mm. These are average diameters, and hole sizes that differ within each circular distribution or amongst circular distributions are contemplated.
  • Ranges of between 0.2 and 5 mm may generally be used.
  • the circumferential edge 68 of the platen 50 may have engaging grooves or cogs 70 . These cogs 70 would be used to engage with driving gears 72 and 74 .
  • a motor (not shown) would drive these driving gears 72 and 74 to rotate the abrasive platen 50 .
  • Abrasion resistant coatings, sacrificial coatings, hardened metal (e.g., hard chrome plating (Rc 80) and the like can be used to strengthen and harden the holes.
  • Figure 2 shows an approximately 32.9 cm diameter (13 inch) platen 50 with a centering post 62 which may be a removable centering post 62 inserted into a hole 64 in the surface 66 of the platen 50 .
  • the first circular distribution of holes 52 at a diameter of about 62.8 mm (2.5 inch) comprises 30 holes having diameters of about 1.5748 mm (0.062 inches).
  • the third circular distribution of holes 56 at a diameter of about 29.2 cm comprises 180 holes of about 1.5748 mm (0.062 inches).
  • the second circular distribution of holes 54 is at a diameter of 22.8 cm (9.0 inches). Radial, rather than circular patterns of holes may be easily placed on the surface 66 of the platen 50 . Designs or other patterns, or even random distributions of holes may be placed onto the surface as long as a vacuum can be supported on the backside of an abrasive sheet.
  • Smoothness and flatness are two characteristics which are used in the art to measure the quality of lapping and polishing performance. Smoothness can be measured by profilometers (either, for example, confocal or stylus) and is measured in linear dimensions and standard deviations or variations from uniformity. Flatness is conventionally measured in terms of light bands, using equipment such as LAPMASTERTM Monochromatic Lights (e.g., Models CP-2 and CP-1) in combination with flat glass over the surface to be evaluated for flatness. The use of light band units (e.g., the number of lightbands per unit of horizontal dimension on the surface being evaluated, e.g., per inch) can measure surface flatness within millionths of an inch.
  • Curvature of radiating lines away from a line of contact between the glass and the surface against which light is being projected would indicate a degree of convexity to the surface and lines curving towards the point of contact would indicate a degree of concavity.
  • Straight, parallel, evenly spaced lines indicate true flatness.
  • Normal lapping procedures of the prior art are able to achieve 1-2 lightbands of smoothness, but the process commonly takes hours, depending on the material started with. Particularly when the material is hard (e.g., tungsten carbide or special alloys), conventional lapping is performed in hours, not necessarily including the necessary cleaning time.
  • the use of the apparatus, processes and materials of the present invention can easily achieve 4-5 lightbands of smoothness in minutes (e.g., 5 minutes or less), and with apparatus and processes combining all of the improvements described in the present invention,.
  • 1-2 lightband smoothness has actually been achieved in less than an hour (e.g., 15 minutes or less, even at 10 minutes), which time included replacement of sheets at the various stages and time for normal cleaning operations.
  • Other conventional parameters of lapping have been exceeded by practice of the technology of the present invention.
  • each lapping step will more nearly approximate the degree of damage created in the previous step. Therefore, if 50 micron particles are used in one step and 10 micron particles are used in a second step, the second step will remove approximately 50 microns (the damaged depth remaining from the previous step) and itself leave a damaged depth of about 10 microns.
  • the second step will remove approximately 50 microns (the damaged depth remaining from the previous step) and itself leave a damaged depth of about 10 microns.
  • micro fracturing continues to be reduced until microfracturing pickout as little as or less than 90%, 80%, 70%, 60%, and even 50% of the actual average diameter of the abrasive particles occurs in the work piece.
  • This is a potentially improved characteristic of the lapping effect of the present invention. No other lapping operation is known to provide this reduction in pick-out.
  • This is a definable aspect of a process according to the present invention, and may be seen in many different materials, such as in tungsten carbide, blends or alloys of metals (e.g., copper and tungsten), plastics, composites, etc.
  • the process also tends to smooth out non-homogeneous mixtures with less gouging of material, thus leaving fewer holes or pits in the surface because lapping and polishing, rather than gouging, is being effected.
  • a primary method of material removal from the work piece is for the individual abrasive particles to roll along between the piece part and the platen, rolling off or flattening high spots, or the abrasive particles are dragged along by the moving platen and shear off high spots.
  • the average normal clamping force is high, very large localized forces are concentrated against individual grains or areas of the piece part material at its surface. These localized forces are strong enough to weaken and break the bond between the grain in the piece part and the main bulk of the piece part at the grain boundary. Subsequently, the loosened grain will be forced out of its original position and leave a void, pocket or pit where it was originally located. These pits are referred to in the art as "pick-outs" and are very undesirable.
  • the normal (perpendicular) force can be generally much lower than in lower speed lapping processes, being as low as 10% of the forces normally encountered in lower speed lapping, such as only 20 pounds (8 kg) of normal force for a 10 cm by 10 cm work piece.
  • the contact pressures in the practice of the present invention may range from 0.1 to 100 psi, but are more preferred between 0.1 and 10 psi, still more preferred between 0.1 and 5 psi, and most preferred between 0.1 and 3 or 0.5 and 3 psi. Because this normal force is so much less, the localized forces on individual grains and abrasive particles are reduced and much less fracturing of the piece part surface and grains on the piece part surface occur.
  • Another significant advantage of the use of the abrasive sheets at high rotational speeds according to the present invention is that wear on the platen surface itself is greatly reduced.
  • the abrasive action works equally forcefully against the platen face and can eventually wear off the surface of the platen to a degree where the platen would have to be replaced. Even though the wear would of course tend to be even, there is no functional reason to continually sacrifice or wear out the platen. Some uneven patterns of wear may develop in the platen, and these would be translated into uneven lapping of the piece part.
  • the piece part holder assembly be held by a ball or gimbal pivot type of device located as low as possible toward the high speed abrasive surface. This is the best design found to align the total piece part assembly so all the individual parts (e.g., the platen carrying the abrasive sheet and the work pieces) are floated equally by the thin boundary layer of coolant fluid on the surface of the disk which may be less than 0.001 inch (0.0254mm) in depth. Boundary layers do not normally remain constant as the distance from the leading edge (contact point or liquid introduction point, or radial distance on the platen or circumferential distance along the tangential distance on the workpiece).
  • the changes in the thickness of the boundary layer cause significant variations in platen separation distances from the work piece and effective variations in penetration of the workpiece by abrasive particles on the sheet.
  • the piecepart tends to lay flat with respect to the platen abrasive and also this boundary layer thickness has a tendency to remain uniform even with slight out-of-perfect-perpendicular alignment between the vertical piece part holder shaft and the high speed abrasive platen. Foreign debris can be accumulated in pivot joints and create unwanted friction.
  • a work holder device is created with the use of a special ball attached to a shaft which ball and shaft combination provides a pivot action close to the bottom of the work piece holder assembly.
  • a sandwich of washers acts as a rigid base to transfer downward a polishing normal force on the vertical shaft to push the piece parts into the abrasive platen.
  • the pivot action is restrained by encapsulating the whole assembly with room temperature vulcanizing (RTV) silicone rubber or other elastomeric resin (e.g., fluoroelastomers) which seals the unit from debris and also provides the function on an elastic restraint that self centers the disk type part holder perpendicular to the axis of the support shaft.
  • RTV room temperature vulcanizing
  • the surfaces of metal objects are polished for many reasons including for optical examination of metallurgical characteristics, to create a smooth, low-wear, tight hydraulic or fluid seal and others.
  • this polishing is done at low speed (e.g., 5-200 rpm), with rotating flat platen disk wheels of various types of construction molding aluminum, steel, plastic cloth and others.
  • the wheel surface is very flat and the workpiece to be polished is held with controlled pressure by hand or work holder.
  • Water or other fluid, such a lubricant or wetted abrasive particles are introduced as a slurry, or disks of fine abrasive sheets are "stuck" or bonded to the rotating wheel.
  • This process is slow to produce a highly polished surface, and it is labor intensive if not automated. Inaccurate platen or shaft machining, loose bearings, or weak machine structure and framework may cause polishing accuracy problems.
  • the present invention enables very high quality polishing which can be achieved in a fraction of the conventional lapping time by using abrasive sheeting, such as 3M brand of micro abrasive disk sheets, for polishing at very high speeds of 2,000 rpm and more using disks about 8-10" in diameter.
  • abrasive sheeting such as 3M brand of micro abrasive disk sheets
  • Options also may change the pressure as a function of process time or the workpiece rotated to distribute polishing across the surface.
  • a unique method to provide a very “flat” and accurate stable rotations platen disk surface would be to mount the platen to a "weak" shaft which allows the rotating disk mass to seek a true “smooth” center at speeds above its first rotating natural frequency.
  • the motor drive speed would be increased above its natural frequency, the workpiece part presented in contact for polishing; then removed prior to reducing the disk RPM below its critical harmonic speed.
  • the greatest needs for the liquid are 1) to control friction between the abrasive surface and the work piece, 2) control the temperature of the sheet and the work piece, and 3) to wash away residue of abrasive and abraded material from the work piece.
  • These effects do not have to be performed at the same location between the sheet and the work piece and do not need the same amount of liquid (e.g., water, lubricant, coolant, etc.) to accomplish the separate tasks.
  • the inventor has recognized that the amount of water needed to affect friction (a surface phenomenon, and essentially two-dimensional [very thin] amounts of liquid may be effective) tends to be much less than the amount needed to control temperature (a bulk, three-dimensional phenomenon) and waste removal (a three-dimensional and mass flow process).
  • liquid may be applied to the lapping process of the present invention with controlled amounts, specified positions, and timed introduction to perform the process with reduced likelihood of hydroplaning because of reduced amounts of liquid between the abrasive ( as a sheet or other form) and the work piece. This is accomplished in the following manner.
  • the abrasive sheet is of a sufficient size relative to the work piece that less than fifty percent (50%) of the abrasive surface will be in contact with the work piece surface during lapping. Preferably less than 40%, more preferably less than 25%, and most preferably less than 15% of the total surface area of the abrasive sheet is in contact with the work piece during lapping at any specific time.
  • the area where the abrasive and work piece are in actual contact is called the work area. In a zone or area rotationally before the work area, water is placed on the surface of the abrasive sheet.
  • the amount of liquid (e.g., water) provided is preferably less than 120% by volume of that amount sufficient to fill the valleys between the peaks of the raised abrasive particles (100% essentially forming a smooth, continuous layer of liquid over the abrasive material). More preferably it is less than 110%, less than 100%, but at least 30% of that filling volume of liquid.
  • the amount is between 30% and 120%, more preferably between 40 and 115%, still more preferably between 50 and 110%, and most preferably between 90 and 105% of the volume necessary to exactly fill the valleys on the abrasive sheet so that an essentially flat film of liquid appears although surface tension between the peaks and the film may distort the appearance so that slight circular patterns may appear without dry exposure of more than 20% by number of the particles.
  • This approximately 100% volume amount is called the "leveling amount of liquid" in the practice of the present invention.
  • a first amount of liquid equal to 30 to 120% of the leveling amount of liquid is placed on said abrasive surface.
  • the area where this is performed is called the wetting area.
  • a second amount of liquid is applied to said abrasive surface, said second amount being both sufficient to have the sum of said first amount and said second amount equal to at least 120% of said leveling amount of liquid, and equaling at least 30% of the leveling amount of liquid.
  • the total of said first and second amount comprises at least 150%, more preferably at least 170% of said leveling amount.
  • the amount of said second volume is equal to or greater than at least 50% of said leveling amount, and more preferably at least 75% or at least 100% of said leveling amount.
  • This second volume will assist in carrying or washing the total residue on the abrasive sheet (the residue abrasive and the swarf from the piece part).
  • the second volume is applied in what is referred to as a flood area on the abrasive surface.
  • the high rotational speeds will remove a significant amount of the liquid and total residue on the abrasive surface, but because of the high quality sought in the lapping performance of the present invention, this may not always be relied upon.
  • air blades e.g., hypodermic air knives
  • the air blades in combination with the rotational forces, will remove a very high percentage of the applied liquid and the total residue so that an essentially dry surface can be assumed to enter the wetting area.
  • the first amount of liquid may be reduced so that the appropriate percentage of leveling is provided.
  • a water controlled system 340 according to the present invention is shown comprising a platen 342 having an annular distribution of abrasive sheeting 344 .
  • the annular distribution 344 is preferred, but not required in the practice of the present invention.
  • a first liquid (e.g., water) supply means 346 lays over said annular distribution 344 .
  • a second liquid supply means 348 is also shown to overlay the annular distribution 344 .
  • An air blowing means 350 is also shown to overlay the annular distribution 344 on said platen 342 .
  • a work piece 360 is shown over the platen 342 .
  • the rotation direction 370 of the platen 342 is such that liquid 362 deposited from said first liquid supply means 346 is upstream of the work piece 360 .
  • the liquid 364 provided by said second liquid supply means 348 is located downstream of the work piece 360 .
  • the air blowing means 350 is downstream of the second liquid supply means 348 .
  • the air blowing means 350 provides sufficient volume and intensity of air movement to assist in removing liquid 366 which had been on the platen 344 .
  • a platen After a high speed 3,000 rpm, 12" (30.5 cm) diameter rotating abrasive platen has been manufactured and used on a lapping machine, it does not remain perfectly flat as originally machined. A platen which has been ground or damaged by wear or impact away from a required or desired flatness is no longer effective for high precision.
  • a platen should have a deviation in flatness of less than 0.0005 inch (0.0126 mm) at the outer periphery with a need for the best performance to reach 0.0002 inch (0.00508 mm) or less than 0.0001 inch (0.00254 mm).
  • the platen should be flatter than the variations in thickness of the rotating abrasive disk surface.
  • the platens are ground to the above tolerances (e.g., less than 0.0126 mm variation in thickness along an entire circle within the disk surface). These measurements can be made, for example, with a micrometer or other linear measuring device. The flatness is measured by reading the variations in thickness along such circles within the disk surface.
  • the abrasive sheet e.g., the diamond sheeting
  • the abrasive sheet lays relatively flat on the surface of the platen, but is expected to have some variations in thickness of the backing material (e.g., plastic film, such as polyester) and the abrasive coating. However, it is desirable to minimize variations and prevent additive deviations from occurring.
  • This measurement can be made by a dial indicator placed at the outside diameter and the disk rotated by hand for one revolution to measure the maximum excursion.
  • any deviation acts either as a "valley” where the abrasive does not contact the piece part or a "high spot” which is the only area that contacts the piece part.
  • the high spot will have a tendency to hit the piece part and set up a vibration which will reduce the smoothness of the lapping abrasive action.
  • Localized distortions of the platen surface will also have a tendency to penetrate the boundary layer of liquid between the platen (covered with a thin sheet of diamond or other coated abrasive) and the piece part. This can produce a localized scratch or track on the piece part surface. Any surface defect on the platen structure is generally transmitted through the thin abrasive disk and produces a bump or high spot on the disk.
  • An existing platen can be "dressed" as a machine by bringing it up to full high speed RPM and lowering a heavy flat abrasive coated piece unit directly onto the bare rotating platen and grinding or lapping off the bumps.
  • High spots and even full out-of-flatness surface variations can be removed by first using a coarse abrasive and progressively using finer abrasive or lapping abrasive medium.
  • a typical first abrasive may comprise 40 micron metal-bonded diamond and a final abrasive may comprise 3 micron or less diamond or ceramic abrasive depending on if the platen surface is chrome plated, stainless or base steel.
  • the abrasive lapper disk could be oscillated back and forth across the platen, it could be stationary or it could rotate at either slow speed or rotate at a very high speed so the tip speed of the grinding disk will provide uniform removal of platen material at the low surface speed of the inner radius of the platen.
  • Different geometries of adhesive disks could be used. Also a piece part holder already in use for normal lapping could be used to perform this function.
  • a precision ground rotating platen can be fabricated with slightly raised spiral surfaces having different shapes and/or patterns, these shapes or patterns varying from the inside center of the platen toward the outer periphery of the platen.
  • the spiral patterns would create land areas at the top surface of the platen of the various widths, shapes with areas between these land areas that are somewhat lower, perhaps from 0.002 inch to .010 inch ( 0.051 to 0.254 mm) or more.
  • a thin plastic coated abrasive disk that is uniformly coated with precision fine abrasive e.g., the 3M diamond abrasive sheet material cut into disk form
  • precision fine abrasive e.g., the 3M diamond abrasive sheet material cut into disk form
  • the raised land areas could be produced by manufacturing a precision platen and acid etching or photolithographically etching land area geometry configurations.
  • the boundary layer of fluid coolant would be affected by the length of the land area under the piece part, the direction the spiral, radial or circular annular land shapes or a combination of the geometries.
  • the effects on the boundary layer thickness would be the rotation speed of the platen, as related to the vector speed, including the direction of the surface relative speed between the two, the viscosity of the fluid, and the normal force pressure of the piece part holding it to the platen.
  • the boundary layer thickness which would vary over the surface of the piece part, would affect how the individual particles of abrasive (normally protruding about 1/3 of their size above the binding agent) effectively abrades a workpiece from the surface of the abrasive disk.
  • the boundary layer would tend to be thicker and less abrasive material removal is achieved.
  • the local pattern of the surface of the abrasive contact area can be utilized for the optimum grinding action using only one portion of the abrasive disk with the non-raised section between the land areas of the abrasive allowing free passage of grinding debris.
  • this surface area of the abrasive is worn, the disk can be unmounted by the vacuum chuck, rotated to a "fresh" area of the abrasive, and then grinding would be continued. The disk will remain uniform and strong throughout an extended service.
  • the problem to be addressed is hydroplaning, which distorts positioning of the abrasive surface and the work piece relative to each other.
  • relatively thin or flexible work pieces e.g., work pieces thinner than 10 cm, especially thinner than 5 , 2, 1, or 0.5 cm
  • the worst distortion of the positioning occurs because of bending or flexing of the work piece. This is because the flexible sheet may be supported on a relatively inflexible support platen.
  • Two rotating platens may be provided, one each on opposite faces of the piece part or work piece.
  • the work piece is secured against movement between the two abrasive surfaces (on the two rotating platens).
  • the two rotating platens are rotated at the same time, in the same or opposite directions, with similar amounts of liquid applied between each platen and the work piece.
  • the disks do not have to be rotated at the same speeds, and when this is done, the volume flow rate of liquids used need not be as similar since the respective hydroplaning forces are proportional to the speed and the volume flow rate of liquid.
  • the relative speeds of rotation and the relative volume flow rates of water are selected so that the hydroplaning forces are fairly similar at the opposite outer edges of the work piece.
  • a piece part holder can be constructed out of a heavy metal such as steel which has substantial mass very close to the surface of the abrasive disk.
  • the piece part holder unit will be allowed to move freely with the surface by the ball-end holder.
  • a substantial hole can be made within the ball-end device which would allow vacuum to be coupled to the piece part holder.
  • Individual part pockets will firmly hold the flat piece parts tightly against the individual tight fitting part pockets to create and maintain a good vacuum.
  • a thin layer of oil or grease can be applied to the piece part to seal any leakage paths.
  • the hole is usually centered to act as a positioning means to fix the abrasive disk at the center of the platen to obtain good balance for the very high speed system.
  • a larger diameter round section could be removed from a disk to create an annular ring of acting abrasive material somewhat larger than the piece part. This would eliminate the inactive (and raised) uneven section but then the centering registration hole for positioning the disk is lost.
  • a disk can be fabricated with abrasive coated or exposed on the entire surface of the disk.
  • the inside section of the abrasive disk, toward the center of the disk, could be removed by grinding or peeling off the abrasive, leaving the backing material intact with a raised section of the abrasive in an annular outer ring.
  • the raised area is only where the abrasive is raised above the surface of the carrier (by the coating thickness).
  • the disk backing material is usually plastic sheet, which may be reinforced.
  • annular ring Another way to construct an annular ring would be to punch out a center disk section (e.g., a disk of 2 to 6 inches, 5.1 to 15.3 cm) of the disk for separate use and then use a centering plug (e.g., a 5.1 to 15.3 cm thinner disk) with a small locating hole.
  • the plug could be centered on a platen center post and the annular disk centered on the plug.
  • the plug is or may be removed to enable complete freedom of movement of piece parts over an annular disk. This complete movement can be effected since the centering post may also be removed after the annular disk has been positioned and secured by the vacuum.
  • the process of using an annular disk element can be effected where the round sheet has an outer edge and an inner edge defining a cut-out portion and comprises an annular sheet, said inner edge having a diameter which is greater than one-third the diameter of said outer edge.
  • the process may also be performed where said sheet is round and said round sheet has an outer edge and an inner edge defining a cut-out portion and comprises an annular sheet, said inner edge having a diameter which is greater than one-third the diameter of said outer edge.
  • Thin piece parts of about 1"x 2"x .080" (2.54 x 5.08 x 0.23 cm) can be mounted onto an individual piece of pressure sensitive adhesive (PSA) tape and this taped piece part can then be held by a vacuum to a workpiece holder.
  • PSA pressure sensitive adhesive
  • the friction properties of the non-adhesive side of the tape would be controlled by selection of tape backing material or by surface conditioning of the backside of the tape to provide a sufficiently high degree of friction which would resist lateral dynamic forces in a plane along the surface of the thin workpiece as the nominal 14 pounds per square inch (psi's, 25 inches Hg vacuum, 6635 mm Hg) would apply a normal force holding the work piece.
  • a large section of adhesive tape could be used to hold a number of workpieces at the same time. This would allow fast and easy installation of the workpieces by hand or robot.
  • This flexible assembly of pressure sensitive adhesive (PS) secured workpieces could than be held in position against a precision flat surface of a workpiece holder having random vacuum holes over its surface which would all be sealed by the wide and complete expanse of tape covering the vacuum holes and at the same time firmly holding the individual workpieces to the holder.
  • PS pressure sensitive adhesive
  • the group of workpieces would be removed, new tape would be applied to the lapped surface side, and the tape on the unprocessed side would be easily peeled off.
  • the tape would not only fix the parts to the holder surface, but also would protect the precision lapped side from any scuffing action or rubbing on the holder.
  • a coiled spring can be used to apply a self correcting force between the work piece holder plate having a gimbaled spherical bearing and the rotating drive shaft of the rotating piece part holder.
  • This spring could be made of metal or plastic material which would allow the straightening action to be applied but also would introduce vibration damping for excitation vibrations set up by the high speed, contact abrasive action.
  • One or more solid plastic coupling bars could provide damped spring action.
  • a vacuum hose could extend from the shaft and be coiled to provide a spring support action (with perhaps less than one complete turn, one complete turn or multiple turns which nominally lay flat with the upper surface of the work piece holder, which would minimize the creation of uneven "normal" turns).
  • annular abrasive sheet has an outer edge and an inner edge (defining the inner edge of the cut-out portion of the sheet, where it is cut-out from a circular sheet, forming a central, round hole).
  • the annular sheet should be placed on a platen, which is either a) flat, with the outer periphery bent, or beveled, b) or the inner annular section beveled, or both the inner and outer edge being beveled.
  • the outer edge should not extend significantly beyond the outer edge of the bevel or platen (e.g., less than 1 mm, more preferably less than 0.5 mm, still more preferably less than 0.1 mm).
  • the inner edge should in likewise dimensions likewise not extend beyond the interior edge of the bevel or the bend. If the annular disk is positioned on a flat platen, the flat platen may be bent substantially (with the same or like dimension tolerances) at the interior edge of the annular disk to form the lapping abrasive edge on the platen. The only caution which must be exercised is to assure that no folds or wrinkles appear in the annular disk. A preformed annular disk may be shaped to fit on the angled or beveled element.
  • the element may be molded or formed to fit the shape of the platen surface (for example, by having a truncated conical sheet segment with the inner, smaller diameter hole (formed by cutting the cone) fitting the slope of the beveled edge, with the abrasive on the interior, upward facing surface of the cone (within the original cone volume as opposed to being on the external surface of the cone.
  • the annular disk may be secured by adhesive, but the vacuum securement of the present invention is preferred.
  • Operation of the high speed lapping devices envisioned by the present invention are at revolutionary or rotational speeds of at least 500 rpm, or at least 1,500 rpm, and preferably at 2,000 to 3,000 RPM with a fine abrasive sheet, such as the preferred 3M diamond coated abrasive disk of about 12" (30.5 cm) diameter.
  • a fine abrasive sheet such as the preferred 3M diamond coated abrasive disk of about 12" (30.5 cm) diameter.
  • These sheets are normally held to a steel rotating platen by water film surface tension and positioned by a 1 ⁇ 2" (1.27 cm) diameter hole at the center of the disks. These positioning holes were used with a 1 ⁇ 2" (1.27 cm) diameter post at the center of the platen.
  • the 1 ⁇ 2" (1.27 cm) centering post could be made larger in diameter to perhaps 1" (2.54 cm) diameter or more.
  • the post could have a hexagonal shape or an oval shape which would prevent the disk from rotating relative to the tangential surface of the disk by having the apices of the hexagons (or other polygon) resist rotation against a similar cut hole in the sheet or disk.
  • the post could also be made higher so the chance of the self-destructing disk climbing up the height of the post would be diminished during this type of event.
  • Another technique would be to employ a clamp type of device to any of these round or non-round posts to clamp/hold the disk firmly to the surface of the platen at the center areas of the disk which is not used for polishing.
  • the clamp could consist of a spring locked washer pressed on the disk surface with a thread nut engaged with a top threaded post. Springs could also be used to control the amount of force and to evenly spread the force uniformly. Ball insert or other snap latch fixing devices could also be employed.
  • the abrasive sheet When an abrasive disk becomes loose by breaking the conventional water filter "adhesive" surface tension between the disk and the platen, the abrasive sheet has a tendency to rip or bunch-up and wedge between the workpiece holder and the high inertia spinning platen and can easily damage a workpiece part or can destroy portions of the workpiece assembly with the possibility of great danger to the operator.
  • This is a unique problem due to the very high rotational speeds of 1,500, 3,000 or even greater RPM with a platen of 15"(38.1 cm) diameter or more constructed of heavy steel which could generate explosive type failures or at least high velocity projectile failure. As this equipment is operated horizontally for the most part, the whole surrounding area around the machine is susceptible to this danger.
  • Solution Use a diamond or other abrasive disks without using PSA adhesive and first position the disk at the true center of the platen by use of a center hole in the disk positioned over a post positioned at the center of the platen (or by other centering means) and then by holding the abrasive disk to the platen by use of vacuum by use of a rotating union on the hollow rotating platen shaft.
  • the preferred area to apply the vacuum would be at the inner radius of the disk which would seal out air first as the disk is installed at the platen center. Because this inner one-fourth or so of radius is not used as much for lapping because of the slow surface lapping velocity, there would be less direct forces applied at this portion of the disk.
  • the second most preferred vacuum area e.g., the outermost edge region of the disk) would also not be used much and would have large holding force.
  • a high speed lapping system can be a sheet of abrasive material such as fixed diamond abrasive coated or plated on a disk sheet of material. These sheets or disks may be used on a rotating platen disk with a diameter of, for example, 12" (30.5 cm).
  • the apparatus gives a surface speed of about 9,000 to 20,000 feet per minute. If a larger diameter platen wheel of 15" inches is used, the RPM can be lowered somewhat to perhaps 2,500 RPM to achieve the same 10,000 (or 9,000) feet per minute (fpm).
  • the speed can be further reduced to produce 9,000-10,000 fpm at the outer periphery of the disk.
  • Any reduction of angular or rotational speed created by larger diameters is desirable because of the particular danger of a high inertia wheel creating problems if a disk or part is damaged or comes loose.
  • the higher speeds used in the practice of the present invention, plus the controls shown for maintaining accurate address between the abrasive surface and the workpiece allows for much faster and therefore more economic lapping. Work that previously took hours, including intermediate cleanup steps, can be performed in minutes using the apparatus and methods of the present invention.
  • a thicker boundary layer of water or liquid builds up between the part and the surface of the disk and the piece part. This keeps the (e.g., diamond) abrasive particles away from the piece part and allows some fraction of their normal penetration which results in a smoother and flatter surface on the part.
  • One method of utilizing this performance is to have reduced water flow at the first portion of the lapping period for more aggressive material removal with an increased roughness of the surface.
  • the water flow is increased somewhat during the middle portion of the abrasive cycle to get better surface finish and yet have a medium material removal rate and then to substantially increase the water flow rate at the end of the cycle to produce a very smooth and flat surface with a low rate of material removal.
  • This could be easily done with an automatic water flow rate control system. This would change the water flow rate automatically at various stages in the abrasive cycle.
  • the liquid (especially water) introduced as a lubricant between the platen and the work piece is normally filtered to eliminate particles which are 1 micron or larger in their largest dimension.
  • a positive displacement pump such as a gear pump or piston pump can be helpful in determining the optimum quantities of flow and charge during operation of the system, at the beginning, middle and end of operation of the lapping cycle.
  • the rotating platen is round in shape with about a 12" or 15" (30.5 cm to 43.5 cm) diameter.
  • a box is constructed which is rectangular in shape with “square" corners (4 each) and with the walls some distance away from the round platen, typically 6" or more.
  • the box is desirable to be constructed of a soft plastic (or rubber) such as 1 ⁇ 2" thick high density polyethylene which would tend to absorb impact from a heavy metal part free flying, broken loose parts without ricocheting the part back into contact with the rotating disk which would reinitiate this impact action. It also prevents this reinitiated contact from damaging the part.
  • the "square" corners provide a remote area to trap the part and to contain the part as it stopped moving by being impacted in one or more rubber or plastic walls or lined metal walls. Having a distance between the flat walls and the rotating disk which is somewhat larger than the largest size of the piece part, centrifugal force would tend to drive the part off the disk radially and allowing it to roll or move tangentially to a neutral corner of the box away from the disk. At the same way, crumpled abrasive disks are collected by the neutral open corners. Having a ledge over the inside portion of the box also helps trap the parts.
  • a safety box with at least 10% (of the diameter of the platen) clearance on each side of the platen within the safety box area is quite effective. It is more preferred to have the safety box with a clearance of 20%, 30% or even more than 50% of the diameter of the platen (on each side of the platen within the box or at least from at least one side of the platen) in the practice of this aspect of the invention. It is particularly desirable to have the workpiece holder moving assembly lift the workpiece holder out of the safety box so that the box may be cleaned without contacting the platen.
  • a removable bottom section may be constructed on the box for bottom cleaning without having to significantly move the platen, but any openings or movable pieces may add to vibration potential in the system and is therefore not the most desirable engineering approach to the construction of the safety box.
  • the box may have a high center section and be angled or curved in the outer section so that any loose parts or pieces would tend to drop below the rotating platen and not be picked up by the platen and projected back toward the opening in an area above the abrasive surface of the platen (e.g., towards the operator).
  • a tapered bottom of the safety box area toward one or more drain holes allows the expended liquid (and any carried particulates) to be easily collected for disposal, even without opening of the safety box area.
  • the angle of the box bottom to obtain the best flow conditions for the liquid will be selected to provide a washing action on the surface to minimize buildup of ground particles on the surface of the bottom of the safety box. Grooves to concentrate water flow or passage may also be provided.
  • a temporary cover may be provided over the opening of the platen top access hole to provide additional safety to the operator from projectiles and also to contain any mist formed by the high speed shearing and projection of liquids.
  • Duct work can also be installed in the box to withdraw air born vapor and particles as well as the liquids, with reduced pressure removing the undesirable materials at a controlled rate. Filter elements may also be associated with these removal systems.
  • the vertically moving piece part assembly can be mounted on vertical slide and a chain or cable used with a counterweight which is perhaps 10 lbs. (4.54 kg) heavier than the 60 lb. (13.6 kg) assembly.
  • a counterweight which is perhaps 10 lbs. (4.54 kg) heavier than the 60 lb. (13.6 kg) assembly.
  • the piece part assembly Upon loss of electrical power which would interrupt power to the normally used suspension air cylinder or a line leak to the cylinder, the piece part assembly would simply and quickly retract to the upper position, taking it out of contact with the rotating platen and thereby reducing the chance of danger. This could also be a more assured event by using an e-stop (emergency-stop) action switch which would not require power to obtain safe action.
  • Functional mechanical parts which are typically 1 to 2 inches (2.54 to 5.08 cm) in diameter (or shaped other than circular cross-section, such as rectangular) which may be thin (.010inch, 0.254 mm) or thick (.500 inch, 12.7 mm) can be affixed to a precision flat steel, other metal or other material plate by use of paraffin wax as a bonding agent.
  • the plate or part can be coated with wax or the wax simply melted on the plate between the part and plate and the part placed on the plate, heat applied, and the two pieces would have a fully wetted surface of molten wax.
  • the parts could be positioned by mechanical or other means of uniform pressure or force so that they lay flat with a uniform and controlled thickness of molten wax.
  • the parts Upon cooling the part/plate assembly, the parts would be positioned accurately and firmly for the plate ready for lapping action. Then the plate could be attached to a piece part holding device by use of a vacuum chuck or by use of a magnetic chuck if the plate were, for example, steel.
  • the piece part holder could have a ball type pivot close to the lapping action surface. Plates could hold one or many individual parts.
  • the plate/part assembly Upon lapping one side, the plate/part assembly could be heated , the parts removed and, if desired, the parts could be reassembled with heated wax on a plate with precise parallel alignment with no danger of damage to the lapped surface because of separation from the plate with no wax. And this way many plates could be preassembled for high production rates with a single lapper.
  • a simple, eccentric harmonic motion, constant speed rotation can be provided by a DC or AC gear motor hub used to drive a linkage system.
  • This system will provide a smooth continuous motion at a workpiece with most of the time in a given hub rotation cycle being spent with the workpiece operating at the outer periphery of the abrasive disk which has the highest surface speed and also grinding action. Only a very small portion of the cycle time would be spent at the inner radius having a low surface speed and reduced grinding action portion of the disk.
  • These small parts can be affixed to a flat surfaced piece part holder or a holder which has small shallow pocket areas just larger than the length and width of the flat part so that an exposed surface of the part protrudes away from the holder. This will allow the abrasive disk polishing action lateral force to be applied to the piece part and not separate the piecepart from the holder, as it is trapped in the pocket or is held rigidly in the part holder.
  • a medium temperature wax, or other easily removable adherent material can be melted and used to bond a rough surfaced part to the flat smooth surfaced part holder plate.
  • the flat plate in turn can be attached to a rotating pivoting arm which is swept across a portion of the surface of the high speed rotating disk until a smooth flat polished lapped surface is generated on one side of the piece part.
  • the part holder plate which would have 1 or 2 or many more parts attached to it in a fixed mounting pattern could be brought into contact with another mounting plate having a flat surface or a shallow pocketed surface pattern which matches the first part plate.
  • a higher temperature wax higher temperature than the first wax
  • the original lower melting point wax would melt and release the parts from the first plate.
  • the parts would be transferred as a group to the second plate ready to have the rough remaining side lapped as the first plate is readily removed from this group of parts. High production rates at lapping flat parts on both sides with good parallelism could be achieved.
  • the work piece floating on the boundary layer of water allows the abrasive media and the platen imperfections to be averaged out- high spots on the abrasive do the lapping while the low spots are filled with water allowing the lapping action to take place and produce a finished part (work piece) that is flatter than the media and platen.
  • the work piece will only be as flat as the boundary layer.
  • the problem is how to control or minimize the boundary layer thickness and control the shape on a work piece with a small surface area that is not large enough to float on the boundary layer with a minimum amount of down pressure, yet have enough water thickness for lubrication and cooling.
  • Solution Pump water (e.g., through the work holder) into controlled orifices or jets in strategic locations that would encourage a controlled boundary layer to form between the work piece and the abrasive media.
  • the water would also stabilize the workpiece while presenting it to the rotating platen initially and while lifting the work piece off after lapping is complete.
  • Water is injected or otherwise directed to an inside radial area of a piece part holder which is holding a number of discrete piece parts at the same time. This could be particularly helpful when an annular distribution of abrasive is used.
  • the inside portion of the water would develop a second boundary layer under the trailing portion of the piece part holder which contains a second piece part in contact with the narrow annular band of abrasive.
  • Boundary layer water entering under the leading edge of the holder would tend to lift up that first piece part and tend to tilt the second piece part downward. This would cause a ground cone shape to form on the piece part.
  • a second boundary layer would also develop under the second piece part at the trailing site of the holder and lift it upward, which would compensate for the tilting of the first piece part.
  • the whole piecepart assembly would tend to lay flat as it would be supported by both boundary layers at the same time. There would be little tilting of the piece part toward or away from the platen rotational center as the parts are in contact with the (e.g., narrow) annular band of abrasive which would only effect a narrow strip of grinding action.
  • Solution Providing a system where an adequate boundary layer can be generated and maintained while the individual piece parts are being lapped can easily be done by adding a secondary device to the piece part holder device which would have sufficient surface area, and dimensional length to develop a desirable boundary layer.
  • the secondary device is also ground down simultaneously with the piece parts in a sacrificial way.
  • a typical shape of this sacrificial contact device can be a disk of metal such as brass which would be mounted on the inside annular position of a tool piece holder with the to-be-lapped piece parts mounted inboard or outboard of this device on the periphery of a round piece part holder.
  • a typical disk would be 4 inches (10.2 cm) outside diameter, 2 inches (5.08 cm) inside diameter and about 0.60 inches (1.52 cm) Thick. It could be easily attached with vacuum chucking and/or adhesive tape and could be used over and over by loading new piece parts with a partially ground disk.
  • Other geometry sacrificial plates could be used and combinations of materials including other metals such as steel or ceramics.
  • annular sheet provides significant advantages to the performance of many aspects of the present invention, but as with advance, other issues may develop in performance.
  • particulate grit and abraded material and/or liquid lubricant can work its way under the inside edge of the annular section.
  • some particles may lift an edge of the sheet and cause problems with the uniformity of the flatness of the annular sheet. This would cause undesirable effects on the lapping process and quality.
  • the annular section becomes wobbly, does not sit properly on the platen, may be difficult to lay down accurately, and provide other structural difficulties in securing the annular sheet to the platen.
  • a continuous sheet of abrasive material may be provided, including a flat sheet having an annular distribution of abrasive material and a continuous middle section without abrasive thereon.
  • the most expensive way of providing such a sheet would be to coat the abrasive out in an annular distribution, as by roller coating, gravure coating or screen coating of the abrasive and binder.
  • An adhesive binder may be printed onto the backing and the surface dusted with the abrasive grit to form an annular distribution on a continuous sheet. This type of process would again require a new coating step rather than providing a means for using existing sheet material.
  • Another less preferred method of providing an annular distribution of abrasive with a continuous sheet between the inner diameter of the annular distribution would be to cut a circular element out of the abrasive sheet material and then abrade away an interior section of only the abrasive particles (leaving the backing material) to create an annular element. This would be a waste of significant amounts of abrasive surface area, but would provide a useful annular sheet on a continuous backing.
  • the most preferred method according to the present invention is to cut out an annular ring of material of the dimensions that are desired and then fixing or securing a non-abrasive sheet material (hereinafter referred to as the center portion) within the cut-out portion of the annulus.
  • a non-abrasive sheet material hereinafter referred to as the center portion
  • the joint between the annular sheet portion and the center portion should not extend above the average height of the abrasive particles with respect to the backing material. This can be done in a number of ways. A thinner sheet material than the backing material may be used for the center portion.
  • This center portion does not have to provide any significant structural component to the annular ring, but it can provide advantages as noted later if the center portion is relatively stiff and strong (even stiffer and stronger than the annular sheet material section). The presence of such material, stiffened or not, does tend to make the ring easier to work with, avoids wrinkling, and makes the abrasive sheet easier to lay down on the annular work zone.
  • the center portion clearly provides a stabilizing influence on the sheet as it is being applied to the platen.
  • the material for the center portion may be chosen from a wide range of materials because of the minimum physical and/or chemical requirements for the material. Plastic film or paper is the easiest materials to provide for the center portion.
  • centering hole in the middle of the center portion, or even a larger hole than is needed for centering.
  • the larger hole adds no significant structural advantage, and should not minimize the stabilizing or edge protecting effect of the center portion, but some latitude is available in the dimensions of the center portion with respect to the entire size of the annulus without preventing some of the benefits of the present invention.
  • the center portion may be secured to the annular ring by any process which adheres the center portion to the annular portion. This would include, but not be limited to, butt welding, fusion of the sheet material to the annular segment, adhesive stripe between the annulus and the center portion, thermal welding, ultrasonic welding, hot melt adhesive, etc.
  • the application of an adhesive may be the most likely to cause raised areas which could be avoided, but existing process technology makes controls over the dimensions of the adhesive very effective. Additionally, since the adhesive would be much softer than the abrasive material, some sacrificial abrading on the inner edge of the annulus could be performed to lower any edges. Therefore, some conditioning grinding or lapping at the inner edge of the annulus could be performed before the abrasive sheet is used for its primary effort at lapping.
  • Another method for forming such a sheet would be to cut out an annular ring of abrasive sheet and lay it over another plastic circular sheet having an outside diameter approximating that of the annular cut-out (it may be somewhat smaller or larger).
  • This sandwich could be joined together by any method which would maintain a consistent thickness to the abrasive sheet. since the highest quality coating methods could be used in joining these layers (the circular and annular disk), even adhesive securement is useful, where because of process limitations in the application of adhesive to the platen to secure the abrasive sheet, adhesive securement would not be desirable between the abrasive sheet and the platen.
  • Securement might also be made between the annular ring of abrasive and a backing sheet by thermal welding, ultrasonic welding, or any other method, particularly those which seal the entire circumference of the joining line between the annular sheet and the backing sheet to prevent liquid and particles from entering the seam.
  • thermal welding ultrasonic welding, or any other method, particularly those which seal the entire circumference of the joining line between the annular sheet and the backing sheet to prevent liquid and particles from entering the seam.
  • a poor seam closure would allow edges to lift or pull and would be undesirable.
  • annular disk provided with a natural raised outside area of abrasive could be easily used on a flat platen surface.
  • Other structures of abrasive sheets with attached central areas, where the sheet has a height of the central area and the abrasive area relatively equally may need a platen with a raised annular area on the outside of the platen to take the greatest advantage of the annular configuration. It is to be noted that if the central area were minimally abrasive or minimally hard (or a later described, completely free of abrasive), contact between the central area and the piece part during lapping would have negligible or even beneficial (buffing) effects and the sheet could be used on a flat platen.
  • Concentric circles of vents or ports may be located, some or all in the center area or under the abrasive annular distribution.
  • Pressure sensitive adhesive may be used in limited areas, such as in the center area only, where there would be no possibility of adverse affects on the consistent level of the abrasive or buildup effects.
  • the adhesive could be used alone or in combination with vacuum retention in that area or with the vacuum in areas not secured by adhesive.
  • Pressure sensitive adhesive could be located outside the annular area of the abrasive, and thereby not affect the level or evenness of the abrasive surface. It is possible to have some adhesive under the annular ring of abrasive, but this would, of course, detract from the evenness and ease of replacing the sheets.
  • High friction, rough surfaces may be provided on the platen to assist in the draw down of the abrasive sheet.
  • the vacuum holes or vents are sealed by the disk, particularly at the inboard portion of the sheet. It is therefore important that all holes underneath the sheet be in vacuum tight relationship with the sheet to prevent debris from entering the holes, clogging them, and providing deformities on the surface of the sheet. The debris can also grind away portions of the holes or vents, later disturbing the disk surface. The pattern and distribution of the holes can therefore be important.
  • the motor driving the platens and/or work piece holders apply vibration to the entire lapping system.
  • the rotation of the platen itself provides vibration, as does the movement of the abrasive over the face of the work piece.
  • the flow of liquid over the lapping contact zone (between the platen and the work piece), especially where there is any hydroplaning or uneven distribution of the liquid over a moving surface, also creates pressures and forces which can add vibration into the lapping system. These vibrations in the system can cause minor instantaneous variations in the relative positions of the platen and the work piece. These variations, of course, show up in reduced lapping quality in the product and are undesirable.
  • the weight of the frame an the individual elements must be designed to minimize vibration.
  • the joints between elements and attachments of moving parts must also be controlled to minimize vibration.
  • the primary method of reducing or damping vibration is to add mass to the frame and to strategic portions of the apparatus.
  • the frame of the system should weigh a minimum of 100 kg.
  • an energy-absorbing member or layer e.g., a viscoelastic layer
  • the thin elastomer layer mutually bonded to both plates and is sheared across the thickness and, due to its very high viscosity, will absorb the vibration energy and dissipate it into heat. All of the vibration damping systems would be designed for a specific portion of the machine, especially with respect to localized natural frequency, its expected amplitude multiplication (which can easily exceed fifteen times the oscillation excursion of the excitation source), the design and characteristics of the vibration damping/absorbing device, and the different multiple frequencies expected.
  • the secondary spring mass tends to oscillate at the same frequency as the excitation frequency, but out-of-phase, so as to cancel out the excitation frequency force.
  • Another vibration prevention device is the use of a large, thick, heavy flat plate weighing 90 kg or more mounted horizontally in the same plane as the platen at about the same level as the platen. This mass tends to absorb any vibration due to imbalance of the platen/abrasive sheet combination assembly. This prevents the vibration motions from exciting the machine frame in such a way as to oscillate the piece part being ground or lapped. Adhesively bonding a viscoelastic layer to this flat mass plate and bonding another large mass flat plate to it can very effectively reduce the buildup of vibration oscillations,
  • Some other vibration excitation sources can be the platen system being out of balance, the piece part spindle being rotated when out of balance, oscillations being generated by the stick-slip conditions between the abrasive sheet and the work piece, hydrodynamic fluid-induced vibrations at the moving fluid boundary layer interface between the piece part and the platen, sudden motion of machine elements, electrical pulses, etc. Vibrations should be prevented from entering the system, wherever their source. Adding a large mass ring of heavy, dense material to the outboard diameter of a (typically) round workpiece holder in a fashion which allows the center of gravity as close as possible to the moving abrasive surface is a very effective method of minimizing vibrations in the work piece. The mass attenuates vibration excursions and oscillatory vibration forces generated at the abrasive surface contact area. The same mass will also interrupt vibrations originating from the machine motor drive, and platen imbalance (insofar as it would travel down to the workpiece support mechanism).
  • the mass of the frame comprise at least 200 kg, still more preferably at least 350 kg., and most preferably at least 500 kg., with no maximum weight contemplated except by the limitations of reasonableness.
  • the weight of the actual intended commercial embodiment of the frame of the present invention is about 600 kg.
  • the platen, at a revolutionary speed of 3000 rpm with a twelve inch (30.2 cm) diameter, has a natural frequency of about 50Hz.
  • the frame should be designed with a natural frequency above the frequency of the highest useful speed of the platen (and motor) to avoid the frame being vibrationally excited by the motor as it is brought up to specification during operation.
  • the natural frequency of the apparatus frame should be at least 2% above this operating frequency. Greater differences between the operational frequency (the Hz equivalent of the rotational speed of the platen) and the natural frequency of the frame would provide additional levels of vibrational avoidance at the higher speeds, so that natural frequencies more than 3%, more than 5%, more than 10% or more than 20% of the operational frequency are desirable.
  • Operating equipment used by Applicant in the practice of the present invention has been made with 3000 rpm operational speeds (50Hz) and 76 Hz natural vibration frequency.
  • the frame of the machine to be operated at higher speeds and higher frequencies (e.g., 3600 rpm and 60Hz, and 4200 rpm and 72 Hz) by increasing the capability of the motor, replacing the motor, but not significantly modifying the frame.
  • weight and mass may be added to the frame after construction to improve vibration resistance.
  • Damping material such as elastomeric materials may also be added at strategic sites within the frame and apparatus, such as at joints, between a work frame and the main frame, over bolts and nuts (if present), between legs on the frame and the floor, etc.
  • the purpose of these features being to mask the vibration or dampen it, as by increasing the natural vibration frequency of the frame to a meaningful level (e.g., at least 2 Hz or at least 2%) above that of the operational frequency of the lapping apparatus.
  • the relatively much slower surface speeds at the inner radial region of the disk will conversely have a thicker boundary layer because of the slower speeds and the fact that the same volume of liquid is moving over a smaller area (the area defined by the smaller radius) at a slower speed.
  • abrasive particles at the outer radius of the rotating platen more easily penetrate the thinner boundary layer at the outer periphery of the disk and effect material removal more efficiently in that region than where the boundary layer is thicker. Therefore, the abrasive activity is affected not only by the differential in surface speeds between the inner region and the outer region, but also there is another effect because of the variation in the thickness of the boundary layer between radially related regions.
  • the abrasive particles integratly attached to the abrasive sheet may be held away from the work piece and not remove material as efficiently. This causes uneven wear and lapping on the piece part due to the boundary layer effect which has not been previously considered in this technical field.
  • the boundary layer thickness approximate the average height of the abrasive materials protruding from the support surface (e.g., from at least about 0.1 micrometers, and for example from about 1 to about 100 micrometers). It is desirable that the boundary layer thickness approximate that height with a variation of no more than ⁇ 50% of the average abrasive particle height, more preferably ⁇ 30%, still more preferably ⁇ 20%, yet more preferably ⁇ 15%, and most preferably within +10% of the average protrusion of the abrasive particles from the average height of the substrate (e.g., the valleys formed by the binder).
  • the process may be performed with two piece part holders, each rotating in a direction opposite (clockwise versus counterclockwise) from the other.
  • Both holders may be mounted on a common pivot arm.
  • each piece part holder would tend to stabilize the other and would also allow each of the piece part holders to stabilize the other across the width of the platen.
  • a special wobble joint at each piece part holder would allow each to conform to the slightly uneven boundary layer on the platen.
  • Rotating each piece part holder would provide the same amount of abrasive material removal to the exposed surfaces of the piece parts.
  • the normal contact force, surface speed, liquid flow rate, viscosity, etc. would all be optimized in the entire assembly.
  • the assembly pivot cradle would be oscillated to obtain even surface wear.
  • the rounded outer surface of the ball 146 is supported by pairs of spherical-faced bearings 154 , and 156 , and 158 and 160 , which may also be a pair of torroidal bearing elements with concave spherical faces contacting ball 146 .
  • flexing elements 162 and 164 Over said upper spherical faced bearings 154 and 158 are flexing elements 162 and 164 . This may be any spring-like elements, coils, or spring washers which provide a cushioning effect or spring effect between said upper spherical bearings 154 and 158 and bearing securing means 170 and 168 which help to secure the upper bearing elements 154 and 158 against movement and provide a stabilizing and positioning force to the ball 146 .
  • a convenient securing means may be a circular nut with spanner wrench holes, with threads on the sides to fix into the platen neck 172 .
  • a cushioning material 174 and 176 are provided between the shaft 132 and the interior surface 178 of the platen neck 172 . If a force is applied to the face of the platen 134 and the force is slightly uneven distributed against the face 134 , the face of the platen may adjust to the force and level itself by pivoting through ball 146 . The degree of pivoting is cushioned by internal resistance of the ball 146 , and the elastic resistance of the cushioning materials 174 and 176 .
  • a lubricant (not shown) may be provided in any cavities 180 and 182 which exist between the cushioning material 174 and 176 and the ball 146 .
  • the lubricant may be any preferably liquid lubricant such as an oil.
  • the cushioning material 174 and 176 may be any flexible composition, such as, but not limited to, natural or synthetic rubber, silicone or fluorine containing elastomers, spring elements, or the like. Lubricant may be provided by syringe injection into the cavity 180 and 182 or may be provided through a replaceable cap (not shown).
  • Figure 10 shows a preferred flexing element for use with the present invention, a Bellview spring washer 190 .
  • This element is no more than a standard washer whose outer periphery has been bent down to form a truncated cone shape.
  • These Bellview spring washers may be stacked to form a spring-like element.
  • a platen-shaft system 198 may comprise a platen 200 with a front face 202 and an internal anti-pivot shaft 204.
  • the anti-pivot shaft 204 is separated from the inside face of the platen shaft 206 by a distance of A .
  • the platen 200 may not pivot any angle greater than that which would cause the anti-pivot shaft 204 to contact the inside face of the platen shaft 206 .
  • This aspect of the invention may be described as a pivoting lapper workpiece holder system comprising:
  • the workpiece holder system may have said cushioning means comprise a flexible composition, and may have said cushioning means comprises an elastomeric composition, as previously described.
  • said elastomeric composition preferably comprises a silicone elastomer or a fluoroelastomer.
  • the workpiece holder system, between said flexible composition and said at least one upper bearing may have a spring element, and above said spring element and below said flexible composition may be a securing element, said securing element being capable of being adjusted in a direction parallel to said shaft to increase force upon said spring element, said force on said spring element in turn increasing force of said at least one upper bearing to press said bearing against an arcuate surface of said pivoting joint.
  • the workpiece holder system may have at least said flexible composition, spring element, shaft, at least one upper bearing and pivoting joint creating a cavity with said workpiece holder system.
  • the cavity preferably contains a liquid lubricant.
  • the workpiece holder system may have an elongate element which is associated with said workpiece holder so that movement of said workpiece holder, out of its natural symmetric rotation plane as is used during lapping, causes movement of said elongate element, said element extending from said back side of said workpiece holder through an interior channel of said shaft so that said movement of said elongate element when said workpiece holder pivots will cause said elongate element to contact an interior surface of said shaft, restricting the amount of pivoting which said workpiece holder can perform.
  • the elongate element will contact said interior surface of said shaft when said workpiece holder is turned less than 30, preferably less than 20, more preferably less than 15 degrees, and most preferably less than 10 or 5 degrees.
  • the workpiece holder system may use a spring means or spring element which comprises a stacked array of truncated hollow cone elements stacked upon each other.
  • a perfect ball bearing would be very loose and could cause the workpiece holder to contact the platen in a manner to cause abrasive damage from the first contact, while the cushioning material (the elastomer) used in the present invention stabilizes the workpiece holder direction and tilt within a more controllable range.
  • the use of an elastomer is preferred over spring support of the shaft because it also provides an added measure of vibration damping.
  • abrasive sheet which does not have any openings in its surface. This can be done by having a circular sheet with no holes therein coated with an annular ring of abrasive material.
  • a circular abrasive sheet may have the core circle of abrasive scraped or abraded off to leave an annular distribution of abrasive on an impervious sheet backing.
  • An annular disk with an opening in the center may be provided with a 'plug" or circular piece that completely fills the central area.
  • annular disk 112 having annular, flat support area 114 with abrasive on the upper surface 116 may have a plug 118 which abuts (and is preferably secured to) the inside edge 120 of the annular ring 112 .
  • An area 122 between the flat annular surface support area 114 and the inside edge 120 is shown with a bevel, but this is not essential. Securement between the plug 118 and the interior edge 120 may be effected by direct fusion (by heat or solvent) of the two pieces, adhesive or the like.
  • Figure 6 shows a platen 90 with a depressed region 92 and a wall 94 between the flat upper annular support area 95 and the depression 92 .
  • a number of means are available for providing an annular abrasive disk or annular abrasive work surface (not shown) on this flat portion 95 .
  • Figure 7 shows one of these methods.
  • the platen 90 has an abrasive sheet 100 on its surface.
  • the sheet 100 comprises a backing layer 102 and abrasive material 104.
  • a vacuum port 96 (or other securement means) retains the back surface 98 of the sheet 100 against the flat annular surface 95 . The reduced pressure will be passed along the back surface 98 press the sheet 100 against the flat surface 95 .
  • the reduced pressure will also secure the sheet 100 against the wall 94 and the depressed area 92 .
  • the wall 94 is shown with an arcuate slope, but may be more sharp or smooth in the transition from flat area 95 to depressed area 92 .
  • the transition may be by two right angles or by an S-shaped curve or other form.
  • Figure 8 shows a platen 90 with a plug 93 which is secured to the backside 98 of the annular sheet 106 with abrasive 106 on it.
  • the location of the abutment 110 between the backside 98 of the sheet 106 and the plug 93 is shown at an approximately right angle, rather than the edge-on abutment of Figure 5.
  • the abutment 110 of Figure 8 may be by means similar to those described for the joining of the plug 118 and the flat annular support 112 at the abutment 120 in Figure 5.
  • the work surface of the sheet or annular disk would effectively oscillate, rather than present the exact same radial dimension to the work piece. This oscillation, since it is unlikely to repeat in a single rotation of the platen, would expose different areas of the abrasive work surface to the work piece. Abrasive material would be removed in broader (wider) annular patterns, as compared to the more narrow annular patterns that would be worn in the work surface of a perfectly centered abrasive sheet.
  • the degree of off-centering useful or tolerable in the system is related to the rotational speed and the density of the abrasive sheet.
  • the abrasive disk could be either intentionally repositioned at its exact original position or a different position by use of a marker system. Even a felt-tip writing implement could be used to mark on the abrasive disk and/or the platen where it was exactly located on the platen relative to the mark, or a permanent marking system on the platen. An abrasive disk may then be removed and reinstalled at nearly the identical radial and tangential position on the platen without requiring the disk to be redressed each time that it is used.
  • the abrasive disk could be sequentially or progressively or randomly moved tangentially to align "low" wear areas of the disk with "high” elevation areas of the platen which would better utilize all of the expensive abrasive particles of the disk.
  • Small increment tangential repositioning of the disk would reduce the requirement for re-dressing the disk as many of the causes which require re-dressing - platen high spots, thickness variations in the abrasive disk, etc. - tend to then be distributed in areas rather than at specific points which is more tolerable within a lapping system.
  • the abrasive disk can also be preconditioned so that high defect spots or areas are reduced in height to reduce the possibility of local scratching on the work piece surface.
  • a hard material can be held stationary against the disk surface (particularly at an edge) or the hard material may be oscillated slowly and radially to knock off or wear down high spots.
  • Another abrasive material could be rotated with its own high (or slow) velocity against the surface of the abrasive disk to remove high spots or loose materials. Any loose or weak abrasive materials at the inner or outer radius of the disk would be broken loose by this initial conditioning treatment and would be eliminated from the system prior to actual lapping of the work piece.
  • the platen may be enclosed in a sunken box or walled area, with significant space below the platen to a lower surface for the containment area.
  • the surface of the platen and the surface which is contacted by the abrasive sheet should be below the upper edge of the protective walling-in enclosure.
  • the plane formed between the work piece and the abrasive sheet should intersect the wall element at least 1 cm below the highest part of the wall.
  • the distance below that plane to the floor of the containment area should be at least 5 cm, more preferably at least 10 cm, and may be 20-50 below the plane.
  • Abraded material may harmlessly collect in the floor area, and the area cleaned out from above (around the sides of the platen or by moving or removing the platen) or from below (by an access panel or regular drainage system).
  • the collected materials may be more readily disposed of and collected in this manner.
  • the walls of the enclosing elements may be metal, coated metal, composite, abrasion-resistant coated material, or sacrificially coated materials, high friction materials, or energy absorbing materials.
  • the walls may be sloped outwardly so that impacting material may be reflected down towards the floor/collecting area.
  • the entire enclosing structure may be removable most easily down from the bottom of the work area, there may be constant or sporadic drainage allowed through the floor area, and the like.
  • a platen 220 is provided with an upper surface 222 (which is shown in Figure 12 as a flat surface with ports 226 for securing sheets to the surface.
  • On the beveled side edge 224 are additional air vent ports 230 for securing subsequently applied abrasive sheet material 228 to said edge 224 .
  • a circular sheet of abrasive material (not shown) or an annular sheet of essentially two dimensional conformation 228 may be applied to the upper surface 222 of the platen 220 .
  • a flat abrasive sheet (not shown) would be secured by reduced air pressure through ports 226 on the upper surface 222 of the platen 220 .
  • the edge 224 of the platen 220 because of the beveling of the edge 224 of the platen 220 , it is not necessary that the upper surface 222 of the platen 220 be flat. That surface may be rough, smooth, arcuate (e.g., spherical segment), or any other shape, with or without features, since the lapping surface is no longer a face of the platen but is the beveled edge 224 .
  • the edge is beveled at an angle between 1 and 89 degrees away from the top surface 222 of the platen 220 ; preferably the angle is between 5 and 45 degrees, more preferably between 5 and 30 degrees.
  • the beveling of the edge provides a geometry to the edge that when, as shown in Figure 13, a workpiece 240 is addressed by the beveled edge 224 of a platen 220 , the beveled edge 224 is parallel to a surface 232 of the workpiece 240 . Additionally, a relatively clean line contact is made between the beveled face 224 and the face of the workpiece 232 so that a relatively flat lapping contact is made.
  • the shape of the area removed 234 by extended contact with the edge 224 of the platen would be nearly rectangular (for most purposes), and only if the lapping were used in more of a grinding fashion would an angularity in the wall 236 be noticeable while there was only a right angle configuration on the distal wall 238 of the area 234 .
  • An angularity or pitch in the wall 236 while the distal wall 238 was relatively perpendicular to the face 232 of a ground area 234 would be a fingerprint of the practice of the present invention.
  • annular ring with the beveled edge geometry has numerous benefits and improvements over a cylindrical section or disk element for the grinding wheel.
  • Systems of grinding wheels with abrasive on the outside periphery of the wheel are known for systems where the abrasive is part of the wheel material itself (e.g., a grindstone) or coated onto the edge.
  • An abrasive sheet material does not lend itself to facile application or use on such an outer edge, both for technical and mechanical reasons.
  • a sheet material could be applied to the outer edge of a grinding wheel: 1) coat abrasive on a cylindrical sheet and cut continuous sections from the sheet which fit the grinding wheel diameter; and 2) cut strips of abrasive sheet material and adhere them to the surface of the edge.
  • the first method would involve a specific new manufacturing process and technique to manufacture such a continuous circular element, and the tolerances for good fit to the wheel would be quite small. It is possible to have the backing layer of the circular cut element shrinkable to fit the article more tightly to the wheel, but adhesive would have been desirable, and this leads to disuniformity.
  • the vacuum hold-down of the present invention would have helped in this format, but the new manufacturing procedure would have still been needed.
  • the second manner of providing an abrasive edge to the wheel would have required that the strip be attached at its ends to form a circular element. This would require the formation of a joint or weld, which would be likely to provide a weak spot, an elevated patch, a wrinkle, or other aspect which would not lend itself easily to use in the fitting of pre-made abrasive sheeting to the end of grinding wheel.
  • the use of the completely beveled edge on the platen in this aspect of the present invention provides a mechanism for providing a continuous strip of abrasive sheeting made by existing technology and available as a staple in the market place as an abrasive surface on a high speed lapping system which can provide linear lapping and polishing as well as complete surface lapping. It is an attribute and fingerprint of this aspect of the present invention to provide a platen with a beveled exterior edge and a continuous strip of abrasive sheet material on at least the beveled edge.
  • the particle distribution in the abrasive sheet may well result in a gradient of slightly lesser density of particles in the upper, smaller diameter region of the beveled face than in the lower, larger diameter beveled face.
  • This particle density may be as slight as 1, 2, 5, or 10 % depending upon the angle of the bevel and the degree to which the underlying support sheet has been shaped by the fitting process. This minor particle density variation has not been noted as providing any adverse effects on the lapping quality provided by this configuration, and the important fact is that the shaped annular disk conforms well to the beveled face and provides a very consistent and smooth orientation of the abrasive sheet upon the beveled edge.
  • a workpiece 254 and a platen 250 with an abrasive surface 252 address each other.
  • the workpiece 258 has an effective center line A - B .
  • the workpiece 254 is moved so that the center line A - B spends more time inside the outer edge of 260 of the platen 250 while the abrasive surface 252 of the platen 250 and the workpiece 254 are in contact during lapping.
  • FIG. 13 shows that the direction of rotation 256 of the platen 250 is opposite the direction of rotation 258 of the workpiece 254 .
  • This aspect of the invention works even better where the workpiece is rotated at the same time that the platen is rotated, to more evenly distribute the time and position of orientation of the workpiece and the abrasive surface. Even if uneven wear does occur, the dual rotation of the workpiece and the abrasive sheet on the platen will reduce any linear effects or artifacts on the workpiece surface.
  • the rotation 256 258 does not have to be in opposite directions, but this is the preferred mode of practice.
  • the time when a workpiece is in contact with an abrasive sheeting is referred to as the total contact time Tc.
  • the time when the center of the workpiece is inside (not merely directly aligned with) the outer edge of the abrasive surface must be at least 50% Tc when operating at a constant speed. That is if the speed of rotation of the platen decreases, the Tc must be weighted according to the surface area fanned or covered by the workpiece.
  • the workpiece center be within the outer edge at least 60% of the time, more preferably at least 75% of the time, still more preferably at least 80 or 90% percent of the time, and it is most preferred and most convenient to have the center of the workpiece aligned within the outer edge of the rotating platen at least 95% and even 100% of the Tc.
  • the combined effect of moving the center of the workpiece inward of the outer edge and the rotation of the workpiece not only reduce uneven wear on the abrasive surface, but provides a synergistic effect in reducing the potential unevenness of lapping/polishing on the surface by both improving the consistency of the abrasive surface addressing the workpiece and reducing any linear effects that any unevenness in the abrasive surface could cause in the workpiece. Additionally, by having an eccentric or non-repetitive movement of the workpiece with respect to the radial position of the abrasive surface, there is even less likelihood of any linear uneven lapping effects upon the workpiece surface.
  • the lapping set-up may include multiple workpieces.
  • a workpiece will normally cover or be in contact with only a very small fraction of the surface of the abrasive sheet. This leaves space or areas on the abrasive sheet available for additional lapidary work. It is convenient to have multiple workpieces distributed about the periphery of the platen carrying the abrasive sheet. At least one workpiece should be oriented as described above with respect to the relative position of the center of the workpiece and the annular ring center line of the abrasive sheet.
  • At least two of the multiple workpieces should be rotating in opposite directions with respect to each other. That is, when viewed from one direction perpendicular to a platen face, at least one workpiece will be rotating clockwise and another will be rotating counterclockwise. It is preferred that with an even number of workpieces, clockwise and counterclockwise rotation is evenly distributed and alternative between the workpieces, and with an odd number of workpieces, the numerical distribution would be n+1/2 and n-1/2 for clockwise and counterclockwise workpieces, with only one pair of adjacent workpieces rotating in the same fashion.
  • This format of distribution with respect to a lapping surface is useful in the practice of the present invention whether an entire platen surface is covered with abrasive sheeting or whether an annular distribution of abrasive sheeting is provided.
  • the problem of uneven wear occurs in both type of systems, the potential for damage is present in both types of systems, although it may be somewhat magnified in the whole sheet system since there is a large variation in the radius and thus the surface speed of the disk, and so any degree of uneven wear provides greater likelihood for that uneven portion to contribute to damage to the workpiece surface. This is simply a matter of probability in that any damaged area has a greater probability of being in contact with a workpiece when it constitutes a larger percentage of the total abrasive surface area.
  • the extension should cover at least 1%, more preferably at least 3%, still more preferably at least 5%, and most preferably at least 10% of the effective diameter of the piecepart. (Note that the piecepart should be somewhat larger than the width of the ring, which is 100% Tc.)
  • Another operation which proves to be of benefit in the operation of the lapping apparatus is to precondition the outer edges of the abrasive sheeting before actual lapping of a work piece.
  • Such sacrificial lapping on the outer edge for a brief period of time e.g., less than 50%, preferably less than 25% or 10% of the actual Tc for the next intended work piece, e.g., for 1-5 seconds
  • the basic system of the platen covered with abrasive sheet material, rotated at high speeds (e.g., 2,000+ rpm) and a gimbaled workpiece would produce surfaces with light band uniformity of at best 4-5 light bands smoothness, and this was attainable only through constant and severe control of the system.
  • the gimbaled workpiece holder is desired in more conventional lapping apparatus as it is difficult to align the upper workpiece holder perfectly perpendicular to the abrasive platen surface. Even if it is initially aligned, it becomes even more difficult to retain that alignment with disturbance from hydroplaning forces and other machine factors, such as uneven bearings, other dynamic forces, and the like.
  • the combination of the gimbaled workpiece holder with annular sheets of abrasive material attenuates or substantially eliminates some of these effects and problems.
  • a heavy support frame for the workpiece and lapping platen (including rotation engine or motor) is provided in combination with a preferably fixed workpiece holder secured to the heavy frame.
  • the lapping portion of the system (the motor and lapping platen) is carried on a heavy frame.
  • the workpiece support or workpiece platen (along with gearing or in combination with the motor) is positionable in three axes (the x, y and z axes). Each axis is separately controllable, with an extensive amount of positioning being capable in the axis controlling the linear spacing between the abrasive platen and the workpiece (the Z axis), e.g., can be measured in full meters.
  • the fine controls on the system would require that there be at least one hundred (100 ) positions available within any centimeter of movement along either axis, more preferably at least 250 positions, still more preferably at least 500 or 750 positions available within any cm of movement, and most preferably that there be at least 100, 250, 500 or 750 positions available for every millimeter of movement of the platen face along anyone of and all of the three axes of movement of the platen face.
  • the degree of control may also be measured as with respect to the rotation of a control element. That is, there may be 36, 72, 120, 144, 180, 200, 240, 300, or 360 individual positions within a single rotation position of a control or switch. These numbers have been selected merely because of their relationship to 360°, which is the basic unit for a rotation, but any other unit or number may be selected, as between 1 and 100,000.
  • the actual construction the best working model of the present invention uses position control with a stepping motor having 50,000 step increments per revolution, which divides the forward motion from a single rotation into 50,000 units of travel. Units of more 5,000, more than 10,000 and more than 25,000 are particularly desirable.
  • Each revolution of the control means may have as little movement of the directed portion of the platen (e.g., one edge moving along one axis) as less than 0.05 mm, preferably less than 0.005 mm, still more preferably less than 0.001 mm, and the like.
  • Screw pins and screw drives have proved easy to configure into the system because the pitch of the screw can be adjusted to control the amount of linear movement along an axis with respect to any particular amount of screw rotation. For example, with a screw drive having 1 thread per cm, a 360° turn would advance the screw and any part attached thereto by one cm. A 36° rotation would advance the screw 0.1 cm. Similarly, with 5 threads per cm., a complete rotation of the screw head would advance the screw and any attached workpieces or platens 0.2 cm., and a 36° rotation would advance the screw 0.02 cm. Thus the sharpness or fineness of the control can be designed by the threading of screws.
  • the mass of the frame also has a beneficial effect upon the performance of the system. As the system is subjected to vibration forces, it is desirable to minimize these forces. This can be done in a number of ways, but the easiest way to have a major impact on controlling vibration is to increase the mass of the support system and the connectors of the workpiece holders and the abrasive platen.
  • the frame of the system should weigh a minimum of 100 kg. For a lightweight, small manufacturing model. More preferably at least 200 kg, still more preferably at least 350 kg. And most preferably at least 500 kg., with no maximum weight contemplated except by the limitations of reasonableness.
  • the weight of the actual commercial embodiment of the present invention is about 600 kg.
  • the apparatus described in this section would generally be a lapper platen system comprising:
  • a slurry of abrasive particles can be added to the lubricant, coolant (e.g., water) which can be used with the coated diamond abrasive sheets. These loose particles could be larger or smaller than the average diameter of the fixed diamond particles, and have a controlled size distribution to enhance the performance of he abrasive disk.
  • coolant e.g., water
  • Different types of chemical additives could also be added to the liquid composition provided between the disk and the work piece, such as surfactant, viscosity modifying (reducing or thickening) agents,, or acidic or basic solutions, etc.
  • Some selectively chosen foreign matter could also be added to the slurry mix, such as glass beads, plastic beads, fibers, fluorescent materials, phosphorescent materials (for examination of the face of the work piece by other means).
  • the different solid or abrasive materials in the slurry could perform a surface separation effect to obtain flatter contact between the work piece and the abrasive sheeting and also additional material removal mechanism effects.
  • the other additives would have to be considered on an individual basis as a function or relationship of the type of abrasive used in each portion of the grinding cycle and the make-up of the work piece and its compatibility with the chemical make-up of the additives.
  • the combination of different abrasive particles with the diamond sheeting can provide unique lapping effects and intermediate effects between traditional lapping with slurry compositions and the high speed abrasive sheet grinding of the present invention.
  • the thickness of the material abraded away during one step of a grinding or lapping process is equal to the thickness or diameter of the abrasive media particles used in the previous step.
  • a process lapping may start with 50 micron abrasive for the initial grind and be followed with 3 micron particle abrasive which removes approximately 50 microns of material (although as noted above, the practice of the present invention may beneficially reduce this amount of removal to less than 90% of the abrasive particle size).
  • 9 micron abrasive will remove 3 microns of material, 1.0 micron abrasive would remove 1.0 microns of material and 0.1 micron abrasive would remove 1.0 microns thickness.
  • a fine pitch screw system with the capability to be moved in 0.1 micron or less increments does not have the capability to be moved through large distances for initial part loading or mounting in the machine whereas many other devices which have micro motion capability such as piezoelectric actuators or thermal expansion actuators are not capable of large excursions of 4 inches.
  • a servo motor to drive a lead screw provides fast continuous motion of the lead screw and the carriage to which the part holder is mounted, but when the servo motor is stopped at the desired contact position it has a natural tendency to "dither" or oscillate mechanically and positionally due to its control system electronics which corrects for the position error sensed. First it will move past the target, create an error, and then move back again past the target making a new error and correction.
  • stepper motor If a stepper motor is used to drive a screw, then very significant accuracies can be achieved with micro stepping control architecture where a motor can be moved in increments of 50,000 steps per revolution.
  • accuracy of these micro steppers with ball screws having typical pitches of 3-5 threads per inch of travel is marginal with respect to the requirements of lapping with 1 micron or less abrasive media.
  • linear electrical motors directly on a carriage slide device has problems in that these motors again have a limited number of magnetic poles which results in minute speed and force variations along the length of travel of the moving portion of the motor device. Also they exhibit "dither" problems at a fixed position, similar to rotating servo drives.
  • Typical CNC (computer numerical control) machine tools operate with small or fine increments of motion and a cutting tool is driven by the strong machine into the piecepart along a prescribed path with the surface finish and accuracy outcome a function of the size of the incremental steps and the speed of the mill cutter. Damage of a submicron layer of the piecepart is not generally a concern with a CNC positionally driven machine.
  • Determining the exact position at which a new part of unknown size or thickness initially contacts a moving abrasive surface is desirable for controlling grinding process parameters during the grinding process. This initial contact position changes in a potentially significant amount each time a new sheet of abrasive is installed for a series of grinding events with progressively finer abrasive media having a different sheet thickness used for a smoother ground surface.
  • the rate of material removal indicates directly the condition of the abrasive media and indirectly the expected quality of the surface finish. It is extremely difficult to successfully use an exclusively position control system to present a workpiece for contact with a high speed abrasive surface such as the abrasive sheeting used in the present invention. About 10 micrometers of material from a workpiece surface is typically removed in about 15 seconds, and machine tool component parts (such as bearings) typically have fitting gaps larger than those dimensions, and the high friction that would exist with tighter fitting components would have too high a level of friction for the smooth movement of equipment necessary for the best practice of the present invention. An excellent criteria for good grinding or lapping action is control of the pressure force (which is difficult to measure) by incremental position steps which are used to create the desired contact force.
  • a workpiece holder is supported on a linearly movable support (usually vertically with respect to the abrasive surface).
  • the workpiece is advanced into contact with the abrasive surface (while the surface is static or while it is rotating, preferably at a speed that does not cause immediate significant abrasion (e.g., less than 10 microns grinding in 15 seconds).
  • the parallelity of the workpiece surface to be lapped and the abrasive surface is preferably adjusted at this point, as by appropriate adjustment of positioning screws or other alignment elements, particularly mechanical, position oriented, linearly oriented elements (e.g., such as those herein described with at least 50 positions settings per rotation with no more than, for example, 0.05mm linear movement per setting, preferably no more than 0.01 mm, and more preferably no more than 0.005 mm per setting) to place the workpiece surface to be lapped in good parallel alignment with the abrading surface of the sheet.
  • the position is indicated (e.g., a program setting, position setting, etc. is indicated within the system, as on a computer) and the workpiece is retracted and removed from contact with the abrasive surface.
  • the workpiece is then advanced towards the rotatable surface of the platen with the abrasive sheeting thereon, with the surface rotating, preferably at the grinding speeds desired (e.g., greater than 500 rpm with a 12 inch diameter outside diameter platen).
  • the advancement is done with a low friction carriage so that the movement of the workpiece is relatively slow (e.g., less than 0.5m/sec., preferably less than 0.4m/sec., and more preferably less than 0.3m/sec. or less than 0.2 or 0.1 m/sec.) and smoothly progressing. This is best accomplished by a system of elements herein described.
  • This system of elements basically operates in a preferred mode by providing both vertical support forces (e.g., lifting forces as by air pressure, hydraulic pressure, pneumatic pressure, electromechanical pressure, magnetomechanical pressure, etc.) and vertical downward (advancing) forces (gravity, air pressure, hydraulic pressure, pneumatic pressure, electromechanical pressure, magnetomechanical pressure, etc.).
  • the system may also be inverted, with gravity operating as a "lifting" force with respect to the vertical movement between the workpiece and the platen (that is with the platen at a higher elevation than the workpiece and the vertical "downward" force being a vertical upward force (provided, for example by air pressure, hydraulic pressure, pneumatic pressure, electromechanical pressure, magnetomechanical pressure, etc.).
  • the difference between the to forces controls the contact pressure between the workpiece and the abrasive surface at the moment of contact and thereafter.
  • One method of solving this positioning and force application problem is to use a screw drive system to move the piecepart from its remote initial mount installation position to a new position close to the moving abrasive sheet and then change the method of controlling the movement of the piecepart from a position based system to a pressure or forced based system for the grinding event only. After the grinding event cycle has been completed, then the piecepart would be removed from contact with the abrasive and then control would be transferred back to the position based control for a "large distance" physical move of the part while the next grinding or lapping event is being prepared.
  • An example of this lapping event change would be to change from a 9 micron abrasive disk to a 3 micron disk to be used in the next lapping event.
  • the lapping machine would require a number of other functional devices (e.g., at least two distinct systems) to allow the easy transition from a positional mode to a force mode. These functional devices would be used as a part of the grinding procedure.
  • a motor driven lead screw would be used for the first positional mode system.
  • the preferred type of lead screw is not a large pitch acme screw with ball bearings but rather a standard bolt type 50 pitch per inch of screw length which gives about 10 times the linear resolution as a 5 pitch (threads per inch) ball screw. Also by using a standard threaded nut with this screw, there is little or no variation in the nut-to-screw location at any position because the third contact element which creates variations, the balls, are eliminated.
  • the pressure is then appropriately reduced in one of a number of cylinders which may be used to support the piecepart holder, sometimes one but usually at least two cylinders, preferably at lest three or four, and up to six offer definite advantages.
  • pressure in three of the cylinders would support most of the weight of the workpiece carriage assembly and independent pressure to the fourth cylinder can be used to raise and lower the carriage with a nominal low force of only one fourth of the weight of the carriage.
  • pressure to the fourth apparatus cylinder has its pressure reduced, this allows the piecepart to come into contact with the moving abrasive at a controlled rate and pressure.
  • the cylinder pressure was changed by a voltage-to-pressure (E/P) transmitter to provide a very low initial contact force, which increased as the lapping event progressed, decreased at the end of the event, and was then changed more to lift the piecepart away from the surface of the abrasive sheet.
  • E/P voltage-to-pressure
  • the force of the workpiece against the surface of the abrasive surface can be seen as a combination of three possible forces.
  • a third component (either a separate supporting component or a driving, downward component) to control the force or position of the workpiece as it contacts the platen.
  • This second position is registered within the system which moves or controls the movement of the workpiece holder (e.g., a computer registers the specific position of the second position). Movement towards the second position may be done with the platen fixed, the platen slightly rotating, or the platen fully rotating, but only a very small amount of material removal is allowed, such as lapping of more than 10 microns for a 50 micron average diameter abrasive particle into the surface of the workpiece should be avoided in this step. While in the second position, adjustments in general parallelity between the workpiece and the abrasive sheet on the platen may or may not be made. After the second position has been reached, the workpiece is removed from the second position to a third position.
  • This third position may or may not be the same as the first position, but is a position which does not afford contact between the abrasive sheet and the workpiece. This distance may be essentially any distance as the second position has been registered by the workpiece moving system.
  • the workpiece holder is then moved from the third position to a fourth position which may be selected by the operator as approximately before the second position (before with respect to the workpiece's path of movement from the third position towards the abrasive sheet surface), to the second position, or where the second position was before contact had been attained, slightly beyond the second position.
  • the fourth position is selected so that the actual contact forces between the abrasive sheet and the workpiece have a maximum pressure of between the desired range of 0.25 and 100 psi, and more preferably within the other ranges of preferred pressures desired in the lapping process. It is again most preferred that the pressure control mode used for the movement of the workpiece into contact with the abrasive sheet surface assures that the contact pressure is within the desired range. This is effectively done by assuring that the difference in forces (between the supporting upward vertical forces and the lowering downward vertical forces is the same as or preferably less than the intended contact force. The chosen difference forces might have to be smaller than the desired contact force to avoid the additional, but temporary force that would be added because of the momentum of the workpiece and the workpiece holder.
  • That momentum would be absorbed, in part by compressive activities, but the momentum would definitely tend to momentarily add to the contact force between the abrasive sheet and the workpiece.
  • the relative forces e.g., the weight is a constant and the air pressure or hydraulic pressure, for example, may be measured instantaneously or controlled
  • the contact force even in the initial moments of contact can be accurately controlled.
  • the contact forces during lapping can be accurately controlled by using stress gauges or the like to indicate the level of forces that must be provided in the support or driving force system provided in the movement of the workpiece holder.
  • a hydraulic or pneumatic dashpot or damper or snubber can be used along with the air cylinders.
  • This device could be spring loaded to raise its plunger or cylinder rod cylinder into an up position toward the piecepart lift mechanism arm.
  • the dashpot will control the speed at which the piecepart contacts the abrasive.
  • the dashpot can be adjusted for fast travel or slow. This can be used to control the momentum in the moving piecepart and piecepart holder.
  • Force sensors can be mounted on the end of the lifting cylinders (e.g., the air cylinders, hydraulic lifters, electronic or electrostatic lifters, etc.) and also be attached to the piecepart assembly arm. As the force sensors are mounted in series with the air cylinders, they would sense and indicate the actual pressure that the piecepart arm is experiencing. If the cylinders are deactivated, the sensor would still indicate the force that the arm is experiencing directly from the screw drive.
  • These force sensors are typically strain gauges mounted on bending beams but may also be piezoelectric or other type devices. The force gauges may be integrated with the force control and position control devices through a computer with a program set up to perform specific levels of contact pressure during each, every or any lapping stage.
  • This same force sensor can be used to sense the force between the piecepart and the abrasive disk. As the piecepart arm is lowered onto the moving disk some of the force supplied by the driven screw on the air cylinders supporting the piecepart assembly is now supplied by the contact force. The net result is a reduction in the force on the sensor. If all of the weight of the assembly were on the abrasive, the force gauge would read zero.
  • the sensor would change signs (if the sensor were initially in a tension mode) and the total force would be the weight of the assembly plus the new applied force.
  • This additional force could be used where the differential between the lifting (supporting) force and the downward force were intentionally kept small so that the amount of contact force could be actively controlled by a driving force applicator.
  • This driving force applicator would be any system which could apply a downward vertical force in controlled amount onto the workpiece holder. Electric, electronic, hydraulic, magnetic, air pressure or any other force supply could be used.
  • the force sensor can be used to establish the location or position of the piecepart as it just makes contact with the abrasive disk.
  • the abrasive disk is stopped (and if desired, a piece of paper, etc. of known thickness is laid on the stationary abrasive) and the piecepart assembly is lowered until it is just in contact, at which time the force sensor will change its reading to correspond with the amount of force now being applied to the piecepart.
  • Contact is now used as a mechanism to establish the position by use of a precision position scale attached to the piecepart slide arm, or by programming into computer operated controls on the system.
  • the force sensor can be a single readout device or multiple units. Use of multiple units increases the reliability of accuracy in the sense that each of the sensors should give the same reading for a given equally shared load, so one bad sensor should give a different reading which can trigger a sensor accuracy review.
  • Using three sensors mounted in a tripod arrangement gives a "three-point" natural contact for equal loads to each device. Also, any defective device would disagree with two others which increases the redundant reliability factor.
  • the part contact force can be easily read out by "taring out” the weight of the part holder assembly. Three force sensors reduce the offset deflection of the bending beam used for mounting an electrical strain gauge sensor.
  • a linear encoder device such as a Hindenhain brand scale or a LVDT (linear variable differential transformer) can be used to establish the position of the piecepart as it is processed by the machine during the lapping process.
  • the position sensor allows control of the amount of material removed by the grinding process by comparing the position of the piecepart assembly relative to its fixed height slide mount to the changing position as the piecepart is ground or lapped.
  • the Hindenhain brand linear encoder has the ability to determine position changes of 0.1 microns or less, and therefore is quite useful within the objectives of the invention.
  • Another device which could be used to accurately determine position as an alternate to the Hindenhain device is a LVDT device.
  • An edge finder device used by machinist to physically locate the edge of a part to be machined for reference input for a CNC machine controller or for manual machining control may be used to determine that the air cylinder has lifted the assembly off the bottom home position. Another similar unit may be used to confirm that the assembly is in a fully raised position. These units typically are able to locate within 0.001".
  • An edge finder switch can be used to sense liftoff of piecepart contact with abrasive - establishing the "second position".
  • Small pneumatic or hydraulic cylinders can be used either to independently counteract part of the weight of the work holder assembly or be adjusted to exactly counteract the weight of the assembly or to provide more lift than the assembly. This last arrangement would then require a downward force to push the workpiece against the abrasive table.
  • An electronic pressure sensor can be used with the force lifting mode (or the position sensing mode) such as with the air cylinders to be used to calculate the theoretical lifting force of the cylinders.
  • Friction slide forces of typical slides are generally greater than the desired grinding contact forces which can be very low, in the 1 to 20 lbs. range for most parts.
  • a second method of providing pressure force control during lapping or grinding would be to use a linear motor operated in a position mode control for moving the piecepart about the machine and then changing the mode of the motor control just before the part makes contact with the moving abrasive.
  • the motor current on a direct current DC motor represents force for a linear motor (or torque for a rotating motor) the control mode change can be made very quickly by modern controllers.
  • linear motor position mode system would be used with other functional devices much the same as for the FIRST METHOD using a screw drive system.
  • the above described precision position scale which can be used to establish the position of a piecepart starting the lapping or grinding process and to follow the size change as material is removed.
  • the initial position of the piecepart in contact with the abrasive wheel can be determined by observing a change in the current of the linear motor upon making contact between the piecepart and the abrasive platen as less force is required to sustain the weight of the workpiece assembly when part of the weight is borne by the contact force.
  • a lead screw such as a lead screw; air cylinders both of traditional design and AIRPEL low friction design; a dashpot to control descent speed; a force sensor system; or an edge finder switch; or auxiliary lift cylinders.
  • a third method that can effect a solution is the use of hydraulics to both move the piecepart precisely to different positions and also to effect a pressure or force based contact with the moving abrasive media.
  • a single low friction cylinder would be used which would have a number of common input fluid sources which are coupled or decoupled with the use of solenoid valves. The cylinder would be either connected directly to the work holder lift assembly or connected in series with a force sensor.
  • the cylinder and work holder assembly would be positioned very accurately by the use of high pressure low leakage gear pumps such as those with the Zenith brand name.
  • the nominal pressure would typically be less than 100 psi even though the pumps would have the capability of generating more than 1,000 psi.
  • a large capacity gear pump would be used for fast travel and a very small gear pump would be used to make precise minute incremental changes in position.
  • the gear pump would be operated by use of a stepper motor which will allow a fixed increment of fluid to be injected into the cylinder which would raise in proportion to the surface area of the cylinder piston.
  • a 1 inch (2.54cm) diameter cylinder would be used with a pump which has a volume output of 1 cc or less per revolution and a step motor which has 50,000 incremental steps per revolution to obtain very small changes in position per step increment.
  • a precise position measurement device such as a Hindenhain scale or a LVDT is used to indicate position of the assembly
  • a change of position is sensed and a corresponding corrective amount of fluid is injected into the cylinder by an activated gear pump.
  • Large diameter cylinders preferably would be used to reduce cylinder friction so that the cup seal lips are not held too firmly against the cylinder wall because the hydraulic pressure is low due to the large surface area providing adequate lifting force to raise a typical work holder assembly weighing, for example 30-100 pounds, such as approximately 60 lbs.
  • the downward force may be controlled by an air/oil (pneumatic pressurized oil container) source.
  • an air/oil pneumatic pressurized oil container
  • the solenoid valves are controlled so that the hydraulic pressure applied to the cylinder is from an air/oil source.
  • the air pressure is reduced and the cylinder starts to drop but the speed is held in control by a separate adjustable dashpot or by orifice flow restrictors.
  • Contact abrasive pressure during the grinding event is then controlled by an E/P voltage controlled pressure transmitter such as supplied by Wats Co. or Rosemount Co. to change it as desired over the duration of the grinding cycle event.
  • the air/oil device can be used to lift the piecepart from the surface of the abrasive and then through the use of solenoids, transfer can be made back to the gear pump based position control system.
  • a ball check valve can prevent formation of fluid bubbles when a vacuum is generated by reversing a gear pump when a cylinder is bottomed out and can't move.
  • Mechanical stops can be used to limit the motion of the cylinder.
  • a load cell force sensor system can also be used in series with the cylinder to obtain an independent reference of the force which can be compared with a calculated force based on the pressure readout device sensor which gives the pressure of the fluid in the cylinder at all times.
  • the disk needs to be positioned initially accurately on the platen when installed and then maintained in that position by at least one mechanical means.
  • One technique for initial accurate positioning would be to punch a small or larger hole at the center of the disk and have a corresponding pin or post located at the center of the platen. By placing the disk on the pin or post, the disk would be centered and restrained at its true balance position. The disk could be easily prebalanced with respect to the hole without the necessity of placing it on an active platen.
  • the existence of a pin or sub post would not materially affect the use or utilization of the expensive disk or affect the processing techniques of lapping or polishing as the linear velocity vector at the center of the disk area is quite small. The center of the disk is seldom, if ever, actively used in polishing.
  • a simple, inexpensive, stable and adjustable mechanism is to mount the vertical piecepart assembly mounting plates, each of which has a "living hinge" on one end and 1 or 2 adjusting screws on the "free" end.
  • the adjusting screws allow the free end of the plate to be pivoted nominally in a pure axis rotation about the semi-fixed hinged end which creates the ability to adjust the position of a mounted apparatus in one axis.
  • the use of a second similar living hinge plate mounted at a position 90 degrees to, but flat to the first plate allows the nominal adjustment of the plate about the second axis perpendicular to the first.
  • Operation of the lapper of the present invention is typically at 3,000 rpm with a 3M Diamond Coated Abrasive disk having a twelve inch diameter.
  • the disk is held to the steel rotating platen by water film surface tension and positioned by a 0.5 inch (1.27cm) diameter hole at the center of the disk used with a 0.5 inch (1.27cm) diameter post at the center of the platen.
  • the disk lost its surface tension adhesion and was thrown off the platen while polishing a tungsten carbide piecepart.
  • the forces on the disk were such as to lift it off the centering post, and the whole disk was thrown off to the side of the machine, opening a cavity at the top of the machine post.
  • the 0.5 inch (1.27cm) centering post was made larger in diameter to a 1 inch (2.54 cm) diameter or more post.
  • the post could have a non-circular shape with at least one surface positioned against a center post which would resist rotation, such as a hexagonal shape or an oval shape which would prevent the disk from rotating relative to the tangential surface of the disk.
  • the post could also be made higher so the chance of the destructing disk climbing up the height of the post would be diminished during this type of event.
  • Another technique would be to employ a clamp type of device to any of these round or non-round posts to clamp/hold the disk firmly to the surface of the platen at the center area of the disks which is not used for polishing because of the slow lineal velocity in that sector.
  • the clamp could consist of a spline locked washer pressed on the disk surface with a thread nut engaged with a top threaded post. Springs could also be used to control the amount of force and to evenly spread the force uniformly. Ball detent or other snap latch fixturing devices cold also be employed. As previously noted, since this section of the abrasive sheet would not be in lapping contact with a workpiece, adhesive could be used in this area to secure the sheet while vacuum was used in the other area to improve planarity.
  • Solution Use diamond or other abrasive disks without using PSA adhesive and first position the disk at the true center of the platen by use of a centerhold in the disk positioned over a post positioned at the center of the platen (or by other centering means) and then hold the abrasive disk to the platen by use of vacuum by use of a rotary union on the hollow rotating platen shaft.
  • the preferred area to apply the vacuum would be at the inner radius of the disk which would seal out first as the disk is installed at the platen center and also because this inner one fourth or so of radius is not used much for lapping because of slow surface lapping velocity.
  • the second most preferred vacuum area would be the outer 1 ⁇ 2 inch (1.27cm) of disk radius at the periphery of the disk as this would also not be used much and would have large holding force.
  • the adhesive is usually coated on both sides of another thin film, all of which have dimensional tolerances so one area of a disk may be thicker than another and result in non-uniform abrasive wear. All the variations in thickness of the sticky adhesive can be eliminated by use of the vacuum hold-down holes of the platen.
  • a disk By marking a disk with color pen or mechanical cut-outs, notches, etc. and positioning this disk mark on a corresponding mark on a platen, a disk is reinstalled at a location where it "fits" and does not have to be reground to size for the next operation, saving time and disk wear costs.
  • the disk can become damaged and crumpled and tear and then either be thrown off the platen or wedge between the platen and the piecepart holder which can create large dynamic forces which result in dangerous flying shrapnel.
  • a vacuum hold-down the vacuum would have a tendency to suck the abrasive debris particles into the vacuum holes, eroding the hold edge and enlarging them, which would locally distort the working surface of the abrasive disk.
  • centrifugal force from the 500 to 3,000 rpm 12 inch (30.5cm) diameter disk would have a tendency to curl or raise up the inside disk edge.
  • a simple, eccentric harmonic motion, constant speed rotation as provided by a DC or AC gear motor hub can be used to drive a linkage system will provide smooth continuous motion of a workpiece with most of the time in a given hub rotation cycle with the workpiece operating at the outer periphery of the abrasive disk which has the highest surface speed and highest grinding action and a very small portion of the cycle time spent at the inner radius, low surface speed, and reduced grinding action portion of the disk.
  • a piecepart may need to be rough ground flat which requires a rigid (non-pivoting) piecepart holder, but then may need to be processed on a spherical ball piecepart holder to achieve extreme flatness of 1 to 2 light bands or less. It is desirable to do this on one single machine using coarse grinding media of 40 micron particle on the rough finish using the rigid holder and 3 micron particles using the pivot holder.
  • a precision rigid piecepart spindle piecepart holder system can be constructed with vacuum holding of the piecepart for rough grinding the piecepart flat. Then a flat sandwich construction spherical ball pivot piecepart holder can be constructed with an internal vacuum chamber to allow the piecepart to be held or mounted with the same vacuum source and utilize an internal spherical ball for allowing the piecepart to "float" on the abrasive surface rotating in contact with the piecepart holder.
  • the platen can be constructed with an outboard raised circular land area and have a lower inboard area to avoid contact with the piecepart but yet have a further recessed (depressed) lip or edge so the inner radius of the annular abrasive disk is below the inboard area of the platen so that water or debris on the surface of the platen travels above or on the top surface only of the abrasive disk and does not raise the inner radius.
  • This is shown in Figure 25, with platen 1400, abrasive sheet 1402, inboard area 1404, and the distance of the inner radius of the annulus below the inboard area shown as 1406.
  • a piecepart holder can be constructed as a sandwich of two flat surfaced plates with a single ball at the center. This ball will transfer downward abrasive contact pressure force to the piecepart and yet allow the surface of the piecepart to move freely in contact with the moving abrasive surface so that it is in alignment with this non-perfect perpendicular mounting between the holder axis and a normal right angle with the platen surface.
  • the vacuum present at the surface opening port holes of the rigid spindle holder can be transferred through sealed internal passages in the sandwich holder to the piecepart contact surface simply by clipping a flat pancake sandwich holder to the rigid holder. Because both the rigid holder surface and the matching piecepart surface is very flat and smooth, an effective vacuum seal is effected between the two surfaces upon contact. Surfaces need to be cleaned to obtain a good seal.
  • the ball can be sealed with RTV (room temperature vulcanizing rubber), sealants or grease or other material.
  • Two concentric rings of plastic or elastomer can be positioned so as to form a passageway for vacuum transfer from one surface to another and yet seal the passageway from leakage to outside the sandwich.
  • the outer ring can be attached to the sandwich by adhesive or other mechanical or cast-in-place means.
  • the elastomer can flex with a controlled stiffness to allow angular motion centered about the ball.
  • Both sandwich plates can be precision aligned perfectly parallel to each other before attaching the elastomer rings and they would tend to maintain this parallelism for presenting the piecepart to the abrasive surface. Radial pins in a controlled slot length will prevent over travel on the spherical ball pivot and also prevent tangential rotation of one sandwich disk relative to the other for torque input to the holder unit.
  • Pieceparts tend to hydroplane when they are held in contact with high speed platens using a water film that develops a boundary layer between the platen and the piecepart.
  • the resultant piecepart is not ground flat because the boundary layer pressures tip the part upward at the leading edge.
  • a piecepart can be processed, the abrasive disk changed and the piecepart brought into close proximity to the moving abrasive disk, perhaps 1 to 10 mils (0.001 to .010") away. At that time, an excessive amount of water lubricant can be applied to the surface of the disk which would tend to hydroplane the piecepart without having contact with its abrasive particles.
  • a force sensing device can indicate when this physical contact has been made with the water wetted surface.
  • a correlation can be established with the amount of force sensed and the exact water flow rate to determine the precise distance between the piecepart and the abrasive sheet. Then the water flow can be reduced progressively while the piecepart is lowered to the abrasive part surface until grinding or lapping action starts to take place.
  • the water film would act as a protective barrier at first contact and allow an algorithm estimate be made of the necessary vertical action required to remove very limited amounts of piecepart material, perhaps 0.1 micron per second or less.
  • This whole procedure could be automated and computer controlled with the parameters of force, flow rate, rotational speed (or any combination thereof need) correlated to separation distance.
  • Individual parts typically 1(1.27cm) to 2 inches (5.08cm) in diameter or rectangular which may be thin (.010 inch, (0.0254cm)) or thick (0.500 inch, 1.27cm) can be fixtured to a precision flat steel, other metal, or other material plate by use of paraffin wax as a bonding agent.
  • the plate or part can be coated with wax or wax simply melted on the plate between the part and plate and the part placed on the plate, heat applied and the two would have a fully wetted surface of molten wax.
  • the parts could be positioned by mechanical or other means of uniform pressure or force so they lay flat with a uniform and controlled thickness of molten wax.
  • the mechanical alignment pressures should equal or exceed the pressures to be encountered during lapping to assure that there is no movement under the lapping pressure.
  • the parts Upon cooling the part/plate assembly, the parts would be positioned accurately and strongly to the plate ready for lapping action. Then the plate could be attached to a piecepart holding device by use of a vacuum chuck or by use of magnetic chuck if the plate were steel.
  • the piecepart holder would have a ball type pivot close to the lapping action surface. Plates could hold one or many individual parts.
  • the plate/part assembly Upon lapping one side, the plate/part assembly could be heated, the parts removed and if desired, the parts could be reassembled with heated wax on the plate with precise parallel alignment with no danger of damage to the lapped surface because of separation from the plate with the wax In this way many plates could be preassembled for high production rates with a single lapper.
  • These small parts can be fixtured to a flat surfaced piecepart holder or a holder which has small shallow pockets, just larger than the length and width of the flat part so that the exposed surface of the part protrudes away from the holder. In this way, the abrasive disk polishing action is applied to the piecepart and not the holder.
  • a medium temperature wax can be melted and used to bond a rough surfaced part to the flat smooth surfaced part holder plate.
  • the flat plate in turn can be attached to a rotating pivoting arm which is swept across a portion of the surface of the high speed rotating disk until a smooth flat polished lapped surface is generated on one side of the piecepart.
  • the part holder plate which would have 1 or 2 or many more parts attached to it in a fixed mounting pattern could be brought in contact with another mounting plate having a flat surface or a shallow pocketed surface pattern which matches the first part plate.
  • a higher temperature wax (than the first wax) could be melted at the surface of the parts already lapped and as they were held in flat contact with the new plate, the original lower temperature melting point wax could release the parts from the first plate and upon cooling somewhat, the parts would be transferred as a group to the second plate ready to have the rough remaining side lapped as the first plate is readily removed.
  • High production rates of lapping flat parts on both sides with good parallelism could be achieved.
  • a piecepart holder can be constructed out of a heavy metal such as steel which has substantial mass very close to the surface of the abrasive disk. The unit will be allowed to move freely with the surface by the ball-end holder. A substantial hole can be made within the ball-end device which would allow vacuum to be coupled to the piecepart holder individual part pockets to firmly hold the flat pieceparts up tightly against the tight fitting pocket. To create and maintain a good vacuum, a thin layer of oil or grease can be applied to the piecepart to seal any leakage paths.
  • a disk can be fabricated with abrasive coating covered on the whole surface of the disk. Then the inside section of the abrasive toward the center of the disk could be removed by grinding or peeling it off leaving the backing material intact with the centering hold. Here the piecepart could be in contact with the raised section of the abrasive on an annular outer ring only as the abrasive is raised (by coating) from the disk backing material (usually plastic sheet).
  • Another way would be to punch out the center ring of the disk for separate use and then use a centering plug with a small locating hole so the plug could be centered on a platen center post and the annular disk centered on the plug, become fixtured by the vacuum grip platen and the plug removed for complete freedom of movement of pieceparts over a disk as the post could be removed from the platen also.
  • a ball is used to support the applied contact force of the wobble plate.
  • the ball is constrained in a cylindrical hole such that the ball is free to fall loose with the weight of the lower movable section of the wobble plate and the weight of the piecepart combined.
  • There may be 3 adjustable screws at 120 degrees apart which act as parallel location stops to hold the lower piecepart parallel to the wobble plate spindle bottom flat surface. This results in the piecepart being parallel to the moving abrasive surface.
  • the loose ball will allow the free lower section of the piecepart and holder to be held accurately by the 3-point screws.
  • a high speed lapping system can use fixed diamond abrasive coated or plated on a disk sheet of material and be used on a rotating platen disk with a diameter of 12 inches (28.5 cm) when operating at 3,000 rpm which gives a surface speed of about 9,000 feet per minute. If a larger diameter platen wheel of 15 inches (38.1 cm) diameter is used, the rpm can be lowered somewhat to perhaps 2,800 rpm to achieve the same 10,000 (or 9,000) feet per minute (fpm) and if the wheel diameter is 18 inches (47.7 cm) diameter, then the speed can be further reduced to produce 9,000 - 10,000 fpm at the outer periphery of the disk. Any reduction of rotational speed for large diameters is desirable because of the potential danger of a high inertia wheel creating problems if a disk is damaged or comes loose.
  • the surface finish smoothness and flatness of hard parts made of metal or ceramic or other materials vary as a function of the work force on the piecepart as the workpiece is held against the surface of a high speed 9,000 to 10,000 fpm abrasive lapping action.
  • the water flow rate is substantially increased at the end of the cycle to produce a very smooth and flat surface with a low rate of material removal.
  • Changing of the water flow rate to alter the material removal rate and to change the surface smoothness could be easily done with an automatic water flow rate control system which varies the flow rate during an abrasive cycle.
  • the rotating platen is round in shape with about a 12 or 15 inch (28.5 or 38.1 cm) diameter.
  • a rectangular corner box is constructed as described earlier to deflect explosively propelled pieces downward into a collection area. The deflection may be from a vertical surrounding surface coupled with a lip or partial cover which reduces the amount of shrapnel which can move vertically out of the work area, as described above.
  • the box is desirably constructed of a soft plastic (or rubber) such as 1 ⁇ 2 inch (1.27 cm) thick high density polyethylene which would tend to absorb impact from a heavy metal free flying broken-loose part without ricocheting the part back into contact with the rotating disk which prevents it from being thrown again or damaging the part.
  • the "square" corners provide a remote area to trap the part and to contain the part as it stopped moving by being impacted on one or more mutual walls. Having a distance between the flat walls and the rotating disk which is somewhat larger than the largest size of the piecepart, centrifugal force would tend to drive the part off the disk radially and allowing it to eventually roll or move tangentially to a neutral corner of the box away from the disk. In the same way, crumpled abrasive disks are collected by the neutral open corners. Having a ledge over the inside portion of the box also helps trap the parts.
  • the vertically moving piecepart assembly can be mounted on vertical slides and a chain or cable used with a counterweight which is perhaps 10 lbs. (4.6 kg) heavier than the 30 lb. (13.8 kg) assembly.
  • a counterweight which is perhaps 10 lbs. (4.6 kg) heavier than the 30 lb. (13.8 kg) assembly.
  • a method of changing parts quickly so that one side of a piecepart can be lapped, the part turned over and the second flat side be lapped to be parallel to the first side Typically .001 inch (0.025mm) to .002 inch (0.050 mm) or less is removed from each side.
  • This flexible group assembly of PSA bonded workpieces could then be held into position against a precision flat surface of a workpiece holder having random vacuum holes over its surface which would all be sealed by the wide and complete expanse of tape covering all the vacuum holes and at the same time firmly holding the individual workpieces to the holder.
  • the group would be removed, tape applied to the lapped surface side and the tape on the unprocessed side would be easily peeled off.
  • the tape would not only fixture the parts but would protect the precision lapped side from scruffing action of rubbing on the holder.
  • a coiled spring can be used to apply a self correcting force between the workpiece holder plate having a gimbal spherical bearing and the rotating drive shaft of the rotating piecepart holder.
  • This spring would be made of metal or plastic material which would allow the straightening action to be applied but also would introduce vibration damping for excitation vibrations set up by the high speed contact abrasive action.
  • One or more solid plastic coupling bars could provide damped spring action also.
  • a vacuum hose could extend from the shaft and be coiled with perhaps one or less on multiple turns which nominally lay flat with the upper surface of the workpiece holder which would minimize the creation of uneven "normal" direction workpiece contact forces as the workpiece holder turns.
  • the abrasive sheet carrying platen is mounted on a thick heavy steel support plate with leveling jack screws on the four (or three) outer corners to get a nominal axis alignment of the platen with the axis of the piecepart holder to be coincident with the axis of the platen abrasive spindle.
  • a swing arm is mounted on the piecepart holder which is rotated slowly about the stationary platen. The swing arm is extended out to the surface of the platen. This measurement indicates the "Z" axis error perpendicular to the surface of the platen at different "X” and "Y" coordinate positions on the horizontal surface of the platen. Adjustments are then made to align the lower platen mounting plate to the upper piecepart axis.
  • An upper frame can also be constructed for the pivot arm lapper by attaching the bottom portion of the stiff pivot vertical post to a round solid steel rod which in turn is attached to the base of the machine frame. Then two long arms are attached to the upper portion of the post at 90 degrees to each other, aligned with the "X" and "Y” axis. These arms can be fixtured with threaded screws on the outer ends and both "X” and “Y” can be adjusted independently with these screws which are in effect bending this rigid post at the base. Mechanical clamps hold the post in place after adjustment. This alignment adjustment could be automated with stepper motor driven screws, piezoelectric actuators, etc.
  • adjustment actuators There are a variety of different adjustment actuators which can be used. These include, but are not limited to a threaded bolt, motor driven threaded bolt, piezoelectric actuator, and a thermal expansion bolt (e.g., electrically heated thermal expansion bolt).
  • a stepper motor, servo motor, DC or AC gear motor, and the like can be used motor to drive the alignment arms to different positions and make corrective adjustments to align both axis of piecepart and platen as indicated, for example, by an out-of-plane gap sensor.
  • An annular ring disk can be used on a flat rotating platen which is made from the original circular disk of abrasive media by cutting out these rings in a cookie cutter fashion.
  • Typical rings may be 18 inch OD (47.7 cm) x 15 inch (38.1 cm) ID; 15 inch (38.1 cm) OD x 12 inch (28.5 cm) ID; 12 inch (28.5 cm) OD x 8 inch (20.3 cm) ID.
  • a piecepart which is presented in contact with the rotating ring abrasive disk typically would be swept across both the inside diameter portion of the disk progressively to past the outer diameter of the annular ring where both the inner and outer radius of the disk would have diameters and surface speeds and abrasive action and disk wear, fairly constant across the full surface of the disk ring thereby reducing the cone effect wear on a given disk which would produce better flatness and more uniform roughness surface finish on a piecepart.
  • expensive diamond particle type of abrasive disks can be fully utilized for good cost savings and efficient use of the abrasive media.
  • a pivot arm could be used to sweep the workholder back and forth across the annular abrasive disk ring with a preferred contact to occur in a quadrant of the abrasive sheet which provides a stabilizing friction contact force directed away from the rotating axis of the pivot arm.
  • an X-Y table can be used to sweep the width of the annular ring.
  • a single solid circular disk could be cut into multiple annular rings and the core center circle could also be all sold and used as separate units with no manufacturing waste.
  • the disks could also be cut into ellipse or oval shapes with an annular ring shape where the outer and inneredges of the disk would be "moving" relative to the piecepart and not have a tendency to produce nonuniform abrasive wear tracks on the piecepart as much as a true circular abrasive disk.
  • the piecepart is also rotated as it is presented to the abrasive sheet surface and is being lapped. This assures even lapping address by the surface of the piecepart to various radial portions of the annular abrasive distribution.
  • Solution If an 18 inch (47.7 cm) or smaller platen is constructed with concentric paths of vacuum holes spaced at various radius of the platen, or if scattered holes are positioned to not create a circular track and to avoid making abrasive "track” patterns, the exposed holes would be sealed with a pressure sensitive adhesive thin plastic film on either or both the inside or outboard portion of the vacuum holes left exposed when applying the nonadhesive backed abrasive disk material having an annular ring shape with an inside and outside radius, either circular, oval or other shape.
  • This adhesive backed sealing disk or ring can be left on the platen for a duration of time and it can be used to register or accurately position guide the annular abrasive disk onto the true center of the platen for achieving good dynamic balance of the very high speed rotating assembly operating at perhaps 3,000 rpm or 10,000 surface feet per minute. Safety is very much enhanced by good balance and the quality of surface grinding or lapping is also enhanced by good circular location and strong reliable vacuum hold down of the abrasive disks which may be constructed using fine diamond particles or other media.
  • the inboard non-abrasive disks described above to reduce lifting of the annular abrasive sheet by grit, slurry or water would also solve this problem.
  • Some specialty grinding techniques can be improved by having an abrasive media disk with a slightly angled surface relative to the normal typical flat plate surface for high speed (e.g., above 500, above 1000 or about or above 3,000 rpm, e.g., up to and beyond 10,000 sfpm) use of abrasive sheeting such as fine abrasive particle coated disks such as diamond coated disks.
  • Annular rings of diamond or other media coated abrasive disks are generally fabricated in thin disks with thin metal or plastic 0.005 inches (0.12mm) thick, more or less, that is locally elastically conformable to a hard surface.
  • a flat rotating platen can be constructed with a portion of the surface raised somewhat from the flat circular surface and a cone angle created on this surface to which an abrasive annular ring is adhesively bonded or held in position by vacuum holes to this angled raised ring.
  • a piecepart can then be presented to this cone shaped surface at an angle to the platen perpendicular which is approximately the same as the abrasive disk cone angle.
  • the piecepart presentation angle may either be more or less than the abrasive angle to control the portion of the piecepart surface that is in contact with the rotating abrasive for optimized grinding/lapping action.
  • a conventional milling cutter can produce a relatively flat surface with a 16 rms finish.
  • a special media holder can be clamped in the spindle which has a flat precision surface perpendicular to the machine spindle centerline.
  • a flat abrasive with a pressure sensitive adhesive would be attached to the special media holder
  • the abrasive could be die cut into an annular ring, for example 6 inch (14.3 cm) OD and 4 inches (10.2 cm) ID.
  • the abrasive should be in contact with the work piece.
  • the machine table moved in a crossing pattern to evenly distribute the lapping action.
  • a supply of coolant fluid should be used to keep the work piece cool. It could be pumped through the spindle and special holder if available.
  • a typical material removal piece pass would be 0.0001 - 0.0003 inches (0.025 mm to 0.076 mm) in the "Z" direction.
  • the piecepart holder assembly be held by a ball pivot type of device located as low as possible (as close as possible so that the central point of rotation of the pivot is as close as possible to the abrsive sheet surface when contact is made. It is also best to align the total piecepart assembly so all the individual parts are floated equally by the thin boundary layer of coolant fluid on the surface of the disk which may be less than 0.001 inch (0.025 mm) in depth. With this type of gimbal pivot, this boundary layer thickness has a tendency to remain uniform even with slight out-of-perfect-perpendicular alignment between the vertical piecepart holder shaft and the high speed abrasive platen. Foreign debris contaminates pivot joints and create unwanted friction.
  • a work holder is created with the use of a spherical ball attached to a shaft which provides a pivot action close to the bottom of the workpiece holder assembly.
  • a sandwich of washers (between the piecepart holder housing and the ball) act as a rigid base to transfer polishing normal force downward on the vertical shaft to push the pieceparts onto the abrasive platen.
  • the washers apply only a small to prevent slack between the ball and the holder, or the resultant ball friction would prevent free pivot action on the ball.
  • the work piece must be allowed to "float" on the boundary layer. This is done with a gimbal mechanism which puts pressure down on the rotating work piece. It also allows the work piece to "gimbal" in the horizontal plane while an independent driver pin drives the work piece around the centerline of the work holder shaft. The amount of down pressure also effects the boundary layer.
  • the work piece floating on the boundary layer of water allows the abrasive media and platen imperfection to be averaged out, so high spots on the abrasive do the lapping while the low spots are filled with water, allowing the lapping action to take place and produce a finished part (work piece) that is flatter than the media and platen.
  • the work piece will only be as flat as the boundary layer.
  • Water is pumped through the work holder and into controlled orifices or jets in strategic locations that force a boundary layer to form between the work piece and the abrasive media.
  • the water stabilizes the work piece while presenting it to the rotating platen initially and while lifting the work piece off after lapping is complete.
  • a system is provided to effectively extend the too short surface contact length dimensions of the pieceparts to allow them to be presented flat to the abrasive surface.
  • an adequate boundary layer is generated and maintained while the individual pieceparts are being lapped by adding a secondary device to the piecepart holder device.
  • This sacrifical device which would have sufficient surface area and length would be mounted outboard of the piecepart on the piecepart holder device. It would also be ground down simultaneously with the pieceparts in a sacrificial way.
  • a typical shape of this can be a disk of metal such as brass which would be mounted on the outside annular position of a tool piece holder with the to be lapped pieceparts mounted inboard of these on the periphery of a round piecepart holder.
  • the sacrifical piece should have a susceptibility to grinding which is within about 50% of the workpiece (either greater of lesser, preferably lesser) to assist in more uniform grinding.
  • the susceptibility to grinding can be readily measured by grinding identical surface areas of the materials, with similar initial roughness, for the same period of time, at the same speeds and pressures, with the same abrsive sheeting and comparing the amount (e.g., weight) of material removed from each sample by the lapping. As the total exposed surface area is ground down, the pieceparts are held suspended above the high speed moving abrasive by the large surface area of the sacrificial disk.
  • each high spot When the disk rotates at its normal high speed, each high spot will have a tendency to hit the piecepart and set up a vibration which will reduce the smoothness of the lapping abrasive action.
  • Localized distortions of the platen surface will also have a tendency to penetrate the boundary layer of liquid between the platen (covered with a thin sheet of diamond or other coated abrasive) and the piecepart and produce a localized scratch or track on the piecepart surface.
  • Surface defects on the platen structure may be generally transmitted through the thin abrasive disk and produces a bump or high spot on the disk.
  • An existing platen can be "dressed" on a machine by bringing it up to full speed rpm and lowering a heavy flat abrasive coated piece unit directly onto the bare rotating platen and grinding or lapping off the bumps, and high spots. Even full out-of-flatness surface variations can be removed by first using a coarse abrasive and progressively using finer abrasive or lapping abrasive media. The platen, in effect, becomes the workpiece and the workpiece becomes an abrasive surface or sheet.
  • the typical first abrasive may be 40 micron metal bonded diamond and ending up with 3 micron or less diamond or ceramic abrasive depending on if the platen surface is chrome plated, stainless or bare steel.
  • the surface area of the abrasive lapper disk be large enough to cover the total area of the platen with a slight overlap and it could be oscillated back and forth across the platen, could be stationary or rotating at either slow speed or rotating at very high speed so the tip speed of the grinding disk will provide uniform removal of platen material at the low surface speed of the inner radius of the platen.
  • Different geometries of adhesive disks could be used. Also a piecepart holder already in use for normal lapping could be used to perform this function.
  • the surface of metal objects are polished for many reasons including the optical examination of a metallurgical characteristic, to create a smooth low wear tight hydraulic or fluid seal and other uses.
  • this polishing is done on low speed 5-200 rpm or so rotating flat platen disk wheels of various types of construction may be used, such as aluminum, steel, plastic, composite, cloth and other materials.
  • the wheel surface is very flat and the workpiece to be polished is held with controlled pressure by hand or work holder against the rotating wheel with water or other fluid wetted abrasive particles introduced as a slurry or disks of fine abrasive sheets "stuck" or bonded to the rotating wheel.
  • This process slowly produces an accurate, highly polished surface and it is labor intensive and expensive if not automated. Inaccurate platen or shaft machining or loose bearings or weak machine structure frameworks may cause polishing accuracy problems.
  • Options also may change the contact pressure (between the abrasive sheet and the workpiece during lapping) as a function of process time or the workpiece rotated to distribute polishing across the surface.
  • a unique method to provide a very “flat” and accurate stable rotating platen disk surface is to mount the platen to a "weak" shaft which allows the rotating disk mass to seek a true “smooth" center above its first rotating natural frequency. The motor drive speed would be increased above the natural frequency of the rotating platen with abrasive sheeting thereon, the workpiece part presented in contact for polishing, then removed from contact prior to reducing the disk rpm.
  • a precision ground rotating platen can be fabricated with slightly raised spiral surfaces having different shape patterns from the inside center of the platen toward the outer periphery of the platen. These spiral patterns would create short land areas at the top surface of the platen of varying widths and shapes with areas between these land areas that are somewhat lower, perhaps from 0.002 inch (0.05 mm) to .010 inch (0.25 mm) or more. Then a thin plastic coated abrasive disk that is uniformly coated with precision fine abrasive would be mounted to the round platen and held in place by vacuum hold-down holes either on the raised land surface or on the lower surface area or a combination of holes in both areas.
  • the raised land areas could be produced by manufacturing a precision platen and acid etching the land area geometry configurations of the lands.
  • the boundary layer of fluid coolant would be effected by the length of the land area under the piecepart, the direction of the spiral or radial or circular annular land shapes or a combination of these geometries.
  • the effects on the boundary layer thickness would be the rotating speed of the platen, as related to the vector speed, including direction for the surface relative speed between the two, the viscosity of the fluid, the normal force pressure of the piecepart holding it to the platen.
  • the boundary layer thickness which would vary over the surface of the piecepart would affect how the individual particles of abrasive normally sticking 1/3 of their size about the bonding agent, either metal plating or plastic bonding, surface of the abrasive disk. If more liquid is applied, the boundary layer would tend to be thicker and less abrasive material removed is achieved.
  • the local pattern of the surface of the abrasive contact area can be utilized for the optimum grinding action using only one portion of the abrasive disk with the non raised section between the land areas allowing free passage of grinding debris.
  • the disk can be unmounted by the vacuum chuck, rotated to a "fresh" area of the abrasive and grinding continued. The disk will remain uniform and strong through service. This can be done in at least two different ways.
  • a grooved pattern with a preselected distribution of islands on the surface of the platen is created by molding, etching or the like.
  • a thin backing abrasive sheeting (as used in aspects of the present invention) is applied and secured to this textured platen, the backing of the sheet conforms to the pattern. Continuous boundary layers will be broken up by the predesigned variations in the surface of the conforming abrasive sheet, which is very desirable. Since the pattern is chosen (with the highest areas on the platen being fairly uniform and constant), a planar area of contact between the abrasive and the workpiece can be maintained, with areas of non-contact or light contact provided which will break up the boundary layers. It is better to have a flat platen with a groove pattern existing on the abrasive sheet or by using segments of abrasive sheet, as described herein.
  • Abrasive sheets even with diamond abrasive, are now available from 3M with abrasive islands (e.g., diamonds within a matrix) having paths where swarf, liquid and the like may flow between the islands without disturbing the contact between the workpiece and the abrasive on the sheet.
  • abrasive islands e.g., diamonds within a matrix
  • the boundary layer is thicker, the abrasive particles don't penetrate as well through the boundary layer which "floats" or hydroplanes the piecepart, with the result of significant material removal at the outer radius of the platen and reduced removal at the inner radius. This produces uneven wear on the piecepart which is subjected to both extreme areas of the platen radius and the piecepart is not flat or the surface is not uniform in surface damage.
  • An annular ring of abrasive mounted on a platen is used so the relative surface velocity at both the inner and outer radius is close enough that the boundary layer is about the same relative to the height of the coated abrasive (from above 0.1 or from about 1 to 100 microns).
  • Rotating each piecepart holder would provide the same amount of abrasive material removal to all the exposed surfaces of the individual pieceparts.
  • the normal force, surface speed, liquid flow rate, viscosity, etc. could all be optimized
  • the whole assembly pivot cradle could be oscillated to obtain even surface wear.
  • the apparatus can have Fast Fourier Transformation spectrum analysis pattern recognition controls used with an annular ring of abrasive. These characterize vibration by amplitude as a function of frequency. It has been found that when piecepart materials such as ALTIC (aluminum tungsten carbide or aluminum titanium carbide) are brought in contact with high speed platens using the abrasive sheeting (such as the 3M diamond abrasive disks) operated at high surface speeds, especially such as about 10,000 sfpm, that a characteristic significant sound is produced which is quite audible to the human ear at the very first contact between the piecepart and the abrasive surface.
  • ALTIC aluminum tungsten carbide or aluminum titanium carbide
  • the audible signature allows the piecepart to be moved quite rapidly up to the surface of the abrasive and then to be slowed or stopped for restart to allow a very slow, controlled motion approach by driving the piecepart into the moving abrasive surface at a slow prescribed rate with optimized controlled flow of lubricants for a specific abrasive particle size over a fixed period of time.
  • a piecepart surface will not be damaged by too sudden contact due to excessive heat generation or impact.
  • a square piece of ALTIC material about 2 x 2 inches (5.1 by 5.1 cm) was stepper motor driven in small increments to where the contact force between the workpiece and the abrasive moving, at 3,000 RPM for a 12 inch (30.5 cm) diameter platen with about a 1.5 inch (3.77 cm) wide ring of annular shape had an initial contact force of about 2-20 pounds (0.9kg to 9 kg), usually around 9 lbs (4.1 kg).
  • the first portion of the grinding period of about 1 minute removed surface material quite rapidly, but as time went on, the force sensor showed a progressive decrease in contact force with an unchanging machine incremental position. Also the swarf of ground debris visually was quite heavy, but decayed in some proportion to the contact force. A typical amount removed was about 0.005 inches (0.13 mm) over this 1 minute period.
  • the finished surface of the part was very smooth in surface roughness, producing a mirror finish and the flatness was better than 1 lightband as measured by a green optical light flatness measuring instrument.
  • a multiple piecepart holder can be constructed such that the piecepart is held rigidly and precisely on a flat surface by vacuum or other means such as adhesive, melted wax or be established by mechanical measuring equipment and process techniques so the piecepart can be lowered (vertically) so it is just barely within 0.001" of the moving abrasive surface and then when contact is made by further motion, the piecepart holder then is allowed to move freely by use of weak springs which allows perfect flat alignment between the piecepart surface and the grinding surface.
  • weak springs which allows perfect flat alignment between the piecepart surface and the grinding surface.
  • small air cylinders can be used to clamp the piecepart mechanism by driving a lower wobble plate portion of the piecepart (workpiece) holder against adjustable mechanical stops.
  • the free moving spherical section is moved against mechanical stops which rigidize the unit.
  • Moving this portion of the pivot part (workpiece) holder can be effected, for example, by a variety of devices which include (but are not limited to) springs, flash cylinders, electric solenoids, linear electric motors, thermal or electrical screw devices, and the like.
  • the important function is to hold the piecepart holder against local stops to rigidize it, and then the entire rigidized assembly is lowered to present the piecepart in rigid contact (non-pivotable contact) with the abrasive surface (e.g., the abrasive sheet on the platen).
  • This rigid piecepart holder can be rotated axially, but does not have a spherical pivoting action at this time.
  • a piecepart has been initially ground, it can then be followed by conformational spherical grinding without changing to a different lapping apparatus. It is very important with these relatively thin sheets of coated abrasive material that the piecepart be presented to and contact the abrasive with controlled pressure and force rather than attempting just a position controlled presentation. The following equipment and procedures may be used to effect this result.
  • a center slide may be spring retained or activated by a cylinder or an electric solenoid. Pressurize bottom of cylinder to lock part holder "up” against ball for rigid grinding.
  • Solution Construct a lapping machine which has the possibility to micro-align the axis of the piecepart holder mechanism and the abrasive lapper platen. Also use a fine pitch (40 threads/inch) screw to move the piecepart down into contact with the abrasive with a stepper motor having 50,000 steps per revolution. Further, the screw is attached to an in-line force gage which senses when the piecepart comes in contact with the abrasive surface and this position is sensed very accurately with a precision linear encoder device.
  • a linear actuator with a stepper or other motor is used to position the piecepart holder on the annular ring of abrasive of the platen in the quadrant of the platen where the grinding or lapping force action is the most stable depending on the direction of the platen rotation.
  • One method is to first align the platen baseplate with 4 corner jack screws then align the pivot post, then align the pivot arm.
  • a sacrificial outer ring, square, segment pieces or ring with water inlet/outlet slots can assist in assuring that the initial piecepart contact with the platen is level.
  • the sacrificial parts By having the sacrificial parts at a higher elevation with respect to the approach path to the platen abrasive surface (usually by being outboard of the piecepart), the sacrificial material will contact the abrasive surface of the platen before the piecepart. This initial contact with the sacrificial part will level out the workpiece while the sacrificial part is being lapped, without any damage to the workpiece.
  • sacrificial material could be substantially anything that would not interfere with the lapping (e.g., explosive materials, highly abrasive material that would destroy the abrasive surface, etc.), such as porous material filled with lubricant.
  • This technique may be used rigid mounts or spring mounts on the piecepart holder.
  • Boundary Layer Lifting The use of a finite element dynamic fluid flow computer program (FIDAP, by Fluent Company) shows that where a boundary layer of water is uniformly flat under the full downstream length of the piecepart, there is little tilting force on the piecepart. However, if excess water pushes up to form a "dam" at the leading edge of the piecepart, a dynamic pressure head is created under the first portion of the piecepart which tends to tilt the part on the abrasive surface. A leading ramp knife edge can be used to reduce the dam pressure build-up effect. Large leading edge pressure head lifting results if there is a raised front edge or a big dam head of water on front leading edge of the piecepart.
  • FIDAP finite element dynamic fluid flow computer program
  • the tapered ramp knife edge is used at the front to cut off the water dam by lifting it up (as with a snow plow), forcing the front of the piecepart down due to reactive forces.
  • the best procedure is to only use enough lubricant to wet the valleys in abrasive mountains plus a little extra.
  • the platen is started only after the piecepart is in contact with the abrasive sheet surface, using a start slow acceleration, then a quick ramp up to full speed.
  • the platen would normally be brought from a stationary position (zero speed) to a full 3,000 rpm in about 15 seconds, or at least about 100 or 200 rpm/sec. acceleration.
  • Option 1 Have the piecepart stationary until some minimum platen speed (e.g., at least 200 rpm) is reached.
  • some minimum platen speed e.g., at least 200 rpm
  • Option 2 vary the speed of piecepart rotation before the platen start-up and also during processing of grinding event.
  • the piecepart could be rotating or stationary at the time of the piecepart removal. Removal could be made with platen at full speed, partial speed or slowed to a stationary state. The piecepart will tend to stay conformed, flat to the platen at low speeds or stationary and therefore it will not damage the leading edge of the workpiece.
  • Water or lubricant can be varied during the process, with large excess amounts used during start-up initial contact or during removal at low platen speeds or stationary platen.
  • the platen can also be started from a stationary position after the piecepart is placed into contact with the abrasive.
  • An initial "motor mat" tilt angle can also be used with stationary start-up or lift off.
  • a loose material as a contact initial barrier such as powdered plastic, abrasive particles or other materials. These would be used either as pre-coating on piecepart surface or as constant flow input with water lubricant source during initial contact, but stopped or eliminated during normal grinding. Their addition can be restarted prior to lift off to develop a film or layer between the piecepart and platen.
  • the material could also be a thick liquid, such as a polymer solution, grease, etc.
  • Solution Use a sacrificial contaminant ring surrounding piecepart so that the outboard sacrificial ring makes the first contact with the abrasive. Also the piecepart could be potted in an adhesive, epoxy-like device which encompasses the piecepart.
  • a stationary hollow holding ring can be held in a fixed position above the abrasive surface and a piecepart which matches the ring opening can be dropped into the ring to be in contact with the abrasive.
  • a dead weight may be placed on the piecepart top surface.
  • a dead weight with spring between weight and top surface may be used.
  • Two or more stationary standard roller bearings would be mounted to contain the piecepart ring as it is forced against the bearings by the forces induced by the moving water coated abrasive.
  • the low position of the extended spherical portion results in reactive forces kept low toward the abrasive surface and minimizes upward tipping forces on the piecepart.
  • a spherical surface on the extended portion assures only point contact with the support bearing outer-flat surfaces.
  • Another variation is to use support bearings with spherical surfaces to get point contact. This point contact feature minimizes lifting or tipping forces on the piecepart ring.
  • Gear teeth can be used on the outer edge of the piecepart ring so the ring can be turned by a motor driven gear matching contact with the ring gear.
  • Another drive mechanism is the differential speed of the outer periphery of the rotating platen abrasive having a greater contact force than the inner radius abrasive contact thereby setting up a relatively slow differential rotating velocity of the piecepart ring.
  • the heat which would be generated by the friction contact force with the abrasive is at a greater amount at the inside circle, and this also tends to swell and raise this circle due to greater thermal expansion in the inboard (central) area than in the outboard areas which leave contact with the abrasive and are water cooled.
  • the circle will be a "low" spot on the piecepart.
  • the annular ring can be changed from an essentially uniform (evenly distributed particles over any given significant area) surface to one of smaller, parallel, concentric rings with free space grooves between the raised abrasive which is flooded with water coolant. All portions of the piecepart then would leave contact with the raised abrasive as it is rotated.
  • the annular ring could be made with raised tangential abrasive segments with gaps between staggered adjacent inner concentric rings to grind-cool-grind a given area. Also the piecepart rotating axis can be moved sideways during the grinding so that a selected area can be moved out of contact with the abrasive surface.
  • any friction from an outboard antirotation device will impede the free spherical movement of the piecepart as it attempts to align itself perfectly flat to the abrasive surface with a small nominal downward contact pressure force which holds the part surface to be ground in flat contact with the moving abrasive.
  • a typical piecepart is 1 ⁇ 2 to 8 inches in diameter, typical downward contact force is 0.5 to 20 lbs. and more, and the amount of ground off material is typically 0.0001 (0.0025 mm) inch to 0.003 inch (0.0077 mm) to obtain a flatness of typically 1 optical lightband or less.
  • the stationary ball post is replaced with a roller bearing, either a low friction needle bearing, ball bearing, roller bearing or air bearing and this bearing is constrained between two round stationary posts mounted on the opposing plate which act on either side of the bearing so the piecepart can be torsionally rotated in either direction.
  • the outer cylindrical surface of the bearing will be self cleaning as there is only point contact between the bearing surface and the posts during sliding oscillations of each piecepart revolution.
  • a wobble spherical pivot plate that is made in two plate sections attached to each other by use of a free floating trapped spherical ball needs to be restrained or have the two plate sections coupled to each other to transmit rotational torque from the upper plate to the lower plate.
  • a typical "dog" type of system where a post on one plate contacts a surface on the other provides rotational torque, but has the disadvantage of having sliding friction on the ball post to flat surface area which impedes the free pivoting action of the wobble plate which is moving in an oscillating motion to maintain the wobble plate piecepart surface flat to the moving abrasive surface as the wobble plate is rotated during a grinding or lapping action.
  • This friction can create undesirable patterns of uneven ground surfaces in the piecepart, as the spherical pivot action will tend to stick, break loose or stick again due to changing from the high forces of static friction and lower forces of dynamic sliding friction which occurs at each piecepart revolution.
  • a linkage bar with pin pivots at each end can be used to couple the upper plate with the lower plate to obtain good torsional coupling with free motion of the spherical pivot action of the wobble plate.
  • the pins would be solid with a small diameter which are periodically lubricated or they may have ball, roller or sliding bearings at the pivots. The longer the bar and the more horizontal the bar, the less incremental rotation of the lower plate relative to the upper plate with the pivot action.
  • Another method to accomplish the reduction in "stiction” is the use of a hinge linkage system or a living hinge solid flexible spring that is wide to be stiff for rotational forces but weak for spherical pivot.
  • FIG. 3 shows some of the features of apparatus of the present invention in a segmented view of the apparatus 1200 .
  • This apparatus 1200 comprises a rotatable platen 1205 with an annular ring of abrasive 1201 located on an upward face of the platen 1205 .
  • the workpiece holder assembly 1230 comprises a rigid shaft 1232 and an assembly housing 1234 .
  • Two of three air cylinders 1202 and 1203 (the third is removed by the segmentation of the figure) are attached to the housing 1234 by pivoting connections 1236 and 1238 .
  • the air cylinder 1202 is shown by further segmentation to be a spring air return cylinder.
  • the cylinder 1202 is connected through a shaft 1240 to an intermediate plate 1242 .
  • An "up" stop screw 1244 with a ball end 1208 is positioned below the intermediate plate 1242 .
  • a “down” stop screw 1206 is positioned at another position on the intermediate plate 1242 .
  • the rigid shaft 1232 which is driven by shaft bearings 1204 is rigidly attached to the inside surface 1246 of the housing 1234 .
  • a second rigid shaft element 1248 is rigidly connected to the underside 1250 of the housing 1234 to slide or telescope within the first rigid shaft 1232 . This creates a rigid connection from above the housing 1234 to the pivot ball sleeve bearing 1212 below the housing 1232 .
  • a sleeve bearing 1212 for a pivot ball 1211 radially restrains the second rigid shaft element 1248.
  • the sleeve bearing 1212 is connected to or at least associated with a piecepart holder 1252 .
  • the ball nut 1214 is adjustable to allow the telescoping gap distance to be set. This connection or association may be accomplished in many different ways, the requirement being that the piecepart holder 1252 spherically rotates around the pivot ball 1211 .
  • a piecepart 1209 is fixed on the bottom of the piecepart holder 1252.
  • a spring element (not shown) may be used with the ball nut 1214 to control the axial gap movement.
  • a segment of a spherical mass of elastomeric material 1213 such as a room temperature vulcanizing rubber can effectively perform the function of sealing the ball joint from grinding debris and also seal in a ball lubricant. This configuration allows for the solution of a uniquely difficult problem in alignment of the lapping apparatus 1200 .
  • the piecepart holder 1252 To be optimally effective in performing the function of proper alignment of thee workpiece or piecepart 1209 to the abrasive annular ring 1201 , the piecepart holder 1252 must first act in a wobble or adjustable mode to place the piecepart 1209 into alignment with the abrasive ring 1201 . To assure the best high speed lapping, during the actual lapping process, the piecepart 1209 is best held in a more rigid alignment with the abrasive annular ring 1201 . The configuration in Figure X allows this adjustment in modes.
  • the initial contact is made between the piecepart 1209 and the abrasive annular ring 1201 , the force on the top surface of the piecepart holder 1252 is provided by the two air cylinders 1202 and 1203 and the ""up" stop screws 1207 and 1244 with the ball end 1208 .
  • the bottom end 1256 of the "down" stop screw 1206 makes contact with the top surface 1246 of the piecepart holder 1252 to equal the axial gap between the pivot ball 1211 and the ball nut 1254 .
  • Each individual "down" stop screw e.g., 1206
  • Each individual "down" stop screw is adjusted so that in this static position of contact between the piecepart 1209 and the abrasive annular ring 1201 in a non-lapping contact, the "down” lock screws 1206 are in the exact alignment position desired when the piecepart 1209 is eventually brought into contact with the abrasive annular ring 1201 during lapping.
  • the piecepart holder 1252 will be rigidly held in place in proper alignment by the rigid support between the bottom 1256 of the "down" stop screw 1206 and the top surface 1246 of the housing 1234 as the housing 234 is pushed down by the air cylinders 1202 and 1203 . If the air cylinders 1202 and 1203 are deactivated, then the piecepart holder 1252 is allowed to wobble with the pivot ball 1211 in contact with a hardened contact plate 1210 .
  • Vibration of the piecepart 1252 is prevented by insertion of a vibration damping agent or damping device 1261 which provides a connection between the piecepart holder 1252 and the housing 1234 .
  • a vibration damping agent or damping device 1261 which provides a connection between the piecepart holder 1252 and the housing 1234 .
  • the apparatus will be able to shift from a wobble or floating mode to a rigid lapping mode during the rapid operation of the equipment.
  • This configuration is best performed with three sets of "up” and “down” stop screws and three sets of air cylinders. Two, four or more can be used, but three has been found to provide the best results to date.
  • annular rings are cut from round sheets of abrasive disks, there can be significant waste of material from the central round area cut from this disk. This is one reason why printing of patterns of abrasive on a sheets is desirable.
  • the sheets of abrasive are most commonly available in round sheet form, the cutting out of annular rings is the most likely source of the annular rings.
  • this invention also describes an annular distribution (to be included within the meaning of the term "annular rings") of abrasive sheet material which can use the residue of the process where a single piece, continuous annular ring was cut from a round sheet of abrasive.
  • segments or pieces of abrasive sheeting may be lain in an annular distribution within the abrading surface area of a rotating platen.
  • two segments 1301, each of which is a half of an annulus have been cut from the remaining material from the original round sheet of abrasive material (not shown) and then placed end to end to form the annular shape.
  • the vacuum hold down of the platen (not shown) can secure the individual piece 1301 into a secure position onto platen 1320 .
  • the individual pieces 1301 may be secured together at their intersection 1304 by adhesives, fusion, butt welding or the like.
  • the center area 1306 may be left open or may be filled with a central round sheet (which may also be physically joined to the two segments 1301 to prevent flow of material under the segments 1301 and add support.
  • Figure 15(b) shows a multiple number (5) of arcuate segments 1308 aligned around the platen 1320 in an annular distribution. Any number of segments may, of course be used, but the fewer the number of segments, the less work is needed to align them.
  • Figure 15(c) shows a number of distinctly different shapes of abrasive sheet segments on a platen 1320 .
  • An important feature of this configuration is the fact that there are physical gaps 1326 between one of the pairs of segments 1324.
  • One of the problems previously discussed was the effects of removal and passage of detritus, swarf and liquids away from the lapping contact area, especially the problems associated with boundary layer thickness changes, channeling of liquid flow (with or without swarf included), and other effects on the alignment or pressure or exposure of particulate abrasives to the workpiece.
  • This Figure 15c ⁇ shows another benefit of the use of non-butted and non-smoothly joined segments form a residual cut-out sheet. Because the segments allow spaces 1326 ) to exist between the abrading or lapping surfaces (e.g., 1324 ), natural run-off areas are provided which can carry away material without its moving completely within the lapping contact area (e.g., on the surfaces of the segments 1322, 1324 and 1325 ). The dimensions of this gap 1326 are defined by the surface of the platen 1320 and the height of the segments (e.g., 1324 ).
  • This secondary spring-mass will vibrate 180 degrees out of phase with the unwanted natural frequency of the workpiece holder in a direction which is perpendicular to the abrasive surface (this is why it is referred to as a vertical vibration dampening element) and will not be affected by the rotation of the workpiece holder. This is because when a flat spring is used, it flexes in only one direction, which is substantially perpendicular to the abrasive surface.
  • This lower area 1422 has a ledge indentation distance 1406 which is the difference between the level of the lowest point 1422 and the interior surface 1416 of the platen 1402 .
  • the abrasive sheet is shown to be secured to the platen 1402 by vacuum passages 1404 .
  • Debris and liquid 1408 move over the interior surface 1416 towards the contact area 1403 between the abrasive sheet 1405 and the workpiece 1410 .
  • the level of this surface 1422 is preferably lower than the height of the surface of the abrasive sheet 1405 and more preferably below the height of the platen 1402 within the contact area 1403 .
  • Figures 17 (a), (b) and c ⁇ all show how contact with the inside radius cuts off the annular abrasive sheet 1405 which potentially has loose particles from the platen, the center of the surface area of the workpiece does not align with the geometrical center of he curved annular segment of he abrasive which contacts it. However, the vacuum removal passage 1420 is a desirable assurance against such movement.
  • This shift of the geometric center of the workpiece should be at least 1%, preferably at least 3%, more preferably at least 5% of the theoretical matching radial dimension location of piecepart area center and the area center of he contacted segment of the annular abrasive sheet dimension of the workpiece which addresses the abrasive sheet surface.
  • the exact percentage of shift of the geometric center of the workpiece can be precisely calculated by simple arithmatic means, but has not been done so here as it would have to be done for each annular shape (e.g., ID and OF considerations). The speed of rotation does not by itself affect this calculation.
  • Another factor in the movement effects of the workpiece holder (and consequently to the workpiece) shifting during the high speed lapping of the present invention is the forces being applied to the workpiece (and consequently to the workpiece holder ) by the high rotational speeds of the workpiece holder.
  • the forces caused by debris and liquid flow under the workpiece also contribute to this effect.
  • These forces can cause the workpiece holder to want to swivel about the ball pivot joint, or other pivoting joint, which secures the second rigid shaft member to the workpiece holder.
  • This problem is again unique to the high speed rotation of the lapping system, particularly in combination with the abrasive sheet which is less forgiving to shifting of the workpiece than a liquid slurry on a slower speed rotating platen.
  • the extent and seriousness of the problem can be reduced by making at least one geometric reconfiguration of the relationship of elements. It has been found that to correct for out-of-balance swiveling of the workpiece holder due to rotation of the workpiece holder with a mass center of gravity located below (or above) the pivot can be reduced by moving the center of the pivot joint closer to the center of gravity of the workpiece holder. It has been found that to correct for out-of-alignment problems due to the dynamic abrasive contact friction forces on the surface of the workpiece that it is desirable that the location of the workpiece gimbal axes be located as close as possible to the surface of the abrasive sheet.
  • Figures 18 and 19 show constructions which address solutions to this problem and which move the center of gravity of the workpiece holder closer to the rotational center of the pivot connection to the shaft.
  • Figure 18 shows a lapping assembly 500 which addresses this problem.
  • the shaft 501 is connected to a primary support plate 502 having X and Y axis pivoting connections such as gimbal bearings and pivot shafts 506 and 508 connected to downwardly extending arms 504 on the primary support plate 502.
  • a pivoting second support plate 510 is connected to the workpiece holder 512 .
  • the workpiece 516 is connected to the workpiece holder 512 and is in contact with the abrasive sheet 520 on the rotating platen 518 .
  • the abrasive sheet happens to be shown in this configuration as larger than the workpiece, but that is not required.
  • the abrasive sheet 520 may be the same or smaller in the radial dimension or radial direction (with respect to the platen) than the workpiece 516.
  • the workpiece holder 512 is shown with arms 514 which carry mass upwardly, even beyond the line of the pivot shafts 506 and 508 . This mass distribution keeps the center of gravity closer to the plane of the gimbal bearings 506 and 508 than using a workpiece holder which was flat on all sides (e.g., a slab with rectangles on all sides).
  • Another configuration that would work is shown in perspective in Figure 19.
  • the lapping assembly 530 is shown with a shaft 532 attached to a first external gimbal arm 534 .
  • the first external gimbal arm 534 is attached through gimbal bearings and pivot shaft 536 to a second external gimbal arm 538 .
  • This second external gimbal arm 538 is connected through gimbal bearings and pivot shaft 540 to a piecepart holder 542 .
  • the piecepart holder 542 holds the workpiece 544 .
  • this configuration also demonstrates a method for lowering the plane of the axes of the pivot gimbal running through the gimbal bearings 536 and 540 close to the abrasive contact surface of the workpiece 544 . This geometric orientation reduces the tilting torque on the workpiece and assists in the maintenance of proper alignment within the lapping system.
  • FIG. 20 provides a description of this aspect of the invention.
  • a lapping system 550 is shown with an annular abrasive sheet 552 , an arm 554 carrying two piecepart holders 556 and 558.
  • Each of the piecepart holders 556 and 558 support a multiplicity of pieceparts 560 and 562 .
  • the piecepart holders 556 and 558 rotate so that the individual pieceparts 560 and 562 are exposed to the abrasive sheet 552 .
  • Each of the piecepart holders 560 and 562 are aligned on wobble plates (not shown) and are operated by the processes described above in the practice of the present invention.
  • the arm 554 may also have alignment mechanisms associated with it to assure proper alignment with respect to the annular ring 553 and the rotatable platen (not shown).
  • the different pieceparts 560 and 562 do not even need to be of the same size or cross section.
  • one set e.g., 560
  • the other set e.g., 562
  • pieceparts located at the center of the piecepart holder such as pieceparts 566 and 564 may be eliminated in this grouped set-up of pieceparts. If this were not done, pieceparts 566 and 564 would be continually lapped over the process, while other parts located in a ring, such as shown for parts 560 and 562 would be processed only intermittently.
  • FIGS. 20(b) and c ⁇ show alternative platen shapes 620 and 622 which provide sloped transitions 624 and 626 from the central areas 628 and 630 to the flat raised areas 632 and 634 .
  • the slopes should never present an angle that would bend the abrasive sheet past an angle of 65 degrees (e.g., forming an apex of less than 65 degrees by bending it more than 25 degrees away from horizontal), preferably not past an angle of 70 or 75 degrees, and most preferably not past an angle of 75 or 80 degrees, or more than 85 degrees.
  • an angle of 65 degrees e.g., forming an apex of less than 65 degrees by bending it more than 25 degrees away from horizontal
  • preferably not past an angle of 70 or 75 degrees preferably not past an angle of 70 or 75 degrees, and most preferably not past an angle of 75 or 80 degrees, or more than 85 degrees.
  • two separate supports 1253 and 1252 form the substance of the wobble plate.
  • a cushioning, compressible element 1261 is provided between the wobbling piecepart holder 1252 and the bottom 1250 of the housing 1234 .
  • the compressible element 1261 should make contact between both the wobbling piecepart holder 1252 and the bottom 1250 of the housing 1234 .
  • Viscoelastic material, springlike elements, elastomers, rubbers, and layered structures may be used.
  • double sides polymer backed adhesive tape was rolled into a tube and cut to the proper length. The tube was placed between the wobbling piecepart holder 1252 and the bottom 1250 of the housing 1234 . As they are brought together, the two surfaces compress and flatten the cushioning, compressible element. This element assists in reducing the vibration within the wobble plate element and the piecepart assembly.
  • the contact force application has been repeatedly identified as a desirable focus of control within the practice of the invention.
  • An additional aspect of this control is the speed with which the workpiece (and the workpiece holder ) approaches the rotating platen.
  • velocity control devices such as fluid dampers (oil dampers preferred, but other fluids, including gases, may be used).
  • the workpiece be rotated at a rate of at least about 100 rpm, preferably at least 150 rpm, and more preferably at least 200, at least 300 rpm, which for a 30.8 cm diameter disk at 500 rpm, there should be at least 3 to 4, and preferably more than 4 rotations of the workpiece during 10 seconds of lapping. It is preferred that the workpiece be rotated at least 3 or 4 times in a 10 second interval during lapping in the practice of the present invention.
  • the work piece may be rotating as it is brought into contact with the abrasive sheet surface.
  • the water will therefore be much deeper (a thicker boundary layer) than with a continuous and uniformly coated abrasive sheet, and the piecepart will not hydroplane.
  • the more water that is present the better is the grinding, as more heat is also carried away by the larger volume of coolant water.
EP98301690A 1997-03-06 1998-03-06 Procédé et dispositif de polissage pour le polissage à grande vitesse avec un plateau abrasif rotatif Withdrawn EP0868976A3 (fr)

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US812748 1997-03-06

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Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999050022A2 (fr) * 1998-03-31 1999-10-07 Applied Materials, Inc. Conditionneur de polissage mecano-chimique
US7367872B2 (en) 2003-04-08 2008-05-06 Applied Materials, Inc. Conditioner disk for use in chemical mechanical polishing
WO2009137685A2 (fr) * 2008-05-07 2009-11-12 Zygo Corporation Configuration de machines de rodage et de polissage
US9352442B2 (en) 2013-07-02 2016-05-31 Seagate Technology Llc Lapping carrier
CN106475914A (zh) * 2016-10-31 2017-03-08 南京航空航天大学 一种钛合金表面氨基模塑料磨料气射流抛光方法
WO2018114488A1 (fr) * 2016-12-23 2018-06-28 Scanlab Gmbh Miroir de balayage avec corps d'équilibrage et procédé d'équilibrage d'un miroir de balayage
CN109304817A (zh) * 2017-07-26 2019-02-05 株式会社迪思科 刀具保持器具
CN110000685A (zh) * 2019-05-07 2019-07-12 洪小芳 一种五金件加工用的高效抛光装置
CN111403885A (zh) * 2020-03-31 2020-07-10 重庆思睿创瓷电科技有限公司 一种用于滤波器的对位压合工艺及工装
CN112197754A (zh) * 2020-09-17 2021-01-08 倪可 一种建筑测量用三角架
CN112911850A (zh) * 2020-12-30 2021-06-04 西安熊福芳电子科技有限公司 一种便于移动的智能监控设备控制操作台
CN112935963A (zh) * 2021-02-05 2021-06-11 许昌学院 一种家具设计用装饰板打磨装置
CN113267425A (zh) * 2021-06-25 2021-08-17 郑州磨料磨具磨削研究所有限公司 一种半固体挤压磨料流软硬度的测试装置及其测试方法
CN113916747A (zh) * 2021-10-14 2022-01-11 重庆科技学院 一种应用于黏弹性流体测试启动压力梯度的修订方法
CN114932501A (zh) * 2022-06-02 2022-08-23 中国船舶重工集团公司第七一六研究所 一种光纤插芯研磨装夹机构
CN114952441A (zh) * 2022-06-15 2022-08-30 无锡市明鑫数控磨床有限公司 一种风电trb轴承立式磨削加工工艺
CN114952554A (zh) * 2022-06-20 2022-08-30 武汉船用机械有限责任公司 一种自动化打磨装置
CN115401534A (zh) * 2022-08-30 2022-11-29 大连理工大学 一种微阵列模具保形抛光方法
CN115847225A (zh) * 2023-03-02 2023-03-28 成都裕鸢航空智能制造股份有限公司 一种金属板表面打磨抛光装置及打磨抛光方法
CN116484667A (zh) * 2023-03-13 2023-07-25 北京交通大学 一种支撑连接器结构的拓扑优化与安定评估方法
CN116923719A (zh) * 2023-09-18 2023-10-24 成都庆龙航空科技有限公司 一种通用的无人机仿型托架
CN117047609A (zh) * 2023-10-10 2023-11-14 玛格瑞斯(盐城)新型建材有限公司 一种人造板生产加工用磨边装置
CN116484667B (zh) * 2023-03-13 2024-04-19 北京交通大学 一种支撑连接器结构的拓扑优化与安定评估方法

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EP0257013A2 (fr) * 1986-08-19 1988-02-24 Léon Biebuyck Procédé et machine pour meuler et polir mécaniquement une surface en matériau minéral, plus spécialement en verre
JPH07283178A (ja) * 1994-02-21 1995-10-27 Toshiba Corp 半導体製造装置及び半導体装置の製造方法
JPH07283177A (ja) * 1994-02-21 1995-10-27 Toshiba Corp 半導体装置の製造方法及び半導体製造装置

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EP0257013A2 (fr) * 1986-08-19 1988-02-24 Léon Biebuyck Procédé et machine pour meuler et polir mécaniquement une surface en matériau minéral, plus spécialement en verre
JPH07283178A (ja) * 1994-02-21 1995-10-27 Toshiba Corp 半導体製造装置及び半導体装置の製造方法
JPH07283177A (ja) * 1994-02-21 1995-10-27 Toshiba Corp 半導体装置の製造方法及び半導体製造装置

Cited By (36)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999050022A2 (fr) * 1998-03-31 1999-10-07 Applied Materials, Inc. Conditionneur de polissage mecano-chimique
WO1999050022A3 (fr) * 1998-03-31 2000-03-09 Applied Materials Inc Conditionneur de polissage mecano-chimique
US6200199B1 (en) 1998-03-31 2001-03-13 Applied Materials, Inc. Chemical mechanical polishing conditioner
US6361423B2 (en) 1998-03-31 2002-03-26 Applied Materials, Inc. Chemical mechanical polishing conditioner
US7367872B2 (en) 2003-04-08 2008-05-06 Applied Materials, Inc. Conditioner disk for use in chemical mechanical polishing
WO2009137685A2 (fr) * 2008-05-07 2009-11-12 Zygo Corporation Configuration de machines de rodage et de polissage
WO2009137685A3 (fr) * 2008-05-07 2010-02-25 Zygo Corporation Configuration de machines de rodage et de polissage
US8123593B2 (en) 2008-05-07 2012-02-28 Zygo Corporation Configuring of lapping and polishing machines
US9352442B2 (en) 2013-07-02 2016-05-31 Seagate Technology Llc Lapping carrier
CN106475914A (zh) * 2016-10-31 2017-03-08 南京航空航天大学 一种钛合金表面氨基模塑料磨料气射流抛光方法
WO2018114488A1 (fr) * 2016-12-23 2018-06-28 Scanlab Gmbh Miroir de balayage avec corps d'équilibrage et procédé d'équilibrage d'un miroir de balayage
US11402605B2 (en) 2016-12-23 2022-08-02 Scanlab Gmbh Scanning mirror having balancing body, and method for balancing a scanning mirror
CN109304817A (zh) * 2017-07-26 2019-02-05 株式会社迪思科 刀具保持器具
CN110000685A (zh) * 2019-05-07 2019-07-12 洪小芳 一种五金件加工用的高效抛光装置
CN111403885A (zh) * 2020-03-31 2020-07-10 重庆思睿创瓷电科技有限公司 一种用于滤波器的对位压合工艺及工装
CN112197754A (zh) * 2020-09-17 2021-01-08 倪可 一种建筑测量用三角架
CN112197754B (zh) * 2020-09-17 2022-03-15 浙江海致建设有限公司 一种建筑测量用三角架
CN112911850A (zh) * 2020-12-30 2021-06-04 西安熊福芳电子科技有限公司 一种便于移动的智能监控设备控制操作台
CN112935963A (zh) * 2021-02-05 2021-06-11 许昌学院 一种家具设计用装饰板打磨装置
CN112935963B (zh) * 2021-02-05 2022-12-02 许昌学院 一种家具设计用装饰板打磨装置
CN113267425A (zh) * 2021-06-25 2021-08-17 郑州磨料磨具磨削研究所有限公司 一种半固体挤压磨料流软硬度的测试装置及其测试方法
CN113916747A (zh) * 2021-10-14 2022-01-11 重庆科技学院 一种应用于黏弹性流体测试启动压力梯度的修订方法
CN113916747B (zh) * 2021-10-14 2023-09-15 重庆科技学院 一种应用于黏弹性流体测试启动压力梯度的修订方法
CN114932501A (zh) * 2022-06-02 2022-08-23 中国船舶重工集团公司第七一六研究所 一种光纤插芯研磨装夹机构
CN114932501B (zh) * 2022-06-02 2023-12-26 中国船舶集团有限公司第七一六研究所 一种光纤插芯研磨装夹机构
CN114952441B (zh) * 2022-06-15 2023-10-13 无锡市明鑫数控磨床有限公司 一种风电trb轴承立式磨削加工工艺
CN114952441A (zh) * 2022-06-15 2022-08-30 无锡市明鑫数控磨床有限公司 一种风电trb轴承立式磨削加工工艺
CN114952554B (zh) * 2022-06-20 2023-07-21 武汉船用机械有限责任公司 一种自动化打磨装置
CN114952554A (zh) * 2022-06-20 2022-08-30 武汉船用机械有限责任公司 一种自动化打磨装置
CN115401534A (zh) * 2022-08-30 2022-11-29 大连理工大学 一种微阵列模具保形抛光方法
CN115847225A (zh) * 2023-03-02 2023-03-28 成都裕鸢航空智能制造股份有限公司 一种金属板表面打磨抛光装置及打磨抛光方法
CN115847225B (zh) * 2023-03-02 2023-04-28 成都裕鸢航空智能制造股份有限公司 一种金属板表面打磨抛光装置及打磨抛光方法
CN116484667A (zh) * 2023-03-13 2023-07-25 北京交通大学 一种支撑连接器结构的拓扑优化与安定评估方法
CN116484667B (zh) * 2023-03-13 2024-04-19 北京交通大学 一种支撑连接器结构的拓扑优化与安定评估方法
CN116923719A (zh) * 2023-09-18 2023-10-24 成都庆龙航空科技有限公司 一种通用的无人机仿型托架
CN117047609A (zh) * 2023-10-10 2023-11-14 玛格瑞斯(盐城)新型建材有限公司 一种人造板生产加工用磨边装置

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