Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B27/00—Tools for turning or boring machines; Tools of a similar kind in general; Accessories therefor
  • B23B27/14—Cutting tools of which the bits or tips or cutting inserts are of special material
  • B23B27/141—Specially shaped plate-like cutting inserts, i.e. length greater or equal to width, width greater than or equal to thickness
  • B23B27/143—Specially shaped plate-like cutting inserts, i.e. length greater or equal to width, width greater than or equal to thickness characterised by having chip-breakers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/02—Compacting only
  • B22F3/093—Compacting only using vibrations or friction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D18/00—Manufacture of grinding tools or other grinding devices, e.g. wheels, not otherwise provided for
  • B24D18/0009—Manufacture of grinding tools or other grinding devices, e.g. wheels, not otherwise provided for using moulds or presses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D7/00—Bonded abrasive wheels, or wheels with inserted abrasive blocks, designed for acting otherwise than only by their periphery, e.g. by the front face; Bushings or mountings therefor
  • B24D7/02—Wheels in one piece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
  • B30B11/02—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
  • B30B11/02—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space
  • B30B11/022—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space whereby the material is subjected to vibrations

Definitions

• this invention relates to impaction and compaction methods and apparatus for forming or densifying particulate material such as powder metals, ceramics, cermets, and other similarly processed materials into compacts. More particularly, this invention relates to high kinetic energy cyclic impacting of particulate material in a die to form a compact.
• the latter forms particles into shaped preforms by confining the loose particles in a shaped closure having at least one moveable side, subjecting each particle of the mass and at least a portion of the mold to an acceleration of a magnitude of at least 25 to 50 G's, and preferably in the range of 500 G's to 5000 G's, or greater, to generate at each particle a force causing such particle to impact with adjacent particles and form a homogeneous, fused article.
• the acceleration is provided by rapidly impacting the mold at the movable portions thereof at opposed ends of a distinct displacement of the contents of the mold, and usually in a vertical direction between an oscillating table and an underdamped pneumatic system tuned to oscillate out of phase with the table. This process is contrasted to the present invention which transmits substantially all of the kinetic energy to the particulate matter inside the die by impaction of the die punch while the die is held motionless and prevented from vibrating.
• U.S. Patent No. 4,770,849 entitled “Dynamically Loading Solid Materials Or Powders Of Solid Materials” discloses an impaction method and apparatus with which solid materials are dynamically loaded by impact with a piston fired at the material in a suitable support. A punch that serves as a body of material that introduces an impedance mismatch, is inserted between the piston and the material.
• the compaction and impaction methods of the prior art have several drawbacks. Some use very heavy press machines that are expensive to procure and operate. These methods are also prone to compact distortion and non-uniform density, both of which can result in defects such as laminations. The great pressures can result in rapid die wear and short die life. It is, therefore, highly desirable to produce green compacts having a more uniform density using less pressure than previously taught in the art.
• Punch faces are conventionally placed on punch tips to provide the "negative" or the negative relief impression surface to be formed on the surface of the green compact such as the grooves and raised and angled surfaces of a cutting tool insert.
• the punch is typically a steel shank with carbide tip brazed in place.
• the carbide tip is then ground or electro-formed and polished to produce the negative relief impression surface.
• Short runs, about 1000 inserts or less, may be made using less expensive plastic tips. Shaping the carbide tip is a slow, difficult and, therefore, expensive process.
• Plastic tips are easily shaped to final form, but because plastic materials are so soft the tips do not hold up very well under the high loads which are required for conventional or standard pressing.
• a carbide tip typically will last for production of tens of thousands of inserts and a plastic one is typically worn out producing less than one thousand. It is, therefore, highly desirable to have a machine and process that extend the useful life of plastic tips and use plastic tips for longer runs to produce more green compacts than conventional machines and processes are capable of and of those found in the prior art.
• Summary of the Invention provides a process and apparatus for producing solid articles from loose particulate materials that are particularly useful in the production of green compacts used in sintering processes.
• the process includes forming a charge by charging a mass of loose particulate material into the cavity of a die that is part of a die set that further includes at least a first die punch.
• the first die punch is operably disposed to slide within the cavity such that it is limited to reciprocating motion in a linear direction within the cavity and, at least in part, together with the die, defines a closed volume within the cavity.
• the process further includes preloading the first die punch against the charge within the cavity and applying a cyclical reciprocating impacting force to the first die punch along the linear direction while holding the die fixed so as to substantially prevent damping of the impacting force.
• the process may further include charging the mass of loose particulate materials into the cavity between the first die punch and a second die punch that is operably disposed to slide within the cavity such that the second die punch is limited to reciprocating motion in a linear direction within the cavity, preloading the second die punch against the charge within the cavity, and simultaneously applying the first cyclically reciprocating impacting force to the first die punch and a second cyclical reciprocating impacting force to the second die punch along the linear direction while holding the die fixed so as to prevent damping of the impacting forces.
• the first and second cyclical reciprocating impacting forces may be substantially equal and may be applied asynchronously or substantially synchronously.
• the process may further include using first and second reciprocating rams to impart kinetic energy to the first and second die punches by striking to apply the first and second reciprocating impacting forces, respectively.
• the process may further include applying the reciprocating impacting forces for a period of time on the order of not more than several seconds.
• a more particular embodiment of the invention applies the reciprocating impacting forces with a frequency of about 30 cycles per second for a time of up to one second.
• the apparatus includes a die set having a die with a cavity therethrough and at least a first die punch mounted on the apparatus so that it can be operably disposed to slide within the cavity.
• the first die punch, at least in part, together with the die defines a closed volume therein for accepting a charge of the particulate material.
• a motion limiting means is provided for limiting the first die punch to linearly reciprocating motion within the cavity.
• a first preloading means is used for preloading the first die punch against the charge and a fixing means is used to hold the die fixed during the impaction process.
• a first motive means is used for applying a first cyclical reciprocating impacting force to the first die punch.
• a more particular embodiment of the apparatus includes a second die punch mounted on the apparatus so that it can be operably disposed to slide within the cavity such that the first and second die punches, together with the die, define the closed volume and provide the motion limiting means operable for limiting the first and second die punches to the linearly reciprocating motion within the cavity.
• This embodiment includes a second preloading means for preloading the second die punch against the charge and a second motive means for applying a second cyclical reciprocating impacting force to the second die punch.
• the first and second motive means may be fluid powered devices or, more particularly, pneumatic actuators (e.g., air hammers). Electrically powered devices may also be used for motive means of the present invention (e.g., electromechanical linear actuators, including those known as "voice coil” actuators). Control means are preferably used to operate the first and second motive means either asynchronously or synchronously.
• the present invention is advantageous over the prior art because it provides better compacts having a more uniform density, shorter processing time, and with smaller and less expensive machines than in the prior art. Another advantage is that the invention allows production of green compacts that have less flash along the edges of the compact and, thus, require less machining or finishing. Green compacts made by the present invention have greater strength than those made using prior art methods and machinery and, therefore, are less prone to damage such as chipping and cracking in subsequent handling. This is advantageous from a cost standpoint because of the reduced scrap rate the present invention affords.
• the present invention is advantageous over the prior art because it provides green compacts having less spring back after the compaction, thus, allowing the green compacts to be more easily removed or ejected from the dies with less damage and a lower scrap rate.
• the more uniform density provides a further advantage by allowing production of less distorted sintered products made from green compacts of the present invention.
• Another more particular advantage of the present invention is that green compacts for cutting tool inserts may be produced with deeper and better chip breaking grooves, and other surface features, than in the prior art.
• Another advantage of the present invention is that it allows for greater use of plastic tips for the punches instead of more expensive tips (e.g., carbide tips).
• the present invention provides a significant extension of the life of all punch faces and molds including plastic ones. This extended life may allow plastic punch faces to be used for full production. This may allow perhaps as much as a tenfold increase of useful life (e.g., for up to about 10,000 inserts from an inexpensive plastic punch face from about 1000 inserts as is presently capable).
• the present invention may allow the expensive, time consuming carbide faces to be replaced altogether for many applications, thus, providing a net savings on tool costs.
• FIG. 1 is a schematic illustration of a compacting machine employing electromechanical impaction apparatus in accordance with a first exemplary embodiment of the present invention
• FIG. 1 A is an enlarged view of a die set used in the machine of FIG. 1 ;
• FIG. 1 B is an enlarged view of the electromechanical impaction apparatus used in the machine of FIG. 1 ;
• FIG. 2 is a perspective view illustration of a green compact for a cutting tool insert produced in accordance with the present invention
• FIG. 2A is a cross-sectional view of the insert taken along the line 2A-2A of FIG. 2;
• FIG. 2B is a perspective view illustration of an alternative plastic tipped die punch used in the machine of FIG. 1 ;
• FIG. 3 is a schematic illustration of a compacting machine employing air hammer impaction apparatus in accordance with a second exemplary embodiment of the present invention;
• FIG 3A is an enlarged view of a grinding wheel die set used in the machine of FIG 3, and
• FIG 3B is a perspective view of a green compact for a grinding wheel, produced in accordance with the present invention and with the apparatus of FIG 3 Description of the Invention
• FIGS 1 , 1A and 1B Illustrated in FIGS 1 , 1A and 1B is a compacting machine 5 having at least a first or an upper impacting apparatus 10 with a die set 20 mounted in a die fixtu ⁇ ng cross member 22 fixedly mounted to columns 23 of a machinery frame 24 of the compacting machine 5
• the upper impacting apparatus 10 is one embodiment of an apparatus that may be used to form a compact by an impacting process of the present invention
• the die set 20 has a die 26 fixedly mounted to the fixturing cross member 22, with at least an upper die punch 28 operably disposed to slide within a linear cavity 34 of the die such that the upper die punch, at least in part, together with the die defines a closed volume 29 therein for accepting and containing a charge 30 of a mass of the particulate material which is to be compacted
• the die 26 has a smooth linear inner wall 32 that surrounds the cavity 34 which in part forms the closed volume 29 in the die set 20
• An upper preloading means for preloading the upper die punch 28 against the mass or charge 30 is provided by a pneumatic upper preload actuator 40 mounted on a top cross member 42 which, in turn, is supported by the columns 23
• the upper preload actuator 40 has a cylinder 43 and an extensible actuator rod 44 which is connected to an upper slidable cross member 46 by way of an upper sub-frame 48
• the upper die punch 28 includes a shank 50, having a punch face 49 at its lower end, which contacts the charge 30
• the shank 50 is operably disposed to slide through an aperture 54 in the upper slidable cross member 46, and has a shouldered head 56 at its upper end, extending beyond the aperture
• the upper slidable cross member 46 has a cover 58 over the shouldered head 56 that traps the head between the cover and the top surface 59 of the slidable cross member with a clearance C therebetween 7
• the upper slidable cross member 46 is operably disposed to slide along the columns 23 such that its cover 58 can be brought to bear against the shouldered head 56, and thus preload the die punch 28 against the charge 30.
• An upper motive means for applying a cyclical reciprocating impacting force to the upper die punch 28 is illustrated in the form of an electromechanical upper impact actuator 60 mounted to the upper sub-frame 48.
• the impact actuator 60 shown is of the type often referred to as a "voice coil” actuator, and typically includes a coil 62 wound on a non-ferrous base 64 and a field core assembly 66.
• the coil 62 is situated in a gap 67 between the field and the core and must be mechanically confined to allow motion of the coil along the force vector.
• force is generated.
• Direction A and amplitude is determined by the magnitude and direction of the current flow.
• Voice coils are most often used in acoustic speakers, so this particular application of a voice coil device is unique.
• BEI Sensors & Systems Company, Kimco Magnetics Division is a commercial source of voice coil devices.
• the coil 62 has a short bar 68 attached to it, and together they serve as a reciprocating ram 69.
• a cover aperture 70 is centered along the machine axis 36 through the cover 58 and allows the bar 68 to pass through the cover and strike the shouldered head 56, thereby transferring kinetic energy generated by the upper impact actuator 60 to the upper die punch 28 with the cyclical reciprocating motion and impacting force of the ram 69.
• the impacting force is used to impart substantially all of the kinetic energy to the charge 30 with a cyclical reciprocating motion, causing the mass to be compacted and form the final compact in only a few seconds at most.
• the fixing means fixturing cross member 22, holds the die 26 stationary, so as to substantially prevent any damping of the impacting force, prevent unwanted vibrations of the die set, and cause substantially all of the kinetic energy to be imparted to the charge 30. Because the compacting force comes from the upper impact actuator 60, very little force is required from the upper preload actuator 40. As the mass of the charge 30 compacts under the impacting force, which is applied with the cyclical reciprocating motion, the upper preload actuator 40 continuously holds the upper die punch 28 against the charge 30 by urging the upper slidable cross member 46 and the upper sub-frame 48 towards the die 26. In other words, the upper preload actuator serves to merely hold the upper die punch 28 against the charge 30 and prevent the die set from coming apart.
• the preferred embodiment of the invention is the compacting machine 5 with the upper impacting apparatus 10 and a substantially identical second lower impacting apparatus 110.
• the die set 20 preferably has a lower die punch 128 which is operably disposed to slide within the cavity 34, in opposition to the upper die punch 28, such that the lower die punch 128, upper die punch 28, and die 26 define the closed volume 29.
• the smooth linear inner wall 32 and the conformal linear cavity 34 also provide a motion limiting means for limiting the lower die punch 128 to linearly reciprocating motion within the cavity 34.
• a second preloading means for biasing the lower die punch 128 against the mass or charge 30 is provided by a pneumatic lower preload actuator 140 mounted on a machine base 142 of the compacting machine 5.
• the columns 23 extend upward from the machine base 142.
• the lower preload actuator 140 has a cylinder
• the lower die punch 128 includes a shank 150, having a second punch face 149 at its upper end, which contacts the charge 30.
• the shank 150 is operably disposed to slide through an aperture 154 in the lower slidable cross member 146, and has a shouldered head 156 at its lower end, extending beyond the aperture.
• the lower slidable cross member 146 has a cover 158 over the shouldered head 156 that traps the head between the cover and the bottom surface 159 of the slidable cross member with a clearance C therebetween that allows limited axial travel of the shank 150 within the aperture 154.
• the lower slidable cross member 146 is operably disposed to slide along the columns 23 such that its cover 158 can be brought to bear against the shouldered head 156, and thus preload the die punch 128 against the charge 30.
• the lower or upper preload actuators can also be used to eject the green compacts.
• the present invention yields a green compact that is easier to eject and requires low power pneumatic actuators, which improves the ejection step and lowers scrap rate.
• a second motive means for simultaneously applying a second cyclical reciprocating impacting force to the lower die punch 128 is illustrated in the form of a lower impact actuator 160 mounted to the lower sub-frame 148.
• the first and second motive means as illustrated by the upper and lower impact actuators 60 and 160, respectively, are preferably controlled by an electronic controller 400 that can control their operation such that they may impart kinetic energy to the charge 30 with impacting forces that are substantially equal, and either asynchronous or substantially synchronous.
• FIGS. 2 and 2A Illustrated in FIGS. 2 and 2A is a green compact 200 for a cutting tool insert typical of the present art, substantially similar to that disclosed in U.S. Patent No. 5,584,616.
• the green compact 200 and its corresponding insert have various surface features including a chip groove 204 with a depth D and used for chip breaking.
• the chip groove 204 is formed between a pair of cutting faces 205 sloping downwardly from sides 206 of the compact 200 and chip breaker faces 207 that slope upward from respective ones of the cutting faces.
• the present invention provides a better apparatus and process for forming green compacts and cutting tool inserts with such intricate surface features.
• a cutting tool insert is formed by sintering the green compact, and looks substantially like the green compact 200 illustrated in FIG. 2.
• FIG. 2 Illustrated in FIGS. 2 and 2A
• FIG. 2B illustrates another more particular embodiment of the present invention, a plastic tip 208 having a plastic punch face 49 disposed at the end of the metal shank 50 which contacts the charge 30.
• the plastic punch face 49 includes a raised portion 209 which corresponds to the surface features of the chip groove 204 of the green compact 200.
• FIG. 3B Another type of green compact for which this invention was developed is a grinding wheel green compact 300 having a bore 302, as illustrated in FIG. 3B.
• the grinding wheel green compact 300 may be produced in accordance with the present invention using a compacting machine 5 with a grinding wheel die set 210 as illustrated in FIGS. 3 and 3A.
• FIGS. 3 and 3A illustrate an embodiment of the 10
• a pneumatic controller 410 is preferably used to control the operation of the upper and lower air hammers 61 and 161 , such that they may impart kinetic energy to the charge 30 with impacting forces that are substantially equal, and either asynchronous or substantially synchronous.
• the grinding wheel green compact 300 is formed within a cylind ⁇ cally shaped cavity 34 within an annular die 226 of the grinding wheel die set 210.
• the upper and lower annular die punches 188 and 190 and the charge 30 are disposed around a center post 228 of the grinding wheel die set 210.
• the center post 228 is used to form the bore 302 of the grinding wheel green compact 300.
• Flat annular upper and lower stop plates 232U and 232L, respectively, are placed in contact over the upper and lower annular die punches 188 and 190, respectively.
• the upper and lower air hammers 61 and 161 each have pneumatic cylinders 220 and pneumatic rams 222.
• the upper and lower punch tools 236 and 238 each have a tool shank 240 and a shouldered tool head 242 at one end of the shank, away from the die set 210.
• the upper and lower slidable cross members 46 and 146 engage respective ones of the tool heads 242, which, in turn, engage the upper and lower stop plates 232U and
• each pneumatic ram 222 impacts one of the tool shanks 240, and transfers kinetic energy generated by the air hammers to the charge 30.
• the fixturing cross member 22 used in the compacting machine 5 illustrated in FIGS. 1 , 1A and 1 B is not used in the compacting machine 5 with the grinding wheel die set 210 as illustrated in FIGS. 3 and 3A.
• This fixing means is enhanced by imparting kinetic energy to the charge 30 with impacting forces that are substantially equal and synchronous or sufficiently synchronous to prevent unwanted vibrations of the die set and to cause substantially all of the kinetic energy to be imparted to the charge 30.
• the annular die is held up off of the lower stop plate 232L with spacers 243 (shown with dotted lines in FIG. 3A) to permit the lower annular die punch 190 to project out of the bottom of the annular die 226 by the approximate distance it will travel along the axis 36 during impacting as the charge 30 is compressed (about the thickness of the spacers 243).
• the center post 228 is inserted into lower annular die punch 190
• the charge 30 is loaded, and then the upper annular die punch 188 is inserted into the top of the annular die 226.
• the upper annular die punch 188 is set so it also projects out of the annular die 226 approximately the distance it will travel along the axis 36 during impacting.
• the upper stop plate 232U is placed on the upper annular die punch 188 and then the assembly of the grinding wheel die set 210 together with the rubber pads 250 set in place as shown in FIG. 3A is positioned in the compacting machine 5 between the upper and lower punch tools 236 and 238, respectively. This operation may be done manually or may be automated.
• a preload is applied to the upper and lower stop plates 232U and 232L, respectively, through the upper and lower punch tools 236 and 238, respectively.
• the preload is preferably set to a value between two and ten percent of the load required to compact the charge 30 to a desired or predetermined density using only static pressing.
• the spacers 243 are removed.
• the preload on the powder of the charge keeps the annular die 226 from dropping down around the lower annular die punch 190 by pressure and friction against the inside surface of the annular die 226. During impacting the friction between the charge 30 and the annular die 226 prevents the annular die from moving either up or down from the impacting process, for both synchronous or asynchronous modes.
• the preload is released and the grinding wheel die set 210 is removed from the compacting machine 5 for ejection or removal of the grinding wheel green 12
• motive means contemplated by the present invention include, but are not limited to, a hydraulically powered driver; an electrically powered motor providing power to a mechanical linkage or cams which, in turn, provides a cyclical reciprocating motion and impacting force; and a piezo-electric crystal stack, energized by an electrical oscillator circuit.
• Compacts such as green compacts for cutting tool inserts or grinding wheels, may be produced in accordance with a process of the present invention as will now be described.
• the process includes forming a charge by charging a mass of loose particulate material into the cavity of the die of the die set.
• the die set includes at least a first die punch and, preferably, an opposing second die punch.
• the die punches are operably disposed to slide within the cavity, and are thus limited to reciprocating motion in a linear direction.
• the die punches, together with the die define the closed volume within the cavity that holds the charge.
• first and second cyclical reciprocating impacting forces are simultaneously applied to the first and second die punches, respectively, along the linear direction, while holding the die fixed so as to substantially prevent damping of the impacting forces.
• the process in some instances may be practiced with just one die punch and by applying one cyclical reciprocating impacting force to the single die punch, but, as stated above, the preferred method uses first and second cyclical reciprocating impacting forces, simultaneously impacting opposed first and second die punches, respectively, such that the first and second cyclical reciprocating impacting forces are substantially equal, and may be simultaneously applied asynchronously or synchronously with respect to each other.
• the process may further use first and second reciprocating rams to impart kinetic energy to the first and second die punches by striking to apply the first and second reciprocating impacting forces, respectively.
• the process may further include applying the reciprocating impacting forces for a period of time on the order of not more than several seconds. These short time periods enhance the invention's value considerably over the prior art. It is has been found that for making small grinding wheels and tool inserts the 13
• reciprocating impacting forces may be applied with a frequency of about 30 cycles per second for a time of up to one second.
• the green compact 200 depicted in Figs. 2 and 2A, might also be formed with a central hole similar to that of the insert of U.S. Patent No. 5,584,616, by employing a center post and post supporting technique like that shown and described in connection with the center post 228 of Fig. 3A.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)

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Cited By (10)

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Citations (5)

• 1999
  • 1999-03-16 EP EP99911435A patent/EP0988142A1/en not_active Withdrawn
  • 1999-03-16 CN CN99800483.9A patent/CN1263497A/zh active Pending
  • 1999-03-16 WO PCT/US1999/005756 patent/WO1999051426A1/en not_active Application Discontinuation
  • 1999-03-16 CA CA002291091A patent/CA2291091A1/en not_active Abandoned
  • 1999-03-16 JP JP55048599A patent/JP2002514270A/ja active Pending
  • 1999-03-16 IL IL13303399A patent/IL133033A0/xx unknown

Patent Citations (5)

Non-Patent Citations (1)

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