WO2022054097A1

WO2022054097A1 - Tangential cnc cutting tool and tool holder design

Info

Publication number: WO2022054097A1
Application number: PCT/IN2021/050895
Authority: WO
Inventors: Viswesh SRINIVASAN
Original assignee: Srinivasan Viswesh
Priority date: 2020-09-11
Filing date: 2021-09-11
Publication date: 2022-03-17

Abstract

This invention proposes an intelligent fabrication method of fabricating revolved parts. Also, an intelligent tool holder design 400A is proposed in this system, which allows user to center the shaped wire 401 cutting tool to the theta axis 422 of an XYZA CNC tangential cutting system. Also, an intelligent wire shape is proposed in this invention, consisting of notches 601, 801, 802 in a plane perpendicular to the shape of wire 401, which prevents the cut part from falling on the hot wire, thus avoiding shape defects to the cut part.

Description

“TANGENTIAL CNC CUTTING TOOL AND TOOL HOLDER DESIGN”

FIELD OF INVENTION

[001] This invention is related to CNC tangential cutting system holding a cutting tool made of shaped wires. This invention proposes an intelligent tool holder design and manufacturing method, which eliminates shape defects and improve accuracy of the cut parts.

[002] V-carving is a popular material removal method to carve 3D designs in materials, which produces designs with chamfered, filleted edges. While the designs in the middle have to be carved to a blind depth, the outer edges of the design need to be through cut. This invention proposes an innovative tool design which can achieve the above two functions effectively.

[003] This invention also proposes an intelligent wire shape design which eliminates shape defect when manufacturing revolved objects like spheres using wire cutting method.

[004] The present application is based on, and claims priority from an Indian Application Number 202041037612 filed on 01st Sep, 2020, and an Indian Application Number 202141006401 filed on 16th Feb, 2021, and an Indian Application Number 202141011409 filed on 17th Mar, 2021 the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF INVENTION

[005] It is often required to fabricate revolved shapes like spheres, Domes etc. Currently setups like lathe, pottery wheel arrangement for rotating material against a heated/charged wire of required cross section is used. These methods have limitations that part has to be loaded, unloaded one by one, which results in low productivity. Hence there is a need to develop CNC based automatic fabrication methods.

[006] In tangential cutting CNC systems, holding a cutting tool made of shaped wire, it is important to centre the tool to the theta axis, as otherwise it results in shape defects.

[007] V-carving is a popular material removal method to carve 3D designs in materials, which produces designs with chamfered, filleted edges. While the designs in the middle have to be carved to a blind depth, the outer edges of the design need to be through cut. Typically, two separate manufacturing operations are used for achieving this. Hence there is a need to develop an innovative tool design which can achieve the above two functions effectively, in a single cutting operation.

OBJECT OF INVENTION

[008] The principal object of this invention is to develop an innovative tool holder design which can hold a cutting tool made of shaped wire, perfectly centered on a tangential cutting CNC system’s theta axis.

[009] Another object of this invention is to develop an intelligent cutting method for revolved shapes, which eliminates shape defects and also achieves high productivity.

[0010] Another object of this invention is to develop an innovative tool design which can achieve V-carving of blind depth and through cut depth designs, in a single cutting operation. [0011] These and other objects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES

[0012] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0013] FIG. 1: Vcarving composite knife design

[0014] FIG. 2: Vcarve design with blind depth and through depth edges

[0015] FIG. 3: Vscoop composite tool

[0016] FIG. 4: REVOLVED PARTS FABRICATION

[0017] FIG. 5: REVOLVED PARTS FABRICATION TOOL HOLDER

[0018] FIG. 6: REVOLVED PART DEFECT1

[0019] FIG. 7: REVOLVED PARTS CUTTING LAYOUT

[0020] FIG. 8: Single notched shaped wire [0021] FIG. 9 : POSITION OF NOTCHED WIRE AFTER 180 DEG CCW ROTATION

[0022] FIG. 10: NOTCHED WIRE CLOCKWISE ROTATION

[0023] FIG. 11: NOTCH LOCATION IN COMPLEX SHAPED WIRE [0024] FIG. 12: DOUBLE NOTCHED WIRE.

DETAILED DESCRIPTION OF INVENTION

[0025] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. For example, it should be noted that while some embodiments are explained with respect to cutting of designs in EPS, EPE foam material using heated wire, any other application may also incorporate the subject matter of the invention with little or no modifications. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0026] The embodiments herein describe an innovative tool design which can achieve V-carving of blind depth and through cut depth designs, in a single cutting operation. Referring now to the drawings, and more particularly to FIGS. 1 through 12, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.

[0027] Figure 1 shows a V-carving tool 100A, made of a metal heating wire bent into a V shape, with vertical legs 102, 102 A and two inclined edges 101, 101 A.

[0028] The V-shaped wire is mounted on a plate 103.

[0029] Plate 103 is mounted on theta axis of a 4 axis XYZA CNC machine. [0030] Such a tool can carve designs, but cannot through cut the material at desired locations.

[0031] Figure 2 shows the typical V-carved design, with some designs like 203, 204 carved to blind depth in the middle. But some designs like edges 201, 202 etc. need to be through cut. These outer edges are needed to have a non-zero material thickness 205 at the edges to avoid a knife edge, which is weak and can break.

[0032] In this invention it is proposed to mount a hot knife cutting tip 104 at the center of the V- tool.

[0033] The knife 104 is mounted on a handle plate 105.

[0034] The knife 104 can move up down relative to the V-tool edges, as the plate 105 is fixed to a Linear Motion (LM) block 107, which slides on LM rail 106, which in turn fixed on plate 103.

[0035] 104 A is the tip of the knife and 10 IB is the tip of the V-tool.

[0036] The up/down motion of the knife is CNC controlled by a motor 108.

[0037] Current is passed through the V-tool from 102 A to 101 A to 101 to 102, thus heating the V-tool.

[0038] Current is also passed through an insulated heating element inside the knife tube body and current flows to ground through the knife tube body. Two different isolated power supplies are used to heat the V-tool and the knife, so that there is no short circuit when knife body touches the V-tool.

[0039] Thus, both the V-tool and the knife are hot and can cut materials like foam. [0040] When cutting edge/profiles like 201,202 etc, the knife 104 is moved down with 104A knife tip below the 10 IB V-tool tip by distance sufficient to through cut the material.

[0041] When cutting, the V-tool assembly is moved in tangential control mode along the XYZ profile, such that V-scoop edges will always scoop and cut the material.

[0042] When cutting blind depth middle-profiles like 203, 204, the knife is programmed to lift up, such that the knife tip 104A is at same level as V-tool tip 101B orjust below it.

[0043] Thus, the composite cutting tool with combination of V tip 101 and a retractable straight edge cutting tip 104, is able to carve complex designs in a single CNC cutting operation.

[0044] At the end of the cut, before heating current is turned off, the knife tip 104A is moved above the V-tool tip 101B. This is to avoid the molten foam from solidifying and gluing the tips together.

[0045] In another embodiment, at the end of cut, the knife 104 is oscillated up/down for some time, after the heating current is turned off. This is to avoid the molten foam from solidifying and gluing of the knife 104 with the Vedges 101, 101A.

[0046] In another embodiment, the V-tool can be half-V shaped. In another embodiment the edges 101,101 A can be curved, to get filleted edges on the material being carved. [0047] In another embodiment the edges of the V-tool 101, 101A can be at different angles.

[0048] In another embodiment, the V shape can be obtained by a composite tool as shown in fig3 ( as explained in “Figure 8” of PCT/IN2018/050540 )

[0049] In another embodiment, the CNC has a material surface height measurement sensor, to compensate for surface height variations.

[0050] In embodiment, the V-tool is a milling tool, with cutting edges at periphery and a hollow centre. Through the hollow centre, another long milling tool of smaller diameter is used, in the same retractable configuration as 104 in figure 1.

[0051] Such a composite endmill can be rotated at high RPM to carve designs as shown in figure 2 in a three axis XYZ CNC machine.

[0052] Fig 5 shows a shaped cutting wire 401 bent to the cross-section shape of the required revolved part to be fabricated, with suitable compensation for melting allowance.

[0053] Cutting wire 401 is typically resistive heating element like NiChrome wire, through which current is passed or it can be wire EDM (Electrical Discharge Machining) etc.

[0054] 402 is the center point of the left and right edge (401A, 401B) of the shaped wire 401.

[0055] 403, 404 are vertical legs of the bent wire 401.

[0056] 405, 406 are screw terminals to which the wire legs 403,404 are locked respectively [0057] The screw terminals 405,406 are both locked to slot 408 on plate 407. The slot 408 allows distance between 405 and 406 to be adjusted to match distance between 403 and 404.

[0058] The plate 407 is in turn mounted on slot 410 on plate 409. Slot 410 can be a simple slot or it can be a linear motion (LM) guide.

[0059] Plate 409 is in turn mounted on shaft 412.

[0060] In one embodiment the shaft412 is ahollow shaft through which wires 420, 421 passes through and connect to screw terminals 405, 406.

[0061] In one embodiment 412 is a solid shaft and power is given to terminals 405, 406 through slip rings.

[0062] In one embodiment, shaft 412 is driven by motor 411

[0063] In another embodiment, shaft 412 is driven by gear or timer belt drives.

[0064] When shaft 412 rotates, the wire 401 also rotates about axis 422, thus cutting the raw material 309 to required shape.

[0065] It is important that the center point 402 of the bent wire is located on the axis 422 with minimum deviation.

[0066] The shaft 412 is in turn mounted on a CNC machine with XYZ degrees of freedom (417, 418, 419) respectively.

[0067] Typical cutting sequence as follows:

[0068] Figure 7 shows a block of material 501 from which revolved objects 502, 503, 504, 505, 506 etc. are cut. [0069] The center 422 of the cutting tool 400 is moved to point 507 at start of cut.

[0070] The tool 400 is moved in Z minus direction, by a distance H (424) plus some allowance.

[0071] Then the tool is moved by CNC by a distance R (423) to point 502. Then the tool 400 is rotated about axis 422 by 180 degrees.

[0072] Referring to Figure 4, the object 302 will tend to fall on the bottom section of the wire 301 and can get damaged at end of 180 degrees rotation of the bent wire 301.

[0073] To avoid this damage, it is proposed to move the tool down by a small distance (say 3 mm) at the end of the 180-degree rotation of the tool.

[0074] Then the tool is moved at the same Z height, theta angle to point 507 or 509.

[0075] Then tool is optionally lifted up in Z plus direction above the material 501.

[0076] Then tool is moved to point 509 and the cutting cycle is repeated to cut part 503.

[0077] Subsequent columns can be either adjacent as in part 505, or in a honey comb nesting, as shown by part 506 in Fig 7.

[0078] Fig 6 shows the defective shape of cut part, when 402 is not lying on or very close to axis 422. 401 A, 401B are the starting positions of the cutting edges. 401A1, 401B1 are the positions of the cutting edges after 180 deg rotation, with 422 being the center of rotation. [0079] In systems with rigid tools like end mills, special collets ensure this concentricity. But when the cutting tools is a flexible wire, collet system is not possible and hence need a special arrangement as described in this invention.

[0080] It is proposed to have one or two nuts 414, 416 attached to the plate 409, with bolts 413, 415 passing through the nuts 414, 416. The bolt can be rotated in sync to fine adjust the position of plate 407 along the slot 410, This can be used to adjust to ensure the centre of bent wire 402 is lying on the axis 422 or very close to 422.

[0081] Circular shaped bent wire is used as an example. Wire can be bent to any other shapes like semi-circle, V, U etc.

[0082] In particular, for 4-axis tangential V-carving with heated tool, similar arrangement to centre the V-tip to the axis 422 is very useful.

[0083] The shaped wire 401 is typically bent to shape using pliers etc. These wires tend to have spring back. Hence it is very difficult to maintain close tolerances on dimensions of the wire shape.

[0084] Also, user typically has to cut parts of varying sizes and hence tend to maintain an inventory of wires.

[0085] Every time the wire is changed, fine adjustment is needed to ensure wire centre and axis 422 are collinear. The proposed micro-meter style adjustment screws help in this fine adjustment, ensuring defect free output parts.

[0086] The screw 413, 415 arrangement is shown in fig2 as an illustration. It can be any other fine adjustment mechanism. [0087] In one embodiment, there are micro-meter stages on plate 409, allowing fine adjustment in both X & Y directions.

[0088] The shape of the wire is obtained using Variable Distance Offset (VDO) method explained in patent 201947045353.

[0089] However, the setup in fig4,5 for cutting revolved parts has a problem that at the end of 180 degrees cut, the cut piece 302 will fall on the hot wire 301 and can get damaged.

[0090] Innovative methods are proposed in this invention to overcome this problem.

[0091] In one embodiment, it is proposed to rotate the wire for an angle less than 180 degrees, say 178 or 179 degree. This will leave a small uncut bridging material between the foam block 309 and the foam piece 302 being cut, thus preventing the foam piece from falling on the wire.

[0092] But this method leaves a long uncut connecting material, which needs to be again manually removed by the user.

[0093] This invention proposes an innovative wire shape, which minimises the uncut bridging material length, thus reducing manual work after the machine cut.

[0094] Fig. 8 shows the bent shaped wire 401, similar to Fig. 5.

[0095] 401 A, 401B are the two side edges of the wire 401.

[0096] It is proposed to introduce a notch 601 on only one of the edges, say 401B as shown in Fig. 8.

[0097] The notch 601 can be of any shape like triangular, semicircle etc. [0098] The size of the notch is 602 and can be chosen based on the diameter of the part being cut.

[0099] Notch size is bigger for bigger diameter parts, as more bridging material is needed to support the cut piece weight from falling or sagging down.

[00100] The notch is in a plane almost perpendicular to the plane on which the circular shape of wire 401 is formed.

[00101] Fig. 8 shows the front view, top view, side view of the shaped wire 401 with notch 601.

[00102] The starting position of the notch is as shown in Fig. 8, with the notch on the right edge 201B protruding backwards.

[00103] Now, wire will rotate 180 degree in counter-clockwise direction.

[00104] Fig. 9 shows the position of the wire after the above 180 degree rotation.

[00105] After this 180 degree rotation, CNC will move the wire forward in direction 603 shown in Fig. 5 for the next cut.

[00106] This will leave an uncut bridging material between the foam block 309 and piece of revolved part 302 being cut by the heated rotating wire 301/401.

[00107] Fig. 7 shows the CNC machine indexing to multiple positions 502, 503, 504, etc to cut multiple revolved parts with wire 401.

[00108] After cutting part 502, the wire will be moved forward to position 509 between the parts 502, 503. At this position 509 the CNC will lift the wire 401 outside the material 501, rotate 180 degree to bring the notch back to the right side, then plunge again into the material, move to centre of 503 and rotate 180 degree again in counter clockwise direction to cut the part 503 and so on.

[00109] Alternately, the start position of the notch can be on the left side as shown in Fig. 10 and wire can rotate in clockwise direction by 180 degrees before moving forward in 604 direction for the next cut.

[00110] Fig. 11 shows a complex cross section shape to which the wire 401 is bent. The notch 601 can be in any one periphery position like 701, 702, 703, 704, 705 etc.,

[00111] Position 705 may be preferred, as the moment arm radius of the cut foam piece’s weight is minimal at point 705.

[00112] Fig. 12 shows the shaped wire 401 with double notch 801, 802 on one edge 40 IB of the wire 401. The notches 801, 802 are at a small offset distance 803 from each other. The notches 801, 802 are in a plane almost perpendicular to the plane on which the circular shape of wire 401 is formed.

[00113] Now this double notched wire can cut the part 502 by rotating 180 degrees in CCW direction and then directly go to the centre of 503 and now rotate in CW direction by 180 degrees and so on.

[00114] The uncut bridging material will be on left side of 502 and right side of 503 and so on.

[00115] Thus, the need for the wire to lift up at point 309 and rotate 180 degree and then go down again is avoided. [00116] Cutting wire 401 is typically resistive heating element like NiChrome wire, through which current is passed or it can be wire EDM (Electrical Discharge Machining) etc.

[00117] The shape of the wire 401 is obtained using Variable Distance Offset (VDO) method explained in patent 201947045353.

[00118] Patent 202141010178 explains a composite shaped wire made of SS tube with insulated NiCr wire inside, which is held and rotated 360 degrees to cut a revolved part. Such composite shaped wire can also have the proposed notches 601, 801, 802 etc.

[00119] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

CLAIMS im: ) A tangential CNC cutting system 100 holding a composite cutting tool 100 A comprising of a V-shaped resistive heating wire (102A-101 A-101-102) and an up/down moveable hot knife 104 with insulated resistive heating element inside, mounted to be almost near the V-tool center, The V-shaped wire and the knife 104 are heated by two isolated power supplies, with the knife 104 programmed to be in down position when V-carving outer edge designs like 201, 202 and knife 104 programmed to be in retracted up position when V-carving inner design edges like 203, 204, with the CNC system manipulating the theta angle of the tool and keeping it tangential to the XY path vector, such that the V edges will scoop the material being cut always. ) A composite cutting tool 100A comprising of a V-shaped resistive heating wire (102A-101 A-101-102) and an up/down moveable hot knife 104 with insulated resistive heating element inside, mounted to be almost near the V-tool center, The V-shaped wire and the knife 104 are heated by two isolated power supplies. ) A composite cutting tool 100 A of claim2, where the knife 104 is programmed to oscillate up/down for some time, after the heating current is turned off, to avoid the molten foam from solidifying and gluing of the knife 104 with the V-edges 101, 101A. ) The composite tool of claim 2, where the V-tool has one straight edge and one inclined edge forming a half V-tool. 5) The composite tool of claim 2, where the V-tool edges 101, 101 A are curved to cut filleted edges.

6) The composite tool of claim 2, where the V-tool edges 101, 101A are at different angles.

7) A revolved part CNC cutting 4-axis system 400 holding a cutting tool made of shaped resistive heating wire 401, with center 402, mounted on slotted plate 407, which in turn is mounted on plate 409 with slot 410 or a Linear motion guide 410, with plate 409 in turn mounted on a hollow shaft 412, which is capable of rotating about axis 422, with plate 409 having one or more micro-meter style adjustment screws 413, 415, capable of fine adjusting the plate 407, and thus fine adjusting the center 402 of the heated wire 401 to be in alignment with axis 422 of theta axis of the cutting system 400.

8) A revolved part CNC cutting 4-axis system 400 holding a cutting tool made of shaped resistive heating wire 401, with adjustment micro meter setup consisting of slot LM guide 410, screws 413, 415, nuts 414, 416 between the shaft 412 and cutting wire holding plate 407 to fine adjust and align the center 402 of the shaped wire 401 to the axis of rotation 422 of the theta axis.

9) A revolved part cutting system 400 of claim7, cutting revolved objects by the rotating shaped wire 401, programmed to move down by a small distance at the end of 180 degrees rotation of the shaped wire 401, to avoid the cut part 302 from falling on the heated wire 401. 10) A tangential CNC cutting system 100 having a center adjustment mechanism between the tool being held and the axis 422 of rotation of the theta axis, as explained in claim 7.

11) A revolved part cutting system 400 of claim? with shaped wire 401 of cross section shape 1, having a notch 601 in a plane perpendicular to the plane of shape 1, such that when heated wire 401 is rotated by 180 degree, it will leave an uncut bridging material between the foam block raw material 301 and the revolved part 302 being cut, thus preventing the revolved cut part 302 from falling on the heated wire 301.

12) A revolved part cutting system 400 of claim? with shaped wire 401 of cross section shape 1, having multiple notches 801, 802 on side 40 IB of the wire 401, in a plane perpendicular to the plane of shape 1, such that when heated wire 401 is rotated by 180 degrees, it will leave an uncut bridging material between the foam block raw material and the revolved part being cut on one side, thus preventing the revolved cut part from falling on the heated wire 401. When the wire 401 is further rotated 180 deg in the opposite direction, it leaves uncut bridging material on opposite side, thus allowing chain cutting of multiple revolved parts from a block of foam, without the cut pieces 302 falling on the heated wire 301, 401 at the end of the cut.

13) A revolved part cutting system 400 of claim? with shaped wire 401 of cross section shape2, where the location of notch is chosen to minimize the moment arm radius of the weight of the cut piece, enabling the notch size to be smaller. ) A revolved part cutting system 400 of claim? with shaped wire 401 of cross section shape 1, where wire is rotated less than 180 degrees intentionally to leave an uncut bridging material between the foam block 309 and revolved part 302 being cut by the rotating wire 301, thus preventing the part from falling on the wire.