GB2378409A

GB2378409A - Vice with indentors to establish a positioning reference in workpiece

Info

Publication number: GB2378409A
Application number: GB0218248A
Authority: GB
Inventors: John Patrick Harvey
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-08-06
Filing date: 2002-08-06
Publication date: 2003-02-12
Anticipated expiration: 2022-08-06
Also published as: EP1417070A2; WO2003013774A3; GB2378409B; GB0119071D0; WO2003013774A2; GB0218248D0

Abstract

Manufacture of a spark-erosion electrode from a blank 2 is carried out with the blank 2 clamped in a vice 1. The closing faces 11,(12, Fig 2) of the vice-jaws 9,10 have projections (15+16, Fig 2) and 17 of pyramidal form for indenting the blank 2. The indentations (19+20, Fig 3) and 21 establish references enabling the blank 2 or electrode manufactured from it, to be removed from the vice 1 and returned to it with precisely the same positioning, solely by registration of the indentations (19+20, Fig 3) and 21 with the projections (15+16, Fig 2) and 17. Accuracy of positioning similarly results for transfer of the blank 2 or electrode to another, corresponding vice or of a correspondingly indented blank or electrode to the vice. The projections may be provided as inserts (26, Fig 4) in the respective jaws 9,10.

Description

Spark Erosion This invention relates to spark erosion, and is concerned with methods and devices for use in the manufacture and use of spark-erosion electrodes.

Spark-erosion electrodes are commonly of copper, being manufactured with high accuracy to the required configuration from bar stock, for example under computer control using CNC milling machinery. Once the required electrode has been produced, it is brought into use by securing it to a chuck of the spark-erosion machine; the latter machine is commonly referred to as an EDM (electro-discharge machining) machine. Accurate positioning of the electrode relative to the coordinate axes of the EDM machine is fundamental to the precision with which machining proceeds according to those axes.

It is of especial importance where the machining requires use of several electrodes in sequence, since an error in positioning any one of them will lead to spoiling of the workpiece. The positioning of an electrode accordingly normally entails a lengthy and delicate procedure of clocking the electrode with a dial gauge parallel to one or other of the EDM machine axes, and making adjustments according to precision measurements.

The time and work involved in positioning spark-erosion electrodes in the above respect, can be reduced by adopting the practice in which identical'pallet'chucks are fitted to the CNC and EDM machines. The bar-stock blank from which the electrode is to be manufactured, is clamped to a'pallet'that is used for holding the blank in the pallet chuck of the CNC machine while it is being milled to shape. Once milling of the electrode is completed, the pallet is released from the chuck of the

CNC machine and, as still clamped to the electrode, is transferred to the pallet chuck of the EDM machine to hold the electrode during the spark-erosion process.

Each pallet chuck conventionally has four mutuallyorthogonal arms onto which four corresponding slots of the pallet locate so that once a common datum has been established between the CNC and EDM machines through their identical pallet chucks, accurate electrodepositioning in the EDM machine is carried out automatically upon transfer of the pallet from the CNC machine.

Although the use of pallets and pallet chucks has significant advantage in terms of saving time and work in setting up the electrode in the EDM machine, the secure fitting of a pallet to the electrode-blank requires accurate drilling and tapping of fixing holes in the blank together with accurate drilling and reaming of holes for dowel-pin location. This is of disadvantage where a large number of electrodes are to be prepared, and from a practical point of view generally precludes the fitting of a pallet where small electrodes (for example having a thickness less than 25 mm) are involved.

It is one of the objects of the present invention to provide a method and device for use in the manufacture and use of spark-erosion electrodes, that may be used to overcome disadvantages associated with pallet use.

According to one aspect of the invention there is provided a method for manufacture of a spark-erosion electrode, in which a blank of copper or other malleable material is clamped in a holding device during machining of the blank, wherein the blank is indented by the holding device in the action of clamping it in the holding device so that the resulting indentation establishes a positioning reference therein.

With the method of the invention, the blank is indented in a way that establishes a reference such that if the blank, or the electrode as machined from the blank, is released from the holding device it can be readily returned to that device, or to another comparable device, to have the same relative positioning in the clamped condition. Thus, the present invention enables a positioning-reference to be established in the blank and electrode manufactured from it, in a very simple way, so that accurate positioning for subsequent use of the electrode is achieved reliably and economically.

According to another aspect of the invention, there is provided a method of spark-erosion in which an electrode is held in a holding device that has a pair of jaws for receiving and closing onto opposed faces of the electrode to clamp the electrode in the holding device, wherein the electrode has indentations in said faces and it is positioned between the jaws with projections on the closing faces of the jaws located in register with the indentations prior to clamping.

Furthermore, according to another aspect of the invention, a device for holding a blank of copper of other malleable material during the manufacture of a spark-erosion electrode from the blank, comprises a pair of jaws for receiving the blank, and means for urging the jaws to close hard on the blank to clamp it in the holding device, wherein the opposed closing faces of the jaws have projections therefrom to indent the blank when they are closed on the blank in clamping it as aforesaid.

The holding device according to the invention may take the form of a vice with one jaw slidably mounted on a base that incorporates the other jaw, and there may be one or more projections incorporated in the contact face

of each jaw. The projections may be of pyramid configuration.

A method and device according to the present invention, for use in the manufacture and use of a spark-erosion electrode, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view from the front of a device according to the invention for holding a blank of a spark-erosion electrode during its manufacture and use, this figure including representation of an indented blank and showing enlarged detail of one of a number of indenting projections of the holding device; Figure 2 is a plan view of the holding device of Figure 1; Figure 3 is a perspective view from the rear of the blank represented in Figure 1; and Figure 4 is an exploded sectional view illustrative of a modification according to the invention, of the holding device of Figures 1 and 2.

Referring to Figures 1 to 3, a vice 1 for holding a copper blank such as the block 2 (shown only in Figures 1 and 3) cut from bar stock, has a unitary base 3 of hardened steel. A hardened-steel slider 4 of the vice 1 is retained within a slide-channel 5 of the base 3, on a lead-screw 6. The lead-screw 6 is turned by engagement of a torque wrench (not shown) with a socket 7 on the front 8 of the block 3. When the wrench is turned, the screw 6 turns with it to move the slider 4 along the channel 5 in one direction or another according to the sense of turning.

The slider 4 has a transverse, integral jaw 9 which according to the sense of turning of the screw 6 opens from, or closes onto, a jaw 10 that is integral with the base 3. The opposed, closing faces 11 and 12 of the jaws 9 and 10 respectively, which are both planar, are broken into by a wide horizontal channel 13 and narrow vertical grooves 14 (the grooves 14 arise from the machining of the faces 11 and 12 and have no material effect).

However, two spaced-apart projections 15 and 16, each having the configuration of a quadrilateral pyramid (specifically with square base), are located in the channel 13 of the jaw 9 to extend out of it beyond the plane of the face 11. A single, centrally-positioned projection 17, identical to the projections 15 and 16, is correspondingly located in a wide horizontal channel 18 of the jaw 10 to project out of it beyond the plane of the face 12.

The vice 1, which is manufactured of hardened steel to a high standard with low tolerance limits in order that its clamping action is firm and without variation, is used for holding an electrode blank, such as the block 2, firmly between the jaws 9 and 10 during machining by a CNC milling machine. In this respect, a standard pallet (not shown) is mounted on the underside of the block 3 of the vice 1 so that the vice 1 can be readily retained in the pallet chuck of the CNC machine. Once machining is completed, the assembly of pallet and vice 1 carrying the machined electrode can be transferred to the pallet chuck of the EDM machine.

Thus, an advantageous feature of the vice 1 is that it can be used to hold a blank securely during machining, simply by retaining it within the jaws 9 and 10 and without the necessity for drilling, tapping and reaming to fit the blank itself to the pallet. Accordingly, the advantage of pallet-use in avoiding the necessity for

time-consuming setting up when transfer from CNC to EDM machine is made, is obtained without the disadvantages.

But more notably, there is the advantage that it is readily possible at any stage to release the blank or manufactured electrode from the vice 1, and subsequently return it to be clamped in the vice 1 with precisely the same relative positioning.

In the latter regard, the action of clamping the copper blank within the jaws 9 and 10, presses the pyramid projections 15 to 17 into the copper, so that it is permanently indented. More particularly, the projections 15 and 16 make pyramidal indentations 19 and 20 respectively, as illustrated in Figure 3, and the projection 17 makes indentation 21 as illustrated in Figure 1. The indentations 19 to 21, which owing to the clearance given by the channel 13 and 18 are cleanly made, give precise and unambiguous referencing to enable the electrode once removed from the vice 1, to be returned to it with exactly the same relative positioning. All that is required in this respect, is registration of the indentations 19 to 21 with the respective projections 15 to 17 before the jaws 9 and 10 are closed on the electrode.

Accordingly, there is the advantage that the vice 1 can be used on a CNC machine to manufacture a supply of electrodes for future use, each manufactured electrode being released from the jaws 9 and 10 of the vice 1 when machining is complete, and replaced by a blank. When the electrodes are to be used, the vice 1 (or a vice identical with it) is attached by its pallet to the pallet chuck of the EDM machine, and the electrodes are then, as they become required in turn, clamped in the vice with their indentations in appropriate register with the respective projections 15 to 17. Moreover, once the electrodes have been used and removed from the EDM

machine, they can easily be brought back into use without any setting up required other than to re-establish register with the projections 15 to 17 before clamping.

The provision of the means for accurately positioning the electrode, namely, the cold forming of the reference indentations 19 to 21 in the copper, is of significant advantage. It is achieved'automatically'and simply, during the step of firmly securing the blank for machining, a step required in any case in manufacture of the electrode.

The pyramid configuration of each projection 15 to 17 has advantage in providing distinct multiple facets for accurate registration, but the invention is not limited to this specific configuration, or indeed to the same configuration being used for each projection. Also, more, or fewer, projections than three may be used.

The pallet on which the vice 1 is mounted can be of any of the known forms, the particular form used being dependent on the form of pallet chuck fitted to the CNC and EDM machines to be used. However, it will be appreciated that the principle and advantages of use of the vice are not dependent on the form of pallet used or indeed whether or not a pallet is used.

In the vice 1 of Figures 1 and 2, the projections 15 and 16 are machined as part of the jaw 9, and the projection 17 as part of the jaw 10 of the block 3. However, construction of the vice, and in particular the machining required, may be much simplified by a modification in which each projection is provided separately as an insert to its respective jaw. Figure 4 illustrates how this may be done.

Referring to Figure 4, the relevant jaw 22 is in this case drilled and reamed to provide a two-part bore having first and second parts 23 and 24 of circular-section and a smaller, square-section respectively. The first borepart 23, which is screw-threaded throughout almost all of its length, opens from the rear face 25 of the jaw 22 to receive a projection-insert 26.

The insert 26 is of one-piece construction having a square-section shank 27 that extends from an enlarged, cylindrical head 28. The shank 27 terminates in a sharp, pyramidal end 29, and the insert 26 is entered into the bore-part 23 from the rear face 25 with the end 29 leading. The head 28 is a close fit within the bore-part 23, and the insert 26 is pushed down into it to enter the end 29 into the square-section bore-part 24. The shank 27 is a tight fit within the part 24, and the insert 26 is pushed down fully to bring the head 28 onto the shoulder 30 formed at the transition between the boreparts 23 and 24. In this condition, the end 29 projects from the planar closing face 31 of the jaw 22, and a setscrew 32 is screwed into the part 23 to bear tightly on the head 28 and hold it firmly against the shoulder 30.

The use of inserts such as the insert 26 to form the projections for positioning-reference indentation of the blank and subsequent accurate re-location, has economic and practical advantage. Damage to a projection can be readily dealt with simply by replacing the insert rather than the whole jaw. It also facilitates the use of an especially hard material for the projections where use of such material for the jaw as a whole is uneconomic or creates machining difficulty.

Claims

Claims: 1. A method for manufacture of a spark-erosion electrode, in which a blank of copper or other malleable material is clamped in a holding device during machining of the blank, wherein the blank is indented by the holding device in the action of clamping it in the holding device so that the resulting indentation establishes a positioning reference therein.
2. A method according to Claim 1 wherein the indented blank or electrode machined therefrom is released from the holding device and subsequently returned to it, or is replaced by a correspondingly-indented blank or electrode, for clamping in the holding device, the returned or replacement blank or electrode being clamped in the holding device using the indentation or indentations thereof as a reference for locating it with the same positioning in the holding device as said indented blank or electrode machined therefrom, before release from the holding device.
3. A method according to Claim 1 wherein the holding device has the form of a vice with jaws for receiving and closing onto the blank, and the opposed closing faces of the jaws have projections therefrom for indenting the blank as aforesaid.
4. A method according to Claim 3 wherein the indented blank or the electrode as machined therefrom is released from the holding device and subsequently returned to it, or is replaced by a correspondingly-indented blank or electrode, for clamping in the holding device, the returned or replacement blank or electrode being clamped in the holding device with the blank or electrode

<Desc/Clms Page number 10>

positioned therein with its indentations in register respectively with said projections.
5. A method of spark-erosion in which an electrode is held in a holding device that has a pair of jaws for receiving and closing onto opposed faces of the electrode to clamp the electrode in the holding device, wherein the electrode has indentations in said faces and it is positioned between the jaws with projections on the closing faces of the jaws located in register with the indentations prior to clamping.
6. A method according to any one of Claims 3 to 5 wherein at least one of the closing faces has two projections for indenting the blank as aforesaid.
7. A method according to any one of Claims 3 to 5 wherein one of the closing faces has one projection and the other has two projections for indenting the blank as aforesaid.
8. A method according to any one of Claims 3 to 7 wherein the projections are of pyramid configuration.
9. A method according to Claim 8 wherein the projections are of quadrilateral pyramid configuration.
10. A device for holding a blank of copper of other malleable material during the manufacture of a sparkerosion electrode from the blank, comprising a pair of jaws for receiving the blank, and means for urging the jaws to close hard on the blank to clamp it in the holding device, wherein the opposed closing faces of the jaws have projections therefrom to indent the blank when they are closed on the blank in clamping it as aforesaid.

<Desc/Clms Page number 11>
11. A device according to Claim 10 wherein one of the jaws is slidably mounted on a base that incorporates the other jaw.
12. A device according to Claim 10 or Claim 11 wherein at least one of the closing faces has two projections for indenting the blank as aforesaid.
13. A device according to Claim 10 or Claim 11 wherein one of the closing faces has one projection, and the other has two projections for indenting the blank as aforesaid.
14. A device according to any one of Claims 10 to 13 wherein the projections are of pyramid configuration.
15. A device according to Claim 14 wherein the projections are of quadrilateral pyramid configuration.
16. A device according to any one of Claims 10 to 15 wherein each projection is part of an insert in the respective jaw.
17. A method for manufacture of a spark-erosion electrode, and/or use of the manufactured electrode in spark-erosion, substantially as hereinbefore described with reference to the accompanying drawings.
18. A device for holding a blank of copper of other malleable material during the manufacture of a sparkerosion electrode from the blank, and/or holding the manufactured electrode during spark-erosion, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.
19. A device for holding a blank of copper of other malleable material during the manufacture of a spark-

<Desc/Clms Page number 12>

erosion electrode from the blank, and/or holding the manufactured electrode during spark-erosion, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings, modified as described with reference to Figure 4 of the accompanying drawings.