GB2087777A - Improvements in or relating to electroerosion apparatus - Google Patents

Abstract

Electroerosion apparatus has at least one electrode holder 3 for holding an electrode 2 which may be shaped over its central portion, as shown, for machining a mould cavity in two workpieces 4 and 5 to produce a two-part mould. Means are provided for adjusting the position of the electrode 2 in relation to support means 6 and 7 for the workpieces which are preferably movable, independently, by servomotor 10,11. Preferably, blocking means is provided for stopping movement of the electrode holder 3, and preferably, where mould parts 4 and 5 are to be machined, current supplies to each mould part are independently controllable. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electro-erosion apparatus The present invention relates to electroerosion apparatus.

In electroerosion machines which may conventionally be used for the manufacture of moulds, one of the main problems consists in obtaining perfect coincidence between both mould parts. When each part is made separately, it is essential to carry out afterwards a precise centering operation on each of the mould parts. This operation is generally slow and arduous with consequent production loss.

This problem which in itself is already extremely complicated becomes even more serious when the mating surfaces of the mould parts do not lie in a common plane but instead take the form of irregular curves.

In order to solve these problems, it is known to provide an electrode in a vertical position in an electrode-holder head, with both halves of the mould being held on respective support tables having vertical supporting planes, the tables being simultaneously actuated by means of a shear mechanism, (panto-graphic or similar) in order to obtain simultaneous approaching movement of both mould halves towards the electrode, until the correct spark distance is obtained. By this means, simultaneous machining of both mould halves may be achieved.

But this solution does not solve all the problems efficiently, as, in order to obtain an acceptable result, it can only be applied where the mould parts have nearly symmetrical outlines both in their shape and depth.

Furthermore, work conditions, short circuits and/ or other unforeseen circumstances on one of the halves of the mould may also have an influence upon the other half, as a result of which performance deteriorates considerably.

An object of the invention is to provide improved electroerosion apparatus.

According to the invention, there is provided electroerosion apparatus having at least one electrode holder provided with movement means for adjusting the position of an electrode in relation to a support means for a workpiece.

Preferably, said movement means is operable to move the or at least one electrode holder vertically.

Preferably, there is provided blocking means for stopping movement of the or at least one electrode holder.

Preferably, there is provided support means for supporting two separate workpieces for electroerosion by a common said electrode, when held by a said holder.

There may be provided two independently movable support members for respective workpieces.

Each support member may be provided with a respective device for moving the support member towards and away from said common electrode, when positioned in said holder.

Preferably, each device is a servo-mechanism.

Preferably, the support members are electrically isolated from each other, and are provided with independent current supplies having the common electrode as a common terminal.

Said supplier may be independent outputs of a single current generator.

The current supplies may be operable to machine iron with iron.

Means may be provided for preventing said movement of one of said support members.

In one embodiment, one of said support members is a bed of the apparatus, the other support member being movably mounted thereon.

In said one embodiment, preferably one of said support members is provided with a differential compression system for avoiding relative displacement between said support members.

Preferably, at least one of said support members is provided with means for imparting planetary motion for electroerosion in a tangential direction.

Preferably, there are provided feedback position control circuits, for the two support members and a said electrode holder.

Expediently, only two control circuits are provided, one serving for controlling, selectively, the electrode holder and one support member.

Expediently, said support members are linked by an expandable coupling to establish a container for containing liquid dielectric during electroerosion.

There may be provided a mechanical linkage between said electrode holder and said support member whereby operation of said movement means causes movement of said support members towards and away from said electrode, when the electrode is positioned in said holder.

Expediently, the or at least one electrode holder is provided with means for moving an electrode held thereby in planar motion, rotary motion ortranslational motion, as required for any given machining operation.

Said electrode holder may provide a plurality of positions for said electrode.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a schematic perspective view of an electroerosion machine; Figure 2 shows a schematic view of part of the machine of Figure 1 showing one embodiment; Figure 3 shows a schematic view similar to Figure 2 but showing another embodiment; Figure 4 shows a perspective view of a two-part support table of the machine; Figure 5shows a perspective view of two mould parts which do not have planar mating surfaces; and Figure 6 represents a perspective view of one part of the support table constituted by a vertical surface of the machine bed.

Figure 1 shows a schematic perspective view of an electroerosion machine having an electrode 2 which is shaped over its central portion with the desired shape of a mould cavity which is to be machined into workpieces 4 and 5 in order to produce a two part mould. The electrode 2 is held in an electrode holder or carrying head 3 which is capable of controlled upward and downward vertical movement relative to workpieces 4 and 5 which are mounted on respective support members or support tables 7 and 6. Each of the support tables is mounted for sliding movement on a horizontally extending beam of the machine bed. Movement of the support tables is independently controllable by respective servo motors 10 and 11. Also schematically illustrated in the Figure is a part 1 of an electrode blocking system.

This system is operable to stop upward and downward movement of the electrode. Upward and downward movement of the electrode is achieved by means of a hydraulic cylinder controlled by a differential electro-valve acting upon the flow of hydraulic fluid which supplies the cylinder. The electro-valve is connected to a position detector for detecting the position of the electrode 2. When the electrode 2 reaches a desired position, the detector sends a signal to the electro-valve which thereupon acts upon the hydraulic flow to stop movement of the electrode holder 3, and consequently of the electrode. The position detector is preferably an electro-optical device although mechanical devices may instead be used. By means of the electrode blocking system, it is possible to set the position of the electrode 2 very precisely in relation to the workpieces 4 and 5.With such reliable electrode positioning, the process may be carried out automatically.

Reference will now be made to Figure 2 which shows a schematic cross-sectional view of part of the machine of Figure 1. It may be seen that workpieces 4 and 5 are electrically isolated from their respective support tables by means of mem- bers 8 and 9. Two electrical control units 12 and 13 are provided for respective workpieces. As may be seen from the Figure, each control unit controls not only the associated servo motor 10 or 11, but also controls the supply of electrical current to the associated workpiece, via the common electrode 2.

Each workpiece is electrically isolated from its respective support table by electrical isolators 8 and 9.

Figure 3 shows an alternative arrangement in which a single current supply unit 12 has two outputs connected to respective workpieces, and a third output connected to the electrode 2. The unit 12 must in this case be capable of independent control of the currentto the respective workpieces 4 and 5.

Figure 4 shows workpieces support tables 6 and 7 connected together by an expandable coupling, which may be elastic or telescopic, in order to provide a receptacle for containing liquid dielectric during a machining operation. The expandable coupling is necessary to allow the support tables to move relative to one another.

Figure 5 shows the two workpieces 4 and 5 after a machining operation where the shape of the mould cavity may be seen on the closing surfaces 14 of the thus produced mould parts.

Figure 6 shows a perspective view of a further embodiment of support table 6.

Thus, the machine includes an electrode 2 provided with means for vertical upward and downward movement. Also, the blocking and/or cancelling system 1 can be operated at any given moment thereby arresting the machining operation.

As has already been mentioned, each of the support tables 6 and 7 is provided with means for independent horizontal movement to control the distance of the respective workpiece from the electrode 2. The motion of each of the support tables is controlled by a respective servo motor 10 or 11 of any suitable type (hydraulic, electromechanical, or the like). The servomechanism may be sensitive to the passage of electrical current or to voltage drops between the electrode 2 and the associated workpiece.

It is necessary for each of the support tables 6 and 7 to be electrically isolated from the other in order to allow connection of each workpiece to an independent current generator, having a common terminal constituted by the electrode 2. As mentioned, it is also possible for each of the support tables to be connected to respective channels of a common generator, one of whose outputs is connected to the electrode 2.

Thus, the two mould parts can be machined simultaneously even although they have differing shapes and depths. This is possible because the parameters of each of the generators 12 and 13 or each of the channels if a single generator 12 is used, can be independently adjusted. Thus, each of the mould parts 4 and 5 can be machined at an optimum rate in accordance with its particular characteristics.

Where one of the mould parts is of a different material to the other, the appropriate polarities can be used for each mould part. For example, when one of the mould parts is being machined with direct polarity, the other can be machined with reverse polarity.

It is also possible, where each of the support tables 6 and 7 is electrically isolated, for one workpiece to be connected to a positive supply, and the other to a negative supply. Thus, one of the tables, e.g. table 6, can act as an electrode holder and the other as a workpiece holder.

A further possibility is for the two mould parts 4 and 5 to be opposed to one another and connected to differing polarities by means of an appropriate circuit for machining iron with iron. In this manner, by preventing the feed movement of one of the tables 6 and 7, it is possible to adjust the closing surfaces 14 of the two mold parts in circumstances which hitherto have been regarded as almost impossible. In this way, both machining of the mould as well as adjustment of its mating contact faces, can be carried outwith a single setting of the two mould parts, thus obtaining great centering precision.

Within the scope of the invention, one of the support tables may be constituted by a vertical surface of the bed of the machine, which is motorised in a hydraulic and electromechanical manner, whilst the other support table 7 is mounted within the machine bed and provided with its own feed system. This possibility is illustrated in Figure 6. In this case, it is necessary to provide a differential compensating mechanism in order to avoid unwanted displacement of the inner support table 7, when the outer one 6 is displaced.

It will be apparent that as a result of the provision of independent current supplies to the two work pieces, each mould part can be machined at a rate adapted to its own dimensional structural and/or physical-chemical characteristics.

In certain circumstances, it may be convenient to provide means for moving each of the support tables with motion of the planetary type in order to allow electroerosion in the tangential direction.

It is possible to provide further fastening devices for the machining electrode 2, both for the exterior and interior, but always maintaining electrical isolation in relation to the workpiece support tables.

In one embodiment, there is provided three servo feedback control circuits, one for the electrode holder, and one for each of the displaceable support tables. It is also possible to provide only two feedback control circuits, one being usable both to control the vertical movement of the electrode, and also one of the support tables. In this case, the feedback control circuit will be switchable selectively between the electrode holder, and the support table.

In a further embodiment, the electrode holder may be coupled by means of a mechanical linkage to the workpiece support tables. In this manner, vertical motion of the electrode 2 can result in horizontal motion of the support tables. By this means, it is possible to dispense with the servo motors for one or both support tables.

The above described improvements in electroerosion apparatus are applicable to all forms and types of electroerosion apparatus, especially those for the production of mould parts. They are also applicable to any other type of machine utilised for mould manufacture of electroerosion.

Although in the illustrated embodiment, the electrode holder 3 is shown holding only a single electrode 2, in certain circumstances it may be desirable for the holder to simultaneously hold a plurality of electrodes, for example when two or more separate mould cavities are required in the mould parts.

As will be appreciated by those skilled in the art, it is normally necessary for both the electrode 2, and the workpieces to be immersed in a dielectric fluid, such as paraffin, during machining operations.

However, the means for supplying the dielectric fluid is not illustrated and is not specifically described herein. All that is described in this connection is the dielectric fluid container illustrated in Figure 4.

Claims (35)

1. Electroerosion apparatus having at least one electrode holder provided with movement means for adjusting the position of an electrode in relation to a support means for a workpiece.

2. Apparatus according to claim 1 wherein said movement means is operable to move the or at least one electrode holder vertically.

3. Apparatus according to claim 1 or 2 wherein there is provided blocking means for stopping movement of the or at least one electrode holder.

4. Apparatus according to any one of the preceding claims wherein there is provided support means for supporting two separate workpieces for electroerosion by a common said electrode, when held by a said holder.

5. Apparatus according to claim 4 wherein there are provided two independently movable support members for respective workpieces.

6. Apparatus according to claim 5 wherein each support member is provided with a respective device for moving the support member towards and away from said common electrode, when positioned in a said holder.

7. Apparatus according to claim 6 wherein each device is a servo-mechanism.

8. Apparatus according to any one of claims 5 to 7 wherein the support members are electrically isolated from each other, and are provided with independent current supplies having the common electrode as a common terminal.

9. Apparatus according to claim 8 wherein said current supplies are independent outputs of a single current generator.

10. Apparatus according to claim 8 or 9 wherein said current supplies operable to machine iron with iron.

11. Apparatus according to claim 10 when dependent on claim 6 or 7 wherein means are provided for preventing said movement of one of said support members.

12. Apparatus according to any one of claims 5 to 11 wherein one of said support members is a bed of the apparatus, the other support member being movably mounted thereon.

13. Apparatus according to claim 12 wherein one of said support members is provided with a differential compression system for avoiding relative displacement between said support members.

14. Apparatus according to any one of claims 5 to 13 wherein at least one of said support members is provided with means for imparting planetary motion for electroerosion in a tangential direction.

15. Apparatus according to any one of claims 5 to 14 wherein there are provided feedback position control circuits, for the two support members and a said electrode holder.

16. Apparatus according to claim 15 wherein only two control circuits are provided, one serving for controlling, selectively, the electrode holder and one support member.

17. Apparatus according to any one of claims 5 to 16 wherein said support members are linked by an expandable coupling to establish a container for containing liquid dielectric during electroerosion.

18. Apparatus according to any one of claims 5 to 17 wherein there is provided a mechanical linkeage between said electrode holder and said support members whereby operation of said movement means causes movement of said support members towards and away from said electrode, when the electrode is positioned in said holder.

19. Apparatus according to any one of the preceding claims wherein the or at least one electrode holder is provided with means for moving an electrode held thereby in planar motion, rotary motion or translation motion, as required for any given machining operation.

20. Apparatus according to any one of the preceding claims wherein said electrode holder provides a plurality of positions for said electrode.

21. Electroerosion apparatus substantially as hereinbefore described with reference to the accompanying drawings.

22. An electroerosion machine wherein at least one of the electrodes of the machine is provided with ascending and descending motions, also having optionally equipped a blocking system of same in any position.

23. A machine in accordance with claim 22 wherein the machine has at least two tables for supporting vertically or horizontally semi-moulds, with both being provided with horizontal feed and retrocession movements in relation to the electrode and controlled by independent servo-mechanisms and to the electroerosion machine itself.

24. A machine in accordance with claims 23 wherein each one of said tables, electrically isolated amongst themselves and in relation to the machine itself, can optionally have a wire connected, either from two independent generators whose common point shall be the electrode or two or more channels coming from a same generator and which will also have the electrode as a common point.

25. A machine in accordance with any one of claims 22 to 24 wherein each one of the tables can optionally be connected to the outputs of a same generator with an appropriate circuit for machining iron with iron, in which case one of the feed and retrocession servo-mechanism can be cancelled to obtain an improved adjustment between the contact surfaces of the semi-moulds.

26. A machine in accordance with any one of claims 22 to 25 wherein independently from the movements of each one of the tables, the electrode holder can be provided with any other motion, either coplanary, rotary or transfer, as per the concrete requirements of each case.

27. A machine in accordance with any one of claims 22 to 26 wherein with the outputs being independent, each semi-mould can be adopted to the most convenient operational rate in accordance with its own dimentional, structural and/or physicalchemical characteristics.

28. A macchine in accordance with claim 27 wherein one of the motorised tables can be the table of the machine itself and another mounted on top of same, in such a way that, for avoiding any relative displacement between both, one of them is optionally provided with a compression differential system.

29. A machine in accordance with any one of claims 22 to 28 wherein each one of said motorised tables can have other motions of the planetary type in order to provide the erosioning system of the tangential form as is required in each case.

30. A machine in accordance with any one of claims 22 to 29 wherein other fastening systems have been proivded for the machining electrode, both for the exterior and interior, but always maintaining its electrical isolation in relation to the workpiece holding tables.

31. A machine in accordance with any one of claims 22 to 30 wherein the machine has three servo feed control circuits, one for the electrode holder and one for each one of the displaceable tables.

32. A machine in accordance with claim 31 wherein it also has been provided that the control circuit of the vertical servo be switchable to one of the tables whilst for the other table an independent circuit has been used in orderto simplify the realisation of the machine avoiding a control circuit.

33. A machine in accordance with any one of claims 22 to 32 wherein the two-piece holding tables have been shaped by splitting the conventional one into two halves and joined up with an elastic or telescopic linkage system between same and will be made tight at the same time in order to provide a sealed closing which will avoid any leaking ofthe dielectric.

34. A machine in accordance with claim 30 wherein in the case of the electrode being fastened on a different place of the vertical head, the movement of same is used by means of suitable mechanical couplings, in order to take forwards or backwards both piece holding tables, having the option of doing without the feed servo-mechanism on one or both tables.

35. An electroerosion machine substantially as hereinbefore described with reference to the accompanying drawings.