GB1574048A

GB1574048A - Guide and holding device for a wire electrode

Info

Publication number: GB1574048A
Application number: GB6420/77A
Authority: GB
Original assignee: Ateliers des Charmilles SA
Current assignee: Ateliers des Charmilles SA
Priority date: 1976-02-18
Filing date: 1977-02-16
Publication date: 1980-09-03
Also published as: SE7701689L; DE2704945A1; CH593114A5; FR2341396A1; JPS52100698A

Description

(54) IMPROVEMENTS IN OR RELATING TO A GUIDE AND HOLDING DEVICE FOR A WIRE ELECTRODE (71) We, ATELIERS DES CHARMILLES S.A., of: 109, rue de Lyon, Geneva (Switzerland), a Swiss body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The invention relates to electrical discharge machining machines having a wire electrode.

It is known to guide an electrode formed of a thin metal wire by means of two adjusted parallel surfaces each forming a lateral bearing for the electrode. It is also known to hold such an electrode in contact with guide surfaces by mechanical means, for example a rigid plate exerting a given pressure on the electrode, or pneumatic means, for example by suction of the electrode against the guide surfaces as described in British Patent No. 1.380.620.

When the guide device cooperates with several electrodes disposed parallel to one another, the mechanical holding arrangement can only be used if the electrodes each have exactly the same thickness, as any variation of the thickness may cause a variation of the friction of the electrodes on the guide surfaces. The pneumatic arrangement enables the use of electrodes of different thickness; however, the electrode diameter must not be less than the width of the conduit through which the fluid is sucked. Also, each electrode must occupy a large part of its guide path in order to limit leakages to an acceptable value.

An aim of the invention is to eliminate the drawbacks and limitations of the known arrangements.

The invention proposes a device for guiding and holding at least one wire electrode in an electrical discharge machining machine, comprising a respective substantially V-section guide channel forming a bearing for the or each electrode, and means for applying fluid pressure to press the elctrode into contact with said guide channel, wherein the pressure-applying means comprises at least one elastic membrane deformable in response to differential fluid pressure applied on opposite faces thereof to transmit pressure to the electrode(s).

In embodiments in which the membrane comes to contact with the electrode(s), the pressure differential may be produced by applying pressurized fluid to the side of the membrane away from the electrode(s) or by evacuating fluid from the side of the membrane which contacts the electrode(s). In either case, when the membrane is deformed it comes into contact with and partly takes the shape of the electrode(s), thus enabling the use of several electrodes of substantially different thicknesses.

The accompanying drawings show, schematically and by way of example, five embodiments of the invention. In the drawings: Fig. 1 is a cross-section of the first embodiment with its membrane in an inoperative position; Fig. 2 shows the first embodiment with its membrane in an operative position; Fig. 3 is a cross-sectional view of the second embodiment; Fig. 4 is a longitudinal cross-section of the third embodiment; Fig. 5 is a cross-sectional view of the fourth embodiment; Fig. 6 is a cross-section along line VI-VI of Fig. 5; and Fig. 7 is a cross-sectional view of the fifth embodiment.

The device shown in Figs. 1 and 2 includes a generally flat base or body 1 guiding several wire electrodes 2, each elec trode 2 bearing against two planar nonparallel guide surfaces 3 and 14 forming a V-section guide channel in the body 1. A plate 4, on which an elastic membrane 6 is fixed by a bush 5, is held in spaced-apart relationship against the body 1 with the membrane 6 disposed between the plate 4 and the electrode-guiding body 1.

The first embodiment is designed to enable an over-pressure to be provided in a chamber 8 disposed between the membrane 6 and plate 4. For this purpose, the plate 4 includes an adaptor 7 for connecting a pipe supplying a pressurized fluid.

In Fig. 1, the membrane 6 is shown in its rest position, i.e. when no pressure differential is exerted on its opposite faces.

Fig. 2 shows the membrane 6 deformed under the action of a pressurized fluid supplied to chamber 8. In this manner, the membrane 6 is applied against the body 1 and the electrode 2 so that it takes the shape of the outer part of the electrode 2 and presses them into their guide channels.

In the second embodiment, shown in Fig.

3, the electrodes 2 are pressed in their guide channels by evacuating of a chamber 9 between the membrane 6 and body 1.

Chamber 9 is connected by auxiliary ducts 11 and 12 to a collector chamber 10 provided in the body 1, this chamber 10 being connected to a fluid evacuation pipe, not shown, by an adaptor 13.

Hence, when the pressure in chambers 9 and 10 drops, the membrane 6 is deformed and takes the shape of the outer parts of the electrodes 2 to hold them against their guide channels.

Fig. 4 shows a device enabling not only guiding of an electrode, but advancing it to compensate for wear during machining.

The device comprises two parts 17 and 19 each having, for each of several parallel electrodes 2, a portion of a guide channel.

The part 19 is movable relative to the part 17 which is fixed. Rods 21 fixed on part 17 parallel to the generatrix of the guide surfaces (i.e. parallel to the electrodes) serve to guide the part 19.

Each of the parts 17 and 19 has a respective elastic membrane 22, 23 and a pressurized-fluid delivery adaptor 18, 20 enabling different pressures to be exerted on the two membranes.

During machining, a greater pressure is exerted on the membrane 23 than on membrane 22 so that each electrode 2 is held fixed on the piece 19 which is moved by a servo-control mechanism, not shown, the piece 17 serving to guide the electrodes.

If during machining of a workpiece 24 the electrodes 2 must be advanced relative to part 19 to compensate for wear, the pressure exerted on the upper membrane 23 is made less than that exerted on the membrane 22 so that each electrode 2 is held on the fixed part 17. Part 19 is then moved away from part 17 by a given distance under the action of a device, not shown, the electrodes 2 remaining fluxed.

Then the pressure exerted on membrane 23 is once more made greater than that exerted on the membrane 22 so that each electrode 2 is once more fixed to the piece 19 and guided by the piece 17, Machining can thus be continued while once more controlling the electrode advance by displacement of the piece 19.

A current-supplying omnibus bar 25 connects a series of electric contacts 26, only one of which is shown in Fig. 4, each contact 26 being associated with an electrode 3 for supplying electric current to it.

By using a membrane, it is possible to limit leakages to a given value, whatever be the number of guides and electrodes.

This limitation of leakages also enables a very precise adjustment of the pressure exerted by the membrane on each electrode, which is particularly useful for varying the friction of the electrodes in an automatic feed systems with take-up of the electrode wear. Also, the use of an elastic membrane coated with an adhesive offers the advantage of enabling the removal of several electrodes from their guide surfaces while conserving their relative positions during renewal of these electrodes.

The two embodiments shown in Figs. 5 to 7 have the advantage of enabling application of a bearing and guiding force on an electrode in the immediate proximity of the point at which it leaves the electrode carrier, i.e. adjacent the machining zone.

One thus avoids a danger of buckling the electrode wire and a very precise guiding is provided while reducing the risk of producing undesirable transverse vibrations of the electrode wire.

In the embodiment according to Fig. 5, a guide body 1 having guide channels in the form of dihedral grooves serves to guide one or several wire-electrodes 2. This body 1 is fixed on a support 30 which is rigidly connected to a part 17 comprising an elastic membrane 22.

The periphery of membrane 22 is gripped between a flange 31 of an internal hollow of the part 17 and a gripping block 32 disposed in this hollow. The block 32 is -held in position by an elastic ring 33, and has a duct 34 enabling the delivery of a pressurized fluid, for example air, via a supply pipe connected to an adaptor 35 to apply pressure on one face of the membrane 22.

The other face of membrane 22 acts on a part 36 having a stud 37 and carrying a spring blade 38 bearing against a rigid part 39. The latter has two grooves 40, 41 disposed transverse to the wire electrode 2. Two elongate strands 42, 43 of an elastomer are disposed in these grooves in a manner to exert a constant bearing force against the electrode 2 under the elastic action of the blade 38.

A slight play 44 is left between the stud 37 and the rigid part 39 to allow the latter to adapt to possible irregularities of the electrode 2. When it is desired to transmit a greater force to apply the electrode 2 against the guide body 1, a pressurized fluid is delivered via the adaptor 35 to displace the membrane 22 and part 36 whose stud 37 comes to abut against the rigid part 39.

The latter is hence pushed against the electrode 2 with deformation of the strands 42 and 43 of elastomer. The embodiment shown in Fig. 7 also has a support 30, guide body 1, part 17 with its adaptor 35 and a block 32 gripping a membrane 22.

The pressure of fluid supplied acts via the membrane 22 on a rigid part 39 carrying a lining 45 arranged to press the electrode 2 into contact with a guide channel of the guide body 1.

The part 17 also carries a rigid piece 46 having a transverse groove 47 in which an elongate strand 48 of an elastomer is received. The strand 48 elastically urges the electrode 2 against a second body 1' also having a guide channel. The strand 48 of elastomer exerts a substantially constant bearing force on the electrode 2 and, when one desires to obtain a greater bearing force, a pressurized fluid is made to act on the membrane 22 to push the lining 45 against the electrode 2.

WHAT WE CLAIM IS: - 1. In an electrical discharge machining machine with at least one wire electrode, an electrode guiding and holding device comprising a respective substantially Vsection guide channel forming a bearing for the or each electrode, and means for applying fluid pressure to press the electrode into contact with said guide channel, wherein the pressure-applying means comprises at least one elastic membrane deformable in response to differential fluid pressure applied on opposite faces thereof to transmit pressure to the electrode(s).

2. A device according to claim 1, comprising several said guide channels forming bearings for several parallel elctrodes, and a common elastic membrane for simultaneously transmitting pressure to said electrodes.

3. A device according to claim 1, comprising two parts each carrying a portion of one said guide channel, said parts being movable relative to one another along a longitudinal direction of said guide channel and of said electrode, said parts each having a respective elastic membrane on the faces of which a selected pressure differential can be applied whereby, in use, one of said parts feeds the electrode and the other part guides the electrode.

4. A device according to claim 1, comprising at least one bearing piece exerting a predetermined thrust on the electrode towards said guide channel, said bearing piece being disposed in proximity to the end of said guide channel nearest a machining zone of the machine.

5. A device according to claim 4, in which said bearing piece is an elongate strand disposed transverse to the electrode, said strand being housed in a groove in a rigid part disposed facing said guide channel.

6. A device according to claim 5, in which said rigid part is connected by a spring to another part submitted to the action of the membrane, and comprising abutment means between said two parts, whereby when no pressure differential is applied to the membrane, said bearing piece exerts said predetermined thrust on the electrode and when the membrane is deformed by application of a pressure differential said bearing piece exerts a thrust greater than said predetermined thrust on the elctrode.

7. A device according to claim 5, in which said rigid part is held in a fixed position relative to said guide channel, whereby said bearing piece exerts said predetermined thrust on the electrode, and further comprising a mobile part submitted to the action of the membrane and contacting the electrode to thrust it against said guide channel as a function of the pressure differential on the membrane.

8. A device according to any preceding claim, in which said membrane is disposed between the electrode and a chamber having a duct for the supply of pressurized fluid.

9. A device according to any one of claims 1 to 7, in which said membrane forms a wall of a chamber in which the electrode is disposed, said chamber having a fluid-evacuation duct.

10. In an electrical discharge machining machine, an electrode-wire guiding and holding device constructed and arranged substantially as described with reference to and as shown in the accompanying draw ings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. part 39. The latter has two grooves 40, 41 disposed transverse to the wire electrode 2. Two elongate strands 42, 43 of an elastomer are disposed in these grooves in a manner to exert a constant bearing force against the electrode 2 under the elastic action of the blade 38. A slight play 44 is left between the stud 37 and the rigid part 39 to allow the latter to adapt to possible irregularities of the electrode 2. When it is desired to transmit a greater force to apply the electrode 2 against the guide body 1, a pressurized fluid is delivered via the adaptor 35 to displace the membrane 22 and part 36 whose stud 37 comes to abut against the rigid part 39. The latter is hence pushed against the electrode 2 with deformation of the strands 42 and 43 of elastomer. The embodiment shown in Fig. 7 also has a support 30, guide body 1, part 17 with its adaptor 35 and a block 32 gripping a membrane 22. The pressure of fluid supplied acts via the membrane 22 on a rigid part 39 carrying a lining 45 arranged to press the electrode 2 into contact with a guide channel of the guide body 1. The part 17 also carries a rigid piece 46 having a transverse groove 47 in which an elongate strand 48 of an elastomer is received. The strand 48 elastically urges the electrode 2 against a second body 1' also having a guide channel. The strand 48 of elastomer exerts a substantially constant bearing force on the electrode 2 and, when one desires to obtain a greater bearing force, a pressurized fluid is made to act on the membrane 22 to push the lining 45 against the electrode 2. WHAT WE CLAIM IS: -

1. In an electrical discharge machining machine with at least one wire electrode, an electrode guiding and holding device comprising a respective substantially Vsection guide channel forming a bearing for the or each electrode, and means for applying fluid pressure to press the electrode into contact with said guide channel, wherein the pressure-applying means comprises at least one elastic membrane deformable in response to differential fluid pressure applied on opposite faces thereof to transmit pressure to the electrode(s).