GB2331476A

GB2331476A - Electrode guide

Info

Publication number: GB2331476A
Application number: GB9724454A
Authority: GB
Inventors: Michael Oliver Cervenka; Stuart Engall; Alan Martin Smith; Clive Nicholas Walker
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1997-11-20
Filing date: 1997-11-20
Publication date: 1999-05-26
Also published as: GB9724454D0; GB2331476A9

Abstract

An electrode guide for an EDM apparatus is adapted to provide lamina electrolyte flow around each electrode. The wire electrodes 6 are supported and gripped in triangular section grooves 8 and held in place by a cover plate. The non-matching profiles of groove and electrode create a plurality of channels around each electrode when clamped in the guide. The electrode grooves are intersected by a chamber 28 in the bed of the guide so that, in use, electrolyte fluid supplied to the chamber flows along the channels around the electrodes. A seal arrangement is provided on one side of the chamber to stem flow in the channels surrounding the electrodes in a direction away from the machining face of the guide.

Description

2331476 ELECTRODE GUIDE The invention relates to an electrode guide. In

particular the invention concerns an electrode guide supporting at least one electro-discharge machining (EDM) electrode for cutting-or drilling a hole in which, during operation, a continuous flow of electrolyte is maintained around the tip of the electrode, or tips of the electrodes in the case of a multiple electrode arrangement.

Electrode-discharge machining (EDM) apparatus comprises a wire electrode, or a plurality of such electrodes in the multiple electrode arrangement, connected to a cathode of a pulsating current power source and supported by an insulating guide. An anode terminal of the power source is connected to a workpiece. A supply of electrolytic fluid is directed at the electric discharge gap between an electrode tip and the workplece. The electrode wire is fed forward at a suitable speed commensurate with the loss of electrode length due to tip erosion and workpiece penetration.

A continuous supply of electrolytic fluid is maintained to sustain the machining process and to flush debris away from the machining gap. Where appropriate the fluid is directed into the gap from a fluid nozzle but in the case of hole drilling, especially deep hole drilling, the efficiency of this method reduces with the depth orpenetration. An objective of the present invention is to seek an improvement in the efficiency of the fluid flow to the electrode tip by promoting lamina flow along the exposed length of the electrode or electrodes towards the machining gap.

According to the present invention there is provided an electrode guide for electrodischarge machining apparatus comprises an electrode guide body formed with one or more internal guide slots in which are located a like number of wire electrodes, an internal chamber intersecting the guide slots and inlet means in communication with the chamber for admitting thereinto electrolyte fluid, wherein the guide slots are formed with walls which co-operate with the wire electrodes to define alongside each electrode at least one axially extending channel leading from the internal chamber along which electrolyte fluid may flow.

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 illustrates an EDM electrode guide, mounting seven wire electrodes partly dissembled, and Figure 2 is a detail cross-section through the guide showing the electrode slots and the electrolyte channels.

The electrode guide of the drawing comprises a main body part 2 and a demountable cover plate 4 made of an electrically insulating material, such as TUFNOL. An array of wire electrodes 6 is mounted between the main body 2 and the cover plate 4. The electrodes 6 are located in individual grooves, or guide slots generally indicated at 8, which run the full length of the body part 2. When the guide is fully assembled ready for use the cover plate 4 is secured to main body 2 by means of a plurality of threaded studs and retaining nuts indicated at 10, 12 respectively. The electrodes 6 are laid individually in the grooves 8 with their machining tips, shown towards the left side of the illustration, projecting an appropriate distance from an end face 14 of the main body.

The main body 2 of the guide is formed basically in the shape of a rectangular solid. Towards one end, opposite the machining face 14 and towards the right side of the drawing, the body has increased width additional side portions 15 useful for mounting the guide on an EDM apparatus. This is not of concern to the invention and is not described further.

An upper side 16 of the guide body 2 (orientation in the illustration only) is formed with a recessed electrode bed 18 running the full length of the guide and into which the rectangular cover plate 4 may be fitted. The cover plate retaining studs 10 are spaced apart along the length of the recess 18. Also along the full length of a centre portion of this recessed bed 18 there are formed a plurality of parallel electrode receiving channels or guide slots 8. In the preferred embodiment being described the slots 8 are formed by V-shaped grooves milled into the surface of electrode bed 18 so that a plurality of parallel upstanding, triangular section ribs 19 are formed. The dimensions of the ribs and grooves are chosen commensurate with the diameters of the wire electrodes 6 to provide a snug fit. The cover plate 4 has a smooth plane under surface 20 which when in position just contacts the surfaces of the electrodes exposed in the open sides of the guide slots closing the upper slots or grooves which remain open only at their ends. Thus, each electrode is held snugly located along tluee linear contacts, that is in contact with the two angled sides of the groove and a third with the cover plate. The arrangement also creates three longitudinal spaces 22,24,26 alongside each wire electrode which are open at the ends of the guide body, in particular at the machining end face 14.

A chamber 28 is formed in the electrode bed 18 lying transversely with respect to the ribs 19/grooves 8 to a depth exceeding that of the grooves. Preferably the position of the chamber 28 is located towards the machining face 14 of the guide body 2. The plenum volume 30 thus created is in open communication with the longitudinal spaces 22,24,26 alongside each wire electrode 6.

The cover plate 4 is formed with a tapping hole 32 in register with the position of the chamber 28 and an inlet nozzle 34 is secured in the hole. The nozzle 34 is connected to a supply of electrolyte fluid (not shown) by means of a supply pipe or conduit 36.

Alongside the fluid plenum chamber 28 on its opposite side relative to the guide body end face 14 there is provided means, generally indicated at 38, for sealing the longitudinal channels thereby producing unidirectional fluid flow along the channels towards the machining tips of the electrodes. This seal means 38 comprises a blade or member 40 comprised of flexible rubber material located in a slot 42 milled into the bed 18 of the guide body 2 transversely with respect to the electrode grooves 8. The slot 42 intersects all of the grooves 8 and extends a short distance either side thereof. The seal member 40 substantially fills the slot 42 and its height rises at least as far as the peaks of the inter-groove ribs 19.' In the preferred embodiment the seal member 40 comprises a thin rectangular block of rubber material. The electrodes 6 when assembled into the guide are laid in the grooves and pushed through the seal member piercing it. Alternatively, the material of the seal member may be compressible by the wire electrodes 6 and providing it is sufficiently compliant conforms to the profiles of the electrodes to form an effective seal against the face 20 of the cover plate and stem electrolyte flow.

In use, the electrodes 6 and the electrode guide are assembled and installed in conventional manner in an EDM machine. The machine may include a refeed mechanism for automatically adjusting the projecting length of the machining tips of the wire electrodes, in well-know manner. In this connection it must be noted that the additional contact force exerted by the seal member 40 on the electrodes is within allowable limits of the refeed mechanism in order to avoid either electrode damage during refeed operation or failure to operate.

In a normal sequence of operation steps electrolyte flow under pressure is commenced just before a pulsating current source connected to the machining electrodes 6 is energised and EDM operation can begin. According to the invention the electrolyte fluid flow or a portion of it is conducted by the supply conduit 36 into the plenum chamber volume 30. The fluid pressure forces the electrolyte fluid along the channels 22,24, 26 alongside the electrodes. Provided the flow has sufficient pressure, or the pressure is adjusted accordingly, the flow is jetted forwards towards the machining tips, Since the fluid channels are spaced apart around each wire electrode lamina electrolyte flow is promoted substantially evenly around the electrodes in the direction of the electrode tips.

Although the embodiment has been described in its preferred form it will be understood that certain changes and alterations may be made within the scope of the invention. Clearly the invention may be configured for use with different numbers of electrodes, and materials may be altered also. The illustrated shapes and forms of the various grooves and chambers although preferred as described and shown are not unique. The EDM wire electrodes of the preferred embodiment are conventional wire-drawn components and therefore have a substantially constant diameter according io the wire gauge. In order to provide the electrolyte flow channels around the wire, frictional engagement and lateral support for the wires the grooves of the guide bed in conjunction with cover plate must contact each electrode at at least three points around its circumference with sufficient force to prevent electrode slip during use but still permit operation of the refeed mechanism without causing damage to the electrodes. Triangular section grooves are formed to meet these requirements well, by providing three lines of contact which accommodate dimensional tolerances well and three flow channels, of relatively substantial flow area.

The seal arrangement 38 may be realised in other forms too. In the described embodiment the sealing blade 40 engages directly the internal surface 20 of the cover plate 4. Therefore, it urges the electrodes against the cover plate and must be sufficiently compliant to mould itself reasonably well around the electrodes. A certain amount of leakage is tolerable. In other embodiments a second seal member is mounted in the internal surface of the cover plate opposite the seal blade 40 so that the two seal members co-operate. In either of these two arrangements the seal blade 40 may be provided with slits or incisions through which electrodes are passed. Further still the seal member 40 may comprise a pack of bristles of non-conducting material which are easy for the electrodes to pass through but which adequately contain the electrolyte flow. Other seal arrangements meeting these general requirements maybe envisaged within the scope of the invention.

In another variation of the invention although the electrode grooves extend the full length of the guide, the specially shaped grooves may be formed only between the electrolyte chamber or the seal arrangement and the machining face of the guide. However, this increases the complexity of guide manufacture and is not favoured.

Claims

An electrode guide for electro-discharge machining apparatus comprises an electrode guide body formed with one or more internal guide slots in which are'located a like number of wire electrodes, an internal chamber intersecting the guide slots and inlet means in communication with the chamber for admitting thereinto electrolyte fluid, wherein the guide slots are formed with walls which co-operate with the wire electrodes to define alongside each electrode at least one axially extending channel leading from the internal chamber along which electrolyte fluid may flow.

An electrode guide as claimed in claim 1 further comprising means for promoting unidirectional fluid flow along the axially extending channels alongside each electrode towards a machining tip of the electrode.

An electrode guide as claimed in claim 2 wherein the means for promoting unidirectional fluid flow comprises means provided at one side of the internal chamber for stemming electrolyte flow along the electrode guide slots.

4 An electrode guide as claimed in claim 3 wherein the means for stemming electrolyte flow comprises a compressible member disposed transversely of the electrode guide slots.

An electrode guide as claimed in claim 4 wherein the compressible member is arranged to seal around the or each electrode.

6 An electrode guide as claimed in claim 4 or 5 wherein the compressible member comprises a blade of rubber material.

An electrode guide as claimed in any of claims 4 to 6 wherein the compressible member is provided with slits through which pass the electrodes.

8 An electrode guide as claimed in any of claims 2 to 7 wherein the guide body comprises a bed part on a sur,face of which the guide slots are formed, and a co,er plate for attachment over the guide slots to close them and wherein the means for promoting unidirectional fluid flow is located between the bed of the guide and the cover plate.

9 An electrode guide as claimed in claim 8 wherein the means for promoting unidirectional flow comprises means mounted in the guide bed which engages the cover plate.

An electrode guide as claimed in claim 8 wherein the means for promoting unidirectional flow comprises first means mounted in the guide bed which cooperates with second means in the cover plate.

1 An electrode guide substantially as hereinbefore described with reference to the accompanying drawings.