GB2077171A

GB2077171A - Electroerosive wire-cutting method and apparatus

Info

Publication number: GB2077171A
Application number: GB8107977A
Authority: GB
Original assignee: Inoue Japax Research Inc
Current assignee: Inoue Japax Research Inc
Priority date: 1980-03-13
Filing date: 1981-03-13
Publication date: 1981-12-16
Also published as: GB2077171B; IT8148018A0; DE3109722A1; IT8148018A1; DE3109722C2; FR2477932B1; IT1170802B; FR2477932A1

Abstract

An electroerosive wire-cutting method and apparatus wherein a high-velocity stream of the cutting liquid medium produced through a small-opening nozzle (122a) is injected into a low-velocity stream of the cutting liquid medium produced through a large-opening nozzle (121a) and directed towards the region of the cutting gap(s). The high- velocity cutting-liquid stream has a thickness substantially equal to the thickness of the cutting slot(s) being formed behind the advancing wire electrode (1) in the workpiece (7) and is directed at a region of the cutting gap behind the advancing wire electrode. Gases (e.g. oxygen or ozone) and/or abrasive particles may be entrained in the high-velocity cutting-liquid stream. <IMAGE>

Description

SPECIFICATION Electroerosive wire-cutting method and apparatus The present invention relates generally to electroerosive wire-cutting and, more particularly, to a new and useful method of and apparatus for electroerosively cutting an electrically conductive workpiece with a continuous wire electrode across a cutting gap flushed with a cutting liquid medium. The invention particularly relates to a method and apparatus of the type described wherein the flushing liquid medium is supplied to the cutting gap in a novel manner to basically improve the performance of the electroerosive wire-cutting process in various aspects.

The process of electroerosive wire-cutting generally makes use of a continuous wire electrode composed of, say, brass or copper, and having a thickness ranging between 0.05 and 0.5 mm. The wire electrode is axially transported continuously along a given continuous guide path from a supply to a takeup through a workpiece disposed in a predetermined cutting zone. The cutting zone is commonly defined by a pair of cutting guide members which support the wire electrode across the workpiece. Wire traction and braking means allow the continuous wire to be tightly stretched between the supply and takeup and to be axially driven between the cutting guide members while traversing the workpiece, thus presenting the continuously renewed electrode surface juxtaposed in a cutting relationship with the workpiece across a cutting gap.The cutting gap is flushed with a cutting liquid medium and electrically energized with a high-density electric current which is passed between the wire electrode and the workpiece to electroerosively remove material from the latter. The cutting process may be performed with any of various electroerosive machining arrangements. In electricai discharge machining (EDM), the cutting liquid medium is a dielectric liquid and the electric current is supplied in the form of a succession of electrical pulses. In electrochemical machining (ECM), the liquid medium is a liquid electrolyte and the machining current is a high-amperage continuous or pulsed current.

In electrochemical-discharge machining (ECDM) the cutting medium has both electrolytic and dielectric natures and the machining current preferably is applied in the form of pulses which facilitate the production of electrical discharges through the liquid medium.

As the electroerosive material removal proceeds, the workpiece is displaced relative to the wire electrode transversely to the axis thereof. This allows the wire electrode to advance transversely to the workpiece and consequently a cutting slot to be formed behind the advancing wire electrode. The continuous relative displacement along a preseiected path results in the formation of a desired contour corresponding thereto and defined by this cutting slot in the workpiece.

In the performing the electroerosive wirecutting process, the cutting zone is conveniently disposed in the air or usual environment, and a nozzle is used to deliver the cutting liquid medium to the cutting gap. The cutting liquid is conveniently a water medium which may be ionized or deionized to various extents to serve as a desired electroerosive cutting medium. It is desirable to keep the cutting gap flushed with a sufficient volume of the cutting liquid and traversed thereby at a sufficient rate to allow the electroerosive action to continue with stability, the cutting chips and other gap products to be carried away with smoothness, and the wire electrode to be cooled with effectiveness. This requires the cutting liquid to be projected under an elevated pressure.In the conventional arrangement in which the cutting zone or nozzle is exposed to the air, however, the cutting liquid, due to a pressure drop caused when it leaves the nozzle, tends to be splashed away so that most of it flows out without coming into the narrow cutting-gap spacing provided between the thin wire electrode and the workpiece. When the delivery of the cutting liquid to the cutting gap is insufficient or the cutting gap is incompletely filled with the cutting liquid, there develop gaseous discharges therein which impair the electroerosive process and removal of the gap products and eventually cause breakage of the wire electrode due to an excessive heat which then develops.An uncontrolled increase of the liquid pressure in an attempt to ensure full delivery of the cutting liquid into the cutting gap will bring about an uncontrolled deflection or vibration of the wire electrode which again impairs the cutting stability. In short, there have been undue limitations of cutting stability and efficiency which accrue from the conventional gap flushing technique in the electroerosive wire-cutting process.

The present invention therefore seeks to provide an improved electroerosive wire-cutting method which assures; an increased cutting stability and efficiency and moreover to provide an electroerosive wire-cutting method which allows a cutting liquid medium to be delivered into and passed through the narrow cutting-gap spacing in a sufficient volume and at a sufficient rate of flow, thereby enabling the cutting stability and efficiency to be improved over the prior art.

The present invention also seeks to provide an electroerosive wire-cutting apparatus which is relatively simple in construction and suitable for executing the method described; and moreover to provide an electroerosive wirecutting apparatus which includes novel means for delivering the cutting liquid into the cut ting gap, which means contributes to a marked improvement in cutting stability and efficiency over the prior art.

Other objectives will become apparent from the description of the invention which follows.

In accordance with the present invention, in a first aspect thereof, there is provided a method of electroerosively cutting an electrically conductive workpiece with a continuous wire electrode, in which method the wire electrode is axially transported to traverse the workpiece while defining a cutting gap therewith flushed with a cutting liquid medium and is electrically energized to electroerosively remove material from the workpiece whilst the latter is displaced relative to the wire electrode transversely to the axis thereof, thereby forming a cutting slot behind the advancing wire electrode in the workpiece, and in which method the cutting gap is flushed with the cutting liquid medium by: a) directing a low-velocity stream of the cutting liquid medium shaped with a relative large cross section towards the region of the cutting gap, and b) directing towards the cutting gap and injecting into the low-velocity stream, a high-velocity stream of the cutting liquid medium shaped with a cross section narrower than the cross section of the low-velocity stream and having a width substantially equal to the width of the aforesaid cutting slot.

The low-velocity stream may have a pressure of 1 to 5 Kg/cm2,and the high-velocity stream may have a pressure between 5 and 100 Kg/cm2, preferably at least 10 Kg/cm2.

The cutting liquid preferably comprises a water, which may have a specific resistivity of 102 to 105 ohm-cm. The cross section of the high-velocity stream may have a width slightly greater or smaller than the width of the cutting slot and, when smaller, should be substantially equal to the thickness of the wire electrode. Preferably, the high-velocity stream of the cutting liquid medium is directed at a portion of the gap region behind the advancing electrode.

In accordance with a specific feature of the invention, the cutting liquid medium, particu larly formed in the aforementioned high-veloc ity stream, may contain gases and/or finely divided abrasive particles. The gases may be oxygen in the form of 02, or 03 (ozone).

Specifically, the method according to the invention comprises producing the low-veloc ity stream with a first nozzle with a relatively large opening and producing the high-velocity stream with a second nozzle with an opening smaller than the opening of the first nozzle and of a width substantially equal to the width of the cutting slot.When the wire electrode is advanced relative to the workpiece along a non-linear path (i.e. a path which is curved or has one or more corners), in accordance with a further feature of the invention, at least the second of the aforementioned nozzles is displaced, preferably along a circular path arranged about the axis of the wire electrode, in response to a change in the direction of relative advance between the wire electrode and the workpiece along the non-linear path so that the high-velocity stream may always be oriented towards a portion of the gap region behind the advancing wire electrode.

The invention also provides, in a second aspect thereof, an apparatus for electroerosively cutting an electrically conductive workpiece with a continuous wire electrode, which apparatus includes means for axially transporting the wire electrode, means for guiding the wire electrode to traverse the workpiece while defining a cutting gap therewith in the presence of a cutting liquid medium, a power supply for electrically energizing the cutting gap to electroerosively remove material from the workpiece, means for advancing the workpiece relative to the wire electrode transversely to the axis thereof whereby a cutting slot is formed behind the advancing wire electrode in the workpiece, and means for flushing the cutting gap with the cutting liquid medium, which flushing means comprises::- a) a first nozzle means having a relatively large opening for producing a lowvelocity stream of the cutting liquid medium and directing it towards the region of the cutting gap, and b) a second nozzle means having an opening smaller than the opening of the first nozzle means and of a width substantially equal to the width of the aforesaid cutting slot for producing a high-velocity stream of the cutting liquid medium and directing towards the cutting gap and injecting into the low-velocity stream of the cutting liquid medium, the high-velocity stream.

The width of the opening of the second nozzle means may be slightly greater or smaller than the width of the cutting slot, and, if smaller, should be substantially equal to the thickness of the wire electrode.

Specifically, the apparatus further includes first pumping means for forcing the low-velocity stream of the cutting liquid medium out of the first nozzle means at a pressure between 1 and 5 Kg/cm2, and second pumping means for forcing the high-velocity stream of the cutting liquid medium out of the second nozzle means at a pressure between 5 and 100 Kg/cm2, preferably upwards of 10 Kg/cm2. A source of water of specific resistivity between 102 and 105 ohm-cm, when such water is chosen to constitute the cutting liquid medium, may be connected to the first and second nozzle means via first and second conduit means, respectively. Means may be associated with the second conduit means fof introducing gases, e.g. oxygen in the form of 02, or 03, or finely divided abrasive materials into the high-velocity stream of the liquid water.

In accordance with a further important fea ture of the invention, at least the second of the aforementioned nozzle means is oriented in the direction of a portion of the cutting gap region behind the advancing wire electrode.

To maintain this orientation for the wire electrode when caused to advanced relative to the workpiece along a non-linear path (i.e. which is curved or has one or more corners) by the advancing means, nozzle displacement means may be provided and associated with the latter. The nozzle displacement means displaces at least the second of the aforementioned nozzle means so that the high-velocity stream may be always directed towards the portion of the cutting gap region behind the advancing wire electrode in spite of a change in the direction of advancement of the wire electrode relative to the workpiece. Guide means may be provided for guiding this nozzle displacement along a circular path about the axis of the wire electrode.

In accordance with the present invention, a favorable fluid distribution is provided in which an abundant and substantially breakupfree volume of the liquid medium carried in a thick, low-velocity stream under a moderate pressure fills the environment of the cutting zone and acts to isolate the latter from the atmosphere. A thin, high-velocity stream of the cutting liquid medium injected under an elevated pressure into this moving "liquid curtain (pressure cushion)" is firmly retained therein and held thereby against substantial breakup and divergence. Furthermore, the high-velocity stream has an extremely small thickness sized to be substantially equal to the width of the cutting slot being formed behind the advancing wire electrode.Accordingly, a sufficient amount of the cutting liquid medium in the directed high-velocity stream is allowed to focus, without hindrance, at the region of the cutting gap under the elevated pressure which remains enough, and to pass through the area of the cutting gap with a rate of flow which remains sufficiently high. The moving "liquid curtain" served by the low-velocity stream effectively prevents the surrounding air from being trapped into the high-velocity stream of the cutting liquid medium, thus maintaining its density at a desired level, and also provides a low-friction partition for the high-velocity stream to allow the latter to smoothy travel towards the focused region of the cutting gap.Constant renewal of the cutting liquid medium throughout the entire area of the cutting gap achieved in this manner establishes optimum conditions for the progress of electroerosive action with stability, cooling the wire electrode and removal of the gap products.

These and other features and advantages of the present invention will become apparent from the following description of certain embodiments thereof made with reference to the accompanying drawings in which: Figure 1 is a schematic diagram partly in section and partly in a block-diagram form illustrating an electroerosive wire-cutting arrangement incorporating the principles of the present invention; Figure 2 is a schematic diagram essentially in section illustrating a nozzle assembly for flushing cutting liquid medium to the region of a cutting gap according to the present invention; and Figure 3 is a plan view diagrammatically illustrating the nozzle assembly of Fig. 2.

Referring first to Fig. 1, the electroerosive wire-cutting arrangement makes use of a continuous wire electrode 1 of a known metallic composition and having a thickness of 0.05 to 0.5 mm. The wire electrode 1 is axially driven from a supply reel 2 to a takeup reel 3 by a traction unit 4 to continuously travel through a cutting zone defined between a pair of cutting guide members 5a and Sb. A suitable tension is given to the traveling wire electrode 1 by a braking unit 6. A workpiece 7 is disposed in the cutting zone between the guide members 5a and 5b and is traversed by the traveling wire electrode 1. The workpiece 7 is securely mounted on a worktable 8 which is displaced in an X-Y plane by a pair of motors 9 and 10 operated by drive signals furnished from a numerical controller 11.The motor 9 is designed to displace the workpiece 7 along a predetermined X-axis and the motor 10 is designed to displace the workpiece 7 along a predetermined Y-axis orthogonal to the X-axis. The numerical controller 11 has input data preprogrammed therein which represents a desired path to be followed by the relative displacement between the workpiece 7 and the axis of a linear stretch of the wire electrode 1 traveling between the guide members 5a and 5b. A nozzle assembly 1 2 which will be described later is disposed in the cutting zone to supply a cutting liquid into a region of the cutting gap defined between the wire electrode 1 and the workpiece 7.An electroerosion power supply 1 3 has output terminals electrically connected to the wire electrode 1 and the workpiece 7 to electrically energize the cutting gap or to apply an electric current of precisely regulated parameters between the wire electrode 1 and the workpiece 7 so that material is electroerosively removed from the workpiece 7. In operation, the data stored in the numerical controller 11 is reproduced and converted into drive signals which are applied to the motors 9 and 10, thereby displacing the workpiece 7 relative to the wire electrode 1 in the preset X-Y plane along the preprogrammed path. Thus, the wire electrode 1 stretched in a direction transverse to the X-Y plane is advanced relatively along this path, forming an electroerosioncutting slot behind it.The continued relative displacement along this path results in the formation in the workpiece of a wire-cut con tour defined by the cutting slot and corresponding to the preprogrammed path.

The nozzle assembly 1 2 disposed in the cutting zone constituted by the wire electrode 1 and the workpiece 7 in Fig. 1 may be embodied in a form shown at 1 20 in Figs. 2 and 3. The assembly 1 20 comprises a first nozzle member 121 and a second nozzle member 1 22. The first nozzle member 1 21 has a large nozzle opening 121 a for producing a low-velocity stream of the cutting liquid medium and directing it towards a region of the cutting gap. The second nozzle member 1 22 has a narrow nozzle opening 1 22a for producing a high-velocity stream of the cutting liquid medium.The narrow opening 122a of the second nozzle member 1 22 is arranged in the large opening 121 a of the first nozzle member 121 and to be co-axial therewith.

The narrow opening 1 22a of the second nozzle member 1 22 has a width substantially equal to the width, shown by a character 1, of the cutting slot shown by a character S. The end of the narrow opening 1 22a is shown slightly projecting from the end of the large opening 121 a. The assembly further includes a ring member 1 23 to which the first and second nozzle members 121 and 122 are fixedly secured by means of a clamp 1 24.

The ring member 1 23 is rotatably guided by rollers 1 25 and 1 26 rotatably held in engagement therewith and is rotated by a roller 1 27 drivingly in engagement therewith. The roller 1 27 is rotated by a motor 1 28 which is in turn driven by drive signals supplied by a control circuit 14 also shown in Fig. 1. As indicated in Fig. 2, the guide rollers 1 25 and 1 26 and the driving roller 1 27 are secured to fixed planes, thus being in a fixed relationship with the guide members 5a and 5b and hence with the axis of the wire electrode 1 supported by these members.The rotatable ring member 1 23 has its center of rotation coincident with the center axis of the wire electrode 1. As the ring member 1 23 which carries the nozzle members 121 and 122 rotates, the direction of the low-velocity and high-velocity streams issuing from these nozzles are changed. The second nozzle 1 22 is directed so as to orient the high-velocity stream which issues through it art a point in the cutting gap behind the wire electrode 1 advancing in the workpiece 7, leaving the cutting slot S as seen in Fig. 3.

It is generally preferred to arrange the nozzle assembly 12, 1 20 on the side of the workpiece 7 in which the axially traveling' wire electrode 1 enters into the workpiece 7 or such that the streams of the cutting liquid medium flow towards and into the cutting gap in the same direction in which the axially traveling wire electrode 1 enters into the workpiece 7. Optimum results have been found to be achieved when the wire electrode 1 travels from below to above the workpiece 7 as shown in Fig. 2 and the nozzle assembly 12, 1 20 is arranged below the workpiece 7 so that the cutting liquid medium is forced to flow into the cutting gap from below the workpiece 7.

The first and second nozzles 121 and 122 are fed with the cutting liquid medium drawn from a reservoir 15 by pumps 16 and 17, respectively. The pump 1 6 is used to produce through the nozzle 121 the low-velocity stream of the cutting liquid medium pressurized at a pressure of 1 to 5 Kg/cm2. The pump 1 7 is used to produce through the - nozzle 1 22 the high-velocity stream of the cutting liquid medium pressurized at a pressure of 5 to 100 Kg/cm2, preferably upwards of 10 Kg/cm2. The low-velocity stream from the first nozzle 121 may be divergent to cover a relatively large area surrounding the region of the cutting gap and the wire electrode 1 going out of the cutting slot s (as shown) or coming into the cutting slot s (when its direction of axial travel is reversed).There is practically no breakup or scattering in this stream which has both a low rate of flow and pressure as it is projected out of the nozzle 121.

Thus, an abundant and substantially breakupfree volume of the liquid medium is carried in the low-velocity stream to fill the environment of the cutting region and to isolate the latter from the atmosphere. The second nozzle member 1 22 has the nozzle opening 1 22a sized to provide the thickness of the highvelocity stream substantially equal to the width of the cutting slot S. The high-velocity stream injected by the nozzle 1 22 into the low-velocity stream which acts as a moving "liquid curtain" and "pressure cushion" is thus firmly retained therein and held thereby against substantial breakup and divergence.

Accordingly, a sufficient amount of the cutting liquid medium in the directed high-velocity stream is allowed to focus, without hindrance, at the region of the cutting gap under the pressure which remains enough and to pass through the area of the cutting gap with a rate of flow which remains sufficiently high. The moving "liquid curtain" served by the lowvelocity stream effectively prevents the surrounding air from being trapped into the highvelocity stream of the cutting liquid medium, thus maintaining its density at a desired level and also provides a low-friction partition for the high-velocity stream to allow the latter to smoothly travel towards the focused region of the cutting gap. Constant renewal of the cutting liquid medium throughout the entire arep of the cutting gap achieved in this manner establishes optimum conditions for the progress of electroerosion action with stability,cool- ing the wire electrode 1, and removal of the gap products.

While the traveling wire electrode 1 traversing the workpiece 7 is tightly stretched between the cutting guide members 5a and 5b, the wire electrode 1 in the cutting zone while advancing tends to be deflected backwards due to a machining pressure (i.e. discharge pressure or gaseous expansion pressure) inherent in the electroerosion process. This deflection may cause a short-circuit condition between the wire electrode 1 and the workpiece 7 or uncontrolled vibrations of the stretched wire electrode, both of which are undesirable. In order to achieve counterbalance this machining pressure, it is desirable, as mentioned before, to keep the high-velocity stream of the cutting liquid medium oriented at an area in the cutting gap immediately behind the advancing wire electrode 1 as shown in Fig. 3.As long as the wire electrode is advancing along a straight path this orientation is maintained with the position of the nozzle member 122 fixed as shown. When the wire electrode is to advance along a curved path or a corner defined by two straight or curved lines connected together, the position of the nozzle member 1 22 must be changed to maintain this counterbalancing orientation.

The control circuit 14 (Figs. 1 and 2) is adapted to receive control signals of the numerical controller 11 which are applied to drive motors 9 and 10 for the worktable 8, that is for the workpiece 7. These signals define a desired contouring path of advance of the workpiece 7 relative to the wire electrode 1 and hence of advance of the wire electrode 1 relative to the workpiece.The control circuit 1 4 derives from these signals an "angular" sensing signal which represents an angle of the tangent to the contouring path at each preset point thereon with respect to a predetermined coordinate axis and, from this "angular" sensing signal, produces an "angular" drive signal to be furnished to the motor 1 28. Thus, when a change in the direction of advance of the wire electrode occurs in the contouring path, an "angular" drive signal is provided to the motor 1 28 to rotate the ring member 1 23 and hence to alter the angular position of the nozzle member 1 22 carried thereon.The drive signal continues until the nozzle member 1 22 takes a position at which the desired orientation of the high-velocity stream is achieved.

The cutting liquid medium may advantageously be a water having a specific resistivity ranging between 102 and 105 ohm-cm. The liquid medium may contain gases and/or finely abrasive particles. In the arrangement of Fig. 1, a mixing chamber 1 8 is therefore provided at a portion of the liquid conduit through which the cutting liquid medium, e.g.

a water, is passed under a high pressure exerted by the pump 1 7 to produce through the nozzle (second nozzle 1 22 in Figs. 2 and 3) the high-velocity stream which is directed at a portion of the cutting gap behind the advancing wire electrode 1. The gases which are preferably oxygen in the form of a either O2 or O, (ozone) are supplied from a source 1 9 and introduced at the mixing chamber 1 8 into the high-velocity stream. It has been found that ozone is particularly advantageous, when contained at a proportion of 10 to 55 % by volume in the high-velocity, cutting liquid stream, to improve the removal rate and cutting stability. The abrasive particles which may be SiO2, B4C, Al203 or any other abrasive grains are supplied from a source 20 and introduced at the mixing chamber 1 8 into the high-velocity stream.

There are thus provided, in accordance with the present invention, new and useful electroerosive wire-cutting methods and apparatus.

Claims

1. A method of electroerosively cutting an electrically conductive workpiece with a continuous wire electrode, in which method the wire electrode is axially transported to traverse the workpiece while defining a cutting gap therewith flushed with a cutting liquid medium and is electrically energized to electroerosively remove material from the workpiece whilst the latter is displaced relative to the wire electrode transversely to the axis thereof, thereby forming a cutting slot behind the advancing wire electrode in the workpiece, and in which method said cutting gap is flushed with said cutting liquid medium by:: a) directing a low-velocity stream of said cutting liquid medium shaped with a relatively large cross section towards the region of said cutting gap, and b) directing towards said cutting gap and injecting into said low-velocity stream, a highvelocity stream of said cutting liquid medium shaped with a cross section narrower than the cross section of said low-velocity stream and having a width substantially equal to the width of said cutting slot.

2. The method defined in claim 1 wherein said low-velocity stream has a pressure of 1 to 5 Kg/cm2, and said high-velocity stream has a pressure of 10 to 100 Kg/cm2.

3. The method defined in claim 1 or 2 wherein said cutting liquid medium comprises a water.

4. The method defined in claim 3 wherein said water has a specific resistivity ranging between 102 and 105 ohm-cm.

5. The method defined in claim 4 wherein said high-velocity stream of said water medium has gases entrained therein.

6. The method defined in claim 5 wherein said gases are oxygen introduced into said water medium at a proportion of 10 to 55 % by volume.

7. The method defined in claim 6 wherein said oxygen is ozone.

8. The method defined in claim 4 wherein said high-velocity stream of said water medium has finely divided abrasive particles en trained therein.

9. The method defined in any preceding claim wherein said narrower cross section has a width slightly greater than the width of said cutting slot.

10. The method defined in any one of claims 1 to 8 wherein said narrower cross section has a width slightly smaller than the width of said cutting slot.

11. The method defined in claim 10 wherein the width of said narrower crosssection is substantially equal to the thickness of said wire electrode.

1 2. The method defined in any preceding claim wherein in the step (b) said high-velocity stream of the cutting liquid medium is directed towards a portion of said gap region behind said advancing wire electrode.

1 3. The method defined in claim 1 2 wherein the step (a) comprises producing said low-velocity stream with a first nozzle with a relatively large opening, and the step (b) comprises producing said high-velocity stream with a second nozzle with an opening smaller than the opening of said first nozzle and of a width substantially equal to the width of said cutting slot.

1 4. The method defined in claim 1 3 wherein said wire electrode is advanced relative to said workpiece along a non-linear path, said method further comprising displacing at least the second of said nozzles in response to a change in the direction of advance of said wire electrode relative to said workpiece along said non-linear path so that said high-velocity stream may always be directed towards a portion of said gap region behind said advancing wire electrode.

15. The method defined in claim 14 wherein said at least the second of said nozzles is displaced along a circular path arranged about the axis of said wire electrode.

16. An apparatus for electroerosively cutting an electrically conductive workpiece with a continuous wire electrode, which apparatus includes means for axially transporting the wire electrode, means for guiding said wire electrode to traverse the workpiece while defining a cutting gap therewith in the presence of a cutting liquid medium, a power supply for electrically energizing the cutting gap to electroerosively remove material from the workpiece, means for advancing the workpiece relative to the wire electrode transversely to the axis thereof whereby a cutting slot is formed behind the advancing wire electrode in the workpiece, and means for flushing said cutting gap with said cutting liquid medium, which flushing means comprises:: (a) first nozzle means for directing a lowvelocity stream of said cutting liquid medium shaped with a relatively large cross-section towards the region of said cutting gap, and (b) second nozzle means for directing towards said cutting gap and injecting into said low-velocity stream of said cutting liquid medium, a high-velocity stream of said cutting medium shaped with a cross-section narrower than the cross-section of said low-velocity stream and having a width substantially equal to the width of said cutting slot.

1 7. The apparatus defined in claim 1 6 wherein the means (a) includes a first nozzle with a relatively large opening for producing said low-velocity stream of said cutting liquid, and the means (b) includes a second nozzle with an opening smaller than the opening of said first nozzle and having a width substantially equal to the width of said cutting slot.

1 8. The apparatus defined in claim 1 7 wherein the width of said opening of the second nozzle is slightly greater than the width of said cutting slot.

1 9. The apparatus defined in claim 1 7 wherein the width of said opening of the second nozzle is slightly smaller than the width of said cutting slot.

20. The apparatus defined in claim 1 9 wherein the width of said opening of the second nozzle is substantially equal to the thickness of said wire electrode.

21... The apparatus defined in any one of the claims 1 7 to 20 wherein the means (a) further includes first pumping means for forcing said low-velocity stream of said cutting liquid medium out of said first nozzle at a pressure between 1 and 5 Kg/cm2, and the means (b) further includes second pumping means for forcing said high-velocity stream of said cutting liquid medium out of said second nozzle at a pressure between 10 to 100 Kg/cm2.

22. The apparatus defined in claim 21, further comprising a source of a water of specific resistivity between 102 and 105 ohmcm constituting said cutting liquid medium connected to said first and second nozzles via first and second conduit means, respectively.

23. The apparatus defined in claim 22, further comprising means associated with said second conduit means for introducing gases into said high-velocity stream of the liquid water.

24. The apparatus defined in claim 25 wherein said gases are oxygen.

25. The apparatus defined in claim 24 wherein said oxygen gas is ozone.

26. The apparatus defined in claim 22, further comprising means associated with said second conduit means for introducing finely divided abrasive particles into said high-veloc,- ity stream of water.

27. The apparatus defined in any one of the claims 1 7 to 26, further comprising means for orienting at least the second of said nozzles in the direction of a portion of said cutting gap region behind the advancing wire electrode.

28. The apparatus defined in claim 27 wherein said wire electrode is advanced relative to said workpiece along a non-linear path, by said advancing means, said orienting means including drive means associated with said advancing means for displacing at least the second of said nozzles so that said highvelocity stream may be always directed towards said portion of said cutting gap region in spite of change in the direction of advancement of said wire electrode relative to said workpiece.

29. The apparatus defined in claim 28, further comprising guide means for permitting at least the second of said nozzles to be displaced along a circular path about the axis of said wire electrode.

30. An apparatus as defined in any one of the claims 1 6 to 29, substantially as herein before described with reference to, and as illustrated in any single figure or group of associated figures of the accompanying drawing.

31. A method as defined in any one of the claims 1 to 15, substantially as hereinbefore described with reference to any single figure or group of associated figures of the accompanying drawing.

32. A workpiece having a wire-cut contour or slot formed by a method as defined in any one of the claims 1 to 1 5 and 31, or by means of an apparatus as defined in any one of the claims 1 6 to 30.