METHOD FOR THE PRODUCTION OF A METAL COMPONENT, IN PARTICULAR A VANE COMPONENT OF A TURBOMACHINE

Abstract

A method for producing of a metal component that is electrochemically machined to remove material, wherein an electrode is positioned adjacent to and, by a duct gap, spaced from a component portion to be machined, and in the presence of an electrolyte a current and a voltage are applied to the electrode and the component. The electrode is moved toward the component from an initial position to a terminal position. In a first operating mode material is removed using a permanently applied current and voltage, a constant electrolyte flow through the duct gap, and a constant advancement of the electrode from the initial position toward the component while maintaining a first gap width. Upon achieving a predetermined removal depth, a changeover to a second operating mode occurs and the electrode is moved cyclically between a non-operating position and an operating position having a second gap width smaller than the first gap width. A current pulse and voltage pulse are applied only in the operating position, and the electrolyte flows through the gap at least in the non-operating position. The second operating mode is maintained until a desired final geometry.

Claims

1. Method for the production of a metal component, in particular a vane component of a turbomachine, which for generating a three-dimensional shape is electrochemically machined in order for material to be subtracted, to which end at least one electrode is positioned so as be adjacent to and, by way of a duct gap, spaced apart from a component portion to be machined, and in the presence of an electrolyte a current and a voltage are applied to the electrode and the component, and the electrode is moved in the direction of the component from an initial position to a terminal position, wherein the material in a first operating mode is subtracted by way of a permanently applied current and a permanently applied voltage, a constant electrolyte flow through the duct gap, and a constant advancement of the electrode from the initial position in the direction of the component while maintaining a first gap width, and in that by achieving a predetermined subtraction depth, an automatic changeover to a second operating mode takes place in that the electrode is moved in a cyclical manner between a non-operating position and an operating position having a second gap width which is smaller than the first gap width, wherein a current pulse and voltage pulse are applied only in the operating position, and the electrolyte flows through the gap at least in the non-operating position, wherein the second operating mode is maintained until the final geometry to be generated has been achieved.

2. The method according to claim 1, wherein the first gap width is between 0.2 and 0.3 mm, and the second gap width is between 0.03 and 0.1 mm.

3. The method according to claim 1, wherein the permanently applied current and the current pulse are between 1500 and 20,000 A.

4. The method according to claim 1, wherein the permanently applied voltage and the voltage pulse are between 6 and 200 V.

5. The method according to claim 1, wherein the frequency of the movement between the non-operating position and the operating position, and the current pulse frequency, are between 5 and 15 Hz.

6. The method according to claim 1, wherein the pressure of the electrolyte flowing through the duct gap is between 5 and 20 bar.

7. The method according to claim 1, wherein the electrode is moved by way of the same drive motor in both the first and the second operating mode.

8. The method according to claim 7, wherein a torque motor is used as a drive motor.

9. The method according to claim 1, wherein a plurality of electrodes are moved simultaneously relative to the component in the first and the second operating mode, wherein each electrode is moved by means of a separate drive motor.

10. The method according to claim 9, wherein the electrodes, bearing on one another, overlap one another on the periphery and conjointly delimit the gap.

11. The method according to claim 10, wherein at least three electrodes are used, wherein the two outer electrodes slide along a positionally fixed sealing component that delimits the duct gap.

12. The method according to claim 10, wherein four electrodes which delimit the duct gap encircling the component are used.

13. A device for carrying out the method according to claim 1, comprising at least one electrode which by means of a drive motor is movable relative to a component which for generating a three-dimensional shape is to be electrochemically machined by subtracting material, to which end the electrode is positioned so as be, by means of a drive motor, adjacent to and, by way of a duct gap, spaced apart from a component portion to be machined, and in the presence of an electrolyte a current and a voltage are applied to the electrode and the component, wherein the operation of the drive motor, a power generator, and a pump installation that conveys the electrolytes is controlled by means of a control installation, wherein the control installation is configured in such a manner that the electrode in a first operating mode in the case of a permanently applied current and a permanently applied voltage, and a constant electrolyte flow through the duct gap, is movable at a constant advancement in the direction of the component while maintaining a first gap width, and that the electrode by reaching a predetermined subtraction depth by way of an automatic changeover to a second operating mode is movable in a cyclical manner between a non-operating position and an operating position having a second gap width which is smaller than the first gap width, wherein a current pulse and voltage pulse is applied only in the operating position, and the electrolyte flows through the gap at least in the non-operating position, wherein the second operating mode is maintained until the final geometry to be generated has been achieved.

14. A device according to claim 13, wherein at least three electrodes which are disposed so as to be offset around the circumference of the workpiece are provided, said three electrodes by way of the mutually contacting reproduction faces thereof engaging across one another in portions during the entire adjustment movement from the initial position to the terminal position, and by way of the reproduction faces thereof delimiting a closed duct gap that encircles the circumference of the workpiece.

15. A device according to claim 14, wherein an electrode that is provided between two electrodes on the reproduction face has two sliding faces by way of which said electrode slides on respective outer sliding faces of the two adjacent electrodes.

16. A device according to claim 14, wherein two mutually opposite electrodes have the reproduction faces reproducing the upper and lower side of the workpiece, while the at least one third electrode, disposed between said two mutually opposite electrodes, has a reproduction face that reproduces the edge region of the workpiece.

17. A device according to claim 16, wherein a fourth electrode, disposed opposite the third electrode, is provided, said fourth electrode likewise having a reproduction face that reproduces the edge region of the workpiece.

18. A device according to claim 14, wherein in the case of three electrodes the two outer electrodes slide along a positionally fixed sealing component that delimits the fluid duct.

19. A device according to claim 14, wherein in the case of four electrodes two mutually opposite electrodes engage across the two other electrodes.

20. A device according to claim 14, wherein the motion axes of the linear drive units of two adjacent electrodes are set at a mutual angle of 90?, or in that the motion axes of the linear drive units of two adjacent electrodes are set at a mutual angle of smaller than greater than to 90?.

21. A device according to claim 14, wherein the linear drive units for readjusting the angle between the motion axes of two adjacent linear drive units are movable along a circular path, wherein each linear drive unit is preferably movable along the circular path by way of a servomotor.

22. A device according to claim 13, wherein the or each drive motor is a torque motor.

23. A device according to claim 14, wherein each electrode is assigned a sensor installation that communicates with a control installation, the position of the electrode being detectable by way of said sensor installation, wherein the control installation controls the operation depending on the sensor detection.

24. A device according to claim 13, wherein a positioning installation for automatically positioning the workpiece in the operating position in an operating chamber is provided.

25. A device according to claim 24, wherein the workpiece by means of the positioning installation is rotatable about the longitudinal axis of said workpiece during the transfer of the workpiece to the operating position and/or while the workpiece is located in the operating position.

26. A device according to claim 24, wherein a magazine into which a plurality of workpieces to be machined are introducible and which is assigned to the positioning installation is provided, said workpieces being automatically retrievable by way of the positioning installation or a changeover installation.

27. A device according to claim 26, wherein each workpiece is received in a workpiece holder which is acquirable by way of the positioning installation or the changeover installation.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0045] In the drawing:

[0046] FIG. 1 shows a flow diagram for explaining the method according to the invention;

[0047] FIG. 2 shows a first electrode assembly of an ECM device having three electrodes in the initial position;

[0048] FIG. 3 shows the electrode assembly from FIG. 2 in the terminal position;

[0049] FIG. 4 shows a second electrode assembly of an ECM device having four electrodes in the initial position;

[0050] FIG. 5 shows the electrode assembly from FIG. 4 in the terminal position;

[0051] FIG. 6 shows a sectional partial view of an ECM device with an illustration of the electrodes and the linear drive units of the latter;

[0052] FIG. 7 shows a schematic illustration of an ECM device having pivotable linear drive units; and

[0053] FIG. 8 shows a schematic illustration of an ECM device having all components.

DETAILED DESCRIPTION OF THE INVENTION

[0054] FIG. 1 in the form of a flow diagram shows the substantial steps of the method according to the invention.

[0055] The method starts at step S1; the person operating the device triggers the start of the operation. Prior thereto, the person has stocked any potential magazine that is assigned to a positioning installation of the device with the number of workpieces to be machined in the entire operating cycle.

[0056] After the start of the operation, the introduction of a workpiece to be machined into the operating chamber is performed in step S2. To this end, the positioning installation, for example, or a changeover installation, can retrieve a workpiece from the magazine and hand said workpiece over to the positioning installation. In any case, the workpiece is introduced into the operating chamber of the device by way of the positioning installation, the ECM processing being performed in said operating chamber.

[0057] Having introduced the workpiece into the operating chamber and tightly closed the operating chamber, the ECM processing is performed thereafter. According to step S3, the processing in the first operating mode is performed first. In this operating mode, the so-called generator sinking, feeding of the electrodes is performed in a constant manner at a duct gap width of approx. 0.2 to 0.3 mm, and with a permanently applied current in the range of several 1000 A, a permanently applied voltage of approx. 6 to 200 V, and a permanent flow of electrolyte, that is to say that the electrodes by way of a more or less constant advancement are moved in the direction of the component, the electrochemical subtraction of material being performed during said movement. The subtracted products are discharged from the duct gap by way of the flow of electrolyte.

[0058] The subtraction depth which in FIG. 1 is illustrated by xactual is permanently detected during the first operating mode (see step S4). It is permanently checked whether the actual subtraction depth corresponds to a predetermined subtraction depth xnominal, attaining the latter corresponding to the switchover moment at which a switchover to the second operating mode is to take place. A suitable measuring or sensor installation, or a corresponding plurality of such installations, is provided for detecting the subtraction depth, the electrode position, for example, being able to be exactly detected by said installation or installations, on account of which, proceeding from the initial position of the electrode(s) it can be determined how much material has been subtracted, or how large the subtraction depth is, respectively.

[0059] If the result is that xactual ? xnominal, the first operating mode according to step S3 is thus continued.

[0060] However, if the result is that xactual=xnominal, the central control installation controlling the operation of the ECM device immediately switches over to the second operating mode according to step S5. A pulsed ECM operation is run in this second operating mode. The current, here also in the range of several 1000 A, and the voltage in the range from 6 to 200 V, is now applied only in a pulsed manner, the pulse frequency being in the range between 5 and 15 Hz. The electrode or electrodes by way of the respective drive motor, preferably a torque motor, of the linear drive units that move the electrodes is or are readjusted at a corresponding frequency between an operating position, in the case of a current being applied, and a non-operating position, in the case of a current being absent. The gap width of the duct gap in the operating position is significantly smaller than in the first operating mode, said gap now being only in the range between 0.03 and 0.1 mm. On account of this pulsed operation, a highly precise reproduction and an outstanding surface quality of the machined workpiece can be obtained.

[0061] A permanent detection of the subtraction depth xactual is also performed in the second operating mode according to step S6. Said subtraction depth xactual is in turn compared to a comparison depth, presently the final depth xfinal which simultaneously marks the attainment of the terminal position of the electrode feed. This permanent detection of the position is in turn also performed by way of the control installation and by way of the measuring or sensor installations which have already performed the detection of the position in the first operating mode.

[0062] If the result is that xactual ? xfinal, the second operating mode according to step S5 is thus continued in a permanent manner.

[0063] If the result is that xactual=xfinal, the entire ECM procedure is terminated. According to step S7, the retrieval of the machined workpiece from the operating chamber is performed by way of the positioning installation, wherein the workpiece is then transferred into the magazine again by way of the positioning installation or by way of the changeover installation.

[0064] It is thereafter checked in step S8 whether the entire method, or the cycle, respectively, has been terminated by processing the last workpiece. In the affirmative, the operating method is completely terminated according to step S9. Otherwise, the routine reverts back to before step S2, that is to say that a new workpiece is acquired and introduced by way of the positioning installation or the changeover installation, the further steps adjoining here.

[0065] FIG. 2 as part of a device 1 according to the invention for electrochemically machining a metal workpiece 2 shows an electrode assembly 3, in the example shown comprising four separate electrodes 4, 5, 6, 7 which are all movable relative to the workpiece 2 by way of separate linear drive units (not shown in more detail here). The electrodes 4 to 7 form cathodes, while the workpiece 2 forms the anode. The electrodes 4 to 7 are movable in a linear manner along the motion axes 8, 9, 10, 11 by way of the linear drive units, wherein the motion axes 8 to 11 in the exemplary embodiment shown are mutually perpendicular.

[0066] When in operation, a permanent, closed, gap-type fluid duct 12 that encircles the workpiece 2 (shown in the cross section here) is provided, said fluid duct 12 in the exemplary embodiment shown being delimited radially, or externally, respectively, and sealed exclusively by way of the reproduction faces 13, 14, 15, 16 of the electrodes 4 to 7. An electrolyte which serves for the electrochemical machining of the workpiece 2 and by way of which subtracted products are simultaneously transported out of the fluid gap 12 flows in a manner perpendicular to the illustration plane under suitable pressure through the fluid duct 12.

[0067] FIG. 2 shows the initial position with the as yet still non-machined workpiece 2. As can be seen, the electrodes 4 to 7 engage in one another, or mutually overlap in a peripheral manner, respectively. To this end, the mutually opposite electrodes 5 and 7 on the peripheries have planar sliding faces 17 and 18, respectively, which externally bear in a contacting and sealing manner on corresponding sliding faces 19, 20 of the likewise mutually opposite electrodes 4 and 6. Mutually interacting sliding faces are thus provided on adjacent electrodes. Having engaged in each case across two adjacent electrodes 4 and 6, the electrodes 5 and 7 in the region of the reproduction face have a quasi V-shaped geometry, wherein the actual reproduction geometry which is intended to reproduce the rounded edge of the workpiece 2 is configured between the sliding faces 17 and 18, respectively.

[0068] Each reproduction geometry 13 to 16 is in portions embodied in such a manner that said reproduction geometry in the terminal position shows the negative of the face portion of the completely machined workpiece 2 which is to be machined by the respective electrode 4 to 7. In the case of the electrodes 4 and 6, this is the upper and the lower side of the workpiece 2, the latter being a vane component for a turbomachine. In the case of the electrodes 5 and 7, these are the corresponding two edges of the workpiece 2 that have a small radius.

[0069] As described, FIG. 2 shows the electrode assembly 3 at the start of the actual ECM operation. The electrodes 4 to 7 are diverged to a relatively large extent; the degree of overlap is not yet very high. Thereafter, upon switching on the conveyance of electrolyte and applying the current and the voltage, the electrodes 4 to 7 in a first operating mode, the so-called generator sinking, with a constantly applied current and voltage, and by way of a linear adjustment path, are moved in a linear manner in the direction of the motion axes 8 to 11, thus in the direction of the arrows, and consequently pushed toward one another. By virtue of the current applied, which can be several 1000 ampees, and the voltage, which can be between 6 and 200 V, a subtraction of the workpiece material according to the ECM method takes place on the surface of said workpiece, that is to say that the workpiece volume is reduced. The respective surfaces are shaped by the respective opposite portions of the reproduction faces 13 to 17 of the respective electrodes 4 to 7.

[0070] The linear readjustment movement at a constant current and voltage in the first operating mode (generator sinking) is maintained until a defined sink depth, thus a defined intermediate position, has been attained. This is detected by way of a suitable measuring technology or sensor system. Thereafter, an automatic switchover to a second operating mode, the so-called PECM mode, is performed by way of the central control installation. In said second operating mode, the current and the voltage are applied only in a pulsed manner at a frequency of 5 to 15 Hz, for example. A current pulse is applied when the respective electrode is in the operating position. When the current is switched off, the electrode is slightly moved away from the workpiece 2 such that the fluid duct 12 is opened wider, the gap width thus being somewhat enlarged, enabling the electrolyte to better flow therethrough. Thereafter, the respective electrode is fed again and moved to the operating position, whereupon a current is applied again, etc. An intermittent operation is thus provided both in terms of the current and in terms of the positioning of the electrode. It is to be noted herein that the gap width in the first operating mode, thus in generator sinking, is slightly larger than in the second operating mode, thus in the PECM operation. While the gap width in the first operating mode is approx. 0.2 to 0.3 mm, said gap width in the second operating mode is, for example, 0.05 to 0.1 mm when a current is applied, thus consequently when subtracting takes place. The gap width in the second operating mode is enlarged to, for example, 0.2 to 0.3 mm, by diverging the electrodes.

[0071] Two different operating modes are thus performed within a single processing procedure, that is to say a readjustment procedure, from an initial position shown in FIG. 2 to the terminal position shown in FIG. 3, in which the electrodes 4 to 7 are converged to a large extent (cf. FIG. 3). The overlap regions of the sliding faces 17, 18, and 19, 20 are accordingly greatly enlarged as compared to the initial position. As can be seen, the reproduction faces 13 to 16, by way of the face portions that define the final contour of the workpiece 2 after the ECM processing, that is to say the portions in the region of the upper and the lower side and in the region of the two edges, are mutually complementary, defining the unequivocal three-dimensional final geometry that is reproduced on the workpiece 2. As the electrodes 4 to 7 are in mutual contact during the entire readjustment procedure from the initial position according to FIG. 2 to the terminal position according to FIG. 2 and seal the fluid gap 12, this final geometry is extremely homogeneous across the entire circumference of the workpiece, since a reproduction face of the respective adjacent electrode is opposite each location around the circumference of the workpiece 2, a subtraction of material accordingly taking place at each position. This subtraction of material that takes place at each position is ensured during the entire readjustment movement, independently of the operating mode, such that an extremely homogeneous subtraction and thus also an extremely homogeneous surface pattern can be achieved.

[0072] The respective electrodes 4 to 7 extend across the entire length of the workpiece to be machined, the latter in the example shown being a vane part of a turbomachine. Said vane part at the front and the rear end is delimited by way of a vane root and a shroud ring, the electrodes 4 to 7 plunging therebetween.

[0073] FIGS. 4 and 5 show a further partial view of an ECM device 1 according to the invention, wherein the same reference signs are used for the same components. Only three electrodes 4, 5, 6 are provided here, said electrodes 4, 5, 6 having respective reproduction faces 13, 14, 15. As is the case in the design embodiment according to FIGS. 2 and 3, the electrode 5 by way of the sliding faces 17 thereof engages across the respective adjacent sliding faces 19 and 20 of the electrodes 4 and 6.

[0074] In the case of this embodiment, only one electrode 5 that reproduces on the edge is provided. A positionally fixed duct component 21 is provided on the opposite side, the two electrodes 4 and 6 by way of edge portions 22, 23 (shaped somewhat differently here) bearing in a sliding and sealing manner on said duct component 21.

[0075] Here too, the electrodes 4 to 6 by way of respective linear drive units are capable of being converged in a linear manner along the motion axes 8, 9, 10, said electrodes 4 to 6 by way of the sliding faces 17, 19, and 20 sliding on one another, while the electrodes 4, 6 by way of the edge regions 22, 23 thereof slide on the duct component 21. In the terminal position shown in FIG. 5, the degree of overlap of the electrodes 5 with the electrodes 4 and 6 has again been significantly enlarged, in a manner similar to the exemplary embodiment according to FIGS. 2 and 3. The edge portions 22, 23 of the electrodes 4, 6 bear on one another on the opposite edge side of the workpiece 2. By virtue of the geometry of the respective reproduction faces 13, 15 of the two electrodes 4, 6 in the transition toward the edge portions 22, 23 it is possible also in the case of this design embodiment having only three electrodes for the edge of the workpiece 2 in this region to be configured in a rounded manner so as to correspond to a predefined geometry.

[0076] FIG. 4 in an enlarged detailed view again shows a fragment of an ECM device 1 according to the invention, having a machine frame 24 on which an operating chamber 25 in which the actual ECM processing takes places is provided. Shown in an exemplary manner are the four electrodes 4, 5, 6, 7 and the respective linear drive units 26, 27, 28, 29.

[0077] Each linear drive unit 26 to 29, of which only one will be described hereunder as the drive units are of a fundamentally identical construction, comprises a drive motor 30 in the form of a torque motor 31, comprising a drive spindle 32 to which an electrode holder 33 that is displaceable in a linear manner is connected. The drive spindle having an external thread is rotated by way of the torque motor 31. Said drive spindle is guided in a positionally fixed nut 34 and coupled to the electrode holder 33. Depending on the direction of rotation of the spindle, the electrode holder 33 is conjointly moved in a linear manner with the spindle 32 in the case of the spindle being rotated. The respective feed of the individual electrodes 4 to 7 is performed in this way. The construction, or the configuration, respectively, of the linear drive units 26 to 29 shown is merely exemplary. Other linear movement concepts are also conceivable; however, a common factor therein should be a torque motor 31 which enables a very rapid intermittent positioning operation (because the latter is at a higher frequency) required for the PECM operation and also allows highly precise positioning, on the other hand.

[0078] All linear drive units 26 to 29 are separately actuatable, meaning that the superordinate control installation actuates each torque motor 31 separately such that the movement of the electrodes can be performed in an optimal manner.

[0079] The linear drive units 26 to 29 in the case of the design embodiment according to FIG. 6 are positionally fixed. The torque motors 31 are thus immobile; only the spindles 32 and the electrode holders 33 are guided so as to be movable in a linear manner. This means that the angle between the motion axes of the linear drive units 26 to 29 is fixed, said angle being 90?, as is shown in an exemplary manner in FIG. 2.

[0080] In order for there to be a potential for variation in terms of the axis angle, a partial view of a device 1 in which the individual linear drive units 26 to 29 are movable along a circular path (as is represented by the arrows P1) is shown in FIG. 7. To this end, for example, a circular guide path 35 on which the linear drive units 26 to 29 are mounted by way of separate slide components or similar (not shown in more detail here) is provided. Said slide components are rotatable about the center Z which lies in the center of the operating chamber 25. This is performed in an exemplary manner by way of a respective actuator or drive motor 36, preferably in the form of a torque motor or servomotor which each of the linear drive units 26 to 29 shown there has.

[0081] In this way, it is possible for the relative mutual angle of the linear drive units 26 to 29 to be readjusted in relation to one another should this be required for reasons of the geometry of the workpiece or of the electrode geometry of the replaceable electrodes, respectively.

[0082] FIG. 8 finally shows a schematic illustration of a device 1 according to the invention for carrying out the ECM method. Only the two linear drive units 26, 28 are shown in an exemplar manner here; the other two linear drive units are orthogonal to the former. Also illustrated are the two assigned electrodes 4, 6 and the workpiece 2 that is located therebetween.

[0083] The workpiece 2 is received or clamped, respectively, in a workpiece holder 37 which is acquired by a receptacle installation 38 of a positioning installation 39, or is clamped therein, respectively. The positioning installation 39 has a respective spindle (not shown) on which the receptacle installation 38 is disposed. By way of said receptacle installation 38 it is possible for the workpiece 2 to be moved into and out of the operating chamber 25, as is illustrated by the double arrow P2.

[0084] It is conceivable herein that the spindle, or the receptacle installation 38, respectively, to be rotated about the longitudinal axis thereof while the workpiece 2 is moved to the operating position, and/or while the workpiece is located in the operating position, such that the workpiece in the case of a respective twist thereon can be threaded between the electrodes 4 to 7.

[0085] A magazine 40 and an optimal changeover installation 41, illustrated by dashed lines here, are furthermore assigned to the positioning installation 39. A plurality of workpieces 2 to be machined, which are already fixedly disposed on respective workpiece holders 37, are received in the magazine 40. This magazine 40 can be stocked in advance by the person overseeing the device 1. When in operation, the changeover installation 41 acquires the respective workpiece holder 37 of the next workpiece to be machined, for example, and transfers said workpiece holder 37 to the positioning installation 39 which acquires said workpiece holder 37 by way of the receptacle installation 38 which is coupled to the spindle (not shown in more detail). The changeover operation of a machined workpiece 2 after processing is performed in the reverse order, said machined workpiece 2 by way of the changeover device 41 being retrieved from the positioning installation 39 and transferred into the magazine 40.

[0086] Furthermore shown is a conveying and supplying installation 42 by way of which the electrolyte required for the ECM operation is supplied to the operating chamber 25 and discharged from the latter again in a closed circuit. The installation 42 comprises a suitable pump which makes available the required operating pressure.

[0087] Furthermore illustrated is the power supply 43, comprising a generator by way of which the electrodes 4 to 7, which form the cathodes, and the workpiece 2, which forms the anode, are supplied with the required operating current of several 100 to several 1000 amperes.

[0088] Furthermore shown is a central control installation 44 which controls the operation of all operating components of the device 1 according to the invention, thus the power supply installation 43 or the generator, respectively, the installation 42 for the supply of electrolyte, the positioning installation 39, and the changeover installation 41. Assigned to said central control installation 44 are respective sensor installations which determine corresponding operating or position parameters, etc., the control installation 44 controlling the operation based on said parameters. The measuring or sensor installations comprise respective sensors for the highly accurate detection of the respective electrode position, this being required for the actuation operation of the torque motors 31 in both operating modes. Moreover, the respective positioning of the electrodes in the operating positions, or the deployed positions, in the PECM operation, etc., is also controlled by way of said control installation 44. The same applies of course to the positioning installation 39; here, the respective occupation of the terminal position of the workpiece 2, thus the operating position, is detected, such as of course also respective positionings or completions of procedures in the context of the changeover of parts, etc.

[0089] Furthermore, a highly precise actuation of the power supply 43, thus of the generator, is required in the PECM operation, since the latter is only pulsed. The pulse frequency of the generator 43, and thus also the frequency at which the torque motors 31 retract and deploy the electrodes, is in the range of usually 5 to 10 Hz, but can also be higher, for example up to 15 Hz.

[0090] The control installation 44 is in particular responsible for switching the operating mode of the device 1 according to the invention from the first operating mode, in which the electrodes 4 to 7 with a permanently and usually constantly applied current are preferably fed in a constant manner, to the second operating mode, the PECM operation, in which a pulsed subtraction of material is performed. The trigger which serves for switching over from the first to the second operating mode is the detection of a corresponding position or intermediate position which is occupied by the electrodes 4 to 7 and which indicates that sufficient material has been subtracted by way of the respective electrode. A quasi rough subtraction by way of a relatively large subtraction of material is thus performed in the first operating mode, while the fine processing to the final contour is performed in the second, pulsed PECM mode. All this is performed in a single device by the operating mode switchover, and in a single motion cycle, and in a single clamping, meaning that the workpiece 2 remains at all times in one and the same position, and consequently does not have to be re-clamped, despite two different operating modes being carried out. This applies of course also to the electrodes 4 to 7 which are likewise used in the same position without any changeover procedure during both operating modes.

[0091] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.