DE2512331A1 - ELECTROEROSION PROCESS FOR THE PROCESSING OF WORK PIECES AND DEVICE FOR PERFORMING THIS PROCESS - Google Patents

Description

Γ Λ TE> * TA. & VV ALT

Dipl. Ing. E. HOLZEB R 9 A UO S KIT KG

PHIUPPIXE-WELBEII -STIiASSK 14

R.926

Augsburg, March 20, 1975

Rolls-Royce (1971) Limited, Norfolk House, St. James's Square,

London SWlY 4JS, England

Electrical discharge machining processes for machining workpieces and Apparatus for carrying out this process

The invention relates to an electrical discharge machining process for Machining of workpieces in which an electrode is stepped motor-driven for the purpose of removing material by spark erosion

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drifted to the workpiece and a liquid is fed between the workpiece and the electrode.

In a known electrical discharge machining process Material removed from a workpiece by spark erosion. This process is known as the electric spark process. The electric spark process has proven to be very useful and is widely used for making recesses used in workpieces that are often impossible to manufacture with conventional machining tools.

A difficulty encountered in the electric spark process is that the spark erosion process due to its nature causes a local melting of the material, which results in the subsequent local re-solidification of the material forms a so-called cast skin.

This casting skin is often cracked and of dubious metallurgical quality and can therefore be subjected to high stresses which can later lead to the formation and spread of fatigue cracks in the workpiece.

The invention includes a method and apparatus for overcoming this difficulty by

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Removal of the cast skin by means of electrochemical processing.

The electrochemical machining of workpieces is known per se. However, although it has been found that the electrochemical machining process is for removal the cast skin can be applied, generally not possible, after the production of a recess The electrical spark process simply feeds the workpiece to a machine for electrochemical machining and appropriately shaped electrodes to be used to remove the cast skins.

This problem arises from the following considerations. About the electrochemical machining process To be able to perform, it is necessary that the machining electrode has the shape of the recess to be produced corresponds exactly. A short circuit between the electrode and the workpiece must be avoided to prevent damage to the electrode and workpiece. on the other hand large distances between the electrode and the workpiece, which allow positional tolerances serve to lead to extended and unpredictable processing times, which is a waste of energy means and the dimensional accuracy is detrimental.

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These problems reach insurmountable proportions, when the size of the recesses to be produced becomes very small. With plug-in engines, it is often necessary in turbine blades or combustion chambers cooling channels with a Manufacture diameter in the range of 0.5 mm. Electrodes with a diameter of about 0.38 mm is used and the mechanical strength of these electrodes is so low that they are easily bent and accurate positioning of the electrodes in an existing small bore proved impossible Has.

In the sense of overcoming the difficulties just mentioned, a method of the type set out at the beginning according to the invention characterized in that one for both electrochemical machining and spark erosion machining suitable liquid is used and that the power source feeding the electrode is designed and is operated that material is removed from the workpiece simultaneously by electrochemical action and by spark erosion will.

A device for carrying out this method, with one in a stationary position with respect to the workpiece Bracket movably guided relative to the workpiece

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trode and with means for moving the electrode relative to the workpiece is according to the invention by means for feeding the liquid suitable for both electrochemical machining and spot erosion machining of the workpiece between the electrode and the workpiece and characterized by a power source for feeding the electrode, the is suitable for electrochemical and spot erosion machining.

The invention makes use of the fact that under certain circumstances a liquid is sufficient as Dielectric for electrical discharge machining and also, to a sufficient extent, as an electrolyte for an electrochemical one Editing can work.

One such liquid has been shown to be tap water from the Barnoldswick area in Yorkshire, which, as measured on a Wayne-Kerr measuring bridge, has a conductivity of 154 jU-S .

Since Barnoldswick tap water is not readily available in other parts of the world, it is at various Other weak electrolytes have been tried to increase the properties of Barnoldswick tap water

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reproduce.

It has been found that one solution is to produce cooling bores in forged turbine blades of sodium sulfate of the same conductivity as that. Barnöldswick tap water is suitable. In addition, was found that a weak electrolyte was used to produce cooling bores in cast turbine blades is suitable, which consists of a mixture of a potassium chloride solution and a sodium acetate solution, the Solutions are preferably in a conductivity ratio of 5: to one another, namely in a conductivity ratio from 100 ^ S of potassium chloride to 20 | LlS of sodium acetate.

This allows recesses in workpieces to be designed in a way that was previously not possible.

In addition, the invention is suitable for simultaneous Production of a large number of recesses in a workpiece.

According to a preferred embodiment of the invention Procedure, a diluted electrolyte is placed between the electrode and the work-

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piece passed and the electrode are fed from the power source negative electrical impulses, both to the Spark erosion and electrochemical machining are suitable. In addition, the time of the breakthrough will be the electrode is scanned through the workpiece and after the breakthrough, the supply of electrical impulses to the Electrode continued for a certain time «

The inventive method is particularly for Manufacture of transverse cooling bores in turbine blades of gas turbine engines applicable, wherein these transverse channels from the outer surface of the blade in question to one formed within this blade, the shovel running in the longitudinal direction of the cooling duct and with the speed of the stepping motor is slowed down when the electrode breaks down, so that there is sufficient time for the electrochemical processing the inner ends of the transverse bores are present, but excessive penetration of the electrode is avoided, what about electrical spark erosion machining of the blade on the opposite side of the cross bores Side of the longitudinal cooling channel could lead.

The invention is described below with reference to

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accompanying drawings described in detail, for example. In the drawings show:

Fig. 1 is a section through a front

direction according to the invention,

Fig. 2 is a view of a turbine

blade,

Fig, 3 is a cross section through the

Turbine blade shown in Fig. 2 along the
Level III-III,

Fig, M is a plan view of the in

Fig. 2 shown blade in
Direction of line IV-IV,

Fig. 5 is a partial longitudinal section

the blade in plane V-V in Fig. 3,

Fig. 6 is a table in which test

results with the in Fig »I.

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shown device are put together,

7 shows a schematic representation

another embodiment of the invention,

Pig · 8 is a cross-sectional view of a

partially produced hole in a workpiece,

Pig, 9 a section similar to FIG. 8

in a later production stage,

Fig-. 10 a section through a plant

piece with a differently shaped hole,

FIG. 11 shows a section similar to FIG. 10

with another hole shape,

Fig. 12 is a section through a work

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piece with a hole with yet another shape,

Fig. 13 shows a detail

View of a holder in which the electrode is movable relative to a workpiece is held,

14 'shows an enlarged illustration

part of the holder according to FIG. 13,

15 shows an arrangement for the same

early production of a number of holes in a workpiece,

16 is a block diagram showing

the electrical circuit of the device shown in FIG shows,

Figures 17A and 17B are sections through blades

a gas turbine, and

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Pig. 18 a tablet showing the own

properties of various ones shown in Figs. 17A and 17B Assembles cooling holes.

1 shows a device 10 for the electrical machining of a workpiece 11. The workpiece 11, at which is a pipe section in the illustrated embodiment is not shown in one Holder supported and by means of an electrical line 12 with a connection of an electrical power source -13 tied together. A second line 14 connects the power source with a tool 15 which has several electrodes 16.

The tool 15 is of an electrical discharge machining type type known per se and can be constructed according to a manner described in GB-PS 1,319,911 be. The tool 15 is held in a holder, not shown, which is fixed with respect to the workpiece 11, which is designed so that the tool can be moved towards and away from the workpiece, as by the arrow 17 is indicated. The holder can also be designed so that it can move if necessary the tool 15 allows in other directions,

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In the workpiece 11 bores 18 are produced by electrical ¹ spark erosion machining and during this process dielectric oil, which is composed of three parts of odorless kerosene and one part of Dow Corning silicone oil EDM 1005, is sprayed from nozzles 19 over the electrodes and the workpiece » The power source 13 is designed in the usual way for the electrical spark machining process and generates current pulses between the workpiece and the tool with a peak amplitude of about 85 V, for which purpose a flip-flop with a capacity of 0.67 μ ¥ is used.

The power supply also includes a feedback loop, per se for use in conjunction with machines working according to the electric spark process is known and by means of which it is effected that the Tool 15 is moved towards the workpiece as machining progresses and that the electrodes are always in the correct position Be kept at a distance from the workpiece. After the electrodes 16 have broken through the wall of the workpiece, the point erosion process is ended and the feed of dielectric oil stops, but the electrodes 16 remain in the bores 18 of the workpiece. Then a pump 19 is switched on, which draws in an electrolyte 20 from a container 21 and pressurizes it

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through a hose 22 and a hose connector into the interior 24 of the workpiece

At one end 25 of the workpiece, a second connection piece 26 is arranged, which by means of a tap is lockable. This tap is opened first to allow the electrolyte dielectric fluid from inside of the workpiece can be rinsed out. After closing the tap 27, the electrolyte is removed from the interior of the workpiece pushed out through the bores 18. The power source is now operated in such a way that between the electrodes 16 and the workpiece 11 continuously a DC voltage of 12 V is applied, whereby the workpiece is the anode. So the conditions for a electrochemical machining of the bores 18 created and the electrochemical machining is during a appropriate period of time until the electrical spark machining process originating cast skin on the walls of the bores 18 is eliminated.

The workpiece 11 can now be removed from the holder in order to insert the next workpiece. The electrolyte emerging through the bores 18 is collected in a trough 28 which is shaped like a funnel

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and returns the electrolyte to the container 21.

Contamination of the electrolyte by small amounts of dielectric oil is not a problem, since the dielectric oil, which has a lower density than the electrolyte (a 0.5 percent solution of NaCl in Water) and immiscible with the electrolyte is and therefore floats in the container 21 on the electrolyte 'so that it can be easily removed.

It will be appreciated that the electrodes 16 can have any desired cross-section and that after There is a constant size gap around each electrode. Consequently not only does the cast skin have an essentially constant thickness, but also the use according to the invention the electrode already positioned from the electrical discharge machining leads to an essentially uniform current density between the electrode and the workpiece and for removing a metal layer of substantially constant thickness from the workpiece around the electrode.

The panel of Fig. 6 shows the results that

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when using the in Pig. I device shown in Connection with a tubular workpiece made of a nickel-based alloy and with a wall thickness of 1.6 mm be achieved.

The electrodes 16 are tungsten wires with a diameter of 0.375 mm, and by means of these electrodes are bores 18 using the electric spark method with diameters of 0.425 now manufactured. The cast skin in these holes has a thickness of 0.05 and nine tests were carried out with electrolytes of different strengths to find the optimal Find conditions for electrochemical machining. It should be noted that in all of these attempts the current for electrochemical machining at the end of the machining process is less than the initial current was. This can easily be explained by the fact that the distance between the bore wall and the electrode increases as the machining process progresses and therefore the bore diameter becomes larger.

Weaker electrolytes (Trials 7 to 9) are preferred as they allow finer control of the electrochemical Allow editing process. The extension

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the processing time does not seem essential, because it is still small in relation to the total processing time. The low machining current enables a very fine finishing of the bores 18.

As is easy to see, the device shown in FIG. 1 can be designed in a simple manner for drilling cooling ducts in rotor blades and guide vanes of gas turbines. Reference is made in particular to FIGS. 2, 3 and 4 below. These figures show a guide vane J> 0 of a gas turbine which contains three longitudinal cooling channels 31, 32 and 33. The cooling channel 33 », which has an elongated cross section and can be produced either during casting or by spark erosion machining, cools the blade trailing edge 34 via a large number of bores 35»

The bores 35 can easily be produced by the method according to the invention. This can not be shown Connection pieces are manufactured to the cooling channel 33 in the manner described with reference to FIG to be able to connect to the electrolyte supply.

The longitudinal cooling channels 31 and 32 are connected to one another by means of transverse bores 36, which according to

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can be produced by means of an electrode 37 using the electric spark method shown in Fig. 5 and described in British Patent Application No. 04333/7 ^. The electrode 37 is through a tube 38 made of stainless Steel passed down with a thin bore, which is electrically insulated from the blade by insulation 39 and at the lower end 40 has a curvature. The steel tube directs the electrode 37 to produce the transverse bore 36 by about 90 µm. After making a Bore 36 after the electric spark method can without Withdrawal or disruption of the electrode 37 to supply a source of electrolyte to the channels 31 and 32 of the blade and also to the bore 4l of the stainless steel pipe to be connected to Rinse out any dielectric oil that is still present and remove those from electrical discharge machining to enable the resultant cast skin in the manner described above.

In some blades, not shown, further cooling bores lead from the longitudinal channel to the blade leading edge 42 and these holes can of course in the same way as the holes getting produced,

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It has also been discovered that there are liquids which are suitably dielectric for electrical discharge machining and sufficient for electrochemical machining are electrolytic. By using such a liquid, not only can the delays caused by the Rinsing out the dielectric fluid before the electrochemical one Machining can be avoided, but the electrical discharge machining and electrochemical machining can take place at the same time.

Reference is now made to FIG. 7, in which a Tungsten electrode 43 and a workpiece 44 are shown as elements of a circuit, the workpiece with respect to the electrode has positive potential.

The electrode 43 is a collet and a Support, which are indicated schematically by the block 45, connected to a stepper motor 46, which is in operation moves the support and consequently the electrode towards and away from the workpiece 44.

A digital servo amplifier 47 is connected to the connection line 48 connected to the electrode so that it receives the signals supplied to the electrode and causes

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that the stepping motor 46 the electrode 43 as in the conventional one Electric spark method withdraws a given piece from the workpiece 44 at a time.

An electrolyte is placed between the workpiece from a source not shown and connected to a nozzle 49 and passed the end of the electrode.

The electrolyte used is tap water from the Barnoldswick area of Yorkshire in England, which is a relatively weak electrolyte with a conductivity of 154 / iS (measured with a Wayne-Kerr measuring bridge with a standard conductivity test cell) having. However, it is possible to use other weak electrolytes as well.

In particular, it has been found that a solution of sodium sulfate in deionized water with a conductivity of 154 / xS, ie the same .Leitbarkeit as the Barnoldswick tap water, is suitable for the production of bores in forged turbine blades, which is from a Ni cke Ib as is Ie alloy with 20 % cobalt, 15 % chromium, 5 % molybdenum, 5 % aluminum and 12 % titanium. However, this solution is suitable

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not for the machining of cast turbine blade 1 materials with a composition of 10 % cobalt, 10 % tungsten, 9 % chromium and the remainder nickel, since it leads to a preferred removal of intercrystalline material, which results in a rough surface. A mixture consisting of solutions of potassium chloride and sodium acetate in deionized water has proven to be the most suitable liquid for machining cast turbine blade materials. The mixture has a conductivity ratio of 5: 1, namely a conductivity ratio of 100 μs of potassium chloride to 20 μs of sodium acetate.

The power source between the workpiece and the electrode not only carries a continuous direct current too, which is desirable for electrochemical machining is, but also supplies a direct current superimposed on this direct current with periodically changing Voltage for electrical discharge machining,

To generate the periodically changing voltage for electrical discharge machining, the circuit a relaxation oscillator 50, the one between the positive and negative connection parallel to the electrode

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connected capacitor 51 and a resistor connected between this capacitor and the negative terminal 52 contains. The output of the circuit leading to electrode 43 is at 53 with that between the capacitor and the resistor 52 running line connected.

To start up, the electrical current is switched on and a constant flow of electrolyte between the electrode 43 and the workpiece 44 passed.

The electrode 43 is simultaneously moved by the stepping motor towards the workpiece 44 and, when the distance between of the electrode and the workpiece is 0.125 mm, for example, the electrochemical machining of the begins Workpiece. The electrode continues to move towards the workpiece until it almost touches the workpiece, whereupon the capacitor 51 discharges, the electrical energy during the electrochemical processing time recorded and saved. The discharge acts on the workpiece at the point of application of the electrode and removes a small amount of metal from it, which is washed away by the electrolyte.

The discharge of the capacitor generates a signal

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which is scanned by the servo amplifier 47 «, This Signal actuates the servo amplifier 47, which the Stepping motor 46 controls so that it reverses its direction of action and the electrode 43 by a bit retracts about 0.125 mm from the surface of workpiece 44 being machined. After withdrawing the electrode by this distance, the stepper motor changes its direction of action and begins, move the electrode back toward the workpiece 44 while again performing electrochemical machining takes place. When the electrode approaches the workpiece again, the is discharged again Capacitor 51 »which causes a further current pulse and a further electrical discharge machining on the workpiece.

It can be seen, however, that the size of the resistor is the size of the after discharge of the capacitor controls DC voltage applied between the workpiece and the electrode. It is therefore possible through Change in the size of the resistance and, consequently, this DC voltage, the electrochemical part of the processing to be changed in relation to the machining share achieved by the spark erosion »by changing this

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relative processing shares can also be the form of the means the recesses made of the electrode can be changed.

8 and 9 show typical sections through a Bore created by means of a cylindrical electrode. The workpiece here is a rotor blade of a gas turbine, which is shown in section and at which a cooling bore 35 between the blade outer surface 42 and an inner cooling channel 33 is made,

In Fig. 8, the electrode 43 is at the point at which it breaks through the wall 54. As can be seen is, is the recess. 35 roughly conical in shape and has a rounded outer edge. This form occurs since the spark erosion takes place on the material in front of the electrode, while the electrochemical Machining takes place on the side walls 55 and 56 of the bore. While the electrode is through the When the blade material passes through it, the material near the outer surface 42 is consequently for a longer period of time Time subjected to electrochemical action than the material located at the inner end of the bore. The rounding of the outer bore edge 57 is due to the electrochemical action during the period

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supports during which the tool moves forward into the workpiece before a spot erosion period is moved in and also results from the concentration of the electric field lines at the edge of the hole,

At the bottom of the hole, a certain cast skin 58 from the point erosion process is present, which is removed in the manner explained below. The breakdown time of the electrode will be as later is electrically sensed and the speed of the stepper motor is slowed down. The stepper motor however, continues to lead the electrode into the bore 33 up to the position shown in FIG. 9. While No spot erosion machining takes place in this phase because of the distance between the electrode and the workpiece is too big for a spark discharge »The electrochemical However, action continues until the inner end 59 of the bore has reached the desired diameter. the The casting skin 58 is then removed and the sharp edge 60 the bore has merged into a rounding 6l according to FIG. 9. In practice, this process only takes a few seconds and it is triggered by the breakthrough signal actuated timer used to determine depth

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which reaches the electrode before being pulled out of the hole and into the next drilling position is moved on.

The timer, which can be set to the desired time, also ensures that the electrode does not reach the wall 63 opposite the bore and electrical machining of this opposing wall surface 64 begins. Moving further forward The electrode through the hole during the last part of the drilling cycle assists in breaking up of the hydroxides that have formed during the drilling process, so that they can be removed from the incoming electrolyte can be transported away.

As can be seen from FIGS. 10 and 11, the shape of the bores can be modified. This leaves can be achieved by changing the resistance 52. When most of the entire drilling process is performed by electrical discharge machining occurs, when the resistance is high, the more parallel bore 65 generated according to FIG. If, on the other hand, strongly converging, venturi-like holes such as the hole are to be produced in Fig. 11, the value of the resistance is reduced and the electrochemical action

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prevails.

It will be appreciated that the amount of electrochemical machining can also be increased by increasing the strength of the electrolyte can be enlarged. This fact can be exploited to drill holes with unusual Shapes such as shown in Fig. 12 to generate.

In the arrangement of Figure 12, the electrode is relatively weak first using one electrolytic or dielectric liquid and penetrated into the workpiece using a resistor 52 sized so that a parallel bore arises in the workpiece. The electrolyte is then exchanged for a stronger electrolyte and the electrode is partially pulled out of the hole. During the electrochemical processing, the Hollow 67 and a remaining one that may still be there Cast skin from the previous machining is removed.

Those skilled in the art will appreciate that a wide variety of hole or recess shapes by varying the Parts of the electrochemical effect and the spark

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erosion effect on the entire machining process can be.

It has been shown that a certain longitudinal oscillation of the electrode, as is the case with electrical discharge machining is common to improve the drilling process. It has also been found that when the electrolyte is through the guide tube flows through, much better results can be achieved than if the flow is below Using the nozzle 68 shown in Fig. 14 is directed at the drilling site. These two details are shown in Fig. which is a detailed view of a suitable mechanical arrangement.

According to FIG. 13, a machine frame 69 carries a work table 70 which is surrounded by a container J1 for collecting the used electrolyte. A vertically arranged guide 72 is movably connected to the frame 69 via a base part 73 and a screw spindle 74. The vertical position of the guide part 72 can be adjusted when setting up the machine by turning a handwheel which is attached directly to the screw spindle

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Electrode 43 passed through _e The upper end of the electrode 43 is held in a collet 77, which is attached to a vibration generator 78 that transmits the longitudinal vibrations to the electrode 72 is performed. This slide 79 is moved by means of a screw spindle 80 driven by the stepping motor f6. In this way, vibrations are superimposed on the movement of the electrode generated by the stepping motor.

One surrounding the stationary guide tube 76 Cuff 68 is firmly attached to the base part 73 and prevents bending of the guide tube. The cuff, which is shown in more detail in FIG. 14, also serves to supply the electrolyte to the electrode.

From Fig. 14 it can be seen that the electrolyte in the direction of arrow 81 through a channel 82 in a Annular chamber 83 formed in the cuff flows in. From this annular chamber 83 run obliquely radially inward and downward channels 84 which coincide with similar channels 85 formed in the guide tube 76. By

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The electrolyte flows through these channels into the interior of the guide tube and through the space 86 of the Down through the electrode and the guide tube. A powerful electrolyte stream flows in this way the outside of the electrode downwards «, the better flow direction in this embodiment of the electrolyte has the further advantage that the workpiece can be attacked by stray currents Minimum is reduced.

The cuff 68 is at its upper end with a screw thread 87 for a fixed connection to the base part 73 provided.

In a modification of the invention, not shown, the electrically driven stepper motor is by a Replaces hydraulically driven stepper motor, which has a swinging spindle valve for moving the slide in forward and backward directions during the drilling process having.

The spark breakdown can be detected in two ways. In the case of relatively short bores, a voltage-sensitive device, which the peak

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Measure voltage between the workpiece and the electrode, apply. Before the point erosion? ear process takes place, this voltage is in the range of 120 V, but as soon as the electrode approaches the workpiece and a spot erosion takes place, the voltage drops to about 40 volts. When the electrode breaks however, the voltage rises again to 120 V. The voltage change on breakdown is then used as a signal to slow down the speed of the stepper motor used.

In the case of relatively deep holes, i.e. if the ratio of the length of the hole to the main diameter of the hole is greater than about 20: 1, the voltage change is not strong enough and it is then better to sample the breakthrough by measuring the frequency, with which the electrical spark discharge takes place. On breakthrough, this frequency drops rapidly by one high value to a low value and a suitable electrical circuit (not shown, but known per se) are used to switch means for switching the stepper motor to slow speed to operate.

The device shown in Fig. 13 can easily

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be modified so that a plurality of holes can be drilled at once. For this it is necessary to arrange a plurality of guide tubes 76 and to use a corresponding device for feeding the electrodes through these guide tubes. Such means are known per se and are also used in conventional drilling according to the E lekt ro funke η process η.

It has been found that the use of multiple electrode assemblies leads to certain undesirable effects Effects can lead. For example, if one looks at the blade shown in FIG the last electrode 88 must penetrate a greater thickness of material when drilling than the electrode 89, so that if all electrodes are moved forward at the same time, when the electrode 88 breaks into the channel 33, the electrode already begins to drill the surface 90 of the channel 33 opposite the drilled holes. This problem can be solved in that the current supply to the electrode 89 after a certain time after the breakdown has been scanned through the wall to be pierced at 91 is switched off.

Reference is now made to FIG. 16, which

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a block diagram of the electronics used to carry out the method described above Circuit represents. The structure of each individual circuit block is not described in detail, since it is used for easily understood by those skilled in the art.

The start of a drilling cycle is initiated by manually pressing the start button 92. This will be at the same time the electrolyte pump 93, the tilting oscillator 50, the digital servo amplifier 47 and the vibration generator 78 switched on. The servo amplifier operated the stepping motor 46, which feeds the electrode towards the workpiece.

At the beginning of the processing operation, the potential appearing at the inverting input 94 of the operational amplifier 95 drops relative to the potential appearing at the non-inverting input 96 when the circuit is open. The operational amplifier generates an output signal which is fed to a discriminator 97 which ignores the signal. When the electrode breaks down, the potential at input 94 rises essentially to the value of the potential at input 96 and the operational amplifier switches off. This is sensed by the discriminator 97 and its that

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Output signal 98 fed to digital servo amplifier leads to a slowdown in the speed of the Stepper motor. Simultaneously with this slowdown a counter 99 is switched on, which can be preset so that it only has a certain number of steps of the stepper motor allowed. The set number of steps therefore determines the time during which after the breakthrough the electrode 43 is still being processed. At the end of this period, the counter sends an output signal 100 to the digital servo amplifier 47, which is the Stepper motor gives the command to reverse the direction and to withdraw the electrode. After the electrode has been withdrawn from the workpiece, a microswitch 101 is actuated by the carriage 79 and a signal is sent to the stepping motor 102 for the workpiece 44 and to the digital servo amplifier 47 »which then runs another cycle of stepper motor operation initiates the production of another hole in the workpiece. A cycle counter 103 counts the Total number of holes drilled and when its count reaches a preset value the energizes Counter 103 an electromagnet 104 to open the start button 92, and there are on the machine for the next workpiece set the original values again.

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FIGS. 17A and 17B show sections through a forged gas turbine blade and cast by one Gas turbine blade in which various recesses are formed according to the method described above. The panel of Fig. 18 shows the dimensions of these recesses.

From Fig. 17A it can be seen that a bore 105 at a very oblique angle into a longitudinal one Cooling channel 106 runs into it and that in this case great care must be used to prevent the rear wall IO7 of the longitudinal channel 106 is processed o This is achieved in that the power supply to the electrode is switched off immediately if the electrode breaks is.

Typical made according to the technique described above Recesses can easily be examined with the help of optical microscopes to determine the surface quality determine the recess walls, further to determine the dimensions at the inner end of the recess and to check whether on the surface of the longitudinal channel opposite the drilled recess in an undesirable manner Material has been removed.

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The machining process described above has for the production of air outlet ducts in cooled turbine blades for jet engines proven. The conical profile of the holes ensures that the cooling air flowing from the thin end to the base of the conical shape flows, is so dispersed that the best possible surface cooling is achieved and not like it this is the case with bores with parallel wall surfaces is, a cooling leading to cold spots is achieved.

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Claims (18)

Claims Workpieces in which an electrode is used for the purpose of ablation of material brought to the workpiece by means of a stepper motor driven by spark erosion and a liquid is fed between the workpiece and the electrode, characterized in that one for both electrochemical Machining as well as electrical discharge machining suitable liquid is used and that the power source feeding the electrode is so designed and operated that material is removed from the workpiece simultaneously by electrochemical Exposure and is eroded by spark erosion, 2. The method according to claim 1, characterized in that the time of complete breakthrough of the electrode is scanned through the wall to be drilled through the workpiece and that then still during a predeterminable Duration of electric current is supplied to the electrode. 3. The method according to claim 2, characterized in that the electrode continues for a predetermined period of time - 36 - 509839/0382 continues to move forward into the workpiece after the electrode has broken through. 4. The method according to claim 3 » characterized in that the speed of the stepping motor is reduced after the Peststellen the breakthrough of the electrode for the purpose of slowing down the electrode advance speed. 5. The method according to claim 3 or 4, characterized in that the electrode according to said predeterminable Period of time is withdrawn from the workpiece and that then the electrode for the purpose of further processing of the workpiece is brought into a different position relative to the workpiece. 6. The method according to claim 5, characterized in that that the number of operations carried out the workpiece is counted and that the machining is ended when the count has reached a certain value will, 7. The method according to any one of claims 1 to 6, characterized in that the workpiece consists of a nickel-based - 37 - 509839/0382 alloy is cast and that said liquid is an electrolyte consisting of a mixture of a potassium chloride solution and a sodium acetate solution in the conductivity ratio 5: 1, being the conductivity of the sodium chloride, with a Wayne-Kerr bridge and a Standard conductivity test cell measured, 100 / iS amounts to. 8, method according to any one of claims 1 to 6, characterized characterized in that the workpiece consists of an extruded Nicke Ib as is Ie alloy and said liquid is an electrolyte that is a solution of sodium sulfate in deionized water with a conductivity of 150 ^ .S, measured with a Wayne-Kerr measuring bridge and a standard conductivity test cell, contains. 9. Electro-erosion process for machining workpieces, in which an electrode is used for the purpose of erosion of material brought to the workpiece by spark erosion and a dielectric liquid between the Workpiece and the electrode is fed, characterized in that the electrode after completion of the electrical discharge machining remains in their relative position with respect to the workpiece and the dielectric liquid - 38 - 509839/0362 is removed from the workpiece, and that then an electrolyte between the electrode and the workpiece and fed by electrochemical action further material from Workpiece is removed. 10. Apparatus for carrying out the method according to any one of claims 1 to 8, with one in relation to one another the workpiece fixed holder relative to the workpiece movably guided electrode and with means for Moving the electrode relative to the workpiece, characterized by means (19, 22; 49; 68) for feeding the both for electrochemical machining as well as electrical discharge machining of the workpiece suitable liquid between the electrode (16; 43) and the workpiece (11; 44) and through a power source (13) for feeding the electrode, which is suitable for electrochemical and spark erosion machining, 11. The device according to claim 10, characterized in that the means for moving the electrode one Have stepper motor (46). 12. Apparatus according to claim 10 or 11, characterized in that the liquid for producing Holes in the workpiece (11) a diluted electrolyte - 39 - 509839/0382 contains and that the electrical circuit is designed so that the electrochemical and electrical discharge machining can take place at the same time, 13. Device according to one of claims 10 to 12, characterized by means (95) for determining the point in time the complete breakthrough of the electrode (43) through the workpiece wall to be pierced and through Means (47) which cause the electrode to be advanced further into the workpiece. 14, device according to claim 13, characterized by means (47) which reduce the electrode advance rate after the electrode has broken through «, 15 · Device according to claim 14, characterized by a counter (99) which counts the steps of the stepping motor (46) after the electrode has broken through, and by means which stop the movement of the electrode after a predeterminable number of steps has been reached. 16. Device according to one of claims 10 to 15, characterized by means (102) for changing the Relative position between the electrode (43) and the workpiece (44) before the next recess is made in the workpiece. - 40 509839/0362 17. The apparatus according to claim 16, characterized by a counter (103) which the number of im Workpiece (44) made recesses counts and the processing before gang ended as soon as the count one has reached a specifiable value «, 18. Apparatus for carrying out the method according to claim 9 »with one in one with respect to the workpiece fixed holder relative to the workpiece movably guided electrode and with means for moving the Electrode relative to the workpiece, characterized in that the electrical circuit of the device is designed in this way is that initially a recess in the workpiece by electrical discharge machining with feeding a dielectric liquid between the Electrode (16) and the workpiece (11) can be manufactured that further means for removing the dielectric Liquid without changing the relative position of the electrode with respect to the workpiece and for supplying an electrolyte are provided by the recess produced for the purpose of enlarging the same by electrochemical action. - 41 - 509839/0362