MXPA99011281A - Method of and arrangement for electrochemical machining - Google Patents

Abstract

La invención se relaciona con un método para maquinar electroquímicamente una pieza de trabajo eléctricamente conductora en un electrolito, mediante la aplicación de impulsos eléctricos entre la pieza de trabajo y un electrodo eléctricamente conductor, uno o más impulsos de maquinado (MP) alternando con impulsos de voltaje (PP) para depositar capas de pasivación sobre la pieza de trabajo. La amplitud de los impulsos de voltaje se ajusta durante un procedimiento de ajuste en el cual la amplitud de los impulsos de voltaje se incrementa gradualmente desde cero hasta el voltaje al cual la pieza de trabajo comienza a disolverse en el electrolito. Después de cada incremento de voltaje se mide la resistencia del espacio entre el electrodo y la pieza de trabajo. El valor del voltaje para la mayor resistencia del espacio se almacena en una memoria y se utiliza durante el maquinado adicional. El intervalo de tiempo abarcado por los impulsos de voltaje puede ser dividido en intervalos de tiempo (Dt) y por cada intervalo de tiempo el voltaje se ajusta a la resistencia máxima del espacio durante ese intervalo de tiempo.

Description

METHOD OF AND ARRANGEMENT FOR ELECTROCHEMICAL MACHINING The invention relates to a method, an arrangement and a power supply for a process for electrochemically machining an electrically conductive part by applying electrical machining pulses between the workpiece and an electrically conductive electrode while electrolyte is supplied between the workpiece of work and the electrode. Electrochemical machining is a process in which an electrically conductive part is dissolved at the location of an electrode while electrolyte and electric current are supplied. For this purpose, the electrode is brought to the vicinity of the workpiece and, while the electrolyte is fed into the space between the workpiece and the electrode, a powerful current is passed through the workpiece and the electrode Via the electrolyte, the work piece is positive with respect to the electrode. The current is applied in the form of machining pulses that have a given amplitude and duration. In the intervals between the machining impulses the electrolyte is renewed. During the application of the machining pulses, the electrode and the workpiece move towards each other with a given feed rate, as a result of which the electrode forms a cavity or possibly a hole in the surface of the work piece. work, the shape of this cavity or hole has a shape that corresponds to the shape of the electrode. This process can be used, for example, to machine intricate cavities or holes in or to form hard metals or alloys. The accuracy of reproduction with which the shape of the cavity or the hole in the workpiece follows the shape of the electrode is important for the quality of the result. However, many publications have appeared in the form of articles in newspapers and patent documents, in which proposals have been made to improve the precision of precision of electrochemical machining. Therefore, an object of the present invention is to provide a method and arrangement of electrochemical machining with good reproduction accuracy. For this purpose, the method of the type defined in the opening paragraph is characterized in that the machining pulses alternate with electrical passivation pulses of the same polarity as the machining pulses, the voltage of the passivation pulses has an amplitude, which is inadequate to dissolve the work piece and a passivation film on the work piece. In the intervals between the machining pulses, during the renewal of the electrolyte, passivation pulses of an amplitude are applied such that a layer of passivation of metal oxides is formed around the electrode on the workpiece. During the next machining pulse, this layer is removed selectively on the final face of the electrode. In this way, the machining impulse in the direction of feeding is more effective. This improves reproduction accuracy due to the fact that comparatively more material is dissolved from the workpiece at the end face of the electrode and in the cavity to be machined at the smaller spokes of the workpiece formed at the edges and slopes of the lateral surface of the cavity. An additional advantage that must be mentioned is that the energy consumption of the process is lower and that the speed of dissolution of the work piece in the direction of feeding is greater. This is because, due to the local passivation layers, the energy of the machining pulses is no longer used for the undesirable removal of material from the side surfaces of the workpiece cavity. Preferably, a distance is maintained between the workpiece and the electrode, which is smaller during the machining pulses than during the passivation pulses. The increase in the distance between the workpiece and the electrode during the passivation pulses is achieved due to the fact that at a greater distance, the electric field of the passivation pulses has less effect on the final face of the electrode than on the side walls of the cavity in the work piece. In this way, a thinner passivation layer, or even no passivation layer at all, is achieved more accurately than the opposite part of the end face of the electrode, ie at the bottom of the cavity in the workpiece, is formed anywhere in the cavity to be machined. The amplitude, duration and waveform of the machining pulses are selected in such a way that the activation of the surface to be machined occurs only in the case of the smallest distance between the machining pulses. In that case, the dissolution of the anode during the application of the machining impulses occurs only in those places of the work piece where the space is smaller than the critical distance. The rest of the work piece is protected by a layer of passivation and does not dissolve. This results in very high reproduction accuracy. In a variation of the method according to the invention, the workpiece and the electrode make a mutual oscillating movement, the distance between the workpiece and the electrode reaches a minimum during the machining pulses. The amplitude of the voltage of passivation pulses plays an important part. Too low a voltage does not have or has little effect because the passivation layers are too thin. On the contrary, too high a voltage causes the previously formed passivation layers to disappear on the lateral surfaces of the cavity and causes the reproduction precision to deteriorate. Even higher voltage will eventually produce the same effect as normal machining pulses and will cause the workpiece to dissolve in several undesirable places in the cavity to be machined. To optimize the amplitude of the passivation pulses, a variant of the method according to the invention is characterized in that the amplitude of the voltage of the passivation pulses is adjusted at least once during the electrochemical machining, the amplitude of the passivation pulses in a series of successive passivation pulses is changed until the value of the resistance measured between the workpiece and the electrode has reached the maximum, after which the electrochemical machining is continued with an amplitude of the passivation pulse corresponding to the maximum of the value of the resistance. During a series of successive passivation pulses, the amplitude of the voltage of the passivation pulses is gradually changed, for example increasing from zero to a given maximum value at which the workpiece begins to dissolve. In each subsequent passivation pulse a slightly higher voltage was applied and the space resistance was measured and stored. From the measured resistance values the highest value was chosen and the corresponding amplitude of the voltage was set and sustained for some time during the subsequent machining of the work piece. The amplitude of the voltage of the passivation pulses was optimized in this way for a maximum resistance of the space. This implies that the formation of the passivation layers on the lateral surfaces is also maximal and that the reproduction precision is optimal. For this purpose, the arrangement according to the invention is characterized in that the arrangement comprises: - an electrode; - means for positioning the electrode and the workpiece in a spatial relationship to maintain a space between the electrode and the workpiece; means for supplying electrolyte in space; a first source of electrical power supply, which is electrically connectable to the electrode AND the workpiece for supplying machining pulses to the workpiece and the electrode; - a second source of electrical power supply of the same polarity as the first source of power supply and having an output voltage, which is controllable by means of a control signal, second power supply source, which it is electrically connectable to the electrode and the workpiece to supply passivation pulses to the workpiece and the electrode; means for alternatively connecting the first and second sources of energy supply to the workpiece and the electrode; - means for generating a variable control signal to change the output voltage of the second power supply source during successive passivation pulses; means for measuring during the successive passivation pulses the electrical resistance of the space between the workpiece and the electrode at a time during the passivation pulses and for storing the information values of the resistance which are representative of the strength of the space in such a instant, and to store the corresponding control signal values of the control signal at that instant; and means for calculating a maximum value of the information values of the resistance, and means for maintaining the control signal for the second power supply source in the value of the control signal corresponding to the maximum value.

The second source of power supply is controllable and its voltage is gradually raised, the value of the voltage for which the measured space resistance is maximum is stored. When a variable space distance is used, any value of the distance between the work piece and the electrode will correspond to another optimal amplitude of the voltage of the passivation pulses. This is particularly the case when the workpiece and the electrode make an oscillatory movement one in relation to the other and the distance between them is, in fact, never constant. To prevent this problem, a further variant of the method according to the invention is characterized in that the passivation pulses are divided into time intervals and for each individual time interval the instantaneous amplitude of the voltage of the passivation pulses is changed until the value of the resistance measured between the workpiece and the electrode has reached a maximum during the individual time interval, after which the electrochemical machining with passivation pulses is continued, whose instantaneous amplitude varies according to the amplitude found for each time interval and which corresponds to the maximum value of the resistance in such time interval. The time lapse of each of the passivation pulses is divided into a plurality of intervals and in each interval the amplitude of the voltage during successive passivation pulses is changed until the maximum resistance in that range is found. The voltage of the corresponding optimum interval of the passivation pulse in this interval is stored. After finishing this adjustment procedure all the stored optimum interval voltages are generated consecutively in the correct sequence within the time lapse of the passivation pulses, as a result of which the amplitude of the voltage of the passivation pulses has a waveform , which is optimized for the variation in space distance. For this purpose, one embodiment of the arrangement according to the invention is characterized in that - the means for generating variable control signals include means for changing the output voltage of the second power supply source at different times within the time lapse of an impulse of passivation; - the means for measuring and storing are adapted to store the information values of the resistance which are representative of the instantaneous resistance of the space at the different instants within the passivation pulse and for storing the corresponding control signal values of the signal of control in the different instants; calculating means that are adapted to calculate the individual maximum values of the information values of the resistance of the corresponding instants within successive passivation pulses and to generate a control signal having an instantaneous value, which in the different instants is equal to the values of the control signal that correspond to the individual maximum values. The voltage of the second power supply source thus varies within the time span of a passivation pulse whose waveform is best adjusted to the size of the variable space during the passivation pulse. The adjustment procedure mentioned above for determining and maintaining the optimum amplitude waveform for the voltage of the passivation pulses can be repeated as frequently as necessary during the additional electrochemical machining of the workpiece. A variant of the method according to the invention is characterized in that in the time intervals between the successive machining pulses additional electric pulses of opposite polarity are applied between the work piece and the electrode, these last mentioned pulses, which have a voltage whose amplitude does not exceed the amplitude at which the electrode begins to dissolve in the electrolyte, and / or in the time intervals between successive machining pulses, the passivation pulses alternate with electrical pulses of opposite polarity, these latter mentioned impulses, which have a voltage whose amplitude does not exceed the amplitude at which the electrode begins to dissolve in the electrolyte. The process is now supplemented and / or alternated with electrical pulses of opposite polarity in the intervals between the machining pulses. The purpose, effect and setting of the voltage amplitude of the pulses of opposite polarity are described more fully in International Application WO 97/03781. Such Request describes between which optimal limits the amplitude of the voltage of the pulses of opposite polarity should be adjusted, on the other hand, to prevent the electrode from dissolving and in this way the accuracy of the machining be reduced and, on the other hand, to achieve a greater efficiency of the machining, in combination with a well-defined surface condition, for example in the form of a certain luster. When chrome-nickel steel is machined it is found that under these working conditions, a reduced concentration of toxic hexavalent chromium is left in the finished electrolyte solution, as a result of which, it is easier to meet the requirements with respect to the environmental pollution. The space resistance can be calculated by measuring. the current through the voltage across the space between the electrode and the workpiece and storing the measurement data in a memory. Current and voltage are preferably measured by means of analog to digital converters coupled to a computer in which the measured data is stored. The computer calculates the maximum resistance of the space by analyzing the measurement data. The computer also generates the control signal to control the output voltage of the second power supply source. During the adjustment procedure the output voltage of the second power supply source changes gradually under the order of the control signal of the computer. After the computer has found the maximum resistance value, the corresponding control signal is generated continuously by the computer for a given time. These and other aspects of the invention will be described in greater detail with reference to the accompanying drawings, in which: Figure 1 shows schematically one embodiment of an arrangement for carrying out the method according to the invention; Figure 2 shows waveforms of signals, which appear in a variant of the method according to the invention; Figure 3 shows the change in the condition of the electrolyte between the electrode and the work piece when a variant of the method according to the invention is carried out; Figure 4 shows a waveform of a signal, which occurs in a variant of the method according to the invention; Figure 5 shows a waveform of an AC pulse train for carrying out the method according to the invention; Figure 6 shows an electrical block diagram of a modality of an array for carrying out the method according to the invention; Figure 7 illustrates the formation of the passivation layers in the machining cavity of the workpiece when a variant of the method according to the invention is carried out; Figure 8 shows waveforms of the voltage across the resistance between the electrode and the workpiece when a variant of the method according to the invention is carried out; Figure 9A and Figure 9B are flow charts of the process steps of the variant of the method according to the invention; Figure 10 shows waveforms of additional signals that occur in a variant of the method according to the invention; and Figure 11 shows waveforms of additional signals, which occur in another variant of the method according to the invention. In these figures, the parts that have a similar function or purpose have the same reference symbols. Figure 1 shows an arrangement for the electrochemical machining of a workpiece 2. The workpiece 2 is arranged on a table 4, which moves at a feed speed Vk towards an electrode 6, which makes an oscillatory movement with respect to the workpiece 2, which is effected by means of a crankshaft 8, which is driven by the motor 10. The workpiece is made of, for example, a type of steel containing chromium. An electrolyte, for example an aqueous solution of alkali metal nitrate, flows in space 5 between the workpiece 2 and the electrode 6 and is circulated at a pressure Px from a reservoir 3. The workpiece 2, the table 4 and electrode 6 are electrically conductive. The electrode 6 and the table 4 are connected to an electric power supply source 12, which supplies electrical pulses to the electrode 6 and the table 4. The electrical pulses include machining pulses having a polarity for which the table 4 and , accordingly, the workpiece 2 is positive with respect to the electrode 6, pulses which alternate with passivation pulses having the same polarity but having a voltage and waveform which will be described later. During the machining pulses, the metal of the workpiece 2 enters the anode solution in the electrolyte. During the passivation pulses, the surface of the work piece 2 is locally passivated. A curve I in Figure 2 represents a size variation S (t) of the space 5 between the electrode 6 and the work piece 2. A curve II in Figure 2 represents the variation of the voltage U through the space 5 during the adjustment procedure which will be described below, and a curve III represents the variation of voltage through space 5 during the subsequent machining period. The machining pulses MP are applied in a time interval ti, indicated in the curve IV of Figure 2, in which the electrode 6 is closer to the work piece 2. During these machining pulses the voltage across the space 5 has a waveform with a global minimum, as indicated in curve II in Figure 2. The machining pulses alter with PP passivation pulses at the time of the ti interval, indicated by a curve V in Figure 2. It should also be noted that the waveforms shown from assembly U through space 5 are simply an approximation of the real voltage waveforms. Figure 3 gives an impression of the process occurring in space 5. In the initial stage of approaching electrode 6 to workpiece 2 in the case of a comparatively large space Smax, the electrolyte flow is turbulent in nature and the electrolyte contains bubbles of vapor and gas. In this step, the space between the electrode 6 and the workpiece has a comparatively high electrical resistance, which is evident from the first maximum in the voltage U in the curve II of Figure 2. When the electrode 6 approaches , the pressure in the electrolyte increases and the vapor and gas bubbles dissolve, as a result of which, the electrolyte is homogeneous and uniform in space and a high current density is achieved with a small space size. As a result of this, the electrical resistance decreases, which is evident from the occurrence of a global minimum in the voltage U in the curve II of Figure 2. As a result of the increase in the distance between the electrode 6 and the piece of work 2 and the summary generation of steam and gas bubbles, the electrical resistance is again increased to a second maximum as shown in curve II of Figure 2. The power supply can be so great that the electrolyte begins to boil violently and consequently cavitation occurs in space. The cavitation gives rise to a temporary increase in the electrical resistance of the electrolyte, which manifests itself as a local maximum in the variation of the voltage U between the electrode and the workpiece during the machining pulses. Figure 4 shows in greater detail the variation of the voltage U with the local maximum U3max, which occurs there after the global minimum Umin. It should be noted that such violent cavitation can be avoided by applying groups of machining impulses, groups which alternate with the passivation impulses. Such a pulse train is shown in Figure 5. In this way, the process proceeds more stably with a more accurate result using the same minimum space size. Figure 6 shows an electrical block diagram of an electrochemical machining arrangement according to the invention, which includes a power supply source 12 according to the invention. The power supply source 12 comprises a current source 14 for supplying the machining pulses, current source which supplies a current I whose magnitude is controllable by means of a control signal CS1, and a controllable voltage source 16 for provide the passivation pulses, voltage source which supplies an output voltage Up which is controllable by means of a control signal CSU. The negative terminal of the current source 14 and the negative terminal of the controllable voltage source 16 are both connected to the electrode 6 via a series resistor 18. The positive terminal of the current source 14 is connected to the work 2 via a switch 20. The switch 20 is closed at time intervals ti (see Figure 2) under the control of a signal Si, which is supplied by a synchronization unit 22. The positive terminal of the voltage source controllable 16 is connected to the work piece 2 via a switch 24. The switch 24 is closed at time intervals tu (see Figure 2) under the control of a signal Su, which is also supplied by the synchronization unit 22 , which also synchronizes the motor 10. The analog voltage U between the electrode 6 and the work piece 2 is measured on the terminals 32 and 34 by means of an analog-to-digital converter 26 and is converted into a digital signal. DU, which is stored, analyzed and processed on a computer 28. Current I through space is measured by measuring the voltage drop across the series resistor 18 on terminals 36 and 38 by means of a second converter from analog to digital 30, which converts the drop of the analog voltage into a digital signal DI, which is processed by the computer 28 in a manner similar to the digital signal DU. Instead of a series 18 resistance, a current transformer or any other suitable interface can be chosen. The analog-to-digital converter 30 can be dispensed if at the appropriate times the input terminals of the analog-to-digital converter 26 are switched from the voltage measurement via terminals 32 and 34 to the current measurement via terminals 36 and 38 The synchronization unit 22, the analog-to-digital converters 26 and 30 and the computer 28 are supplied with the clock pulse (not shown in Figure 6), which ensure that data acquisition and data processing are synchronized with the appearance of alternating machining and passivation pulses and electrode oscillation. The position of the table 4 is verified by means of a position sensor 40, which supplies a signal DS, which is a measure of the displacement of the table 4. The computer 28 generates the SCI control signal for the current source 14 and the control signal CSU for the controllable voltage source 16 via suitable interfaces 42 and 44, which can be constructed, for example, as digital-to-analog converters. The angle of rotation of the crankshaft 8 is measured by means of a sensor 46, which supplies a signal DP to the computer 28, which signal is a measure of the relative distance between the electrode 6 and the work piece 2.

By controlling the feed rate Vk of the table 4 the space 5 can be adjusted in such a way that the local maximum U3max occurs as shown in Figure 4. This local maximum can be detected by analyzing the voltage U by means of the analog-to-digital converter 26 and the computer 28 or by means of an oscilloscope. However, if desired, any other operation point of the size of the space 5 can be chosen, ie also one for which the local maximum U3max does not occur in the voltage U. Figure 7 illustrates the effect of the passivation pulses . The amplitude of the voltage Up of the controllable voltage source 16 is selected to form layers of passivation PL in the machining cavity in the workpiece 2. However, the amplitude of the voltage Up is not so high that the workpiece is Dissolve neither so high that the passivation layers dissolve again. Due to the oscillating movement the distance d2 entered the end face of the electrode 6 during the machining pulses, is smaller than the distance di between the side wall of the machining cavity and the electrode 6. In the case of a correct choice of the amplitude and duration of the machining pulses is achieved that the work piece dissolves only frontally, ie on the side opposite the face of the end of the electrode 6 in the feed direction, and not in the place of the layers of passivation PL. This results in very good reproduction accuracy, the shape of the cavity in the workpiece follows the shape of the electrode 6 very accurately. Intricate profiles and perforated slopes can be achieved with an accuracy of 10 arc minutes. The locally deposited passivation layers PL provide not only a high machining accuracy, but also a better energy efficiency and a higher machining speed. This is because no energy is wasted for the undesirable removal of material from the side walls of the machining cavity. For an optimum effect therefore, it is desirable that the voltage Up of the passivation pulses have an amplitude which is not greater than that of the passivation layers PL or even that dissolves the work piece 2 and that is not too much. small that is not enough or hard passivation layers are formed. In both cases, the machining pulses will dissolve the workpiece 2 whenever possible and will produce a relatively large machining cavity in all directions and therefore reduce the reproduction accuracy. The optimal amplitude of the passivation pulses is that amplitude for which the resistance of the space 5 is greater. This is why then the growth of the passivation layers PL, which has a poor electrical conduction, is maximum and the precision of reproduction is also maximum. To achieve an optimum adjustment of the voltage amplitude of the passivation pulses the electrochemical machining arrangement (Figure 6) performs an adjustment procedure in which the Up voltage of the passivation pulses is gradually increased from zero volts to the Uap voltage, to which the workpiece 2 enters the anode solution, during a plurality of successive oscillations of the electrode 6. For this purpose, the computer 28 applies a suitable control signal CSU to the controllable voltage source 16 via the interface 44.

After each increase in voltage Up the resistance of the space 5 is measured by means of the analog to digital converters 26 and 30. The value of the measured resistance and the corresponding control signal CSU are stored as numerical values in the main memory of the device. the computer 28. Of all the resistance values found, the computer determines the largest value and the associated amplitude of the voltage Up. The adjustment procedure now ends and the machining process continues for a given time TM, using the voltage amplitude Up so found. As a result of the oscillatory movement of the electrode 6, the distance between the workpiece 2 and the electrode 6 in the feed direction changes continuously during the passivation pulses. Each value of the distance between the workpiece and the electrode corresponds to another optimal amplitude of the voltage of the passivation pulses. To allow this, the time span of the passivation pulse is divided into intervals. The optimum amplitude for each time interval is now determined, the space resistance is maximum in that time interval. After completing the adjustment procedure, the computer 28 supplies such a series of control signals to the controllable voltage source 16 within the time lapse of each passivation pulse, since the amplitude of the passivation pulse gives a variation which is optimized by the variable size of the space. An example of such varying amplitude of the passivation pulses is given in curve III of Figure 2. This elaborate adjustment procedure will now be described in greater detail with reference to the diagrams of Figure 8 and a flow diagram in the Figures 9A and 9B. Figure 8, curve I shows the distance S between the work piece 2 and the working electrode 6. The rotation of the crankshaft 8 produces a sinusoidal variation of the distance S, which reaches a minimum Smin during the machining pulses MP. Each revolution of the crankshaft 8 corresponds to an oscillation having a period T. The adjustment procedure covers a group of m oscillations, and consequently has a duration mT. The adjustment procedure, that is, the group of m oscillations, is followed by a machining period TM, in which, the work piece is machined further by means of the machining pulses MP and the passivation pulses PP which they have a variation of amplitude determined in the preceding adjustment procedure. The duration of the machining period TM depends on the operating conditions and can be set according to the needs. After completing the machining period TM, the adjustment procedure, which again covers m oscillations, is repeated. The number of times the adjustment procedure is repeated also depends on the operating conditions and the desired result. In the simplest case, the adjustment procedure is performed only once, and the workpiece is electrochemically machined successively in the next machining period. Each group has a sequence number i that goes from 1 to a value determined by the total duration of the machining process. Each oscillation in group i has a sequence number j that goes from 1 to m. In addition, each oscillation, that is, also the oscillations in the machining period TM, is divided into time intervals of a length Dt. Each interval has a sequence number k, which ranges from 1 to n. In Figure 8, each passivation pulse PP has been divided into 8 intervals, that is, n = 8, but obviously a larger or smaller number of intervals is also possible. The number of intervals required depends on the magnitude and the change with time of the relative movement between the work piece and the electrode. More ranges result in the resolution with which the optimum waveform of the amplitude of the voltage of the given passivation pulses is raised, and the precision position is improved. Curve II in Figure 8 shows the gradual increase in the amplitude of the passivation pulses. In the oscillation j = 1, the first step is applied, starting from zero volts. For all the intervals k = 1 to k = n, the steps are the same. In addition, the penultimate oscillation of the sequence number j = m-1 and the last oscillation of the sequence number j = m are shown. In the last oscillation that has the sequence number j = m, the amplitude of the voltage is equal to the voltage Uap at which the workpiece enters the dissolution of the anode. After expiring each time interval k (k = l ... n), the resistance R of the space is measured and stored in the memory of the computer. In addition, the corresponding value of the control signal CSU is stored as a numerical value. Those n resistance measurements are repeated for each oscillation j (j = l ... m), and the result is illustrated in curve III, in which the resistance values for the individual intervals are shown. For each interval, the maximum resistance Rmax is determined in the series of m measurements. It has been assumed, by way of example, that the values of the resistance per interval measured in the penultimate oscillation have the sequence number j = m-1, they are also the maximum resistance values Rmax (j = m-1, k = 1) to Rmax (j = m-1, k = n) for each interval. However, this is not necessary. The maximum resistance of the space for each individual interval k can be found in oscillations that have a different sequence number j. The computer knows the value of the corresponding control signal CSU for each value found for the maximum resistance Rmax. After completing the adjustment procedure, that is, in the machining period TM, the computer 28 generates the corresponding values of the CSU control signal in the correct sequence within the time lapse of each passivation pulse. The curve IV in Figure 8 gives an example of the variation of the voltage U through space in the machining period TM. The machining process and adjustment procedure proceed as shown in the flow diagrams of Figures 9A and 9B. The blocks in those Figures have the following inscriptions: BO home Bl: i = 1 B2: U * k = 0, k = 1 ... n B3: R * = 0, k = 1 ... n B4: Ukn = 0, k = 1 ... n B5 : j = 1 B6: check DP switch 20 ON; switch 22 OFF generate machining pulse B7: k = 1 B8: Ukji = (Ukji + dU) < Uap switch 20 ON; switch 22 OFF B9: wait Dt B10: measure I ^ JÍ BU: Rkji = Ukji / Ikji B12: Rkji > R * k? B13: R * k = Rkji B14: U * k = Ukji B15: k = k + 1 B16: k > n? B17: j = j + 1 B18: j > m? B19: ECM (U * k, TM) B20: i = i + 1 B21: stop ECM? B22: End In block Bl, the sequence number i of the group is set to the initial value of 1. In block B2, all individual optimal voltages U * for all intervals k are set to the initial value of zero. In block B3, all individual maximum resistance values R * for all intervals k are set to the initial value of zero. In block B4, the initial values of the amplitudes of the passivation pulse to be increased by all the intervals k, are set to zero. In block B5, the counter j, which keeps track of the number of oscillations that have elapsed, is set to the initial value of 1. After the assignment of these initial values, the machining process begins. In block B6, the DP signal is verified, which indicates the position of the electrode. In the case of the correct position, the current source 14 is connected by opening the switch 20 and the controllable voltage source 16 is turned off by opening the switch 24. Subsequently, a machining pulse is applied. This machining impulse has a given duration, which is also determined by the computer. After the machining pulse has ended, the interval counter k is set to a value of 1 in block B7. In block B8, the amplitude Ukji in the kth step of the jesus oscillation of the iéséssi? Mmoo group of the passivation impulse, is increased by a value of one step dU. The resulting amplitude should not exceed the Uap voltage.

In addition, the current source 14 is disconnected by opening the switch 20 and the controllable voltage source is switched on by closing the switch 24. Subsequently, a waiting time of the period of a Dt interval in the block is observed.

B9 After this, in the BIO block the instantaneous value of the current Ikji is stored in the késl or interval of the jési to oscillation. The ith group is measured and stored. In block 11, the value of the instantaneous resistance Rkji is calculated by dividing the instantaneous voltage Uk3i by the instantaneous current I ^ i. In block B12 it is verified whether the value of the instantaneous resistance Rkji thus found is greater than the value of the individual maximum resistance R * k of the interval. If this is not the case, a jump is made to block B15. If the value is greater, the value of the individual maximum resistance R * k becomes equal to the value of the instantaneous resistance Rkji, which is done in block B13. In addition, in block B14 the corresponding individual optimum voltage U * is made equal for the instantaneous value Uk3i. In block B15, it is examined whether the interval control k is greater than n. If this is not the case, all the intervals have not yet been traversed, and the program returns to block B8, the voltage for the next interval increases by one step, the current is measured, the resistance is calculated and the value of the Maximum resistance with the value of the associated instantaneous voltage are stored. This continues until all the intervals have been traveled. Once the intervals have been completed, the oscillation count j is increased by one in block B17 and compared with the value of m in block B18. If the number of oscillations that have elapsed is less than or equal to m, the program returns to block B6 and a machining pulse is subsequently applied, and in the subsequent passivation pulse the voltage is increased in one step. This continues by m oscillations. Subsequently, in block B20, the electrochemical machining process continues with the individual optimum range voltages U * k (k = l ... n) during the TM period. After this, in block B20, the counter of group i is increased by one. In block B12 it is decided if the machining process has lasted long enough. If the machining process must continue for a longer time, the group meter i must be increased before the decision to stop is made. A criterion for stopping the machining process can be, for example, the displacement of the table 4 by means of the signal DS of the position sensor 40 or the elapsed process time. If the machining process has not yet been completed, a return to block B2 follows and a new adjustment procedure begins, followed by another TM machining period. When the final value is reached, the machining process ends in block B22. The method and arrangement described above were used to machine a test sample. The material of the sample was 40X13 steel in an annealed condition, the machining area was 2 cm2 and the electrolyte was 8% NaN03. In the machining process, the voltage of the machining pulses was 7 V, the duration of the machining pulses was 2 ms, the electrolyte pressure near the entrance to the space was 350 kPa, the electrolyte temperature was of 18 ° C, the frequency of the oscillations of the electrode was 47 Hz, the amplitude of the oscillations was 0.2 mm. The voltage of the passivation pulses was +2.8 V in the case of a minimum space, and +3.8 V in the case of a maximum space +3.8 V. An analysis of the results of the machining has shown that, in comparison With conventional machining methods, the use of the electrochemical machining method according to the invention, provides an increase in machining productivity by a factor of 1.25 and a reduction in energy consumption by a factor of 1.2. The error of reproduction of the electrode to the surface to be machined was not greater than 0.01 mm. If desired, the passivation pulses shown in curve III of Figure 2 and curve IV of Figure 8 can be supplemented and / or can be alternated with electrical pulses of opposite polarity. The purpose, effect, and fixation of the voltage amplitude of the pulses of opposite polarity are described more fully in International Application WO 97/03781. Such Request describes between which optimum limits the amplitude of the voltage of the pulses of opposite polarity should be adjusted and, on the other hand, to prevent the electrode from dissolving and in this way the accuracy of the machining be reduced and, on the other hand, to achieve a high machining efficiency in combination with a well defined surface condition, for example in the form of a certain luster. In many aspects, the arrangement described in the International Application is similar to the arrangement shown in Figures 1 and 6. However, for the generation of voltage pulses of opposite polarity in the intervals between the machining pulses, the polarity of the source "Controllable voltage 16" (Figure 6) should be temporarily reversed, or an additional controllable voltage source of opposite polarity should be provided, as well as an additional switch comparable to switch 24. Curve II in Figure 10 illustrates how machining pulses alternate with negative voltage pulses. Instead of the positive passivation pulses, negative impulses are now applied, which gives the workpiece a high luster. Negative voltage pulses may be applied before, during or after completion of the machining method described hereinbefore. Figure 11 shows an alternative in which in the intervals between the machining pulses a negative voltage is first applied and subsequently a positive passivation pulse, whose waveform and amplitude are determined according to the adjustment procedure described hereinabove. In this way, it has been assumed that the electrode and the workpiece perform an oscillating movement with respect to each other, a machining pulse is applied during the smallest distance between the work piece and the electrode. Increasing the distance promotes the ease with which the electrolyte can be renewed. However, strictly speaking, such a change in distance is not necessary if the operating conditions and the desired results allow this. Instead of a revolving crankshaft, it is possible to use another drive mechanism to generate an oscillatory or other movement to change the distance between the electrode 6 and the workpiece 2. For this purpose, a drive construction can be used. electric or hydraulic with a pinion and a cogwheel, or a feed screw driven electrically or hydraulically. The electrode 6 can then be made to come into contact with the workpiece 2, after which the size is adjusted. During the machining process the size of the space is adapted to achieve a substantially constant feed rate, on average, which is substantially equal to the dissolution speed of the work piece 2.

Claims (13)

CHAPTER REIVINDICATOR OR Having described the invention, it is considered as a novelty and, therefore, the content is claimed in the following CLAIMS:

1. A method for electrochemically machining an electrically conductive workpiece by applying electrical machining pulses between the workpiece and an electrically conductive electrode, while electrolyte is supplied between the workpiece and the electrode, characterized in that the machining pulses alternate with electrical passivation pulses of the same polarity as the machining pulses, the voltage of the passivation pulses has an amplitude, which is unsuitable for dissolving the work piece and a passivation film on the work piece.

2. The method of compliance with the claim 1, characterized in that the amplitude of the voltage of the passivation pulses is adjusted at least once during the electrochemical machining, the amplitude of the passivation pulses in a series of successive passivation pulses is changed until the value of the resistance measured between the workpiece and the electrode have reached the maximum, after which the electrochemical machining is continued with an amplitude of the passivation pulse corresponding to the maximum value of the resistance.

The method according to claim 2, characterized in that the passivation pulses are divided into time intervals and for each individual time interval the instantaneous amplitude of the voltage of the passivation pulses is changed until the value of the measured resistance between the workpiece and the electrode has reached a maximum during the individual time interval, after which the electrochemical machining continues with pulses of passivation whose instantaneous amplitude varies according to the amplitude found for each time interval and which corresponds to the maximum of the value of the resistance in such a time interval.

4. The method according to claim 1, 2 or 3, characterized in that the distance is maintained between the work piece and the electrode, which is smaller during the machining pulses than during the passivation pulses.

The method according to claim 4, characterized in that the workpiece and the electrode make an oscillatory movement in relation to each other, the distance between the workpiece and the electrode reaches a minimum during the machining pulses.

6. The method according to claim 1, 2, - 3, 4 or 5, characterized in that in the intervals between the successive machining pulses additional electric pulses of opposite polarity are applied to the workpiece and the electrode, these latter mentioned impulses which have a voltage whose amplitude does not exceed the amplitude at which the electrode begins to dissolve in the electrolyte.

The method according to claim 1, 2, 3, 4 or 5, characterized in that in the time intervals between the successive machining pulses, the passivation pulses alternate with electrical pulses of opposite polarity, these latter mentioned impulses the which have a voltage whose amplitude does not exceed the amplitude at which the electrode begins to dissolve in the electrolyte.

8. An arrangement for electrochemically machining an electrically conductive workpiece, by applying electrical machining pulses to a workpiece and an electrically conductive electrode while supplying electrolyte between the workpiece and the electrode, characterized in that the array comprises : an electrode; - means for positioning the electrode and the workpiece in a spatial relationship to maintain a space between the electrode and the workpiece; - means for supplying electrolyte in space; - a first source of electrical power supply, which can be electrically connected to the electrode and the workpiece to supply machining pulses to the workpiece and the electrode; - a second source of electrical power supply of the same polarity as the first source of power supply and having an output voltage which is controllable by means of a control signal (CSU), second power supply source the which is electrically connectable to the electrode and the workpiece to supply passivation pulses to the workpiece and the electrode; - means for alternatively connecting the first and second sources of energy supply to the workpiece and the electrode; - means for generating a variable control signal for changing the output voltage of the second power supply source during successive passivation pulses; means for measuring during the successive passivation pulses the electrical resistance of the space between the workpiece and the electrode, at an instant during the passivation pulses and for storing the information values of the resistance which are representative of the resistance of the space at such time and to store the corresponding control signal values of the control signal (CSU) at such time; and means for calculating a maximum value for the information values of the resistance, and means for maintaining the control signal (CSU) for the second power supply source in the value of the control signal corresponding to the maximum value.

The arrangement according to claim 8, characterized in that the means for generating the variable control signal include means for changing the output voltage of the second power supply source at different instants within the time lapse of a pulse of passivation; the means for measuring and storing are adapted to store the information values of the resistance which are representative of the instantaneous resistance of the space at different instants within the passivation pulse and for storing the corresponding control signal values of the control signal at different times; - means for calculating which are adapted to calculate the individual maximum values of the information values of the resistance of the corresponding instants within successive passivation pulses and to generate a control signal having an instantaneous value, which in the different instants, is equal to the values of the control signal that correspond to the individual maximum values.

The arrangement according to claim 9, characterized in that the arrangement includes means for changing the distance between the electrode and the workpiece, a distance which is smaller during the supply of the machining pulses than during the supply of the passivation impulses.

The arrangement according to claim 10, characterized in that the arrangement includes means for producing the oscillatory movement between the workpiece and the electrode, and means for synchronizing the means for alternately connecting the first and second supply sources of energy with the oscillating movement of the work piece.

12. An electric power supply source for use in the electrochemical machining method of an electrically conductive workpiece, by applying electrical machining pulses between the workpiece and an electrically conductive electrode, while electrolyte is supplied between the workpiece and electrode, characterized in that the source of electrical power supply comprises: - a first source of electrical power supply, which can be electrically connected to the electrode and the workpiece to supply machining pulses to the workpiece. work and the electrode; - a second source of electrical power supply of the same polarity as the first source of power supply and having an output voltage, which is controllable by means of a control signal (CSU), second power supply source which can be electrically connected to the electrode and the workpiece to supply passivation pulses to the workpiece and the electrode; - means for alternatively connecting the first and second sources of energy supply to the workpiece and the electrode; - means for generating a variable control signal (CSU) to change the output voltage of the second power supply source during successive passivation pulses; means for measuring during the successive passivation pulses the electrical resistance of the space between the workpiece and the electrode at a time during the passivation pulses and for storing the information values of the resistance which are representative of the strength of the space in such a and to store the corresponding control signal values of the control signal at that instant; and - means for calculating a maximum value of the information values of the resistance, and means for maintaining the control signal (CSU) for the second power supply source in the value of the control signal corresponding to the maximum value. The power supply according to claim 12, characterized in that - the means for generating the variable control signal include means for changing the output voltage of the second power supply source at different times within the time lapse of a passivation impulse; the means for measuring and storing are adapted to store the information values of the resistance which are representative of the instantaneous resistance of the space at different instants within the passivation pulse and for storing the corresponding control signal values of the control signal at different times; - calculation means that are adapted to calculate the individual maximum values for all the information values of the resistance of the corresponding instants within successive passivation pulses and to generate a control signal having an instantaneous value, which in the different instants, is equal to the values of the control signal that correspond to the individual maximum values.