Generator for generating processing pulses at the electrode gap of a device for the electrochemical processing of workpieces

Abstract

A generator for generating processing pulses at the electrode gap (3) of a device for electrochemically machining workpieces (1), comprising a power supply device (7) and switching devices (9) for pulse-wise connection of the power supply device (7) to connecting cables (5, 6) that are led to the electrode gap (3), with a circuit (8, 9, 13, 15) for increasing the steepness of the edges (25, 27) of current pulses flowing through the electrode gap (3) by recuperating field energy stored in the connecting cables (5, 6) during the pulses, wherein the circuit (8, 9, 13, 15) is provided for recuperating field energy stored as a result of the inductance (10) of the connecting cables (5, 6) and for recuperating the field energy by charging a capacitor (13) by a current that the inductance (10) generates after the connecting cables (5, 6) have been separated from the power supply device (7) by the switching device (9). and the circuit (8,9,13,15) comprises a diode (8) preventing the discharge of the capacitor (13) via the power supply device (7), characterized in that the connecting cables (5, 6), the power supply device (7), the capacitor (13) and the diode (8) are connected in series in such a way that they are arranged on a common current path at least for the current flowing during the recuperation of the field energy stored in the connecting cables (5, 6).

Description

[0001] The invention relates to a generator for generating machining pulses at the electrode gap of a device for the electrochemical machining of workpieces, comprising a power supply device and switching devices for pulse-wise connecting the power supply device to connecting cables which are led to the electrode gap, with a circuit for increasing the steepness of the edges of current pulses flowing through the electrode gap by recuperating field energy stored in the connecting cables during the pulses, wherein the circuit for recuperating field energy stored as a result of the inductance of the connecting cables and for recuperating the field energy by charging a capacitor by a current which the inductance generates after the connecting cables have been separated from the power supply device by the switching device,is provided and the circuit comprises a diode preventing the discharge of the capacitor via the power supply device.,

[0002] When generating high-frequency machining current pulses flowing through the electrode gap, the problem arises that the increase in the current flowing through the electrolyte in the electrode gap after connecting the power supply unit to the connecting cables is limited by the inductance of the connecting cables. Accordingly, the pulse length within which a desired current strength is achieved in the electrode gap cannot be arbitrarily reduced, nor can the pulse frequency be arbitrarily increased.

[0003] DE 41 07 910 A1 describes a pulse generator for electrical discharge machining. It has a capacitor into which magnetic energy stored in a spark gap inductance is transferred in the form of electrical energy. The electrical energy temporarily stored in the capacitor can be discharged via the spark gap when a pulse is applied to a spark gap. The spark gap inductance includes, among other things, the wiring between the spark gap and the pulse generator.

[0004] Pulse generators for the aforementioned purpose are known from WO 2006 / 111 345 A1 and EP 1 714 725 A1. These pulse generators utilize a controllable current generator and a high-frequency electronic switch connected in series to commutation of the current in the microsecond range. To compensate for the influence of the inductance of the connecting cables, energy is stored in an inductance as field energy, and during the pulses, the energy is switched to the electrode gap to achieve a faster current rise.

[0005] The disadvantage of such a generator operating as a current pulse generator is that a short-term increase in the resistance created by the electrode gap results in corresponding increases in voltage, which can lead to electrical breakdown at the electrode gap. Furthermore, the frequency of the current pulses is adversely affected by the fact that a certain pause between pulses is necessary to build up the current in order to increase the current or to allow the current to rise. Furthermore, a complex control system is required to control the voltage and regulate the current.

[0006] Another pulse generator which uses additional voltage sources to be applied to the electrode gap to control the current increase is disclosed in DE 10 2006 008 994 A1.

[0007] The invention is based on the object of creating a new pulse generator of the type mentioned at the beginning, which makes it possible to generate current pulses with pulse lengths in the microsecond range at the electron gap with low construction costs.

[0008] The generator according to the invention which achieves this object is characterized in that the connecting cables, the power supply device, the capacitor and the diode are connected in series in such a way that they are arranged on a common current path at least for the current which flows during the recuperation of the field energy stored in the connecting cables.

[0009] Advantageously, the field energy inevitably built up in the inductance of the connecting cables during the duration of the pulses is used to increase the current rise per unit time during the next pulse and the steepness of the falling edge of the current pulse is increased by recuperation at the end of each current pulse.

[0010] Advantageously, according to the invention, the field energy inevitably built up during the pulse duration by the inductance of the connecting cables can be used to increase the steepness of the two pulse edges. The duration of the pauses between the pulses can thus be reduced compared to the pulse generator known from the prior art, and the pulse frequency can be increased accordingly.

[0011] The ability to generate current pulses with pulse lengths in the microsecond range opens up further possibilities for electrochemical workpiece processing, in particular, it enables higher-quality machining of titanium and titanium alloys. Furthermore, the high-frequency effects of electrochemical metal machining can be utilized, enabling even higher machining accuracy. The manufacturing effort for the generator according to the invention is significantly reduced compared to the aforementioned prior art generator.

[0012] In a preferred embodiment of the invention, the circuit for recovering the field energy is provided for applying a voltage to the connecting cables that is higher than the voltage of the power supply device. The increased voltage correspondingly increases the increase in current per unit time.

[0013] In a further preferred embodiment of the invention, the circuit for recuperating the field energy is provided for charging a capacitor by a current which the inductance generates after the connection cables have been separated from the power supply device by the switching device when the magnetic field built up by the inductance collapses.

[0014] It is practical to have a voltage that is higher than the voltage of the power supply device across this capacitor charged by the inductance.

[0015] The said circuit preferably comprises a switching device which can be switched from the blocking position to the through position together with the first-mentioned circuit.

[0016] It is advisable to apply the voltage across the capacitor, which is higher than the voltage of the power supply device, to the connecting cables via these two switching devices.

[0017] The power supply device, i.e. a current or voltage source, is preferably an adjustable device.

[0018] The invention will be further explained below with reference to an embodiment and the accompanying drawings relating to this embodiment. They show: Fig. 1 a schematic representation of a device for electrochemical machining of a workpiece, Fig. 2 a circuit diagram of a device in the Fig. 1 used pulse generator, and Fig. 3 is an oscillogram explaining the generation of a current pulse by a voltage pulse of the pulse generator according to the invention.

[0019] A device for electrochemically machining a metallic workpiece 1 by a machining electrode 2 with an electrolyte flowing through a gap 3 between the workpiece 1 and the electrode 2 comprises a pulse generator 4 and connecting cables 5 and 6 connecting the pulse generator 4 to the workpiece 1 and the electrode 2.

[0020] The pulse generator 4 has a voltage source 7 as its power supply, the voltage of which is adjustable. The voltage source 7 is connected via a diode 8 and an electronic switching device 9 to the connecting cables 5, 6, which have an inductance 10. The gap 3 between the workpiece 1 and the machining electrode 2 forms a load, which is simplified as a resistor 11.

[0021] A capacitor 13 and a diode 14 are connected in parallel to the electronic switching device 9, which receives a positive control voltage pulsed from a generator 12. A second electronic switching device 15, which also receives control pulses from the generator 12, can connect the capacitor 13 to ground potential.

[0022] A filter capacitor 16 is connected in parallel with voltage source 7. 17 and 18 denote protective diodes for the switching devices 9, 15. A resistor 19 represents the resistance of the switching devices 9 in the off state. A resistor 20 represents the resistance of a measuring branch. 21 denotes a protective resistor connected in parallel with capacitor 13.

[0023] When the pulse generator is in operation, with the switching devices 9,15 blocked, a direct voltage U Sof the voltage source 7 to the switching device 9. By current flowing through the diode 14 and / or the protective diode 17, the capacitor 13 is charged with the voltage U S the voltage source 7.

[0024] When a positive control voltage pulse is generated by the control pulse generator 12, the interruptions by the switching devices 9, 15 are canceled and at least the voltage U S the voltage source 7 is applied to the series circuit of the inductance 10 and the gap resistor 11, initially exclusively to the inductance 10. A current I begins to flow through the connecting cables 5, 6, the initial time-related increase İ of which is proportional to the applied voltage.

[0025] When the positive control voltage is switched off at the end of the control voltage pulse, the switching devices 9, 15 interrupt the relevant line branches. The current I flowing through the inductor 10 cannot drop instantly to zero and, with current flow through the diodes 8 and 14, causes the capacitor 13 to charge. When the voltage of the capacitor 13 exceeds the voltage U S the voltage source 7, the diode 8 prevents a current that discharges the capacitor 13 from flowing through the voltage source 7.

[0026] When the switching devices 9,15 are switched into the conducting state again by the next control voltage pulse of the control pulse generator 12, the capacitor 13 is charged via the switching devices 9,15 up to the level of the voltage U S the voltage source 7. If the voltage falls below U S Due to the voltage of the capacitor 13, the voltage U Sthe voltage source 7 via the diode 8 and the switching device 9 via the series circuit of the inductance 10 and the resistor 11.

[0027] By charging the capacitor 13 to a voltage greater than the voltage U S of the voltage source 7, an increased voltage is available at the connecting cables 5, 6 in front of the inductor 10 when a control pulse is switched on by the generator 12. Due to the proportionality between the current increase per time λ and the voltage, a steeper rise in the current pulses flowing through the gap resistor 11 results. The falling edge of the current pulses also becomes steeper due to the charging of the capacitor 13 described above.

[0028] Turn 22 in Fig.Figure 3 shows the voltage drop across the connecting cables 5, 6, across the inductance 10 and the gap resistor 11. Curve 23 represents the resulting current flowing through the electrode gap 3 and the resistor 11, respectively. At time t1, the switching devices 9 and 15 switch to conduction; at time t2, the conduction is interrupted again. After time t1, the voltage across the connecting cables 5, 6 upstream of the inductance 10 increases during the discharge of the capacitor 13, as shown by voltage peak 24. This increase results in a steep rise in the current, as shown by edge 25. At time t2, at which the switching devices 9, 15 interrupt again, the voltage at the connecting cables 5, 6 in front of the inductance 10 drops steeply due to the charging of the capacitor 13 and a negative voltage peak 26 occurs. The negative voltage peak 26 ensures a correspondingly steep falling edge 27 of the current pulse.

Claims

[1] Generator for generating processing pulses at the electrode gap (3) of a device for the electrochemical processing of workpieces (1), comprising a power supply unit (7) and switching devices (9) for pulse-wise connecting the power supply unit (7) to connecting cables (5, 6) which are led to the electrode gap (3) with a circuit (8, 9, 13, 15) for increasing the steepness of the edges (25, 27) of current pulses flowing through the electrode gap (3) with recuperation in the connecting cables (5, 6) during the pulses of stored field energy, wherein the circuit (8, 9, 13, 15) is for recuperating field energy stored as a result of the inductance (10) of the connecting cables (5, 6) and for recuperating the field energy by charging a capacitor (13) by a current which the inductance (10) after disconnection of the connecting cables (5, 6) from the power supply unit (7) by the switching device (9) generated, is provided for and the circuit (8,9,13,15) includes a diode (8) that prevents the discharge of the capacitor (13) via the power supply device (7), , characterized by , that the connecting cables (5,6), the power supply unit (7), the capacitor (13) and the diode (8) are connected in series such that they are arranged on a common current path at least for the current which flows during the recuperation of the field energy stored in the connecting cables (5,6). [2] Generator according to claim 1, characterized by , that the circuit (8,9,13,15) is intended for the recuperation of the field energy stored during the connection of the power supply device (7) with the connecting cables (5,6). [3] Generator according to claim 1 or 2, characterized by , that the circuit (8,9,13,15) is designed to recuperate field energy by applying a voltage to the connecting cables (5,6) that is higher than the voltage of the power supply unit (7). [4] Generator according to claim 3, characterized by , that the increased voltage is across the capacitor (13) charged by the inductor (10). [5] Generator according to any one of claims 1 to 4, characterized by , that the circuit (8,9,13,15) includes a switching device (15) which can be switched from blocking position to through position together with the first-mentioned circuit (9). [6] Generator according to claim 5, characterized by , that the voltage above the capacitor (13), which is higher than the voltage of the power supply device (7), can be applied to the connecting cables (5,6) via the two switching devices (9,15). [7] Generator according to any one of claims 1 to 6, characterized by , that the power supply device (7) is an adjustable device.

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