JPH0679532A - Electric discharge machining process and its device - Google Patents

Abstract

PURPOSE:To accelerate electric discharge machining speed by letting the wave form of discharge current steeply rise between each electrode of an electric discharge machine and a work. CONSTITUTION:It is noted that inductance has a function of trying to maintain current having been flowing as is, electric discharge machining is thereby carried out in such a way that feeder lines LN1 and LN2 are connected to electric discharge electrodes 7 and 8 so as to let working current be supplied to the feeder lines from a power supply 6. A side path 14 and a transistor switch 13 are provided in the vicinity between the electrodes of the feeder lines, current at a specified level is supplied to the feeder lines from an auxiliary power supply 11 in advance with the transistor switch 13 closed before electric discharge between the electrodes is started, it is thereby possible that the wave form of discharge current steeply rises by supplying working current to both the electrodes via the feeder lines with the transistor switch 13 closed in response to detection of electric discharge started between the electrodes on the part of an electric discharge detecting section 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining method and apparatus, and more particularly to an electric discharge machining method and apparatus for improving machining speed.

[0002]

2. Description of the Related Art In an electric discharge machine such as a die-sinking electric discharge machine or a wire electric discharge machine, a pole between a machining electrode (hereinafter simply referred to as "electrode") and a work electrode (hereinafter simply referred to as "workpiece") is used. A voltage is applied between them to perform electric discharge machining on the work. As a power source in an electric discharge machine, usually, for example, 150 to 30
A high-voltage power supply of 0 V and a low-voltage power supply of about 70 to 100 V are used. After the electric discharge is started between the electrode and the work by the high-voltage power supply, the low-voltage power supply (main machining current) is supplied between the electrodes to perform electric discharge machining. To do. The supply of current from these power sources to the electrodes and the work is performed via a power supply line (cable).

By the way, the machining speed at the time of machining a sintered alloy by a die-sinking electric discharge machine or machining by a wire electric discharge machine is
The same average current varies depending on the pulse discharge current waveform supplied from the power supply. For example, processing using a current waveform having a gradual rise as shown in FIG. 9A (usually used when processing iron with copper as an electrode,
The machining speed is several times higher when using a pulsed current with a steep rising waveform as shown in Fig. 7 (b) (the consumption of the electrode is large), compared with the low consumption of the electrode that consumes less. It will be faster. Normally, the pulse voltage supplied from the power source is a rectangular wave pulse with a sharp rise and fall as shown in FIG. 7C, but the power supply line connecting the power source and the machine (electrode, work) has an inductance component. Because of this, the waveform of the current flowing between the poles has a slow rising waveform as shown in FIG. 4A, and it is difficult to improve the processing speed.

FIG. 7 shows a block diagram of a power supply system of a conventional electric discharge machine. The output of the high-voltage pulse power supply including the high-voltage power supply 1, the transistor switch 3 and the resistor R2 is connected to the power supply lines LN12 and LN11, and the electrode 7
And a pulse voltage is supplied to the work 8. Similarly, the output of the low-voltage pulse power source, which is composed of the low-voltage power source 6, the transistor 4, the resistor R1, and the diode D for preventing backflow from the high-voltage power source, is also connected to the power supply lines LN12 and LN11, and the electrode 7
And a pulse voltage is supplied to the work 8. ON / OFF control of the transistors 3 and 4 is performed as follows. That is, the pulse control unit 10 first sends a signal for turning on the transistor 3 to the preamplifier 2 to supply a high voltage between the electrodes. When the discharge detection unit 9 detects the start of discharge between the electrodes, for example, by monitoring a decrease in the voltage between the electrodes, a discharge detection signal is sent to the pulse control unit 10. Upon receiving this discharge detection signal, the pulse control unit 10 sends a signal for turning on the transistor 4 to the preamplifier 5,
Supply machining current to the gap. The pulse control unit 10 counts the time from the start of discharge, and when a predetermined time τON has elapsed, sends a signal to the preamplifiers 2 and 5 to turn off the transistors 3 and 4. After that, a predetermined rest time τOFF is provided and the above control is repeated.

FIG. 8 is a waveform timing chart for explaining the operation of the circuit configuration shown in FIG. The voltage between the electrode 7 and the work 8 is discharged by the high-voltage power supply supplied by the ON operation (c) of the transistor 3, and the voltage between the electrodes is as shown in (a), while the discharge start timing (d) of the transistor 4 is reached. The inter-electrode current flowing along with the ON operation of No. 2 has a waveform as shown in (b). This slow rise of the inter-electrode current is caused by the inductance component of the power supply line as described above.

As described above, in the conventional electric discharge machine, the rise of the machining gap current waveform becomes gradual due to the inductance component of the power supply line, which has been a major impediment to increasing the machining speed. In order to solve such an obstructing factor, conventionally, a coaxial cable or a twisted cable is used as an output cable (power supply line), or a current in the reverse direction is applied to the shield side of the coaxial cable as disclosed in JP-A-2-274423. A proposal has been made for a configuration that causes the current to flow.

[0007]

However, in the method using the coaxial cable or the twisted cable, since the machining gap (between the electrode and the work electrode) changes from the open state to the substantially short state, impedance to the coaxial cable is increased. Although matching cannot be achieved and the rising characteristic is improved, it is not sufficient. Further, even when a reverse current is applied to the shield side of the coaxial cable, it is impossible to use a non-inductive wiring with no return line for that purpose, so the problem still remains.

Therefore, an object of the present invention is to provide an electric discharge machining method and apparatus which makes the rise of the waveform of the electric discharge current flowing between the electrodes steep and enables the electric discharge machining speed to be increased.

[0009]

In order to solve the above-mentioned problems, an electric discharge machining method according to the present invention is arranged such that a power supply line and a pair of electrodes are connected to each other on the side of a feed line for supplying a machining current. A side path is provided in the power supply line, a current of a predetermined level is supplied to the power supply line through the side path before the discharge between the electrodes is started, and the side path is cut off when the discharge between the electrodes is started to flow a machining current between the electrodes. Is configured as follows. Further, the electric discharge machining apparatus of the present invention continues the power supply line connecting the power supply and both electrodes, the side path provided in parallel with the interelectrode space on the interelectrode side of the power supply line, and the current flowing through the side path. A bypass opening / closing means, a detecting means for detecting a discharge state between the electrodes,
Before the start of the discharge between the electrodes, the side opening / closing means is closed, and a current of a predetermined level is made to flow from the power source to the power supply line through the side path, and when the detecting means detects the start of the discharge between the electrodes, the side path is opened. An electric discharge machining apparatus comprising: a control unit that opens and closes the opening and closing unit to control a machining current from the power source to flow between the electrodes.

[0010]

In the present invention, paying attention to the fact that the inductance acts so as to maintain the current that has been flowing up to that point, a current of a predetermined level is made to flow in the power supply line in advance, and it responds to the detection of the discharge start between the electrodes. By supplying a machining current between the electrodes via the power supply line, the rising of the waveform of the discharge current flowing between the electrodes becomes steep, and the electrical discharge machining speed can be increased.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a configuration diagram for explaining an example of an electric discharge machining method and apparatus according to the present invention. In FIG. 1, the components designated by the same reference numerals as those in FIG. 7 indicate components having the same function. The high voltage power supply 1 is connected to the wire electrode 7 via the transistor switch 3, the resistor R2 and the power supply line LN3, and the low voltage power supply 6 is for preventing the high voltage backflow from the transistor switch 4, the resistor R1, the power supply line LN2 and the high voltage power supply 1. Is connected to the electrode 7 via the diode D1. The operation of the transistor switches 3 and 4 is
It is controlled by the control signal supplied from the pulse control unit 10 and amplified by the preamplifiers 2 and 5.

A side path 14 parallel to the gap between the feed lines LN1 and LN2 is provided between the feed lines LN1 and LN2, and a diode D2 is provided on the power supply side between the feed line LN2 and the feed line LN1 connected to the work 8. And the auxiliary power supply 11 are connected. A low voltage (for example, 5 to 10 V) is applied between the electrode 7 and the work 8 from the auxiliary power supply 11 via the diodes D2 and D1. Transistor switch (opening / closing means for bypass) 13
Is connected between the power feeding line LN12 side of the diode D1 and the work, and its operation is controlled by a control signal supplied from the preamplifier 12. The operations of the transistors 3, 4 and 13 are controlled by a control signal output from the pulse control unit 10 upon receiving a discharge detection signal from the discharge detection unit 9. The power supply line LN1 may be independent or shared with the low voltage power supply 1 and the high voltage power supply 6.

In this embodiment, the transistor 13 is first turned off.
A predetermined current is is supplied from the auxiliary power supply 11 to the feeding line LN1 and LN2 via the diode D2 in advance to supply the high voltage pulse from the high voltage power supply 1 and turn off the transistor 13 when the discharge is started. At the same time, the transistor 4 is turned on, and a discharge current is supplied from the low voltage power source 6 between the electrodes. As shown in FIGS. 2 (a) and 2 (b), the machining current rises up to the current that was previously passed through the feeder line at the moment of switching, and then gradually changes toward the set current value of the low-voltage power supply. That is, the transistor 1
When 3 is in the ON state, the current from the auxiliary power supply 11 flows through the power supply lines LN1 and LN2, and when it is in the OFF state, it flows between the electrode 7 and the work 8.

FIG. 3 is a waveform timing chart for explaining the operation of each part of the embodiment shown in FIG. When the transistor 13 operates (corresponding to the high level in FIG. 7D), a current as shown in (c) flows through the power supply lines LN1 and LN2 and the transistor 13. This current is (d)
The pulse gradually rises from the rising time t0 of
The predetermined current value is is reached. When the transistor switch 3 is operated at a time t1 when a time τd (time from the ON time t0 of the transistor switch 13) until the current value reaches approximately is is passed (e), between the electrode 7 and the work 8, Discharge ignition pulse (voltage between electrodes) as shown in (a)
Is supplied. The time τd varies depending on the material and length of the power supply line and can be experimentally determined in advance. When the discharge is started from a time point (discharge start point) t2 when the time τW until the discharge is started between the electrodes is started, an inter-electrode current as shown in (b) flows between the electrode 7 and the work 8. The inter-electrode current becomes a current with a steep rise due to the predetermined current value that has been passed through the power supply line in advance. At the start of discharge, (f)
As shown in, the transistor switch 4 is turned on and low voltage power is supplied between the electrodes. After the electric discharge machining time τon elapses, the transistor switches 3, 4 and 13 are in the OFF state during the time τa until the next electric discharge preparation time (time t3). In FIG. 7A, τoff indicates the time from the discharge end time t3 to the next time t1 ′ when the high voltage power is supplied.

FIG. 4 shows an example of the configuration of the auxiliary power supply 11. The output current is detected by the current sensor 112 and output to the voltage control unit 111. The voltage control unit 111 adjusts the variable power supply 110 based on the difference between the detected current and the predetermined value is to set the output current to the predetermined value.

FIG. 5 shows another configuration example of the auxiliary power source 11, in which a variable resistor 114 is connected in series to the power source 113 and the output current is controlled by adjusting the resistance value of the variable resistor 114.

FIG. 6 shows still another configuration example of the auxiliary power supply 11. In this example, the transistor switch 116 is connected in series to the power supply 115, the control signal from the pulse control unit 10 is supplied to the gate of the transistor switch 6 in synchronization with the OFF operation of the transistor switch 13, and a short circuit between electrodes occurs. Generation of large current is prevented. Also, it is separated when not needed. Further, if the power supply 115 is configured as shown in FIG. 4 or 5, the current can be controlled arbitrarily.

In FIG. 1, as the connection points a and b of the auxiliary power supply are closer to the output of the low-voltage pulse power supply (that is, the power supply 6 and the resistor R1), the connection points c and d between the transistor switch 13 and the power supply line are connected to the electrode 7 The closer to the workpiece 8 is, the shorter the length of the electric wire other than the above-mentioned power supply line is, and the influence of the inductance component of the electric wire can be reduced. The provision of the bypass 14 on the interelectrode side of the power supply line in parallel with the interelectrode means that the connection points c and d are provided in the vicinity of the interelectrode between the electrode 7 and the work 8. Furthermore, it goes without saying that a coaxial cable or a twisted cable can be used as the power supply line.

Although the case where the auxiliary power supply 11 and the diode D2 are provided has been described above, the present invention can be realized without the auxiliary power supply 11 and the diode D2. That is, before the discharge between the electrodes is started, the transistor 13 is closed and a current from the low-voltage power supply 6 is made to flow in the bypass 14 in advance. Is opened to allow the machining current from the low voltage power source 6 to act between the electrodes. In this case, since the current flowing through the power supply line in advance has the same level as the machining current, the waveform of the discharge current flowing between the poles becomes steeper. However, from the viewpoint of energy saving, it is preferable that the auxiliary power supply 11 is used and a lower level current than that of the low voltage power supply 6 is made to flow in the power supply line in advance.

[0020]

As described above, according to the electric discharge machining method and apparatus of the present invention, a sharp rising discharge current can be supplied, and the machining speed is greatly improved.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an electric discharge machining method and apparatus according to the present invention.

FIG. 2 is a current waveform diagram for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a waveform timing chart explaining the operation of the embodiment shown in FIG.

FIG. 4 is a diagram showing a configuration example of an auxiliary power supply of the embodiment shown in FIG.

5 is a diagram showing another configuration example of the auxiliary power supply of the embodiment shown in FIG.

FIG. 6 is a diagram showing still another configuration example of the auxiliary power supply of the embodiment shown in FIG.

FIG. 7 is a configuration block diagram of a conventional electric discharge machine.

FIG. 8 is a waveform timing chart for explaining the operation of the apparatus shown in FIG.

FIG. 9 is a waveform diagram for explaining problems of the conventional method and apparatus.

[Explanation of symbols]

 1 High-voltage power supply 2, 5, 12 Preamplifier 3, 4, 13 Transistor switch 6 Low-voltage power supply 7 Machining electrode 8 Work electrode 9 Discharge detection part 10 Pulse control part 11 Auxiliary power supply 14 Side path LN1, LN2, LN3 Feed line

Claims (3)

[Claims] 1. A side path is provided in parallel with the gap between the electrodes of a power supply line that connects a power source and both electrodes and supplies a machining current, and the bypass is provided through the bypass before the start of discharge between the poles. An electric discharge machining method characterized in that a current of a predetermined level is caused to flow through a power supply line, and when the electric discharge between the electrodes is started, the bypass is cut off so that a machining current is caused to flow between the electrodes. 2. A power supply line connecting a power source and both electrodes, a bypass provided on the interelectrode side of the power supply line in parallel with the interelectrode, and a bypass opening / closing means for continuing a current flowing through the bypass. Detecting means for detecting the discharge state between the electrodes, and closing the bypass opening / closing means before the start of the discharge between the poles to cause a current of a predetermined level from the power source to flow through the bypass to the power supply line to detect the current. An electric discharge machining apparatus comprising: a control unit that opens the bypass opening / closing unit and controls the machining current from the power source to flow between the poles when the means detects the start of discharge between the poles. 3. The electric discharge machining apparatus according to claim 2, wherein the power source includes a machining power source that supplies a current for electrical discharge machining between the electrodes, and an auxiliary power source that supplies a current of the predetermined level.