JP2918748B2 - Electric discharge machining method and apparatus - Google Patents

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 "work") is used. The workpiece is subjected to electrical discharge machining by applying a voltage therebetween. As a power source in the 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 high-voltage power supply starts discharging between the electrodes and the work, a low-voltage power supply (main machining current) is supplied between the electrodes to perform electric discharge machining. Do. The supply of current from these power sources to the electrodes and the work is performed via a power supply line (cable).

[0003] By the way, the machining speed at the time of machining of a sintered alloy by a die sinking electric discharge machine or machining by a wire electric discharge machine is as follows.
The average current varies depending on the pulse discharge current waveform supplied from the power supply. For example, processing using a current waveform with a gradual rise as shown in FIG. 9A (usually used when processing iron using copper as an electrode,
The processing speed is several times higher when using a pulse current having a steep rising waveform as shown in FIG. Speed up. Normally, the pulse voltage supplied from the power supply is a rectangular wave pulse having a sharp rise and fall as shown in FIG. 3 (c), but the power supply line connecting the power supply and the machine (electrode, work) has an inductance component. Therefore, the waveform of the current flowing between the poles has a slow rising waveform as shown in FIG. 3A, and it is difficult to improve the processing speed.

FIG. 7 is a block diagram showing a configuration of a power supply system of a conventional electric discharge machine. The output of a high-voltage pulse power supply comprising a high-voltage power supply 1, a transistor switch 3 and a resistor R2 is connected to power supply lines LN12 and LN11,
And a pulse voltage is supplied to the work 8. Similarly, the output of the low-voltage power supply 6, the output of the low-voltage pulse power supply including the transistor 4, the resistor R1, and the diode D for preventing backflow from the high-voltage power supply are also connected to the power supply lines LN12 and LN11.
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 controller 10 first sends a signal to turn on the transistor 3 to the preamplifier 2 and supplies a high voltage between the electrodes. When the discharge detection unit 9 detects the start of the 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 to turn on the transistor 4 to the preamplifier 5,
Supply machining current between the poles. The pulse controller 10 counts the time from the start of the discharge, and sends a signal to the preamplifiers 2 and 5 to turn off the transistors 3 and 4 when a predetermined time τON has elapsed. Thereafter, a predetermined pause time τOFF is provided, and the above-described control is repeated.

FIG. 8 is a waveform timing chart for explaining the operation of the circuit configuration shown in FIG. The discharge between the electrode 7 and the work 8 is caused by the high voltage power supplied by the ON operation (c) of the transistor 3, resulting in a voltage between the electrodes as shown in (a). On the other hand, at the discharge start timing (d) of the transistor 4. The inter-electrode current flowing as a result of the ON operation has a waveform as shown in FIG. This slow rise of the interpole current is caused by the inductance component of the feeder line as described above.

As described above, in the conventional electric discharge machine, the rise of the current waveform between the electrodes becomes gentle due to the inductance component of the power supply line, and this has been a major obstacle to increasing the machining speed. In order to solve such an obstruction factor, conventionally, a coaxial cable or a twisted cable is used as an output cable (feeding line), or a current in a reverse direction is applied to a shield side of the coaxial cable as disclosed in JP-A-2-274423. Has been proposed.

[0007]

However, in the method using a coaxial cable or a twisted cable, since the machining gap (between the electrode and the work electrode) changes from an open state to a substantially short state, the impedance to the coaxial cable is reduced. Matching cannot be achieved, and the rising characteristics are improved but not sufficient. Also, in the case where a reverse current flows on the shield side of the coaxial cable, the problem cannot be solved because it is impossible to use a non-inductive wiring with no inductance for the return line.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric discharge machining method and apparatus capable of increasing the electric discharge machining speed by steepening the rise of a discharge current waveform flowing between electrodes.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an electric discharge machining method according to the present invention comprises a power supply line connected to both electrodes and a power supply line for supplying a machining current. A bypass is provided, and a predetermined level of current is supplied to the power supply line via the bypass before the discharge between the gaps is started, and a high-voltage pulse voltage is supplied from the power supply to start the discharge between the gaps. It is configured to cut off the bypass and start a machining current between the poles after the start of the discharge between the poles. In addition, the electric discharge machining apparatus of the present invention includes a power supply line that connects a power supply and both electrodes, a bypass provided in parallel with the gap between the poles of the power supply line, and interrupts a current flowing through the bypass. By-pass opening and closing means, detecting means for detecting a discharge state between the poles, and closing the bypass opening and closing means before the start of discharge between the poles to supply a predetermined level of current from the power supply to the power supply line via the bypass. Control means for controlling so that the bypass opening / closing means is opened and the machining current from the power supply flows between the poles when the detection means detects the start of discharge between the poles.

[0010]

In the present invention, attention is paid to the fact that the inductance acts so as to maintain the current that has flowed so far, and a predetermined level of current is supplied to the power supply line in advance to respond to the detection of the start of discharge between the electrodes. By supplying the machining current between the poles via the feeder line, the rising of the discharge current waveform flowing between the poles is sharpened, and the electric discharge machining speed can be increased.

[0011]

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

A bypass 14 is provided in parallel between the power supply line LN1 and the power supply line LN2, and a diode D2 is provided on the power supply side between the power supply line LN2 and the power supply 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 (side opening / closing means) 13
Is connected between the power supply line LN12 side of the diode D1 and the work 8, and its operation is controlled by a control signal supplied from the preamplifier 12. Transistors 3, 4 and 13
Is controlled by a control signal output from the pulse control unit 10 in response to 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 on by O
N, a predetermined current is passed between the power supply lines LN1 and LN2 from the auxiliary power supply 11 via the diode D2 in advance, a high-voltage pulse is supplied from the high-voltage power supply 1, and the transistor 13 is turned off when the discharge starts. At the same time, the transistor 4 is turned on, and a discharge current is supplied from the low-voltage power supply 6 between the electrodes. As shown in FIGS. 2 (a) and 2 (b), at the moment of switching, the machining current rises to the current previously supplied to the power supply line, and then gradually changes toward the set current value of the low-voltage power supply. That is, transistor 1
When the switch 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 the switch 3 is in the OFF state, flows between the electrode 7 and the work 8.

FIG. 3 is a waveform timing chart for explaining the operation of each section of the embodiment shown in FIG. When the transistor 13 operates (corresponding to the high level in FIG. 4D), a current as shown in FIG. 4C flows through the power supply lines LN1 and LN2 and the transistor 13. This current is (d)
Gradually rises from the rising time t0 of the pulse shown in
The above-mentioned predetermined current value is is reached. When the transistor switch 3 is operated at a time point t1 when a time τd (time from the ON time point t0 of the transistor switch 13) until the current value reaches approximately is (e), a gap between the electrode 7 and the work 8 is generated. Discharge firing pulse as shown in (a) (inter-electrode voltage)
Is supplied. The time τd differs depending on the material and length of the power supply line, and can be experimentally predetermined. When the discharge is started from a time point (discharge start point) t2 at which a time τW until the discharge starts between the electrodes, a current between the electrodes as shown in FIG. The inter-electrode current is a current having a steep rise due to a predetermined current value previously flowing through the power supply line. At the start of discharge, (f)
As shown in (1), the transistor switch 4 is turned ON, and low-voltage power is supplied between the electrodes. When the electric discharge machining time τon elapses, the transistor switches 3, 4, and 13 are turned off during the time τa until the next electric discharge preparation time (time t3). In FIG. 9A, τoff indicates a time from the discharge end time t3 to the time t1 'at which the next high voltage power is supplied.

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

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

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

In FIG. 1, the closer the connection points a and b of the auxiliary power supply are to the output of the low-voltage pulse power supply (that is, the power supply 6 and the resistor R1), the closer the connection points c and d between the transistor switch 13 and the power supply line are to the electrodes 7 It is more preferable to be closer to the workpiece 8 or the work 8, and the length of the wires other than the above-described power supply line can be reduced, and the influence of the inductance component of the wires can be reduced. Providing the bypass 14 on the side between the poles of the power supply line in parallel with the poles means that the connection points c and d are provided near the gap between the electrode 7 and the work 8. Further, it goes without saying that a coaxial cable or a twisted cable can be used as the power supply line.

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

[0020]

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

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing one 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 for explaining the operation of the embodiment shown in FIG. 1;

FIG. 4 is a diagram showing one configuration example of an auxiliary power supply of the embodiment shown in FIG. 1;

FIG. 5 is a diagram showing another configuration example of the auxiliary power supply of the embodiment shown in FIG. 1;

FIG. 6 is a diagram showing still another configuration example of the auxiliary power supply of the embodiment shown in FIG. 1;

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

FIG. 8 is a waveform timing chart for explaining the operation of the device shown in FIG. 7;

FIG. 9 is a waveform chart for explaining a problem of the conventional method and apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High voltage power supply 2, 5, 12 Preamplifier 3, 4, 13 Transistor switch 6 Low voltage power supply 7 Processing electrode 8 Work electrode 9 Discharge detection part 10 Pulse control part 11 Auxiliary power supply 14 Bypass LN1, LN2, LN3 Feeding line

Claims (3)

(57) [Claims] 1. A side path is provided in parallel between a pole and a power supply line for connecting a power source and both electrodes and supplying a processing current, and a bypass is provided through the side path before the start of discharge between the poles. with flowing a predetermined level of current to the feed line, by supplying a high-voltage pulse voltage to start discharge between said electrode from said power source, discharge between the electrode
An electric discharge machining method , wherein after the start, the side path is cut off so that a machining current flows between the poles. 2. A power supply line for connecting a power supply to both electrodes, a bypass provided in parallel with the gap between the poles of the power supply line, and a bypass opening / closing means for interrupting a current flowing through the bypass. Detecting means for detecting a discharge state between the electrodes; and closing the bypass opening / closing means before the start of the discharge between the poles, causing a predetermined level of current to flow from the power supply to the power supply line via the bypass, and performing the detection. An electric discharge machining apparatus comprising: control means for opening the bypass opening / closing means when the means detects the start of electric discharge between the poles, and controlling the machining current from the power supply to flow between the poles. 3. The electric discharge machining apparatus according to claim 2, wherein the power supply comprises a machining power supply for supplying a current for electric discharge machining between the poles and an auxiliary power supply for supplying the current at the predetermined level.