JPH059209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a machining power source in a wire cut electric discharge machining apparatus.

Conventionally known power supplies for wire cut electrical discharge machining include a capacitor connected in parallel in the gap between the wire electrode and the workpiece, and on/off control using a switching transistor for this capacitor. One is to process the workpiece using the energy stored in the capacitor during charging, and the other is to directly control the on/off of the current flowing through the gap between the electrodes using a switching transistor to machine the workpiece. There are things to process. However, the former method has a drawback in that the discharge current in the gap between the electrodes varies. This is because when charging a capacitor, the interelectrode voltage has a time constant due to the charging resistor, so if discharge occurs during the charging process, the discharge will have a low peak current value. Since the amount of energy removed by one discharge is determined by the magnitude of the discharge current, the surface roughness of the machined surface of the workpiece is determined by the largest value of the discharge current. However, since the machining speed is faster when the discharge current for each shot is larger, if the discharge current varies, the machining speed for surface roughness will decrease. Also,
An example of the latter is disclosed in Japanese Patent Publication No. 44-13195. Briefly, this has a circuit configuration including a main switching circuit with a large peak current value and a sub-switching circuit with a small peak current value and only applying voltage to the gap between the electrodes. In this device, a voltage is applied to the gap between the electrodes in the sub-switching circuit, and after detecting the occurrence of discharge in the gap, the main switching circuit is closed for a predetermined period of time to allow the desired current to flow. A uniform discharge current is obtained, thereby increasing the machining speed for the surface roughness of the machined surface of the workpiece.

FIG. 1 is a circuit configuration diagram showing a conventional machining power source for a wire-cut electrical discharge machining apparatus. In the figure, 1
2 is a wire electrode, 2 is a workpiece, and 3 is a power supply line such as a coaxial cable, and this power supply line 3 is connected to the gap between the wire electrode 1 and the workpiece 2. E ₁ is a voltage source, R ₁ is a resistor, and Tr ₁ is a transistor, which constitutes a sub-switching circuit (first switching circuit), and E ₂ is a voltage source, R ₂ to _{R o} are resistors, Tr ₂ to T _{r o} are transistors, and these constitute a main switching circuit (second switching circuit). 4 is an oscillation circuit that controls the transistors Tr ₁ to _{T 0} , and 5 and 6 are detection lines for detecting the occurrence of discharge in the gap between the electrodes.

Figures 2 a and b are diagrams showing the ideal inter-electrode voltage waveform and inter-electrode current waveform of the inter-electrode gap in Fig. 1, respectively, and Fig. 3 a and b are diagrams showing the actual inter-electrode gap in Fig. 1. FIG. 3 is a diagram showing the inter-electrode voltage waveform and inter-electrode current waveform, respectively. In each of the above figures,
I ₁ , I ₂ and V ₁ , V ₂ indicate current values and voltage values, respectively.

Next, the operation of the above-mentioned conventional machining power source for a wire-cut electrical discharge machining apparatus will be explained using FIGS. 1, 2 a and b, and 3 a and b. first,
Transistor Tr ₁ receives the signal from oscillation circuit 4 and
When turned ON, a voltage is applied to the gap between the poles. Therefore, after a certain delay time, a discharge occurs in the gap between the electrodes. When the oscillation circuit 4 detects the discharge in the gap between the electrodes through the detection lines 5 and 6, the transistor
All or some of Tr ₂ to T _ro are turned on to flow a current through the gap between the electrodes for a predetermined period of time, then transistors Tr ₁ to _{T ro} are turned OFF for a specified period of time, and transistor Tr ₁ is turned on again. This results in
By keeping the current waveform constant, it is possible to increase the machining speed with respect to the surface roughness of the machined surface of the workpiece 2. However, those described above also have drawbacks. That is, in normal wire cut electrical discharge machining, it is necessary to narrow the current pulse width and increase the peak current value. However, if the residual inductance in the main switching circuit and the power supply line 3 is large, the rise of the current is delayed, and a current waveform with a narrow current pulse width and a high peak current value cannot be obtained. For this reason, it is generally necessary to minimize the residual inductance of the main switching circuit and to use a low-inductance cable for the power supply line 3. However, if you do this, the stray capacitance of the circuit will increase, making it difficult to turn on the width switching circuit.
Then, first, this stray capacitance is charged, and when discharge occurs, an oscillating current flows into the gap between the electrodes due to the stray capacitance and the residual inductance in the current path. At this time, if the reverse half-wave of the oscillating current flows before the main switching circuit is turned on, the current in the gap between the electrodes may momentarily drop to zero and the discharge may be interrupted. This aspect is clearly illustrated in Figure 3, which shows that the transistor
Since Tr ₂ to Tr _o are ON, voltage source E ₂ is present in the gap between the electrodes.
The appearance of the voltage value V ₂ is illustrated.
Generally, it takes about several hundred nanoseconds from when a discharge occurs in the gap between the electrodes to when transistors Tr ₂ to _{Tr o} are turned on.
Since a time of ~1 μsec is required, the probability that the discharge will be interrupted during this time is quite high. As described above, when the discharge is interrupted, it becomes difficult for current to flow through the gap between the electrodes, resulting in a disadvantage that the machining speed is significantly reduced.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and includes a first switching circuit and a second switching circuit connected in parallel to the gap between the wire electrode and the workpiece. In a wire-cut electrical discharge machining power source that generates intermittent discharge using a switching circuit, a circuit formed by connecting an inductance and a capacitor in series is connected in parallel to the gap between the electrodes, and when a discharge occurs in the gap between the electrodes, the When the discharge occurs, the second switching circuit is turned ON for 1/4 cycle or 1/2 cycle of the current flowing through the inductance and capacitor.
and the current value is set to a current value that compensates for the inverse half wave of the current waveform of the oscillating current caused by the stray capacitance and residual inductance of the circuit, and The first switching circuit is equipped with a voltage source with a higher discharge voltage, and the second switching circuit is
It has a configuration that has a larger peak current value than the first switching circuit, eliminates discontinuation of discharge in the gap between the electrodes, and ensures that the desired current flows through the gap between the electrodes, thereby increasing the machining speed. It is an object of the present invention to provide a machining power source for a wire-cut electric discharge machining device that can prevent the deterioration.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a circuit configuration diagram showing a machining power source for a wire-cut electrical discharge machining apparatus which is an embodiment of the present invention. The same parts as in FIG. do. In the figure, 7 is an inductance (L) and 8 is a capacitor (C), and the inductance (L) 7 and the capacitor (C) 8 are connected in series and in parallel with the interpolar gap. The other circuit configurations are substantially the same as those shown in FIG. 1 above.

Figures 5a and 5b are diagrams respectively showing the interelectrode voltage waveform and interelectrode current waveform of the interelectrode gap in Figure 4, and Figures 6a to 6d are the A portion surrounded by the dashed-dotted line in Figure 5b. FIG. 3 is a diagram showing the current waveforms of the current waveforms decomposed and enlarged.

Next, regarding the operation of the machining power supply for the wire cut electric discharge machining apparatus which is an embodiment of the present invention described above,
This will be explained using FIG. 4, FIGS. 5 a and b, and FIGS. 6 a to d. First, transistor Tr ₁ is connected to oscillation circuit 4
When it receives a signal and turns on, voltage is applied to the gap between the electrodes. Therefore, after a certain delay time, a discharge occurs in the gap between the electrodes. Due to the occurrence of this discharge, an oscillating current due to the stray capacitance and residual inductance of the circuit begins to flow, and at the same time, the capacitor (C)
Current begins to flow from 8 through inductance (L) 7. When the oscillation circuit 4 detects discharge through the detection lines 5 and 6, all of the transistors Tr ₂ to _{T o}
Initially, some transistors are turned on to allow current to flow through the gap between the electrodes for a predetermined period of time, and then the transistors Tr ₁ to _{Tr o}
is turned off for a predetermined period of time, and transistor Tr ₁ is turned off again.
Turn it on. This aspect is clearly illustrated in Figures 5a and b and Figures 6a-d. In particular, in the diagrams showing the exploded and enlarged current waveforms of the part A surrounded by the dashed-dotted line in FIG. 5b, FIG. 6a shows the current waveforms from the sub switching circuit and the main switching circuit, and FIG. Figure 6c shows the oscillating current waveform due to the stray capacitance and residual inductance of the circuit.
shows the current waveform caused by the inductance (L) 7 and the capacitor (C) 8, and Fig. 6d shows the current waveform obtained by combining the current waveforms a to c above, and this combined current waveform is the actual polarity. This becomes a current between the electrodes that flows through the gap. Therefore, by appropriately adjusting the values of inductance (L) 7 and capacitor (C) 8, the reverse half wave of the oscillating current waveform as shown in Figure 6b can be compensated for, and the above-mentioned discharge can be achieved. It is possible to prevent interruptions. Here, the values of inductance (L) 7 and capacitor (C) 8 are 1/ of the current.
4 cycles or 1/2 cycle is set as the time from the occurrence of discharge until transistors Tr ₂ to _Tro of the main switching circuit turn on, and the current value is determined by the stray capacitance and residual inductance of the circuit. The current value may be set to compensate for the reverse half-wave of the current waveform of the oscillating current.

Here, numerical examples in a preferred embodiment of the present invention will be explained. The inductance of the conventionally used power supply line 3 must be about 0.1 μH or less, and the stray capacitance of such a low inductance cable is 0.01 μF.
It will be about. The inductance formed by the loop from one output end of the power supply line 3 through the wire electrode 1 and the workpiece 2 to the other output end of the power supply line 3 is approximately 0.3 μH. When the stray capacitance of the power supply line 3 of 0.01μF is discharged through the loop inductance of 0.3μH, and the no-load voltage is 90V, the peak current value of the oscillating current is
11.7A, and its half-wave width is 0.17 μsec, which corresponds to the current waveform in FIG. 6b. On the contrary,
Inductance (L) 7 as 0.8μH, capacitor (C)
When 0.04 μF is used as 8, the peak current value of the oscillating current is 14.5 A, and its half-wave width is 0.56 μsec, which corresponds to the current waveform in FIG. 6c. Also, after discharge occurs in the gap between the electrodes, the transistor
The time it takes for Tr ₂ to Tr _o to turn on is about 0.4 μsec with normal technology, which is shown in Figure 6 a.
It is expressed as the time from when current begins to flow from the sub switching circuit to when current begins to flow from the main switching circuit.

In the above embodiment, the case where the inductance (L) 7 and the capacitor (C) 8 are connected in series was explained, but the inductance ( L)7 may be realized by only the residual inductance of the power supply line 3 or by the residual inductance including the lead wire, and the same effect as in the above embodiment can be achieved.

As described above, according to the machining power supply for a wire-cut electric discharge machining apparatus according to the present invention, a sub-switching circuit equipped with a voltage source higher than the discharge voltage, and a main switching circuit having a peak current value larger than that of the sub-switching circuit. The configuration consists of an inductance and a capacitor connected in series in parallel with the gap between the wire electrode and the workpiece, which effectively prevents the discharge in the gap between the electrodes from being interrupted due to the stray capacitance and residual inductance of the circuit. In addition, it has the excellent effect of making the discharge current uniform and thereby preventing a decrease in the machining speed of the workpiece as much as possible.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram showing a machining power supply for a conventional wire-cut electrical discharge machining device, and Figs. 2 a and b show the ideal inter-electrome voltage waveform and inter-electrome current waveform for the inter-electrode gap in Fig. 1, respectively. Figures 3a and 3b are diagrams showing the actual inter-electrode voltage waveform and inter-electrode current waveform of the inter-electrode gap in Fig. 1, respectively.
The figure is a circuit configuration diagram showing a machining power supply for a wire-cut electrical discharge machining apparatus which is an embodiment of the present invention, and FIG.
and b are diagrams showing the inter-electrode voltage waveform and inter-electrode current waveform of the inter-electrode gap in Fig. 4, respectively, and Fig. 6 a
- d are diagrams each showing an exploded and enlarged current waveform of a portion A surrounded by a dashed-dotted line in FIG. 5b. In the figure, 1... wire electrode, 2... workpiece, 3... power supply line, 4... oscillation circuit, 5, 6
...detection line, 7 ... inductance (L), 8 ... capacitor (C), E ₁ , E ₂ ... voltage source, R ₁ to _Ro ... resistance, Tr ₁ to _{T o} ... transistor . In addition,
In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A wire-cut electrical discharge machining device that generates intermittent discharge by a first switching circuit and a second switching circuit, each connected in parallel to the gap between the wire electrode and the workpiece. In the machining power supply, a circuit formed by connecting an inductance and a capacitor in series is connected in parallel to the gap between the electrodes, and the current flowing through the inductance and the capacitor is 1/4 cycle or 1 when discharge occurs in the gap between the electrodes. /2 cycle is set to the time from the occurrence of the discharge until the second switching circuit is turned ON, and the current value is set to the inverse of the current waveform of the oscillating current caused by the stray capacitance and residual inductance of the circuit. A circuit configuration is provided in which the current value is set to compensate for the half wave, and the first switching circuit is provided with a voltage power source higher than the discharge voltage, and the second switching circuit has a current value higher than the first switching circuit. A machining power source for a wire cut electrical discharge machining device, characterized in that it has a configuration having a large peak current value. 2. A patent claim characterized in that the first switching circuit includes a capacitor, and the capacitor is charged with electric charge to generate a discharge, this discharge is detected, and a current is caused to flow from the second switching circuit. A machining power source for a wire cut electric discharge machining device according to item 1. 3. The machining power source for a wire-cut electrical discharge machining apparatus according to claim 1, wherein the inductance is realized by a residual inductance of a power supply source or a residual inductance including a lead wire of a capacitor.