JPH0360611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention enables electrolysis in wire cut electrical discharge machining by applying a voltage of opposite polarity to that during electrical discharge machining between the wire electrode and the workpiece to reduce the average machining voltage to zero. The present invention relates to an electric discharge machining source that prevents electrolytic corrosion of workpieces.

Conventional technology In electric discharge machining that uses water as a machining fluid, electrolytic action occurs, and especially when rough machining workpieces that are susceptible to electrolytic corrosion such as cemented carbide, electrolytic corrosion occurs, resulting in disadvantages such as making the workpieces brittle. It was hot. Further, during finishing processing, an oxide film etc. were formed and stable electric discharge could not be generated. Furthermore, there were other drawbacks, such as selective electrolytic corrosion of particles due to electrolysis, which roughened the surface of the workpiece, resulting in poor finished surface roughness.
In order to prevent this, it is already known to apply a reverse voltage to the gap between the electrode and the workpiece when not machining, in contrast to when machining, thereby reducing the average machining voltage to zero and preventing electrolysis. be.

As a method of applying this forward and reverse voltage with a simple configuration, there is a method shown in FIG. 3. In Fig. 3, 1 is a wire electrode, 2 is a workpiece, 3 is a DC power supply, R is a resistor, C is a capacitor, and T is a transistor as a switching element. A periodic pulse signal is input to the base of the transistor T. death,
The transistor T is turned on and off, and while the transistor T is on, the capacitor C is charged from the DC power supply 3 through the workpiece 2, the wire electrode 1, the capacitor C, and the transistor T. Note that at this time, current also flows through the circuit including the DC power supply 3, the resistor R, and the transistor T.

Next, when the transistor T is turned off, the charging voltage of the capacitor C is applied between the workpiece 2 and the wire electrode 1 via the resistor R, and
This will cause a discharge to occur between the two.

In this way, when transistor T charges capacitor C, the work 2 side becomes positive and the wire electrode 1 side becomes negative, but when transistor T is off and the charging voltage of capacitor C is applied between work 2 and wire electrode 1. is applied to the wire electrode 1 side with a positive voltage and the workpiece 2 side with a negative voltage, and between the wire electrode 1 and the workpiece 2, positive and negative voltages are applied alternately.
The opposite voltage will be applied.

Problems to be Solved by the Invention However, in the conventional method described above, current flows both when charging the capacitor C to the resistor R and when discharging the charge from the capacitor C, and energy loss due to this resistor R is caused. It had the disadvantage of being large.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the drawbacks of the prior art and to obtain a bipolar discharge power supply that has a simple configuration, has little energy loss, and has good power supply efficiency.

Means for Solving the Problems The present invention provides a charging circuit that connects a wire electrode, a workpiece, a capacitor, and a first switching element in series and is connected to a DC power supply, and controls the on-off operation of the first switching element. The above problem was solved by connecting a second switching element, which performs on-off operations at opposite timings, in parallel with the series circuit of the wire electrode, workpiece, and capacitor of the charging circuit.

Function When the first switching element is turned on, current flows from the DC power supply to the first switching element, the capacitor, the workpiece, the wire electrode, and the DC power supply, charging the capacitor, and the first switching element is turned off and the second switching element is turned off. When the switching element is turned on, the charging voltage of the capacitor is applied to the gap between the workpiece and the wire electrode via the second switching element. As a result, voltages of opposite polarity are applied to the gap between the workpiece and the wire electrode when charging and discharging the capacitor, resulting in a bipolar discharge power source.

Embodiment FIG. 1 is a circuit diagram of an embodiment of the present invention.
2 is a wire electrode, 2 is a workpiece, 3 is a DC power supply, C is a capacitor, T1 and T2 are transistors as switching elements, and D1 and D2 are diodes. The wire electrode 1, the workpiece 2, the capacitor C, the first transistor T1, and the first diode D1 are connected in series to a DC power supply, and the second transistor T2 and the second diode D2 are connected in series,
It is connected in parallel with the series circuit of the wire electrode 1, work 2, and capacitor C. In this embodiment, the first transistor T1 is a PNP type transistor, and the second transistor T2 is a PNP type transistor.
It is composed of NPN type transistors, and a pulse as shown in FIG. 2b is input to the bases of both transistors T1 and T2. When one transistor is on, the other transistor is off. One transistor is turned off when the other transistor is turned on. Note that the first and second diodes D1 and D2 are inserted to protect the first and second transistors T1 and T2, respectively.

Therefore, when the first transistor T1 is on, the circuit from the DC power supply 3 to the DC power supply 3 through the first diode D1, the first transistor T1, the capacitor C, the work 2, and the wire electrode 1 is closed, and the circuit is closed to the DC power supply 3. will be charged. Next, when the first transistor T1 is turned off and the second transistor T2 is turned on, the charging voltage of the capacitor C is applied to the gap between the wire electrode 1 and the workpiece 2 via the second transistor T2 and the second diode D2. is applied, causing a discharge.

Now, assuming that the voltage of the DC power source 3 is E and the gap voltage between the wire electrode 1 and the workpiece 2 is _VG , the wire electrode 1 and the workpiece 2 are
To explain in detail the voltage V _G applied to the gap between the first and second transistors T1, FIG.
The pulse applied to the base of T2 in FIG. 2a represents the gap voltage V _G between the wire electrode 1 and the workpiece 2, and the positive pulse shown in FIG. 2b is applied to the first and second transistors T1, When applied to the base of T2, the first transistor T1 is turned on. At this moment, the voltage E of the DC power supply 3 is applied to the gap between the wire electrode 1 and the workpiece 2, with the workpiece 2 side being positive, but after that, the gap resistance between the wire electrode 1 and the workpiece 2 and the capacitance of the capacitor C are applied. The capacitor C is gradually charged by a time constant determined by , and as a result, the gap voltage V _G gradually decreases.
Next, when a negative pulse is applied to both bases, the second transistor T2 is turned on, and the charging voltage of the capacitor C is applied between the wire electrode 1 and the workpiece 2 with the wire electrode 1 side being positive.

That is, as shown in Figure 2a, the gap voltage
The rise and fall of V _G jumps by the voltage E of the DC power supply 3, applying a voltage of positive and negative polarity between the wire electrode 1 and the workpiece 2. When this operation is repeated, the voltage shown in Figure 2a is shown. As such, the area A1 above the 0v line and the area A2 below the 0v line are equal, and the average machining voltage is applied between the wire electrode 1 and the workpiece 2 to be 0.

Then, as shown in Fig. 2, both transistors T
1. If the duty ratio of the pulse that turns T2 on and off is 1/2 (the plus width and minus width are the same), the same voltage with different polarity will be applied alternately between the workpiece 2 and the wire electrode 1. By changing the pulse width (with a duty ratio of 1/2), this voltage can be varied from ±E/2 to ±E, and the intensity of the discharge pulse can be adjusted by changing the pulse width. Further, by changing the duty ratio of this pulse, the magnitude of the positive and reverse voltages applied to the gap between the wire electrode 1 and the workpiece 2 can be changed.

In addition, since the discharge current is made small during finishing machining, the stray capacitance of the first and second transistors T1 and T2 and the power supply will have an adverse effect. The effect can be reduced by inserting a resistor, inductor, etc. between the two. That is, a parallel circuit of a resistor and a switch may be inserted between the wire electrode 1 and the second diode D2, and the switch may be turned on during rough machining and turned off during finishing machining. In this case, the resistance only needs to have a small value, so energy loss can be reduced.

Effects of the Invention As described above, the present invention can provide a bipolar discharge power source that can apply bipolar voltages between a workpiece and a wire electrode with a simple configuration, and has low energy loss, resulting in high power supply efficiency. You can obtain processing power. Since a bipolar voltage is applied between the workpiece and the wire electrode, electrical corrosion and rust can be prevented even when water is used as the machining fluid, making it suitable for wire cut electrical discharge machining of cemented carbide. It is particularly useful because it is difficult to form an oxide film during finishing, resulting in stable processing.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figures 2a and b are diagrams showing the gap voltage and pulse waveforms applied to the base of the transistor in the same embodiment, and Figure 3 is a diagram of a conventional bipolar discharge. It is a circuit diagram of a processing power supply. 1...Wire electrode, 2...Work, 3...DC power supply, T1, T2...Transistor, C...Capacitor, D1, D2...Diode, V _G ...Gap voltage.

Claims (1)

[Claims] 1. A charging circuit in which a wire electrode, a workpiece, a capacitor, and a first switching element are connected in series and connected to a DC power supply, and a charging circuit that is connected in series to a DC power source and turns on and off at a timing opposite to the on-off operation of the first switching element. An electric discharge machining power supply characterized in that a second switching element that performs an on-off operation is connected in parallel with a series circuit of a wire electrode, a workpiece, and a capacitor of the charging circuit. 2. The electric discharge machining power supply according to claim 1, wherein a resistor is inserted and connected in series to a series circuit of a wire electrode, a workpiece, and a capacitor connected in parallel with the second switching element. 3. The electric discharge machining power supply according to claim 1, wherein an inductor is inserted and connected in series to a series circuit of a wire electrode, a workpiece, and a capacitor connected in parallel with the second switching element.