JPS6350133B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrical discharge machining power supply in a wire electrical discharge machine.

Conventional technology In a wire electrical discharge machine that performs electrical discharge machining by discharging the charge stored in a capacitor through a current limiting resistor, after rough machining, the machined surface of the workpiece is improved in surface roughness or the shape is corrected. In this case, the surface roughness can be improved by reducing the machining power.
Therefore, in order to reduce the current pulse width, it is necessary to reduce the capacitance of the capacitor or to reduce the charging voltage of the capacitor. However, since there is stray capacitance in the circuit, reducing the capacitance of the capacitor is naturally limited. Furthermore, if the voltage stored in the capacitor is set too low, discharge becomes difficult to occur, so there is a limit to this as well.

Therefore, in order to obtain the best machined surface roughness, it is necessary to perform machining near the limit where machining becomes unstable, and the question is how to stabilize machining in such a region. is important. Experiments have shown that stable machining with good surface roughness can be achieved by increasing the voltage of the DC power supply that charges the capacitor and increasing the current limiting resistor.

This is because the gap between the electrode and the work increases or decreases during machining, and if the DC power supply voltage is low, it is difficult for discharge to occur when the gap becomes large, and if the discharge temporarily stops, even if the gap becomes smaller, the discharge will not occur. It is thought that this does not occur immediately and the discharge becomes unstable. However, if the voltage of the DC power source is high, it is difficult for the discharge to stop even if the gap becomes large, so even if the gap increases or decreases, the discharge easily occurs and stable discharge can be obtained.

In other words, in a wire electrical discharge machine, water exists as a machining fluid between the wire electrode and the workpiece, and as a result, a leakage current occurs between the electrode and the workpiece as an electrolytic current, and the capacitor is sufficiently charged to the DC power supply voltage. There isn't. This leakage current increases when the electrode and workpiece are close together and decreases when they are separated, so if the voltage of the DC power source is increased and the current limiting resistor is increased, the leakage current is small when the electrode and workpiece are apart, and the capacitor The charging voltage becomes higher, and discharge is more likely to occur even if the electrode and workpiece are far apart. Furthermore, if the electrode and workpiece are brought close to an appropriate value, the leakage current will be large and the charging voltage of the capacitor will be low, making it possible to obtain a good surface roughness.

For the reasons mentioned above, in order to obtain stable machining, the DC voltage should be high and the charging limiting resistance should be large, and in order to improve the surface roughness of the workpiece, the charging voltage of the capacitor should be lower. Therefore, in machining to obtain such microsurface roughness, the charging voltage is lowered and the machining is performed near the limit of stability or instability, but the distance between the wire electrode and the workpiece becomes smaller during machining. If the opposing area between the wire electrode and the workpiece increases, such as when machining too much or a recess, the leakage current will increase for the reasons mentioned above, and the charging voltage of the capacitor will drop too much, resulting in no discharge. .

Therefore, in order to eliminate this drawback, it is necessary to control the charging voltage of the capacitor so that it does not change even if the distance between the wire electrode and the workpiece increases or decreases. For example, it is necessary to control the charging voltage of the capacitor so that it does not change. It is considered effective to do so. However, experiments have shown that such control makes the discharge unstable. This is thought to be because when the distance between the wire electrode and the workpiece is large, discharging tends to stop temporarily if the charging voltage is constant. In other words, if the distance between the wire electrode and the workpiece is small, it is necessary to control the capacitor's charging voltage so that it does not drop, but if it is large, the capacitor's charging voltage must be controlled to increase, otherwise machining will become unstable. It is thought that it will become.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a wire electrical discharge machining power source for finishing which improves the drawbacks of the prior art described above, improves surface roughness in finishing, and provides stable machining.

Composition of the Invention The present invention is an electric discharge machine for a wire electric discharge machine that charges a capacitor from a DC power supply via a current limiting resistor and a switching element that turns on and off, and applies the charging voltage of the capacitor between a wire electrode and a workpiece to cause discharge. In the power supply, a detection circuit connects a transistor in parallel with the current limiting resistor and the switching element via a resistor, and detects a voltage difference between the charging voltage of the capacitor and the voltage of the DC power supply when the switching element is conductive. , a wire electrical discharge machining power supply configured to input the output of the detection circuit to the base of the transistor when the switching element is conductive, and to flow a current corresponding to the voltage difference to the capacitor via the transistor.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention.
1 is a DC power supply, C1 is a capacitor for charging and discharging,
P is a wire electrode, W is a workpiece, T1 is a switching element that turns on and off a transistor, R1 is a current limiting resistor that limits charging to capacitor C1 via transistor T1, and T2 is a preamplifier to be described later, which constitutes a class A amplifier. It is a transistor made into R2 is also a current limiting resistor that limits charging to capacitor C1 via transistor T2;
R3 and R4 are resistors that divide the voltage at point a in the circuit diagram, that is, the voltage between transistor T1 and resistor R1, 2 is an analog switch, C2 is a capacitor,
3 is a differential amplifier that compares the reference voltage V1 with the charging voltage charged in the capacitor C2 and outputs the result, D is a diode, 5 is a preamplifier that operates the transistor T2 as a class A amplifier, and 6 is used to turn on and off the transistor T1. Preamplifier 4 is an oscillator, analog switch 2, preamplifiers 5 and 6
make it work. The output of the preamplifier 5 is input to the base G2 of the transistor T2, and the output of the preamplifier 6 is input to the base G1 of the transistor T1.

Next, the operation of this embodiment will be described.

The analog switch 2 is turned on by the pulse output from the oscillator 4, and the preamplifiers 5 and 6 are operated. As a result, the transistor T operates in class C due to the constant voltage output from the preamplifier 6.
1 conducts, the capacitor C1 is charged via the current limiting resistor R1, and the workpiece W is charged by the charging voltage of Y.
Electric discharge occurs between the electrode P and the electrode P, and electric discharge machining is performed. On the other hand, when the transistor T1 is turned on by the pulse output from the oscillator 4, the analog switch 2 is turned on, so a voltage obtained by dividing the voltage at point a in the figure by resistors R3 and R4 is applied to the capacitor C2. becomes. That is, the voltage of DC power supply 1 is V ₀ , and the charging voltage of capacitor C1 is Vc
Then, a voltage of V ₀ −Vc will be generated at point a, so the DC power supply voltage will be applied to capacitor C2.
A voltage corresponding to the difference between V ₀ and the charging voltage of the capacitor C1 is applied to charge the capacitor C1.

The charging voltage generated by charging the capacitor C2 is input to the differential amplifier 3 and compared with the reference voltage _V1 , and an output corresponding to the difference is input to the preamplifier 5 via the diode D. Therefore, the output of preamplifier 5 is DC power supply voltage V ₀ and capacitor C
A voltage corresponding to the difference between the two charging voltages Vc is generated, and this output is input to the base G2 of the transistor T2, making the transistor T2 conductive and functioning as a class A amplifier. This transistor T2
and the current flowing through resistor R2 is the DC power supply voltage.
The current flows in proportion to the difference between V ₀ and the charging voltage Vc of the capacitor C1, and this current charges the capacitor C1, so that the charging voltage is held constant.

The above is the operation of this embodiment. To explain in more detail the reason why the surface roughness of the workpiece is improved and stable machining is obtained, the output pulse from the pulse oscillator 4 is shown in Fig. 2A. Similarly, in FIG. 1, the transistor T2 etc. are not provided, and the capacitor C is simply connected by the transistor T1.
The voltage at point a when assuming that 1 is charged,
That is, it shows the voltage between the transistor T1 and the resistor R1, and C shows the voltage at point a in the embodiment of the present invention of the circuit shown in FIG.

Now, the reference voltage V ₁ is set to a value slightly higher than the limit value at which machining becomes unstable. Assuming that the transistor T2 etc. are not provided, the transistor T1 is made conductive by the output of the oscillator 4, the capacitor C1 is charged, and if the leakage current between the workpiece W and the electrode P is small, the capacitor C
1 is charged to near the voltage V ₀ of DC power supply 1,
As shown in Figure 2 (b), the voltage at point a is almost
Become an OV. Then, after that, the workpiece W and the electrode P
Electric discharge occurs during the process, and electrical discharge machining is performed, but,
When the leakage current increases due to an increase in the opposing area between the workpiece W and the electrode P, the charging voltage of the capacitor C1 increases.
Vc does not rise to the voltage _V0 of the DC power supply 1, and when a difference occurs, the voltage at point a also rises, as shown in Figure 2B. Since the reference voltage V ₁ is close to the limit voltage for obtaining stable machining, the capacitor C
The charging voltage Vc of DC power supply 1 decreases, and the voltage V ₀ of DC power supply 1 decreases.
The difference between the two becomes large, and in the case of (b) in FIG. 2, no discharge occurs. Therefore, in the present invention, a circuit such as a transistor T2 is provided to compensate for the drop in charging voltage of the capacitor C1 due to this leakage current. The analog switch 2, which is turned on by the pulse of the oscillator 4 that makes the transistor T1 conductive, applies the voltage at the point a to the capacitor C2 to charge it, and the difference between this charged voltage and the reference voltage _V1 is calculated by the differential amplifier 3. Since it is input to the preamplifier 5 via the diode D, and its output is applied to the base G2 of the transistor T2 operating in class A,
Depending on the difference between the DC power supply V ₀ and the charging voltage Vc of the capacitor C1, the capacitor C is charged via the transistor T2.
1, and the reference voltage V ₁ is charged as shown in Figure 3 C.
It will be charged up to. That is, the decrease in the charging voltage Vc of the capacitor C1 due to the leakage current between the workpiece W and the electrode P is caused by the decrease in the charging voltage Vc of the capacitor C1 due to the leakage current between the work W and the electrode
2, and the charging voltage Vc is kept at a constant voltage that is always higher than the reference voltage _V1 . Conversely, if the workpiece W and the electrode are separated, the charging voltage Vc will be charged to a value close to the DC power supply voltage _V0 , which is higher than the reference voltage _V1 , so the discharge will be stabilized and stable machining will be possible. It is possible to obtain processing with very small surface roughness.

Effects of the Invention As described above, since a circuit is provided that automatically compensates for the drop in the charging voltage of the capacitor due to the leakage current between the workpiece and the electrode according to the degree of the drop, the charging voltage of the capacitor remains constant. Therefore, machining can be performed with a voltage close to the limit value that allows stable machining by lowering the DC power supply voltage, so the machined surface of the workpiece has minute surface roughness and stable machining can be performed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is an operation explanatory diagram. 2... Analog switch, 5, 6... Preamplifier, T1, T2... Transistor, P... Electrode,
W...Work.

Claims (1)

[Claims] 1. Charge a capacitor from a DC power source via a current limiting resistor and a switching element that turns on and off.
In an electrical discharge machining power supply for a wire electrical discharge machine that applies a charging voltage of the capacitor between a wire electrode and a workpiece to generate electrical discharge, a transistor is connected through a resistor in parallel with the current limiting resistor and the switching element, and the switching element is a detection circuit that detects the voltage difference between the charging voltage of the capacitor and the voltage of the DC power supply when the switching element is conductive; and an output of the detection circuit is input to the base of the transistor when the switching element is conductive; A wire electrical discharge machining power supply that allows current to flow through the capacitors according to the voltage difference.