JPS63102825A - Power source for electric discharge machining - Google Patents

Abstract

PURPOSE:To simplify a control means, by providing power sources for normal voltage and reverse voltage which are applied between a workpiece and an electrode by switching elements so that the averaged machining voltage is made to be zero. CONSTITUTION:Control is made such that a normal voltage E1 is applied between a workpiece W and an electrode P from an oscillator 2 for a predetermined period so as to allow a capacitor C1 to discharge several times for carrying out electric discharge machining, and thereafter, a reverse voltage E2 is applied between the workpiece W and the electrode P while the application time of the reverse voltage is controlled so that the application time of the normal voltage and the application time of the reverse voltage are made to be zero in average during one entire cycle. Accordingly, the control and the arrangement are simple in comparison with those of the conventional system in which a reverse voltage is applied for every discharge to make the averaged machining voltage zero, and therefore, it is possible to stabilize electrical discharge.

Description

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

Conventional technology Electrolysis occurs in electric discharge machining using water as the machining fluid, and electrolytic corrosion occurs especially when rough machining workpieces that are electrolytically corroded, such as cemented carbide, which makes the workpiece brittle.This is a disadvantage of chopsticks. was there. In addition, during the second cut of wire-cut electric discharge machining, there is a drawback that the surface of the workpiece becomes rough due to selective electrolytic corrosion of particles due to the electrolytic action, resulting in poor finished surface roughness. In order to prevent this, it is already known that when not machining, a reverse voltage is applied to the gap between the electrode and the workpiece in the opposite direction to that during machining, thereby reducing the average machining voltage to zero and preventing electrolysis. . for example,
JP-A-60-201826, JP-A-60-180
Publication No. 724.

Problems to be Solved by the Invention As described in the above-mentioned Japanese Patent Laid-Open No. 60-201826, applying positive and reverse voltages between the workpiece and the electrode 2
In this method, a capacitor is connected in parallel between the workpiece and the electrode, and the average machining voltage is zero by applying forward and reverse voltages from each power supply to the gap between the workpiece and the electrode using a switching element. In a capacitor discharge type electrical discharge machining power supply, in order to apply a reverse voltage between the workpiece and the electrode after the capacitor is discharged, the switching element operates to apply a reverse voltage from the reverse voltage power supply to the gap between the workpiece and the electrode. , it is necessary to coincide with the end of discharge of the capacitor.

In other words, it is necessary to charge the capacitor with a positive voltage power supply, and then apply a reverse voltage between the workpiece and the electrode from a reverse voltage power supply as the capacitor discharges, but the timing of applying this reverse voltage is difficult due to the delay of the circuit elements. For example, if the switching element for applying a reverse voltage is activated and a reverse voltage is applied between the workpiece and the electric current l1 before the capacitor is discharged,
Since the energy of the capacitor is reversed, the load on each power supply becomes abnormally large, making it impractical.

Therefore, an object of the present invention is to provide a capacitor discharge type electrical discharge machining power supply, which has a power supply for positive voltage and a power supply for reverse voltage, and applies positive and reverse voltages between the workpiece and the electrode using switching elements, respectively, and averages the voltage. It is an object of the present invention to provide an electric discharge machining power source that can control the machining voltage by a simple control means.

Means for Solving the Problems The present invention provides a first switching element in which a capacitor is connected in parallel between a workpiece and an electrode, a positive voltage is applied from a power supply between the workpiece and the electrode, and a first switching element that applies a positive voltage between the workpiece and the electrode, and In an electrical discharge machining power supply having a second switching element that applies a reverse voltage from the power supply, a smoothing means for smoothing the voltage between the workpiece and the electrode and detecting an average machining voltage is used, and the output of the smoothing means is compared with a reference voltage. , a comparator that outputs when there is a match,
pulse output means that is triggered by the output of the comparator and outputs an output of a predetermined time width; positive voltage application control means that turns on and off the first switching element at a predetermined period during output from the pulse output means; and the pulse output means. The above problem has been solved by providing a reverse voltage application control means for turning on the second switching element while the output from the second switching element is stopped.

Operation: While an output pulse is being output from the pulse output horn means for outputting an output with a predetermined time width, the first switching element is turned on and off at a predetermined period by the positive voltage application tIl control means, and the workpiece is turned on and off at a predetermined period. A capacitor connected in parallel between the workpiece and the electrode is charged and discharged, and an electric discharge is generated between the workpiece and the electrode to perform electrical discharge machining. As a result, the output of the smoothing means increases in the positive direction. When the output pulse from the pulse output means is turned off, the reverse voltage application control means turns on the second switching element to apply a reverse voltage between the workpiece and the electrode.

Therefore, the output of the smoothing means decreases, and when the output voltage and the reference voltage match, an output is output from the comparator, which triggers the pulse output means to output an output pulse of a predetermined width. In this way, a positive voltage is applied between the workpiece and the electrode, starting a discharge, and this operation is repeated. If the reference voltage is set to a value such that the average machining voltage applied to the workpiece and electrode is zero, the reverse voltage application time will be equal to the positive voltage application time determined by the pulse output means. Controlled, positive and reverse voltages are applied between the workpiece and the electrodes so that the overall average machining voltage is zero.

Embodiment FIG. 1 is a circuit diagram of an embodiment of the present invention, where P is an electrode and W
is a workpiece, and El is a voltage for charging a capacitor C1 through a limiting resistor R1 when the transistor T1 as a switching element is turned on, and applying the charging voltage of the capacitor C1 between the workpiece W and the electrode. It is a direct current power supply for positive voltage.

E2 is a power source for applying a reverse voltage between the workpiece W and the electrode 1, and the reverse voltage is applied via the transistor T2 as a switching element and the current limiting resistor R2. Then, the gap voltage VQ between the electrode P and the workpiece W is divided by resistors R3 and R4, and the variable resistor R
A constant voltage set by V is added and smoothed by a smoothing circuit 3, and the output VL of the smoothing circuit 3 is input to a comparator 4. The charging voltage of the capacitor C3 of the integrator composed of the resistor R10 and the capacitor C3 is input to the comparator 4.
A transistor T3 as an analog switch is connected in parallel with the capacitor C3, and the output of a first oscillator 1 such as a one-shot multivibrator as a pulse output means to be described later is connected to the base of the transistor T3.

Further, the output of the comparator 4 is input to a NAND circuit N1,
The output of the oscillation B1 is inputted via the inverter 11 to the other input terminal of the NAND circuit N1. The output of the NAND circuit N1 is input to the set input terminal of the oscillator 1 via the inverter I2, and is also input to the driver circuit 6.
is driven to turn on the transistor T2.

Furthermore, the output of the L2 first oscillator 1 is input to the AND circuit A1, and the output of the second oscillator 2 that oscillates at a predetermined frequency is connected to the other input terminal of the AND circuit A1. The output of T1 is configured to turn on and off the switching element T1 via the driver circuit 5. That is, in this embodiment, the second oscillator 2.
AND circuit A1. The driver circuit 5 and the like constitute a positive voltage application control means, and the inverters 11, 12 . Pendant circuit N1. The driver circuit 6 and the like constitute a reverse voltage application control means.

FIG. 2 is an explanatory diagram showing the signal waveform and timing in this embodiment. As shown in FIG. 2, the output pulse period of the first oscillator 1 and the oscillation period of the second oscillator 2 are significantly different. However, the oscillation period of the second oscillator 2 is small, and the oscillation period of the second oscillator 2 is small.
The period of the oscillator 1 is very sharp. The second oscillation period is a predetermined period, and this period, that is, the oscillation frequency, can be set to a predetermined value. However, on the other hand,
The output pulse width (T in FIG. 2) of the first oscillator 1 is constant, but the width when the output is stopped is not constant as will be described later. That is, the first oscillator 1 is composed of a one-shot multivibrator, which outputs a pulse of a constant width each time a trigger input is received, and the trigger input is not input at regular intervals. There is.

Therefore, the operation of this embodiment will be explained with reference to FIG.

The second oscillation Z2 is emitted at the oscillation frequency set as shown in FIG. Due to the output, the AND circuit A1 closes its gate, supplies the output pulse of the second oscillator 2 to the driver circuit 5, and turns the transistor T1 on and off. As a result, from the power supply E1 for positive voltage, 1 to transistor T1. The capacitor C1 is charged via the current limiting resistor R1, and this charging voltage causes an electric discharge between the workpiece W and the electrode 1, thereby performing electric discharge machining.

The gap voltage between the workpiece W and the electrode 1 at this time has a waveform that increases and decreases in the positive direction each time the capacitor is charged and discharged, as shown in FIG. 2 (g).

The gap voltage Vg applied to the gap between the workpiece W and the electrode 1 is divided by resistors R3 and R4, and a predetermined voltage set by resistor R6 and variable resistor RV is added to the divided voltage, and a smoothing circuit Smoothed by 3. On the other hand, the first oscillator 1
The output of the comparator 4 turns on the transistor T3 as an analog switch, so the capacitor C3 has not started charging, and the input of the comparator 4 is the input V from the smoothing circuit 3.
The voltage L is higher than the input voltage VC at the other input terminal, and the output S1 from the comparator is at the T level as shown in FIG. 2(D). Also, since the output of the first oscillator 1 is input to the Nandts gate N1 via the inverter 1, the output $2 of the Nandts gate N1 is at H level as shown in FIG. The output S3 of I2 becomes L level (see Fig. 2 (v)), and the driver circuit 6
is not driven and the transistor T2 is in an off state.

Therefore, when the output of the first oscillator 1 that outputs a pulse for a predetermined period disappears, the AND circuit A1 is closed, the output of the second oscillator 2 is not supplied to the driver circuit 5, and the transistor T1 is turned off. On the other hand, when the output of the first oscillator 1 disappears and becomes a truvel, the truvel output is inputted to the NAND circuit N1 via the inverter 11, and the comparator 4
Since the output S1 of is currently a trubel, the NAND circuit N1
The output S2 of inverter ■2 becomes the trubel, and the output S2 of inverter ■2
3 is a trubel, which turns on the transistor T2 via the driver circuit 6 to apply a reverse voltage between the workpiece W and the electrode 2 from the power source E2 for reverse voltage. Therefore,
The output VL of the smoothing circuit 3 decreases, and since the output of the first oscillator 1 becomes a torque level, the transistor T3 serving as an analog switch is turned off, and the capacitor C3 is charged with the voltage V2 via the resistor R10. Then, as shown in FIG. 2 (c), the charging voltage VC of the capacitor
When the output VL of the smoothing circuit 3 matches, the comparator 4 outputs a torque output signal S1. As a result, NAND circuit N
The output S2 of Impark 1 becomes the l'' level, and the output S3 of Impark 2 becomes the torque level.

Then, when the output S3 of the inverter 2 becomes a torque level, the first oscillator 1 is triggered and outputs a torque pulse with a constant width, and this output turns on the transistor T3 of the analog switch, and the capacitor C3 is turned on. Discharged and connected to NAND circuit N via inverter ■1
Since the output of the trubel is input to the output of the NAND circuit N1, the output $2 of the NAND circuit N1 connects the trubel, and the output S of the inverter I2
3 connects the torque bell, turns off the transistor T2 via the driver circuit 6, and stops applying a reverse voltage between the workpiece W and the electric current ff1P. On the other hand, the output of the first oscillator 1 opens the AND circuit A1, and the second oscillator 2
The output is supplied to the driver circuit 5, the transistor T1 is turned on and off, and electrical discharge machining is started as described above. Then, electrical discharge machining by applying this positive voltage is performed during the pulse width output from the first oscillator 1, and when this output disappears, the transistor T2 is turned on as described above, and a reverse voltage is generated between the workpiece W and the electrode 2. However, the time to apply this reverse voltage is determined by the variable resistor R.
By setting the value of V and the time constant of the integrating circuit of resistor R10 and capacitor C3, the comparator 4 outputs an output when the average machining voltage of the positive and reverse voltages applied between the workpiece W and the electrode 2 becomes zero. , to control the reverse voltage application time.

In this way, the present invention, as shown in the above embodiment, applies a reverse voltage for a period of time until the average machining voltage becomes zero after performing multiple discharges by applying a positive voltage using the second oscillator 2. By adjusting the reverse voltage application time, the average machining voltage is made zero.

In the above embodiment, the comparator 4 compares the output VL of the smoothing circuit with the charging voltage VC of the capacitor C3. It may be possible to simply compare it with a set reference voltage by taking some measures.

Effects of the Invention As described above, the present invention performs electrical discharge machining by applying a positive voltage between the workpiece and the electrode for a predetermined period of time to cause converse discharge multiple times, and then applying a reverse voltage between the workpiece and the electrode. The reverse voltage application time was controlled so that the average machining voltage was zero during the whole cycle of the positive voltage application time and the reverse voltage application time, so the reverse voltage was applied every - discharge. Compared to conventional methods that reduce the average machining voltage to zero, this method is easier to control, has a simpler configuration, and has a more stable discharge.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, and Fig. 2 is a circuit diagram of an embodiment of the present invention.
It is an explanatory diagram showing each signal waveform and timing in an example. 1... first oscillator, 2... second oscillator, 3...
- Smoothing circuit, 4... Comparator, 5.6... Driver circuit, El, R2... DC power supply, T1. T2...Transistor, C1-C3...Capacitor, R1...R
11...Resistor, T3...Analog switch, P...
・Electrode, W...Warri. Patented applicant FANUC Co., Ltd. Figure 1

Claims (2)

[Claims] (1) A capacitor is connected in parallel between the workpiece and the electrode,
An electrical discharge machining power supply having a first switching element that applies a positive voltage from the power supply between the workpiece and the electrode, and a second switching element that applies a reverse voltage from the power supply to the workpiece and the electrode. a smoothing means for smoothing the voltage of and detecting an average machining voltage; a comparator for comparing the output of the smoothing means with a reference voltage and outputting an output when they match; and an output for a predetermined time period triggered by the output of the comparator. a pulse output means, and the above-mentioned first pulse being output from the pulse output means.
An electric discharge machining power supply characterized by having a positive voltage application control means for turning on and off the switching element at a predetermined period, and a reverse voltage application control means for turning on the second switching element while the output from the pulse output means is stopped. . (2) The electric discharge machining power source according to claim 1, wherein the reference voltage is constituted by a charging voltage of a capacitor of an integrating circuit that starts charging when the output of the pulse output means stops.