JPH0538627A - Electric discharge machining device - Google Patents

Abstract

PURPOSE:To reduce bad influence or irregular electric discharging by suppressing generation of electric discharge at side faces and the secondary discharge through the splashing powder from machining likely to occur when the discharge machining involves instability. CONSTITUTION:A switching element 7 and a capacitor 3 are connected in series to a DC power supply 1, and a current suppressing resistance 6 is connected in parallel with this switching element 7 while a machining electrode 4 and a work to be processed 5 are connected with the capacitor 3. The switching element 7 is turned off with the off signal prepared by a switch control circuit according to eventual instability of electric discharge, and the charging current to the capacitor 3 is lessened by the resistance 6. When machining becomes unstable, the charging current from the capacitor 3 to the machining electrode 4 and the work 5, i.e., supply energy, is decreased so as to suppress generation of electric discharge phenomenon.

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 power supply circuit for an electric discharge machining apparatus, and more particularly to an electric discharge machining power supply circuit for suppressing the influence of secondary discharge to suppress the generation of unintended discharge.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing an electric discharge machining power supply circuit of a conventional electric discharge machining apparatus, and FIG. 8 is a waveform diagram showing a voltage / current between a machining electrode and a workpiece, that is, a pole in the electric discharge machining power supply circuit. Is. In the figure, 1 is a DC voltage source, 2 is a variable resistor, 3 is a capacitor connected in series to the DC voltage source 1 via a variable resistor 2, and 4 is a processing device connected to one terminal of the capacitor 3. The electrodes 5 are workpieces connected to the other terminal of the capacitor 3.

The electric discharge power supply circuit of the conventional electric discharge machine is constructed as described above, and the DC voltage of the DC voltage source 1 is applied to both ends of the capacitor 3 through the variable resistor 2, and electric energy is accumulated in the capacitor 3. And capacitor 3
The voltage between both ends of the DC voltage gradually increases and approaches the DC voltage value of the DC voltage source 1. Then, the processing electrode 4 and the workpiece 5
Since the gap (hereinafter referred to as “between poles”) is controlled to a very narrow gap that can induce a discharge phenomenon near the DC voltage of the DC voltage source 1, the voltage across the capacitor 3 is near the DC voltage of the DC voltage source 1. When it reaches, the discharge phenomenon occurs between the electrodes, and the energy stored in the capacitor 3 flows as a discharge current between the electrodes. By repeating this, the workpiece 5 is gradually dissolved. The waveforms of the voltage and current between the electrodes at this time are shown in FIG. The variable resistor 2 is for limiting the charging current to the capacitor 3 and can change the time until the voltage across the capacitor 3 reaches the DC voltage value.

[0004]

In the electric discharge machining power supply circuit of the conventional electric discharge machining apparatus as described above, the capacitor 3 is connected in series to the DC voltage source 1 through the variable resistor 2, and machining is performed at both ends of the capacitor 3. Since the work electrode 4 and the work piece 5 are connected to each other, the charge to the capacitor 3 cannot be stopped and the discharge that accompanies it cannot be stopped regardless of the state between the electrodes. .. Therefore,
When the electric discharge machining becomes unstable, the machining electrode 4 is moved toward the machining advancing direction in order to eliminate the instability by the servo feed control of the numerical controller that detects the machining state between the electrodes and controls the machining gap. However, even in this case, since the electric discharge is performed between the electrodes in the same manner as the stable machining, the electric discharge in the lateral direction with respect to the machining axis of the machining electrode 4 cannot be eliminated. As a result, there is a problem in that it is not possible to suppress the occurrence of secondary discharge through the processed powder.

The present invention has been made to solve the above problems, and when electric discharge machining becomes unstable and the machining electrode is allowed to escape in the direction opposite to the machining direction, the gap between the machining gap and Electric discharge machining apparatus capable of reducing supply energy or stopping supply of supply energy to suppress or eliminate side discharge and secondary discharge through machining powder to reduce adverse effects caused by these discharges. The purpose is to obtain the electric discharge machining power supply circuit.

[0006]

A discharge machining apparatus according to the present invention is a capacitor connected in series to a DC power source and connected in parallel between a machining electrode and a workpiece to generate a high frequency pulse for discharge. And the amount of return from the deepest value in the machining advancing direction of the machining electrode due to the servo feed control of the numerical control device that outputs an ON signal at all times and the EDM is always in an unstable state. Is a predetermined value or more, the switch control circuit that outputs an OFF signal until just before electrical discharge machining stabilizes is provided between the DC power supply and the electrical discharge machining power supply circuit. It is configured to include a switching element which is operated and in which current suppressing resistors are connected in parallel.

Further, another electric discharge machining apparatus according to the present invention is provided between the DC power supply, the machining electrode and the work piece, and is driven by the output signal of the oscillator to generate a high frequency pulse for electric discharge. An electric discharge machining power supply circuit that has elements and an ON signal is always output, and the electric discharge machining is unstable, and the numerical control device returns from the deepest value in the machining progress direction of the machining electrode by servo feed control. A switch control circuit that outputs an OFF signal until just before the electrical discharge machining stabilizes when the amount is a predetermined value or more, and it is provided between the oscillator and the switching element and receives the output signal of the oscillator and the ON signal of the switch control circuit. And a gate means that prevents the current from flowing to the switching element when it receives an off signal from the switch control circuit. Than it is.

[0008]

In the present invention, during stable electric discharge machining, the capacitor of the electric discharge machining power supply circuit is repeatedly charged and discharged, and the machining electrode updates the deepest value in the machining progress direction by the servo control of the numerical controller. While the machining continues, the numerical controller once again releases the machining electrode in the machining direction once the electric discharge machining becomes unstable. When the escape amount is equal to or larger than the predetermined value, the switch control circuit outputs the OFF signal until just before the stabilization. Then, the switching element provided between the DC power supply and the electric discharge machining power supply circuit is turned off by the off signal, and the charging current to the capacitor, which has been flowing in the switching element until now, is connected in parallel to the switching element. Since the current flows through the current suppressing resistor, the charging current flowing through the capacitor becomes small. Therefore, it takes a very long time for the voltage across the capacitor to reach the DC voltage value, and unintentional discharge during this period is reduced, which is equivalent to stopping the current supply.

According to another aspect of the present invention, once the electric discharge machining becomes unstable, the numerical control device performs an operation of escaping the machining electrode in the machining progress direction, and when the escaping amount is equal to or greater than a predetermined value, switch control is performed. The circuit outputs the off signal until just before it stabilizes. In this case, the gate means provided between the oscillator and the switching element receives the off signal and turns off the switching element by preventing the output signal of the oscillator from flowing through the switching element. Therefore, the direct current power supply is cut off from the machining electrode and the workpiece, the current supply to the gap between the electrodes is stopped, and no discharge occurs during this period.

[0010]

FIG. 1 is a circuit diagram showing an electric discharge machining power supply circuit according to an embodiment of the present invention, and FIG. 2 is a TR in the electric discharge machining power supply circuit.
Timing chart of control signal and voltage / current waveform between poles, FIG. 3 is a block diagram showing the switch control circuit of the same embodiment, and FIG. 4 shows the relationship between the movement of the machining electrode and time and when discharge instability occurs. FIG. 6 is a waveform diagram showing a TR control signal to the transistor with respect to the escape amount of the processing electrode.

In FIG. 1, 1 is a DC voltage source, 2 is a variable resistor, 3 is a capacitor, 4 is a machining electrode, 5 is a workpiece, 6 is a fixed resistor for suppressing current, and 7 is a switching element. It is a transistor. For DC voltage source 1,
The variable resistor 2, the transistor 7 and the capacitor 3 are connected in series. The processing electrode 4 is connected to one terminal of the capacitor 3, and the workpiece 5 is connected to the other terminal of the capacitor 3. The fixed resistor 6 is connected in parallel to the series circuit of the variable resistor 2 and the transistor 7.

In FIG. 3, 10 is the T of the transistor 7.
A switch control circuit for generating an R control signal, which includes an encoder position detection sensor 11, an axis position control unit 12,
The return amount counter 13, the off position set value setter 14, the on position set value setter 15 and the output unit 15
The position feedback pulse signal from the position detection sensor 11 is transmitted to the shaft position control unit 12. When electric discharge machining is stable in the axis position control unit 12 which receives a servo feed control command from a numerical controller (not shown) that detects the machining state between the machining electrode 4 and the workpiece 5 and controls the machining gap. Performs servo feed control of the machining axis while updating the deepest value of the machining axis of the machining electrode 4, but when the machining axis returns in the escape direction due to the influence of instability or the like, a return amount counter 13 that counts the return amount is displayed. Transfer the return amount. The return amount counter 13 is preset with a set value of the return amount for turning off the TR control signal and a set value of the return amount for turning on after turning off the TR control signal by the off position set value setter 14 and the on position set value setter 15. When the set value is reached, the output section 15 outputs an ON signal or an OFF signal which is a TR control signal. Figure 9
The machining axis of the machining electrode 4 advances in the machining progress direction during stable machining, but once unstable, the machining axis is returned to the feeding direction of the machining progress direction. When this return amount exceeds the OFF position set value, TR
When the control signal becomes an OFF signal and then the machining gap state becomes stable and the machining axis reaches the ON position set value before the machining deepest position, the TR control signal becomes an ON signal.

Next, the operation of the electric discharge machining power supply circuit of this embodiment will be described. The machining electrode 4 advances in the machining advancing direction simultaneously with the start of machining, and when the machining electrode 4 and the workpiece 5 approach a certain distance, electric discharge is started. After that, when the processing is progressing stably, the TR control signal from the switch control circuit 10 is an ON signal, and the transistor 7 is turned ON. In this case, since the fixed resistor 6 has a resistance value sufficiently larger than that of the variable resistor 2, most of the charging current to the capacitor 3 is supplied through the variable resistor 2.
The voltage across the capacitor 3 gradually rises and the DC voltage source 1
Approaching the voltage value of. At this time, since the gap between the electrodes is controlled to be a very narrow gap that can induce the discharge phenomenon with the above voltage, the discharge phenomenon occurs, and the energy stored in the capacitor 3 flows between the electrodes as a discharge current. . By repeating this, the machining electrode 4 updates the deepest value in the machining progress direction by the servo control of the numerical controller, and the machining is continued while the workpiece 5 is gradually melted.
However, when the machining becomes unstable once, the TR control signal from the switch control circuit 10 is turned off for a predetermined time until the machining gap state becomes stable and the machining axis reaches the ON position set value before the deepest machining position. Transistor 7 as a signal
To turn off. Therefore, the charging current to the capacitor 3 is supplied only through the fixed resistor 6 which is a current suppressing resistor. Since the fixed resistor 6 has a very large resistance value, the charging current is small, and it takes a very long time for the voltage across the capacitor 3 to reach the voltage value of the DC voltage source 1. The discharge and the secondary discharge through the machining powder are reduced and can be considered as equivalent to the suspension of the power supply. Therefore, the processing can be stabilized and the processing speed can be improved.

FIG. 5 is a circuit diagram showing an electric discharge machining power supply circuit according to another embodiment of the present invention, and FIG. 6 shows an output signal of an oscillator, a TR control signal, and a voltage / current waveform between electrodes in the electric discharge machining power supply circuit. It is a timing chart. In this embodiment, a transistor, a variable resistor 2, a processing electrode 4 and a workpiece 5 are connected in series to a DC voltage source 1. Reference numeral 8 is an AND gate which is a gate means, the input side of which is connected to an oscillator 9 which oscillates a pulsed output signal and a switching control circuit 10 which outputs a TR control signal,
The output side is connected to the base of the transistor 7. The structure of the switching control circuit 10 is the same as the structure shown in FIG.

Next, the operation of the electric discharge machining power supply circuit of this embodiment will be described. The machining electrode 4 advances in the machining advancing direction simultaneously with the start of machining, and when the machining electrode 4 and the workpiece 5 approach a certain distance, electric discharge is started. After that, if the electrical discharge machining is proceeding steadily, T from the switch control circuit
The R control signal outputs an H level ON signal, and AND
The gate 8 is opened to transmit the output signal from the oscillator 9 to the transistor 7, the transistor 7 is switched to generate a high frequency pulse, and the electric discharge machining is advanced. However, when the electric discharge machining becomes unstable once, the TR control signal from the switch control circuit outputs the OFF signal which is L level for a predetermined time as in the above-mentioned embodiment, the AND gate 8 is closed and the oscillator 9 is closed. The output signal of is cut off and the transistor 7 is turned off. Therefore, the direct current power supply 1 is cut off from the machining electrode 4 and the workpiece 5, and the current supply between the machining electrode 4 and the workpiece 5 is stopped. The secondary discharge through is no longer generated.

[0016]

As described above, according to the present invention, when the machining becomes unstable, the energy supplied from the electric discharge machining power supply circuit between the machining electrode and the workpiece is reduced or the energy supply is stopped. Since the occurrence of the electric discharge phenomenon is suppressed by this, it is possible to reduce or eliminate the electric discharge in the side direction and the secondary electric discharge through the machining powder, and it is possible to stabilize the electric discharge machining and improve the machining speed. ..

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an electric discharge machining power supply circuit according to an embodiment of the present invention.

FIG. 2 is a timing chart of TR control signals and voltage / current waveforms between electrodes in the same electric discharge machining power supply circuit.

FIG. 3 is a block diagram showing a switch control circuit of the same embodiment.

FIG. 4 is a waveform diagram showing the relationship between the movement of the machining electrode and time, and showing the TR control signal to the transistor with respect to the escape amount of the machining electrode when discharge instability occurs.

FIG. 5 is a circuit diagram showing an electric discharge machining power supply circuit according to another embodiment of the present invention.

FIG. 6 is a timing chart of an oscillator output signal, a TR control signal, and a voltage / current waveform between the electrodes in the electric discharge machining power supply circuit.

FIG. 7 is a circuit diagram showing an electric discharge power supply circuit of a conventional electric discharge machine.

FIG. 8 is a waveform diagram showing a voltage / current between electrodes in the same electric discharge machining power supply circuit.

[Explanation of symbols]

 1 DC Voltage Source 3 Capacitor 4 Processing Electrode 5 Workpiece 6 Fixed Resistor (Current Suppression Resistor) 7 Transistor (Switching Element)

Claims (2)

[Claims] 1. An electric discharge machining power supply circuit comprising a capacitor connected in series to a DC power supply and connected in parallel between a machining electrode and a workpiece to generate a high frequency pulse for electric discharge, and always. Outputs an ON signal, and the electric discharge machining is stable when the electric discharge machining is unstable and the amount of return from the deepest value in the machining advancing direction of the machining electrode by the servo feed control of the numerical control device is equal to or more than a predetermined value. It is provided between the switch control circuit that outputs the OFF signal until immediately before, and the DC power supply and the electric discharge machining power supply circuit. The switch control circuit is turned on / off by the ON / OFF signal, and the current suppressing resistors are connected in parallel. An electric discharge machine comprising a switching element. 2. An electric discharge machining power supply circuit comprising a switching element which is provided between a DC power supply, a machining electrode and a workpiece and which is driven by an output signal of an oscillator to generate a high frequency pulse for electric discharge. And always output an ON signal,
When the electrical discharge machining is unstable and the return amount from the deepest value in the machining progress direction of the machining electrode by the servo feed control of the numerical control device is equal to or more than the predetermined value, the OFF signal is output until just before the electrical discharge machining stabilizes. Provided between the switch control circuit and the oscillator and the switching element, the output signal of the oscillator is passed to the switching element when the ON signal of the switch control circuit is received, and the switching element when the OFF signal of the switch control circuit is received. An electric discharge machine comprising: