JPS637889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a power supply device for electric discharge machining, in particular, a device for supplying intermittent pulse voltage from a DC power source to a machining gap formed between an electrode and a workpiece by turning on and off a semiconductor switching element. The present invention relates to an improvement in a power supply device for electric discharge machining that processes a workpiece.

In recent years, electrical discharge machining power supplies have been widely used, which fill a machining fluid into a machining gap formed between an electrode and a workpiece to generate pulse discharge in the machining gap to machine the workpiece. .

FIG. 1 shows such a conventional electrical discharge machining power supply device, which operates between an electrode 12 and a workpiece 14 by turning on and off a semiconductor switching element 10 by a control circuit 11. An intermittent pulse voltage is supplied from a DC power source 18 to a machining gap 16 formed in the machining gap 16 . In this way, when the switching element 10 is turned on and off to supply a pulse voltage to the machining gap 16, the insulation of the machining gap 16 is broken and a pulse current is generated. Here, since a line inductance 20 of 1 μH or less exists between the DC power source 18 and the machining gap 16, the value of this inductance 20 is L, the voltage of the DC power source 18 is V _S , and the machining gap 1
If the arc voltage of 6 is V _G (approximately 20V),
When a pulse voltage is applied to the machining gap 16 to generate a pulse discharge, the current I _p flowing through the machining gap 16 linearly follows the following equation I _p = (V _S − V _G )t/L as time t passes. It will continue to increase. Therefore, the current value I _p after t ₁ hour has elapsed since the semiconductor switching element 10 is turned on becomes I _p = (V _S − V _G ) t ₁ /L, and the line inductance 20 has 1/2 LI _p ² energy. Accumulated. Therefore, when the semiconductor switching element 10 is switched from the on state to the off state, the energy stored in the inductance 20 of the line 1/2LI _p ²
Therefore, even if the semiconductor switching element 10 is assumed to be an ideal switch with a turn-off time of 0, the current flowing through the processing gap 16 cannot instantaneously become 0, and a so-called surge voltage is generated across the semiconductor switching element 10. Occur.

In order to protect the circuit from such surge voltage and also to be able to instantaneously cut off the current flowing through the machining gap 16, in the conventional device, the machining gap 16
A capacitor 24 is connected in parallel through a diode 22 to
In addition, a resistor 26 was connected to this capacitor 24. This switches the switching element 10 from the on state to the off state,
The surge voltage generated when the current flowing through the machining gap 16 is turned off is charged to a capacitor 24 via a diode 22, and the energy charged in this capacitor 24 is finally converted into thermal energy in a resistor 26 and consumed. Was.

However, in such conventional devices, the energy stored in the capacitor 24 is ultimately consumed as thermal energy in the resistor 26, making it impossible to effectively utilize the energy supplied to the device. There is a drawback in that the heat generated by the device 26 causes a decrease in the reliability of the power supply device itself, which contains a large amount of semiconductors.

In particular, the semiconductor switching element 10 used to apply a pulse voltage to the machining gap 16 is frequently turned on and off, and therefore generates a large amount of heat. If this happens, this switching element 10 itself may become damaged.

The present invention has been developed in view of the above-mentioned problems in the prior art, and its purpose is to efficiently utilize input power and to reduce the heat generation inside the device, especially the semiconductor switching element that supplies pulse voltage to the machining gap. An object of the present invention is to provide a power supply device for electrical discharge machining that can effectively prevent heat generation.

To achieve this objective, the apparatus of the present invention supplies an intermittent pulse voltage from a DC power source to the machining gap formed between the electrode and the workpiece by turning on and off a semiconductor switching element, and In a power supply device for electric discharge machining that performs machining, a capacitor that is connected in parallel to the machining gap via a diode and absorbs a surge voltage generated in the circuit;
The present invention is characterized in that it includes a DC fan motor connected in parallel to the capacitor and rotates using charging energy of the capacitor, and the semiconductor switching element is air-cooled by the fan motor.

Next, preferred embodiments of the present invention will be described based on the drawings. Note that members corresponding to those of the conventional device shown in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

FIG. 2 shows a preferred embodiment of the electric discharge machining power supply device of the present invention, and the power supply device of the embodiment is as follows:
By turning on and off the semiconductor switching element 10 by a control circuit 11, an intermittent pulse voltage is supplied to the machining gap 16, and the workpiece 14 is electrically machined.

The characteristic feature of the present invention is that instead of the resistor used in the conventional device to consume the energy stored in the capacitor 24, a DC fan motor 30 is connected in parallel to the capacitor 24, The purpose is to drive the DC fan motor 30 using the accumulated energy and air-cool the semiconductor switching element 10.

In the embodiment, the DC fan motor 30 rotationally drives a fan 32 disposed opposite the semiconductor switching element 10 to cool the semiconductor switching element 10 with air.

With this configuration, when switching the semiconductor switching element 10 from the on state to the off state and interrupting the pulse current in the machining gap 16, the energy 1/2 LI _p ² stored in the line inductance 20 is generated. The surge voltage is charged to the capacitor 24 via the diode 22,
From this charging capacitor 24 to the DC fan motor 3
A current is supplied to the armature circuit of No. 0, and the fan motor 30 is driven.

Therefore, according to the device of the invention, the machining gap 16
In interrupting the current, the energy stored in the line inductance 20 - 1/2 LI _p ² is effectively used to drive the fan motor 30, and as in the conventional system using the resistor 26, the energy stored in the line inductance 20 is effectively used to drive the fan motor 30, Since a large amount of heat is not generated internally, and the semiconductor switching element 10, which generates heat through repeated on/off operations, can be air-cooled by the fan motor 30, the reliability of the power supply device itself, which includes many semiconductor elements, is improved. can do.

In particular, in such a power supply device for electrical discharge machining, if the discharge frequency or peak value of discharge current in the machining gap 16 is increased to increase the speed of electrical discharge machining,
Although the amount of heat generated by the semiconductor switching element itself increases, according to the device of the present invention, since the voltage across the capacitor 24 is the armature voltage of the DC fan motor 30, the discharge frequency or the peak value of the discharge current can be increased. The voltage across the capacitor 24 increases, and the rotation speed of the DC fan motor 30 increases. Therefore, even if the amount of heat generated by the switching element 10 increases with the discharge frequency or the peak value of the discharge current in the machining gap 16, the rotational speed of the DC fan motor increases accordingly, increasing the cooling capacity of the semiconductor switching element 10. temperature rise is effectively suppressed.

In the above embodiment, the armature circuit of the DC fan motor 30 is directly connected to both ends of the capacitor 24, but the device of the present invention is not limited to this, and for example, as shown in FIG. The armature circuit of the fan motor 30 may be connected in parallel to both ends of the capacitor 24 via a semiconductor switching element 34 that repeatedly turns on and off at high speed. In this case, the conduction pulse width of the semiconductor switching element 34 may be controlled by the control circuit 36 so that the voltage across the capacitor 24 is always at a constant value.

FIG. 4 shows a semiconductor switching element 34.
An example of a circuit of a control circuit 36 that performs PWM control is shown, and this control circuit 36 includes a capacitor 24
The voltage v _io across is differentially amplified by a differential amplifier 38, and a triangular wave oscillator 40 outputs a triangular wave V _S of a constant frequency as shown in FIG. Then, the comparator 42 compares the output v _io of the differential amplifier 38 and the output V _S of the triangular wave oscillator 40,
The comparison output is input to a drive circuit 46 via a photocoupler 44. Drive circuit 46
is the comparator 42 input in this way.
Based on the output of , a voltage _VGS in FIG. 5 is applied to the semiconductor switching element 34, and the semiconductor switching element 34 is subjected to PWM control.

In this way, in the device of this embodiment, the control circuit 3
6 detects the voltage across the capacitor 24 and performs PWM control on the semiconductor switching element 34 so that the voltage across the capacitor 24 becomes a constant value. When the discharge frequency or discharge current peak value increases and the electrostatic energy charged in the capacitor 24 increases, the conduction pulse width of the semiconductor switching element 34 increases, and as a result, the rotation speed of the DC fan motor 30 also increases. Therefore, in the apparatus of this embodiment, as in the case of the previous embodiment, when the discharge frequency or discharge current peak value increases in the machining gap 16 and the amount of heat generated by the switching element 10 increases, the increase in the amount of heat generated increases. Since the cooling capacity of the DC fan motor also increases accordingly, the temperature rise of the semiconductor switching element 10 is effectively suppressed.

As explained above, according to the present invention, the surge energy stored in the inductance of the circuit is temporarily stored in the capacitor when the semiconductor switching element that turns on and off the pulse discharge is turned off.
This is used as a power source to drive the DC fan motor and cool the semiconductor switching element, so the power supplied to the device can be used efficiently, and furthermore, heat generation inside the device can be effectively suppressed and temperature rises can be prevented. This makes it possible to prevent the reliability of the power supply device from decreasing accordingly.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a conventional electric discharge machining power supply device, FIG. 2 is an electric circuit diagram showing a preferred embodiment of the electric discharge machining power supply device of the present invention, and FIG. 3 is another embodiment of the present invention. 4 is an electric circuit diagram of the control circuit shown in FIG. 3, and FIG. 5 is a signal waveform diagram of the circuit shown in FIG. 4. The same members in each figure are given the same reference numerals, 10 is a semiconductor switching element, 12 is an electrode, 16 is a machining gap, 18 is a DC power supply, 22 is a diode, 24
is a capacitor, and 30 is a DC fan motor.

Claims (1)

[Claims] 1 Supplying intermittent pulse voltage from a DC power source to the processing gap formed between the electrode and the workpiece by turning on and off the semiconductor switching element,
A power supply device for electrical discharge machining that processes a workpiece includes a capacitor connected in parallel to the machining gap via a diode to absorb surge voltage generated in the circuit, and a capacitor connected in parallel to the capacitor to absorb charging energy of the capacitor. 1. A power supply device for electrical discharge machining, comprising: a DC fan motor that rotates by using a DC fan motor, and the semiconductor switching element is air-cooled by the fan motor.