JPS6179521A - Power supply circuit of electric discharge machining device - Google Patents

Abstract

PURPOSE:To obtain a surface in good finish, by providing an induction coil further additionally a stray capacity of a circuit in the power supply circuit supplying an electric discharge current to a machining gap. CONSTITUTION:An electric discharge circuit, comprising a DC power supply 1, current limiting resistor 3, switching transistor 5, transistor control circuit 7, induction coils 9 and a machining gap 11, further additionally provides stray capacities 13 of the circuit. If electric discharge energy is decreased by increasing a resistance value of the resistor 3, the stray capacity 13 is charged with an electric current flowing in the transistor 5, mainly supplying an electric discharge current flowing in the gap 11. An electric charge staticizing the stray capacity 13 by the induction coil 9 is discharged through a large impedance. Accordingly, an electric discharge machining device, providing a shallow dent of electric discharge, obtains a machined surface in good finish.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application This invention relates to an electric discharge machining apparatus, and more particularly to a power supply circuit that supplies a discharge current to a machining gap.

b. Conventional technology Conventionally, in pulse power supply circuits that utilize the switching characteristics of transistors, which have been used as power supply circuits for electric discharge machining equipment, the energy per machining pulse is reduced in order to reduce the roughness of the finished surface. When it is made small, the practical limit of the roughness of the finished surface obtained is about 2 to 3 μmRmax.

The reason for this is that stray capacitance exists in the power supply circuit from the machining power source to the machining gap. That is, when the energy per discharge pulse is reduced by reducing the current value (Ip), I.

When the value falls below a certain value, the discharge current cannot be maintained during the on-time of the pulse. The discharge at this time is not substantially caused by the pulse current supplied by the switching of the transistor, but by the stray capacitance. Observing the waveform of the discharge current at this time, the peak value of the discharge current becomes an approximately constant value when Ip, which is set by the transistor switching circuit, becomes smaller than a certain value, and (
It can be seen that even if p is made smaller, the actual discharge energy and discharge current peak value do not become smaller.

Problems to be Solved by the Invention As mentioned above, in a conventional power supply circuit that utilizes the switching characteristics of transistors, the discharge energy and discharge current peak value Ip are subject to a certain level of convergence due to the stray capacitance of the circuit. It is difficult to lower it.

There is a relationship between the discharge current wave height l11o and the finished surface roughness Rmax, for example, as R axoc l p '=, and if to remains at a constant value, there is a limit to the finished surface roughness, and this value The following is a problem that cannot be trivialized.

This invention focuses on the fact that in conventional pulse power supply circuits that utilize the switching characteristics of transistors, stray capacitance in the circuit that cannot be controlled deteriorates the processing surface, and by actively utilizing and controlling stray capacitance, it is possible to improve The purpose of this invention is to provide a power supply circuit that can obtain a high-quality finished surface.

Means for Solving the d0 Problem' In order to achieve the above object, the gist of the present invention is that a guide wire is provided in a power supply circuit that supplies a discharge current to a machining gap. .

80 Effects Since the structure is as described above, when discharging by the power supply circuit of the present invention, the electric charge charged in the stray capacitance of the circuit flows through the induction wire, so that the peak value of the current becomes low. Therefore, the discharge marks on the finished surface of the workpiece become shallow, and a good finished surface can be obtained.

r.Example Next, an example of the present invention will be described based on the drawings. FIG. 1 shows an embodiment of a discharge circuit comprising a power supply circuit and a machining gap according to the present invention. That is, this circuit uses a DC power source 1. Current limiting resistor 3. Switching transistor 5. The transistor control circuit 7 consists of a guiding wire 9 and a machining gap 11, and a stray capacitance 13 of the circuit is further added.

In this circuit configuration, if the discharge energy is reduced by increasing the resistance value of the current limiting resistor 3, the current flowing through the transistor 5 is first applied to charging the stray capacitance 13 of the circuit, and the discharge flowing through the machining gap 11 Current is mainly supplied from the stray capacitance 13.

In the conventional power supply circuit, the charge stored in the stray capacitance 13 is discharged through the machining gap and the small impedance included in the circuit, so the peak value of the current is high, the discharge duration is short, and the charge is relatively short. This causes deep discharge marks.

In this invention, since the induction coil 9 is provided, the charges stored in the stray capacitance 13 are discharged through a relatively large impedance. Therefore, the peak value of the current is low,
The discharge waveform has a long discharge duration, so the discharge marks become shallower, and the roughness of the finished surface becomes smaller, resulting in a good finished surface.

In this example, the roughness of the finished surface is 1 μmR.
When lowering maxJ:I, better results can be obtained without using forced liquid flow.

Q0 Effects of the Invention As understood from the above explanation, the present invention has the structure set forth in the claims, so that the stray capacitance of a pulse power supply circuit that utilizes the switching characteristics of conventional transistors can be actively reduced. It is very possible to provide a power supply circuit for an electric discharge machining apparatus that can obtain a good finished surface by using and controlling the present invention.

[Brief explanation of drawings]

FIG. 1 shows a discharge circuit showing an embodiment of the present invention.

Claims (1)

[Claims] A power supply circuit for an electric discharge machining apparatus, characterized in that a guide wire ring is provided in the power supply circuit for supplying a discharge current to a machining gap.