Wire discharge machining power source

Details Wire discharge machining power source Wire discharge machining power source

1985-11-22

1987-07-07

Pellinen, A. D.

Electric heating

Metal heating

Cutting or disintegrating

219 69C, B23H 102

Patent

active

046788840

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a wire discharge machining power source, wherein in wire-cut discharge machining a voltage having a polarity opposite to that of a voltage applied during electric discharge machining, is applied between a wire electrode and a workpiece to set an average machining voltage to zero, thereby preventing electrolytic effect and hence galvanic corrosion.
In electric discharge machining using water as a working fluid, an electrolytic effect occurs. In particular, when a workpiece such as a carbide, which is easily subject to galvanic corrosion, is machined roughly, the workpiece tends to be embrittled, resulting in inconvenience. In second cutting, the surface of the workpiece is roughened by selective galvanic corrosion of particles constituting the workpiece due to the electrolytic decomposition. A finished surface is roughened, thus resulting in inconvenience. In order to prevent this, a technique is known to those skilled in the art wherein a voltage having a polarity opposite to that of a voltage applied during machining is applied between an electrode and a workpiece during nonmachining, and an average voltage applied throughout machining and nonmachining periods is set to zero to prevent the electrolytic effect.
A reverse voltage applied between the workpiece and the electrode may vary in accordance with a change in thickness of the workpiece and a leakage current flowing from the gap between the workpiece and the electrode and the like. When a peak value of the reverse voltage is too large, the electrode is greatly damaged. When positive discharge is performed with small energy, damage to the workpiece which is caused by reverse voltage discharge worsens the roughness of the machined surface. However, when a peak value of the reverse voltage is too small, the time for applying the reverse voltage must be prolonged, thus degrading machining efficiency. In order to solve the above problem encountered in electric discharge machining of the type wherein the zero average voltage is obtained by application of the reverse voltage, a reverse voltage peak value must be controlled.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wire discharge machining power source with a circuit for applying, between a wire electrode and a workpiece during nonmachining, a voltage having a polarity opposite to that of a voltage applied during machining, so as to prevent an electrolytic effect, wherein variations in peak value of the reverse voltage are eliminated, the reverse voltage applying time can be automatically controlled, and the average machining voltage can be set to zero.
In order to achieve the above object of the present invention, there is provided a wire discharge machining power source for turning on a switching element to apply a voltage between a wire electrode and a workpiece so as to cause an electric discharge and for applying a reverse voltage having a polarity opposite to that of the voltage applied during machining when the switching element is turned off, the reverse voltage being applied between the wire electrode and the workpiece through a transistor and a resistor. A reverse voltage application time control circuit detects an average machining voltage applied between the wire electrode and the workpiece, and generates a pulse with a pulse width corresponding to the average machining voltage; and a reverse voltage regulating circuit generates an output with a value corresponding to a holding voltage of a sample/hold circuit for detecting and holding a difference between a reference voltage and a voltage between the transistor and the resistor upon application of the reverse voltage, the output from the reverse voltage regulating circuit being generated for a period corresponding to the pulse width of the pulse from the reverse voltage application time control circuit.
According to the present invention, in wire-cut discharge machining, the reverse voltage having a polarity opposite to that of the voltage appli

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patent: 4303957 (1981-12-01), Bell, Jr. et al.
patent: 4339650 (1982-07-01), Tanaka et al.
patent: 4347425 (1982-08-01), Obara

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