Electric heating – Metal heating – Cutting or disintegrating
Patent
1988-01-15
1989-05-23
Pellinen, A. D.
Electric heating
Metal heating
Cutting or disintegrating
219 6913, B23H 102
Patent
active
048332895
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electric discharge machining control apparatus for controlling an electric discharge machining power source of a wire electric discharge machine, and more particularly, to an electric discharge machining control apparatus adapted for finish machining after rough machining.
BACKGROUND ART
Presently, many of wire electric discharge machines use water as a machining fluid. In this case, a leakage current flows between a wire electrode and a workpiece, whereby electrolysis is effected. In rough machining, the leakage current does not raise any special question. In finish machining which requires control of discharge energy over a necessary range for a desired machining accuracy, however, the magnitude of the leakage current, which influences the discharge energy, arouses a question. Thus, if the energy for each cycle of electric discharge during the finish machining is large, the roughness of the machined surface of the workpiece worsens. In order to improve the surface roughness, therefore, the discharge energy must be reduced, and the peak current must be minimized. On the other hand, a predetermined amount of discharge energy must be produced to maintain stable electric discharge. Since the leakage current, however, changes as the machining conditions, including the wall thickness of the workpiece, the type of machining work, etc., vary, so it is hard to obtain a suitable amount of discharge energy under various machining conditions. If the peak current is adjusted to straight machining, for example, the leakage current increases during a corner machining process, so that a sufficient voltage for stable electric discharge cannot be obtained between the workpiece and the wire electrode.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide an electric discharge machining control apparatus designed so that stable electric energy can be produced despite a change of leakage current, thus ensuring stable electric discharge and satisfactory surface roughness.
In order to achieve the above object, an electric discharge machining control apparatus according to the present invention comprises a peak voltage detecting circuit for detecting the peak value of a machining voltage applied between a wire electrode and a workpiece; and control means for controlling the machining voltage applied between the wire electrode and the workpiece in accordance with the peak voltage value detected by means of the peak voltage detecting circuit.
According to the present invention, as described above, if the value of a leakage current produced between the wire electrode and the workpiece changes, the machining voltage applied between the wire electrode and the workpiece is controlled so as to compensate the change of the leakage current. Even though the leakage current increases when the mod of finish machining is changed from straight machining over to corner machining, therefore, the machining voltage applied between the wire electrode and the workpiece can be increased to a required value for stable electric discharge. Thus, the effective machining voltage can be kept at a proper value. As a result, although the voltage or electric energy applied between the wire electrode and the workpiece, in the finish machining, is set to a small value for stable straight machining, the electric energy can be increased when the straight machining, which entails a less leakage current, is switched over to the corner machining in which the leakage current increases. Accordingly, stable electric discharge machining can be performed even during the corner machining process, so that the roughness of the machined surface can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of an electric discharge machining control apparatus according to an embodiment of the present invention;
FIG. 2 shows waveform indicative of an output from one-shot multivibrators of FIG. 1;
FIG. 3 shows a waveform indicative of a machining gap voltage;
FIG. 4
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Evans Geoffrey S.
Fanuc Ltd.
Pellinen A. D.
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