Electric heating – Metal heating – Cutting or disintegrating
Patent
1997-08-11
1999-11-16
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
B23H 102
Patent
active
059862327
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electrical discharge machining apparatus and method for machining a workpiece by electrical discharges using a tool electrode. In particular, the invention relates to an apparatus and method whereby, using a water-based dielectric fluid, electrical power pulses are supplied to a gap formed between a tool electrode and a workpiece.
BACKGROUND TECHNOLOGY
When a direct current voltage is supplied to a gap while water or a water-based dielectric fluid is supplied to a machining gap formed between a conductive workpiece and a tool electrode, the quality of the workpiece, which is typically held at a positive polarity relative to the tool electrode, may be adversely affected by electrical corrosion due to an undesirable flow of current through a dielectric fluid having a reduced electrical resistivity. In order to suppress this electrolytic effect, Japan Patent Publication 5-37766 discloses an electrical discharge machining power supply comprising a first power supply, which applies a high frequency alternating current voltage to the machining gap, and a second power supply, which supplies a direct current to the machining gap immediately upon commencement of an electrical discharge. In this disclosure, the first power supply is applied to the machining gap through a connecting circuit such as a transformer or capacitor. Therefore, a portion of the current fed from the second power supply to the machining gap may flow through the connecting circuit to the first power supply, reducing machining energy.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an electrical discharge machining apparatus and method which maintains high machining efficiency while quickly suppressing undesirable electrolytic effects.
Other objects of the present invention will in part be described below, and will in part become clear to practitioners of the art through implementation of the invention.
In order to achieve the above and other objectives, the electrical discharge machining device of the present invention, which machines a workpiece by generating an electrical discharge in a machining gap formed between a workpiece and a tool electrode, comprises an electrical discharge detector which detects the electrical discharges generated at the machining gap; a pulse generator which generates a pulse signal response, to the electrical discharge detector, which becomes inactive after electrical discharge commences; a first switching circuit which applies a voltage pulse of one polarity to the machining gap in response to the pulse signal; a second switching circuit which applies a voltage pulse of the opposite polarity to the machining gap in response to the pulse signal; a flip-flop which stores one of two states; a gate circuit which gates the pulse signal to the first switching circuit when one state is stored in the flip-flop, and which gates the pulse signal to the second switching circuit when the other state is stored in the flip-flop; a circuit which supplies a high frequency pulse to the flip-flop while a pulse signal continues; a circuit which supplies a single pulse to the flip-flop each time the pulse signal stops; and a machining current supply circuit which supplies a machining current to the machining gap after electrical discharge commences, in response to the electrical discharge detector.
Furthermore, the method of the present invention for machining a workpiece by generating electrical discharges in the machining gap formed between a workpiece and a tool electrode comprises the steps of alternately applying a voltage pulse of one polarity and a voltage pulse of the opposite polarity to a machining gap; detecting electrical discharge generated at the machining gap; interrupting application of a voltage to the machining gap after commencement of an electrical discharge; supplying machining current to the machining gap after the commencement of an electrical discharge; applying a voltage pulse, having a polarity opposite to that of the vo
REFERENCES:
patent: 5345053 (1994-09-01), Kaneko et al.
patent: 5380974 (1995-01-01), Kaneko
patent: 5416290 (1995-05-01), Magara et al.
patent: 5475195 (1995-12-01), Delpretti
patent: 5753882 (1998-05-01), Goto et al.
Kaneko Yuji
Toyonaga Tatsuo
Evans Geoffrey S.
Sodick Co. Ltd.
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