Electric heating – Metal heating – Cutting or disintegrating
Patent
1989-07-05
1992-12-15
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
219 6912, 219 6919, B23H 102, B23H 702, B23H 716
Patent
active
051719568
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electric discharge machine of a type having a short-circuit detecting apparatus for positioning a workpiece and a tool electrode, and more particularly, to an electric discharge machine which is capable of preventing electrolytic corrosion attributable to an application of a short-circuit detecting voltage applied from a short-circuit detecting apparatus in between a workpiece and a tool electrode.
BACKGROUND ART
At start of electric discharge machining, positioning of a workpiece and a tool electrode must be made. Conventionally, short-circuit detecting means is employed for detection of the workpiece being brought at its reference surface in contact with the tool electrode, while the workpiece and the tool electrode are moved relatively to each other. The thus detected contact position is used as a basis for the positioning. More specifically, a typical short-circuit detecting means comprises a comparator having first and second input terminals which are supplied with a short-circuit detecting voltage and a reference voltage, respectively. The comparator is so arranged as to generate a signal, indicative of the workpiece being brought in contact with the tool electrode, in response to a change in the voltage appearing at the first input terminal connected to the tool electrode through a diode for shutting an electric discharge machining voltage, which change occurs when the workpiece and the tool electrode are brought in contact with each other so that the tool electrode is grounded through the workpiece.
In an electric discharge machine equipped with a short-circuit detecting means of the aforementioned type, the short-circuit detecting voltage is always applied, and hence the same voltage is applied in between the workpiece and the tool electrode through the diode when the electric discharge machining voltage is turned off. As a result, corrosion is liable to occur on the workpiece, in particular, of an electrolytically corrosive type.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an electric discharge machine which is capable of preventing a workpiece from being corrosively damaged attributable to an application of a short-circuit detecting voltage which is applied from short-circuit detecting means in between the workpiece and a tool electrode.
In order to achieve the object, an electric discharge machine of the present invention comprises detection means for applying a short-circuit detecting voltage in between a workpiece and a tool electrode so as to detect short-circuit of the workpiece and the tool electrode, and means for selectively prohibiting an application of the short-circuit detecting voltage applied from the short-circuit detecting means in between the workpiece and the tool electrode.
As mentioned above, according to the present invention, since the application of the short-circuit detecting voltage from the short-circuit detecting means in between the workpiece and the tool electrode is selectively prohibited, the short-circuit detecting voltage can be prevented from being applied in between the workpiece and the tool electrode, and hence the workpiece can be prevented from being damaged attributable to the application of the same voltage, under a condition accompanied with no short-circuit detection for relative positioning of the workpiece and the tool electrode, e.g., under a condition where no electric discharge machining is effected, whereby it is possible to produce molded products free from corrosive flaws.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing an essential part of a wire-cut electric discharge machine according to a first embodiment of the present invention;
FIG. 2 is a schematic view, showing an electric discharge machine according to a second embodiment of the present invention;
FIG. 3 is a schematic view showing an electric discharge machine according to a third embodiment of the present invention; and
FIG. 4 is a view schematic showing a conventional
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Haruki Obara
Izumiya Syunzo
Evans Geoffrey S.
Fanuc Ltd.
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