The objects of the present invention are to offer a method and device for controlling a wire cutting EDM wherein two sets of switching elements corresponding to different inductance of electrode wires are controlled respectively for adjusting the slope of discharging current, so that the wire cutting EDM maintains a large current slope in normal discharge condition to promote the machining speed of wire cut EDM and a small current slope in arc discharge to prevent the wire electrode from breakage.

The controlling discharge current slope method of the wire cutting EDM of the present invention comprises following steps of: (a) applying a detecting voltage between the wire electrode and the workpiece by a discharging detecting circuit to predict whether it will be normal discharge or arc discharge next time; (b) determining the discharging periods of normal discharge or arc discharge based on the result of predicted discharging condition,(c) during normal discharge duration, driving the normal discharge switching elements to send the discharging energy between the wire electrode and the workpiece through the normal discharge electrode wires; (d) during arc discharge duration, driving the arc discharge switching elements to send the discharging energy between the wire electrodes and the workpiece through the arc discharge electrode wires.

The controlling discharging current slope device of the wire cutting EDM of the present invention comprises: an electrical discharge detecting circuit for detecting and judging whether it will be in a normal discharge or an arc discharge condition prior to sending out the discharging current;arc discharge switch elements for selectively turning on as receiving the amplified timing controlling signal from the arc discharge driver circuit to control the discharging duration of the wire cut EDM. The function condition is as follows: the normal discharge switch elements and the arc discharge switch elements are switched between electrode wire circuits having different inductance to adjust the discharging current slope, so as to maintain a larger current slope in normal discharge condition and to maintain a small current slope in arc discharge conditions.