GB1423856A - Electric discharge machining circuit - Google Patents

Abstract

1423856 Electro-erosion M MIRONOFF 17 May 1973 [1 June 1972 25 Oct 1972] 23513/73 Heading B3V An electrical discharge machining circuit comprises a capacitor Cu for delivering erosion pulses to the machining gap, means for delivering a voltage pulse to the gap to pre-ignite a discharge channel in the gap, which means includes a voltage threshold means D2 and a transformer T whose primary winding passes a current only when the voltage across the threshold means D2 reaches a predetermined value. In one embodiment, the capacitor C u is charged by a voltage source U o and when the charging voltage U ch reaches a voltage U z a Zener diode DZ conducts causing a current pulse to be induced in the secondary of the transformer T at a voltage U p higher than the charging voltage of the capacitor C u . A pre-ignition pulse is thus applied to the gap and enables the capacitor C u to discharge through the gap. The polarity of the discharges are set by an inverter I n and their duration controlled by an adjustable inductance Ld. The pre-ignition pulse energy is controlled by resistors R 1 , R 2 . In another embodiment (Figs. 6 and 7, not shown), another capacitor (C) is charged by the source U o through a potentiometer (P) to a voltage (V) whereupon transistors (T r1 , T r2 ) are switched to cause the transformer (T i ) to produce the pre-ignition pulse. In another circuit described which does not fall within the scope of the claims, at least one capacitor (C pr ) (Fig. 4, not shown) is charged to a voltage (U<SP>1</SP> d ) within a time (t<SP>1</SP>ch) (Fig. 5, not shown) by a separate, higher voltage D.C. source (U<SP>1</SP>d), whereupon a pre-ignition pulse is released to the gap to enable the voltage (U ch ) across the capacitor C u to be discharged into the gap.