Electric discharge machine with control of the machining pulse's current value in accordance with the delay time

Claim 1

An electric discharge machine comprising a main switch circuit for supplying a current high in current peak value between electrodes which are made up of an electrode and a conductive workpiece and an auxiliary switching circuit for supplying a current low in current peak value between said electrodes, to intermittently cause electric discharge between said electrodes thereby to machine said workpiece; said electric discharge machine further comprising control signal forming circuit means for turning switching elements of said main switching circuit and said auxiliary switching circuit on and off, said control signal forming circuit means comprising: initial voltage applying means for applying an initial voltage across said electrodes with the aid of said auxiliary switching circuit; a decision time setting circuit for setting a time long enough to decide whether discharge occurring between said electrodes is normal; a detector circuit for detecting the occurrence at least one of the group of discharge and short-circuiting between said electrodes; an initial voltage application continuing means for causing, when said detector circuit detects the occurrence of discharge after said time set by said decision time setting circuit has passed, the application of the initial voltage across said electrodes by said auxiliary switching circuit to continue until said detector circuit detects the occurrence of discharge; means for driving, when said detector means detects the occurrence of discharge after the application of the initial voltage by said initial voltage application continuing means is continued, said main switching circuit to supply a normal current between said electrodes according to a given surface roughness; and means for driving, when said detector circuit detects at least one of the group of the occurrence of discharge within the time set by said decision time setting circuit and the occurrence of short-circuiting, at least one of said main switching circuit and said auxiliary switching circuit to immediately apply a current smaller than said normal current between said electrodes.