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Abstract

A controller for a wire cut electric discharge machine which can provide stable finish machining and corner-region machining with high corner-form accuracy. An electric discharge gap detection device detects a voltage between a wire electrode and a workpiece. A machining rate detection device obtains an average machining voltage and a drop voltage value Ex which is a difference between the obtained average machining voltage and a no-load voltage. A comparison device obtains the ratio Es/Ex between a reference drop voltage value Es stored in a reference machining rate relative value storage device and the obtained drop voltage value Ex. In machining of a corner portion, when the drop voltage value Ex exceeds a entrance-into-corner determination reference machining rate, a set feed speed switch device supplies a corner set feed speed, and when the machining of the corner portion finishes, so that the drop voltage value Ex decreases to a leaving-from-corner determination reference machining rate or lower, the set feed speed switch device supplies a normal set feed speed. A feed pulse calculation device obtains a feed speed which makes the rate of machining constant, on the basis of the ratio Es/Ex and the supplied feed speed, to thereby drive motors. Since the rate of machining is kept constant, the surface accuracy of finish machining is high and stable machining can be performed.

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