To improve the working efficiency by determining the electric discharge machining start position, calculating the working effective length of a pipe electrode, then executing the small hole machining of a workpiece, and judging the completion of the small hole machining when it reaches the feed quantity of the pipe electrode corresponding to the machined small hole distance from the electric discharge machining start position.
In small hole electric discharge machining, the thickness of a workpiece 2, the set position of an electrode guide 11, and the working distance of small hole machining are inputted to a controller 15. The electric discharge machining start position of a pipe electrode 1 to the workpiece 2 is determined, and the working effective length of the pipe electrode 1 corresponding to the machined small hole distance to the workpiece 2 is calculated. A working voltage is applied between the pipe electrode 1 and the workpiece 2, and the small hole machining to the workpiece 2 by the pipe electrode 1 is executed. When the small hole machining to the workpiece 2 is advanced, and the feed quantity of the pipe electrode 1 corresponding to the machined small hole distance from the small hole electric discharge machining start position to the workpiece 2 reaches a prescribed value, the completion of the small hole machining to the workpiece 2 is judged.
MITSUYASU TAKASHI
KOMATSU TATSUJI
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