| 摘要 |
PURPOSE:To aim at avoiding abnormal machining by providing calculators for calculating the change rate of the ratio between the frequency of short-circuit and instant electric discharge and the frequency of abnormal electric discharge or the difference value therebetween so that abnormal machining is predicted and discriminated in accordance with data from the calculators to automatically change over the pull-up of an electrode at a regulated time. CONSTITUTION:A Td measuring meter 12 measures the unload time Td of each of electric discharge waveforms, and an electric discharge waveform sorter 13 delivers signals which are sorted into three kinds, instant electric discharge D1, normal electric discharge D2 and open D3 in accordance with the result of the measurement by the measuring meter 12. Further, an electrode feed control device 15 performs an electrode servo-feed in accordance with the frequencies of the instant electric discharge D1, the normal electric discharge D2 and the open D3. Meanwhile first and second calculators 20, 22 calculate the change rate of the ratio between the instant electric discharge D1 and the normal electric discharge 2. Further, when an abnormal machining determinator 27 determines abnormal machining, it delivers a signal to a control device 28 to automatically change over the rest time, thereby it is possible to avoid abnormal machining.
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