Study on discharge states detection method of VHF micro-EDM pulse generator used in polishing of optoelectronic device

摘要

The gap average voltage measurement method is commonly used to detect the discharge state in micro electrical discharge machining (Micro-EDM), which is simple and effective for the discharge states detection of transistor pulse power and relaxation type pulse power. In order to further explore the ultimate machining ability of micro-EDM, a very high frequency (VHF, frequency range 30MHz～300MHz) micro energy pulse generator based on the principle of circuit resonance has been developed in a previous study. It has smaller discharge energy and nanoscale discharge erosion ability compared with the traditional pulse power. Furthermore, defects in micro-EDM such as thermal damage, recast layer and heat affected zone are significantly reduced. A simulation circuit model was established to analyze the effect of the gap average voltage measurement method applied to VHF pulse generator. The results show that the inter-electrode discharge states cannot be distinguished effectively and sensitively by this means. In order to detect the discharge state of VHF pulse generator, a novel method to detect discharge state based on impedance change of inter-electrode channel was presented, which is not affected by the pulse power. Hence, when the detection circuit was fixed, the detection sensitivity and the accuracy of threshold voltage was not varied according to different pulse parameters. Both simulation and experimental studies were undertaken to verify the effectiveness of the proposed method. The results demonstrate that the discharge states of VHF pulse generator can be distinguished by this detection method.