Improving performance of micro-hole EDM based on frequency detection method

Electrical discharge machining (EDM) mainly uses the spark discharge generated between the workpiece and the tool electrode for material erosion; however, abnormal discharge status such as arcing and short circuit often occurs in the process of EDM, and normal discharge will also change into abnormal under certain conditions, which increases the difficulty of discharge state detection. To improve the detection accuracy of discharge states, the amplitude frequency characteristics of discharge voltage signal were studied and a discharge state detection system based on frequency detection was developed. The results showed that the amplitude of voltage signal of spark in the high-frequency range (> 30 MHz) is greater than that of the arcing. Spark and arcing can be effectively distinguished by detecting the amplitude of high-frequency component of the voltage signal. Combined with high-frequency component amplitude detection, voltage detection, and current detection, a discharge state detection system is developed, which can accurately distinguish open circuit, spark, arcing, and short circuit. The discharge state coefficients are calculated and used as the feedback signals of the adaptive control system for micro-EDM drilling process. Compared with the general control based on the average voltage method, using adaptive control can increase the average machining efficiency by 22.4%, reduce the average burned area of the inner surface of micro-holes by 38.2%, and reduce the number and size of micro-cracks in the recast layer.