Improving EDM performance by adapting gap servo-voltage to machining state

Abstract

Electrical discharge machining (EDM) has become popular after its development over 70 years, but its potentialities have still not yet been fully exploited. That is because EDM process is so complicated that it seemed impossible to form a closed-loop control of EDM process because of lack of an efficient quantitative description of the process. In this case, EDM performance which is composed of machining ability and machining rate has been stagnant for decades. In this paper, a close-loop control system for EDM was built to adapt an EDM crucial parameter, gap servo-voltage, to the timely varied machining states in machining for the purpose of improving EDM performance. To this end, the discharging pulses in the gap between electrode and work-piece were firstly discriminated from sampled signals of gap voltages and currents, and then arcing ratio was calculated to be a control index representing machining state. Gap servo-voltage was taken to be a control variable corresponding to the index since it is the sole parameter among process parameters that can immediately change machining situation by physically changing gap distance which is proportion to gap servo-voltage, and is thus the most efficient parameter to modify machining state. Through adjusting gap distance by adaptively regulating gap servo-voltage, arcing ratios were forced to follow an arcing ratio expectation closely with restricted variations around the expectation. Thus, both an efficient and stabilized machining can be achieved simultaneously. Comparable experiments demonstrated that the potentiality of the conventional EDM Tool assisted by the established adaptive gap servo-voltage control system has been exploited and EDM performance was enhanced greatly that machined depth had been improved nearly 3 times from the conventional EDM, and more than 2 times than the EDM assisted by another adaptive electrode-discharge-time control system; and the machining rate was also much faster than those of the other two.