High efficient electrical discharge machining by servo voltage adaptive control

Gap distance determines the amount of effective discharging pulses in the gap; the larger the distance is the fewer amounts of effective discharging pulses are and vice versa. To achieve a high efficient machining process, it is required to increase the discharging ratio up to a certain limit beyond that arcing pulses will dominate the gap burning work-piece surface. It is easy for pulse to penetrate the gap in a condition of heavy chips accumulation in the gap and the consequence is that discharging ratio grows rapidly. In this case the gap distance which is determined by servo voltage should be enlarged to increase the difficulty of pulse penetrating in the gap. On the contrary, if the chips accumulation is light, the gap distance should be narrowed so that the penetration of gap by pulse voltage becomes easy with the consequence of discharging ratio filled with a large amount of effective discharging pulses rising. The adaptive control system is suitable for the requirement. In this paper, servo voltage is a control variable in the developed adaptive control system to drive the discharging ratio following a value which is also adapted to the machining condition in machining so that the discharging ratio will not surpass the discharging ratio limit. Based on real-time estimation of EDM process model parameters, a two-step ahead of prediction control strategy was employed to compute the control variable. By comparing open-loop machining with the machining assisted by the proposed control system, it can be found that this control system balanced the machining rate and machining stability quite well and achieved much larger machining rate than open-looped one. Moreover, the machining rate of the system is much faster than that of open-loop machining in precision machining. (C) 2018 The Authors. Published by Elsevier B.V.