GAP CONTROL OF ELECTRICAL DISCHARGE GRINDING WITH HIGH BANDWIDTH DUAL STAGE ACTUATORS

Electrical discharge grinding process has four types of discharge states and abnormal states, such as arcs and short circuits have great impact on the machining efficiency and the surface finish of workpieces, for example, polycrystalline diamond cutting tools. The aim of this study had been to develop a new servo system with high bandwidth dual stage actuators, which can quickly change the gap width to eliminate these harmful discharge states. The structure of the dual stage system is that a piezoelectric actuator stands on a linear actuator and both move along one axis. The piezoelectric actuator, which has high bandwidth but short travel distance, was used for the gap width control and the linear actuator, which is relatively slow but has long travel distance, tunes the feed rate of the workpiece to match the erosion rate. The gap information obtained from the electrical discharge waveform was used as a feedback signal. The linear actuator system adjusted its velocity based on the average piezoelectric displacement value. Hence, an electrical discharge machine was developed with a one-axis dual stage system. The results from simulations and experiments showed that the new system provided a high bandwidth response, as well as enhanced the machining rate and stability.