Improvement of Machining Stability of Micro EDM Using Electrostatic Induction Feeding Method

Abstract

This paper describes the machining characteristics of the electrostatic induction feeding method. With the conventional relaxation pulse generator normally used in micro electrical discharge machining, since the gap voltage begins rising after the end of the previous discharge, it is difficult to keep the minimum necessary discharge interval between pulse discharges to recover the dielectric breakdown strength of the gap. Thus, localized discharge and abnormal arc easily occur, resulting in machining instability. Moreover, since discharge even occurs before the capacitor is fully charged due to the long time constant of the RC circuit, it is difficult to obtain uniform discharge energy per pulse. In contrast, with the electrostatic induction feeding method, since only a single discharge occurs for each cycle of the periodic pulse voltage, the discharge gap can be cooled regularly during the discharge interval, resulting in stable machining. Therefore, machining characteristics of the electrostatic induction feeding method were investigated using the machining system newly developed for micro-hole drilling. Machining results show that the machining speed of this pulse generator is higher than that of the relaxation pulse generator in micro-hole drilling, especially when rotation speed of the tool electrode is low.