The Effect of Graphite-Powder-Mixed Kerosene on Tool Wear in Micro ED Milling

This study investigates the tool-wear-reduction mechanism of graphite-powder mixed kerosene (GPMK) in micro electric-discharge machining (EDM). RC discharge circuits produce small, short discharge pulses and are therefore widely used in micro-EDM, rather than transistor circuits. In this case, given that an anode has higher energy proportion than a cathode by the massive electron collision to the positively charged workpiece, a tool electrode is negatively charged for a high material-removal rate (MRR) and low tool-wear length (TWL). In the discharge phase, however, the stray inductance of the RC discharge circuit reverses the direction of the current before the discharge plasma channel disappears; a reverse current increases the TWL and reduces processing efficiency. In this study, the TWL was decreased with GPMK by creating a circumstance that facilitates the early extinction of discharge plasma channel before the generation of the reverse current in two ways. The widening of the discharge gap by GPMK reduces the intensity of the discharge energy and enables the plasma channel to be extinguished before the reverse current generation. Furthermore, as the tool electrode approaches the workpiece, a small amount of energy discharges before the capacitor is fully charged, and these initial discharges quickly disappear before the reverse current flows. The machining performance and the quality of micro ED milling with GPMK were evaluated and compared with those of pure kerosene. With optimal machining conditions, MRR was increased by 61%, and GPMK decreased the TWL and surface roughness by 61% and 23%, respectively. This technique was also successfully applied to micro-molding fabrication.