Powder additives influence on dielectric strength of EDM fluid and material removal

Abstract

Electrical discharge machining (EDM) is used to machine difficult-to-machine materials having high hardness and toughness. One of the recent advancements in the EDM process is the powder mixed electrical discharge machining (PMEDM) process, in which the metallic or abrasive additives in the form of fine powders are added to the dielectric fluid. PMEDM was found to improve machinability in terms of higher material removal rate (MRR) and enhanced tool wear index (TWI), by reducing the breakdown strength of the dielectric. In PMEDM process, machining happens with relatively larger spark gap with enhanced machining characteristics. This paper investigates the influence of powder mixing on the breakdown strength of the liquid dielectric and the gap voltage. Determination of dielectric strength was carried out with a specially designed experimental set-up adhering to ASTM standard D1816 - 97. Tests were conducted using silicon carbide, alumina, copper and aluminium powders. The effect of varying the grain size was also studied. An experimental set-up was also designed and realised to measure the influence of powder mixing on the gap voltage and MRR in machining of titanium alloy. The results have shown significant improvement in MRR and TWI.