Effects of gas medium on submersed gas-flushing electrical discharge machining of different metal materials

This paper presents an investigation of the effects of the gas medium on the submersed gas-flushing electrical discharge machining (EDM) of different metal materials. Two metal materials, specifically TC4 titanium alloy and Cr12 steel, are selected as the processing objects, which are immersed in water-based working fluid. The material removal rates (MRRs), relative electrode wear rates, surface morphologies (SMs), and surface recast layers (SRLs) of these two materials during EDM were studied with both air and argon as the gas medium (Air-EDM and Ar-EDM, respectively). The experimental results showed that the MRR of Ar-EDM processing of TC4 is nearly four times that observed using Air-EDM. In contrast, the MRR of Ar-EDM processing of Cr12 is one seventh that found with Air-EDM. At the same time, a relatively thin SRL and an improved SM can be obtained by Ar-EDM with both TC4 and Cr12. During Air-EDM, heat is produced from oxidation reactions, which makes the MRR with Cr12 higher than that with TC4, and the quality of the surface morphology is poor. The results from simulations of single-pulse discharge show that the difference in thermal conductivity between TC4 and Cr12 is responsible for the different material removal rates during Ar-EDM machining.