Performance evaluation of SiC powder mixed electrical discharge machining: a case of wire cut mode with re-circulating molybdenum wire

A review of the available literature on powder mixed electrical discharge machining (PMEDM) indicates that most of the research has been done for “die sinking machining mode” whereas the “wire cut machining mode” has not received due attention despite being an important process variant. This work employs silicon carbide (SiC) powder mixed dielectric fluid for machining of AISI D2 in “wire cut” mode with re-circulating molybdenum wire (an economic and chemically stable proposition as a tool). The effect of five process parameters (powder concentration, peak current, pulse on time, nozzle flushing pressure and stand-off distance) has been evaluated on surface roughness, kerf width, material removal rate, and wire wear ratio using Taguchi’s approach followed by analysis of variance (ANOVA) for determining statistically significant factors at 95% confidence level. It is found that for surface roughness, higher current and low to moderate concentration levels (2 to 4g/l) deteriorate surface quality; higher values of pressure and stand-off distance are also seen to adversely affect it. For material removal rate, pulse on time as well as its interactions with powder concentration and current, are statistically significant. A higher pulse on with smaller and moderate powder concentrations (2g/l and 4g/l) reduces MRR. For the wire wear ratio, the current is the sole significant factor (PCR of ~65%). SEM analysis of the machined workpiece for the maximum MRR condition quantifies the recast layer as ~19microns. An indirect comparison with the reported values for non-powdered EDM process indicates that for the similar wire (molybdenum), the use of SiC powder maintains the surface roughness and kerf values, for a much harder D2 material used in this work.