Multiresponse optimization in wire electric discharge machining (WEDM) of HCHCr steel by integrating response surface methodology (RSM) with differential evolution (DE)

HCHCr steel is widely used in cold forming molds, press tools, and die making industries, primarily due to excellent wear resistance, high compressive strength, greater dimensional stability, and high hardness. Due to poor machinability and surface integrity, HCHCr is considered as a difficult to cut material and hence there is a need to study the machinability characteristics. The current chapter deals with the study on wire electric discharge machining (WEDM) characteristics of HCHCr steel using brass electrode. The quadratic models of WEDM characteristics, namely, surface roughness, material removal rate, and tool wear rate were developed in terms of pulse on time, pulse off time, and wire feed using response surface methodology (RSM). The minimum number of experiments was planned as per orthogonal array. The constructed models were statistically tested through analysis of variance and were found to be adequate at 95% confidence interval. The established mathematical models were later employed with differential evolution (DE) to optimize the machining parameters. DE program provides the minimum values of surface roughness and the tool wear rate as well as the maximum material removal rate and the corresponding best combination of pulse on time and wire feed for a given pulse off time. The higher roughness was observed for the surface machined at higher pulse on time, higher pulse off time with higher wire feed rate. The XRD analysis clearly indicates the formation of ferrous oxide and cementite on the machined surface.