Effect of process parameters in electric discharge machining of D2 steel and estimation of coefficient for predicting surface roughness

D2 steel is widely used in tool and die making industry for a variety of applications. Due to its superior mechanical properties, machining of this material by conventional methods is challenging. In the present work, the effect of process parameters in EDM of D2 steel on surface roughness is investigated and process parameters are optimised to achieve least surface roughness. It is found that Ra decreased by 6.92% for change in current from 3 A to 4.5 A, and then it is increased by 67.82% for further increase in current. The change in spark gap and pulse-on time resulted in the increase in surface roughness by 8.78% and 22%, respectively. At optimum levels of process parameters, the least surface roughness achieved is 2.14 μm. SEM image reveals that due to cyclic nature of melting and cooling of the metal in EDM, it resulted in creating network of cracks and formation of recast layers on the machined region.