Effect of process parameters on surface roughness in EDM of tool steel by response surface methodology

In this investigation, response surface methodology (RSM) is used to investigate the effect of four controllable input variables namely: discharge current, pulse duration, pulse off time and gap voltage on surface roughness (Ra). A face centred central composite design matrix is used to conduct the experiments on AISI D2 tool steel with copper electrode. The response is modelled using RSM on experimental data. The significant coefficients are obtained by performing analysis of variance (ANOVA) at 95% confidence level. It is found that discharge current and pulse duration are significant factors. RSM is a precision methodology that needs only 30 experiments to assess the conditions and is very effectual. The model sufficiency is very satisfactory as the coefficient of determination is found to be 98.1%. The electro discharge machined surface morphology was examined with a scanning electron microscope (SEM). It is observed from the SEM micrographs that there is a clear deterioration of surface with increase in discharge current.