Optimization of powder mixed electric discharge machining using dummy treated experimental design with analytic hierarchy process

Abstract

The analytic hierarchy process (AHP) is widely used for the optimization of multiple responses from an experimental study. In the present study, a method to obtain more reliable global weight of different alternatives has been described for a powder-mixed electric discharge machining (EDM) process. Seven different process parameters were tested to study their effect on material removal rate (MRR), tool wear rate (TWR) and surface roughness (SR) using a specially designed Taguchi orthogonal array that could accommodate factors with varying number of levels. A three-level array L27 was modified to include two-level factors using dummy treatment. The process conditions that affected the three responses were identified and optimized together using AHP for high carbon high chromium (HCHCr), EN31 and hot die steel (HDS) workpiece material. Addition of powder in the dielectric improved the MRR as the electrical conductivity of powder reduces the dielectric insulating strength. Current, powder, and electrode material significantly affected the TWR. Kerosene as dielectric was observed to be a superior alternative than EDM oil. Graphite electrode worked best for HCHCr and EN31 and W–Cu electrode worked best for HDS as they globally optimize the three output variables. Also, Cu powder suspended in the dielectric resulted in an optimal solution for HCHCr and HDS and tungsten powder was seen to be a better choice for EN31 to globally optimize the responses. To overcome problems of poor finish at high current setting in EDM, the dielectric should be mixed with powder.