Optimisation of Dry Electrical Discharge Machining of High Speed Steel using Grey-Relational Analysis

Abstract

Dry electrical discharge machining (DEDM) is considered as a green format of the conventional oil dielectric EDM where a gas is used as the dielectric medium. This paper details experimental results when DEDM of high speed steel workpieces using multi-response optimisation. Experimental trials were performed to investigate the influence of current, pulse on-time, duty factor, gas pressure and spindle rotational speed on material removal rate (MRR), surface roughness (Ra) and radial over cut (ROC). Grey relational analysis (GRA) based on Taguchi approach was employed for multi-objective optimisation of DEDM responses. Confirmation trials were subsequently conducted and results showed that process responses can be successfully optimised using GRA. Results showed that current, duty factor and air pressure were found to be statistically significant factors at 90% confidence level, with percentage contribution ratios (PCRs) of 72.8%, 4.3% and 3.7% respectively. Micro pores and minor surface cracks were visible in the majority of specimens.