Experimental investigation on microhardness, surface roughness, and white layer thickness of dry EDM

Abstract

In this research, the environment-friendly dry electrical discharge machining (EDM) process is investigated to improve the microhardness, surface finish, and white layer thickness of the machined surfaces using graphite-argon gas as a dielectric medium. The graphite powder, mixed with compressed argon gas, has been used to replace the existing dielectric medium in the EDM process. Gas pressure, discharge current, pulse width, and gap voltage were working as input parameters to reduce surface roughness and enhance the microhardness and white layer thickness. The Taguchi L16 orthogonal array is applied to the design and analysis of the experimental results. The minimum surface roughness (2.23 µm) of the HN31 steel has been attained by increasing the gas pressure up to 1.0 MPa and the minimum values of pulse width (40 µs), gap voltage (40 V), and discharge current (6 A). The maximum microhardness (501.04 HV) has been obtained at 1.2 MPa of gas pressure, 120 µs of pulse width, 60 V of gap voltage, and 18 A of discharge current. The maximum white layer thickness (16.24 µm) is achieved by the maximum values of gas pressure (1.2 MPa), pulse width (160 µs), gap voltage (70 V) and discharge current (18 A). The SEM analysis had been done to reveal the white recast layer thickness and surface roughness of the machined surfaces of the dry EDM process. The SR is increased by the recast layer, pores, and microcracks on the machined surfaces. Finally, the multi-criteria optimization technique: Weight Product Method (WPM) is applied to predict optimum process parameter settings: GP: 1.2 MPa, PW: 120 µs, GV: 50 V, and DC: 18 A to meet the best machining performances (MH=493.32 HV, WLT= 14.28 µm, and SR= 3.82 µm). The validation tests were done to confirm the predicted results obtained by both the Taguchi and WSM methods.