Performance evaluation of graphite and titanium oxide powder mixed dielectric for electric discharge machining of Ti–6Al–4V

Abstract

Ti–6Al–4V is the most commonly used titanium alloy in aerospace, marine, and biomedical applications. Due to the properties of poor machinability in conventional machining, Electrical Discharge Machining (EDM) is considered a prospective alternative for machining this strategic material. This study aims at enhancing the performance of powder mixed EDM (PMEDM) in the machining of Ti–6Al–4V with the application of two different types of powders, namely Graphite (Gr) and Titanium Oxide (TiO2) powders, with different concentrations in dielectric—kerosene. The effect of these powers and their relative quantities are studied in terms of metal removal rate (MRR), tool wear rate, Surface Roughness, and surface integrity. Machining is performed using the copper electrode and kerosene as the dielectric medium. A separate container and a submersible pump are used to limit the quantity of powder and keep the powder in suspension, respectively. Design of experiments guided by Design-Expert software is employed to minimize the number of experimental runs and develop empirical models of response parameters in terms of the variable parameters—peak current, powder type, and powder concentration. Findings indicate that TiO2 powder has a much higher effect on MRR compared to graphite powder, as the maximum MRR in the case of TiO2 powder is recorded 41.01\xa0mm3/min against 11.98\xa0mm3/min for graphite powder, i.e., 3.42 times higher. Similarly, the tool wear ratio for TiO2 powder is 0.0704 against 0.1219 for graphite powder at the maximum MRR, which is 1.73 times lower compared to that of graphite powder. The same ratios at the minimum MRR for TiO2 is 0.0098, and for graphite power is 0.0282, which is again 2.88 times lower compared to that of graphite powder. In terms of average surface roughness, Ra, the performance of TiO2 is far better compared to graphite powder since the maximum surface roughness attained with TiO2 powder is 3.265\xa0μm against 9.936\xa0μm for graphite powder at the highest MRR and the same attained at the lowest MRR are 2.228\xa0μm and 2.411\xa0μm for TiO2 and graphite powders respectively. The mechanism of the effects of PMEDM on surface texture has also been observed using SEM images to study the influence of powder concentration on surface morphology.