Effects of process parameters on performance measures in multi-axis near-dry EDM using copper and brass electrodes

Inconel-718 (IN-718) is a nickel-based superalloy widely employed in aerospace, nuclear, and gas turbine applications owing to its excellent high-temperature strength, oxidation resistance, and mechanical stability. However, its low thermal conductivity, high toughness, and pronounced work-hardening tendency make it difficult to machine using conventional methods. This study investigates the machining performance of an in-house developed multi-axis near-dry electrical discharge machining (MX-ND-EDM) system for machining IN-718 using copper and brass tubular electrodes. A compressed air-assisted liquid mist was utilized as the near-dry dielectric medium to improve flushing efficiency and reduce dielectric consumption. The effects of discharge current, gap voltage, and pulse-on time on material removal rate (MRR) and electrode wear rate (EWR) were evaluated using a Taguchi L 9 orthogonal array and signal-to-noise ratio analysis. Experimental results revealed a significant influence of electrode material on machining performance. The brass electrode produced the highest MRR of 10.21571 mm³/min, nearly twice that achieved with the copper electrode (5.37241 mm³/min), indicating superior erosion efficiency and spark energy transfer. Conversely, the copper electrode exhibited lower wear characteristics, with EWR values ranging from 4.582 to 5.742 mm³/min, while the brass electrode showed higher EWR values between 12.119 and 14.075 mm³/min. These variations were attributed to differences in the thermophysical properties of the electrode materials. Surface characterization further revealed crater formation, localized melting, material transfer, and re-solidified debris on the electrode surfaces. The findings demonstrate the feasibility of MX-ND-EDM as a sustainable machining approach for IN-718 and provide insights into electrode selection for balancing productivity and tool life under near-dry machining conditions.