Post-processing of WAAM-Inconel via sustainable-EDM with brass and copper tools

The inherent microstructural variability, poor surface finish, and dimensional inaccuracies of wire arc additive manufacturing (WAAM)-fabricated Inconel superalloys necessitate effective post-processing to achieve the required functional performance. Therefore, this study quantitatively evaluates the post-processing capability of near-dry electrical discharge machining on WAAM-fabricated Inconel and develops linear regression models. Experiments were conducted using a Taguchi-L9 design with three levels each of three parameters-current, duty cycle, and dielectric flow rate-while material removal rate (MRR), tool wear rate (TWR), and surface roughness were considered as performance variables. All experiments were performed for both copper and brass tool-electrodes, and the resulting response variables were quantitatively compared. The MRR obtained with brass (0.121-3.451 mm³/min) was considerably lower than with copper (0.906-12.34 mm³/min) and showed non-linear behaviour with increased instability at higher discharge currents and duty cycles. Copper consistently exhibited lower TWR, with near-zero or negative wear, while brass ranged from 0.340-5.279 mm³/min. The maximum surface profile height (Rz) ranged from 7-26 μm for brass and 13-41 μm for copper. These results indicate that copper enables high-productivity machining with superior performance, while brass is better suited for finishing applications. Except for the brass TWR model, which showed a lower adjusted R², all regression models were statistically significant and explained a substantial proportion of the variability in MRR, TWR, and Rz. The relatively poor fit of the brass TWR model is attributed to the inherently non-linear relationship between process parameters and TWR, which a simplified linear regression model cannot fully capture.