Surface integrity and kerf characteristics in Wire-EDM of WAAM-fabricated hybrid ER70S-308L steel: A Taguchi-based parametric analysis

Abstract

Wire-Arc Additive Manufactured (WAAM) components exhibit surface irregularities, necessitating optimized processing techniques to achieve precision and reliability. This study investigates the wire electric discharge (ED) machining performance of WAAM-fabricated hybrid ER70S-308L steel (a compositional hybrid formed by simultaneous deposition of ER70S and 308L stainless steel wires), focusing on material removal rate (MRR), kerf width (KW), kerf taper (KT), and surface integrity. A Taguchi-based design of experiments (DoE) was employed, considering discharge current (I), pulse-on time (T_on), pulse-off time (T_off), and wire speed (W_s). Results indicate that Ton significantly influences MRR (34.13 %) and top KW (47 %), while current predominantly affects KT (87.54 %) and bottom KW (91.99 %). Surface morphological analysis reveals key interfacial features, including recast layers, micro-cracks (6–10 μm), and spherical globules, attributed to intense thermal effects during machining. Predictive models were developed with high accuracy (R²: 78.53–99.15 %) for MRR, KW, and KT. To achieve a balanced machining outcome, multi-response optimization was performed using the desirability function approach (DFA). The optimal parametric setting (I = 5 A, T_on = 10 μs, T_off = 20 μs, W_s = 5.5 m/s) yielded the highest composite desirability index of 0.8518, simultaneously enhancing material removal rate and kerf geometry. The findings provide critical insights into surface modification and interfacial phenomena in subtractive processing of WAAM hybrid steels, supporting the development of efficient machining strategies for advanced manufacturing. These findings can benefit applications in aerospace, tooling, and repair of large structural components where precision post-processing of WAAM parts is essential.