Experimental investigation and parametric optimization of machinability and surface characteristics in wire EDM of...

This study investigates the machinability of Inconel 718 (IN718) in wire electrical discharge machining (WEDM) using molybdenum wire and demineralized water as the dielectric fluid, aiming to optimize machining efficiency and surface quality. The effects of current, pulse duration (T_on), and pulse interval (T_off) on machining time (MT), material removal rate (MRR), and surface roughness (SR) were analyzed. The overall evaluation criteria (OEC) method was employed to optimize multi-response outputs. Surface morphology was examined through SEM, and elemental analysis was performed using EDS. The results showed that increasing current and T_on enhanced MRR but also led to higher SR due to deeper crater formation. A high T_on combined with insufficient T_off caused process instability, increasing MT and reducing MRR. Conversely, increasing T_off improved surface finish by enhancing debris removal, though excessive T_off slightly reduced MRR. Current was the most influential factor across all responses, as evaluated by ANOVA. Optimal machining conditions, when equal importance was given to efficiency and surface quality in OEC, were identified as 2 A current, 40 µs T_on, and 9 µs T_off. SEM analysis revealed that lower discharge energy produced a uniform recast layer with fewer defects, while higher energy resulted in larger globules, micro-pores, and debris accretion. EDS analysis revealed the presence of carbon, oxygen, and molybdenum on machined surface, indicating element migration and possible formation of secondary phases in the recast layer. These findings offer a practical basis for optimizing machining efficiency and surface quality in WEDM of IN718 for high-performance aerospace and thermal applications.