Optimisation of Process Parameters in Wire Electrical Discharge Machining of Inconel 718 Superalloy Using Taguchi-Grey Relational Analysis and Response Surface Methodology

Wire Electrical Discharge Machining (WEDM) is a non-conventional precision machining process that has assumed critical importance in the aerospace, defence, and energy sectors owing to its ability to machine electrically conductive hard-to-cut materials irrespective of mechanical hardness. Inconel 718, a nickel-based precipitation-hardenable superalloy exhibiting high creep resistance, excellent high-temperature mechanical properties, and superior oxidation and corrosion resistance, presents significant machinability challenges for conventional cutting tools due to its high work-hardening rate, low thermal diffusivity, and affinity for tool material at elevated cutting temperatures. This study investigates the simultaneous optimisation of four critical WEDM process parameters — pulse-on time (Ton: 105–135 µs), pulse-off time (Toff: 45–65 µs), servo voltage (SV: 20–40 V), and wire feed rate (WF: 4–8 m/min) — on three response variables: material removal rate (MRR), surface roughness (Ra), and kerf width (KW). A L27 Taguchi orthogonal array experimental design incorporating zinc-coated brass wire (0.25 mm diameter) in dielectric fluid (deionised water, conductivity 18 µS/cm) was used. Multi-response optimisation via Grey Relational Analysis (GRA) identified optimal parametric combination as Ton = 120 µs, Toff = 55 µs, SV = 30 V, WF = 6 m/min, yielding MRR of 42.6 mm³/min, Ra of 1.84 µm, and KW of 0.312 mm. ANOVA results indicate Ton as the dominant parameter (39.2% contribution to MRR; 51.4% to Ra). Response surface methodology confirmed the GRA-optimal combination through regression model validation (R² = 0.94). SEM-EDS analysis of machined surfaces reveals recast layer formation of 8–14 µm thickness and residual micro-crack density inversely correlated with servo voltage. The results provide process window guidelines for WEDM of Inconel 718 in near-net-shape turbine component manufacturing.