Optimization of Surface Roughness by Design of Experiment Techniques during Wire EDM Machining

Wire electrical discharge machining (WEDM) is widely used to machine precision parts from electrically conductive materials; however, achieving a low surface roughness remains a long-standing challenge. This study investigates the effects of three process parameters, namely pulse-on time (Ton), pulse-off time (Toff) and wire feed (WF), on the surface roughness of 6061 aluminium alloy. The study has three objectives: first, to determine the individual and interaction effects of these WEDM parameters on surface roughness; second, to develop a regression model for surface roughness in the WEDM of 6061 aluminium alloy; and third, to identify the combination of parameters that minimises surface roughness. The experiments were designed using response surface methodology (RSM) with a face-centred central composite design of 20 runs, including six centre-point replicates. Trial cuts were first performed to confirm the parameter ranges, after which the formal experiments were carried out. The surface roughness parameters Ra, Rq and Rz were measured, and Ra was analysed using analysis of variance (ANOVA), perturbation plots, three-dimensional (3D) surface plots and two-dimensional (2D) contour plots. A quadratic regression model was developed, its adequacy was checked, the parameters were optimised, and the model was validated through confirmation runs. The results identified Ton as the dominant parameter, whereas Toff and WF showed weaker individual effects, although their interaction was significant. A lower Ton, a higher Toff and a lower WF produced smoother surfaces. The optimal parameters were Ton = 3.055 µs, Toff = 34.330 µs and WF = 8.060 m/min. The validation runs confirmed the reliability of the model, with prediction errors not exceeding 10%.