Multi-Objective Optimization of Green Electrical Discharge Machining Ti–6Al–4V in Tap Water via Grey-Taguchi Method

Ti–6Al–4V is widely used in manufacturing field for its exceptional merits, but it belongs to difficult-to-cut material. Electrical discharge machining (EDM) became an important machining method for this material. This paper aims to combine grey relational analysis and Taguchi methods to solve the EDM parameters optimization problems of Ti–6Al–4V material. Using tap water as working liquid is good for environment, because it is healthy and safe to the operators. The process parameters include peak current, open circuit voltage, lifting height, pulse width, and pulse intermission. The tool electrode wear rate, workpiece material removal rate, and the workpiece surface roughness are selected to estimate the machining results. Experiments were executed on orthogonal array and grey relational analysis, and then the results were verified through the contrast experiment. The results indicate that the workpiece material removal rate increased from 5.90 mm3/min to 6.02 mm3/min, the tool electrode wear rate reduced from 0.41 mm3/min to 0.17 mm3/min, but the surface roughness dropped from Ra2.15 µm to Ra2.07 µm. The corresponding improvement is 2%, 59%, and 4%, respectively. By using X-ray diffraction, it is confirmed that titanium oxide are formed on the workpiece surface.