Experimental study on green electrical discharge machining in tap water of Ti–6Al–4V and parameters optimization

Ti–6Al–4V is widely used in the aerospace, automobile, and biomedical fields, but is a difficult-to-machine material. Electrical discharge machining (EDM) is regarded as one of the most effective approaches to machining Ti–6Al–4V alloy, since it is a non-contact electro-thermal machining method, and it is independent from the mechanical properties of the processed material. This paper aims to combine grey relational analysis and Taguchi methods to solve the problem of EDM parameters optimization. From the viewpoint of health and environment, tap water as working fluid has good working environment, since it does not release harmful gas. The process parameters include discharge current, gap voltage, lifting height, negative polarity and pulse duty factor. The electrode wear ratio (EWR), material removal rate (MRR) and surface roughness (SR) as objective parameters are chosen to evaluate the whole machining effects. Experiments were carried out based on Taguchi L9 orthogonal array and grey relational analysis, and then verified the results through a confirmation experiment. Compared the machining parameters A1B1C3D2 with A1B2C2D2, MRR increased from 1.28 mm3/min to 2.38 mm3/min, EWR decreased from 0.14 to 0.10 mm3/min and SR decreased from Ra 2.37 μm to Ra 1.93 μm. The process parameters sequenced in order of relative importance are: the ratio of pulse width to pulse interval, discharge current, lifting height and gap voltage. The results showed that using tap water machining Ti–6Al–4V material can obtain high MRR, decrease the machining cost and have no harmful to the operators and the environment.