A comprehensive investigation on the effect of processing conditions on the dry drilling performance of electron beam melting-manufactured Ti6Al4V

Commercial utilisation of additively manufactured components would often need post-process machining to meet the geometric tolerances. It is of vital significance to understand the machining behaviour of the material manufactured by additive route compared to the traditional routes. This work investigates the influence of processing variables on the dry drilling performance of the Ti6Al4V produced by electron beam melting (EBM). The machinability behaviour is investigated by analysing the cutting force, chip morphology, tool wear, form error, hole size and burr formation. When the spindle speed increases, three varying trends in force were observed for the investigated conditions (3000-5000 RPM). The cutting force increased when spindle speed increased from 3000 to 3500 RPM. Further, it decreased between 3500 and 4500 RPM and increased subsequently. Smooth uniform spiral chips were evident only at low spindle speed (3000 RPM), and short distorted chips were formed at high spindle speed (4500-5000 RPM), indicating favourable and non-favourable machining conditions, respectively. It was also noticed that thin, soft chips with less stiffness were formed at the combination of low feed rate (40 mm/min) and high spindle speed, which led to a 62% reduction in cutting force. Hole diametric deviation indicated that mostly oversized holes were formed with a minimum deviation of 1.8% at 3000 RPM/120 mm/min. At high spindle speed, the crown burr formation was evident irrespective of the feed rate, which is attributed to the high-temperature effect. Overall, a better surface quality of the hole was found at low spindle speed (3000-3500 RPM) and a feed rate of 40-120 mm/min.