Quality improvement in mechanical micro-drilling of titanium alloy under dry conditions

Titanium alloy (Cp-Ti) grade-II is considered a hard-to-cut material due to low thermal conductivity, work hardening behaviour, and affinity with cutting tool materials. In this study, micro-holes are machined on titanium alloy (Cp-Ti) grade-II under dry conditions. Experiments are carried out by varying the machining parameters like cutting speed (5 m/min, 6.9 m/min, and 8.8 m/min), feed (5 μm/rev, 7.5 μm/rev, and 10 μm/rev), and drill diameter (Ø0.2 mm, Ø0.3 mm and Ø0.4 mm) at three levels based on full factorial design. The machined holes are characterised by responses like exit burr height, taper angle, and circularity, regression-based models are developed using response surface methodology. The optimal levels of machining parameters for multiple responses are ascertained. In the later part of the study, two methods providing a backup of aluminium and copper foil on the top and bottom surface of workpieces are experimentally evaluated. The copper foil backup method significantly reduced exit burr height and taper angle while improving circularity slightly. Whereas aluminium foil only reduced exit burr height. Finally, the effectiveness of backup methods is also analysed using recorded thrust force signals.