Burr formation and hole quality when drilling titanium and aluminium alloys

Following a brief review of key factors affecting burr size and hole quality, the paper details experimental work involving the drilling of Ti-6Al-4V titanium alloy together with Al7010-T7451 and Al2024-T351 aluminium alloys. Chemical vapour deposited (CVD) diamond coated carbide drills were used for the aluminium workpieces while uncoated carbide tools were employed for the titanium material. An experimental design based on response surface methodology was implemented to identify the effects of cutting speed and feed rate (each at 3 levels) on burr size, hole diameter and out of roundness as well as tool flank wear. Exit burr size was smallest when operating at the intermediate feed rate level for all three workpiece materials, with reductions in burr height of up to 50% and 75% for the titanium and aluminium alloys respectively. Out of roundness did not exceed 0.03 mm while the deviation on hole diameter was less than 0.04 mm in all trials, even after drilling 60 holes.