The Effect of Cutting Speed and Feed Rate on Hole Surface Integrity in Single-shot Drilling of Metallic-Composite Stacks

Experimental work was carried out to evaluate the influence of cutting speed (Ti/CFRP/Al: 30/120/120 and 36/144/144m/min) and feed rate (0.05, 0.08, 0.12 and 0.15 mm/rev) on workpiece surface integrity following single-shot drilling of multilayer metallic-composite stacks (Ti-6Al-4 V/CFRP/Al-7050) using CVD diamond coated tooling. When operating with the lower cutting speed set of 30/120/120m/min and a feed rate of 0.08 mm/rev, average hole surface roughness (Ra) was ∼ 0.60, 0.87 and 0.27 μm in the Ti, CFRP and Al layers respectively after 30 holes. Roughness values in the stack increased to 0.84, 1.6 and 0.43 μm Ra when employing the higher cutting speed of 36/144/144m/min, with the drill lasting only 20 holes. Microhardness depth profile evaluation of the machined surfaces showed no appreciable variation in both the Ti and Al material, irrespective of cutting conditions. Matrix cracking and burn were apparent in the CFRP layer as feed rate increased due to greater wear of the drill corner.