Peck drilling of CFRP/titanium stacks: effect of tool wear on hole dimensional and geometrical accuracy

The effect of tool wear on dimensional and geometrical accuracy of holes machined by peck drilling in carbon fibre reinforced plastic (CRFP) and titanium (Ti) stacks is studied. Coated and uncoated tungsten carbide drills of both fine and ultra-fine microstructures are employed to assess the importance of grain size and coating on hole accuracy. Hole profiles show two maxima: one at the hole entry and the other at the CFRP/Ti interface. Hole cylindricity as function of tool wear shows a minimum. It firstly decreases due to flank wear and subsequent reduction of the drill diameter. Then the rise of tool instability prevails with the result that an increase of the cylindricity with tool wear is brought about. Less wear-resistant drills attain this minimum in a shorter time of cutting.