Comparative tool wear study based on drilling experiments on CFRp/Ti stack and its individual layers

Carbon fiber reinforced plastic and titanium (CFRP/Ti) stacks are being widely used in aerospace industries due to its high strength-to-weight ratio. Drilling is one of the most widely used machining processes in aerospace industries. However, the wear mechanism in the drilling process of CFRP/Ti stack is still not fully understood deterring the development of new drills for the stacks at the present time. This paper presents the comparative tool wear study based on the drilling experiments on CFRP/Ti stack as well as its individual plates (CFRP-only and Ti-only) with uncoated and coated tungsten carbide drills. The ultra-hard ceramic coatings used for this study include AlxTi1−xN and nanocomposite (nanocrystalline AlTiN grains surrounded by Si3N4 matrix). The dominating tool wear mode when drilling CFRP-only was edge rounding wear. When drilling Ti-only, the severe edge chipping and flank wear substantially reduce the tool life. Surprisingly, the tool life in drilling CFRP/Ti stack was improved more than three times of that in drilling Ti-only for each drill used in our experiment. The main reason for the remarkable improvement comes from the elimination of severe edge chipping prevalent in drilling Ti-only. In drilling CFRP/Ti stack, the severe edge chipping was eliminated by the carbon fibers in CFRP layer brushing off the Ti adhesion and smoothing the cutting edge. Discounting the severe edge chipping in drilling of Ti-only, the total wear volume after drilling CFRP/Ti stack is close to the sum of the wear volumes from the flank wear in drilling Ti-only and the edge rounding wear in drilling CFRP-only. Because the severe edge chipping was eliminated in drilling CFRP/Ti stack, the coated drills with the excellent resistance against edge chipping and the better resistance against flank wear did not show substantial advantages over the uncoated drill.