Influence of metal chips on drilling quality of carbon fiber reinforced plastic and titanium stacks

The mechanism in drilling of carbon fiber reinforced plastic (CFRP) is different from that of CFRP and titanium stacks. The evacuation of the titanium chips through the hole causes damage to the CFRP. To investigate the quality characteristics of CFRP-layer in drilling of CFRP/Ti stacks, an automated drilling prototype is developed and the drilling experiments of single CFRP and CFRP/Ti stacks are designed respectively for purpose of analyzing the influence of the titanium chips formation with various cutting parameters on the drilling performance of CFRP-layer. The chips morphology are firstly observed, then the mechanism of entrance spalling, high surface roughness (Ra), and hole diameter out of tolerance is studied. The results show that, low feed rate and high cutting speed generates long and folded chips wrapped around the drill, which damage the CFRP strongly. The damage can be controlled by optimization of the cutting parameters. Low feed rate helps to eliminate the entrance spalling, but enlarger the hole diameters in both the CFRP and the titanium layers. To prevent the chips from wrapping on the drill, the cutting speed should be selected in a moderate range. Therefore, the cutting parameters on the titanium layer can be recommended as the feed rate between 0.09 mm/r to 0.13 mm/r, and the cutting speed in a range of 12 m/min to 24 m/min.