Influence of main cutting edge structure on hole defects in CFRP/titanium alloy stacks drilling

Tool structure plays an important role in CFRP/titanium alloy (Ti) stacks drilling. The purpose of this paper is to study the performance of drills with different main cutting edge structures in CFRP/Ti stacks drilling. The effects of the main cutting edge structure on thrust force, chip morphology, interface damage and burr are analyzed. The results show that the interface damage is the least after candle stick drill drilling, because the outer corner tip structure can remove part of heat that left on the machined surface in the cutting stage of the main cutting edge. Compared with the other two kinds of drill bits, the height of burr produced by candle stick drill at titanium alloy layer is the smallest. The reason is that outer corner tip structure of the candle stick drill can counteract part of the radial cutting force which produced by the main cutting edge, and push the material inside to facilitate material removal. The outer corner structure of the drill bit has an important influence on the thrust force, the interface damage and the exit burr, so the special drill design for CFRP/Ti stacks must focus on the outer corner structure.