Drilling temperature and hole quality in drilling of CFRP/aluminum stacks using diamond coated drill

Composite/metal stack materials, most often consisting of carbon fiber reinforced polymer (CFRP) composites and aluminum or titanium alloy (Al or Ti), have been widely used in the aviation industry. It is still a challenge to make holes on the composite/metal stack materials with high quality. This paper aims to investigate the influence of drilling parameters on the drilling of stack materials consisting of T800/X850 CFRP and 7075-T651 Al with regard to drilling force, drilling temperature, hole diameter and hole surface quality. Diamond coated drill bits with double point angles were employed in the drilling tests. The drilling temperature was measured utilizing a rotational motion temperature measuring system. It is indicated that maximum drilling temperature increases with the increase of spindle speed, while, it decreases with increasing feed rate. The thrust force and drilling temperature increase abnormally during drilling of the Al layer, which can be attributed to the evacuation difficulty of the long and flexible Al chips. It is found that sudden drops in the surface profile of CFRP are caused by the cavities owning to the resin degradation effects. The influences of different stack sequences on the drilling temperature and hole surface quality have also been discussed.