On the quantitative analysis of drill edge wear when machining CFRP/Ti6Al4V stacks

Mechanical drilling of composite/metal stacks is a challenging task due to the rapid tool wear leading to poor hole quality and short tool life. To control effectively the wear process of tools, a scientific understanding of phenomena behind the drill wear progression remains a subject of fundamental importance. The present work aims to quantify the mechanisms of the drill edge wear during the machining of CFRP/Ti6Al4V stacks using diamond-coated twist drills. The novelty of this study lies in identifying the phenomenon of the wear mode transition during the stacks machining. A quantitative analysis was conducted to correlate the flank wear extents at different positions of drill edges with the material removal volume at the constant cutting speed and feed rate. The wear rate of each drill edge segment was studied with respect to the material removal volume. A mechanism transition from adhesion to abrasion is identified after drilling a certain number of stack holes, being the cause of the phenomenon that the drill wear rate decreases with increasing the material removal volume. The results discussed in this paper offer several implications for the structure design and edge reinforcement of drill bits specialized for the machining of CFRP/Ti6Al4V stacks.