Study of the One-Shot Drilling of CFRP/Ti6Al4V Stacks with a Double Tip Angle Cutting-Tool Geometry

The drilling of dissimilar materials in hybrid structures is one of the main machining operations in the aeronautical field. In order to reduce cycle-time, the aerospace industry is searching for the implementation of One-Shot (OS) strategies to drill CFRP/Ti6Al4V hybrid stacks with double-pointed angle cutting-tools, due to its good behavior when CFRP is drilled. However, there is a lack of information about its behavior when CFRP/Ti are drilled. For this reason, in this paper a study of the influence of the double tip geometry on the final quality of the bores has been carried out. Macro (diameter, burrs and delamination) and micro-geometric features (surface roughness) have been evaluated, and their deviations have been directly related with the main wear mechanism present in the process, adhesion and abrasion. Increasing in diameter can be related with the adhesion of Ti, while increase in delamination and burr heights are associated with a severe loss of cutting capacity due to abrasive wear. As was expected, double tip angle is not the best choice for drilling Ti alloys due to quick generation of burrs. In the opposite way, it offers good results in the machining of CFRP.