Numerical and experimental study of the drilling of multi-stacks made of titanium alloy Ti-6Al-4V: interface and burr behavior

Machining and especially drilling of multi-stacks is a challenge task. In fact, drilling of multi-layers generates several damages such as burr at the hole exit and the decohesion of the interface of the layers. It is important to note that the decohesion phenomenon favors the accumulation of the chips at the interface of the layers. In this case, it will not be possible to use the automated system (such as robots) for drilling and fastening in the aeronautical field. This work gives focuses on the numerical and an experimental study during drilling of a multi-stack made of titanium alloy (Ti/Ti), which is usually encountered during the assembly of the aircraft door at Boeing Company. The impact of the machining parameters on the thrust force, responsible of the decohesion of the layers as well as the burr size, has been investigated experimentally and numerically. The proposed model is based on the behavior law of Johnson-Cook for the titanium parts and the cohesive zone for the interface. The main experimental and numerical results have shown that the feed rate and the thickness of the bottom layer have a great influence on the size of the decohesion zone. However, the burr at the hole exit is strongly influenced by the feed rate.