Drilling of thick composite material with a small-diameter twist drill

Composite materials are increasingly used in aeronautics. The assembly of aircraft structures requires the machining of different parts. The drilling of thick composite plates is a particularly delicate operation because of the fast rise in the temperature of the tool and the material. This causes defects at the hole entry, on the wall of the hole, and at the exit of the plate. These defects reduce the resistance to structural failure, and therefore, it is important to find a solution to minimize and to remove them if possible. The cutting conditions are the main parameters that affect the quality of the machining. This paper focuses on the choice of the feed rate corresponding to the critical case of delamination determined in the case of a twist drill with a small diameter. The feed rate is calculated by means of two models developed in the laboratory. The first model is analytical; it allows determining the critical thrust force at delamination at the exit of the hole as a function of the characteristics of the material and the load applied by the tool. The second allows predicting the drilling thrust force based on the feed rate. The combination of these two models can determine the critical feed rate with respect to the delamination at the exit of the hole.