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Aeronautic structure parts are increasingly manufactured using long fiber composite materials. A modification of the assembly hole drilling process is necessary to adapt it to the specific qualities of these materials. At the entry and at the exit of the part, delaminations are generated by the use of a conventional twist drill. The delamination of the composite materials is related directly to the thrust force (FZ) of the tool. So, it is interesting to study the drilling of thick plates for the composite assemblies. In this paper, several types of tools will be examined and an analytic model will be developed for the calculation of the critical thrust force (FZ) in drilling with a conventional twist drill. Finally, the present study can be used to choose the optimal tool that provokes the minimum of delamination in composite materials drilling.

The drilling process is currently applied for bolt or rivet assembly of composite structures. As for metallic structures, the twist drill is the most commonly used cutter. At the hole exit, some delamination is generated with the use of a conventional twist drill. In this paper, an analytical model to calculate the critical thrust force in drilling composite materials is developed. This model relates the drilling critical thrust force to the delamination conditions (opening of cracks). It takes into account the chisel edge effect and the principal cutting edge effect of the twist drill. A close correlation between the experiment and the presented analytical model results is obtained. Finally, this study can be used to minimise drilling delamination at hole exit.