CFRP drilling: Fundamental study of local feed force and consequences on hole exit damage.

• New experimental approach is developed in case of drilling an inhomogeneous work material.
• A specific post-processing method is proposed in order to quantify the mechanical load on the hole bottom.
• This contributes to limiting delamination or uncut fibers by improving the ply sequences of the CFRP.

Carbon Fiber-Reinforced by Plastic (CFRP) is now commonly used in the aircraft industry. The main challenge is to manufacture this difficult-to-cut work material, considering its quality criteria and economical aspects. Drilling is the main machining operation required for the assembly of the aircraft structure. In this paper, results are presented and discussed regarding exit delamination studied at a local scale. Because of the anisotropic properties of CFRP, the fiber cutting modes change with the composite sequence combined with the drill revolution parameters. The local feed forces generated by the cutting edge on the hole bottom may be correlated with delaminating aspects. A posttreatment method is proposed to analyze precisely these feed force and cutting torque distributions. Appropriate ply sequences are identified in order to limit the mechanical load concentration and the risk of delamination or uncut fibers