Comparative studies on the effect of pilot drillings with application to high-speed drilling of carbon fibre reinforced plastic (CFRP) composites

Drilling is one of the most widely used machining processes in the aerospace industries. However, maintaining delamination free and high productivity in the machining of carbon fibre reinforced plastic (CFRP) can be a challenge due to the excessive thrust force or the relative low feedrate. The paper presents an improved method for machining the 2-mm thickness CFRP plate with three proposed patterns of pilot holes in high-speed drilling. Pilot drilling pattern (a), well adopted in the past, can reduce the thrust force dramatically, but it significantly increases both dynamic loading and drilling torque and causes excessive tool wear that occurred on the periphery of the drill tool. The paper also provides a FEA simulation, which is used to solve the Johnson-Cook constitutive material model and related damage modelling, and to further explain the excessive drill tool deflection induced by the pilot drilling pattern (a) in comparison with none pilot drilling. The paper then describes another two patterns, pilot drilling pattern (b) and pattern (c), that have provided advantages of reducing both the thrust force and drilling torque significantly and conducive to achieve delamination free drilling performance, as well as extending tool.