Abstract: The formation of the exit defects in carbon fibre-reinforced plastic plates is investigated and their features in terms of drilling conditions is characterized. It is found that spalling and fuzzing are the major mechanisms of exit defects and spalling is usually a severer damage. The spalling, consisting of a main region and a secondary region, is caused by chisel and cutting edge actions, in which the former plays a key role. The fuzzing, however, exists in the cutting region where the included angle between the fibre direction of the surface ply and that of the cutting speed is acute. A severer spalling damage corresponds to a low spindle speed, a high feed speed, a large feed rate and a great thrust force. There exists a critical ratio of cutting speed to feed speed, which is about 3 000~4 000, beyond which the spalling size can be minimized.

Key words: Carbon fibre-reinforced plastics, Drilling conditions, Fuzzing, Spalling