Cutting mechanisms in drilling of aramid composites

The results of an experimental research on the drilling of aramid fibre reinforced plastics are reported. A drilling machine has been instrumented in order to detect the thrust force and the torque as a function of the depth of the hole. The signals of the transducers were acquired by an analog to digital converter card inserted in a personal computer. The apparatus enabled analysis of the cutting mechanism of commercially available twist drills intended for the drilling of aramid fibre reinforced plastics. Relationships have been evidenced between the trends of the thrust force and the torque with regard to the tool bit geometry and the composite structure, for different feed rates and for different composite constructions. The thrust force shows irregular courses which are discussed in terms of non-uniform distribution of the thrust force along the tool cutting edges and of poor interlaminar strength of composites. A continuous decrease of the thrust force mean value has also been found which has been attributed to the heat build-up at the cutting front. The torque is strongly influenced by friction at the lands of the twist drill. © 1991