Cryogenic drilling of carbon fibre reinforced thermoplastic and thermoset polymers

Carbon fibre reinforced polymers (CFRP) are suitable materials for high-end applications due to the high strength to weight ratio. This important advantage counteracts to their machinability because the inherent anisotropy and the heterogeneity lead a high difficulty to reach good quality in terms of surface integrity, dimensional and geometrical tolerances. Hereupon, this paper determines the effect of the cryogenic and dry drilling as well as tool feed rate on delamination, uncut fibres, hole diameter and roundness when applying thermoplastic and thermoset CFRP as workpiece material. Scanning electron microscopy (SEM), and specific cutting and thrust energies aided to explain the damages' phenomena. The results showed that hole quality varies along hole depth and depends both on composite's matrix and drilling strategy. Delamination and uncut fibres are distinct at the hole entrance and exit since they depend on surrounding matrix/fibre layers. Cryogenic drilling reduced both delamination at the hole exit and uncut fibres at the hole entry for the thermoset materials. Finally, the variation in hole diameter and roundness was minimized when drilling thermoplastic matrix by using cryogenic cooling.