On the machining behavior of carbon fiber reinforced polyimide andPEEKthermoplastic composites

Polyimide (PI) and polyetheretherketone (PEEK) are superior high-performance thermoplastics being extensively used in the fields of fiber-reinforced polymer composites. However, there is very limited literature addressing the machining behavior of the PI and PEEK composites. The present paper aims to conduct a comparative study into the machining characteristics of these two representative high-performance thermoplastic matrix composites under varying cutting conditions. Machinability aspects of the carbon/PI and carbon/PEEK thermoplastic composites were evaluated in terms of drilling forces, machining temperatures, delamination damage, surface morphologies, hole dimensional accuracy and tool wear. The results indicate that the carbon/PEEK composites generally show a much poorer machinability than the carbon/PI composites in terms of higher drilling forces, higher cutting temperatures, larger delamination extents and excessive tool wear. Since the carbon/PEEK composites exhibit certain ductility leading to the continuous chip formation, the cut hole surface morphologies and dimensional accuracy are much better than those gained in the carbon/PI composites. Both the cutting speed and the feed rate affect significantly the drilling forces and the resulting delamination damage. The fundamental wear mechanisms of drilling carbon/PI composites are abrasion wear in the form of edge rounding and slight chip adhesion, while for the carbon/PEEK composites, they are abrasion, serious chip adhesion because of the high drilling temperatures promoted at the drill-work interface and catastrophic failures of coating peeling and edge fracture.