A comparative study on drilling characteristics of unidirectional thermosetting CF/epoxy and thermoplastic CF/PEEK composites

Thermoplastic carbon fiber reinforced polyetheretherketone (CF/PEEK) composites are increasingly utilized as substitutes for thermosetting carbon fiber reinforced epoxy (CF/epoxy) composites in high-end equipment, due to their superior mechanical performance and sustainable manufacturability. For both composite components, drilling is an indispensable operation in the manufacturing process. To distinguish the drilling characteristics of the two composites, comparative experiments on drilling unidirectional CF/epoxy and CF/PEEK under different parameters were conducted in this paper. Several aspects, including chip formation, drilling temperature, thrust force, hole damage, and dimensional accuracy, were examined. Particularly, the impact of fiber cutting angle on exit and hole wall damage was considered. Results demonstrate that due to the higher ductility and toughness of PEEK, CF/PEEK produces continuous chips, higher drilling temperatures, higher thrust forces, and smaller damage areas than that of CF/epoxy. However, CF/PEEK has more serious hole wall subsurface damage and poorer dimensional accuracy since PEEK is sensitive to temperature. Consequently, unlike CF/epoxy, increasing spindle speeds at the low feed cannot improve the hole quality of CF/PEEK. Moreover, the hole damage distribution of both composites is strongly associated with the fiber cutting angle. This study provides guidance for high-performance machining of CF/PEEK.