A comparative study on milling-induced damages and residual tensile strength during milling of thermoplastic and thermoset carbon fibre reinforced polymers

Thermoplastic carbon fibre reinforced polyetheretherketone (CF/PEEK) and thermoset CF/epoxy composites have been widely applied in various industries. However, there is still a lack of knowledge concerning the milling performance and residual mechanical behavior of these two types of composites. To address this issue, we conducted a comprehensive investigation of the machinability during milling of both composites, with a focus on cutting force, machining temperature, chip characteristics, and milling-induced damages. To our knowledge, this is the first report documenting the correlation between surface integrity under different cutting conditions and residual tensile behaviour in both composites. The results demonstrate that CF/PEEK exhibits better machining quality than CF/epoxy due to its ductile matrix and strong interface bonding with fibres. Furthermore, downmilling was found to be preferable to up-milling for minimizing top layer surface damage, while petal-shaped chips with good integrity were found to be generated by CF/PEEK during milling. Moreover, CF/PEEK exhibited a significantly higher residual tensile strength (12.05%-63.22%) compared to CF/epoxy.