An innovative approach to evaluate the machined surface of UD-CF/PEEK laminate milling with considering the crystallinity and friction property variation

The machined surface quality of aerospace composite components is crucial for their service performance. However, the machined surface quality characterization of CFRTP (carbon fiber reinforced thermoplastic) material and its impact on the material's mechanical performance are not fully investigated. In this paper, an innovative method with considering the physical properties variation was proposed to evaluate the milling surface quality of UD-CF/PEEK, which was characterized by three indices, namely, surface roughness (Sq), surface crystallinity (χsurface), and cross-sectional wear area (Scrs). Orthogonal designed experiments about side milling of UD-CF/PEEK were conducted to investigate the effects of fiber orientations and milling parameters on the resulting surface quality indices. The crystallinity analysis of the machined surfaces and chips were conducted by X-ray diffraction and Differential Scanning Calorimetry for the first time. Notably, it is discovered that the cutting temperature is the primary factor influencing the crystallinity of the machined surface. Meanwhile, this study first indicated the correlation between cutting force, temperature and the friction property (coefficient of friction and wear resistance) of the machined surface. This will lay a foundation for the establishment of a relatively comprehensive machined surface characterization method for CFRTP material.