Occurrence and formation mechanism of surface cavity defects during orthogonal milling of CFRP laminates

Carbon fiber reinforced polymer (CFRP) has been commonly used in the aviation industry and related machining demands are increasing. During machining CFRP, severe machining defects, such as delamination, burrs and subsurface damages etc., usually occur due to the prominent anisotropy and heterogeneity of CFRP. Surface cavity defects are a major manifestation of subsurface damages leading to the decline of the machined surface quality. This paper aims to investigate the occurrence and formation mechanism of the surface cavity defects in a continuum of fiber cutting angles (θ) ranging from 0°-180° by circular orthogonal milling of unidirectional CFRP laminate disks. The experimental results showed that the surface cavities only occur on 50-60% of the against fiber cutting region (0° < θ < 90°). It was found that the surface cavities were mainly caused by the occurrence and propagation of fiber-matrix debonding followed by bending-induced fiber fractures and shear-induced fiber fractures. Results also showed that the surface cavities could be avoided by employing “inclination milling” strategy during edge trimming of typical multidirectional CFRP laminates.