Drilling Defects and Process Optimization in Carbon Fiber-Reinforced Polymer Composites: A Review

Carbon fiber-reinforced polymer (CFRP) is favored as the primary material for thin-walled components in fields such as aerospace due to its excellent properties, including light weight, high specific strength, high specific stiffness, and ease of integrated manufacturing. These thin-walled parts require assembly and connection with other components using rivets or bolts, necessitating the drilling of a large number of holes in CFRP. However, owing to its macroscopic heterogeneity, anisotropy, and low interlaminar bonding strength, CFRP is prone to defects during drilling, such as delamination, burrs, tearing, fiber pull-out, and surface voids. These defects can significantly compromise the connection quality and fatigue life of the components and may even lead to part rejection. To avoid drilling defects and achieve high-quality machining of CFRP, it is essential to fundamentally understand the intrinsic relationship between its material characteristics, such as anisotropy and interlaminar properties, and machining-induced damage. This paper systematically reviews the primary defects in CFRP drilling and their formation mechanisms, identifying drilling forces, drilling heat, and tool wear as the core contributing factors. Based on this analysis, various process optimization methods from different perspectives are proposed to mitigate these drilling defects and improve surface quality, including the optimization of cutting parameters, tool improvement, enhancement of the drilling environment, optimization of drilling process strategies, and the application of advanced drilling technologies. Finally, the paper summarizes the research on CFRP drilling and provides an outlook on future developments.