Machining-induced burr distribution along hole contours in unidirectional carbon fibre-reinforced polymer (UD-CFRP) composites

Machining-induced burr formation in carbon fibre-reinforced polymer (CFRP) composites is difficult to predict and control, mainly due to the anisotropy and inhomogeneity of the fibrous composite, as well as the rapid tool condition change due to the abrasive tool wear. The main aim of this study is to develop a model to determine the density and distribution functions of risky fibre cutting angles where machining-induced burrs are expected to be formed when hole-machining CFRPs. Four models were introduced, and their adequacy was analysed. The coefficients of the models were determined using datasets of three previous research projects (i.e., 2 380 808 data points) and validated through a fourth one (208 571 data points) where hole machining experiments were carried out using different tools, parameters and setups. The normality of the risky fibre cutting angles was tested through the Shapiro-Wilk and Kolmogorov-Smirnov statistical tests, and the distribution was found to be not Gaussian. The developed trigonometric model shows a good fit to the data points, i.e., the determination coefficient is at least 0.949 for each dataset. The results indicate that machining-induced burr formation is most probable at a fibre cutting angle of 118–133°, and 60 % of burr occurrences fall within the 110°–160° range when the critical fibre cutting angle is 133° These findings provide a foundation for the industrial adoption of advanced machining strategies for fibrous polymer composites, enabling a significant reduction of machining‑induced burrs in CFRPs.