Study of burr and tear defects at the entrance and exit surface during drilling of Kevlar composites

Kevlar fiber is tougher than carbon fiber. Burr and tear defects at the drilling surface are more serious. It is necessary to analyze and study the influencing factors of the burr and tear defects at the surface of the drilling hole. In this paper, a method for analyzing the relationship between cutting parameters and defects at the surface of drilling holes of Kevlar composites was proposed. This method takes the force change in the cutting process and the tear and burr length after machining as the quantitative index to analyze the optimal processing parameters. Force analysis was conducted at the entry and exit during drilling by a twist drill to explore the generation mechanism of burr and tear defects at the surface of Kevlar composites. Then, drilling experiments were carried out with different kinds of support and back-up plates and different machining parameters. Next, the burr and tear length was quantified with the method of image recognition. Finally, the burr and tear defects of different machining parameters could be analyzed comparatively. The experimental results show that the support and back-up plate can reduce the burr and tear defects, which become more serious with the increase in the axis force. The most influential factor on cutting force and hole quality is the feed rate, and the difference of the effect on axial cutting force can reach 72.19.