Novel drill bit based on the step-control scheme for reducing the CFRP delamination

Exit damages such as burrs and delamination frequently occur during the CFRP drilling. Tool geometry strongly influences drilling performance. In this paper, the advantages of dagger drill and brad-spur drill are analyzed and a pulling-shearing effect is proposed. According to the pulling-shearing and the cut-push effects, a step-control scheme for reducing the CFRP delamination is proposed to design a novel drill bit. Theoretical and geometrical analyses of the drilling process and drilling tests have been carried out on CFRP composites. The results indicate that the pulling-shearing and the cut-push effects can be successfully implemented by the novel drill with V-shaped cutting edge. Due to the pulling-shearing and the cut-push effects, the fibbers along the hole edge can be cut off cleanly when the novel drill penetrates the last ply. Then the damages can be reduced significantly. The changing trend reflected from the tests is basic anastomotic with the step-control scheme. Compared with the dagger drill and the brad-spur drill, the novel drill has a good performance on reducing the thrust force as well as the damages. However, some defects such as the tearing are easy to generate when the feed per revolution is high.