Design of a new tool with intermittent-sawtooth structure for damage reduction in drilling of CFRP composites

Drilling pilot holes on CFRP components is inevitable for assembling process in manufacuting industries. However, the drilling-induced damages frequently occur and affect not only the load carrying capacity of components but also the reliability. Therefore, it is of great urgency to enhance drilling performance of CFRP components for manufacturers. In the article, the defect mechanism at the exit during drilling CFRP is analyzed associated with drill geometries. Cutting fibers at the exit by the main cutting edge in the axial direction is modeled into a unique two-dimensional cutting model with the side support from the machined hole wall based on the elastic foundation beam theory. Moreover, orthogonal cutting mechanisms of fibers are analyzed in two directions in terms of the fiber deformation and fracture as well as the debonding between the fiber and the matrix. Then damage-free cutting direction is revealed. According to the damage-free cutting direction, a novel one-shot drill is proposed with the intermittent-sawtooth structure on its secondary and minor cutting edges. The effect of the intermittent-sawtooth structure on the damage reduction was presented theoretically and geometrically. The verification experiment was also conducted, and encouraging reductions on drilling damages were successfully achieved with the novel drill.