The effect of pilot hole on delamination when core drill drilling composite materials

Removal of chips is a serious problem when core drill drilling polymer composites. As the chip is formed it moves to the inner hole of core drill. A hole is pre-drilled to eliminate the thrust caused by the removal chip, thus the threat for delamination is significantly reduced. The diameter of the pre-drilled hole is set equal to the inner hole of core drill. A smaller diameter of pilot hole cannot solve the problem of removal chips, while a larger one tends to cause undesired delamination during pre-drilling. Although valuable efforts have been made for the analysis of drilling-induced delamination, little has been reported on the effect of pilot hole diameter on delamination for core drills. The design of drill tools can be improved using obtained results.