Analysis of thrust force and delamination in drilling GFRP composites with candle stick drills

Drilling is an indispensable process for assembling the composites components. The drilling-induced delamination damage generally refers to the peel up delamination on the entrance surface and the push down delamination on the exit surface. Many researchers have carried out studies on drilling force and delamination damage in composites using special drills. Candle stick drills have been recognized as advantageous tools for the reduction of thrust force and delamination damage in drilling composites. Drilling experiments of glass fiber-reinforced plastic (GFRP) composites and finite element simulations were carried out in this paper. Three candle stick drills with different drill tip geometries and one twist drill were compared in terms of thrust force, peel up delamination, and push down delamination. The results revealed that, compared to twist drill, not all candle stick drills could get relatively good drilling results. What is more, drilling results of candle stick drills had a great relationship with the drill tips geometry angles. Finally, an optimized candle stick drill with appropriate drill tip geometry achieved relatively excellent drilling results. © 2017, Springer-Verlag London Ltd., part of Springer Nature.