An analytical delamination model of drilling aramid fiber–reinforced plastics by brad drill

Aramid fiber reinforced plastic (AFRP) composites have been widely used in aerospace, defense, and automotive industries. Proven by practical experience, a brad drill can effectively reduce drilling-induced damages in drilling of AFRP due to its unique tool geometry. While the delamination mechanism and the associated analytical model of the brad drill are crucial for improving hole quality and machining accuracy, these aspects were rarely discussed in the literature. This study reports the first work on the delamination mechanism in the context of drilling AFRP by brad drill through detailed analysis of tool/material interactions. A novel analytical model of the critical thrust force (CTF) is proposed for the prediction of both hole wall and hole exit delamination. Model analysis shows that the hole wall delamination is more likely to occur prior to hole exit delamination when the remaining uncut material is thinner than 0.38 mm. When the thickness of the uncut material is greater than 0.4 mm, no hole wall delamination will occur. Through analysis of thrust force components generated by different cutting edges on the total CTF, the contribution of cutting spurs on the thrust force is found to be more effective at suppressing hole wall delamination. The model and the associated experimental validation of this study have laid down a foundation for the design and optimization of drill bits in the future.