Bi-directional drilling of CFRPs: From principle to delamination suppression

Carbon Fiber Reinforced Plastics (CFRPs) are widely used in aerospace, automotive and other transportation industries because of their excellent material and mechanical properties. Nevertheless, up to now, drilling is still regarded as the most important process in the machining of CFRPs, and the delamination is one of the most challenging damage in drilling process. In this concern, we propose and implement a bi-directional drilling method for CFRPs hole-making. In this paper, the exit delamination formation mechanism was firstly analyzed to clarify the effect of bi-directional drilling on delamination suppression. The critical thrust force was calculated by considering both conventional and bi-directional drilling conditions. Based on the model, it can find that bi-directional drilling process itself can provide support without employing any extra facility. Finally, experimental validation indicates that the calculated critical thrust force showed a reasonable agreement with the experimental results based on conventional and bi-directional drilling. The hole exit delamination damage under the bi-directional drilling reaches the desired suppression effect with a reduction of 11.3%–27.9% compared to conventional drilling based on experiment results. Through an in-depth understanding of critical thrust force, the findings of this paper not only provide a new processing technology for drilling CFRPs, but also open a new avenue to improve the quality of drilling CFRPs by reducing delamination.