Research on entrance delamination characteristics and damage suppression strategy in drilling CFRP/Ti6Al4V stacks

Carbon Fiber Reinforced Polymer (CFRP) and CFRP/Ti6Al4V stacks are now commonly used in the aircraft industry. In the integrated drilling process of CFRP/Ti6Al4V stacks, the entrance delamination defects of CFRP is often more serious than that in drilling single CFRP. Considering the anisotropy of CFRP, this paper analyzed the entrance delamination defects caused by the CFRP drilling phase and the influence of titanium alloy drilling phase on the evolution of entrance delamination defects of CFRP. A series of drilling experiments were carried out on CFRP and CFRP/Ti6Al4V stacks respectively. The causes and differences of entrance delamination defects in the drilling process of CFRP and CFRP/Ti6Al4V stacks were compared from the aspects of drilling force, temperature and titanium alloy chip formation. In addition, the entrance delamination defects suppression strategy called high and low frequency vibration-assisted drilling method (CVAD) in drilling CFRP/Ti6Al4V stacks was investigated. The results indicate that in the single CFRP drilling process, the entrance near 135° cutting angle of CFRP fiber presents slight type I and type III delamination defects due to the tool structure and fiber anisotropy. However, in the CFRP/Ti6Al4V stacks drilling, the thermal-mechanical effect of high temperature titanium alloy chips leads to the evolution of more serious type I elliptical delamination defects at the entrance of CFRP. By using CVAD method to reduce the titanium alloy chip size and drilling temperature, the entrance delamination defects of CFRP/Ti6Al4V stacks can be effectively suppressed. The findings of this paper can contribute to identifying the formation of entrance delamination defects in CFRP and providing guidance for improving the processing quality of CFRP/Ti6Al4V stacks.