Numerical Study of Step Drill Structure on Machining Damage in Drilling of CFRP/Ti Stacks

The tool structure is an important factor affecting the damage of CFRP/Ti stacks machining. However, the impact of tool structure on the formation process of stacks hole damage cannot be fully revealed through experimental methods alone. In contrast, finite element simulation can effectively overcome the limitations of experiments. In this study, a numerical simulation model is established to investigate the relationship between step drill structure and formation process of CFRP/Ti stacks hole damage. Based on this, the research discusses the effect of step drill structure on the burr height of Ti layer, delamination of CFRP, aperture deviation, defects in hole surface. The results show that when the stacking sequence is CFRP to Ti, the burr height of Ti at hole exit decreases first and then increases with the rising of the ratio of primary drill bit diameter to secondary drill bit diameter (k). When k is 0.6, the burr height of Ti at hole exit is the lower. As k increasing from 0.4 to 1.0, delamination factor of CFRP increases by 2.57%, which are affected little by the step drill structure due to the support of Ti. Besides, the aperture size deviation decreases first then increases with the rising of k, and the minimum aperture size deviation is 2.09 μm when k is 0.6. In addition, as k is 0.6, the hole wall defect is fewer. In conclusion, step drill with k of 0.6 is suitable for drilling of CFRP/Ti stacks.