Investigation on the non-coaxiality in the drilling of carbon-fibre-reinforced plastic and aluminium stacks

The non-coaxial stacked holes caused by cutting deformation is a common problem in stack drilling, particularly for low-rigidity structure, and the non-coaxiality in carbon-fibre-reinforced plastic and aluminium (CFRP/Al) stack drilling has not been studied. Because of the non-homogeneous behaviour and poor machinability of CFRP, the non-coaxiality in CFRP/Al stack drilling is significantly different from previous studies on Al/Al stack drilling. Focusing on the non-coaxiality in CFRP/Al stack drilling, this paper proposed the mechanism of the non-coaxiality through both experiments and numerical study. Severe non-coaxiality occurrences were observed in the CFRP/Al stack drilling experiments. To explain the observation, the macroscopic mechanics theory of composite was applied to obtain the engineering constants of composite laminates, which are necessary for the numerical model. This application leads to the development of an optimized simulation model to predict the interlayer gaps and non-coaxiality. The numerical results that predict the non-coaxiality are consistent with the experiments, which verified the rationality of simulation model. Furthermore, the effect of the thrust force and clamping force on both interlayer gaps and non-coaxiality were studied. The interlayer gaps gradually increase with the increase in thrust force but decrease with the clamping force. Moreover, the thrust force has a complicated effect on the non-coaxiality. The non-coaxiality first decreases and subsequently increases with the increase in thrust force, which can be attributed to the “tilt effect” in the lower layer. In addition, the non-coaxiality increases with the clamping force in the simulation experiment range. The work in this paper enables us to understand the particularity of the non-coaxiality in CFRP/Al stack drilling and select the appropriate cutting parameters for CFRP/Al stack drilling.