Countersink accuracy control of thin-wall CFRP/Al stack drilling based on micro peck strategy

Abstract

The countersink accuracy problem caused by the deformation of thin-wall stacked structures is common in aircraft manufacturing, particularly for stacks with low stiffness. In the countersinking process of carbon fiber reinforced plastic (CFRP) and aluminum (Al) stacks, the cutting edge is quickly and severely worn due to the hard machinability of CFRP, resulting in the rapid increase of thrust force and then deformation. Focusing on the countersink accuracy control in CFRP/Al stacks, this paper first developed a CFRP countersinking thrust force model that considers tool wear and verified by experiments to help to investigate the stack deformation; then the micro peck strategy with quantitative analysis and theoretical modeling, which aims to decrease deformation and improve countersink accuracy, has been proposed based on the thrust force model and studied for its effectiveness in multivariate simulations and experiments. The research results indicate that both the increase of flank wear land of the tool and the decrease of stiffness of the stacks are the primary factors that undermine the countersink accuracy because they can affect the stack deformation, but using the micro peck strategy will minimize the adverse impact of these factors. The work in this paper includes two advantages: the micro peck method can be applied to the aeronautical manufacture with complex actual machining conditions; the theoretical model enables us to select appropriate peck parameters for the CFRP/Al stack countersinking process.