Study on the evolution and suppression strategy of the interlayer gap in the drilling of CFRP/Al stacked materials

Abstract

In aircraft assembly operations, interlayer gap formation during drilling through stacked materials positively affects interlayer burr size. Removing these burrs needs disassembly, deburring, and reassembly, and these processes are time-consuming, expensive, and non-value-added. This study visualizes the real-time variation of the interlayer gap to understand its evolution process and proposes a method of designing feed motion for reducing the interlayer gap. First, a real-time measurement method of the interlayer gap and deflection using a 2D laser displacement sensor is proposed, and the evolution of the interlayer gap in the drilling of stacked materials is described. Besides, a simplified analytical model of the stacks is built to explain the development of interlayer gaps during stack drilling. Then, a variable feed method based on the discrete sine curve is proposed to suppress the interlayer gap. Finally, the drilling experiments of the constant feed and the discretized sine curve feed are performed to compare the change of interlayer gap, and the results showed that the maximum interlayer gap (excluding the effect of chips), the maximum interlayer gap (not excluding the effect of chips), the final interlayer gap and the average interlayer gap was reduced by 25.2 %, 45.1 %, 72.7 % and 35.9 %, respectively. In addition, a small interlayer gap corresponds to a small flexural deformation, which helps reduce the material's stress. The bending deformation of the Al layer is reduced by 54 %, and its maximum stress value can be reduced by 22 %.