Optimization design for countersink depth error prediction and compensation of CFRP/Al stacks

Abstract

The countersink depth accuracy is one of the most important quality indexes of the rivet holes in modern aerospace industry, especially in the drilling of thin-walled carbon fiber reinforced plastic (CFRP) and aluminum (Al) stack. However, the carbon fiber of CFRP is a kind of typical difficult-to-machine material, which results in the terrible wear of the cutting tool, and then the continuously increase of thrust force in the practical machining process, leading to the significant stack deformation and making it difficult to achieve the required countersink depth tolerance. Focusing on the countersink depth control in the drilling of the thin-walled CFRP/Al stack, this paper attempts to optimize the integrated methodology [10] in order to predict and compensate for the stack deformations more accurately. In this paper, an analytical flexible countersinking thrust force model that considers both tool wear and stack deformation is first developed with detailed theoretical analysis. Then a finite element model is established to identify the key features of the stack deformation in the countersinking process. An optimized iterative algorithm, which consists of three nested iterative loops, is designed to calculate the feasible stack deformation and make decision for the error compensation. Finally the optimized methodology are verified by groups of cutting experiments, and the results have shown that the methodology could effectively guarantee the countersink depth accuracy. The work in this paper enables us to understand the generating mechanisms of the countersink depth error in the drilling of the thin-walled CFRP/Al stack, and provides a novel approach to improve the countersink depth accuracy.