Investigation on the countersink errors in the drilling of thin-wall stacked structures

The countersink accuracy is an important quality index in modern aircraft manufacturing industry. However, the wide use of the thin-wall stacked structures with low stiffness brings about complex and diverse countersink errors due to the inevitable stack deformation in the machining process. This paper provides a new insight into the study on the problem of countersink errors including the quantitative exploration of formation mechanism, evaluation method, and influence factors through both theoretical and experimental analyses. The principles and laws of stack deformation, especially the interlayer gap and the interaction features that are peculiar to stack drilling, have been firstly investigated by analytically modeling with Fourier series approach in this study. Then, the formation mechanism and evaluation method of three types of countersink errors are theoretically revealed, and a calculation method is presented based on the stack deformation model. The influence of the machining parameters, such as the original interlayer gap, the cutting force, and the cutting position with different stiffness, on the countersink errors has been quantitatively analyzed in order to provide new potential optimization method for the further improvement of the countersink accuracy. Finally, the theoretical model is verified by multivariate simulations and experiments, and the results show that the proposed model has positive referential significance for the analysis of countersink errors. The work in this paper promotes the understanding of the effect of machining deformation on countersink errors through the fundamental insight and contributes to develop better designs of machining conditions for the stack countersinking process.