Research On Deformation Prediction Method Of Thin-walled Structures Based On Finite Element Analysis

With the continuous update of the aerospace product design philosophy, moreand more thin-walled structures are used in aircraft structure. But because of thecomplex structure, the poor rigidity, the distinctly machining distortion, and the poordimensional stability, the thin-walled structures pose a serious challenge to theaviation industry. Owing to the lack of common support on the process technologyof the thin-walled structures, at present, the processing level of the thin-walledstructures in our country lags far behind compared to the advanced level abroad.Low manufacturing accuracy and long-term stability severely restricts the rapiddevelopment of new aircraft. Therefore, the research on the deformation predictionmethod of thin-walled structures can predict the deformation state of the workpiecebefore machining, and has very important practical significance on the optimizationprocess, and decrease production costs and improve production efficiency.Start from the analysis of the materials initial stress state, the change process ofthe residual stress in the aluminum alloy pre-stretched plate is researched. Based onthe elasticity theory, the stress-strain model during the release process of materialsresidual stress is developed. And the internal distribution law of the residual stress isindirectly obtained by using layer removal method, measurement result shows thatthe surface layer is in tension, and the inner layer is a tensile stress, the stressdistribution is "M" shape. Furthermore, compared with the experimental results, thedeformation of the workpiece obtained by finite element simulation has very goodconsistency with the experimental results, which verifies the correctness of thestress-strain model.Then, a three-dimensional finite element simulation model for the millingprocess is established by selecting the reasonable materials constitutive model,determining the exact failure criterion, dividing the appropriate grid and choosingthe correct unit. The simulation results of the stress state and the milling forces arein good agreement with the actual situation, which shows that the finite elementmodel can be a true reflection of the milling process, and has high accuracy. Basedon this model, the parameters are optimized to achieve the highest minimum andcosting purposes of calculation accuracy, which laid the foundation for the accuratecalculation of the deformation prediction.Considering the coupled effect of the residual stress, the milling force, and theclamping force, the cutting process of the thin-walled structure is calculated usingthe finite element method, from the blank materials to the milling forming. And thedeformation states of the different working steps obtained by the finite element method is in good agreement with the measuring result by the coordinate measuringmachine. The above method can accurately predict machining distortion ofthin-walled structures, and provide a new approach to correct the processingdistortion.