Study On Laser Welding Deformation And Stresses Of Al-Li Alloy Large Thin-wall Structure Based On Shell Element

Large thin-walled structures of domestic aircraft fuselage are expected to be manufactured by laser welding technology.But its welding deformation and residual stresses are very complicated and have great uncertainties.At the same time,the welding numerical simulation of large thin-walled structure has the characteristics of long calculation time,inaccurate calculation and difficult convergence due to its large size and large amount of weld seams.In order to solve these problems,this paper makes full use of the advantages of the shell element model with fewer meshes and less calculation.High-efficiency simulation of stresses and deformation on laser welding for the large thin-walled structure of aircraft fuselage are performed in the context of dual laser beam bilateral synchronous welding technology.Firstly,the process of dual laser beam bilateral synchronous welding of Al-Li alloy skin-stringer structure is introduced and employed.The skin-stringer welding structure with good weld formation and no obvious macroscopic defects is obtained.The thermal field,residual stresses field and deformation field of the finite element model of dual laser beam bilateral synchronous welding are verified by the cross-section morphology of the weld and the measured residual stresses and deformation data.Secondly,the optimization of mesh model,the determination of element type,and the optimization of fixed time step are performed for the structure of Al-Li alloy skin-stringer test piece.The calculation results and efficiency of the simulation model under various modeling parameters are compared and analyzed.At the same time,the calculation results of stresses and deformation are compared with the experimental measurement data to verify the calculation accuracy of each model.The necessary model parameters such as the optimal mesh model,the optimal element type,and the optimal fixed time step,which can balance both the calculation accuracy and efficiency,are obtained and applied to the subsequent large-scale structures.Thirdly,taking the typical structure of Al-Li alloy skin-stringer as the research object,the simulation of dual laser beam bilateral synchronous welding is carried out by using the optimization results of various model parameters.The results of the shell element model and the full solid element model are compared to further verify the applicability of the model parameters such as the optimized mesh model,element type,and fixed time step.The results show that the total number of elements and nodes in the shell element model is reduced by 46.0% and 60.7% respectively,the number of iterations is reduced by 7.2%,and the calculation efficiency is increased by 58.9%,compared with the full solid element model of the same size.In addition,it is found that the change of welding direction has a certain effect on the deformation of typical structure after welding.Finally,the optimized model parameters are used to solve the laser welding simulation of the large thin-walled structures of aircraft fuselage.The effects of different welding sequences and welding directions on the residual stresses and deformation of the aircraft panel structure are analyzed.It is indicated that different welding sequences and welding directions effect the residual stresses only in a certain extend.Based on the cross-symmetric welding sequence,optimized welding directions in the aircraft panel structure can effectively reduce the angular deformation to obtain a smaller overall deformation.Therefore,the welding deformation of the actual aircraft fuselage structure can be effectively controlled.