Prediction Of FSW Deformation For Large Size Components Based On Strain Mapping

Friction stir welding(FSW)is a new type of solid-state bonding technology,which has been widely used in welding of light alloy such as magnesium alloy and aluminum alloy.In recent years,it has been widely used in rail transit industry and aerospace industry.In the actual production process,the residual deformation of large size complex components after welding has a great impact on the assembly accuracy and service life,so it is necessary to carry out the prediction of the residual deformation of large size complex components after welding.In order to solve this problem,the numerical simulation method has been widely used by scholars at home and abroad as another effective method to predict the deformation after welding of large size complex components.Thermoelastoplastic method is widely accepted by researchers at the present stage for welding deformation prediction.However,thermoelastoplastic method has a large amount of calculation and a long time to calculate.Therefore,it is very important to develop and research a high-efficiency and high-precision post-welding deformation prediction method.Based on the idea of intrinsic strain method(i.e.,strain-based mapping method),this paper discusses the characteristics of two equivalent mapping methods for plate friction stir welding,and carries out the effective prediction and welding sequence optimization of the friction stir welding for the side wall profile structure of subway vehicles.The main research work is as follows:Based on the sequential thermodynamic coupling method,the welding process of small and large size plate friction stir welding was simulated by ABAQUS software.The moving heat source was used to analyze the temperature field and the residual stress and deformation after welding were analyzed by thermoelastoplastic method.The residual stress field and the amount of deformation at different release times were compared,and the change rules were compared and analyzed.Research on mapping method of equivalent temperature load based on inherent strain.The residual plastic strain obtained by the thermoelastoplastic method of small size plate was extracted,and the transverse and longitudinal natural strains were obtained by calculating the formula.The natural strains were transformed into the anisotropic thermal expansion coefficients of the material and applied to the large size plate for welding deformation prediction.The predicted deformation results were compared with the results of thermoelastoplastic method and experimental results.The results show that the equivalent temperature load mapping method can effectively predict the post-welding deformation.Research on mapping method of equivalent initial stress load based on inherent strain.The residual plastic strain of the element obtained by the thermoelastoplastic method of small size plate was extracted,and the initial stress load was calculated by the formula.The initial stress load was applied to the corresponding element by modifying the input file,and the residual deformation after welding was predicted by an elastic calculation.Comparing the predicted deformation results with the thermoelastoplastic method and the experimental results,the results show that the equivalent initial stress load mapping method can effectively predict the post-welding deformation.On this basis,the different mapping methods are compared and analyzed in detail.The finite element model of the gasket and fixture was established to analyze the welding deformation under the contact constraint of the gasket and fixture,and to compare it with the fixed constraint.On this basis,the equivalent temperature load mapping method is used to successfully predict the post-welding residual deformation of large-size plates under contact constraints,and a detailed comparative analysis is made.Equivalent temperature load mapping method based on inherent strain is applied to predict the post-welding deformation of the profile structure of subway vehicle side wall by friction stir welding,and the deformation of the profile structure is analyzed.In order to accord with the actual welding situation,the birth and death unit technology is adopted in the simulation process.On this basis,the influence of welding sequence was studied,and the optimal welding sequence was determined.In this paper,based on theoretical basis and numerical simulation,the natural strain temperature loading method and the natural strain initial stress loading method are studied,and the characteristics of the two methods are studied,which provides theoretical support for welding deformation prediction of large size structures,and also provides guidance for deformation control.