Numerical Simulation Of Temperature Field And Flow Field In Friction Stir Welding

With the rapid development of China's rail transit construction,the overall performance requirements for rail vehicle structures are also rising.Friction Stir Welding(FSW),a new solid-phase connection technology is widely used to the production of rail vehicles.Friction stir welding is a process of thermal-mechanical coupling.The temperature change of materials and the flow of plastic materials during welding all affect the post-weld residual stress,residual deformation,and the quality of weld formation,and thus have a safety impact on the service life of components.Therefore,it has important engineering value and practical significance for the study on FSW temperature field and flow field.Based on the theory of heat transfer and the theory of computational fluid dynamics,this thesis establishes a three-dimensional calculation model of friction stir welding,and studies its temperature field and flow field.The research work is as follows:(1)Analytical formulae for heat generation.The formulas of heat generation with concave shoulders and taper pins were deduced,and the existing formulas were compared and analyzed.The effects of shoulder concave angle and pin taper angle on the heat production and the proportioning among different parts were discussed.Under the same welding process parameters,the influences of shoulder concave angle and pin taper angle on the energy per unit length of weld and maximum temperature were analyzed.(2)Simulation analysis of the temperature field.Improved friction coefficient prediction-correction scheme based on the energy per unit length of weld,welding moving heat source,original friction coefficient prediction-correction scheme and improved friction coefficient prediction-correction scheme were added to the model through ABAQUS subroutine DFLUX.The FSW temperature field of the four different tools including flat shoulder-cylinder pin,flat shoulder-taper pin,concave shoulder-cylinder pin and concave shoulder-taper pin were numerically simulated.The influences of original and improved schemes on the FSW temperature field were compared and analyzed.(3)Simulation analysis of the flow field.Using FLUENT fluid analysis software,the FSW welding flow field of the four different types of tools including flat shoulder-cylinder pin,flat shoulder-taper pin,concave shoulder-cylinder pin and concave shoulder-taper pin were numerically simulated.The effects of shoulder concave angle and pin taper angle on the horizontal and vertical flow characteristics of the metal material in the central area of welding were analyzed.The influences of welding speeds and rotation speeds on the flow charateristics under the case of flat shoulder-cylinder pin are futher analyzed.Through the simulation of FSW temperature field and flow field,the variation law of the welding material temperature and the flow characteristics of the material in the welding center region are obtained,and the work provide technological references for the follow-up study of the residual stress,residual deformation and improvement of weld quality.