Study Of3D Coupled Thermo-flowing Model Of Friction Stir Welding Process

As a green welding technology, friction stir welding has been widely used in aerospace,track transportation, shipbuilding and other fields, has an extremely broad market application prospect.The process of FSW is combined with metal plastic flow, temperature transition, crystal microstructure transformation,stress and strain deformation,it is a multiphysics field coupling complex nonlinear process.Study of the relevant fields of welding process is of great significance to find out the weld forming mechanism and optimize the friction stir welding process parameters.This paper is based on the method of the computational fluid dynamics, and a mathematical model about the process of the FSW which combines the flowing field with the temperature field is established. In this model, the source formula of heat by the shoulder and the pin is considered, and the discussion for the welding process of the basic metal viscoplastic constitutive relation as well as the basis of various assumptions during the welding steady state are given. The model is more suitable for adopting the actual flow turbulence model, which is added in the control equation of the turbulent kinetic energy equation. Besides, this model sets up all the hot boundary expression of mathematical equations and flow boundary condition, completes the mathematical analysis model of friction stir welding.On this basis, the multiple physical field coupling analysis software COMSOL Multiphysics is used and a numerical model is established about the6061aluminum alloy friction stir welding process and the simulation is carried out, to analyze the basic characteristics of temperature field and velocity field of the welding consumables. The simulation result about the temperature field shows that, the highest temperature of the welding materials in the simulation only reach77%of the melting point, which proves that the friction stir welding is still belong to a kind of solid phase connection technology. The temperature distribution in the horizontal plane is oval. The temperature gradient ahead of the stirring tool is larger than which in the back of the tool. On both sides of welding line, the temperature and the temperature gradient in the advancing side is higher than which in the retreating side. The simulation results about the flowing field shows that, the welding material within the shoulder of the tool is distributed as a funnel in the vertical plane, and two reverse funnels appears. The flowing of the metal in different thickness is influenced by the rotating shoulder and rotating pin. On the surface, the flowing field distribution is influenced by shoulder rotating, the lower surface is influenced by pin rotating, the middle area is the results affected by both.This paper provides a theoretical reference for the numerical simulation of the FSW which is based on computational fluid dynamics. Moreover, the distribution and mechanism of the temperature field and flowing field in the steady state is studied. It has a guiding role for predicting the highest temperature region during the welding process. The mechanism of the plastic metal flowing in the vertical plane is explored with the method of numerical simulation. It can effectively explain the mechanism of the welding and estimate the defects in the welding process.