Numerical Simulation Of Evolution In Molten Pool Of The Electron Beam Welding Ofaluminium Alloy

The flow of molten pool is a key factor that influences the electron beam welding process, temperature field determines the scope of the fluid zone, and fluid flow also influences the energy that the electron beam applies to the workpiece, thus proves that flow field also influences the distribution of the temperature field. In this article we carry on the secondary development to ANSYS by Visual Basic software, establish a thermal-fluid coupling model based on the energy balance, mechanical balance and fluid flow balance, and design the reasonable test to verify the rationality of the simulation results.In the model analysis, we mainly consider four aspects: the equilibrium between the electron beam energy, the energy carries off by evaporated metal and the energy the electron beam applies to the workpiece, the equilibrium between the recoil pressure of metal vapor that the weld pool surface is being acted on and additional pressure caused by surface tension, the laws of momentum conservation and mass conservation of the liquid metal in weld pool. In this paper, based on the heat source model analysis, we improve the simulation precision by using Visual Basic to carry on the second-development that combine with the batch-processing characteristic of the ANSYS10.0, calling ANSYS to accomplish parameterized modeling, breaking away from ANSYS platform to modify welding parameter, calling ANSYS result files and combining secondary development program to accurately extract the solid-liquid line and gas- liquid line.The simulation results of temperature field show that, in the electron beam welding process, the highest temperature of liquid metal in molten pool,which locate at the bottom of the keyhole, can reach to more than 3000K, and in the meantime the heating rate is very fast, so additional pressure caused by the metal evaporation is the largest at that location, which is about 10-4Pa when reach the balance. Through the simulation results of flow field, we can see that before reaching the stable state, the flow velocity of the liquid located at the bottom of the melt pool is the largest, whose value is 0.5m/s or so. However, when reach the quasi-steady state, the flow velocity becomes the lowest instead, and at the same time the flow direction of the fluid almost parallel with the welding direction. In the different domain of the fluid, there are some quasi-balance points that the liquid metal flow to, which are caused and maintained by the recoil pressure of the metal vapor and the additional pressure caused by surface tension. When the electron beam bombards these points, the fluid metal located at these points will rapidly vaporize and spray outward, which may causes weld defect. The experimental verification demonstrates that the temperature field and the flow field are in good agreement with experimental results.