Numerical Simulation Of Phase-Transition Heat Transfer And Fluid Dynamic Characteristic In Welding Pool

Welding is a complex process involved in heat and mass transfer, melting and solidification of metal. There is a very significant affection to welding quality, such as the energy distribution of welding heat source, the fluid flow welding current and heat transfer process in the molten pool. Scientific method is adopted to establish the mathematical model of molten pool and arc welding. Quantitative analyses for welding current and temperature field are used for molten pool. A description is given of the phase-change heat transfer and fluid flow characteristics in molten pool and an analysis of the welding heat source form and the energy distribution is studied. What researched in this article has an important practical and theoretical significance to achieve automatic control in the welding process.Based on welding technology and CFD software FLUENT the process of metal phase change, heat-transfer and fluid flow characteristics are analyzed, which has a strong impact on the formation of molten pool. In this paper, the theoretical and numerical simulation analysis including the impact of material parameters i.e. hot physical parameters etc., are applied to investigate the temperature dependence, latent heat of melting and the heat transfer coefficient on the surface of work pieces.(1) Gaussian heat source model to establish the moving arc heat source model and the impact of welding process parameters in the temperature field are analyzed. It is shown that molten pool volume, melting width and penetration depth augment with the increasing of welding current or the decreasing of welding speed. Along with the improvement of welding speed, temperature gradient in molten pool area near fusion line increases, while the aspect ratio of the molten pool reduces.(2) Those are welding heat cycle as well the metallurgical factors of the metal itself which affect the changes of metal organization in welded seam and heat working zone. The organization and performance of a certain droplet are decided by the heating rate, the highest heating temperature, station time at highest temperature and the cooling rate later. Along with the improvement of welding speed, the temperature gradient in molten pool near fusion line increases and the heat working zone of the melting pool becomes smaller.(3) In the process of molten pool formation, the influence for the flow of molten metal on the molten pool development is analyzed, and the inertia force, thermal buoyancy, surface tension and other factors are also taken into account. Joined in the welding heat source, the surface temperature of the melt near to the center of heat source is the highest, the farther apart from the central region, the lower of the surface temperature. As a result of uneven temperature distribution in the molten pool, the surface tension is varied where the higher of the temperature, the smaller of the surface tension. The difference of surface tension results in the liquid flow from the low surface tension zone to that of high surface tension and altitude difference so that the melt re-melts and the convection forms under the gravity. Generally, the temperature coefficient of surface tension is a negative value which means that the surface tension of molten metal decreases as the temperature is increasing. Therefore, the surface tension of molten pool gradually increases from the center to the edge in the molten pool.(4) By taking laser welding process as a studied object, numerical simulation is applied to analyze the deep laser welding pool behavior under the moving heat source function. The impact of laser fusion welding process parameters on the behavior of molten pool is studied. Based on the uncertainty of the solid-liquid interface, non-uniform coefficient is introduced to the solid-liquid interface and the metal vaporization phenomena in the process of laser weld is analyzed.