Numerical Simulation Of Short Circuiting Transfer In GMAW Based On Fluent

CO2arc welding has been widely applied because of its high efficiency and low cost. But the large spatter and bad bead shape are two remarkable shortcomings of short-circuit transfer and limit its more development.During its welding process, in the first stage, metal transfer can be considered to be globular model, with relatively low voltage and current. Many theories models such as static force balance theory, pinch instability theory, spring-mass theory and fluid mechanics theory have been developed to simulate this metal transfer process of GMAW. But there are always some drawbacks, and many assumptions are applied to complete their simulations, especially in terms of electromagnetic force.A two-dimensional axisymmetric numerical model is developed to simulate the dynamic process of short circuiting transfer in CO2Arc Welding by use of computational fluid dynamics software’FLUENT’. Based on the fluid dynamics theory and electromagnetic theory, the process of droplet formation, evolution and transfer to the wielding pool is simulated using volume of fluid (VOF) model and MHD method, the governing equations and related source terms are solved by means of User-defined function and User-defined scalar in FLUENT. Meanwhile to test the accuracy of the simulated results, the welding experiments are performed and the high-speed photography system is used to record the real process of metal transfer. The results show that the simulated results are in reasonably good agreement with the experimental ones.In the second stage, according to traditional theory, after the droplet touch the wielding pool, the voltage drops to approximately1/5of original value and the current rises to nearly3times than before in about3milliseconds. As well as the droplet transfers to the wielding pool, large amount of energy has been accumulated due to high current density, it is widely accepted that the energy accumulated within hundreds of microseconds before the rupturing time point of the short circuit liquid bridge influences directly the spatter level in CO2short circuit transfer welding. Since this process is very complicated and hard to integrate energy function, magnetic field and electric field together, there are very few scholars researching in this field. In this paper, the main objective is to utilize the commercial computational fluid dynamics (CFD) software’FLUENT’to simulate the whole process of short-circuit metal transfer in CO2arc welding. Volume of fluid (VOF) model, User-defined function, User-defined scalar and MHD method are applied in the simulation process, the governing equations and related source terms are solved by means of in FLUENT.We divided the research into two parts according to the transfer process, during the first stage, although it is a lot like normal metal transfer in GMAW, we focus on the precise control of electromagnetic force and the integration of temperature field. In the second part, we will introduce and utilize MHD method to simulate and analyze the rupturing process of liquid bridge.To assess the validity of metal transfer simulation, welding experiments are carried out and the high-speed photography is used to record the real process of metal transfer. The results show that the simulation results are in reasonably good agreement with the experimental ones and it can improve our understanding of metal transfer in the welding and assess the modeling capability using FLUENT.