Simulation Of The Behavior Of Droplet And Pool In The CO₂ Welding Short-circuit Transition Process

CO₂ gas shielded arc welding is a welding method which is a low cost, little deformation, high efficiency and easy to automate, mainly used in the thin sheet and all position welding. Short-circuit transition is a transitional form of droplet which widely used in CO₂ gas shielded arc welding, under the conditions of the thin wire, small current and low voltage. Because of bad weld forming and big splash, it is large extent to restrict its further promotion and application.CO₂ gas shielded arc welding quality is determined by the pool behavior, while in the process of short circuit transition, behavior of droplet will have a major impact on the pool behavior, so welding parameters of CO₂ gas shielded arc in the short transition is important to melting droplet and pool behavior, which is also important to the quality of welding joints.From the characteristics of CO₂ gas shielded welding and the mechanism of the droplet short-circuit transition proceeding, droplet formation and the force conditions are analyzed according to "Quality-Spring" theory. Based on the MATLAB numerical analysis platform, we simulate the impact of welding current on droplet shape and size of the transition frequency, in the end, the main forces on the droplet are analyzed. Droplet transfer characteristics and control law play an important role in the stability of the welding process,welding quality and productivity. In another word, the welding parameters determine the form and features of droplet transfer, while the droplet transfer would affect the stability of welding parameters, so establishing the quantitative relationship between welding parameters and droplet transition are of great significance.In the welding process the actual short-circuit transfer CO₂ gas shielded arc weld, the heat of the droplet will have a significant impact on temperature field distribution of the molten pool, which is always ignored in the current welding temperature simulation. In this thesis, the double-ellipsoid heat source model and the droplet heat source model are analyzed respectively, it also sets up a new composite heat source model based on the double-ellipsoid heat source and heat droplet for CO₂ arc welding. The temperature field of low carbon steel was calculated using ANSYS finite element software, which is verified by the experiments. Thermal cycling curves has been simulated and calculated. The results show that the combined heat source model is better than a single double-ellipsoid heat source model, the simulation results are closer to experimental results. The accuracy, validity and practicability of the composite heat source model are verified.Finally,based on the above conclusions and characteristics of CO₂ welding process, using ANSYS simulation method to study the relationship between pool geometry and welding parameters, which are verified by the corresponding welding experiment. The purpose is not only to reduce the cost of welding test, but also provide a theoretical basis for welding process. Comparing the experiment value and the conclusions under different welding parameters, the model results established by ANSYS and the actual results were well matched.