Physicomathematical modeling of the formation features of fillet welds of bridge metal structures under submerged-arc welding

Introduction. The weld formation under the submerged-arc welding of bridge metal structures is investigated. The work objective is to study possibilities to increase the welding performance during the arc welding of fillet seams. Materials and Methods. Methods of computer analysis are used to optimize the technology. With their help, a physicomathematical model of fillet weld formation under the submerged-arc welding has been developed. It is based on a system of equations for thermal conductivity and equilibrium of the weld pool surface. In this system, the formation of an arc cavern is determined through the flux boiling isotherm under the action of the arc column radiation; heat transfer by the flux vapor inside the arc cavern and the influence of the spatial position on the formation of the weld pool are taken into account. Results. New mathematical relationships that describe physical phenomena under the submerged-arc welding of fillet welds are proposed. The key feature of the proposed model is in the fundamental difference between the submerged-arc welding and the gas-shielded arc welding, i.e., during submerged-arc welding, the arc burns in a gas-vapor cavern that appears due to the melting and evaporation of flux. Numerical simulation of the temperature distribution during production of the fillet welds in 1F and 2F positions is carried out. The process constraints under the single-run welding of the fillet welds are specified. It was determined that the single-run submerged-arc welding of fillet welds in 1F position exhibits high-quality formation of welds for almost the entire range of metal sheet thicknesses. During production of fillet welds in 2F position, high-quality formation is provided only for sheet thicknesses up to 8 mm. At heavy thicknesses, the formation of the seam is disrupted due to the melt flow from the vertical wall. In this case, the leg length decreases; a typical undercut is formed; so the weld will be asymmetric and less strong.Discussion and Conclusions. Comparison of the numerical analysis results with actual data on welding modes under the production of bridge metal structures shows that the existing fillet welding technologies have already reached their maximum efficiency rate. Further productivity gain is possible by forming oversized legs only with multiarc or multielectrode welding methods.