Numerical simulation of electron-beam welding with a longitudinal oscillation of the beam based on the experimental determination of the keyhole form

The research examines the process of electron-beam welding in the keyhole mode with the use of beam oscillations with different focusing regimes on the example of stainless steel - grade 502. We study the impact of longitudinal beam oscillation and their parameters on the shape of the keyhole, the character of the processes of heat and mass transfer and weld’s parameters, to develop methodological recommendations for electron-beam welding with oscillation. A numerical three-dimensional mathematical model of electron beam welding is presented. The model was developed on the basis of the combined solution of heat conduction equation and Navier-Stokes equation in the moving coordinate system with taking into account phase transitions at the interface of solid and liquid phase. The boundary conditions at the free surface of the weld pool and on the keyhole walls are presented by thermocapillary convection (Marangoni effect). As input parameters the form of keyhole and distribution of the beam energy on the keyhole walls based on experimental data on the parameters of the secondary signal in the plasma over the welding zone by using the method of a synchronous accumulation are used. The keyhole was approximated by an oblique elliptical cone with a spherical apex. Such an approach eliminates the need to take into account all the complex factors that affect the formation of the keyhole. Calculations of thermal and hydrodynamic processes have been carried on a cluster using a simulation package COMSOL Multiphysics. Comparison of the calculated and experimental cross sections of the welds showed good agreement. With the help of the proposed method during the research characteristic features of the beam power distribution for different focus modes were identified. The analysis of the significance of various factors on the formation of the keyhole geometry has been conducted.