Physical substantiation of discretization scheme in modeling of deep penetration melting of metals in laser and related technologies

The problem of adequate reproduction by numerical models of hydrodynamic processes in keyhole mode in laser and electron beam welding and related technologies is considered. The problem manifests itself in the contradictory conclusions of models concerning the relative contributions of thermocapillary and ablative mechanisms in keyhole formation. The problem solution involves bringing the results of numerical model in line with experimental data, according to which, under technological conditions, the main contribution to the keyhole formation is made by the thermocapillary mechanism with insignificant evaporation. The distortion of these contributions is a consequence of inadequate reproduction of thermocapillary mechanism specific features in keyhole mode. The reason is the grid step choice without taking into account the real scale of thermocapillary flow in keyhole mode. A method for choosing a physically justified spatial and temporal step of the computational grid is proposed. Estimates have been made for the recommended discretization for characteristic spot sizes used in laser welding and additive manufacturing technologies by selective laser melting. The recommended grid step is compared with the discretization commonly used in models.