Numerical simulation of the growth of a sessile drop of metal melt on a horizontal substrate under direct feeding of laser energy and powder

The paper proposes a new method for studying the dynamics of non-isothermal processes in laser direct additive manufacturing (L-DED) technologies of metal products by growing a sessile drop. Its growth is performed with stationary laser radiation acting on the substrate and metal powder, which is supplied by a jet of inert gas to the focusing area of the laser beam. Heat and mass transfer of a metal melt with Newtonian rheology is considered laminar with a temperature-independent density. The heated powder is instantly melted on the surface of the bath and added as a continuous mass flow through the free surface of the growing droplet with a given distribution. Dynamic conditions on its free surface depend on the value of surface tension, Marangoni shear stress and normal pressure from the action of a jet of gas with powder. Modeling of wetting of solid surfaces by the melt is performed within the framework of the modified Voinov model. The numerical solution of the problem is performed in three-dimensional and axisymmetric formulations by the mixed finite element method using the ALE free surface tracking algorithm. The features of heat and mass transfer in a growing droplet and the evolution of its free surface are investigated. A significant effect of the gas flow and the mass flow rate of the powder on the structure of melt convection in the droplet and the evolution of the free surface with the formation of a crater is shown.