Modeling of whole-phase heat transport in laser-based directed energy deposition with multichannel coaxial powder feeding

The whole-phase heat transport model of laser-based directed energy deposition (L-DED) with multichannel coaxial powder feeding is the basis of investigating the underlying physical mechanisms, such as molten pool evolution, thermal history, grain growth, stress and deformation evolution. The existing heat transport models usually ignore or simplify some important physical processes, which limits the simulation accuracy of the models to some extent. In this paper, a modeling framework for whole-phase heat transport for coaxial L-DED is developed. Considering the interaction among the laser beam, coaxial multipowder stream and substrate, a comprehensive whole-phase heat transport model including a parametric model of powder-scale laser-powder coupling and deposition heat transport model is developed. A parametric model for laser-powder coupling can enable one to avoid the influence of the parameters of the coaxial multichannel powder-fed head on the number and structure of the model. The spatial relations between the laser beam, coaxial multipowder stream and substrate are modeled based on homogeneous transformation theory, which effectively addresses coordinate transformation on the complex spatial position and pose. The influence of two typical spatial laser beam profiles (SLBPs): the Gaussian profile (GP) and super-Gaussian profile (SGP), on the whole-phase heat transport is studied. The results show that under the conditions of the SGP and GP, the peak temperature of the coaxial multipowder stream on the deposition surface is below the melting point. The peak temperature distribution and powder heat flux for the coaxial multipowder stream shows a distribution with a lower center, higher sides and cruciform tower-like shape. The peak temperature and heat flux of the coaxial multipowder stream under the SGP are less than that under the GP. Dimensionless number analysis indicates that under both the SGP and GP, the Marangoni convection and thermal conduction jointly dominate the heat transport behavior within the molten pool. Compared to the GP, the Marangoni effect and the heat accumulation capacity of the molten pool under the SGP are weaker, but the heat dissipation capacity of the molten pool is stronger. The use of the SGP is favorable for reducing the thermal deformation of various parts during L-DED.