A thermal finite element model with efficient computation of surface heat fluxes for directed-energy deposition process and application to laser metal deposition of IN718

In this study, a numerically efficient thermal finite element process model is developed to predict the melt-pool characteristics of directed-energy deposition (DED) process. The model uses a new technique to compute the effective surface heat loss terms in the form of a volumetric heat sink term in order to avoid the redefinition of surface heat fluxes from the free-surfaces after addition of every layer. In addition, thermal model incorporated the heat losses due to evaporation and Marangoni effect by changing the conductivity at the liquid state. The melt pool dimensions of IN718 were experimentally measured by in-situ thermal monitoring and by ex-situ optical microscopy of the cross-sections of the deposited tracks. The proposed model accurately predicts the experimental melt-pool dimensions of single-track and multi-layer depositions over the range of process parameters.