Investigation of molten pool geometry and flow field based on powder-scale modeling in laser directed energy deposition

Laser directed energy deposition (DED-LB) technology is currently facing challenges in controlling geometry accuracy of metal components. There is an urgent need to develop a numerical model that is more efficient and accurate compared to existing models and to analyze the dynamic behavior of the melt pool under the interaction of process parameters during DED-LB process to optimize parameters with fewer experimental studies to reduce costs. Therefore, a three-dimensional powder-scale multi-physics model is proposed during the single-track DED-LB process in this study. The powder particles are added by a Lagrangian particle model in this model without the need for assuming that the powder particles entering the molten pool are added by the mass source term, which improves model accuracy and efficiency. The effects of energy per unit mass (EUM, J g-1), mass per unit length (MUL, g mm-1), and standoff distance (SD, mm) intensities on transient molten pool motion and flow field are comprehensively investigated. It is discovered that the proposed model is able to predict the single-track height, width, depth, and dilution rate, or less than 9% relative error from experimentation, providing a useful tool for track geometry to predict. Furthermore, the flow velocity, width, and depth of melt pool also gradually are improved with higher EUM, MUL, and SD intensity and fluctuate within a small range. However, the height is improved and then decreases with higher SD intensity, and is improved with higher EUM or MUL. Overall, this study contributes to developing an optimizing process approach to improve formation accuracy for DED-LB manufacturing.