Numerical simulation and experimental research of molten pool flow field and temperature field by hollow-laser direct energy deposition

Hollow-laser Direct Energy Deposition (HL-DED) significantly surpasses traditional Laser Directed Energy Deposition (L-DED) methods, marked by its superior adjustability of energy density, exacting control of energy distribution, and versatility in creating cladding layers of varied geometries. This novel technique ensures a markedly uniform and stable melt path. In this paper, the HL-DED process was systematically analyzed by combining numerical simulation and experimental research. A novel three-dimensional transient computational fluid dynamics (CFD) simulation model is established based on the Flow 3D software to study the flow and heat and mass transfer behaviors. At the optimized processing parameters, the single-track and multi-track cladding layer processes were carried out respectively. Results show that the model can well predict and explain the flow of the molten pool and the morphology of the cladding layer in the HL-DED process. In the initial stage of single-track cladding, the molten pool exhibits a symmetrical bimodal distribution configuration characterized by the peak flow rate of 0.09 m/s, with temperatures being higher at the periphery and lower at the center. In the stabilization phase, the dynamics of the molten pool are primarily influenced by gas-powder momentum transfer, showing increased peak flow rates up to 0.26 m/s. Concurrently, the peripheral temperatures rise from 2001 K to 2122 K (0.06 % increase), but central temperatures ascend from 1400 K to 1800 K (0.29 % increase). The flow and temperature distribution patterns in multi-track cladding closely mirror those observed in single-track layers, maintaining a symmetrical bimodal temperature distribution with peak flow rates reaching 0.105 m/s. The temperature distribution evolves from a unimodal to a bimodal pattern, with the left peak approximately 100 K higher than the right, before reverting to a unimodal configuration. Simulation outcomes closely align with experimental findings, offering valuable insights for refining the experimental adjustment of the internal optical coaxial powder feeding process.