Thermo-Fluid Characterizations of the Powder-Bed Fusion Additive Manufacturing Processes using Laser and Electron Beam
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The powder-bed fusion (PBF) process is a subdivision of Additive Manufacturing (AM) technology where a heat source at a controlled speed selectively fuses regions of a powder-bed material to form three-dimensional (3-D) parts. Two of the most commercial PBF processes are selective laser melting (SLM) and electron beam additive manufacturing (EBAM), which can fabricate full-density metallic parts in a layer-by-layer fashion. In this study, thermal behavior and melt-pool dynamics in the PBF process are investigated by developing 3-D multiphysics-based thermo-fluid models for both SLM and EBAM containing Ti-6Al-4V alloy as a powder-bed material. The laser and electron beams are modeled as conical volumetric heat sources having the Gaussian distribution. The temperature-dependent properties of Ti-6Al-4V and the heat source parameters are incorporated in the model as the user-defined functions. The melt-pool geometry and its thermo-fluid behavior are investigated numerically, and results for temperature profile, variation in thermo-physical properties, the melt-pool velocity and geometry, and cooling rate are obtained under various heat source specifications. Results, obtained from the SLM and EBAM models under the same irradiation conditions of the melt pool, are also compared to describe their deterministic features to be considered for industrial applications. The comparison shows that under the same irradiance level and beam interaction time, the SLM process gives a smaller melt-pool volume but a faster average cooling rate than those in the EBAM process. The thermo-fluid models for SLM and EBAM are validated by comparing the simulation results for the melt-pool geometry with experimental results and comparing the numerical melt-front position with the analytical solution for the classical Stephan problem of melting of a phase-change material.