Thermal and thermomechanical studies of beam-based powder-bed additive manufacturing processes

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University of Alabama Libraries

Powder-bed beam-based metal additive manufacturing (AM) such as electron beam additive manufacturing (EBAM) and selective laser melting (SLM) has a potential to offer innovative solutions to many challenges faced in the manufacturing industry. However, due to complex heat transport and thermomechanical interactions, the physical process of powder-bed AM has not been fully understood. This dissertation research focuses on the process thermal analysis, thermomechanical modeling and deformation studies of powder-bed metal AM parts. The primary objectives of this research are: (1) to develop a 3D finite element (FE) thermal model to study the powder porosity effect in EBAM, validated by near infrared thermography; (2) to apply the developed thermal model and study, supported by experiments, the thermal response under different process parameters; (3) to simulate the SLM process using the developed 3D thermal model; (4) to develop a 3D thermomechanical FE model to study temperature, stress and deformation characteristics in EBAM overhang parts for different powder sintering conditions; (5) to investigate different support structures for overhang deformation in EBAM; (6) to investigate an overhang support design method for structure optimization. The major findings are summarized as follows. (1) For beam process parameters of 632 mm/s speed, 6.7 mA current and 0.55 mm diameter, the peak temperature is ~2700 °C and melt pool size is 2.94 × 1.09 × 0.12 mm (length, width and depth). (2) Process parameters affect thermal characteristics. For 482 vs. 1595 mm/s speed, given 7.7 mA current and 0.65 mm diameter, the peak temperatures are 2572 vs. 2326 °C and the melt pool lengths are 2.35 vs. 1.25 mm. (3) In SLM, the residual heat can increase the melt pool size from raster scanning; e.g., the melt pool depth changes from ~0.085 mm to ~0.11 mm at given parameters. (4) In thermomechanical simulations, the results revealed that decreasing the powder-bed porosity (50% vs. 35%) can reduce the process temperatures, part residual stresses and overhang deformations. (5) A contact-free heat support beneath an overhang may effectively minimize overhang deformations. (6) The proposed support design methodology may eliminate part overhang deformations using less support materials.

Electronic Thesis or Dissertation
Mechanical engineering