Powder-bed Fusion (PBF) is a growing additive manufacturing (AM) technology that is capable of speedily fabricating functional components for aerospace, automotive, microelectronics, and biomedical applications. In the laser PBF (L-PBF) process, the metallic powders are melted by a computer-controlled moving laser beam and rapidly cooled and solidified in a convective medium. Titanium alloy, especially, Ti-6Al-4V, is one of the primary choices for PBF-AM material selection in the aerospace and biomedical industries because of its extensive usability in spacecrafts, aircrafts, and medical implants. Manufacturing Ti-6Al-4V parts by PBF process has significant advantages over the conventional manufacturing techniques because of its low castability and challenging machining process. However, controlling the phase formation, melt-pool dynamics, surface roughness, and mechanical properties of the material in the L-PBF process requires optimization of the process parameters which is extremely challenging. Most of the studies emphasize the application-based experimental analyses such as build-part microstructure, morphological characteristics, powder metallurgy, and mechanical properties of the material. However, studying the L-PBF process behavior with the help of numerical modeling is very convenient to determine the complex heat transport and interactions among the thermo-fluid, mechanical, and metallurgical phenomena. Studies on the L-PBF process modeling show that the temperature-dependent properties including density, thermal conductivity, latent heat of fusion, the specific heat capacity, convective heat transfer coefficient, and emissivity play an important role in determining the geometry of the melt pool. Besides these thermal properties, assigning the correct heat source parameters (e.g., power, scanning speed, and spot size) and various porosity levels are also important to develop a robust multi-physics thermal model. In this study, a 3-D computational fluid dynamics model with Ti-6Al-4V powder-bed is developed incorporating a moving conical volumetric heat source and thermo-physical properties of Ti-6Al-4V alloy to conduct the simulations of the L-PBF process. The melt-pool dynamics and its thermal behavior are investigated numerically and results for temperature profile, cooling rate, velocity in melt-pool, variation in density, thermal conductivity, specific heat capacity, and enthalpy are obtained for different laser irradiation conditions. A custom Ytterbium fiber laser system is applied to perform selective laser melting experiments of both Ti-6Al-4V powder-bed and solid specimens. The microstructures of the cross-sectional areas are examined by a scanning electron microscope to observe the melt-pool dimensions. Finally, the simulation results for melt-pool geometry are compared with the experimental results for the same to validate the numerical model for the L-PBF process. Thus, investigating the heat transport phenomena, temperature distribution, and melt-pool dynamics in PBF with a combination of simulations and experiments can successfully determine the desired part quality and process optimization.


Heat Transfer and Melt-Pool Evolution During Powder-Bed Fusion of Ti-6Al-4V Parts Under Various Laser Irradiation Conditions

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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