Keynote Speaker (by invitation only) at Digital Twin Symposium 2019, presented by Leila Ladani
Powder bed fusion (PBF) is the main technology for metal additive manufacturing. In this technology laser or e-beam is used to melt metal powder and create a part by successive addition of layers. The complexity of the physics involved and the variabilities in the process has posed challenges to researchers to make the processes repeatable and certified. Although PBF process is in many aspects similar to welding process, it is more complex due to the size of the localized melt pool and that it is being repeated cyclically to form the whole part. Laser and E-beam each have their own characteristics that dictate different outcome. Complex heat transfer mechanisms in different phases of material, the dynamic of melt pool, shrinkage due to solidification, powder flowability and wettability, radiation and evaporation are only some of the active mechanisms during this process. The build outcome including the surface roughness, shape of the bead, and dimensional accuracy greatly depend on how these physical mechanisms interact. Advanced multi-physics and multi-scale computational modeling is necessary to understand the fundamental physics of this process. This talk focuses on a review of simulation techniques and discoveries made on our group through multi-physics finite element simulation melting and solidification process for both E-beam and Laser. The intricate differences in finite element simulation of beam interaction with powder in the optical source (laser) vs the E-beam is discussed. A two-step process of modeling the bead geometry and shape is described and the physical mechanisms and governing equations are discussed. The results demonstrate that the forced rigidity method paired with the incorporation of coupled fluid flow and heat transfer physics is a promising step towards building more complete and accurate finite element models.