  Thermal multi-phase flow simulations are indispensable to understanding the
multi-scale and multi-physics phenomena in metal additive manufacturing (AM)
processes, yet accurate and robust predictions remain challenging. This book
chapter summarizes the recent method development at UIUC for simulating thermal
multiphase flows in laser powder bed fusion (LPBF) and directed energy
deposition (DED) processes. Two main method developments are discussed. The
first is a mixed interface-capturing/interface-tracking computational framework
aiming to explicitly treat the gas-metal interface without mesh
motion/re-meshing. The second is a physics-based and non-empirical deposit
geometry model for DED processes. The proposed framework's accuracy is assessed
by thoroughly comparing the simulated results against experimental measurements
on various quantities. We also report critical quantities that experiments can
not measure to show the predictive capability of the developed methods.
