Evaporation Model for Keyhole Dynamics During Additive Manufacturing of Metal

The molten-pool flow, particularly the keyhole effect, plays a critical role in the formation of defects in additive-manufacturing and welding processes. In this study, we derive an evaporation model for metal alloys considering the gas-flow structure and material composition and implement it in a multiphysics thermal-fluid flow model, which utilizes the volume of fluid (VOF) in the finite volume method (FVM) to capture free surfaces and the ray-tracing method to track multireflections of laser within the keyhole. The current derived evaporation model is validated against in situ x-ray imaging results via multiple cases: (1) stationary laser melting of a $\mathrm{Ti}\text{\ensuremath{-}}6\mathrm{Al}\text{\ensuremath{-}}4\mathrm{V}$ base plate under 1-atm ambient pressure, (2) stationary laser melting of a 304L stainless-steel base plate under 0.0002-atm ambient pressure, (3) laser scanning of a $\mathrm{Ti}\text{\ensuremath{-}}6\mathrm{Al}\text{\ensuremath{-}}4\mathrm{V}$ base plate under 1-atm ambient pressure. The simulation results indicate that our evaporation model is applicable for both common and near-vacuum environment, while Anisimov's evaporation model, which is widely used in keyhole simulation, is unsuitable in near-vacuum keyhole simulation. Moreover, the absorbed energy distribution, recoil pressure, $z$-direction recoil force and keyhole growth are analyzed in the simulations.