Spattering and denudation in laser powder bed fusion process: Multiphase flow modelling

To understand the physical mechanisms of the spattering and denudation phenomena in the laser powder bed fusion process, we develop a multiphase flow model by bi-directionally coupling the discrete element method and finite volume method, where the exchanges of both momentum and energy between the powder particles and gases are incorporated. It is the first time that the dynamic behaviours of both the gas phase and powder particles during the spattering and denudation phenomena are reproduced in computational modelling, which agree well with the published experimental observation. The metal vapour spouts out and decelerates sharply along the jetting direction while expanding radially, which induces remarkable vortex flows of the ambient gas. With comparative simulation cases, the vapour jetting and the consequent vortex flow are demonstrated to be dominant in the spattering and denudation phenomena, and the thermal buoyancy effect is proved to be negligible. Moreover, the influence of the jetting angle is investigated: no remarkable effect within the range of 60 degrees - 120 degrees; while larger than 150 degrees, the accumulation zone is eliminated leading to a completely exposed denudation zone. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.