Computational modeling of the melt pool dynamics in laser-based powder bed fusion metal additive manufacturing (PBF-LB/M) promises to shed light on fundamental mechanisms of defect generation. These processes are accompanied by rapid evaporation so that the evaporation-induced recoil pressure and cooling arise as major driving forces for fluid dynamics and temperature evolution. The magnitude of these interface fluxes depends exponentially on the melt pool surface temperature, which, therefore, has to be predicted with high accuracy. The present work utilizes a diffuse interface finite element model based on a continuum surface flux (CSF) description of interface fluxes to study dimensionally reduced thermal two-phase problems representative for PBF-LB/M in a finite element framework. It is demonstrated that the extreme temperature gradients combined with the high ratios of material properties between metal and ambient gas lead to significant errors in the interface temperatures and fluxes when classical CSF approaches, along with typical interface thicknesses and discretizations, are applied. It is expected that this finding is also relevant for other types of diffuse interface PBF-LB/M melt pool models. A novel parameter-scaled CSF approach is proposed, which is constructed to yield a smoother temperature field in the diffuse interface region, significantly increasing the solution accuracy. The interface thickness required to predict the temperature field with a given level of accuracy is less restrictive by at least one order of magnitude for the proposed parameter-scaled approach compared to classical CSF, drastically reducing computational costs. Finally, we showcase the general applicability of the parameter-scaled CSF to a 3D simulation of stationary laser melting of PBF-LB/M considering the fully coupled thermo-hydrodynamic multi-phase problem, including phase change.

翻译：基于激光的粉末床熔融金属增材制造（PBF-LB/M）中熔池动力学的计算建模有望揭示缺陷生成的基本机制。这些过程伴随着快速蒸发，因此蒸发诱导的反冲压力和冷却成为流体动力学与温度演变的主要驱动力。这些界面通量的大小随熔池表面温度呈指数依赖关系，因此必须对该温度进行高精度预测。本研究采用基于连续表面通量（CSF）界面通量描述的弥散界面有限元模型，在有限元框架内研究代表PBF-LB/M的降维热两相问题。研究表明，当应用经典的CSF方法以及典型的界面厚度和离散化方案时，极端的温度梯度结合金属与环境气体之间材料属性的高比率，会导致界面温度和通量出现显著误差。预计这一发现也适用于其他类型的弥散界面PBF-LB/M熔池模型。本文提出了一种新颖的参数缩放CSF方法，该方法旨在在弥散界面区域产生更平滑的温度场，从而显著提高求解精度。与经典CSF相比，所提出的参数缩放方法为达到给定精度水平预测温度场所需的界面厚度限制至少放宽一个数量级，从而大幅降低了计算成本。最后，我们通过一个考虑完全耦合的热-流体动力学多相问题（包括相变）的PBF-LB/M稳态激光熔化三维模拟，展示了参数缩放CSF方法的普遍适用性。