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 defect generation mechanisms. These processes are typically 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, must be predicted with high accuracy. The present work utilizes a diffuse interface model based on a continuum surface flux (CSF) description on the interfaces to study dimensionally reduced thermal two-phase problems representing 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. A novel parameter-scaled CSF approach is proposed, which is constructed to yield a smoother temperature rate 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 CSF approach compared to classical CSF, drastically reducing computational costs. Finally, we showcased the general applicability of the parameter-scaled CSF to a three-dimensional simulation of stationary laser melting of PBF-LB/M considering the fully coupled thermo-hydrodynamic multi-phase problem, including phase change.

翻译：激光粉末床熔融金属增材制造（PBF-LB/M）中熔池动力学的计算模型有望揭示基本缺陷生成机制。此类过程通常伴随快速蒸发，蒸发诱导的反冲压力与冷却效应成为流体动力学和温度演化的主要驱动力。这些界面通量的量级取决于熔池表面温度的指数函数，因此必须高精度预测该温度。本研究采用基于连续表面通量（CSF）描述的扩散界面模型，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CSF方法及典型界面厚度与离散化方案时，极端温度梯度与金属-环境气体材料属性高比值共同导致界面温度及通量出现显著误差。本文提出一种新型参数缩放CSF方法，该方法通过构建扩散界面区域中更平滑的温度变化率，显著提升求解精度。与经典CSF相比，该参数缩放CSF方法在达到给定温度场预测精度时所需的界面厚度限制宽松至少一个数量级，从而大幅降低计算成本。最后，我们通过考虑包含相变的完全耦合热-流体动力学多相问题的PBF-LB/M静止激光熔融三维仿真，验证了参数缩放CSF的普适适用性。