Visualisation and numerical analysis of laser powder bed fusion under cross-flow
Visualisation and numerical analysis of laser powder bed fusion under cross-flow
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DOI：
10.1016/j.addma.2020.101690
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发表时间：
2021-01-01
影响因子：
11
通讯作者：
Moore, A. J.
中科院分区：
文献类型：
--
作者：
Bitharas, I;Burton, A.;Moore, A. J.
除了防止氧化外，粉末床上的惰性气体横流还可以提取工艺副产品，这对于金属零件增材制造过程中的工艺可重复性和制造质量至关重要。在这项研究中，首次采用高倍率纹影成像来可视化交叉流、激光羽流和单个粉末颗粒之间的相互作用。新的三维多物理场交叉流模拟，包括蒸汽射流和激光羽流，用于计算加工区域的能量、动量和物质输运，以了解和量化观察到的相互作用。在加工过程中，观察到金属烟雾以及大量空气中的粉末颗粒和结块在扫描区域内靠近粉末床。这些粒子在一系列随机碰撞中相互作用，影响构建的一致性。在岛屿扫描上方的大气中形成了折射率梯度，它在处理区域之外延伸了几十毫米。这些副产物的萃取速率受交叉流的速度控制，与建筑物的质量有关。观察到垂直于激光扫描方向的横流可以最有效地去除相邻激光扫描中的空气颗粒，从而限制了激光-粒子和粒子-粒子的相互作用。该模型表明，远离蒸汽射流的折射率梯度是由金属浓度而不是加热气体的温度引起的。
As well as preventing oxidation, a cross-flow of inert gas over the powder bed extracts process by-products, making it critical for process repeatability and build quality during the additive manufacturing of metallic parts. In this study, high-magnification schlieren imaging was employed to visualise the interactions between the cross-flow, laser plume and individual powder particles for the first time. Novel 3D multiphysics simulations of the cross-flow, including the vapour jet and laser plume, were used to calculate energy, momentum and species transport over the processed area in order to understand and quantify the observed interactions. During processing, metallic fumes as well as a significant number of airborne powder particles and agglomerates were observed to remain close to the powder bed, over the scanned area. These particles interact in a range of stochastic collisions that affect the build consistency. Refractive index gradients were formed in the atmosphere above the island scans, which extended many tens of mm beyond the processing area. The rate of extraction of these by-products, regulated by the velocity of the cross-flow, was related to the quality of the builds. A cross-flow perpendicular to the laser scan direction was observed to remove airborne particles from adjacent laser scans most effectively, limiting laser-particle and particle-particle interactions. The model demonstrated that the refractive index gradients away from the vapour jet are due to the metal concentration rather than the temperature of the heated gas.