Transient Thermo-Fluid Behavior in Metal Laser Powder-Bed Fusion Process: Exploring the Size Effect in Making Small Features

激光粉末-床融合集团的金属添加剂制造极大地实现了具有复杂部件几何结构或优化拓扑的新颖设计，适用于轻型高强度结构、受自然启发的生物医学植入物和高效热交换器等应用。这种集成设计和制造创新具有实现提高美国工业生活质量和成熟技术能力的潜力。然而，在制造具有复杂几何形状的部件时，存在许多小特征(例如，0.5 mm或更小)，它们不具有与较大尺寸的大块部件相同的加工特性。这些未知的特征给保证零件质量带来了困难，阻碍了采用激光粉床熔化技术生产具有精细特征的零件。该奖项通过在处理小长度尺度方面推进工艺科学来解决上述挑战，其中工艺特征对特征尺寸变得敏感。需要探索的基础科学是高功率激光扫描随机分布的金属颗粒在短扫描过程中温度和熔体流动的时变响应。此外，与肯塔基州制造业妇女分会的外联活动将建立一个平台，帮助妇女促进多样化的制造业劳动力。该项目的目标是了解金属激光粉末-床融合过程中的尺寸效应，特别是阐明激光扫描开始和结束时的动态热场和流动场。研究重点是用于工艺物理研究的一维线扫描、二维栅格区扫描和三维单个支柱制造，以及用于与小几何形状和工艺条件相关的力学评估的晶格包含试件。采用两步法对该过程进行数值研究：离散元方法模拟粉末颗粒扩散，多物理模型模拟单道、单层和多层单支柱结构的热流体现象，重点研究熔池动态响应和凝固形态。实验研究将使用钛合金粉末的激光粉床融合系统来制造设计的试件，通过熔池测量和显微组织分析来验证工艺模型并量化尺寸对工艺特性的影响。这项研究如果成功，将揭开人们对短距离小区域激光扫描过程中热和流体行为的基本理解。所获得的知识将对提高质量和可靠性的复杂几何零件的有效添加制造具有实用价值。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Metal additive manufacturing in the laser powder-bed fusion group has greatly enabled novel designs with sophisticated part geometry of cellular arrangements or optimized topology for applications like lightweight high-strength structures, nature-inspired biomedical implants and high-efficiency heat exchangers, etc. Such integrated design and manufacturing innovations have the potential to realize products that improve the quality of life and maturing the technological capability of the U.S. industry. However, in making components with complex geometries, there are many small features (e.g., 0.5 mm or less) which do not share the same processing characteristics as larger sized bulk components. These unknown characteristics pose difficulty in ensuring part quality and impedes adopting the laser powder-bed fusion to produce parts with delicate features. This award addresses the above-mentioned challenges by advancing the process science in tackling small length scales, where the process characteristics become sensitive to the feature dimensions. The fundamental science that needs to be explored is the time-varying response of the temperatures and the molten flows in high-power laser scanning of metallic particles of stochastic distributions during short scanning. Further, outreach activities with the Women in Manufacturing, Kentucky Chapter will establish a platform that helps engage women to promote a diverse manufacturing workforce.The goal of this project is to understand the size effect in the metal laser powder-bed fusion process, in particular, to elucidate the coupled dynamic thermal and fluid fields during the start and end of laser scanning. The research focuses on one-dimensional line scans, two-dimensional raster-area scans and three-dimensional individual strut fabrications for the process physics study, as well as lattice-included specimens for mechanical evaluations related to the small geometry and process conditions. A two-stage approach will be employed to numerically study the process: a discrete element method to simulate powder particle spreading and multi-physics modeling to simulate the thermo-fluid phenomena for single-track, single-layer as well as multi-layer single strut fabrications, with particular emphases in the melt-pool dynamic response and solidified morphology. The experimental study will employ a laser powder-bed fusion system using titanium alloyed powder to fabricate designed specimens, with melt pool measurements and microstructures analysis to validate the process model and quantify the size effect on process characteristics. The research, if successful, will unveil the basic comprehension of the thermal and fluid behavior during short-distance and small-area laser scanning. The knowledge obtained will be practical for effective additive manufacturing of complex geometry parts with improved and reliable quality.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.