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

激光粉末床融合组中的金属增材制造极大地实现了新颖的设计，具有复杂的细胞排列部件几何形状或优化的拓扑结构，可用于轻质高强度结构，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有可能实现提高生活质量的产品，并使美国工业的技术能力成熟。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），这些特征与较大尺寸的散装部件不具有相同的加工特性。这些未知的特性给零件质量的保证带来了困难，也阻碍了采用激光粉末床熔合技术生产出具有精细特征的零件。该奖项解决了上述挑战，通过推进过程科学在处理小长度尺度，其中过程特性变得敏感的特征尺寸。高功率激光扫描随机分布金属颗粒时，温度和熔流随时间变化的响应是需要探索的基础科学。此外，与肯塔基州制造业妇女分会的外展活动将建立一个平台，帮助妇女促进多元化的制造业劳动力。本项目的目的是了解金属激光粉末床熔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场耦合。研究的重点是一维线扫描、二维光栅区域扫描和用于过程物理研究的三维独立支柱制造，以及用于与小几何形状和工艺条件相关的机械评估的包含晶格的样品。将采用两阶段方法对该过程进行数值研究：采用离散元方法模拟粉末颗粒扩散，采用多物理场建模模拟单轨、单层和多层单支柱制造的热流体现象，特别强调熔池动态响应和固化形态。实验研究将采用激光粉末床熔合系统，使用钛合金粉末制造设计样品，通过熔池测量和微观结构分析来验证工艺模型，并量化尺寸对工艺特性的影响。如果研究成功，将揭示近距离小面积激光扫描过程中热学和流体行为的基本认识。所获得的知识将为复杂几何零件的有效增材制造提供实用的改进和可靠的质量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.