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

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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.