Additive manufacturing (AM) has created a new paradigm of integrated materials, design and manufacturing innovations for effective product development and realization across a broad range of industries. Metal AM technologies such as selective laser melting (SLM), which uses a powder-bed and a high power laser, are especially beneficial in making complex-geometry, high-performance components without incurring tooling costs, giving early adopters a competitive advantage in the global market. One of the key challenges that hinder efficient metal AM technology implementation in industry is part quality inconsistency that is significantly affected by porosity in AM parts. Pores, with sizes of one to one hundred microns, are internal defects generated during the process and that cause large variations in part performance. Pore formation in metal AM is complex and not fully understood, making it difficult to predict for quality control. This award corroborates basic research needs of the porosity issue in metal AM parts. The project tackles original research on the coupled multi-scale and multi-physics process of heating, melting and solidification of numerous microscopic metallic particles in SLM. Research findings will not only establish correlations between the process parameters, material properties and pore attributes, but may also lead to novel techniques for mitigating pore defects, and thus, have a potential to accelerate metal AM adoption in U.S. industry. In addition, this project will contribute toward workforce training for metal AM industrial needs and attract high school students into advanced manufacturing technologies.
The objectives of this research are to distinguish pore formation mechanisms in SLM and to theoretically predict, analyze and experimentally characterize the porosity in SLM parts. In this collaborative research between the University of Louisville (UofL) and the University of Alabama (UA), a hybrid numerical modeling technique will be developed for particle-resolved simulations capable of capturing different pore formation mechanisms in SLM. The model will be validated by SLM experiments of small-scale specimen fabrications, incorporating an infrared thermal imager for process temperature and melt-pool dynamics. The fabricated specimens will be measured using micro-scale x-ray computed-tomography and analyzed to attain statistical data of detailed porosity attributes for comparison with the results from numerical modeling. The research efforts will be extended to study the relationship between process parameters and morphology and distribution of porosity in SLM, and to estimate process windows that minimize pore defects. If successful, this study will distill knowledge of a convoluted multi-physics phenomenon and will offer significant insight detailing the key to particular mechanisms of different pore formations. The research results will be included in the training materials for the Additive Manufacturing Competency Center on the University of Louisville campus, providing practitioners of the SLM technology with better understanding of the relationship between processing parameters, porosity formation, and mechanical properties of critical AM-fabricated components.
