Thermomechanical and Powder Sintering Aspects in Electron Beam Additive Manufacturing - Applications to Overhang Support Designs

本研究的目的是更新粉末床电子束添加剂制造(EBAM)中部分悬臂几何形状的支撑结构设计。假设烧结粉的导热性差是零件缺陷的根本原因，如与零件悬垂(或类似)几何形状有关的翘曲。因此，支撑结构所需的功能并不是从承重的角度出发的；相反，在功能支撑设计中，应该研究EBAM过程中导致残余应力和变形的复杂的热和机械现象。具体地说，这项研究将表征烧结粉末的孔隙率及其对热性能的影响，开发包含孔隙率相关热性能的有限元热机械模拟来预测EBAM中的温度和应力，评估悬臂几何形状对EBAM中部件热机械行为的影响并与翘曲严重程度相关，并研究不同的支撑模式以评估所设计的支撑的有效性。本研究的结果将通过改进和有效的支撑结构来提高EBAM技术的性能和效率。因此，该项目将直接惠及金属添加剂制造(AM)技术的用户，增强该国工业的全球竞争力。与ebam的主要用户之一马歇尔太空飞行中心合作，研究小组可能会进一步应用这些发现来解决AM技术中存在的实用问题。此外，本研究对工艺的新认识将有助于对其他粉基AM工艺的研究，如选择性激光烧结。此外，研究团队将与国家制造科学中心合作，及时向AM行业广泛传播项目成果。这项研究的进一步社会影响包括恢复高中生对工程和技术的兴趣，特别是来自代表不足的群体的兴趣。

The goal of this research is to renovate the support structure designs for part overhang geometries in powder-bed Electron Beam Additive Manufacturing (EBAM). It is hypothesized that the poor thermal conductivity of sintered powders is the root cause of part defects such as warping associated with part overhang (or similar) geometries. Hence, the required function of support structures is not from the weight-carrying standpoint; rather, the complex thermal and mechanical phenomena of the EBAM process, which lead to residual stresses and distortions, should be studied for functional support designs. Specifically, this research will characterize sintered powder porosity and its effects on thermal properties, develop finite element thermomechanical simulations incorporating porosity-dependent thermal properties for temperature and stress predictions in EBAM, evaluate overhang geometry effects on the part thermomechanical behaviors in EBAM and correlate with warping severity, and investigate different support patterns to evaluate the effectiveness of a designed support.The outcome of this research will enhance the performance and efficient usage of the EBAM technology through improved and effective support structures. Thus, the project will directly benefit the users of metal Additive Manufacturing (AM) technologies, strengthening the global competitiveness of the nation's industry. Collaborating with one of primary EBAM users, Marshall Space Flight Center, the research team may further apply findings to tackle pragmatic problems that exist in AM technologies. Moreover, new process understanding from this research will benefit studies on other powder-based AM processes such as selective laser sintering. In addition, working with the National Center for Manufacturing Sciences, the research team will disseminate the project results timely and widely to the AM industry. Further societal impacts of this research include reviving high school students' interest in engineering and technology, particularly, from underrepresented groups.