Laser Finishing of the Multi-Scale Surface Structure of Additive Manufactured Parts

这项研究的目的是通过应用激光重熔来改善添加制造的金属零件的表面光洁度和机械性能(如疲劳寿命)。2015年和2016年发布的几份技术路线图确定了研究改善添加制造零件的表面光洁度并表征该工艺对零件性能的影响的迫切需要。本提案关注的激光重熔工艺为磨平和改进附加制造部件提供了重要的、但尚未开发的机会，它可以集成到现有的基于激光的附加制造设备中，从而创建一种改善已建表面光洁度的工艺。在这个集成项目中，将研究基于主要粉末的激光附加制造工艺和二次激光重熔工艺(充分结合部分熔化的粉末颗粒，减少气孔，并使表面光滑)。拟议研究的协作结构将初级制造过程中的专业知识(德国不来梅大学)和激光精加工过程中的专业知识(美国威斯康星大学麦迪逊分校)结合在一起。对表面形貌和性能结果的新理解将通过减少制造限制来扩展添加制造的潜力。这项工作的科学贡献可以概括为三个部分：(1)提供对粉末床激光添加制造所产生的多尺度表面形貌的基本理解和描述，以及这与工艺参数和原料的关系；(2)了解这些表面激光重熔背后的物理现象以进行平滑并创建适当的模型，以及(3)了解与完工零件相比，这种平滑处理对表面性能的影响(例如，疲劳寿命)。拟议的研究将通过给予设计者新的自由度，以合理的成本制造独特的、特定于客户的高质量零件，从而有助于走向大规模定制。该项目通过专注于基于激光的工艺来实现这一点，这种工艺可以在同一机器中制造部件并完成它，从而为定制制造高性能产品打开了机会。创建的基本模型将为在聚合物部件的添加制造、定向粉末方法和多材料工艺中追求类似的改进奠定基础。这些模型还可以反馈到上游，以改进添加剂制造设计软件，以便设计工程师对最终结果有更多的了解和控制。将该项目所学知识融入本科和研究生课程，培训未来的劳动力，增加来自代表性不足群体的学生的参与，以及与公众接触，将产生进一步的社会影响。

The goal of this research is to improve surface finish and mechanical properties (e.g. fatigue life) of additively manufactured metallic parts through the application of laser remelting. The crucial need for research on improving the surface finish of additively manufactured parts and characterizing the impact of the process on part performance has been identified by several technology roadmaps published in 2015 and 2016. The laser remelting process on which this proposal is focused presents significant, yet unexplored opportunities for smoothing and functionally improving additively manufactured parts, and it can be integrated into existing laser-based additive manufacturing equipment creating a process that improves the as-built surface finish.Both the primary powder-based laser additive manufacturing process and the secondary laser remelting process (to fully incorporate partially melted powder particles, reduce porosity, and smooth the surface) will be studied in this integrated project. The collaborative structure of the proposed research brings together expertise in the primary build process (University of Bremen, Germany) and expertise in the laser finishing process (University of Wisconsin-Madison, USA). The new understanding of surface topography and property outcomes will expand the potential of additive manufacturing by reducing the manufacturing limitations.The scientific contribution of this work can be summarized into three parts: (1) providing fundamental understanding and description of the multi-scale surface topography created by powder-bed laser additive manufacturing and how this relates to the process parameters and feedstock, (2) understanding the physical phenomena behind laser remelting of these surfaces for smoothing and creating appropriate models, and (3) understanding the impact that this smoothing has on the performance of the surface as compared to the as-built part (e.g. fatigue life).The proposed research will contribute to the movement toward mass customization by giving designers a new level of freedom to create unique, customer specific, high quality parts at a reasonable cost. This project achieves this by focusing on laser-based processes that can build a part and finish it in the same machine, opening up opportunities for customized manufacturing of high performance products. The fundamental models created will form a foundation for pursuing similar improvements in the additive manufacturing of polymeric parts, directed powder methods, and multi-material processes. These models can also be fed back upstream to improve additive manufacturing design software such that design engineers will have more awareness of and control over the final outcomes. Further societal impact will result from, integrating the knowledge gained in this project into undergraduate and graduate courses, training the future workforce, increasing the participation of students from underrepresented groups, and outreach to the public.