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

本研究的目标是通过应用激光重熔来改善增材制造金属零件的表面光洁度和机械性能（例如疲劳寿命）。2015年和2016年发布的几个技术路线图已经确定了对改善增材制造零件表面光洁度和表征工艺对零件性能影响的研究的迫切需求。该提案所关注的激光重熔工艺为平滑和功能改进增材制造部件提供了重要但尚未开发的机会，并且它可以集成到现有的基于激光的增材制造设备中，从而创建改善完工表面光洁度的工艺。（以充分纳入部分熔化的粉末颗粒，减少孔隙率，并使表面光滑）将在这个综合项目中进行研究。拟议研究的合作结构汇集了主要构建过程（不莱梅大学，德国）和激光加工过程（威斯康星大学麦迪逊分校，美国）的专业知识。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大增材制造的潜力。这项工作的科学贡献可以概括为三个部分：（1）提供对由粉末床激光增材制造产生的多尺度表面形貌的基本理解和描述，以及这如何与工艺参数和原料相关，（2）了解这些表面的激光重熔背后的物理现象，以平滑和创建适当的模型，以及（3）理解与完工部件相比，这种平滑对表面性能的影响（例如疲劳寿命）。拟议的研究将有助于向大规模定制的运动，给设计师一个新的自由度，创造独特的，以合理的成本为客户提供特定的高质量零件。该项目通过专注于基于激光的工艺来实现这一目标，这些工艺可以在同一台机器上构建零件并完成，为高性能产品的定制制造提供了机会。所创建的基本模型将为在聚合物零件的增材制造、定向粉末方法和多材料工艺中进行类似的改进奠定基础。这些模型还可以反馈到上游，以改进增材制造设计软件，使设计工程师能够更好地了解和控制最终结果。进一步的社会影响将来自于将本项目中获得的知识融入本科和研究生课程，培训未来的劳动力，增加代表性不足群体的学生的参与，以及与公众的联系。

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.