CAREER: Viscosity-tunable Photopolymers with Metal Powder Mixtures for Cost-effective, High-speed and Large-area Metal Additive Manufacturing

现代金属增材制造（AM）主要依赖于逐点打印方案，其中制造时间随着部件的尺寸（特别是部件的横截面积）而显著增加。这样的加工限制阻止了金属增材制造成为运输、建筑和许多其他应用中大规模生产零件的可行替代品。为了克服这一挑战，该学院早期职业发展（CAREER）奖支持未经测试的金属AM工艺的基础研究，即首先通过使用数字光投影固化光聚合物和金属粉末的混合物来一次性打印整个层，然后进行脱脂和烧结，从而实现高速生产。新工艺依赖于一种独特的感光聚合物，其性能可调，可平衡印刷层固化深度和感光聚合物悬浮液中金属粉末的均匀混合。如果成功的话，这种金属增材制造系统将是同类产品中的第一个，将有利于运输、机械和建筑等重工业，并为美国工业在全球市场上提供竞争优势。项目团队还将组织为工程师量身定制的网络研讨会和研讨会，以了解如何将新的金属AM系统纳入实践，并向K-12学生介绍AM的基本原理，提供实践活动（即，本研究的总体目标是了解金属增材制造系统的工艺机制，该系统利用光聚合物和金属粉末混合物的光聚合，基于光投影而不是扫描，重点关注金属粉末沉积，固化能力和可能的氧化相关缺陷的挑战。该项目将首先研究热固性-热塑性聚合物的组合，以理解和控制光聚合物的粘度。固化性和粉末填充的数值模型，然后将被用来表征固化深度和填充密度作为光聚合物粉末混合物中的粒度分布的函数。热重分析和显微结构分析也将用于研究光聚合物粉末混合物的脱脂和烧结行为。此外，固态烧结模型将被开发，以评估最终的零件质量。研究结果将揭示影响光聚合物-粉末混合物的流变特性以及固化、脱脂和烧结过程中的行为的原理。新的AM方法有可能允许以高速制造完全致密，复杂和大型的金属部件，而不会氧化或变形。获得的新知识预计也将支持其他增材制造工艺的进步，例如陶瓷的粘合剂喷射3D打印，以提高制造速度和零件质量。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Modern metal additive manufacturing (AM) mostly relies on a point-by-point printing scheme, in which the fabrication time increases substantially with the size of a part, in particular, the cross-sectional area of the part. Such a processing constraint prevents metal AM from being a viable alternative for large-scale production of parts in transportation, construction and many other applications. To overcome the challenge, this Faculty Early Career Development (CAREER) award supports fundamental research for an untested metal AM process, whereby a whole layer is first printed at once by curing a mixture of photopolymer and metal powder using digital light projection, followed by debinding and sintering, resulting in high-speed production. The new process hinges on a unique photopolymer with tunable properties, to balance the print-layer curing depth and homogeneous mixing of metal powder in a photopolymer suspension. If successful, this metal AM system, first of its kind, will be beneficial to heavy industries such as transportation, machinery and construction, and provide a competitive edge to U.S. industries in the global market. The project team will also organize webinars and workshops tailored for engineers to learn how the new metal AM system can be incorporated into practices, as well as introduce basic AM principles to K-12 students, offering hands-on activities (i.e., LEGO 3D printing) to inspire their interest in STEM professions.The overall goal of this research is to understand the process mechanism of a metal AM system that utilizes photopolymerization of a photopolymer and metal-powder mixture based on light projection rather than scanning, with emphases on challenges in metal powder sedimentation, curing capacity and possible oxidation-related defects. The project will first investigate the combination of thermoset-thermoplastic polymers to comprehend and control the viscosity of photopolymers. Numerical models of curability and powder packing will then be utilized to characterize the curing depth and the packing density as a function of particle size distributions in a photopolymer-powder mixture. Thermal gravimetric and microstructural analyses will also be employed to study debinding and sintering behaviors of photopolymer-powder mixtures. Moreover, a solid-state sintering model will be developed to evaluate the final part quality. The research findings will reveal principles that influence the rheological properties as well as behaviors during the curing, debinding, and sintering of photopolymer-powder mixtures. The new AM approach has the potential to allow fabrication of fully-dense, complex, and large metal parts at a high speed without oxidation or deformation. The new knowledge obtained is expected to also support advances in other AM processes, such as binder-jet 3D printing of ceramics, to improve the fabrication speed as well as the part 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.