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

现代金属添加剂制造(AM)主要依赖于逐点印刷方案，在该方案中，制造时间随着零件的尺寸，特别是零件的横截面面积而显著增加。这样的加工限制使金属AM无法成为运输、建筑和许多其他应用中大规模生产零件的可行替代方案。为了克服这一挑战，该学院早期职业发展(CALEAR)奖支持未经测试的金属AM工艺的基础研究，该工艺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一次打印整个层，然后进行脱脂和烧结，从而实现高速生产。新工艺依赖于一种具有可调特性的独特光聚合物，以平衡印刷层固化深度和光聚合物悬浮液中金属粉末的均匀混合。如果成功，这种金属AM系统将是第一个此类系统，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。项目团队还将为工程师组织网络研讨会和工作坊，以了解如何将新的金属AM系统应用到实践中，并向K-12学生介绍基本的AM原理，提供动手活动(即乐高3D打印)，以激发他们对STEM专业人员的兴趣。本研究的总体目标是了解金属AM系统的过程机理，该系统利用光投影而不是扫描的光聚合来实现金属AM系统，重点关注金属粉末沉积、固化能力和可能的氧化相关缺陷方面的挑战。该项目将首先研究热固性-热塑性聚合物的组合，以了解和控制光聚合物的粘度。然后将利用固化和粉末堆积的数值模型来表征固化深度和堆积密度作为光致聚合物-粉末混合物中颗粒尺寸分布的函数。热重和微观结构分析也将被用来研究光聚合物-粉末混合物的脱脂和烧结行为。此外，还将开发一个固态烧结模型来评估最终零件的质量。研究结果将揭示影响光致聚合物-粉末混合物固化、脱脂和烧结过程中的流变性和行为的原理。新的AM方法有可能在没有氧化或变形的情况下高速制造完全致密、复杂和大型的金属部件。预计获得的新知识还将支持其他AM工艺的进步，如陶瓷的粘合剂喷射3D打印，以提高制造速度和部件质量。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.