GOALI: Understanding the Physical Mechanisms of Distortion and Controlling its Effects in Sintering-based Additive Manufacturing Processes

增材制造（AM）涉及通过添加一层又一层的材料来构建3D对象。纳米/微粒的烧结是许多增材制造工艺的关键步骤之一。这一步骤经常导致增材制造零件的形状变形，阻碍其接近净形状的制造。这项学术与工业联络资助机会（GOALI）奖支持综合实验和理论研究，以充分了解AM中控制形状变形的机制。这样的理解将能够识别关键的增材制造工艺参数，以消除不需要的扭曲，或控制扭曲，以实现4D打印的新方法。该项目的成果有可能降低增材制造零件的成本，对航空、汽车和核工业产生积极影响。这项工作所带来的精密制造将有助于确立美国在工业4.0中的领导地位。由于增材制造在航空航天工业中被用于制造大型部件（例如飞机机翼），该项目的研究成果将成为其制造的关键推动因素。近净形增材制造将消除后处理，从而减少温室气体排放。该项目将与来自弱势学校的K-12学生合作，让他们接触以stem为基础的职业。该项目将通过开发跨学科课程，在先进制造、计算科学和纳米材料等跨学科领域培养多样化的美国劳动力。该项目侧重于确定质量传递机制及其对基于烧结的增材制造过程中形状变形的相对贡献。初步研究表明，在烧结部分变形过程中，一定存在远距离质量输运。研究的实验部分将包括纳米和/或微颗粒的三维结构的制造，操作显微镜观察聚焦离子束（FIB）切割截面在烧结过程中的颗粒团簇的运动，以及烧结后的广泛的非原位观察。紧密耦合的建模工作将涉及中尺度相场模型的发展，以发现非均匀烧结中远距离质量输运的物理机制。此外，将开发一个宏观连续体模型，该模型具有模拟全尺寸零件和预测工业相关配置的形状变形和/或残余应力的能力。将开发一个预测模型来量化诸如粒度、粘合剂含量、约束和温度梯度等参数对零件变形的影响。该研究将建立和实验验证设计准则，以尽量减少AM零件烧结过程中的变形。最后，不均匀烧结将作为一种全新的技术来实现控制变形，即4D打印。该奖项反映了美国国家科学基金会的法定使命，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。

Additive Manufacturing (AM) involves building of 3D objects by adding layer upon layer of material. Sintering of nano/microparticles is one of the critical steps in many AM processes. This step often leads to shape distortion of AM parts, preventing their near-net-shape manufacture. This Grant Opportunities for Academic Liaison with Industry (GOALI) award supports an integrated experimental and theoretical research to fully understand the mechanisms controlling shape distortion in AM. Such understanding will enable identification of critical AM process parameters to either eliminate distortions when undesirable, or to control distortions to enable novel methods of 4D printing. The outcomes of this project have the potential to reduce cost of AM parts, positively impacting aviation, automotive, and nuclear industries. The precision manufacturing enabled by this work will help establish American leadership in Industry 4.0. As AM is adopted in aerospace industry for fabrication of large parts (e.g., aircraft wings), research outcomes from the project will be key enablers for their fabrication. Near-net-shape AM will eliminate post-processing, leading to a reduction in greenhouse gas emissions. The project will involve collaboration with K-12 students from disadvantaged schools to expose them to STEM-based careers. The project will train a diverse US workforce in the interdisciplinary areas of advanced manufacturing, computational sciences, and nanomaterials through the development of interdisciplinary curricula.This project focuses on identifying the mass transport mechanism(s) and their relative contributions to shape distortion in sintering-based AM processes. The preliminary studies have demonstrated that a long-range mass transport must be operational during part distortion in sintering. The experimental portion of the research will consist of fabrication of 3-D structures of nano and/or microparticles, operando microscopy to observe movement of particle clusters in Focused Ion Beam (FIB)-cut sections during sintering, and extensive ex-situ observations post sintering. A closely coupled modeling effort will involve the development of a mesoscale phase-field model to discover the physical mechanisms of long-range mass transport in non-homogeneous sintering. In addition, a macroscale continuum model will be developed that has capabilities to simulate full scale parts and predict shape distortion and/or residual stresses for industrially relevant configurations. A predictive model will be developed to quantify the effect of parameters such as particle size(s), binder content, constraints, and temperature gradients on part distortion. The research will establish and experimentally validate design guidelines to minimize distortion during sintering of AM parts. Lastly, inhomogeneous sintering will be introduced as a completely new technique to achieve controlled distortion, i.e., 4D printing.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.