Material microstructure and surface considerations in microforming of sheet materials

在电子、计算机、医疗器械和汽车制造等许多不同的工业部门，微型零部件的制造变得更加重要和必要。传统上，这些精密机械零件是通过机械加工制造的。净成形或近净成形工艺，如板材成形工艺，由于生产率高、成本高，往往更适合小型化。这项研究涉及微弯、微拉弯和深拉深、微剪切等微成形新工艺的开发，以及它们在燃料电池堆金属双极板复杂微特征创新制造中的应用。通过在较大零件内形成微零件和微特征，将在微观尺度上对大变形的力学有一个更广泛和基本的理解。 新型微型单轴、平面应变、双向拉伸和弯曲试验将被开发和利用来分析实际微成形过程中存在的不同变形模式，并评估加工硬化、各向异性、塑性不稳定性、成形极限和候选板材损伤发展中的尺寸效应。作为实验工作的补充，将开发基于微观结构和有限元(FE)的先进微成形模型，以考虑微观结构和试件尺寸的影响，例如利用最新的应变梯度塑性理论以及刀盘接触和摩擦。 从上述实验和数值研究中获得的知识将应用于金属双极板的形成，金属双极板是汽车燃料电池堆的关键部件，双极板中的微几何特征对其在燃料电池中的性能有很大影响。为此，将利用最近开发的微型多机架轧机来探索一种新的板形轧制工艺。

The manufacturing of micro-parts has become more important and necessary in many different industrial sectors such as electronics, computers, medical devices and automotive manufacturing. Traditionally these precision mechanical parts are fabricated by machining. The net shape or near net shape processes, such as sheet metal forming processes, are often better suited for miniaturization because of high productivity and cost. The proposed research deals with development of novel micro-forming processes of microbending, micro-draw-bending and deep drawing, micro-shearing and their combined application towards innovative manufacturing of complex micro-features within metallic bipolar plates used in fuel cell stacks. A broader and fundamental understanding of the mechanics of large deformation at the micro-scale will be gained in forming of micro-parts and micro-features within larger parts. Novel miniature uniaxial, plane strain, biaxial tensile and bend tests will be developed and utilized to analyze different deformation modes present in real micro-forming processes and to assess the size effects in work hardening, anisotropy, plastic instability, forming limits, and damage development of candidate sheet materials. The experimental work will be complemented by the development of microstructure and finite element (FE) based advanced micro-forming models to account for microstructural and specimen size scale effects such as by utilizing the recent strain gradient plasticity theory as well as tool-sheet contact and friction. The knowledge gained from the above experimental and numerical investigations will be applied towards forming of a metallic bipolar plate, a critical component of automotive fuel cell stack where micro-geometric features in the bipolar plate strongly influence its performance within the fuel cell. For this purpose, a novel process of shape rolling will be explored using a recently developed miniature multi-stand rolling mill.