微尺度下变厚度柔性轧制尺寸效应对材料变形行为的影响

Due to the exciting advancement in electronic industry and precision machinery, micro manufacturing has become one promising industrial technology, which can be divided into three subcategories - micro massive forming, micro sheet forming and micro profile forming. Today the former two methods have been investigated to identify the special mechanism at micro scale, but micro profile forming is still an unknown area in terms of research. In this project, conventional profile rolling and flexible rolling are introduced into micro domain, which compatibly takes the advantages of conventional rolling and micro manufacturing technologies. From point of view of the significant differences between macro and micro rolling processes in materials, process, tools and equipment, the research is conducted in terms of the basic theories accounting for the problems related to the micro-rolling mechanism, material deformed behaviour, and micro tribology. The mechanism is set up to predict and control the global and local dimensional accuracy of micro components, meanwhile, the generation and evolution of defects are analysed as well. A precise crystal plastic finite element method (FEM) is developed to effectively reflect the characteristics of material deformability in micro profile rolling. A novel technology of micro rolling at elevated temperature is proposed for the sake of homogenizing grained anisotropy with assistance of laser heating. The main purpose of this research is to specifically figure out size effect on the entire procedure of micro profile rolling, and break through its limits on micro rolling, which theoretically underlies the miniaturization of profile rolling processes.

由于电子工业及精密机械的飞速发展，微成形技术已成为工业领域的主流发展方向之一。目前，微成形工艺可分为体积成形、箔板成形及型材成形。前两种成形工艺已被广泛研究，但对型材微成形的探索还不深入。本项目将经典的型材轧制和变厚度柔性轧制工艺引入微观制造领域，以实现宏观型材轧制原有优势与微形成技术的有机融合，针对由尺寸效应引起的微成形中材料、过程、工具及系统设备方面与宏观轧制之间的显著差异，围绕适用于微型材轧制的轧制力学机制，材料变形行为，表面摩擦与润滑的基础理论展开研究，阐明轧件整体及局部几何精度预测与控制和轧件缺陷生成与演变机制，建立有效预测尺寸效应对材料变形行为影响的精确晶体塑性有限元模型，提出通过激光加热减弱材料微观变形不均匀性的升温轧制新技术。本研究旨在掌握尺寸效应对微型材轧制工艺各个环节的影响规律，并全面突破其对微型材轧制造成的限制，为各类型的型材轧制技术向微观尺度的延伸提供理论支持。

由于电子工业及精密机械的飞速发展，微成形技术已成为工业领域的主流发展方向之一。本项目将经典的型材轧制和变厚度柔性轧制工艺引入微观制造领域，以实现宏观型材轧制原有优势与微形成技术的有机融合，针对由尺寸效应引起的微成形中材料、加工、工具及系统设备方面与宏观轧制之间的显著差异，围绕适用于微型材轧制的轧制力学机制，材料变形行为的基础理论展开研究。.通过本课题建立了常温微轧制条件下金属（纯铝及纯铜）变形的数学模型。同时确定了常温微轧过程中轧件断裂的晶体塑性有限元模型，并与实验结果相比较，验证模型的正确性。通过实验室纯铜柔性变厚度微轧制实验，研究了晶粒尺寸、试样尺寸及压下率对轧件边部不均匀变形的影响以及晶粒尺寸、试样尺寸及压下率对显微组织的影响；通过微轧制试验，研究了纯铜、纯铝尺寸效应对金属材料变形行为的影响规律。明确常温微轧过程中，尺寸效应对金属材料变形行为的影响规律。研究微轧制工艺参数及材料内部结构与尺寸效应之间的关系，明确了冷微轧过程中轧件变形的机理。.研究结果表明随着晶粒尺寸的增加或厚度的减小，纯铜的延伸率和抗拉强度逐渐降低；晶粒尺寸和厚度对纯铜的断裂机制有重要影响，随着晶粒尺寸的增加或厚度的减小，试样的断裂机制由混合断裂方式转变为滑移断裂。随着晶粒尺寸的增大或厚度的减小，轧件边部不均匀变形增加，边部凸起越来越明显，宽展不均匀增加,材料塑性越不稳定；轧制力逐渐减小，轧制力不稳定性增加；随着晶粒尺寸的增大，晶界处塞积的位错密度逐渐降低，位错偏聚现象不明显；随着应变量的增大，在纯铜的晶粒内部出现了亚晶组织；随着试样厚度的增大，材料发生塑性变形时，位错密度变大，位错缠结越来越严重，所需的变形力更大。.本研究旨在掌握尺寸效应对微型材轧制工艺各个环节的影响规律，并全面突破其对微型材轧制造成的限制，为各类型的型材轧制技术向微观尺度的延伸提供理论支撑。