Study of size effect in micro-extrusion process of pure copper
Study of size effect in micro-extrusion process of pure copper
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DOI：
10.1016/j.matdes.2011.03.045
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发表时间：
2011-08-01
影响因子：
8.4
通讯作者：
Yang, B.
中科院分区：
文献类型：
--
作者：
Chan, W. L.;Fu, M. W.;Yang, B.
材料变形行为的尺寸效应由晶粒度、零件特征尺寸、成形材料尺寸和界面条件表征。这些因素与材料的流动行为密切相关，进而影响微成形零件的几何精度。本研究开发了一套用于实现微前向、后向、前向杆-后向罐和双杯挤压的通用工装，并对不同晶粒度的纯铜进行了微挤压。从变形载荷、界面摩擦行为和组织演变等方面对尺寸效应现象进行了分析。结果表明，在微挤压过程中，界面摩擦力较大，变形载荷的晶粒度效应对刀具-工件界面摩擦力很敏感。在粗晶情况下，挤压件的微观组织表现为非均匀变形，大量滑移带穿过晶界，实现应变的连续。此外，在常规材料模型的基础上，利用微压缩得到的流动应力曲线对微挤压过程进行了有限元模拟。研究发现，由于尺寸效应，传统的材料模型不适用于微挤压过程中材料变形行为的模拟和界面摩擦的评价。因此，本研究提供了对微挤压过程中尺寸效应的深入了解，这对于进一步制定设计规则以促进微部件的开发至关重要。(C)2011爱思唯尔有限公司。保留所有权利。
The size effect on material deformation behaviors are characterized by grain size, part feature size, forming material size and interfacial condition. These factors have a close relationship with material flow behavior, which in turn affects the geometry accuracy of micro-formed parts. In this study, a general-purpose tooling set for realization of micro-forward, backward, combined forward rod-backward can and double cup extrusions is developed and the micro-extrusions of pure copper with different grain sizes are conducted. The size effect phenomena are analyzed based on the deformation load, interfacial friction behavior and microstructure evolution. It is found that the interfacial friction is high in micro-extrusion processes and the grain size effect on deformation load is sensitive to the friction force at the tooling-workpiece interface. The microstructures of the extruded parts show the occurrence of inhomogenous deformation and a large number of slip bands passing through the grain boundaries to accomplish the strain continuity in the cases with coarse grains. In addition, the flow stress curves obtained from micro-compression are used to model the micro-extrusion processes using finite element (FE) simulation based on the conventional material model. It is found that the conventional material model is not applicable in simulation of the material deformation behavior and evaluation of the interfacial friction in micro-extrusion processes due to the size effect. This research therefore provides an in-depth understanding of size effect in micro-extrusion processes, which is critical to further formulate design rules to facilitate the development of micro-parts. (C) 2011 Elsevier Ltd. All rights reserved.