铜棒材连续挤压周向扩展成形工艺分层缺陷与控制理论研究

High-precision copper bar is an important component in the field of high voltage electricity, electron, information, high speed railway and so on. Applying continuous extrusion technique to produce copper bar has a great advantages，such as high efficiency, low cost, excellent microstructure and property. However, there is a big difference between bars and traditional continuous extrusion in aspects of flow regularity and extending mechanism. The direction of the continuous extrusion bar is circumference, which leads to some problems such as metal replacement and stratified flow. At present, the stratified flow mechanism is still unclear. There is a lack of reliable theoretical guidance on how to determine the deformation process conditions, control metal replacement and stratified flow. Continuous extrusion circumferential expansion deformation velocity gradient and stratified flow model are built in this project by analyzing the relationship between contact stress and seaming, replacement, velocity gradient. The limiting condition and control method for the stratified flow are confirmed. The impact of process parameters on deformation, organization and property is researched. The interaction mechanism of seaming, replacement and stratified flow in metal is learned. The evolution characteristic for microstucture in forming process is revelatory. The problems of optimum structure design for wheel groove and deformation flow channel, control for seaming and stratified flow will be resolved. Research results will provide theoretical basis and practicable technique for bar continuous extrusion circumferential expansion deformation technology and engineering application.

高精度铜棒材是高压电力、电子、信息、高速铁路等领域的重要构件，将连续挤压技术应用于铜棒材的加工具有效率高、成本低、产品组织性能优良的优点。然而，具有大面积扩展比的棒材连续挤压周向扩展成形在流动规律、扩展机理方面与传统连续挤压有很大差异，存在金属置换、分层等困扰学术界和工程界的问题。目前，国内外对连续挤压周向扩展变形的分层流动机理尚不清楚，对如何确定变形工艺条件、控制金属间的置换、分层还缺少可靠的理论指导。本项目通过分析接触应力与焊合、置换及速度梯度的关系，构建连续挤压周向扩展变形的分层流动模型，确定产生分层流动的极限条件及控制方法，研究工艺参数对变形、组织、性能的影响，掌握金属间焊合、置换与分层流动的交互作用机理，揭示成形过程的微观组织演变特征，解决轮槽驱动与变形流道的结构优化设计、焊合与分层流动的控制问题。研究结果将为棒材连续挤压周向扩展成形工艺和工程应用提供理论基础和可行的技术方法。

高精度铜棒材是高压电力、电子、信息、高速铁路等领域的重要构件，将连续挤压技术应用于铜棒材的加工具有效率高、成本低、产品组织性能优良的优点。具有大面积扩展比的棒材连续挤压周向扩展成形在流动规律、扩展机理方面与传统连续挤压有很大差异。本项目针对成形过程存在金属置换、分层等困扰学术界和工程界的问题，提出了表达连续挤压周向扩展成形变形程度的面积扩展比概念，应用解析计算、数值模拟和实验研究相结合的方法，建立了连续挤压周向扩展变形力学模型，研究了工艺参数、模具结构对力能的影响规律，确定了连续挤压扩展成形的极限条件；利用成形过程的微观组织演变规律，揭示了变形金属的焊合、置换、分层流动的微观机理；研究了轮槽变形区内铜材的焊合与置换规律，分析了变形参数与工模具结构的关系，发现了铜材连续挤压周向扩展成形过程存在的紊流和死区加剧了流动速度梯度而产生剪切带是产生分层缺陷的根本原因，提出了利用流道优化设计控制变形流动解决分层缺陷的方法，设计出了圆弧形模腔、圆拱形挡料块、分体式刮刀等工装模具结构。本项目研究成果为铜棒材连续挤压周向扩展成形工艺和工程应用提供了理论基础和可行的技术支持。