【作者】 段先云；

【导师】 阮锋；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 近年来，随着电子产品的微型化，介观尺度的微型、微细零件在电子工业和精密机械两大行业中的应用越来越广泛，其市场需求量逐年快速增长，介观尺度的成形技术也逐渐成为各国制造业大力发展的对象。但是，介观尺度成形面临的许多难题却严重阻碍着它的发展：在介观尺度成形中，流动应力的尺度效应现象在多种试验中均有观察到，但尚无有力的参数来刻画该尺度效应，现有理论模型的适用性和参数的正确性都不尽完备；摩擦尺度效应中，现有模型未能从微观本质上揭示其机理，模型的建立和计算也存在模糊区域；介观薄板成形尤其是拉深成形国内开展研究较少。因此，解决这些问题是提高介观尺度下成形的工艺水平和促进微细成形产业发展的当务之急。本文对国内外介观尺度成形的研究成果，尤其是关于流动应力、模具与工件间摩擦和薄板成形这几方面的内容进行了详细的研究，根据存在的问题制定了理论研究的方向，搭建了若个实验平台并开展了有针对性的试验研究。根据试验中的数据和微观形貌的特点，分别推导、建立了基于SAP的流动应力尺度效应模型和基于润滑区面积比的摩擦系数尺度效应理论模型。将具体的试验数据与模型计算数据进行了对比，验证了文中提出这两个尺度效应模型是正确、可行的。本课题设计了介观尺度的拉深模具并制备了介观圆筒拉深件，通过对拉深件质量的分析，验证了前文的理论和积累了一定的工艺参考。本文具体进行了以下几个方面的研究工作：1.分别对铜单个晶粒、铜单晶、铜多晶的拉伸应力-应变曲线进行了分析和拉伸试验；对压缩面力下的铜双晶不同晶界方向的晶粒、晶界变形进行了模拟和试验，结果表明：晶界处存在明显的应力集中和应力梯度现象；垂直晶界面存在周期性扭曲变形；垂直晶界双晶体中孔洞和裂纹分布位置更集中于滑移线上或临近滑移线某一侧。这些研究为后续的章节提供了基础数据。2.对介观尺度下不同厚度、不同宽度、不同晶粒尺寸的试样进行批量拉伸试验，结果表明：随着尺度的减小，流动应力呈现减小趋势，表现出了明显的尺度效应；分别讨论了厚度、宽度、晶粒尺寸对尺度效应的影响，构建了参数-表层面积比SAP来对尺度效应进行刻画；对产生流动应力尺度效应的机理进行了分析、揭示，推导了介观成形的流动应力-应变的理论模型即SAP相关的过渡式表面层模型，对模型的参数k取值进行了讨论，得出k值的取值范围；结合本文的试验数据，对该模型进行了计算验证。3.基于拉胀测试原理搭建了介观尺度下摩擦系数测试平台，对不同厚度、宽度、晶粒大小的试样分别进行润滑条件下和非润滑条件下摩擦系数的测定，结果表明：随着试样尺度的减小，其摩擦系数呈现增大趋势，表现出了明显的尺度效应。对已有的摩擦尺度效应的理论模型进行了研究、分析，指出了该模型和算法中“开口润滑包”的宽度并非是固定的，该区域对摩擦尺度效应的产生不起关键的作用。4.设计搭建了适合制备介观尺度试样摩擦面形貌的试验台，制备了摩擦面的形貌，对形貌进行了显微形貌观察。对摩擦面的润滑区进行了着重的观察和分析，引入了计算机图形学中图像识别原理，计算了润滑区的面积比例。根据各区域的面积变化对摩擦尺度效应产生的机理进行分析和揭示。结果表明：随着试样尺度的减小，其摩擦面上的润滑区面积比例逐渐减小造成了摩擦系数的增大。推导、建立了基于润滑区面积比的摩擦尺度效应理论模型，对理论模型的主要参数进行了讨论，并用实例进行验证计算。5.设计了适合本实验目的的介观尺度拉深模具，进行了拉深试验，对试验得到的微形圆筒进行高度、破裂方式和壁厚的观察与测试。根据前文的研究结论，对试验现象进行了分析，得到了拉深件的高度、壁厚、失效破裂的影响因素和方式。尽管本文就介观尺度成形的流动应力和摩擦以及拉深模具几方面行了大量的试验研究和理论分析，取得了一定成果，但仍存在一些不足：如摩擦模型中k的取值，若通过模拟或观察到这些过渡层不同的应力状态，将使得k值更加准确；介观拉深模具如果能涉及更多的环节将使研究更完备，这些在后续研究中应积极展开。更多还原

【Abstract】 As the size decreasing of electronic products recently years, the meso scale parts arewidely used and increasing required in electronic and precise machinery industry. Therefore,the producing technology of meso scale parts turned into the vigorously developingtechnology in manufacturing industry of many countries. But problems in meso scale formingstopped the development of this technology. Firstly, the size effect was observed in manyexperiments but the power of parameter on expressing size effect was not enough and themodel applying, variable assignment, calculating method need to be improved. Secondly, thereason of microscopic level for friction size effect still has’t been found and there is manyvague defination of the model setting up and calculating. Thirdly, the research on meso sheetforming, especially deep drawing still has big blank. In order to improve the meso formingcapacity and micro parts industry, it is urgent to solve these problems.In this paper, manymeso forming reports, especially on stress-strain, friction and meso forming were detaillystudied and many experimens were carried out. The theory research and experiment platformwere set up based on these problems. The stress-strain model based on SAP and frictionmodel based on lubricated area were set up according to the micro morphology of specimens.Compared the model data with experiment, the accuracy of stress-strain and friction model ofsize effect were proved. Finally, the mould of meso scale was developed and micro tube wasdrawed, the quality of micro tube was analysed.Detaily, the following research was carried out in this paper:1. By the analysis and experiment,the stress-strain curver of copper single crystal,coppersingle crystal rod, polycrystalline copper were made out. The simulation and experimentabout the defomation of grain and grain boundary of polycrystalline copper in different grainboundary orientation were carried out. It shows there is obvious stress and stress gradientconcentrate on the grain boundary and periodical distorting exists in vertical grain boundary.The position of holes and cracks in polycrystalline copper with vertical grain boundaryconcentrate on or beside the slipping line. These conclusions will be the base data for the nextchapters.2. The stretching experiment of specimens with different thickness, width, crystal sizewas carried out. It shows that the stress decreased while specimen size decreased and thestress-strain size effect is obviously. The relationship between thickness, width, crystal sizeand size effect was discussed, the parameter SAP was set up. The reason and SAP relatedmodel for size effect of stress-strain were discussed and set up and the scope of k in this model was made out. Finally, according to the experimental data, the proving of this modelwas carried out.3. Based on bend-stretching test theory, the friction test bed was developed and themorphology in different thickness, width, crystal size, lubricating condition were tested. Itshows that the coefficient of friction increased while specimen size decreased and the frictionsize effect is obviously. According to the research and analysis about the present model aboutfriction size effect, a serious defect in this model was found.4. The meso scale friction area morphology preparing test bed was developed and thefriction area morphology was made. The friction area morphology, especially the lubricatedarea was observed. With the image recognization technology, the lubricated area proportionwas calculated and the reason of friction size effect was discussed. It shows that the lubricatedarea proportion decreased while specimen size decreased, which lead to the increasing offriction coefficient. Finally, the model was set up and main parameters in this model werediscussed. After calculating and comparing with a sample, the accuracy of the model wasproved.5. The meso scale deep drawing mould satisfied with the experiment’s aim of this paperwas developed. Afte deep drawing experiment, the height, broke mode and wall thickness ofthe tube were observed. According the conclusions of previous chapters, the factorsinfluncing the height, broke mode and wall thickness of the tube was discussed.Also lots of experiment and research about stess-strain, friction and deep drawing mouldin meso scale foming were carried out and some progresses were obtained, but still there areseveral aspects need to be improved. Firsly, if the stress of transitional layer could besimulated or observed, the accuracy of parameter k will be improved. Secondly, if the mesodeep drawing mould could involed several more processes, more conclusions will be reached.All these aspects should be considered during the next study.更多还原