Bi系高温超导带材中的塑性微成形技术

随着塑性成形技术向着"极端"方向发展,塑性微成形方法的研究成为学术界和工业界中的前沿领域之一,Bi系高温超导带材作为目前唯一的一种已实现工业化生产的超导材料,它的加工过程就是典型的多芯多场塑性微成形过程;文章从实验和计算方面介绍该塑性微成形的特征,涉及超导粉体材料的本构行为、拉拔和轧制的加工过程,并对Bi系高温超导带材中的塑性微成形的研究现状进行评述.     

电磁微成形技术研究进展

随着塑性微成形特征尺寸进一步缩小，材料种类不断扩大，单纯依靠模具施加载荷的方法已经越来越难以制备出满足尺寸精度和使用性能要求的微型三维构件，亟需探索新的塑性微成形新原理、新方法和新工艺。电磁微成形技术是一种利用载流导体在磁场中受到洛伦兹力而变形的高应变速率成形方法，能够有效克服微成形过程中成形性能下降、尺寸精度难以保障等问题，具有拓展塑性微成形应用领域的巨大潜力。首先从电磁成形技术的原理与特点出发，介绍了电磁成形过程中高应变速率效应对材料性能的特殊作用，然后综合分析了微成形过程中尺度效应对材料力学行为和成形性能的影响规律及相关机制，详细评述了电磁微成形技术在金属超薄板冲压以及金属表面微纳结构压印中的优势与不足，最后总结并提出了电磁微成形技术在理论和工艺方面所面临的机遇与挑战。     

外壁带凸台环件轧制成形规律

提出了一种外壁带凸台环件的新成形工艺方法，该方法实现了环件的连续成形，既能完成环件的扩径，还能在环件的外壁上成形高质量的凸台。利用ABAQUS有限元模拟软件，建立了外壁带凸台环件轧制成形有限元模型，并分析了轧制成形过程，探究了轧制过程中几何形状、等效应变、凸台高度、轧制力的演变规律，并通过试验验证了成形的可行性。结果表明：成形过程分为扩径阶段与凸台长大阶段，扩径阶段的形变与环件轧制相似，凸台长大阶段的形变与挤压相似；凸台长大阶段所需的轧制力远远大于扩径阶段，并且与进给量相关；凸台截面积对凸台高度的影响较大，而凸台形状对凸台高度几乎没有影响。     

宏域微成形与铋系超导带材的加工

铋系高温超导带材是目前唯一能够实现工业化生产并已在强电、弱电领域应用的超导材料,主要加工手段是多道次的拉拔和轧制塑性成形,是一种典型的"宏观作用,微观成形"多芯多场塑性成形过程,即宏域微成形.本文提出了宏域微成形原理和理论框架,包括:宏域微成形的特征、成形尺度的界定、直接微成形与宏域微成形的相互关系、尺度效应、材料组织效应、摩擦效应和温度效应等.采用基本实验测试、计算建模、理论分析和工艺实验来开展宏域微成形的基础科学研究,并提出了可应用于实际生产的节能高效的工艺方案,以指导铋系超导带材的加工成形.     

双列圆锥滚子轴承内圈闭式轧制成形机理研究

由于双列圆锥滚子轴承内圈截面的复杂性导致环件在轧制成形过程中难以控制,经常出现轧制缺陷。针对圆锥滚子轴承内圈复杂截面这一特点,运用Deform-3D模拟软件建立了内圈环件轧制三维有限元模型,对环件初轧、主轧以及精整成形进行了分析,揭示了内圈在轧制成形过程中的应力应变变化规律,为生产中产品缺陷的分析以及毛坯结构设计提供理论依据。     

微成形技术在塑性加工中的应用研究

快速增长的MEMS市场为微系统工程提供了广阔的发展和应用空间,对微金属零件的需求也日益增多,结合微成形技术和传统塑性加工方法,可以提高微零件精度和生产率,实现批量生产,但是也对微成形技术和塑性加工提出了新要求.尺度效应的影响使得微塑性成形成为一个全新的领域,传统的塑性加工理论无法继续使用.本文在介绍微成形概念的基础上、对其在塑性加工中的应用、进展以及研究方法进行了分析总结,并阐述了相关的关键技术.     

大型环件径轴向轧制成形工艺制定研究

大型环件径轴向轧制成形工艺复杂,合理的成形工艺可以提高大型环件径轴向轧制成形的产品质量。本文对大型环件径轴向轧制成形工艺制定进行研究,给出了成形工艺制定流程和方法,其中包括轧制成形环件冷态和热态尺寸的确定、环件毛坯冷态和热态尺寸的确定、环件径轴向轧制成形工艺的确定。本文的研究成果在大型环件径轴向轧制技术的实际生产中获得了成功应用。     

TBM盘形滚刀刀圈轧制成形数值模拟和试验研究

为了分析盘形滚刀在轧制过程中的变形特点,以17英寸TBM盘形滚刀刀圈为研究对象,依据环件轧制工艺理论,对轧制模具主辊、芯辊和锥辊的运动参数进行了设计;基于DEFORM-3D建立了滚刀刀圈轧制成形的有限元分析模型,模拟分析了刀圈在轧制成形过程中温度场、等效应变场、几何形状和轧制力的变化规律;基于设计的工艺参数和模拟结果,开展了刀圈轧制成形试验研究,验证了研究刀圈轧制成形工艺采用数值模拟方法的可靠性。结果表明:刀圈轧制结束时,其整体温度分布由刀圈芯部到外表面梯度递增,最高温度为1200℃,最低温度为1040℃,等效应变最大值为14.4,最小值为0.178。刀圈稳定轧制阶段,径向轧制力在5×10~5N左右波动,轴向轧制力在1.5×10~5N左右波动。     

热轧参数对铸态AZ91镁合金组织与性能的影响

通过不同道次压下量和轧制道次的热轧成形实验,研究了不同变形条件对AZ91铸态镁合金组织和析出相演变的影响,以及合金在热轧变形中的开裂行为。实验结果表明:对AZ91镁合金多道次、小压下量轧制是实现其累积大塑性变形的途径之一。在实验轧制条件下,AZ91镁合金塑性变形仍以孪生变形为主,动态再结晶并未明显进行,仅在晶界及析出相附近发生部分不连续动态再结晶。轧制变形过程中,β-Mg_(17)Al_(12)相呈短条棒状或颗粒状分布于晶界附近,且尺寸更为细小。在晶界附近分布的脆性析出相成为微裂纹萌生的源头,随着累积变形量的增加,部分Mg_(17)Al_(12)相被轧碎形成二次裂纹,裂纹进一步沿晶界扩展,造成明显开裂现象。     

偏心轴楔横轧轧制区轧制力影响因素分析

两轧辊在轧制区轧制力不对称性是偏心轴类零件楔横轧轧制成形的一个显著特征。本文利用有限元手段对偏心轴类零件楔横轧成形中轧制区轧制力的特点进行了较为系统全面的分析,阐明了工艺因素对轧制区轧制力的影响机理,综合分析了各工艺参数对轧制区轧制力的影响程度。研究结果对偏心轴类零件楔横轧成形的模具设计、轧制工艺参数的选取、旋转条件、偏心极限等问题的研究都具有十分重要的意义。     

Classification of size effects and similarity evaluating method in micro forming

Micro size effects are the particular phenomena in metal micro forming. Therefore, it is the point of the further research on micro-forming processing and theories. The experiential formulas and deformation theories of the conventional forming can be adopted to the micro-forming processing, on condition that the micro size effects are classified as micro size effects on material constitution and micro size effects on processing condition. On the basis of theory of similarity, a new concept, similarity precision is defined as similarity mete-wand of micro size effects. The similarity precision of two kinds of micro size effects above is demonstrated by adopting data of references, and application from conventional forming to micro forming is illustrated in terms of these methods of classifying and evaluating micro size effects.     

微器件弯曲成形研究

微器件的市场需求急剧增加,微弯曲成形在微型产品的制造中起着至关重要的作用。尺度效应的影响使得微弯曲成形成为一个全新的领域。阐述了国内外近十多年来微弯曲成形方面尺度效应、晶粒尺寸以及摩擦等基础理论的发展,总结了微弯曲的成形方法、工模材料、成形系统、数值模拟以及成形精度方面的研究,并提出了利用陶瓷纤维制作微弯曲模,压电陶瓷作为驱动器,通过激光辅助加热的微弯曲成形系统。     

金属薄板微成形技术的研究进展

文章阐述了金属薄板微成形的基本概念和金属微成形中的尺寸效应,综述了微拉深、增量成形、微弯曲和冲裁等薄板微成形技术的研究现状,并简单介绍了作者的研究成果,展望了薄板微成形技术的发展方向和趋势。     

Through-process macro–micro finite element modeling of local loading forming of large-scale complex titanium alloy component for microstructure prediction

The intrinsic multi-heat unequal deformation behavior of the local loading forming requires a through-process macro–micro model to characterize the microstructure evolution during the forming process. In the present work, the phenomena and mechanisms of microstructural developments in local loading forming of titanium alloys are summarized. Mechanism-based unified material models, which characterize the through process microstructure evolution, are developed for integrated prediction of constitutive behavior and microstructure. A through-process macro–micro finite element model is established for the local loading forming of large scale complex titanium alloy component. The model can predict the microstructure evolution as well as macroscopic deformation in multi-step local loading forming process. Model predictions are in good agreement with experimental results. The microstructure evolution in local loading forming is investigated by the established finite element model. It is found that the thermo-mechanical processing route greatly affects the volume fraction of primary alpha but has little influence on the grain size in local loading forming     

精密微塑性成形技术的现状和发展趋势

随着微/纳米科学与技术的不断发展,以形状尺寸微小或操作尺度极小为特征的微型机械系统(MEMS)受到人们高度重视,MEMS技术的发展对微型构件的微细加工技术带来挑战。文章介绍了塑性微成形技术的发展背景及其基本特点,综述了微成形的基本问题、微型零件成形工艺以及成形设备、数值模拟等方面的研究现状,并对其发展趋势进行了展望。     

纯铜径向微压缩塑性变形行为尺寸效应

对不同晶粒尺寸的纯铜多晶体圆柱试样,开展径向微压缩试样。实验结果表明,随着晶粒尺寸的增大,成形力减弱,分散性增大,并出现不规则表面。提出了基于表层晶粒位错堆积的修正表层模型和基于标准偏差理论和晶粒尺寸分布的流动应力波动性公式,分析了微压缩变形中的成形力尺寸效应。从表层晶粒以旋转为主要变形模式的角度,讨论了表层晶粒非均匀塑性变形。与实验结果吻合很好。     

金属微成形技术及其研究进展

作为20世纪80年代后期所发展起来的一门新兴技术,微成形已经广泛应用到工业生产中.介绍了最近金属微成形理论方面的一些研究成果和若干主要的成形工艺,如尺寸效应、体积成形、板料成形等,并进一步指出了塑性微成形技术未来发展的主要方向.     

State of the art in micro forming

Micro forming is an appropriate technology to manufacture very small metal parts, in particular for bulk production, as they are required in many industrial products resulting from microtechnology. This paper gives a review of the state of the art in micro forming of metals. The occurring problems in miniaturisation of forming technologies like micro massive forming and micro sheet metal forming are described. One of the problems are scaling effects, which, e.g. occur in tribological aspects like the friction coefficient, which increases with decreasing specimen size. Scaling effects do not only appear within the process but must be taken into account in all other areas of the forming process chain, demanding finally new solutions especially on tool manufacturing and machine concepts.     

Experimental and numerical investigation on micro deep drawing process of stainless steel 304 foil using flexible tools

Flexible forming technology provides significant application potential in various areas of manufacturing, particularly at a miniaturized level. Simplicity, versatility of process and feasibility of prototyping makes forming techniques by using flexible tools suitable for micro sheet metal forming. This paper reports the results of FE simulation and experimental research on micro deep drawing processes of stainless steel 304 sheets utilising a flexible die. The study presents a novel technique in which an initial gap (positive or negative) is adopted between an adjustment ring and a blank holder employed in the developed forming system. The blank holder is moveable part and supported by a particular spring that provides the required holding force. The forming parameters (anisotropy of SS 304 material, initial gap, friction conditions at various contact interfaces and initial sheet thickness) related with the forming process are in details investigated. The FE models are built using the commercial code Abaqus/Standard. The numerical predictions reveal the capability of the proposed technique on producing micro metallic cups with high quality and large aspect ratio. To verify these results, number of micro deep drawing experiments is conducted using a special set up developed for this purpose. As providing a fundamental understanding is required for the commercial development of this novel forming technique, hence the optimization of the initial gap in accordance with each sheet thickness, thickness distribution and punch force/stroke relationship are detected.     

Joining by laser shock forming: realization and acting pressures

The need to implement more functionality on the same space drives miniaturization and makes hybrid joints under various conditions also in the micro range necessary. Existing solutions often have restrictions due to the principle of joining. Thus, in this article a new high speed joining method for the micro range is presented, which is realized by a plastic forming process based on TEA-CO₂-laser induced shockwaves. In a first step it is shown how sheet–sheet joints can be realized with this method. In order to get knowledge of basic process parameter and for further application of the process, the near-by-field of acting pressure of the initiated shock wave is measured in open and tube environment. The results show that constant maximum acting pressure conditions appear in a tube, while pressure characteristics show high reflection phenomena. Furthermore, it is determined that the ignition point of the TEA-CO₂-laser induced plasma out of aluminum is about 8 mm above the surface.