液压成形设备的设计

着重介绍了液压成形技术的原理、工艺过程及生产异型截面管时两种不同工艺设备的设计.     

邻角精确控制的异型管辊弯成形过程数值模拟

针对汽车立柱用P形异型管多道次辊弯成形存在相邻凹凸角度偏差大、难以满足角度高精度要求的问题,基于弹塑性大变形理论,应用辊弯成形专业设计软件COPRA建立了P形异型管15道次辊弯成形有限元模型。结合实际生产过程,开展了完整成形过程的有限元仿真,分析发现焊管周长来料不足及P形异型管角部在轧辊孔型内金属流动不均、成形不到位是导致相邻凹凸角角度偏差过大的主要原因。结合仿真结果和生产实际,提出了选择合适的压缩系数、分配恰当的截面变形量和修正轧辊辊形三者相结合的邻角精确控制方法。应用所提方法进行了P形异型管辊弯成形有限元仿真,结果表明：仿真最终产品截面与设计截面基本一致,凹凸角的角度分别为90.5°和89.9°,角度偏差均在±1°的误差范围内;异型管辊弯成形金属流动到位,使得角部金属充满轧辊孔型,可改善P形异型管相邻凹凸角的成形质量。利用所提方法通过辊弯成形工业应用,获得了符合要求的P形异型管,其相邻凹凸角度精度分别提高了33.84%和36.70%,有效改善了P形异型管成形质量,可为生产实践提供依据。     

桩身变截面效应对异型摩擦桩承载性能的影响分析

变截面异型桩沿桩身每隔一定距离设置一个变截面环段,通过独特的桩土相互作用,在提升桩侧阻力的同时,充分发挥了桩身的结构强度。为了研究变截面效应对变截面异型桩承载性能的影响,采用有限元方法分析了变截面环数、变截面段直径对变截面异型桩桩周土体位移场、桩身轴力、桩段侧摩阻力的影响;采用规范经验公式和有限元计算的方法,对比不同土质条件下变截面效应对桩的竖向极限抗压承载力的影响。结果表明：当变截面异型桩竖向受荷时,桩周土的破坏形式由变截面环区域的局部破坏,逐渐转变为沿着桩变截面外径的整体剪切破坏;优化变截面的环数可提升变截面异型桩的竖向抗压承载力。变截面异型桩的桩身轴力和桩侧阻力的整体分布趋势同普通管桩一致,变截面段轴力和侧摩阻力远大于非变截面段,且桩身强度优势得到充分发挥。经规范经验公式计算得到的变截面异型桩极限抗压承载力,较数值计算结果偏于保守。该研究为变截面异型桩承载性能的理论分析和试验研究提供思路,同时为工程实际有效应用变截面异型桩提供参考。     

偏心受压下的L型截面钢骨混凝土异型柱试验

目的研究L型截面钢骨混凝土异型柱的破坏特征、破坏机理以及受力性能.方法通过制作3根不同含钢率的L型截面钢骨混凝土异型柱和1根无钢骨的L型截面钢筋混凝土异型柱,对异型柱在单向偏心受压下进行试验研究,利用试件的试验数据,绘制了各种荷载-应变、荷载-位移关系曲线并进行分析.结果通过对L型截面钢骨混凝土异型柱和钢筋混凝土异型柱的单向偏压试验研究,明确了L型截面钢骨混凝土异型柱的破坏特征,受力性能、破坏机理及含钢率对异型柱承载力的影响.结论L型截面钢骨混凝土异型柱跟普通的L型截面钢筋混凝土异型柱相比,具有更高的承载力,更大的延性性能,随着含钢率的增加,构件的承载力及延性也相应增大.     

SRC异型边节点抗震性能试验研究

由于生产工艺要求,大型电厂主厂房不可避免出现型钢混凝土变柱截面异型边节点,为研究其抗震性能,选取3个具有代表性的SRC变柱截面异型边节点和1个柱截面无变化的常规节点进行拟静力试验,研究了SRC异型边节点的破坏形态、滞回特性、承载力、延性、耗能和刚度退化性能.研究结果表明:型钢混凝土异型边节点破坏过程和常规节点类似,破坏形式为"小核心区"剪切破坏;SRC变柱截面异型边节点的承载力、延性、耗能及刚度较常规节点小;梁截面高度的增加能够一定程度提高SRC异型边节点的承载力、延性、耗能及刚度;SRC柱-RC梁异型边节点抗震性能较差;轴压比对异型边节点延性性能影响较大,增加轴压比对试件延性不利.     

扩压管内有摩阻流动的壅塞与临界问题

将扩压管内有摩阻的稳定流动转化为等效多变过程进行研究,得到了揭示摩擦影响工质状态变化规律的解析表达式.研究发现,有摩阻时扩压管的喉部不是临界截面,而是壅塞截面且马赫数Mc＞1.壅塞截面的马赫数、温度比和压力比都与物性和摩擦有关,扩压管截面积如何变化应根据壅塞参数决定.导出了壅塞马赫数、壅塞温度比和壅塞压力比的计算公式,...     

热声谐振管压比影响因素的数值模拟

通过比较等直径管,分析了锥度管对压比的影响.采用Fluent模拟计算了管型对压比的影响,结果表明渐缩型锥管能强化声振动,可提高谐振管的压比.并研究了工作压力对热声异型谐振管压比的影响,结果表明高的工作压力有利于提高热声谐振管的压比.     

非圆截面零件数控加工中参数编程方法的研究

针对非圆截面零件异型轧辊环状孔型的数控加工工艺要求,利用西门子数控系统,分析了异型轧辊环状孔型曲线的加工策略和加工过程中刀具的位置,建立了异型轧辊环状孔型曲线的数学模型,定义了 R 参数,并给出了参数编程方法.编程实例表明,该编程方法工作可靠,工作量小,工作效率高.为 R 参数编程方法在非圆截面零件数控加工中的实际应用提供了技术支持.     

十字形截面钢骨混凝土异形柱单向偏压试验

目的设计一种新型十字形截面钢骨混凝土异型柱,研究其受力性能及破坏机理.方法对3根含钢率不同的十字形截面钢骨混凝土异形短柱和1根无钢骨的十字形截面普通混凝土异形柱进行单向偏压试验.结果十字形截面钢骨混凝土异型柱的承载力要比无钢骨的普通钢筋混凝土异形柱的承载力平均高出54%,随着含钢率的增大,构件的承载力及延性相应增加.结论十字形截面钢骨混凝土异形柱中的钢骨与混凝土能够较好的共同工作直至破坏,这种新型十字形截面钢骨混凝土异型柱为组合结构的发展提供了一种新的结构形式.     

蒸发式冷凝器异型扁管性能分析及数值模拟

针对目前蒸发式冷凝器采用的圆管、椭圆管、弹形管管型的不足,设计开发了新型异型扁管的管型结构,为验证其优良性能,运用FLUENT软件对4种管型管束内强制对流空气进行数值模拟,建立了管束流场的数学模型,采用求解压力耦合方程组的半隐式方法(SIMPLE)进行迭代计算求解,在进口流速为1.5~3.9 m/s范围内分别进行了计算,运用Tecplot10后处理软件直观表征空气的速度场、温度场、压力场,给出了压降损失随空气流速变化关系曲线.数值模拟结果表明,新型异型扁管和其他3种管型相比,压降约降低30%、21%及15%,同时出口截面空气平均温度有所增加.     

基于Dynaform的三通管件液压成形影响因素分析

通过采用Dynaform软件对三通管件液压成形过程进行模拟仿真,确定了影响其成形质量的因素,得到了各参数对管件成形的影响规律,通过控制各参数可有效地提高三通管件液压成形的质量,提高生产效率。     

轴向进给速度对内高压成形三通管影响的有限元分析

利用有限元法证实了内高压成形三通管的可行性,给出了不同轴向进给速度下零件的壁厚及应变分布,并就轴向进给速度对成形的影响进行了分析.结果表明,轴向进给速度的选取对内高压成形三通管具有重要影响.     

管件液压成形过程的有限元分析及实验研究

以圆管变形为管球相间零件为研究对象,对液压成形这种新工艺进行研究.采用计算机数值模拟与试验相结合的方法,分析了圆管液压成形过程.管件液压成形主要有褶皱和破裂两种失效形式,而成形控制中最主要的参数之一是压力,即管件内部压力和轴向压力.在对不同加载路径进行分析后,得出模拟结果与相同条件下的实验结果比较吻合的结论.研究表明了液压成形工艺中加载路径(内压力与轴向压力的配比关系)的重要性,同时也证实了用计算机模拟仿真液压成形过程具有一定的可靠性.     

液压成形管材性能评价方法研究现状

在管材液力成形技术中,管材成形性能的评价方法是应用的基础,对数值模拟技术在液力成形中的应用、工艺参数优化及新产品开发等具有重要意义.总结管材性能评价方法的研究现状,目前判定标准主要集中于管材的硬化指数n,各向异性指数r值,以及几何参数和判定准则形成的成形极限图等方面.指出n,r值可以作为管材液压成形性能的评价标准,管材应力基础上的成形极限图的确定有待进一步研究.     

Influence of loading path on formability of 304 stainless steel tubes

The loading path affects the metal formability remarkably in tube hydroforming, and it is also one of the research focuses. Recently, some scholars abroad proposed a new fluctuant hydraulic loading method, which can improve the formability of tubes in hydroforming. Related studies have shown that this new loading method can improve the tube formability, the distribution of deformation is more uniform and this is useful for avoiding excessive local thinning. In this paper, tube hydroforming experiments without axial feeding were carried out; the influences of the loading methods on formability of stainless steel tubes were studied. Through the comparison of the experimental results under the condition of monotonous increase loading and fluctuation hydraulic loading, the outside diameter distribution, the thickness distribution and the crack expansion forms of deformation zone all fully prove that the uniformity of the distribution of tube deformation and formability have been increased significantly under the condition of fluctuation loading without axial feeding, the reasons should be distinguished from the fluctuation hydroforming with axial feeding. In order to study the forming mechanism, uniaxial tensile test of tubes similar to fluctuation loading deformation is designed in this paper, namely intermittent tensile test. It is found that intermittent uniaxial stretch can improve the tube elongation at fracture by about 40% and the deformation distribution is more uniform than that through uniaxial tensile test of the stainless steel tube. In the process of intermittent tensile tests, changes of metal microstructures brought by the loading and unloading processes are the main reasons that improve the formability of the tubes.     

Characteristics of thickness distribution of tailor-welded tube hydroforming

Both experimental and mechanical analyses were carried out to investigate the characteristics of thickness distribution for tailor-welded tube (TWT) hydroforming with dissimilar thickness. Then, the effects of weld-seam position and thickness difference were also revealed. A multiple-diameter tube was formed to reveal the characteristics and the regularity of thickness distribution during TWT hydroforming. It is indicated that there are obvious fluctuations in thickness distribution though the TWTs have the same expansion ratio. The thinning ratio of thinner tube is bigger than that of thicker tube especially in the zone closed to the weld-seam. The difference in thinning ratio between two tube segments can reach 9%. Consequently, sudden and large fluctuation of thickness appears in the zone nearby the weld-seam. The difference in thinning ratio between thinner and thicker tubes enlarges as the thickness difference increases, but improves as length ratio increases. Different strain states are the main reason to induce nonuniform thickness distribution. The difference in thickness is the main reason to induce different strain states on thinner and thicker tubes.     

Mechanism of weld-line movement within hydroforming of tailor-welded tube

To reveal the reason of weld-line movement in hydroforming of a tailor-welded tube (TWT) with dissimilar thickness,the stress ratio of axial stress to circumferential stress is derived by mechanical analysis and analyzed between the thicker and thinner tubes,as well as the property of the axial strain. During TWT hydroforming,tensile strain along axial direction happens on the thinner tube. On the contrary,compressive strain happens on the thicker tube. Experiments are conducted to varify the weld-line movement regularity and strain distribution. It indicates that the weld-line moves from the thinner part to the thicker during TWT hydroforming. The thinning ratio of the thinner tube is bigger than that of the thicker tube,especially in the zone near weldline. Stress ratio difference between the thicker tube and the thinner tube is the main reason of weld-line movement and non-uniform thinning ratio distribution.     

薄壁管无模内高压成形的实验研究与数值模拟

针对内压和轴压共同作用下的薄壁管无模内高压成形及加载控制稳定性问题进行了实验及数值模拟。实验结果表明,适度的起皱有助于提高薄壁管内高压成形的成形极限。有限元数值模拟证明,在轴压偏高而内压相对偏低的情况下,降低内压的增长率有助于抑制起皱的发展。出于对控制实现的考虑,有必要将内压轴压的匹配关系转换为内压轴向压缩位移的匹配关系。     

薄壁管液压成形计算与有限元模拟分析

采用塑性变形理论对薄壁管成形进行分析,计算胀形力。应用SolidWorks建立胀形模型,应用Dynaform对模型进行有限元分析,模拟在不同的胀形压力和不同的胀形速度下的成形情况。通过大量模拟,分析胀形力及胀形速度对成形的影响。     

内高压成形技术研究与应用进展

内高压成形是近年来发展起来的一种加工空心构件的先进制造技术,适用于制造汽车、航空、航天等行业中使用的各类轻体构件和复杂管件。用其制造的零件具有质量好、刚度好、零件数量少,可减少后续机械加工和组装焊接量和成本低等优点,本文综述了内高压优点、应用范围、适用材料、国内外工业应用情况及研究现状。