管材内压液力成形的稳定性分析

管材内压液力成形过程中 ,管坯在内压与轴向压力的共同作用下发生变形。成形过程中常见的缺陷是起皱和破裂 ,这两种缺陷的产生都和管的失稳有关。本文运用薄膜理论分析了管坯在轴向力单独作用下的压缩失稳 ,得出临界轴向压力的计算公式 ;从失稳应变强度入手 ,分析了圆柱管在内压和轴向压力共同作用下的分散性失稳 ,根据失稳应变强度的计算公式 ,分析了应力状态系数 a、厚向异性指数 rh、应变强化指数 n等因素对管的失稳应变强度的影响规律     

管材液力成形技术的研究进展

针对航空航天、核能工程与新能源汽车等国家重大科技工程领域中具有大膨胀率及大截面变化比等复杂结构特征的管类零件,开展将液压成形与机械力加载相结合的管材液力成形技术的研究.根据零件几何结构特征和施加载荷方向的不同,将该技术进一步分为轴向加载、径向加载以及多向复合加载液力成形工艺.从工模具开发、有限元仿真、加载路径优化及在典...     

管材液压成形技术的发展——从前8届国际塑性加工会议看管材液压成形技术的发展

文章回顾了前8届国际塑性加工会议论文集中关于管材液压成形方面的文献,发现,早期的管材液压胀形技术内压较低,后来发展到可同时实现超高压和轴向补料;可成形零件的轴线由直线变为二维或三维空间曲线,种类大幅增加;适用于内高压成形的材料也由铝、铜、低碳钢等增加了不锈钢、铝合金、镁合金;同时热态内压成形技术也蓬勃发展起来。     

管材液压成形机理与汽车发动机托架成形实验

汽车发动机托架是典型的管材液压成形件,不能单道工序成形并且截面变化复杂。提高材料的塑性,从而提高难点部位的成形极限,是保证均匀、精确成形的关键。文章分析了液压成形机理、失效形式以及两者之间的关系,研究并解决了多工序成形时加工硬化的影响,成功地成形了某汽车发动机托架。经过壁厚测试,证明零件的成形质量符合要求。     

管材径压胀形试验与测试装置的开发

开发了一种管材径压胀形试验装置,包括成形模具及液压控制系统。液压力由手动液压泵提供,径向压力由压力设备提供。采用该装置可以在不同管端约束方式、不同液压力和不同润滑方式下进行管材的径压胀形试验研究。初步试验结果表明,该装置具有结构简单、操作方便、工作可靠等特点,能满足径压胀形试验的基本要求。     

数字液力解码器密封与摩擦特性试验研究

根据数字液力解码器阀体本身设计一个垂直布置的往复高压油液的密封试验台架,通过试验方法探究解码器在不同介质压力、往复速度及压缩率的条件下的密封性能及摩擦特性。结果表明：高压时,数字液力解码器需要较大的启动力,当启动力未达到最大静摩擦力时,其动作响应会存在一定的延迟现象,同时较大的滞后摩擦力会使密封系统的随动性变差;最大静摩擦力和滑动摩擦力随介质压力增加均呈线性增加,0~16 MPa与16~32 MPa两阶段的线性增长率不同,16~32 MPa时增长率变小;在高压高速时,解码器密封部位容易发生泄漏失效;初始压缩率对解码器的密封性能影响明显,初始压缩率为23.25%时,能够满足解码器正常工作时的密封要求。     

一种管材胎模成形方法

在汽车制造中，有许多件是管类件，需要专用设备成形，本文介绍了在没有专用设备的情况下，通过简单的胎模在普通设备上成形管类件的一种方法。     

管材自由胀形时极限载荷及成形极限的确定

基于轮廓形状为余弦曲线及轮廓上任一质点的运动轨迹与轮廓正交的假设及材料各向异性理论,建立直观的数学模型,并借助数值计算方法,快速、准确地确定薄壁管材无模约束自由液压胀形的成形载荷及成形极限。通过对不锈钢及低碳钢薄壁管的液压胀形实验来验证理论模型及计算结果的正确性,并分析及比较胀形中的成形载荷变化规律、管材壁厚及轮廓形状的变化规律。研究结果表明,自由胀形长度l0对于极限载荷pb值的大小有较大的影响,但对极限胀形系数Kmax影响较小;基于该模型计算的极限载荷(破坏时的液压力)及成形极限更加接近实际,可用于管材液压胀形的生产中。     

新型管材冲击液压成形装置的设计

针对常规的管材液压成形技术需要昂贵的专用设备及模具、生产效率低等不足,开发了一种简单实用、可在冲床或压力机上使用的管材冲击液压成形装置,可用于薄壁金属管材的自然胀形、轴压胀形和异形截面中空件的冲击液压成形。该装置无需外部高压供给系统和专用液压成形设备,通过撞击轴压头挤压容腔中液体的方式来为管材提供液压力和轴压力。通过设计轴压头的行程和调节溢流阀的溢流压力值等来实现最大液压力和轴向进给量的合理匹配,并以304不锈钢毛细管和H65黄铜毛细管为试验管材做了相关试验。研究结果表明:该装置结构简单、操作方便;可实现最大液压力与轴向进给量的协调控制;合理的载荷匹配能显著地提高管材冲击液压成形的成形性能;H65黄铜毛细管破裂时所需的液压力小于304不锈钢毛细管破裂时所需的液压力。     

Optimization of loading conditions for tube hydroforming

Tube hydroforming is a developing technology with advanced features of lightness and unified part. This study investigates the best possible regulation for loading conditions between the internal pressure and the axial feeding by hydroforming of a T-shape metal tube. Using conjugate gradient method with finite element method, a program module is generated to check the hydroformed tube quality about its thickness uniformity and the geometry accuracy. Thereby, a batch mode and a sequential mode to optimize the loading conditions of the tube hydroforming process are created and investigated. Regarding the tube quality from the simulation results, the hydroforming process, which follows the loading curve generated by the sequential mode, is better than by the batch mode. The optimal loading procedure generated by this article can offer another possibility for engineer by determining the internal pressure and the axial feeding in tube hydroforming.     

A theoretical and experimental study on forming limit diagram for a seamed tube hydroforming

The purpose of this work is to establish the forming limit diagram (FLD) for a seamed tube hydroforming. A new theoretical model is developed to predict the FLD for a seamed tube hydroforming. Based on this theoretical model, the FLD for a seamed tube made of QSTE340 sheet metal is calculated by using the Hosford yield criterion. Some forming limit experiments are performed. A classical free hydroforming tool set is used for obtaining the left hand side forming limit strains, and a novel hydroforming tool set is designed for the right hand side of FLD. The novel device required the simultaneous application of lateral compression force and internal pressure to control the material flow under tension–tension strain states. Furthermore, the suitable loading paths for the left hand side of FLD by theoretical formulas and for the right hand side of FLD by finite element (FE) simulations are calculated. Finally, a comparison between the theoretical results and experimental data is performed. The theoretical predicting results show good agreement with the experimental results.     

日本内高压成形技术进展(英文)

文章回顾了自2003年于日本举行的第一届内高压成形国际会议(TUBEH YDRO2003)后该技术在日本的发展概况。近年来,铝合金热态内高压成形技术得到了较快的发展,利用该技术生产的汽车副车架试制成功,并已应用在轿车上;移动模具的出现提高了内高压胀形极限,使T形三通管制管的成形高度显著提高。文中还讨论了在内高压成形工艺优化、拼焊管内高压成形、锥形管内高压成形、高强钢管内高压成形、液压冲孔、成形极限图及内高压成形设备方面的进展。     

内高压成形技术研究与应用新进展

介绍近年来在内高压成形机理、工艺、设备和应用方面的最新进展。针对大截面差管件,弯曲轴线异型截面构件和枝杈管3类工艺,给出典型零件缺陷形式、形状精度、壁厚分布和工艺参数的影响。详细介绍了皱纹控制与利用,降低整形压力的方法和内压与轴向力耦合作用下管材的塑性失稳起皱分析。最后给出了研制的典型内高压成形件及在汽车、航天、航空中的应用。     

管材数控弯曲中的起皱分析与控制

针对内高压成形过程中,对弯曲件质量的严格要求,研究了低碳钢管材的数控弯管过程。采用数值模拟和实验,分析了不同弯曲半径、芯棒和管坯的间隙、芯棒位置和有无防皱块等参数对起皱的影响。结果表明,随着弯曲半径、芯棒直径、芯棒伸出量的增大及采用防皱块的情况下,管材弯曲起皱的趋势减小;在数值模拟的基础上进行了试验研究,试验结果和数值模拟结果吻合较好。采用二倍管径的弯曲半径,芯棒和管材间隙0.015D的情况下,能够有效地避免了弯曲内侧的起皱和外侧的减薄,成形出合格的副车架弯曲件,满足后续的内高压成形。     

管件液压成形加载路径的多目标优化

在管件液压成形过程中,加载路径对成形过程的影响最为重要。文章给出了一种新的加载路径优化方法,即精英保留非劣排序遗传算法(NSGA-Ⅱ)与成形数值模拟软件集成,实现对加载路径的自动寻优。该方法通过优化算法程序修改加载路径,自动调用数值模拟软件进行分析,在更大的解空间内自动寻找最优方案。文中以某汽车仪表板梁为例,采用该方法对液压成形中的加载路径进行优化分析。结果表明,通过该方法所获取的加载路径较通过人工寻优所获取的加载路径更趋于最优。另外,该方法一次运算能够同时获取多个Pareto最优解,可为加载路径的制订和设计人员的决策,提供更多的选择。     

薄壁管件液压成形工艺改进与疲劳寿命分析

通过对现有U形薄壁管件液压成形工艺的分析,提出应对壁厚不均和疲劳寿命短两方面进行改进;在基于被动液压成形理论分析计算的基础上,提出具体工艺改进方案,并对被动液压成形加载曲线合理区间进行了分析;基于LS-DYNA动力显式有限元分析软DYNAFORM5.6,对薄壁管被动液压成形进行模拟仿真,对改进前后工艺进行对比分析,并结合仿真结果,对改进前后成形工艺加工工件的疲劳寿命进行对比,分析对比结果表明,改进后工艺可显著提高工件的疲劳寿命。     

汽车结构件内高压成形应力极限分析

由极限应力构成的应力成形极限图(FLSD)独立于应变路径,可作为复杂应变路径下成形极限的判据。通过标准成形极限实验获得3A21铝合金板材的成形极限图(FLD);由极限应力应变转换关系,将极限应变转换至主应力空间,建立对应的FLSD;采用LS-DYNA软件对方截面汽车结构件内高压成形过程进行了模拟,应用FLSD预测胀形过程中破裂的发生及极限成形压力。模拟结果与物理实验结果相吻合,证明FLSD可作为管材内高压成形等复杂应变路径下成形极限的判据。     

Mechanism of improvement of formability in pulsating hydroforming of tubes

The mechanism of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes was examined. Free bulging hydroforming experiments of mild steel tubes under oscillating and constant inner pressures were performed. For a high constant pressure, a round bulge with local thinning was observed, whereas wrinkling occurred for a low constant pressure. The occurrence of these defects was prevented by oscillating the internal pressure in the pulsating hydroforming. In the pulsating hydroforming, a uniform expansion in the bulging region was obtained, and thus the formability was improved by preventing the local thinning. It was found from an observation of deformation behaviour, using a video camera, that the tube is uniformly expanded by repeating the appearance and disappearance of small wrinkling. The cause of the uniform expansion for the pulsating hydroforming was also interpreted from the variation of stress components. In addition, a similar deference in deformation behaviour between the oscillating and constant inner pressures was also obtained in finite element simulation.     

Wrinkling behavior of magnesium alloy tube in warm hydroforming

In tube hydroforming with axial feeding, under the effect of coupled internal pressure and axial stress, wrinkles often occur and affect the forming results. Wrinkling behavior of an AZ31B magnesium alloy tube was experimentally investigated with different loading paths at different temperatures. Features of wrinkles, including shape, radius and width, were acquired from the experiments, as well as the thickness distribution. Numerical simulations were carried out to reveal the stress state during warm hydroforming, and then the strain history of material at the top and bottom of the wrinkles were analyzed according to the stress tracks and yielding ellipse. Finally, effects of loading paths on expansion ratio limit of warm hydroforming were analyzed. It is verified that at a certain temperature, expansion ratio limit can be increased obviously by applying a proper loading path and realizing enough axial feeding.