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...     

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。     

管材内液塑性成形中的拉伸失稳分析

针对目前管材内液塑性成形中缺陷对工艺的影响,借助塑性力学分析手段,对轴向和环向的应力比对拉伸失稳极限应变的影响进行了分析。研究表明,胀形过程中,管坯的全部外载荷都是通过内部液压生成;内高压成形过程中,随应变比绝对值的增加,等效应变、环向应变及轴向应变呈指数增长趋势,而厚向应变对应力比的变化不敏感,其中集中性失稳应变量大约是分散性失稳的两倍,且随应变比绝对值的增加,集中性失稳的应变极限增加速度大于分散性失稳,破裂倾向降低明显。     

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。     

镁合金管件热态内压成形研究进展

首先简介了热态内压成形国内外研究现状,然后重点介绍了哈尔滨工业大学在热态内压成形装置和镁合金热态内压成形方面的研究进展。所研制的热态内压成形装置可在一定温度下实现镁舍金大膨胀率变径管、弯曲轴线变截面管的研制。采用AZ31B镁合金管材获得膨胀率30％,最大减薄率6．7％的变径管件;采用AZ61A镁合金管材试制了正方形截面件和某轿车样件,采用AZ31镁合金管材试制了截面带有小圆角的管件。介绍了上述样件的工艺过程,表明镁合金热态内压成形工艺具有广阔的应用前景。     

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。     

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。     

Loading path optimization of tube hydroforming process

Optimization methods along with finite element simulations were utilized to determine the optimum loading paths for closed-die and T-joint tube hydroforming processes. The objective was to produce a part with minimum thickness variation while keeping the maximum effective stress below the material ultimate stress during the forming process. In the closed-die hydroforming, the intent was also to conform the tube to the die shape whereas in the T-joint design, maximum T-branch height was sought. It is shown that utilization of optimized loading paths yields a better conformance of the part to the die shape or leads to a higher bulge height. Finite element simulations also revealed that, in an optimized loading path, the majority of the axial feed needs to be provided after the tube material yields under the applied internal pressure. These results were validated by conducting experiments on aluminum tubes where a good correlation between the experimental results and simulations were obtained.     

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 fast algorithm for strain prediction in tube hydroforming based on one-step inverse approach

This paper presents recent developments of a simplified finite element method called the inverse approach (IA) for the estimation of large elastoplastic strains and thickness distribution in tube hydroforming. The basic formulation of the IA, proposed by Guo et al. (1990), has been modified and adapted for the modeling of three-dimensional tube hydroforming problems in which the initial geometry is a circular tube expanded by internal pressure and submitted to axial feed at the tube ends. The application of the IA is illustrated through the analyses of numerical applications concerning the hydroforming of axisymmetric bulge, made from aluminum alloy 6061-T6 tubing, the hydroforming of square section hollow component and the hydroforming of a free Tee extrusion from welded low carbon steel LCS-1008 tubing. Verifications of the obtained results have been carried out using experimental results together with the classical explicit dynamic incremental approach using ABAQUS^® commercial code to show the effectiveness of our approach.     

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。     

Development of a finite element simulation system for the tube axial compressive precision forming process

Tube axial compressive precision forming including free deformation can be developed into an advanced precision forming process with high quality, high efficiency, low consumption, good flexibility for size changes. However, the mechanism of free deformation existing in the process is complicated and is hard to study with theoretical analysis and experimentally and there has not been sufficient research of the process. In this paper based on an analysis of deformation modes, a rigid-plastic finite element model of forming process is established and some key technology problems related to the simulation are resolved. A corresponding finite element simulation system was then developed. Experiments carried out show that the system developed is reliable and can be used for a further and systematical study of the tube axial compressive precision forming process.     

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。     

Experimental investigation of friction coefficient in tube hydroforming

The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.