Prediction of necking of high strength steel tubes during hydroforming—multi-axial loading

This article studies tubular hydroforming of high strength low alloy (HSLA) and dual phase (DP600) straight tubes under the action of end feeding loads. Experiments demonstrate that higher end feed loads enhance the formability of the tubes and increase the internal fluid pressure for onset of necking and bursting. Because of the action of the internal pressure and the axial compressive load, the onset of localization (necking) is due to a complex three-dimensional state of stress. Using free expansion experiments, approximate upper and lower bound strain-based forming limit curves are determined for the tube materials. These limit curves, in turn, are used to derive upper and lower bound extended stress-based forming limit curves [Simha et al., Prediction of necking in tubular hydroforming using an extended stress-based FLC. Transactions of the ASME Journal of Engineering Materials and Technology 2007;129(1): 36-47]. In conjunction with finite element computations that use solid elements to model the tube, these stress-based limit curves are used to predict upper and lower bound necking pressures under the action of end feed loading. These predictions of necking pressures, when an appropriate coefficient of tube-die friction is used, are found to bracket the experimentally measured necking pressures. Computations using plane stress shell elements to model the tubes are shown to give erroneous results, since the plane stress approximation is not valid when tubes are hydroformed in a die.     

Improvement of Formability by Oscillation of Internal Pressure in Pulsating Hydroforming of Tube

A new history of internal pressure in the hydroforming processes of tubes is developed to attain high formability. The effect of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes is examined using both finite element simulation and experiment. The deformation behaviour during the hydroforming is greatly affected by the oscillation of internal pressure. For a monotonic history of small internal pressure, the wrinkling was caused by insufficient bulging, whereas the necking and bursting occurred for a monotonic history of large internal pressure. The occurrence of these defects can be avoided by oscillating the internal pressure in the pulsating hydroforming. The improvement of formability in the pulsating hydroforming is due to both low pressure and oscillation of pressure. The effects of the amplitude and cycle number of pressure in the pulsating hydroforming on the deformation behaviour are investigated. It is found the oscillation of internal pressure is effective in preventing the occurrence of defects.     

汽车后延臂液压胀形的数值模拟

在基于刚塑性模型的HydroFORM-3D有限元平台上,对汽车后延臂的液压胀形工艺进行数值模拟分析和研究,分别考察了汽车后延臂液压胀形的主要工艺参数,如管内压力、轴向进给量及摩擦条件对成形过程的影响。并与实际试验结果进行验证和比较,结果表明,数值模拟具有较好的计算精度,可以准确地预测出几何变形和厚度变薄量。     

液压成形管件中心轴线抽取算法

管材液压成形技术是一个相对新颖的技术,其在应用过程中仍然有许多问题需要研究和解决。基于有限元法的管材液压成形数值模拟技术发展的时间更短,有待进一步研究和发展。针对这种发展要求,提出了管材液压成形数值模拟中分析模型的构造方法,并且重点介绍了逆向构造中管件中心轴线的抽取算法即边界递进搜寻法,这个算法不仅运行速度快,实现简单,而且具有较强的适应性。     

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.     

Overview on constitutive modeling for hydroforming with the existence of through-thickness normal stress

The hydroforming process is used widely across many industrial fields. High applied pressure during hydroforming makes it necessary to consider the influence of the through-thickness normal stress, while traditional approaches based upon a plane-stress assumption are not appropriate in such cases. Reliable constitutive models that consider the through-thickness normal stress are summarized in this paper, which focuses on the state of the art in the following several aspects: determine the flow stress curve with proper experimental methods and choose the measurement and computational methods to minimize the error as much as possible; select the proper three-dimensional anisotropic yield criterion for the specific material; Define the forming limit model and construct corresponding experimental verification method. The review of existing work has revealed several gaps in current knowledge of the hydroforming process accounting for the through-thickness normal stress. Conclusions are drawn concerning some critical issues and potential future developments in hydroforming modeling.     

国产2.25Cr-1 Mo钢板热处理工艺研究

介绍了国产 2 2 5Cr 1Mo钢板首次用于制造临氢重整反应器所进行的热处理工艺性能评定试验 ,通过对工艺评定试验结果和实际生产中钢板热加工性能的分析和研究 ,探讨了最佳热处理规范     

Determination of Material Parameters of Welded Tube via Digital Image Correlation and Reverse Engineering Technology

Material characteristics play an important role in tube hydroforming (THF). A method, based on digital image correlation (DIC) and reverse engineering (RE) technology, is proposed to determine the material parameters of a welded tube in hydroforming with a single tubular blank. The material parameters of the weld and parent metal are determined by applying membrane theory and the force equilibrium equations, as well as the deformation data which are obtained by DIC and RE technology in the THF process. Finite element simulations of welded THF are performed with these material parameters and the maximum bulge radii and axial profiles of the weld and parent the metal obtained from the simulations are compared with those obtained from the hydroforming experiments to verify the reliability of the proposed method. The results show that the material parameters of the weld are lower than those of the parent metal. With the material parameters adopted in FE simulation there is a good agreement between the simulation and the experiment as for the maximum bulge radii and axial profiles of the weld and parent metal. This verifies that the proposed method is acceptable for determining material parameters of a welded tube.     

脉动液压成形技术与设备

介绍脉动液压成形技术的成形原理、工艺特点及应用领域。从工艺和材料两方面对脉动液压成形提高材料成形能力的机理进行研究,试验证明脉动载荷一方面能够促进管材液压成形时的补料、降低摩擦力的阻碍作用并利用成形过程中小褶皱的出现与消失提高变形的均匀性;另一方面,对于奥氏体不锈钢,脉动载荷可以增强形变过程中的相变增塑效应,从而提高其成形性。自主设计并研制出能实现工业化生产需求的自动化程度高的脉动液压成形设备,为该项技术在汽车、航空及航天制造领域中的推广和应用提供重要的理论指导和实践探索。     

Design optimization of extruded preform for hydroforming processes based on ideal forming design theory

The conventional practice to predict preform shapes in hydroformimg processes based on finite-element analysis and/or experiment is an iterative procedure and requires many trials. In this paper, a computationally efficient direct design method, which effectively improves the design procedure, was introduced. The direct design method based on ideal forming theory, which was successfully applied for the design of flat blanks for stamping processes, was extended for the design of non-flat preform for tube hydroforming processes. A preform optimization methodology for non-flat blank solutions was proposed based on the penalty constraint method for the cross-sectional shape and length of a tube. The hybrid membrane/shell method was employed to capture thickness effect while maintaining membrane formulation in the ideal forming theory. Several classes of examples were analyzed to verify the current formulation.