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.     

管材轴压液力成形中的摩擦与密封

管材轴压液力成形是一种生产中空轴类零件的成形技术,其在汽车和航空航天等领域有广泛的应用前景。管坯和模具间的摩擦是影响管件成形过程的关键因素,现已成为目前人们研究的热点之一。本文对管材轴压液力成形中的摩擦和密封问题进行了概述,提出了一种新的管端密封和导向形式,有效地改善了管坯和模具间的摩擦,同时获得了较好的密封效果。     

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.     

管件液压成形中加载路径的优化设计方法研究

确定合理的加载路径是管件液压成形工艺设计的关键。文章较为系统地介绍了管件液压成形中加载路径的优化设计方法,比较分析了各种方法的优缺点与适用对象,讨论了研究过程中存在的主要问题和研究的发展方向。     

3000kN板材充液成形液压机可靠性分析

对3000kN板材充液成形液压机进行了有限元分析。通过模拟,分别对主机及超高压液室施加满负载,以获得机器在满负载工作条件下的可靠性数据,为产品的后续开发提供依据。     

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。     

Analysis on critical conditions of sidewall wrinkling for hydroforming of thin-walled Tee-joint

Based on the sidewall wrinkling phenomena in hydroforming of thin-walled Tee-joint, an analytical model for tube wrinkling under double side constraints was proposed to calculate the critical wrinkling stress. The effects of stress ratio, diameter-to-thickness ratio and tube material properties on critical condition of sidewall wrinkling were investigated. It is found that the middle of the main tube side wall is the most dangerous position for wrinkling within hydroforming of thin-walled Tee-joint. At a certain internal pressure, the critical wrinkling stress increases with increasing of ratio of hoop stress to axial stress and material strength coefficients, but decreases with increasing of work-hardening exponent and ratio of diameter to thickness. Through the analytical model combining FEM simulation, the critical wrinkling loading path according to the relation between axial feeding and internal pressure was obtained. Experimental results validates that wrinkle can be avoided if the pressure is above the critical wrinkling loading path, otherwise, wrinkle occurs. It is also verified that the analytical model of critical wrinkling stress is reasonable for the thin-walled Tee-joint hydroforming process.     

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.     

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。     

Y型三通管热态内高压成形多目标参数优化

基于Dynaform软件平台,建立Y型三通管热态内高压成形的三维弹塑性有限元模型.以左右冲头进给量、中间冲头后退量和内压力为因子,设计了正交试验方案,运用数值模拟分析方法,得到了三通管在不同加载路径下的支管高度和最小壁厚两个目标参数.探讨了各因素影响指标的主次顺序,采用综合平衡方法,获得了优化的加载路径.结果表明:通过优化的工艺方案可以得到综合质量较高的的Y型三通管.     

圆管液压成形过程有限元模拟及失效分析研究

选择圆管中间膨胀的液压成形为研究对象.应用LS-DYNA软件,实现圆管液压胀形的模拟仿真过程,为具体的成形实验提供了参考.管件液压成形过程的三种主要的失效形式有弯曲、褶皱、破裂,而液压成形控制中最主要的参数就是压力,轴向给进力以及材料性质.研究中针对不同加载路径所得到的不同成形效果与失效进行分析,得到的模拟结果与相同条件下的真实实验结果比较接近.研究表明,成形工艺中加载路径(内压力与轴向给进的配比关系)的重要性,同时也说明了该液压成形模拟仿真具有一定的准确性.     

X形管内高压成形过程的加载路径优化北大核心CSCD

加载路径对X形管内高压成形质量至关重要,只有加载路径的各参数匹配得当,才能获得合格的成形件。利用DYNAFORM软件模拟不同加载路径下X形管的成形性能。并基于Box-Behnken Design试验设计和响应面法,以内压力、轴向进给量、背向位移量以及摩擦因数为试验因素,分别建立以最小壁厚、支管高度和极限圆角半径为目标的响应面模型。通过方差分析和回归方程分析,对X形管内高压成形过程的加载路径进行设计和优化,有效地改善了壁厚分布、减小了极限圆角半径、提高了支管高度。采用软件的数值优化功能筛选出最优的加载路径,并在此加载路径下对X形管内高压成形模拟结果和试验结果进行对比,发现误差在5%以内,并且壁厚分布具有一致性,说明了该加载路径优化方法具有较高的准确性和较好的可行性。     

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。     

遗传算法结合有限元模拟对液压胀形加载路径的优化

加载路径对液压胀形件的最终质量有着至关重要的影响。在优化加载路径的过程中,设计变量的取值区间对模拟时间的减少及最优解的收敛有重要的意义。文章根据塑性理论分析,给出了管形件液压胀形过程中弹性变形阶段、塑性变形阶段及贴模阶段的轴向喂入量及内压力的工程计算表达式。选取应力比为优化变量,依据屈服准则,得出了胀形过程中合理的变量区间。利用有限元软件包、优化算法及工程计算表达式,得到了液压胀形最优的加载路径。实验结果和有限元模拟结果一致性较好,该方法为轴对称件的加载路径优化提供了新的思路。     

基于DYNAFORM的内高压成形中预成形工艺改进

对复杂形状空心构件内高压成形工艺进行了数字模拟研究。采用有限元模拟,对矩形截面空心零件弯曲部位在内高压成形过程中产生起皱、破裂等缺陷进行了分析;针对矩形截面空心件弯曲部位,提出采用椭圆截面充液预成形的方法,控制起皱、破裂缺陷的产生,成形质量较理想。并通过试验进行了验证,采用较低压力可以改善内高压成形过程中材料的分布、提高材料的成形极限、控制缺陷产生并提高产品质量。     

钛T型管液压成形的工艺参数研究

采用Dynaform软件对Φ219 mm×Φ219 mm×5 mm钛T型管的液压成形工艺进行数值模拟研究,以有效支管高度、最大减薄率和最大增厚率为优化指标,对内压加载路径、加压持续时间、左右及中间冲头速度等多种工艺参数组合方案进行优选计算,获得最优方案,并根据最优方案中的工艺参数进行实际的液压成形试验。研究表明:模拟试验中,采用方案3成形效果最好,有效支管高度达到68.41 mm,最大减薄率和增厚率分别为27.38%和54.34%,满足T型管尺寸和壁厚分布要求。与模拟值相比,成形试验得到的钛T型管零件在有效支管高度、最大减薄率和最大增厚率上的误差均在5.1%以内。     

管材内高压成形新加载方式的研究

介绍了管材内高压成形过程中,一种新的内压加载方式--脉冲型加载方式.并通过建立相应的有限元模型,进行了内压脉冲型加载方式下管材内高压成形过程的模拟.通过对不同加载方式模拟结果的比较,分析了脉冲型加载方式对内高压成形中金属流动、变形区变形分布及局部过度减薄等方面产生的影响.模拟结果表明:脉冲型加载在管材内高压成形过程中可以使变形区的变形更加均匀,有利于抑制局部过度减薄、对抑制最后贴膜成形的圆角部位的过度减薄作用明显;脉冲型加载方式使变形更均匀的原因是减小了金属流动阻力,使金属流动更容易.     

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。     

Hydroforming process optimization of aluminum alloy tube using intelligent control technique

In this study, to determine the optimal loading path of tube hydroforming process, a database-assisted fuzzy process control algorithm proposed previously by the authors was applied to T-branch forming with a counterpunch. The tubular material used is aluminum alloy (A6063-T1) and has an outer diameter of 42.7 mm and wall thickness of 1.2 mm. Control variables is axial feed, counterpunch displacement, and internal pressure. The first two variables are dependent on the last one, which is an independent variable. In the control algorithm, new evaluation functions are adopted for buckling at the shoulder part of the branch and for contact fitting with a counterpunch. For a “virtual control system” including fuzzy algorithm with the evaluation functions, an explicit dynamic finite element code is used in the simulation. The experiments are carried out using a fuzzy controlled path obtained by the virtual control system, compared with the conventional manual control path that is attained by a trial-and-error approach. As a result, a T-branch product is successfully hydroformed. This result shows that the fuzzy control algorithm and virtual control system can provide an adequate loading path in the hydroforming process for an aluminum alloy tube.     

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。