管材内高压成形工艺研究

阐述了管材内高压成形基础理论,给出内高压成形区间和加载曲线之间的关系。结果表明:合理的弯曲工艺能控制外侧过度减薄和内侧起皱,避免了弯曲部位过度减薄引起内高压成形过程中的开裂。采用典型截面二维数值模拟和整体零件三维数值模拟相结合的方法,保证零件贴模度良好,安全裕度较高。通过内高压成形工艺开发出某副车架管梁,检测表明产品尺寸及型面均满足设计要求,现已批量化生产。     

加载路径对变截面弯曲三通管内高压成形性能的影响

分析比较现有的变截面弯曲三通管内高压成形性能的相关评价指标,提出一种综合性的评价指标,通过有限元模拟,比较了轴向进给力控制和位移控制的优劣,得出了轴向进给力控制方式更符合金属变形规律,能得到更好的成形效果。同时研究了内压力、轴向进给力对变截面弯曲三通管内高压成形性能的影响,内压力过大会造成支管顶部过度减薄甚至破裂,轴向进给量是获得支管高度必要条件,但是进给量过大会使局部壁厚加厚严重;结果表明折线加载路径下零件的成形质量明显优于线性加载路径。     

提高自由镦粗成形质量的工艺方法与有限元模拟

讨论各种提高镦粗成形质量的工艺方法,分析扭压复合加载成形过程,并比较这些方法的优缺点。扭压复合加载通过把摩擦力转化成促进金属流动的主动力,将提高金属流动性。运用DEFORM 3D软件模拟了Al2017在室温下的扭压复合加载变形过程,其结果证明此方法有利于减小镦粗鼓形和变形力,提高变形均匀性。     

基于数值模拟的方锥件渐进成形规律研究

为了研究渐进成形过程中板料的变形,以方锥件为例,通过数值模拟对成形过程进行了研究.模拟结果表明,法兰边金属难以向变形区流动,变形区壁厚减薄量较大但分布较为均匀.成形过程中,由于受到工具头的周向推挤作用,零件的悬空部分(底部和侧壁)出现了沿工具头运动方向的扭曲,且扭曲程度沿侧壁大致呈抛物线分布.     

背压加载方式对轻量化压缩机涡旋盘成形质量的影响

针对涡旋盘挤压成形过程中金属流动不均匀现象以及峰值挤压载荷过大,模具磨损严重的问题,利用DEFORM-3D对涡旋盘的背压流动控制成形工艺进行了研究,分析了背压成形的原理和金属的变形流动情况.对比研究了恒定背压力、线性变化背压力和两段式背压力等不同背压力加载方式对涡旋盘成形过程中填充度、成形载荷和成形均匀性的影响规律,确...     

轿车副车架内高压成形

用内高压成形技术在国内首次成功地试制出全尺寸轿车副车架样件,经检测尺寸满足设计要求。通过合理的弯曲工艺,避免了角部过度减薄引起内高压成形过程中开裂。采用典型截面二维数值模拟和整体零件三维数值模拟相结合的方法,给出了合理的预成形坯形状,控制壁厚分布和避免终成形合模时在分模面上管材被压出。通过该零件研制,基本掌握用内高压成形制造副车架的关键技术。     

内压对薄壁管充液压弯时的影响

失稳起皱和截面畸变是薄壁管弯曲成形过程中的主要缺陷,通过数值模拟和实验的方法,研究了液压支承下管材的弯曲变形行为,进行了从无内压到内压为18MPa的管材充液弯曲成形,分析了充液弯曲成形过程中的内压值对成形的影响,给出了成形后的不圆度和典型点壁厚减薄率的变化规律,结果显示,随着充液压力的增加,管材的截面不圆度逐渐减小,管材内侧壁厚增厚趋势减小,外侧壁厚减薄趋势增大。并根据模拟结果给出了成形后的典型点的应力状态。     

圆管受轴压和充液内高压成形极限的理论解析

对管材的内高压成形过程进行理论解析,研究变形过程中材料的应力应变状态,从本质上揭示内高压成形工艺变形过程中的力学规律.研究了管材内高压成形提高成形极限的机理,给出了内高压成形时各应力状态在屈服椭圆上的分布,得出了管坯发生塑性变形时内压与轴向力之间的相互关系.最后,讨论了管材内高压成形过程中材料的变形路径在成形极限图上的范围和控制载荷匹配的基本原则.     

AZ80镁合金管材反挤压成形的数值模拟与试验研究

采用Deform-3D软件对AZ80镁合金厚壁管材的反挤压过程进行了数值模拟,模拟了不同挤压温度和挤压速度对反挤压成形过程的影响。结果表明,反挤压过程的等效应变主要集中在凸模与坯料接触处和管壁上,管材的内壁和外壁损伤值较大,容易产生损伤。挤压温度越高,管材成形的温差、等效应力和挤压载荷就越小,挤压变形越均匀。挤压速度越小,金属的流动速率峰值越小,金属流动越均匀,管材温差越小,挤压变形越均匀。通过镁合金管材的反挤压试验,验证了模拟结果的准确性。     

不规则四边形截面管件内高压成形数值模拟

以不规则四边形截面管件为研究对象,作内高压成形.基于dynaform软件平台,建立了内高压成形有限元模型,利用该模型研究了内压和轴向进给对不规则四边形管材内高压成形的成形形状、角充填情况及壁厚减薄情况的影响规律,分析了管材破裂和起皱缺陷产生的原因.模拟结果显示,适当减小内压力,同时增大轴向进给量,可以有效地防止破裂的发...     

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.     

Deformation Behavior of a Thin-Walled Tube in Hydroforming with Radial Crushing Under Pulsating Hydraulic Pressure

Loading path plays a dominant role in tube hydroforming (THF), and the pulsating loading path has been reported capable of improving the formability of a tube in hydrobulging with axial feeding. As a new THF process, the tube hydroforming with radial crushing (THFRC) is receiving increasing attention; however, knowledge on the process still remains insufficient to extend its application to various other fields. In this study, the experiments of THFRC under both the pulsating and the linear hydraulic pressures were carried out to investigate the deformation behavior. The influences of the amplitude and the frequency of the pulsating hydraulic pressure on the shape precision, wall thickness, and the microstructures of the deformed parts were analyzed. Subsequently, metallographic examinations of the deformed specimens were conducted in an attempt to clarify the relationship between the microstructural evolution and deformation behavior. The mechanism of formability improvement in THFRC by the pulsating hydraulic pressure was explored from the perspective of microstructure. Compared with the linear hydraulic pressure, the pulsating hydraulic pressure could generate a higher shape precision, a more uniform wall thickness, as well as less martensites, and larger grain. The microstructural evolution induced by the pulsating loading path is supposed to contribute to the formability improvement of SUS304 stainless steel tubes.     

关键参数对薄壁筒形件充液成形的影响规律

为了研究初始反胀高度(IRBH)、反胀压力(IRBP)和液室压力加载路径3个工艺参数对板料充液成形的影响规律,以不锈钢321材料为研究对象,进行板材充液成形工艺过程的分析。首先,利用数值模拟的方法,在有初始反胀(IRB)的充液成形基础上,研究了初始反胀高度与初始反胀压力的组合形式以及液室压力加载路径对制件成形的影响规律,然后分别研究了有无初始反胀的充液成形过程。最后,通过实验的方法进行验证。结果表明:当初始反胀高度为3.75 mm、初始反胀压力为2 MPa时,充液结束时板料的最大减薄率为4.803%,在所有结果中最小;无初始反胀时,零件壁厚最大减薄率为5%;当在充液拉深后期继续加大液室压力时,板料底部发生波动,出现二次变形,与此同时,板料最大减薄率增大。从而验证了合适的初始反胀高度和反胀压力可以减小制件壁厚的最大减薄率,液室压力加载路径不同,零件的壁厚分布也不同。     

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.     

弯曲预成形和液压成形对汽车装饰尾管壁厚分布的影响

针对某乘用车排气管路中的薄壁装饰尾管的整体制造难题,开展AISI 304不锈钢管材的弯曲预成形及液压成形工艺研究,从而进一步提高该产品的成形质量与成形效率。利用Dynaform软件,首先,研究弯曲预成形工艺对管材壁厚分布的影响规律,再基于此结果,完成在不同加载方式下的管材液压成形分析。结果表明:弯管Δd值较小时,管材第2次弯曲区域的减薄率有降低的趋势,并且随着Δd值的减小,这种趋势更加明显;基于所选定的Δd值,进行了液压成形有限元模拟,相比于线性加载方式,脉动加载使成品件易破裂区域的最大减薄率由17.6%降为12.1%,并且壁厚分布更为均匀;模拟与实验结果基本保持一致,最大偏差值为2.17%,成形出的零件无开裂倾向,且外观尺寸满足要求。     

板材与管材成形性能的研究与进展

介绍了塑性加工领域近年来发现的一些提高金属材料塑性变形能力的方法和机理,包括板材增量成形中拉弯伴随成形、局部接触、反复弯曲、交变加载、高静水压力等方式下引起的板材局部增塑机理;波动液压加载状态下管材液压成形能力的提高机理（有轴向进给）、AISI304不锈钢管材的液压成形增塑机理（有、无轴向进给状态下）;AISI304管材多次拉伸／卸载状态下的增塑机理。这些增塑机理还存在于其它一些塑性加工工艺中,对其合理运用将有效提高产品成形质量和材料利用率,并减少加工道次,甚至可以产生一些新的塑性加工工艺。     

Prediction of forming limits and parameters in the tube hydroforming process

Determination of process limits and parameters for hydroforming was conducted applying widely known plasticity, membrane and thin-thick walled tube theories. Analytical predictions were compared with experimental findings. Simple but useful analytical models to predict buckling, wrinkling and bursting as well as axial force, internal pressure, counter force and thinning in tube hydroforming were verified with experimental results.     

汽车中空异形板件液压成形的实验与仿真分析

为研究基于液压成形的汽车钣金件成形规律,以汽车中空异形板件为研究对象,自行设计并搭建板材液压成形实验测试系统,以此开展板件液压成形的实验研究,借助DYNAFORM有限元软件对板材液压成形进行有限元仿真分析,通过与实验测试结果的对比,验证了建立的有限元模型与数值模拟的正确性。以此为基础,探究压边力、压边力加载路径、液室压力、压边间隙和板材与凹模之间的摩擦系数等关键工艺参数对板材液压成形厚度的影响规律,提出汽车中空异形板件液压成形工艺,为板材液压成形技术在汽车钣金件成形中的应用提供参考。     

高强钢复杂曲面件充液拉深工艺模拟研究

对某高强钢复杂曲面件的充液拉深工艺进行有限元数值模拟,分析了液室加载路径以及最高液室压力对成形结果的影响,得到该零件充液拉深成形合理的液室加载路径及最高液室压力。     

Numerical/experimental investigations for enhancing the sheet hydroforming process

In this work the authors present some results of their research activity aimed to enhance the sheet hydroforming process. The main focus is the adoption of a movable inferior plate through which the control of the blank forming is realised. Tests on hemitoroidal parts using an innovative equipment with a movable die were carried on at the Institute of Metal Research (Chinese Academy of Sciences) in cooperation with the Aalborg University, putting in evidence main defects and fracture causes. Finite element simulations of the modified hydroforming process using a movable inferior plate were performed at the Centre of Excellence for Mechanical Computation (Polytechnic of Bari), with the aim of evaluating critical strain values and their location, strain paths, load curves and stress maps were analysed. Specimens with proper geometrical shape were designed to avoid possible ruptures and to reduce material thinning in the critical regions.