轴向补料对微型管件液压成形性能的影响

为了改善金属微型管件在液压成形过程中的成形性能,设计了一套可轴向补料的微型管件液压成形装置,来研究轴向补料对直径Φ2 mm,壁厚0.3 mm的304微型管件液压成形性能的影响。在微型管件自由胀形实验中通过采用不同加载路径来考察不同补料量对微型管件自由胀裂压力的影响规律。实验结果发现,轴向补料能显著提高微型管件的胀破压力,胀破压力的分布表现出显著的尺度效应。另外,采用GTN细观损伤模型对微型管件自由胀形试验进行数值仿真,结果表明轴向补料能够显著提高微型管件的成形能力。     

渐进冲击液压载荷下T型管的成形规律

为了进一步提高管坯的成形性能，改善传统液压胀形依赖高压源的问题，提出了一种多通管渐进冲击液压胀形方法。以T2紫铜T型管为研究对象，应用设计的胀形装置进行了冲击液压胀形实验研究，通过不同冲击液压载荷下1道次冲击液压胀形、2道次和3道次渐进冲击液压胀形结果的对比，分析了初始内压力、补料量、渐进道次对T型管支管高度、壁厚分布、支管顶部圆角半径的影响。研究结果表明：该方法可以成形出质量较好的T型管；初始内压力对T型管支管的顶部圆角和侧壁贴模性有较大的影响；各道次的初始内压力分别为10、30和32 MPa以及补料量分别为3、3和15 mm的3道次渐进冲击液压载荷下，T型管的成形质量最好。     

金属薄壁管液压胀形极限测试装置的试验研究

分析了金属薄壁管液压胀形中胀形区截面节点的应力和应变状态,分别针对轴向进给力F的作用大于或小于液压力P的作用,金属薄壁管胀形区截面节点的应变状态分别对应成形极限图的左侧和右侧应变状态,开发1套能实现胀形区截面节点不同应变状态的金属薄壁管液压胀形极限测试装置,通过示例,获得了简单加载路径下金属薄壁管液压胀形成形极限图。     

异型变径管内高压成形有限元模拟

通过建立相应的内高压成形有限元模拟模型,用Dynaform有限元分析软件进行模拟分析,研究了异型变径管成形的工艺特点、变形特征及成形参数对成形质量的影响。模拟结果表明,当变径管直径变化率较大时,自由胀形很难成形出理想成品,需采用轴向补料。采用合适的内压加载路径与轴向补料的配合方式能够显著控制起皱、破裂缺陷的产生,使较复杂的异型变径管顺利成形,成形质量较好。     

金属双层管冲击液压胀形装置设计与力学分析

为解决金属双层管液压胀形过程中设备成本较高、成形效率较低、操作工艺较复杂等问题,提出了一种基于冲压成形和液压胀形技术的复合成形方法——冲击液压胀形。首先介绍了双层管冲击液压胀形的成形原理;然后,从成型部分、轴向进给部分、控制部分和辅助部分等4个方面介绍了冲击液压胀形装置;同时分析了双层管胀形过程中的受力状态;最后采用弹塑性理论,对双层管内管和外管的应力应变关系进行了讨论,并根据双层管变形协调条件,获得了胀形内压力pi的判定依据。冲击液压胀形技术将为双层管成形技术的研究提供新的科学依据和技术支撑。     

单侧双排四通管液压胀形壁厚与补料规律研究

以单侧双排四通管液压胀形工艺为研究对象,运用数值模拟方法分析不同加载参数条件下单侧双排四通管液压胀形支管高度、壁厚分布和补料情况,得出单侧双排四通管液压胀形壁厚分布和补料的一般规律.结果表明:单侧双排四通管液压胀形以两支管外侧主管补料为主,支管间内侧主管补料很少.加载参数对支管高度和外侧主管补料影响较大,对最大、最小壁...     

铝合金防碰撞吸能管液压成形加载路径研究

针对防碰撞吸能管成形需要,提出了对铝合金6061圆管液压胀形过程的轴向进给补偿-液压力加载路径控制过程.通过数值模拟方法,采用分析软件ABAQUS 6.10对铝合金6061管材液压胀形的加载路径进行了研究.以成形件不发生起皱、破裂两种失效方式以及最终成形壁厚分布为依据,分析了不同轴向进给和液压力加载路径对成形件质量的影...     

大减径比阶梯管坯液压胀形轴向力加载方式的研究

针对以大减径比、轴向尺寸长阶梯管为管坯的液压胀形,理论确定了胀形管坯各区段的轴向应力,分析了轴向力作用位置对阶梯管坯直臂区及锥形区轴向应力状态和胀形区金属补料效果的影响。提出胀形初始轴向力同时作用于管坯端头及锥形区,仅作用于管坯端头和仅作用于锥形区3种轴向力加载方式。通过模拟阶梯管坯的胀形过程,揭示了不同轴向力加载方式对胀形管坯成形性的影响规律:胀形初始轴向力同时作用于管坯端头及锥形区时,管坯成形稳定性高,胀形区最大壁厚减薄量小,且成形合模力较仅作用于管坯端头方式低68.9%(较仅作用于锥形区方式低39.7%)。在普通液压机上试制出合格样件,验证了理论分析及模拟结果的正确性。     

碳钢/不锈钢双金属复合三通液压胀形数值模拟及试验

为研究液压胀形工艺过程中碳钢/不锈钢双金属复合三通的成形性能,利用有限元模拟软件对碳钢/不锈钢双金属复合三通的液压胀形工艺进行优化计算,分析主要工艺参数对液压胀形支管高度与壁厚均匀性的影响;根据工艺参数模拟计算的结果,对碳钢/不锈钢双金属复合三通进行了实际冷成形试验。结果表明,内压力越大、摩擦系数越小,支管高度越高;摩擦系数越小、轴向进给速度越小,壁厚均匀性越好。实际冷成形试验结果与有限元模拟结果基本吻合。     

基于GTN和韧性断裂准则的SS304微管液压胀形开裂研究

为了提高SS304微管液压成形性能,设计了一种轴向补料液压成形工艺。通过试验并结合GTN损伤模型和韧性断裂准则研究了不同补料量对微管胀破压力和胀形直径的影响规律。试验结果表明,微管胀破压力和胀形直径表现出一定的分散性,并且在0. 6～1. 5 mm范围内进行轴向进给量补料时,轴向补料方法能够显著提高微管胀破压力和胀形高度。数值模拟结果表明:GTN损伤模型和Ayada准则能较好地模拟轴向补料与胀破压力之间的关系;在0. 6～1. 5 mm范围进行轴向补料,Brozzo韧性断裂准则预测管件胀形最大直径的效果要优于其他准则。     

一种新型管材液压胀形装置的设计

开发了一种简单实用、可在单动压力机上使用的管材液压胀形装置,用于薄壁金属管材的自由胀形、轴压胀形和异形截面中空件的液压胀形.该装置不需要复杂的外部供液系统,通过增压活塞挤压缸体中液体的方式来为管材成形提供液压力和轴向力,通过设计增压缸体和控制增压活塞的行程等来实现两个载荷的合理匹配.试验表明,该装置结构简单、操作方便、工作可靠;合理的载荷匹配能显著地提高管材液压胀形的成形性能.     

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。     

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.     

加载路径对变径管内高压成形影响的模拟研究

基于Dynaform有限元模拟软件,在获得合适总轴向进给量以及最大内压力的基础上,重点探讨了轴向进给路径以及内压力加载路径对变径管内高压成形的影响。结果表明：按照前段进给速度大于后段进给速度的双线性轴向进给方式进给能得到一条最优的轴向进给路径;梯形内压加载方式的成形结果要明显优于线性内压加载方式,且当内压区间为40～60MPa时,梯形内压加载方式的成形结果达到最优化。     

Discrete layer hydroforming of three-layered tubes

Discrete layer forming proposed in this study is a hydroforming process which can selectively deform the outer tube to a desired shape without any deformation of the inner tube by piercing small holes in the inner tube. A three-layered tube is assembled from inner, middle, and outer tubes, from either similar or dissimilar materials, and deforms simultaneously when internal pressure and axial feed are applied to the tube. In special working environments, multi-layered tubes with combined material properties, high strength, and corrosion resistance are required to satisfy conflicting performance requirements. The feasibility of proposed discrete layer forming process of three-layered tube was evaluated by a tube hydroforming experiment and process analysis was performed. An optimal loading path to prevent wrinkling around holes was developed by an analytical model and was experimentally verified. The results show that the proposed discrete layer forming process can be successfully applicable to hollow forming of non-axisymmetric multilayered tubes for structural purposes.     

应用JSTAMP／NV的管材液压成形案例仿真

为有效地预测管材液压成形过程中存在的问题,比如：制件在外侧过度减薄和内侧起皱,用JSTAMP／NV对汽车副车架液压成形工艺过程进行有限元模拟分析,得出各工序的仿真结果。应用逆向求解器Hystamp仅需直接指定管坯的尺寸参数、材料和弯曲工艺参数即可自动执行弯曲仿真计算并可在几秒内获取弯曲仿真的结果;应用LS—DYNA执行预成形和液压成形工序仿真的计算,需设定液压成形工序的工艺参数,包括液压加载的曲线和方向以及轴向进给位移。JSTAMP／NV能有效模拟管材液压成形工艺过程并预测成形过程中在变形区出现的屈曲、起皱和破裂等缺陷,可以为工艺试验提供指导。     

Influence of axial feeding on the growth of circumferential thickness deviation in free hydraulic bulging

Loading paths (hereafter referred as LPs) that consist of internal pressure and axial feeding are important manufacturing conditions in tube hydroforming. Among the factors that affect LP design, friction between the forming die and tube causes the most difficulty due to its complicated characteristics. Although there is no friction, a number of issues with LP design remain. In this study, free hydraulic bulging (hereafter FHB) with internal pressure and axial feeding is investigated. In FHB, tubes are freely expended without friction. It has been shown that axial feeding affects the circumferential thickness distribution in the tube periphery. The tubes in this study are straight seamless tubes. Seamless tubes typically have predictable thickness deviations resulting from their manufacturing processes. In general, the degree of thickness deviation will increase as the tube expands. A FEM simulator is used to analyze the mechanism of the growth of thickness deviation.     

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.