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。     

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.     

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...     

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.     

胀形对2219铝合金环形件淬火残余应力的影响

利用ABAQUS有限元软件对2219铝合金环形件淬火过程及后续胀形过程中径向截面上残余应力的分布进行数值模拟,研究了胀形量对淬火残余应力消减率的影响。结果表明:淬火后环件的径向应力在上下端面呈压应力,在-106 MPa左右,在芯部应力值较小;周向应力和轴向应力均呈外部压应力、芯部拉应力的应力分布状态。胀形对环件的径向应力、周向应力和轴向应力均有显著的消减效果。胀形量在0.25%~4.00%范围内增加时,环形件的残余应力减小,周向应力和轴向应力的消减率都增大并趋于定值,且周向应力消减率的增大速度比轴向应力消减率的增大速度快。当胀形量<3%时,周向应力的消减率大于轴向应力的消减率,当胀形量>3%时,周向应力的消减率略小于轴向应力的消减率;当胀形量>2%时,周向应力和轴向应力的平均消减率>80%,环件的淬火残余应力得到很好的消减。     

Forming limit diagrams of tubular materials by bulge tests

This study uses bulge tests to establish the forming limit diagram (FLD) of tubular material AA6011. A self-designed bulge forming apparatus of fixed bulge length and a hydraulic test machine with axial feeding are used to carry out the bulge tests. Loading paths corresponding to the strain paths with a constant strain ratio at the pole of the bulging tube are determined by FE simulations linked with a self-compiled subroutine and are used to control the internal pressure and axial feeding punch of the test machine. After bulge tests, the major and minor strains of the grids beside the bursting line on the tube surface are measured to construct the forming limit diagram of the tubes. Furthermore, Swift's diffused necking criterion and Hill's localized necking criterion associated with Hill's non-quadratic yield function are adopted to derive the critical principal strains at the onset of plastic instability. The critical major and minor strains are plotted to construct the forming limit curve (FLC). The effects of the exponent in the Hill's non-quadratic yield function and the normal anisotropy of the material on the yield locus and FLC are discussed. Tensile tests are used to determine the anisotropic values in different directions with respect to the tube axis and the K and n values of the flow stress of the tubular material. The analytical FLCs using the n values obtained by tensile tests and bulge tests are compared with the forming limits from the forming limit experiments.     

双层管内压弯曲过程轴向应力分析

双层管内压弯曲方法为获得大直径超薄弯管提供了可行的途径,文章对该方法避免内层管起皱的机理进行研究。内压在双层管轴向产生的附加拉应力,可降低弯曲内侧轴向压应力,有助于预防起皱。采用弹性理论,得到双层直管状态下附加轴向拉应力表达式,并对理论模型进行验证。通过数值模拟,分析了弯曲过程中支撑内压、外层管厚度,对内层超薄管起皱和轴向应力的影响规律。理论分析结果表明,双层管极限支撑内压,会随外层壁厚的增加而显著提高,因此对于厚度比较大的双层管,可以通过采用较大的支撑内压,提高附加轴向拉应力的方法避免起皱。模拟结果表明,随着外层管厚度增加,外层管弯曲时不易发生失稳起皱,同时弯管内侧轴向压应力绝对值降低。支撑内压越高,内外层界面贴合越紧密,内层管在承受轴向压应力时,其稳定性越高。     

A simple experimental tooling with internal pressure source used for evaluation of material formability in tube hydroforming

Material properties have powerful impact on the tube hydroforming (THF) process and the quality of the deformed tube, so it is important to select proper materials and evaluate the material formability prior to conducting the process. A simplified and applied tooling, which has no use for any external hydraulic pressure source but internal one, was designed for charactering the material formability in THF. A pressurized-fluid supplier is automatically established to provide the internal pressure and axial load synchronously required for THF, and the ratio of the two loads is achieved by proper design of the supplier. As a stand-alone hydraulic bulging fixture, the tooling can be worked on a conventional press, even on a single action press. Free bulge forming (FBF), bulge forming with axial loading (BFAL), free and restrained bulge forming (free and fixed ends) can be fulfilled by the tooling, and furthermore, bulge forming with proportional loading to some extend can be realized. Comparative bulge forming experiments under various forming conditions were carried out with the tooling to validate this project and the results suggest that restrained conditions on the tube ends highly affect the FBF, while the ratio of the two loads dominates the BFAL.     

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。     

Deformation characteristics during Y-shaped tube hydroforming of 6061 aluminum alloy

To manufacture lightweight tube components for aerospace oil circuit systems, an experiment was run to investigate the deformation characteristics on Y-shaped tube hydroforming of 6061 aluminum alloy. Both strain state and metallurgical structure indicate that there are four kinds of prevailing defects during Y-shaped tube hydroforming: bursting, lack of cylindricity, wrinkling, and thinning due to the poor plastic property of 6061 aluminum alloy. The danger of bursting prevails at the early stage of the operation as a result of excessively high internal pressure. In contrast, wrinkling prevails after the middle stage of the operation as a result of excessively axial feeding and cannot be eliminated during subsequent deformation. Lack of cylindricity is mainly because of insufficient axial feeding and internal pressure but can be eliminated by increasing internal pressure. Elongation and compression deformations are originated on protrusion and main pipe of Y-shape tube respectively all the way through the bulging process. Consequently, minimum and maximum thicknesses are at the top of protrusion and the bottom of Y-shape tube respectively, which induces a V-shape borderline of thickness distribution. According to the excessive plastic deformation, microstructure evolution is originated. Crystal grain of protrusion is elongated and its grain size is about 150 μm. In contrast, crystal grain of the middle zone of main tube is refined greatly, which grain size is 50 μm, decreased by 75%. These are useful to improve the component.     

Study on the Formability and Deformation Behavior of AZ31B Tube at Elevated Temperature by Tube Bulging Test

Internal high pressure forming of tube is widely used to form complex tubular part with different cross sections and curved axis. The ability of tube to undergo expansion deformation is crucial for the forming process. To evaluate the formability of AZ31B extruded tube, bulging test was carried out at different temperatures from RT up to 480 °C. Bursting pressure and maximum expansion ratio (MER) of the tube were obtained. The fracture surface after bursting was analyzed and compared with that obtained by tensile test along axial direction. Hardness changes in different positions along axial direction were also measured. Results show that the MER value remain almost unchanged from RT to 100 °C. In the temperature interval between 100 and 480 °C, an oblique N model can be used to describe the variation of MER value. The first peak and the bottom MER value occurred at 160 and 330 °C, respectively, and about 30.3% expansion ratio was reached at 480 °C. The bursting pressure decreased almost linearly as testing temperature increased. The fracture mode also changed from intercrystalline fracture to gliding fracture. However, burnt structure happened when the forming temperature was about 480 °C. The hardness value of the tube decreased significantly after the bulging test.     

Deformation behavior ofA6063 tube with initial thickness deviation in free hydraulic bulging

Experiment on seamless tubes of aluminum alloy A6063 with initial thickness deviation of 0-20% was conducted through a free hydraulic bulging with tube ends free. The influence of initial thickness deviation on the cross-section profile, thickness distribution, maximum internal pressure and maximum radial expansion was investigated. FEM simulation was also performed in order to examine and help explaining the experimental results. The results indicate that the internal pressure and maximum internal pressure appear to be little influenced by the initial thickness deviation, and that the cross-section profile of the bulged tube changes diversely and can not be a perfect circle. The results also suggest that the increase in initial thickness deviation may lead to a remarkable decrease in maximum radial expansion, and a rapid increase in thickness deviation and the center eccentricity of the inner and outer profiles.     

Effect of tube size on electromagnetic tube bulging

The commercial finite code ANSYS was employed for the simulation of the electromagnetic tube bulging process. The finite element model and boundary conditions were thoroughly discussed. ANSYS/EMAG was used to model the time varying electromagnetic field in order to obtain the radial and axial magnetic pressure acting on the tube, The magnetic pressure was then used as boundary conditions to model the high velocity deformation of various length tube with ANSYS/LSDYNA. The time space distribution of magnetic pressure on various length tubes was presented. Effect of tube size on the distribution of radial magnetic pressure and axial magnetic pressure and high velocity deformafion were discussed. According to the radial magnetic pressure ratio of tube end to tube center and corresponding dimensionless length ratio of tube to coil, the free electromagnetic tube bulging was studied in classification. The calculated results show good agreements with practice.     

钻杆接头超声检测方法研究

钻杆接头形状特殊，其厚度直径比大，形状复杂且品种多样，超声探伤难度大。研究了对钻杆接头轴向、周向和斜面部分进行全覆盖的超声波扫查方法，设计了专用的轴向、周向探头组。将各组探头安装在探头架上，对带有人工缺陷的钻杆接头进行了检测。结果表明，该特殊设计的扫查方式和探头能有效检出试件周向和轴向缺陷。     

螺杆钻具双等壁厚金属定子外高压成形方法研究

为了解决页岩气开采用螺杆钻具双等壁厚定子内螺旋曲面难加工的问题,建立双等壁厚定子的外高压成形数值模拟模型,研究管坯几何尺寸、液压力大小和回弹对定子成形质量的影响规律,通过实验和三维测量验证了数值模拟模型的准确性。结果表明：管坯几何尺寸与壁厚、等效塑性应变、位移、残余应力和间隙值成正比;成形液压力达到150 MPa及以上对等效塑性应变、壁厚几乎没有影响;定子胀型区域的回弹量大于过渡区域和接触区域;当成形液压力为210 MPa,管坯内径为88 mm,定子成形质量最优。     

摩擦因数对轴对称零件冷挤压过程的影响

冷挤压件强度高、刚性好、生产率高,在装备制造业和液压系统中得到了广泛的应用。利用ANSYS软件对轴对称零件冷挤压过程进行了分析,得到了不同摩擦因数下的轴向、径向和周向应力图,对挤压应力的模拟数值进行了分析和拟合,利用最小二乘法对函数进行了逼近。结果表明:轴向拉伸应力,径向拉伸应力和圆周拉伸应力值分布在一条直线上,值随摩擦因数的增加而增加,轴向压应力、径向压应力和圆周压应力近似分布在二次曲线上,对生产具有重要的理论指导意义。     

聚氨酯橡胶硬度对薄壁三通管内高压成形的影响

以外径为Φ24 mm、壁厚为1.5 mm、长度为120 mm的H85黄铜管为例,以壁厚增减量不超过30％为合格品作为前提,以生成最大支管胀形高度的橡胶硬度为最佳参数,结合胀形实验和有限元仿真共同分析了60～90 HA范围内7种不同硬度的聚氨酯橡胶棒对等径三通管成形质量的影响.研究结果表明:随着橡胶硬度的逐渐增大,支管胀...     

An investigation of cold extruding hollow flanged parts from sheet metals

Hole flanging with cold extrusion can avoid necking or fracture as encountered in conventional sheet metal-forming operations. Substantial flange height and lip thickness can be achieved with flange extrusion because the forming load is compressive. Using a hydraulic press, flange extrusions of 5 and 10 mm inner diameters were produced in pieces of cup-shaped galvanized steel, as well as aluminum 5052 workpieces with a thickness of 0.8 mm, both of which had a pre-hole on the cup bottom. As the punch load was exerted on the cup rim, a clamping force was applied to suppress dilation on the cup bottom.The experiments showed that with sufficient clamping force, significant flange height could be extruded. The utmost extruded flange of 5 mm i.d. was 6 times larger than that drawn from the conventional method, whereas that of 10 mm i.d. was 3.8 times larger than that drawn from the conventional method. However, no flange was extruded and buckling occurred on the cup bottom when the clamping force was insufficient. The experiments confirmed the results predicted by the FE simulation. For a selected flange inner diameter, the ratio of the extruded flange height to the increase in cup bottom thickness was directly related to the normalized clamping pressure, i.e. the ratio of clamping pressure to workpiece yield strength. Therefore, both the application of a larger clamping force or the use of low-strength workpiece materials facilitated the extrusion of flange while suppressing the dilation of the cup bottom. Flange extrusions with a larger diameter correspond to a smaller extrusion ratio or reduction of area. Experiments showed that a significant flange height could be extruded with a 10 mm inner diameter for both galvanized-steel and aluminum 5052, while results for extrusions with a 5 mm inner diameter were unfavorable when using galvanized-steel. High-strength materials and a high extrusion ratio required greater clamping force for the flange extrusion process, and consequently caused excessive forming load on the forming dies as well as on the hydraulic press, thus rendering the process less effective.     

过渡区参数对TRB管液压胀形性能的影响及预测

建立了不同过渡区参数的TRB(Tailor-Rolled Blank)管液压胀形有限元模型,提出了一种离散不规则过渡区的新方法,研究了TRB管过渡曲线、过渡区长度和厚度差对胀形性能的影响规律。针对TRB管液压胀形,进行了正交设计,以数值模拟结果为基础,建立了BP神经网络预测模型,并将预测结果与数值模拟结果进行对比分析,验证了预测结果的精度。结果表明:各参数对胀形性能影响的区域不同,但都对最大成形高度影响显著,极差最大达6.47 mm,最小为2.88 mm;凹弧型过渡曲线的成形性能最差,最大的成形高度差为2.88 mm;增大过渡区长度有利于胀形,随厚度差增加,成形性能快速下降,其中厚侧成形高度差值达8.22 mm。单组预测值在误差范围内,预测模型能用于预测其他过渡区参数组合的TRB管胀形。     

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