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针对自由推压缩径管坯弯曲疲劳寿命降低以及缩径时出现端部轴向开裂的问题,通过分析自由推压缩径的变形过程,揭示出缩径后已变形区内、外表面层存在较大的残余应力。使用有限元软件ABAQUS模拟了管坯的3道次自由推压缩径过程,给出已变形区内轴向、周向及径向残余应力沿长度方向、壁厚方向的分布规律,并分析了摩擦因数、缩径凹模出口圆角半径、缩径次数以及管坯的初始壁厚对缩径后残余应力的影响。对管坯进行了3道次缩径试验,实测了几何参量的变化,实测结果与有限元模拟值吻合,试验中发现第3次缩径时管坯出现了轴向开裂现象,证明了管坯内的周向残余拉应力值大于材料的强度极限。 相似文献
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《锻压技术》2020,(7)
采用有限元模拟与试验方法,分析了300 MW Mn18Cr18N钢护环液压缩径时的受力状态和变形规律。研究表明,液压缩径过程中,环坯内壁首先进入塑性变形状态,随着外压的逐渐升高,逐步向外壁扩展。变形过程中,环坯内壁、中壁和外壁变形相互协调。环坯内壁的等效应变和等效应力均始终大于外壁。模具锥角是影响环坯缩径形状的重要因素。由于模具锥角的改变,使得环坯端部受到的径向压力分量Fr和轴向压力分量Fz随之改变。当模具锥角较小时,径向压力分量Fr要明显大于轴向压力分量Fz,这导致采用小角度锥角的模具时,环坯缩径后往往呈现鼓肚形,当模具锥角较大时,轴向压力分量Fz将大于径向压力分量Fr,因此,采用大角度锥角的模具时,环坯缩径后呈现喇叭口形。通过数值模拟和试验验证的手段得出,当模具锥角在50°左右时,环坯可以获得较好的液压缩径效果。 相似文献
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为解决某型飞机拉杆缩径端部直接攻螺纹的问题,首次提出了5A02薄壁铝合金管端热挤压缩径增厚成形方法,设计并制造了成形模具。研究了增厚区直段尺寸、模具肩部长度与模具锥角对薄壁管热挤压缩径增厚行为的影响,并优化了成形工艺路径。试验结果表明:增厚区直段长度和外径过大易导致直段部分失稳起皱;模具肩部过长,材料易在支撑区产生堆积且易出现失稳屈曲,在满足管材可预热的条件下,模具肩部长度应越短越好;采用模具锥角为12°和16°的凹模单道次热挤压成形时,位于缩径区域的管材易出现起皱,且增厚区径向增厚不明显;采用先大锥角后小锥角两道次热挤压成形后,成形件缩径段径向尺寸由1. 00增至4. 06 mm,增厚率为306%,成形效果良好。 相似文献
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应用金属塑性成形理论推导出了筒形件锥形凹模缩口成形中作用于毛坯壁上的最小轴向应力的锥形凹模锥角表达式 ,并分析了摩擦因数对锥形凹模锥角的影响。 相似文献
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介绍了轻型车后桥常用的桥管结构,叙述了桥管缩径变形的特点、变形程度和缩口区壁厚的变化,计算管坯尺寸和缩径力并介绍了缩径模结构。 相似文献
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叙述了缩口变形特点,阐述了缩口变形程度及缩口区壁厚变化,对管坯尺寸及缩口力进行了计算,介绍了铜合金连接管缩口模具结构及凹模的加工技术要求。 相似文献
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C. Yang T. WenL.T. Liu S. ZhangH. Wang 《Journal of Materials Processing Technology》2014,214(11):2461-2467
Extending incremental forming technology into the production of tubular parts has promising prospects; however, fundamental rules of the approach have not yet been fully revealed and knowledge on the technology is lacking. This paper is focused on the dieless incremental hole-flanging of thin-walled tube for producing branched tubing. 316L stainless steel tubes with an outer diameter of 38 mm and thickness of 0.5 mm were used for the experiment and numerical simulations. Considering the uncertainty of initial curl direction of the tube wall at the extrados, where buckling is also prone to occur due to the excessive axial pressure during the forming course, an improved bar tool with a conical surface was proposed. Estimation of the precut hole size and processing route planning were discussed based on the designed branching. Force and deformation behavior along with the defects in the process, which are quite different from those in conventional incremental sheet forming, were summarized. The results prove that it is feasible to produce specific tubular parts by means of incremental forming with obvious flexibility, agility, and expandability. 相似文献
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Technology of sheet hydroforming with a movable female die 总被引:2,自引:0,他引:2
Shi-Hong Zhang Li-Xin Zhou Zhong-Tang Wang Yi Xu 《International Journal of Machine Tools and Manufacture》2003,43(8):781-785
An improved sheet hydroforming process is proposed and investigated experimentally and numerically. A movable female die keeps in contact with the deformed area of the sheet blank so that further deformation of the deformed area is restricted. Under the sealing, the sheet blank under the flange can be drawn in. So the hydroformed part has less thinning than the hydrobulge formed part only, and the limit drawing ratio of the sheet can be remarkably improved. This process is especially suitable for forming of small batch production of sheet metal parts with complicated shapes. The female die can be replaced with other female die of various shapes, and can also be made of very cheap materials such as plaster and hard wood instead of metal when the part number is very small. Thus complex-shaped sheet parts can be formed with less expensive tool systems.In this paper, the hydroforming processes of part A (without a movable die) and part B (with a movable die) were investigated by experiment and by elastoplastic FEM. The effects of various process parameters on the deformation of the sheet blanks were investigated. The forming conditions affecting wrinkling and rupture have been analyzed. The effects of friction and contacting force acting on the experimental results are also discussed. 相似文献
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闭挤式精冲工艺及其成形规律 总被引:4,自引:1,他引:3
针对存在的低塑性和高厚度零件难以精冲成形问题,提出了闭挤式精冲的概念和工艺方法,并阐述了该工艺的过程、原理和特点;设计了该闭挤式精冲工艺实验模具并用该工艺在低塑性材料YL12上精冲出了φ15 mm、高13 mm的高尺寸精度和低粗糙度的圆柱形零件.最后分析了变形区材料的流动规律和产品品质与坯料的关系.结果表明:精冲件外表面的光亮带大小随外环填充率增大而增大;内表面比外表面容易形成100%光亮带;试件表面的光亮带大小还与坯料厚度和模具主、副凹模凹坑深度的匹配有较大关系. 相似文献
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Inner grooved copper tubes have attracted more and more attention in recent years. In mass production of tube–fin heat exchanger plates in ACR (air conditioning and refrigeration) industry, mechanical expansion is a key forming process which joins the fins to the tubes. During the process, the spiral grooves inside the tube with thermally efficient geometries are deformed and the tube–fin joints are influenced by the groove layer. In this paper, tube expansion forming process is studied and effect of the groove shape on forming quality is analyzed. Experiments are performed with tubes of different groove types. FE (finite element) model of the forming process is developed. Influences of the key geometry parameters, such as groove height ratio, apex and helix angle, on strength of the grooves as well as tube wall thinning are investigated. Sections of the tube–fin joints are observed and the die geometry on the joining status is examined. The results indicate that helix angle has significant effect on groove height reduction while groove height ratio is the main factor influencing the deformation resistant force; outer diameter and radius of the front part of the expanding die influence the tube–fin joining status. 相似文献
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Expansion and reduction of thin-walled tubes using a die: Experimental and theoretical investigation
B.P.P. Almeida M.L. Alves P.A.R. Rosa A.G. Brito P.A.F. Martins 《International Journal of Machine Tools and Manufacture》2006,46(12-13):1643-1652
The production of sound thin-walled tubular parts by expansion and reduction using a die is generally limited to components having geometrical features within a compact range. Basic design rules, providing the geometrical and material parameters that govern the process, are mainly derived from the accumulated experience of both manufacturers of tubular parts and suppliers of machine-tools. However, no information is generally available on the influence of interface friction on material flow and on the effect of material damage and strain path on the occurrence of fracture, wrinkling and local buckling. The aim of this paper is to refresh and extend the fundamentals of tube expansion and reduction using a die by means of a comprehensive theoretical and experimental investigation. The emphasis is focused on understanding modes of deformation and on establishing formability principles for the benefit of those who design tubular parts in daily practice. The theoretical investigation is accomplished by the utilization of virtual prototyping modelling techniques based on the finite element method and the experimental work is mainly utilized for supporting and validating the theoretical investigation. 相似文献
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加载方式对黏性介质外压缩径成形的影响 总被引:3,自引:1,他引:2
采用有限元方法分析了加载方式(即注入加载通道的直径和数量)对黏性介质外压缩径过程黏性介质压力场及坯料的失稳起皱过程中压应力变化的影响,并对有限元分析结果进行了验证。研究结果表明,注入黏性介质的加载通道直径较大、数量较多,有利于改善黏性介质压力场的分布,延缓坯料失稳的产生,提高褶皱可消除程度。 相似文献
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Molecular dynamics simulations with the Tersoff potential were used to study the response of twinned SiC nanowires under tensile and compressive strain. The critical strain of the twinned nanowires can be enhanced by twin stacking faults, and their critical strains are larger than those of perfect nanowires with the same diameters. Under axial tensile strain, the bonds of the nanowires are stretched just before failure. The failure behavior is found to depend on the twin segment thickness and the diameter of the nanowires. An atomic chain is observed for thin nanowires with small twin segment thickness under tension strain. Under axial compressive strain, the collapse of twinned SiC nanowires exhibits two different failure modes, depending on the length and diameter of the nanowires, i.e., shell buckling for short nanowires and columnar buckling for longer nanowires. 相似文献
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分析了无芯棒双模拔制变形区的应力状态,测定了单模、双模拔制的不锈钢管壁厚,实践表明,芯棒双模拔制的钢管壁厚变化小,比单模拔制减壁作用大。 相似文献
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