薄壁钢管内胀推弯成形数值模拟及实验研究

针对薄壁管材弯曲成形过程中内壁起皱、外壁拉裂等成形缺陷,采用内胀推弯工艺成形规格为Φ30mm×0.3mm的1Cr18Ni9Ti薄壁管材。有限元模拟了不同内胀压力下,薄壁管成形性能和壁厚分布,并进行了实验研究。结果表明,该工艺可以很好的解决内壁起皱、外壁拉裂等成形缺陷,对生产实践具有一定的指导意义。     

Analysis of wrinkling limit of rotary-draw bending process for thin-walled rectangular tube

The rotary-draw bending process for thin-walled rectangular tube of aluminum alloy may produce a wrinkling phenomenon if processing parameters are inappropriate, especially for tubes with thin wall and small bending radius. To predict this wrinkling rule rapidly and accurately, here, a wrinkling wave function was proposed and a wrinkling prediction model was developed based on the deformation theory of plasticity combined with the energy method, and then the minimum bending radius without the occurrence of wrinkling in the process was obtained. Furthermore, the effects of geometrical parameters and the material properties of the tube on the minimum bending radius were analyzed. The results show that larger thickness-to-width ratio (t/b) and thickness-to-height ratio (t/h) are beneficial to improve the wrinkling limit of the tube. The minimum bending radius becomes smaller with an increase in strain-hardening exponent of the tube, whereas with the strength coefficient decreasing. And the Young's modulus has little effect on the wrinkling limit. These achievements are helpful to develop the bending technique and provide a guideline in rotary-draw bending process for thin-walled rectangular aluminum alloy tube.     

Role of mandrel in NC precision bending process of thin-walled tube

The thin-walled tube NC bending process is a much complex physical process with multi-factors coupling interactive effects. The mandrel is the key to improve bending limit and to achieve high quality. In this study, one analytical model of the mandrel (including mandrel shank and balls) has been established and some reference formulas have been deduced in order to select the mandrel parameters preliminarily, i.e. mandrel diameter d, mandrel extension e, number of balls n, thickness of balls k, space length between balls p and nose radius r. The experiment has been carried out to verify the analytical model. Based on the above analysis, a 3D elastic–plastic FEM model of the NC bending process is established using the dynamic explicit FEM code ABAQUS/Explicit. Thus, the influences of mandrel on stress distribution during the bending process have been investigated, and then the role of the mandrel in the NC precision bending process such as wrinkling prevention has been revealed. The results show the following: (1) Wrinkling in the tube NC bending process is conditional on membrane biaxial compressive stress state; the smaller the difference between the biaxial membrane stresses is, the more possibility of wrinkling occurs. (2) If the mandrels of larger sizes are used, it will cause the neutral axial to move outward and the difference between the in-plane compressive stresses to become more obvious, which may increase minimum wrinkling energy and anti-wrinkling ability. But the larger mandrel sizes make outside tube over-thinning. (3) When the mandrel extension length increases, the neutral axial will move outward and the difference between the biaxial compressive stresses becomes larger, but the significance is less than that of the mandrel diameter. The excessive extension will cause tube to over thin or even crack. (4) The significance of ball number's effect on the neutral axial position and difference between biaxial compressive stresses is between ones of mandrel diameter and mandrel extension. Increasing the ball number will enhance the thinning degree and manufacturing cost. The results may help to better understanding of mandrel role on the improvement of forming limit and forming quality in the process.     

小半径薄壁管材内胀推弯成形制造工艺研究

针对薄壁小半径弯曲管生产过程中易出现的变薄、断裂、起皱等难点,运用中性层偏移理论对弯管受力与变形特点进行分析,采用内胀推弯的工艺生产1Cr18Ni9Ti薄壁小半径弯曲管,并对生产原理、工艺、模具设计作了介绍.实践结果表明,该工艺很好地解决了小半径弯管外壁减薄、断裂等问题,对生产实际具有一定的借鉴意义和参考价值.     

Effects of process parameters on numerical control bending process for large diameter thin-walled aluminum alloy tubes

Numerical control(NC) bending experiments with different process parameters were carried out for 5052O aluminum alloy tubes with outer diameter of 70 mm, wall thickness of 1.5 mm, and centerline bending radius of 105 mm. And the effects of process parameters on tube wall thinning and cross section distortion were investigated. Meanwhile, acceptable bending of the 5052O aluminum tubes was accomplished based on the above experiments. The results show that the effects of process parameters on bending process for large diameter thin-walled aluminum alloy tubes are similar to those for small diameter thin-walled tubes, but the forming quality of the large diameter thin-walled aluminum alloy tubes is much more sensitive to the process parameters and thus it is more difficult to form.     

基于显著性的薄壁铝合金管小弯曲半径数控弯曲工艺参数优化(英文)

薄壁铝合金管小弯曲半径数控弯曲是个多因素耦合、多模具约束下的复杂过程。提出以有限元模拟为基础,基于显著性的工艺参数优化方法,即采用析因因子设计分析工艺参数对成形质量,即最大壁厚减薄率和最大截面畸变变化率影响的显著性,获得影响显著的参数,即管与防皱模间间隙的最优值,并确定其他影响不显著的参数值,包括管与模具间的间隙和摩擦、芯棒伸出量和助推速度。结果应用于规格为d50mm×1mm×75mm和d70mm×1.5mm×105mm(管外径D0×管壁厚t0×弯曲半径R)的铝合金管弯曲,获得了合格的管件。     

无心弯管胎模设计

介绍了在使用无心弯管模弯曲管子的过程中存在的缺陷和采取的措施。通过采用增加弯管模具的夹紧块和镶块对毛坯的刚性约束来消除管内壁起褶的缺陷，采用固定数值法来解决管弯曲卸载后的弹性回跳的缺陷。介绍了在弯管模具设计中，前、后导向轮参数的选取方法以及根据管子的弯曲半径和弯管直径来分情况讨论其弧槽曲线的确定方法，避免在弯曲过程中弯管发生畸变，为设计弯管模具提供理论依据。     

Numerical and experimental study on expansion forming of inner grooved tube

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.     

A modified Johnson–Cook model for NC warm bending of large diameter thin-walled Ti–6Al–4V tube in wide ranges of strain rates and temperatures

Numerical control (NC) warm bending is a proven strategy to form the large diameter thin-walled (LDTW) Ti–6Al–4V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti–6Al–4V tube within wide ranges of temperatures (25–600 °C) and strain rates (0.00067–0.1 s^?1). Moreover, a modified Johnson–Cook (JC) model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90%. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti–6Al–4V tubes.     

Roles of Surface Booster System on Bending of Thin-Walled Copper Tube

Thin-walled C12200 circular copper tube has been widely used in HVAC (heating, ventilation, air conditioning, and refrigeration) industry. Rotary draw bending is a versatile and precise method in forming of thin-walled copper tubes. Wall thinning and sectional fattening are the two main defects that affect tube quality in industrial applications. With traditional die settings, such as adjusting position or type of the mandrel, one factor usually decreases at the expense of increasing the other. An assistant equipment, surface booster system, has been recently developed to relieve both defects at the same time. In the present study, the role of the booster system in the bending process is investigated with finite element simulation. A basic model of copper tube rotary draw bending is established and validated by experiments. Then, cases of different sets of main parameters of the booster system are studied. The relationship between loading force, lower displacement, speed of the booster, and forming characteristics of tube is obtained based on which suggestions about process parameters settings are given. The results provide a better understanding of the role of the booster system in the improvement of forming quality.     

扁管面内绕弯成形起皱的仿真与试验分析

文章研究一种扁管的面内弯曲加工。扁管面内绕弯成形是一个受材料性能和工艺参数等诸多因素影响的复杂变形过程,在成形过程中极易产生起皱等缺陷,导致成形质量难以保证。文章针对起皱的多个影响因素进行试验设计,并建立有限元模型,对成形过程进行数值模拟。研究了各个因素对起皱的影响规律,并给出使扁管起皱较小的各因素的参数设计。研究结果对扁管面内绕弯成形过程工艺参数的选取,提供了理论依据。     

基于数值模拟的薄壁管冷弯成形工艺研究

薄壁管冷弯成形过程中最常见的缺陷有管坯内侧失稳起皱、外侧减薄破裂,为获得质量良好的某车用水冷管接头冷弯件,采用数值模拟方法分别研究了芯棒伸出量e、防皱块与管坯间隙c以及芯棒直径d等工艺参数对冷弯成形质量的影响.结果表明:随着芯棒伸出量e增大,管坯外侧壁厚减薄率γ增大,管坯内侧起皱趋势先减小再增大;随着管坯与防皱块的间隙...     

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。     

铝合金大口径薄壁管数控弯曲实验研究

铝合金大口径薄壁管小弯曲半径数控弯曲成形过程中更容易发生起皱、截面畸变和壁厚减薄等缺陷。文章根据成形缺陷产生的原因对弯管模具结构和设备装置进行了改进,包括模具内锁设计、紧凑型柔性芯棒、模具并紧杆和长内衬顶推。在此基础上,采用实验研究方法,对Φ70mm×1.5mm×105mm(外径×壁厚×弯曲半径)的大口径薄壁铝合金管数控弯曲成形质量及应变规律进行了分析,并研究了顶推装置在大口径薄壁铝合金管数控弯曲成形中的效用。     

薄壁小半径弯管与中压内胀成形工艺

针对薄壁小半径弯曲管生产过程中易出现的交薄、断裂、起皱等难点,吸收了当前国外先进技术--管材内高压成形的优点,在充分考虑国内高压成形技术不足的基础上,改用中压成形弯管的新工艺,很大程度上提升了薄壁小半径弯曲管生产的外观质量.这一工艺特别适用于厨房、卫浴等领域中水龙头的前期工序生产,具有较大的实用意义.     

椭球封头冷拉深缺陷分析

起皱、局部壁厚过度减薄是封头冷拉深常见的缺陷,严重制约着拉深封头质量、成形极限的提高以及生产过程的正常进行。文章采用ABAQUS软件建立椭球封头拉深成形的三维有限元模型,并验证该模型的可靠性;发现了椭球封头拉深过程中易于出现的悬空区起皱和过度减薄两种缺陷,并分析了其形成机理,同时研究了工艺参数对缺陷产生的影响规律。研究发现,悬空区承受双向压应力区域的范围与周向压应力的大小对起皱影响明显,而切向拉应力对壁厚的减薄影响显著。增大压边力、摩擦系数和减小凹模圆角半径,可减小悬空区承受双向压应力区域的面积和周向压应力值,进而减小起皱的倾向,而过大的压边力、摩擦系数和过小的凹模圆角半径,则导致悬空区切向拉应力过大,可加剧壁厚的减薄。     

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。     

薄壁管小弯曲半径数控绕弯成形芯模效用的实验研究

薄壁管数控弯曲中带芯头的柔性芯模是提高薄壁管件成形极限和成形精度的关键因素。文章建立了绕弯过程芯模(包括芯棒和芯头)的理论解析模型,包括了芯模直径d、芯棒伸出量e、芯头个数n、芯头厚度k、芯棒/芯头孔心间距p及芯棒圆角半径r等参数的选取公式的推导,获得了不同弯曲规格下的芯模参数取值范围,验证了解析模型的合理性;实验研究了芯模参数对管材失稳起皱、壁厚减薄和截面畸变的影响规律。通过分段抽芯的工艺方法,完成了38mm×1mm×38mm(1D)高难度不锈钢管件的弯曲。     

圆管压扁-压弯连续变形过程有限元模型的建立及截面畸变研究

为研究圆管压扁-压弯连续变形过程中的截面畸变,基于有限元软件ABAQUS建立了该过程的三维有限元模型,并实验验证了其可靠性。分析了圆管压扁过程中的截面变化规律及弯曲下模圆角半径、模具与管材间的摩擦系数对成形过程截面畸变的影响。结果表明,圆管压扁过程中形成扁管直壁部分的材料在外层周向压应力、内层周向拉应力的合力作用下出现塌陷。形成扁管圆弧部分的材料在外层周向拉应力、内层周向压应力的合力作用下出现扁化。在无芯轴、有芯轴压扁成形前期,圆弧部分均出现扁化,且无芯轴压扁成形中期,直壁部分出现塌陷。但有芯轴压扁过程中芯轴的支撑作用不但抑制了直壁部分的塌陷,而且还矫正了成形后期圆弧部分的扁化。由于圆管压扁-压弯过程中模具与管材的接触区域始终不大,因此成形过程中弯曲下模圆角半径,及模具与管材间的摩擦系数,对截面畸变影响不显著。     

芯管间隙对JAC590Y高强钢矩形管绕弯成形质量的影响

为了判断JAC590Y高强钢矩形管180°绕弯时芯棒与管坯之间的间隙大小对弯管成形质量的影响,基于Dynaform软件对4种芯管间隙下JAC590Y高强钢薄壁矩形管的绕弯成形分别进行了模拟,得出了不同芯管间隙值下弯管的主要畸变参数。结果表明:在芯管间隙处于一定范围内时,弯管的宽度扩展率受芯管间隙值的影响很小,而中面高度缩减率会随着芯管间隙的增大而变大;弯管上最大的壁厚减薄率出现于紧邻距芯棒最远芯头的横截面上顶板与两侧板的交角处,选取较大的芯管间隙有助于降低弯管的最大壁厚减薄率;JAC590Y高强钢薄壁矩形管180°绕弯成形时芯管间隙率的合理范围为0. 01~0. 025。