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。     

芯棒伸出量对0Cr21Ni6Mn9N不锈钢管数控弯曲成形质量的影响

利用有限元模拟软件ABAQUS建立了0Cr21Ni6Mn9N不锈钢管材的数据弯曲、抽芯及回弹全过程有限元模型,并对其可靠性进行了验证;研究了芯棒伸出量e对横截面畸变、壁厚变化、起皱趋势和回弹角的影响规律。结果表明,随着芯棒伸出量的增大,管材横截面畸变率和回弹角减小,当芯棒伸出量大于2.5 mm时,管材出现"鹅头"现象;外侧壁厚减薄率随着芯棒伸出量的增大而增大,内侧壁厚增厚率随着芯棒伸出量的增大而有所减小,但减小趋势不明显;弯管内侧起皱趋势随着芯棒伸出量的增大先减小后增大;最后获得了合适的芯棒伸出量范围为1.5~2 mm。     

模具间隙对薄壁管绕弯成形的影响规律

详细分析了薄壁管绕弯成形过程及其变形特点,基于有限元法对绕弯成形模具芯棒与管坯间隙,压块与管坯间隙,防皱块与管坯间隙以及弯曲凹模与管坯间隙等4个因素与薄壁管成形质量、回弹量的影响显著程度进行了四因素三水平的正交试验分析。结果表明：芯棒与管坯的间隙对成形后薄壁管壁厚及回弹的影响最显著,弯曲凹模与管坯间隙对回弹影响也较显著。     

薄壁管数控绕弯成形壁厚减薄的主要影响因素研究

针对薄壁圆管数控绕弯精确成形过程在多因素作用下容易出现外侧壁厚减薄的物理过程,基于Dynaform建立了数控绕弯三维有限元模型并验证了模型的可靠性.研究了材料参数、顶推装置、弯曲角度、相对弯曲半径、芯棒伸出量、芯头个数对管材数控绕弯成形外侧壁厚减薄的影响规律.结果表明:LF2M铝合金比1Cr18 Ni9Ti不锈钢减薄严重,但是截面畸变程度小于1Cr18Ni9Ti;相比尾部没有安装顶推装置的管坯,加装了顶推的弯管壁厚减薄率降低了大约5％;随着弯曲角度和弯曲半径的增大,减薄率也逐渐增大;芯棒伸长量和芯头个数也是影响减薄的重要因素,芯棒伸出越多,弯管壁厚减薄率越大,增加芯头也会增大减薄率.     

管坯结构对小半径薄壁弯头内胀冷推弯成形的影响

针对Ф40 mm×1 mm铝合金管材且弯曲半径为1倍管径的L形弯管成形,以数值模拟技术为平台,建立了内胀冷推弯有限元模型,研究了管坯端头不同补偿角度对弯管成形质量的影响。结果表明:补偿角度过大时,弯管内侧易产生压缩起皱,降低补偿角度则能有效防止弯管产生压缩起皱,且随着角度的降低,成形弯管减薄区域不断扩大,同时弯管弯曲内侧有效长度不断降低,易造成成形不足;补偿角度为45°时,起皱现象消失,外侧壁厚最大减薄率为7. 1%,整体成形质量较佳。以45°补偿角度进行内胀冷推弯试验,成形出符合要求的1倍弯曲半径弯管,且试验结果与模拟结果整体较吻合。     

大径厚比不锈钢弯管内胀冷推弯成形数值模拟及实验研究北大核心CSCD

通过对规格为Φ70 mm×2 mm的不锈钢管进行内胀冷推弯成形数值模拟和实验研究,讨论了管坯结构、聚氨酯填块填充方式、反推力大小及润滑方式对弯曲角度为118.5°的大径厚比不锈钢弯管成形质量的影响。结果表明:管坯采用补偿端头结构可有效抑制弯曲内侧的材料堆积增厚,降低弯曲内侧的起皱风险;与冲头相接触的聚氨酯填块厚度为30 mm、其余聚氨酯填块厚度为15 mm时,填块的支撑效果更好且更有利于力的传递;反推力会影响内压及材料流动,反推力过小时,管坯内压不足,弯曲内侧不贴模且出现起皱现象,反推力过大时,摩擦力也相应增大,不利于内侧材料流动,会导致材料堆积引起管壁弯曲内侧起皱;弯管成形时摩擦力直接影响材料流动,采用分区域润滑的方式可改善管壁弯曲内侧的材料流动,有效减小管壁弯曲内侧的起皱风险,并有利于提高直端推出量。     

间隙对0Cr21Ni6Mn9N不锈钢管材数控弯曲截面质量的影响

基于ABAQUS/Explicit,建立了0Cr21Ni6Mn9N(21-6-9)不锈钢管材数控弯曲成形的三维弹塑性有限元模型,模拟分析了管模间隙对管材弯曲成形截面质量的影响规律。结果表明:壁厚减薄和截面畸变程度在中间部位严重,在弯曲平面和初始弯曲平面附近较小;随着芯棒与管材间隙的增大,壁厚减薄率减小,截面畸变程度先减小后增大;随着弯曲模与管材间隙的增大,壁厚减薄率和截面畸变程度增大;随着防皱块与管材间隙的增大,壁厚减薄率和截面畸变程度先减小后基本不变;压块与管材间隙对弯管截面质量的影响不显著。     

工艺参数对薄壁矩形管绕弯成形失稳起皱影响的显著性分析

基于三维有限元软件ABAQUS/Explicit,采用所建立的薄壁矩形管绕弯成形过程三维弹塑性有限元模型,结合虚拟正交试验,模拟研究了工艺参数对绕弯成形过程中失稳起皱影响的显著性。结果表明:弯曲半径、芯头个数、芯模与管坯间隙和防皱块与管坯间隙对薄壁矩形管绕弯成形过程中的失稳起皱影响较为显著。     

基于BP神经网络的管材数控弯曲多参数优化方法研究

针对管材数控弯曲成形过程中多工艺参数耦合的特点,基于BP神经网络,结合多目标优化算法研究了弯曲成形工艺参数的优化方法。采用ABAQUS对管材数控弯曲过程进行有限元仿真,并实验验证了结果的准确性。基于MATLAB平台,以芯棒直径、芯棒伸出量、防皱块与管材间摩擦系数等主要工艺参数为优化对象,以外壁减薄率、内壁增厚率(起皱)为优化目标,通过验证的数值模型获得样本数据,利用BP神经网络建立了优化对象和优化目标之间的映射关系,并采用多目标优化算法进行寻优求解,最后通过数值仿真实验验证了优化方法的准确性。结果表明:薄壁管数控弯曲有限元数值模拟结果与实验数据吻合较好,可以为神经网络提供准确可靠的训练样本;BP神经网络结合多目标优化算法可以有效地对弯曲工艺参数进行优化;优化的工艺参数有效地改善了弯曲管材内侧起皱和外侧减薄。     

大径厚比不锈钢管小弯曲半径推弯成形缺陷影响因素研究

针对Φ60 mm×1 mm的1Cr18Ni9Ti薄壁管进行推弯成形数值模拟和试验,研究了其1D弯曲半径推弯成形缺陷。讨论了管坯α坡口的大小、聚氨酯填块厚度和硬度、反推力大小以及润滑方式对推弯成形缺陷的影响。结果表明,α角增大,有利于弯管内侧材料的流动,减少弯管弯曲内侧起皱的风险;聚氨酯填块的厚度小、硬度不足,易引起弯管起皱与端口畸变;当反推力F_2增大到70 MPa时,弯管与模具间的摩擦力增大,管的弯曲内侧起皱;反推力F_2减小为20 MPa时,支撑弯管的内压不足,导致弯管失稳塌陷与端口畸变;对小弯曲半径管推弯成形采用差异化润滑,能抑制起皱和端口畸变。模拟结果与试验结果较为吻合。     

薄壁管数控弯曲截面畸变的实验研究

截面畸变是薄壁管小弯曲半径数控弯曲成形容易出现的成形缺陷之一。文章采用实验法,研究了芯头个数、芯棒伸出量、弯曲角度、压块润滑状态、相对弯曲半径、材料等因素对截面畸变的影响;并提出了减小截面畸变的有效措施。结果表明,增加芯头个数与芯棒伸长量都能减小弯管的截面畸变,但两者都导致弯管壁厚减薄量增大;随着弯曲角度的增加,截面畸变越严重,相对弯曲半径越小,无芯棒与芯头支撑段弯管的截面畸变愈严重;在压块无润滑情况下,弯管的截面畸变和壁厚减薄量都小,并且在同等弯曲条件下,1Cr18Ni9Ti弯管的截面畸变小于LF2M弯管。     

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。     

Sequential multi-objective optimization of thin-walled aluminum alloy tube bending under various uncertainties

Combining the design of experiments (DOE) and three-dimensional finite element (3D-FE) method, a sequential multi-objective optimization of larger diameter thin-walled (LDTW) Al-alloy tube bending under uncertainties was proposed and implemented based on the deterministic design results. Via the fractional factorial design, the significant noise factors are obtained, viz, variations of tube properties, fluctuations of tube geometries and friction. Using the virtual Taguchi's DOE of inner and outer arrays, considering three major defects, the robust optimization of LDTW Al-alloy tube bending is achieved and validated. For the bending tools, the robust design of mandrel diameter was conducted under the fluctuations of tube properties, friction and tube geometry. For the processing parameters, considering the variations of friction, material properties and manufacture deviation of mandrel, the robust design of mandrel extension length and boosting ratio is realized.     

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.     

Effect of mandrel on cross section quality of thin-walled tube numerical controlled bending

The effect of mandrel with the structure of ball and socket on the cross section quality of thin-walled tube numerical controlled （NC） bending was studied by numerical simulation method, combined with theoretical analysis and experiment. Influencing factors of the mandrel include the count of mandrel heads, the diameter of mandrel and its position. According to the principle of NC tube bending, quality defects possibly produced in thinwalled tube NC bending process were analyzed and two parameters were proposed in order to describe the cross section quality of thin-walled tube NC bending. According to the geometrical dimension of tube and dies, the range of mandrel protrusion was derived. The finite element model of thin-walled tube NC bending was established based on the DYNAFORM platform, and key technological problems were solved. The model was verified by experiment. The effect of the number of mandrel heads, the diameter of mandrel and the protrusion length of mandrel on the cross section quality of thin-walled tube NC bending was revealed and how to choose mandrel parameters was presented.     

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。     

Effect of frictions on cross section quality of thin-walled tube NC bending

1 Introduction Thin-walled tube bending parts have been increasingly used in many industry fields such as aviation, aerospace and automobile for their easy satisfaction in light weight, high strength and low consuming. The numerical controlled(NC) rotar…     

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。