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。     

基于Matlab的芯轴最小弯曲半径计算

在薄壁管有芯NC绕弯成形过程中,若弯曲半径过小则芯轴块间易发生碰撞干涉,而最小半径受限于芯轴连接方式和结构参数.通过分析常用芯轴结构特点和发生芯轴块碰撞干涉的位置,关于芯轴直径、球头节个数、球头节间距和芯轴块厚度建立了芯轴最小弯曲半径的解析模型.并采用Matlab工具求解方程得到芯轴的最小弯曲半径,为芯轴的设计和弯曲工艺提供了理论依据.     

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。     

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.     

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。     

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…     

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。     

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。     

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.     

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...     

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。     

Multiple instability-constrained tube bending limits

Understanding the bending limits is critical to extract the forming potential and to achieve precision tube bending. The most challenging task is the development of the tube bending limits in the presence of unequal deformation induced multiple instabilities and multi-factor coupling effects. Using analytical and 3D-FE methods as well as experiments, a comprehensive map of the tube bending limits during rotary draw bending is provided under a wide range of tube sizes, material types and processing parameters. The major results show: (1) For each instability, the intrinsic factors (tube geometrical parameters, D and t, and mechanical properties, m) dependent bending limits are clarified, and evident interactive or even conflicting effects are observed. (2) Under mandrel bending, the significant effects of the intrinsic factors on the wrinkling limit are reduced, the neglected effects of D/t on the thinning limit are magnified; the significant influences of D/t on the flattening limit even become contrary, and the effects of m on wrinkling and thinning limit are opposite to that on the flattening limit. (3) Taking D/t as the basic design parameter, a conceptual multiple defect-constrained bending limit diagram (BLD) is constructed, and a knowledge-based stepwise method for determining and improving tube bending limits is proposed, considering coupling effects of multiple forming parameters, e.g., intrinsic factors, tooling/processing parameters and uncertainties. (4) The method is experimentally verified by several practical bending scenarios for different kinds of tubular materials with extreme size.     

基于有限元模拟的数控弯管过程轴力和弯矩的分析计算

获取管材数控弯曲过程中的轴力和弯矩,有助于对成形机理的了解和后续的回弹分析,以及为选择设备和设计模具提供重要依据。提出了基于三维有限元模拟的数控弯管过程中轴力和弯矩的求解方法,详细阐述了其实现过程。采用该方法,分析了轴力和弯矩随弯曲角的变化特征以及工艺和材料参数对轴力和弯矩的影响规律:随着弯曲过程的进行,塑性变形区的轴力变化不大,弯矩呈指数关系变化,而弯曲变形区刚性端的轴力几乎线性递增,弯矩类似于阻尼正弦曲线变化;弯曲速度和材料强度系数的增大以及弯曲半径和硬化指数的减小会引起轴力和弯矩的增加。文中提出的方法也可推广应用于板材、其他型材和管材的弯曲。     

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。     

Experimental study of oil-filled high-speed spin forming micro-groove fin-inside tubes

This paper presents an oil-filled high-speed spinning process of manufacturing micro-groove fin-inside tubes. In spinning, a high-pressure oil-film, which squeezes the tube outer-wall, is formed as the spinning speed increases. A floating mandrel extrudes the tube inside wall to form the micro-grooves/fins continuously. By experiments of spinning micro-groove fin-inside tubes, this paper analyzes the influences of each process parameter on the formation quality, and optimizes each parameter. The experimental results show that the dynamic pressure can significantly improve the stability of spinning and the quality of finished surface; the minimum thickness of oil-film is decided by the spinning speed and the oil viscosity directly. In the case of full oil dynamic lubrication, there is no obvious scrape on tube surfaces. The main factors affecting the groove depth and the surface roughness are the ratio (α) of the wall thickness of the tube before drawing to the finished one, the material plasticity, the ratio (β) of drawing to spinning, the spinning speed (n), and lubricating state, etc. The axial drawing force mainly depends on the friction between the floating mandrel and the tube internal wall, the friction between the reducing mold and the outer surface, and plastic deformation resistance in the reducing mold area and spinning area as well.     

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.     

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.     

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.     

微小型薄壁内沟槽铜管旋压缩径数值模拟

文章以有限元分析软件MSC.Marc为平台,建立了微小型薄壁内沟槽铜管钢球高速旋压缩径成形的三维弹塑性有限元模型,对缩径过程的变形机理、应力应变分布和受载情况进行了分析;同时,进行了成形过程实验研究。模拟与实验结果表明,沟槽底部的等效应力应变远大于齿形和沟槽管外表面,钢球与沟槽管接触区受三向压应力作用;等效应变沿轴向呈分层分布,沿周向呈间隔分布;轴向进给速度过大,沟槽管容易出现扭曲变形,轴向拉拔力和钢球承受载荷也相应增大。模拟结果揭示的规律与实验结果相一致。该研究有助于改进缩径工艺,提高加工效率。     

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。