大口径薄壁小弯曲半径数控弯管有限元建模和实验

针对大口径薄壁小弯曲半径管件在航空航天领域日益迫切的需求,在对数控弯曲过程的实验和理论分析基础上,选用动态显式有限元平台ABAQUS/Explicit,以50mm×1mm(外径×壁厚)系列不锈钢和铝合金大口径薄壁小弯曲半径管件为例,实现了包括弯管、抽芯、卸模回弹的完整的数控弯曲有限元模型的建立,结合实验研究对比讨论了大口径小弯曲半径管件弯曲过程建模的难点和解决方法。     

CT20钛合金薄壁管材数控冷弯成形行为研究

薄壁管材的小弯曲半径数控弯曲成形十分困难,外侧壁厚减薄是弯管成形中的加工缺陷之一,对于钛合金薄壁管尤为严重。采用模拟与实验相结合的方法,对规格为58 mm×1.5 mm的CT20钛合金管材数控弯曲成形过程中弯曲段的壁厚减薄进行了研究,得到相对弯曲半径对壁厚减薄的影响规律。结果表明,CT20钛合金管材冷弯成形时的极限相对弯曲半径(R/D)为2。     

薄壁纯钛管数控弯曲成形性能研究

研究了薄壁纯钛(CP-Ti)管在不同弯曲半径和不同材料性能下的多缺陷约束数控弯曲成形性能,通过显式/隐式三维有限元模型和实验研究了先进轻量化材料CP-Ti的成形潜力。结果表明:管材的硬化指数、厚向异性指数和杨氏模量的变化对弯曲成形性能有很大影响;与壁厚减薄和截面畸变相比,失稳起皱是抑制大直径薄壁CP-Ti管弯曲成形性能的主要缺陷。升高温度可以提高CP-Ti管的弯曲成形性能,特别是抗起皱性能。     

铝合金小弯曲半径薄壁管数控绕弯模具设计

铝合金小弯曲半径薄壁管数控绕弯成形是多模具约束、多因素影响的复杂成形过程,成形过程中极易出现起皱、破裂等成形缺陷,而模具材料和结构的合理设计对成形质量的影响至关重要。通过分析铝合金小弯曲半径薄壁管的结构特点,结合导管数控绕弯工艺过程,对模具材料选取、模具结构设计及成形仿真等关键技术问题进行了研究,最终确定了铝合金小弯曲半径薄壁管数控绕弯模具的材料、结构形式、尺寸参数,通过数控绕弯成形几何运动仿真、有限元数值模拟与工艺实验,实现了满足设计要求的铝合金小弯曲半径薄壁管数控绕弯成形,证明了小弯曲半径薄壁管数控绕弯模具的可行性,为工程化应用奠定了基础。     

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.     

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。     

薄壁管小弯曲半径数控弯曲壁厚减薄实验研究

外侧壁厚减薄是弯管成形中容易出现的加工缺陷之一,对于薄壁管小弯曲半径(R/D≤2)数控弯曲成形尤为严重.本文采用实验法,对该成形过程中弯曲段的壁厚减薄进行了深入研究,得到芯头个数、芯棒伸出量、弯曲角度、压块与管件摩擦条件、压块速度、相对弯曲半径、材料参数对壁厚减薄的影响规律.结果表明,合理增加压块与管件间的摩擦和压块速度,有助于控制壁厚减薄;1CR18Ni9Ti管变形特点不同于LF2M管,后者更易出现拉裂缺陷.     

低碳钢/铝合金双层管充液弯曲变形规律

为解决传统技术无法制造大径厚比、小弯曲半径铝合金薄壁弯管的难题,提出采用双层管充液弯曲新方法。运用数值模拟研究厚度比和内压对低碳钢/铝合金双层管充液弯曲过程中起皱行为和壁厚分布的影响。结果表明,随着厚度比的增加,起皱的现象得到缓解直至消除,内层弯管外侧减薄率逐渐减小,壁厚分布更为均匀;随着内压的增加,起皱现象逐渐延缓,内层管壁厚最大减薄率增加,因此增加厚度比和内压均有助于提高双层管弯曲成形的稳定性。通过实验成功研制出径厚比为63的铝合金薄壁弯管件,外侧最大减薄率为24%。     

带长直管的小弯曲半径薄壁弯头推弯成形实验研究

带长直管的小弯曲半径(R=1D)薄壁弯头推弯成形极易产生成形不足、失稳起皱等缺陷。通过改变摩擦系数和成形内压两种工艺参数,研究带长直管的小弯曲半径弯头推弯成形。结果表明:管材内部压力的大小对弯头成形效果影响显著,压力太小会造成管材弯曲段产生失稳起皱的现象,压力太大则易造成弯管成形不足和弯管头部破裂等缺陷;管坯外壁与模具型腔摩擦力的大小对弯头成形亦有重要影响,摩擦力过大将阻碍管坯材料沿轴向的流动,降低弯头长度。实验采用聚氨酯填料作弹性介质,二硫化钼作润滑剂,内胀推弯成形带长直管的小弯曲半径薄壁弯头,其外侧壁厚减薄量控制在安全范围之内。     

小弯曲半径薄壁纯锆U形管弯制模具的研制

薄壁纯锆U形管在弯制过程中容易产生椭圆度、回弹、划伤以及弯管内弧褶皱等现象,为了实现小弯曲半径薄壁锆管的弯制成形,根据U形管的弯制特点,并结合实际弯制经验,设计并制作了U形管的弯制模具。该弯制模具主要采用绕管方式进行弯制,U形管一端固定,另一端进行弯制。弯制试验结果表明,该弯制模具能够制作弯曲半径为50 mm和105 mm的φ25.4 mm×1.24 mm薄壁锆U形管,弯制后的U形管成形状态良好,检测结果均能满足GB 151—1999标准及设备生产工艺的要求,并能有效地保证弯管质量。     

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。     

Springback of thin-walled tube NC precision bending and its numerical simulation

The springback is one of the key factors which affect the forming quality of thin-walled tube NC precision bending. The elastic-plastic finite element method was proposed to study the springback process of thin-walled tube NC precision bending and the combination of dynamic explicit algorithm and the static implicit algorithm was proposed to solve the whole process of thin-walled tube NC precision bending. Then, the 3D elastic-plastic finite element model was established based on the DYNAFORM platform, and the model was verified to be reasonable. At last, the springback rule of thin-walled tube NC precision bending and the effect of geometry and material parameters on the springback rule of thin-walled tube NC precision bending were studied, which is useful to controlling the springback of thin-walled tube NC precision bending, and the numerical simulation method can be used to study other effect of parameters on the forming quality of thin-walled tube NC precision bending.     

基于数据库的薄壁管数控弯曲知识库的构建

针对薄壁管数控弯曲生产过程中容易出现各种质量缺陷,需要进行反复调模的问题,文章总结该领域的专家知识,并根据薄壁弯管质量标准、有限元模拟结果和实验结果等大量信息数据,采用基于数据库的技术,研究开发了薄壁管数控弯曲知识库系统。结果表明,该系统可以全程指导数控弯管实际生产过程,迅速有效地供给操作人员专家的建议。     

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.     

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.     

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.     

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 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…     

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.     

助推作用对大口径铝合金薄壁管数控弯曲壁厚减薄和回弹的影响

以有限元软件Dynaform为平台,建立了大口径薄壁管数控弯曲及回弹的有限元模型,分析了压块助推速度和压块与管子之间的摩擦系数对壁厚减薄和回弹角的影响规律。结果表明,压块与管子之间没有摩擦或者压块的助推速度为0.9、助推速度为1.0且压块和管子间摩擦系数为0.1的条件下,管子壁厚减薄超过航空标准中允许的最大减薄量0.4375mm。在压块的助推速度不变的条件下,压块与管子之间摩擦系数从0.1增加到0.3,能够有效地降低管外侧的壁厚减薄,但是回弹角也会明显增大。当压块与管子之间的摩擦系数为定值时,助推速度从1.0增加到1.2,对管外侧壁厚减薄的改善作用不大,回弹角没有明显变化。