型材拉弯成形性的研究进展

拉弯成形可以有效地减少回弹,实现型材的高精度弯曲,因此拉弯成形在飞机、汽车型材弯曲件的生产中得到了广泛的应用.针对型材的拉弯成形,从型材力学性能、截面形状、工艺参数3个方面阐述了目前的研究状况及所取得的成果.     

非对称型材数控拉弯成形回弹研究

针对数控型材拉弯机拉弯成形特点,建立了位移控制拉弯成形的有限单元模型,提出了一种新的描述型材边界条件的方法,模拟了T截面铝型材非对称拉弯成形过程,探讨了预拉伸量和补拉伸量对非对称拉弯零件成形质量的影响。模拟结果表明预拉伸量对零件的成形质量有重要的影响,有限的补拉伸量有助于改善零件的成形质量。数值模拟的型材回弹基本与实验结果一致。     

电流辅助钛合金L型材拉弯工艺研究

钛合金型材弯曲构件由于性能优异而逐渐成为先进民用复合材料机身的主要承力构件,其成形质量直接关系到飞机的装配精度。本文针对OT4M钛合金L型材的拉弯成形工艺进行了研究,建立了拉弯过程的解析模型,并在不同的试验条件下进行了多组热单轴拉伸试验来探究型材的热变形行为,利用绝缘模具开展了钛合金型材的电热拉弯成形试验,结果表明,材料的塑性变形能力受变形温度和速度影响显著,拉弯成形时绝缘模具的应用可使钛合金型材保持在相对较高的温度490℃下成形,进而降低了回弹。     

考虑弯曲回弹的拉弯模外形设计方法

拉弯是型材弯曲成形的重要方法,可以有效减少回弹、提高成形精度,在飞机、汽车弯曲件成形中得到广泛应用。采用弯曲回弹理论分析,结合拉弯零件数字化模型,修正拉弯模模具轮廓;采用圆弧样条表示模具轮廓,给出了拉弯模合理外形的计算方法。在理论分析基础上,通过有限元分析方法计算拉弯型材的回弹量,评估拉弯模型面的回弹修正量及拉弯件校形余量的减少情况。为提高汽车和飞机拉弯件的质量和促进工装的数字化设计提供了合理有效的方法。     

非对称截面型材拉弯成形数值模拟研究

采用ABAQUS软件对某飞机上非对称截面型材的拉弯成形过程进行了数值模拟,建立了位移控制拉弯工艺的有限元模型,并对带凹陷拉弯过程进行仿真。探讨了预拉伸量、补拉伸量及摩擦因数等工艺参数对回弹量与畸变角的影响,得到合适的应用参数,对飞机拉弯件成形质量、加工效率的提高起到了重要的指导作用。     

金属型材三维成形工艺的研究

汽车工业是国民经济的支柱产业。而汽车门框、窗框、流水檐、车身外饰条、行李架等则是一些零部件生产厂商的主导产品,这些产品都是由各种型材弯曲成形的,截面复杂,空间形状多为三维,见图1。随着汽车工业发展的需求,型材拉弯工艺     

T8状态铝锂合金型材冷拉弯成形技术研究

研究了铝锂合金T8状态冷拉弯成形回弹预测及模具补偿修正技术,并进行T和Z截面的2196-T8511和2099-T83铝锂合金型材拉弯成形试验。将模具回弹补偿修正算法应用于拉弯模具修正,回弹补偿后的零件与样板最大间隙为2 mm,证实了T8状态铝锂合金型材拉弯成形的可行性和理论回弹计算及模具回弹补偿修正算法的有效性,这种方法可以用于拉弯成形及模具设计。     

大截面Z型材数控滚弯成形精度的数值模拟研究

为了提高型材滚弯成形外形轮廓的精度,研究了Z型材滚弯成形回弹变形规律,建立了型材成形半径与滚弯机侧滚轮位移的关系,给出了考虑回弹变形的型材滚弯成形工艺参数。基于ABAQUS有限元软件,建立了型材滚弯成形过程的三维模型,分析了主滚轮尺寸、夹紧力和摩擦系数对型材沿长度方向各段曲率变化的影响。结果表明:主滚轮尺寸越大,曲率分布越均匀;并确定出该型材滚弯成形时合理的夹紧力和摩擦系数范围。应用模拟分析确定的最佳工艺参数完成该型材的滚弯成形加工,验证了该参数对滚弯型材外形精度的提高作用。     

飞机球面框型材拉弯回弹有限元模拟技术

针对飞机球面框型材为异形截面的几何特点,基于有限元分析软件Abaqus建立了等效填充离散芯模拉弯成形的有限元模型,通过合理定义边界条件及填充芯模的材料模型,提高了建模效率。根据拉弯过程型材截面弯曲中性层位置不变的假设,建立了夹钳轨迹计算模型,采用位移控制模式对飞机球面框型材拉弯回弹进行了有限元模拟,通过改变中性层位置调整有限元模拟的夹钳轨迹,模拟的回弹结果与实验结果一致,验证了建模方法的有效性。     

铝合金汽车前碰撞横梁拉弯成形回弹量的有限元模拟

基于LS-DYNA软件平台对6061-T6铝合金汽车前碰撞横梁拉弯成形过程中的回弹量进行了模拟;研究了预拉力、补拉力和摩擦因数对回弹量的影响,并对拉弯模具孤面进行修正以补偿回弹量,最后进行了试验验证。结果表明:预拉力的变化影响型材横截面内的应力分布情况,随着预拉力增大至型材横截面积与材料屈服强度的乘积(Aσ_s)时,回弹量减小;在一定范围内,随着补拉力从Aσ_s逐渐增大,有利于减小拉弯成形件的回弹量;摩擦因数越大,回弹量越大;通过修正模具的弧面尺寸可以补偿回弹量;模拟结果与试验结果吻合较好,所建立的有限元模型能准确预测汽车前碰撞横梁的拉弯成形回弹量。     

Flexible 3D stretch-bending technology for aluminum profile

As the consumption of fossil energy from the traffic system increases, the need for 3D structural parts which provide the design engineer a lighter, stiffer, and more energy-efficient structure is required. A new flexible 3D stretch bending process (FSB) with multi-points dies (MPD) is thus being developed. This study seeks to find out the relationship between the springback error and the adjustment parameters for the FSB process. At first, the structure of flexible fundamental unit (FFU) with four degrees of freedom (DOF) MPD was designed and implemented. Then the FSB experiments with different bending radius of curvature and materials were carried out based on prototype of the flexible 3D stretch bending equipment. The experiment results show that the springback error increased linearly along the length of the workpiece. Without using the post-stretch force, the springback error declined from 7.90 % to 0.80 % by adjusting the positions of the FFU. Most importantly, the surface defects of the forming parts such as wrinkle and crack can be eliminated in this process.     

基于响应曲面法的大型锥形件缩口成形工艺设计及多几何参数优化

提出一种适用于大型锥形件的缩口成形方法,通过主应力法对该缩口成形时的轴向缩口力与标准直壁锥形件的缩口力进行对比,得出了最佳成形方案。并基于Deform和响应曲面法讨论了该成形模具中缩口凹模母线弦高χ、内壁直空比l/h和毛坯壁厚S₀、变壁厚尺寸λ分别对缩口件高度和缩口成形力的影响,得到了两个响应变量分别关于四个自变量的回归预测模型,优化出凹模内直空结构和毛坯的最佳几何结构参数,最后通过物理试验得到验证。结果表明：当χ=6.9 mm、l/h=0.3、S₀=29.5 mm、λ=4.8 mm时,毛坯在缩口过程中未发生失稳,实时最大缩口力为1 920 kN,测量缩口件高度为1 108 mm,与模型预测结果误差均小于10%,说明了该工艺方案中缩口凹模和毛坯结构参数的可行性,其成形工艺及模具结构形式将为大型锥形产品的缩口成形提供理论指导。     

弯曲回弹影响因素及控制措施

回弹是材料弯曲成形过程中的主要影响因素之一,严重影响着弯曲件的质量与精度。在已有研究的基础上,对弯曲回弹的影响因素及控制措施做了综合有效深入的研究与分析,对工业生产有一定的现实意义。     

Springback prediction and optimization of variable stretch force trajectory in three-dimensional stretch bending process

Most of the existing studies use constant force to reduce springback while researching stretch force. However, variable stretch force can reduce springback more efficiently. The current research on springback prediction in stretch bending forming mainly focuses on artificial neural networks combined with the finite element simulation. There is a lack of springback prediction by support vector regression(SVR). In this paper, SVR is applied to predict springback in the three-dimensional stretch bending forming process, and variable stretch force trajectory is optimized. Six parameters of variable stretch force trajectory are chosen as the input parameters of the SVR model. Sixty experiments generated by design of experiments(DOE) are carried out to train and test the SVR model. The experimental results confirm that the accuracy of the SVR model is higher than that of artificial neural networks. Based on this model, an optimization algorithm of variable stretch force trajectory using particle swarm optimization(PSO) is proposed. The springback amount is used as the objective function. Changes of local thickness are applied as the criterion of forming constraints. The objection and constraints are formulated by response surface models. The precision of response surface models is examined. Six different stretch force trajectories are employed to certify springback reduction in the optimum stretch force trajectory, which can efficiently reduce springback. This research proposes a new method of springback prediction using SVR and optimizes variable stretch force trajectory to reduce springback.     

冲压工艺参数对回弹的影响及改进方法比较

板料成形都存在回弹,因回弹使得板料零件无法满足使用要求。论文围绕实际工件回弹的情况,通过有限元CAE方法,探讨了预成形压力、摩擦系数、间隙等主要因素对回弹的影响。并提出了减小回弹的几种方法,经实际验证效果良好。     

基于试验设计和灰色关联度的橡皮囊成形回弹影响因素显著性分析

橡皮囊成形是飞机钣金零件的一种重要成形工艺方法,回弹问题是橡皮囊成形的难点,对其影响因素进行显著性分析可有效控制回弹。基于橡皮囊成形有限元数值模拟,将正交试验设计方法与灰色关联度相结合用于分析橡皮囊成形回弹影响因素的显著性,以某实际长直U形件为例分析压力、最大充液速率、最大节点速度、保压时间、弯曲半径、板料厚度以及轧制方向等因素对回弹的影响程度,结果表明,模具圆角半径、压力、板料厚度、保压时间是橡皮囊成形回弹的主要影响因素,而最大充液速度、最大节点速度、轧制方向对回弹的影响较小。分析结果与工艺试验结果相吻合,从而验证了该方法的有效性。     

Modelling of kinetic friction in V-bending of ultra-high-strength steel sheets

The Stribeck friction model was investigated in this study to predict springback of high-strength steel sheets. The coefficient of friction in Stribeck curve depends on sliding velocity and contact pressure. The plane-strain bending process is simulated in ABAQUS/Standard. The influence of forming speed, over-pressing and holding time on springback behaviour of sheets was studied numerically. By plotting the variation of bending angle with punch stroke, we found that the loading curve of finite element analysis showed similar results to the experiments. The unloading curves of FE analysis with friction models based on Stribeck curve and Coulomb law showed good agreement with experiments with error less than 1.5%. Forming speed of up to 50 mm/s does not have significant effect on springback. The effect of holding time on reducing springback is small, but over-press has large effect on reducing springback. The results showed that Stribeck model is suitable for sheet metal forming simulations, especially at higher forming speeds and pressures.     

管线钢管JCO精确弯曲成形技术

为了减小管线钢管JCO成形工艺中成形管坯的椭圆度,基于塑性弯曲工程理论和机器视觉测量技术提出了管线钢管JCO精确弯曲成形工艺。在管坯首道次成形过程中,采用两次预弯法,识别出板材的弹复规律,结合管坯目标成形角,预测出精确的压制行程;在后续成形道次中,利用误差补偿技术循环补偿上一道次的成形误差,实现管坯每道次精确弯曲成形。确定了适合管坯端面的图像处理算法、图像处理流程和直线检测算法,提出了采用正三角形作为标定模板求解摄像机外部参数的标定方法,由单幅图片快速、高精度地标定出摄像机的外部参数,建立了将图像角转换为管坯真实成形角的数学模型。实验结果表明,管坯成形角监测误差在0.2°以内,可控制成形管坯的椭圆度在1.5%以内,减小了成形管坯的椭圆度,改变了成形管坯的椭圆度控制依赖于操作者经验的现状。     

Analytical modeling and numerical simulation for three-roll bending forming of sheet metal

The three-roll bending forming of sheet metal is an important and flexible manufacturing process due to simple configuration. It is suitable for forming large sheet parts with complex, curved faces. Most researches on roll bending forming of large workpiece are mainly based on experiments and explain the process through macroscopic metal deformation. An analytical model and ABAQUS finite element model (FEM) are proposed in this paper for investigating the three-roll bending forming process. A reasonably accurate relationship between the downward inner roller displacement and the desired springback radius (unloaded curvature radius) of the bent plate is yielded by both analytical and finite element approaches, which all agree well with experiments. Then, the three-roll bending forming process of a semi-circle-shaped workpiece with 3,105 mm (length)?×?714 mm (width)?×?545 mm (height) is simulated with FEM established by the optimum tool and process parameters. Manifested by the experiment for three-roll bending forming of this workpiece, the numerical simulation method proposed yields satisfactory performance in tool and process parameters optimization and workpiece forming. It can be taken as a valuable mathematical tool used for three-roll bending forming of large area sheet metal.