拼焊板V形自由弯曲回弹控制影响因素分析

在平截面和平面弯曲等假设条件下,建立了可适用于纵向拼焊板V形小曲率自由弯曲回弹的解析预测模型。在自由弯曲卸载阶段,该模型引入了两母板间相互作用的弯矩,基于单一母板求解了拼焊板回弹后的弯曲角。利用解析模型分析了不同工艺参数对拼焊板V形自由弯曲力和回弹后弯曲角度的影响规律,确定了影响拼焊板V形自由弯曲力和卸载后回弹角的主要影响因素。     

拼焊板V形自由弯曲精确回弹控制技术研究

在平截面和平面弯曲等假设条件下,建立拼焊板V形可适于小曲率自由弯曲回弹的解析预测模型,所建立的回弹预测模型将成形过程分段研究,即区分为贴模阶段和未贴模阶段。分别根据贴模态和未贴模态拼焊板弯矩分布特点,构建两种状态下的曲率分布方程。在自由弯曲卸载分析阶段,引入两母板间相互作用的弯矩,同时考虑弹性模量随塑性变形变化的影响,基于单一母板求解拼焊板母板回弹后的弯曲角。基于2D单应矩阵变换法实现拼焊板回弹后端面弯曲角的在线测量。针对板料中材料参数的波动性问题,基于正交表构建最佳行程预测的神经网络模型的训练样本。根据软硬件接口基于LabVIEW软件平台开发可在线学习的拼焊板V形自由弯曲回弹控制系统软件。设定目标回弹后弯曲角分别为140°和100°时,跟踪在线成形试验结果,成形第5周期最大点误差可分别达到1.42%和2.01%。     

拼焊宽板V形自由弯曲回弹预测及试验验证

在平截面和平面弯曲等一系列假设条件下,建立拼焊宽板V形自由弯曲回弹的解析预测模型,所建立的回弹预测模型考虑差厚拼焊板截面几何的非对称性,确定差厚拼焊板在指数硬化规律下的应力中性层的位置。在自由弯曲卸载分析阶段,引入两母板间相互作用弯矩,基于单一母板求解拼焊板母板回弹后的弯曲角。采用Fortran语言编制计算程序,应用增量数值方法求解差厚拼焊宽板V形自由弯曲模型中行程与弯曲角和回弹后弯曲角的非线性隐式关系。将V形自由弯曲模具装至改造后的拉伸试验机的活动横梁上,在不同的凸模行程下,分别对两种料厚比(0.8/1和2.5/2)拼焊板进行V形自由弯曲试验,试验结果与拼焊板V形自由弯曲预测模型的计算结果较吻合,为拼焊板V形弯曲回弹实时控制技术研究奠定理论和试验基础。     

Q235-A钢管弯曲回弹角建模与分析

分析Q2 3 5—A钢管弯曲回弹过程 ,利用残余应力分布规律、静力矩平衡条件、变形协调条件等回弹理论推出回弹曲率和回弹角的计算公式 ,计算其回弹角并与实测值比较。比较结果表明 ,弯曲角度和弯曲半径与管子直径比值改变时 ,误差不同。在一定条件下 ,误差在 5 %以内     

某汽车保险杠横梁前板成形质量控制研究

针对汽车冲压件的成形质量问题,以某汽车保险杠横梁前板为例,采用正交试验进行工艺参数方案设计,并借助Dynaform软件进行工艺参数分析,以开裂和回弹量为优化目标,完成了压边力、模具间隙、摩擦系数和冲压速度4个工艺参数的优化,利用模面回弹补偿方法对拉延模进行回弹补偿,经3次回弹补偿迭代后,冲压件回弹量符合要求。将补偿后的模面加工,并完成试模。实验表明经工艺参数优化和拉延工序模面补偿后,某汽车保险杠横梁前板成形质量得到有效控制。     

印制板电连接器插孔弯曲回弹研究

电连接器插孔是电气连接和信号传递的重要基本元件,插孔的弯曲回弹和精度是影响连接质量的主要因素,同时也是插孔弯曲工艺制定和模具设计的关键问题。根据回弹理论,对插孔在弯曲条件下的应力应变进行分析,将插孔横截面上弯曲变形区划分为弹性区和塑性区,分别获得了各区域弯曲力矩作用下的回弹角,推导出回弹量的近似计算公式。最后对插孔弯曲回弹进行了数值分析,指出与实际回弹角度存在误差的原因。     

压弯过程中大挠度平面弯曲线的确定

钣金件压弯成形中挠曲线的确定是解析法计算回弹的基础.根据压弯件变形的特点,将弯曲板分为等曲率弹塑性段、弹塑性自由段、纯弹性自由段、无变形自由段.将弹塑性自由段、纯弹性自由段简化为悬臂梁结构,利用材料理想弹塑性模型,建立了他们的挠曲线数学模型.数学模型中的所有参数可以通过数值方法确定.从而为进一步的回弹计算奠定了基础.     

差厚激光拼焊板的拉延切边回弹特性

采用数值模拟和试验的方法,对厚度组合为1.2 mm/0.8 mm的激光拼焊板进行拉延切边工艺分析,重点就压边力大小、摩擦因数、凹模圆角等参数对回弹的影响进行研究,测量各工艺参数下拼焊板拉延切边的凸凹模圆角处的回弹角、总的回弹角和侧壁曲率,还测量出拼焊板成形中的焊缝移动和应力分布情况和分析相互联系,并与拼焊板拉延弯曲回弹进行比较。分析认为,与拉延弯曲回弹相似,压边力、摩擦因数、凹模圆角等工艺参数对拼焊板拉延切边回弹有着明显的影响,而压边力是关键因素;拼焊板拉延切边回弹和拉弯回弹都与焊缝移动有密切的关系,控制焊缝移动将有利于回弹的降低;相比之下,拼焊板拉延切边回弹比拉弯回弹要小。     

基于曲率的二维弯曲回弹补偿计算方法

传统的回弹补偿主要依靠工作人员的经验根据回弹角进行反复补偿,对于复杂型面没有行之有效的方法.以塑性弯曲理论为基础,用解析法求得回弹后的曲率.根据回弹前后曲率的改变,为模面补偿设计提供了自动计算方法.另外,结合试冲压结果,提出用综合辛卜偿系数来表征回弹在实际生产条件中和理想条件下理论计算结果之间的区别.同时也给出了相应的有限元模拟和物理试验来验证.结果表明,该方法在工业应用方面是可行的,也是足够准确的.     

基于自由弯曲技术的管材弯曲回弹预测EI北大核心

为克服有限元模拟中圆弧段采用动力显式算法无法获得准确回弹,值及解析法忽略过渡段S1为变曲率特性的问题,提出一种结合解析法和有限元模拟分析的求解方法,以此来对基于自由弯曲技术的管材回弹数值进行预测。对于过渡段S1,分别使用显式和隐式求解器完成成形和回弹过程的仿真,基于回弹值变化特点引入移动最小二乘法(MLS)对回弹数据进行拟合,建立了过渡段S1的回弹预测模型;同时,对圆弧段S2建立了考虑轴向推力引起的压缩应力的回弹预测模型。仿真结果表明,回弹主要发生在圆弧段,过渡段S1的回弹值在整体回弹值中所占比重较小;经过两组实验结果对比分析,所提出的预测方法与实验所得回弹角误差分别为15.09%与14.76%,传统求解方式(将过渡段S1视为定曲率)与实验所得回弹角误差分别为27.68%与24.32%,回弹角综合预测精度提升了11.08%。     

基于有限元分析的铝合金板料弯曲回弹的影响因素研究

铝合金材料的弯曲成形是飞机板材和型材零件常用的加工方式之一,在卸载过程中,由于板料的弹性回复,不可避免的会出现回弹现象,在实际加工中如何预测工件回弹后的形状,并对模具进行适当修正仍是一个比较难解决的问题。本文利用非线性有限元软件MARC对不同厚度的铝合金板材弯曲加工过程进行了模拟分析,给出了相对弯曲半径,弯曲中心角,及不同弯曲模式与回弹角度之间的关系,并与实验数据进行了比较。结果表明,有限元分析结果与实验结果比较吻合,有限元模拟能有效地分析和预测铝合金板料的弯曲回弹,为实际生产加工过程中工艺参数的选择提供有力的参考。     

基于有限元分析的二轴柔性滚弯过程影响因素的研究

利用弹性介质对钣金件进行二轴柔性滚弯成形是一种先进的钣金制造工艺,将弹性介质(聚氨酯橡胶)的冲压优势和传统滚弯原理结合,成为钣金成形领域的一个新的发展方向。本文利用有限元软件MARC建立二轴柔性滚弯过程的有限元分析模型,成功的模拟了板料滚弯成形及回弹的加工过程,对工件滚弯成形过程的主要影响因素进行了分析,给出了压入深度、柔性层厚度、刚性滚轴半径、材料性能与回弹后曲率半径的关系。分析结果表明,有限元模拟对滚弯过程的工艺参数选取有着一定的指导意义。     

Springback prediction of the vee bending process for high-strength steel sheets

The precise prediction of springback is a key to assessing the accuracy of part geometry in sheet bending. A simplified approach is developed by considering the thickness ratio, normal anisotropy, and the strain-hardening exponent to estimate the springback of vee bending based on elementary bending theory. Accordingly, a series of experiments is performed to verify the numerical simulation. The calculation of the springback angle agrees well with the experiment, which reflects the reliability of the proposed model. The effects of process parameters such as punch radius, material strength, and sheet thickness on the springback angle are experimentally tested to determine the dominant parameters for reducing the springback angle in the sheet bending process for high-strength steel sheets. Moreover, the effects of the thickness ratio, normal anisotropy, and the strain-hardening exponent on the springback angle in the vee bending process for high-strength steel sheets are theoretically studied. Therefore, improving understanding on and control of the springback reduction of the vee bending process in practical applications is possible.     

Tool path correction algorithm for single-point incremental forming of sheet metal

There exists some error between the manufactured part shape and the designed target shape due to springback of this part after forming. To reduce the error, an iterative algorithm of closed-loop control for correcting tool path of the single-point incremental forming, based on Fast Fourier and wavelet transforms, has been developed. Moreover, the data of the springback shapes, after unloading, of the sheet metal parts formed with the trial and corrected tool paths, used for iterative correction of tool path in the algorithm, are obtained with finite element model (FEM) simulation. Then, a truncated pyramid-shaped workpiece, whose average errors are +0.183/?0.175 mm, was made with the corrected tool path after three iterations solved by the above algorithm and simulation data. The results show that the tool path correction algorithm with Fourier and wavelet transforms is reasonable and the means with FEM simulation are effective. It can be taken as a new approach for single-point incremental forming of sheet metal and tool path design.     

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.     

考虑接触演变的板材回弹过程建模与优化

回弹是由工件在卸载后的弹性变形引起的。板料成形过程中为了控制成形件的最终形状,必须进行回弹设计优化。准确预测回弹对于板料成形过程的模具设计非常重要。降低回弹模拟结果与试验结果的偏差是设计过程中的难题。基于NUMISHEET’02的自由弯曲标准考题考虑板材与模具间的接触演变过程,建立了一个有限元模型来预测回弹。采用一个常规的优化方法对有限元分析中的材料和单元模型进行了分析,研究发现不同模型对回弹结果有较大影响。模拟结果与参考文献中的试验结果比较表明了模型的正确性和可行性。     

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.     

Unconstrained bending and springback behaviors of aluminum-polymer sandwich sheets

The bending and springback behaviors of sandwich sheets are more complicated than those of monolithic layer metallic sheet due to the extremely large difference in mechanical properties and in the gauges of polymer core and the skin sheet. In the present study, the bending and springback behaviors of aluminum-polymer sandwich sheets were investigated by using analytical method and conducting experiments and numerical simulations. A simplified analytical model was proposed to calculate the bending moments for sandwich sheet in unconstrained bending process through analyzing the strain and stress distributions of skin sheet and core materials. Then, the analytical model was applied to predict the springback of sandwich sheets after bending. Numerical simulations and experiments of unconstrained bending process for aluminum-polymer sandwich sheets were conducted to investigate the influences of mechanical properties of each layer and thickness ratio of two layers on the folding defects, neutral layer location, and springback. The results show that the neutral layer shifts dramatically toward the compression region of the specimen during bending. The folding angle mainly relates to the strength difference between the skin sheet and the core polymer. The springback angle of sandwich sheet is mainly determined by the mechanical properties of skin sheet.     

Modeling of springback, strain rate and Bauschinger effects for two-dimensional steady state cyclic flow of sheet metal subjected to bending under tension

An elastic-plastic mathematical model is presented for plane strain flow of sheet metal subjected to strain rate effects during cyclic bending under tension. The model calculates the stress, strain, strain rate, flow profile geometry, springback and residual stresses for steady state flow of sheet metal under plane strain along the width. Stress reversals were experimentally quantified using a pure bending moment test and were included in the model through Bauschinger factors. Modeling results for two materials, mild steel and aluminum alloy, were in good agreement with experimental results from bending under tension test devices. The iterative nature of the model, associated with a representative experimental framework proved a valuable approach to improving the modeling of sheet metal forming and springback control.     

往复弯曲统一曲率定理及其试验验证

辊式矫直工艺和辊式矫圆工艺均通过往复弯曲方式达到统一曲率的目的,辊式矫形过程中的往复弯曲变形规律是确定矫形工艺参数的理论依据。针对往复弯曲变形过程,建立一套符号系统,将弯曲曲率和弯矩矢量化。基于小曲率平面弯曲弹复方程和应变叠加原理,引入初始当量应变和当量应变的概念,采用图解法对往复弯曲弹复过程进行分析,在考虑稳定金属材料往复弯曲过程中的形变硬化、Baushinger效应和循环软化,分三种情形证明往复弯曲可以湮灭初始曲率的差异,最终使曲率统一到同一方向、同一数值,提出往复弯曲统一曲率定理。进而,设计模压往复弯曲试验装置,选用不同初始形状、不同材料的板坯进行往复弯曲试验,讨论残余曲率半径和拟合圆弧偏差随弯曲次数的变化规律,验证往复弯曲统一曲率定理的正确性,为辊式矫直和辊式矫圆工艺方案和控制策略的制定奠定了理论基础。