基于几何补偿的高强板汽车覆盖件回弹优化控制

利用板料成形CAE软件DynaForm对高强板汽车覆盖件地板中通道进行回弹仿真分析,结合模具几何补偿,通过对成形工艺参数的正交优化,找到了最优参数组合及各因素对回弹的影响程度,有效地控制了零件在多工序冲压成形过程中产生的回弹.     

面向磁流体增强的骨架结构微成型设计及回弹特性研究

为提高磁流体密封液膜的刚度和抗压力性能,设计一种应用于磁流体密封的翻边Z型增强骨架,该骨架由软磁金属薄板微成型冲压而成。对软磁金属电工纯铁和无取向硅钢进行单向拉伸试验,得到2种材料的应力应变曲线。利用幂硬化准则对Z型骨架成型回弹特性进行理论分析,确定影响回弹的主要因素为材料参数、厚度、弯曲半径、开孔宽度等。利用有限元软件对成型回弹过程进行仿真,应用因素水平分析,以残余应变和最大回弹量为指标,分析板胚厚度、弯曲半径、开孔宽度对回弹的影响。仿真结果表明：在研究的范围内通过增大板胚厚度、减小弯曲半径、减小翅片宽度能有效降低骨架回弹;当厚度为0.3 mm,弯曲半径0.3 mm,翅片尺寸为2 mm×1 mm时骨架成型回弹量最小,运用硅钢材料比纯铁具有更小的回弹量。研究结果对软磁金属的微成型冲压及磁流体密封复合材料设计提供了参考。     

冲压、回弹及应变速率对双相钢成形件碰撞性能影响的模拟

针对冷轧镀锌双相钢板,在完成U型梁冲压成形及回弹模拟分析的基础上,建立了闭口帽型梁的碰撞分析模型;采用映射的方法完成了U型梁的厚度、应力、应变向碰撞结构件的结果传递;在考虑冲压成形、回弹及应变速率等的情况下,对帽型梁的碰撞过程进行了模拟分析。结果表明:在碰撞过程中,由于应变速率较高,它的影响最为明显,在模型的定义过程中需要着重考虑;因为金属变形过程的加工硬化和厚度减薄等因素的影响,冲压结果直接影响碰撞过程的模拟结果;冲压后因回弹使零件内部的应力得到释放,残余应力减小,因此导致碰撞过程中产生相同的变形需要更大的外力,考虑回弹的刚性墙反力要比没有考虑时的高。     

基于改进粒子群算法和小波神经网络的高强钢扭曲回弹工艺参数优化*

针对高强钢复杂件冲压后出现的扭曲回弹现象,运用有限元仿真软件DYNAFORM对复杂件的冲压、回弹过程进行数值模拟,提出了评价复杂件扭曲回弹程度的指标,并运用试验设计和小波神经网络代理模型方法对扭曲回弹进行了优化研究。以某弯曲梁为研究对象,以扭曲回弹为成形目标,通过正交试验设计筛选出对扭曲回弹影响较大的工艺参数作为影响因素。利用拉丁超立方对影响因素进行抽样,通过数值模拟获得样本数据,建立影响因素与成形目标之间的小波神经网络代理模型,利用改进的粒子群算法对该模型迭代寻优获得最优参数。结果表明：采用优化后的工艺参数能有效地减小该弯曲梁的扭曲回弹,该方法为减小复杂件的扭曲回弹提供一种有益的指导。     

基于ANSYS/LS-DYNA的板材多点成形中回弹的数值模拟

利用有限元软件LS-DYNA对板材冲压成形的回弹进行数值模拟,采用动态显式算法模拟板材成形过程,隐式算法模拟卸载回弹过程;对于不同曲率半径、不同屈服强度的圆柱面成形件进行数值模拟,分析得出回弹趋势和回弹分布,这些结果对于减小因回弹带来的误差、提高成形件的成形精度具有十分重要的现实意义。     

On the prediction of the effect of process parameters upon forming limit strains in sheet metals

Plasticity analysis of sheet metal forming requires a detailed knowledge of the influence of process parameters on the stress–strain relationships from yielding up to localized necking, for accurate prediction of forming limits. Achievable strain and stress–strain relationships are sensitive to modulations in process parameters, chiefly temperature and strain rate. However, the effects of changes in strain rate and temperature are often complex as they also depend on the levels of strain, strain rate and the temperature employed. Such variations could be either triggered by the process dynamics of the forming operation or imposed for optimal exploitation of the material ductility. In this study, the influence of such process parameter modulations upon formability has been theoretically modelled, following the Sing–Rao prediction approach. The limit strains thus predicted compare favourably with experimental results for a drawing steel, thus validating the present formalism. This approach can also be adopted to accommodate non-linear straining conditions. Thus, theoretical modelling of strain-path-dependent forming limits, which has not been explored adequately so far, now becomes feasible.     

Substepping algorithms with stress correction for the simulation of sheet metal forming process

The finite element analysis of the sheet metal forming process involves various nonlinearities. To predict accurately the final geometry of the sheet blank and the distribution of strain and stress and control various forming defects, such as thinning, wrinkling and springback, etc., the accurate integration of the constitutive laws over the strain path is essential. Our objective in this paper is to develop an effective and accurate stress integration scheme for the analysis of three-dimensional sheet metal forming problems. The proposed algorithm is based on the explicit “substepping” schemes incorporating with the stress correction scheme. The proposed algorithms have been implemented into ABAQUS/Explicit via User Material Subroutine (VUMAT) interface platform. The algorithms are then employed to analyze a typical deep-cup drawing process and the accuracy of these algorithms has been compared with the implicit “return” algorithm and explicit forward algorithm. The results indicate that the explicit schemes with local truncation error control, together with a subsequent check of the consistency conditions, can achieve the same or even better level of accuracy as “return” algorithm does for integrating large plastic problems like sheet metal forming process.     

基于RP/RT/RE技术的金属板料冲压成形回弹误差补偿系统

针对冲压件回弹误差，建立了基于RP／RT／RE技术的三维复杂形状板料冲压成形回弹误差精度闭环控制系统。以回弹误差为控制目标，以线性控制系统、空间Fourier变换和频域传递函数为理论基础，基于模具实验迭代，建立了模具回弹误差补偿修正算法，并首次将该算法应用于三维复杂形状板料冲压模具制造过程。工程实例表明，该系统对于三雏自由曲面板料冲压模具制造具有良好的工程实用价值，特别能对冲压件回弹误差进行有效补偿。     

卫星天线冲压成形仿真分析

针对用金属板材通过冲压成形制造卫星天线的方法中,冲压卸载后的回弹计算不精确,并且很难预示出能达到规定产品尺寸的最佳模面构形的情况,提出了一种回弹逆向补偿法,该方法成功地解决了这一问题.实际生产证明了该方法的可靠性,这对于其他冲压件模具设计具有普遍的指导意义.     

板材多点成形使用弹性垫后回弹的数值模拟

利用有限元软件LS-DYNA对板材冲压成形的回弹进行数值模拟。使用3mm厚的弹性垫抑制板材成形产生的压痕,但弹性垫的使用加上板材的回弹会导致成形误差的增大。基于数值模拟的结果,提出了修正基本体群成形面补偿回弹。经过两次补偿,精度得到了很好的提高,证明该方法可以很好地补偿多点成形中的回弹。     

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。     

A new model for springback prediction in which the Bauschinger effect is considered

Springback prediction is an important issue for the sheet metal forming industry. Most sheet metal elements undergo a complicated cyclical deformation history during the forming process. For an accurate prediction of springback, the Bauschinger effect must be considered to determine accurately the internal stress distribution within the sheet metal after deformation. Based on the foundations for isotropic hardening and kinematic hardening, Mroz multiple surface model, plane strain assumptions, and experimental observations, a new incremental method and hardening model is proposed in this paper. This new model compares well with the experimental results for aluminum sheet metal undergoing multiple-bending processes. As is well known, aluminum is one of the most difficult sheet metals to simulate. The new hardening model proposed in this paper is not only a generic model for springback prediction but also a hardening model for sheet metal forming process simulation.     

Optimized bending angle distribution function of contour plate roll forming

Regarding the roll forming of contour plates, traditional roll forming techniques often result in peak longitudinal strain during the forming process, which causes defects such as longitudinal bowing and springback. The bending angle, sheet thickness, and the number of forming passes are all important process parameters that cause the aforementioned problems. This study proposes quantifying the projection track regarding the edge of the profile section in the horizontal plane that follows a cubic curve and uses the curve function to reasonably distribute the bending angle to study the maximum forming strain and the average strain for all passes of the sheet between the forming passes. Simultaneously, the influence law of the sheet thickness and number of forming passes was studied. Based on theoretical simulation and experimental verification, the optimal bending angle distribution function is A1: y?=?x³?+?x²?+?x. When the thickness of the sheet is 1.5 mm, both the maximum forming strain between the passes during roll forming and the average strain of all passes are the smallest, which are 3.91 and 0.609%, respectively. Moreover, with the increase in the number of passes, the longitudinal bowing and springback decrease to varying degrees.     

复杂形状板料冲压件回弹评价指标研究

对于 3- D复杂形状板料冲压件 ,现有的回弹评价指标均有一定的片面性 ,难以满足工程实践和理论研究多方面的要求。本文从弹性变形能概念出发 ,提出一种新的回弹评价指标。新指标反映了冲压件回弹过程的几何和力学本质 ,能客观全面地评价复杂零件的整体回弹水平。新指标以相同的参数衡量 2 - D弯曲件和 3- D复杂冲压件的回弹水平 ,做到了评价指标相对于不同评价对象的一致性。     

金属板材数控单点渐进成形回弹的实验研究

主要研究了金属板材数控单点渐进成形过程中的回弹问题 ,分析了影响板材渐进成形回弹的主要因素和变化规律 ,提出了一种通过增大成形角度控制回弹的方法。     

基于神经网络的板料冲压回弹预测系统的研究

文中以NUMISHEET’93标准考题中U形板料作为研究对象,将正交试验法和数值模拟法结合,产生各工艺参数组合下的冲压回弹量,以这些仿真试验结果作为神经网络的训练样本,在NeuroSolution软件环境下建立输入为工艺参数、输出为冲压回弹量的神经网络模型预测模型,以测试样本验证模型的预测精度作为反馈信息,构成闭环系统。该方法为板料冲压工艺参数的优化提供了有效的工具。     

基于AUTOFORM的板料高强度钢零件回弹补偿研究及应用

白车身零部件在冲压成型后都存在回弹,严重影响冲压件的产品质量。传统的修正回弹方法是根据实际产品测量数据,然后修正模具,再重新试模和修正,直到符合品质要求,如此反弹调试,消耗大量的时间及人力物力。因此,精确仿真回弹量以及有效控制回弹已经成为白车身冲压领域最为关注的问题。本文利用专业分析软件,采用AUTOFORM软件对某高强度防撞梁进行了成形性、回弹分析及自动补偿计算,在实际生产中取得了显著的效果。     

An energy approach for predicting springback of metal sheets after double-curvature forming, Part II: Unequal double-curvature forming

Based on the membrane theory of shells of revolution and an energy method, theoretical predictions of springback of metal sheets after an equal double-curvature forming operation has been given in the part I of this paper (Xue et al., An energy approach for predicting springback of metal sheets after double-curvature forming, Part I: axisymmetric stamping. International Journal of Mechanical Sciences 2001;43(8):1893–1914). In Part II, the prediction of springback of metal sheets after unequal double-curvature forming is illustrated. It is shown that the proposed mechanics model and analytical procedure can be conveniently applied to predicting the springback, as well as the strain and stress distributions of metal sheets after unequal double-curvature forming, which is valuable for design of tools with complicated shapes in manufacturing industries.     

Influence of material properties variability on springback and thinning in sheet stamping processes: a stochastic analysis

A very critical issue for stamping operations is the improvement of process robustness. The reliability of final results, in fact, strongly depends on the intrinsic variability due to stochastic behavior of many parameters, namely, operative ones and material properties. A given process performance may undergo a variation around the value which would be obtained neglecting stochastic behaviors of the operative or material parameters (i.e., considering a deterministic parameters behavior). Such variation introduces a significant source of uncertainty within the process design: a possible consequence may be the rejection of some stamped parts. In this paper, reliability analyses aimed to evidence and quantify the effects of material coil-to-coil variations on springback and thinning phenomena is proposed. In particular, an aluminum alloy typical of automotive applications was considered and an S-shaped U-channel process was investigated. The stochastic analysis was performed within several operative windows at the varying of restraining forces. Formerly, a sensitivity analysis was carried out in order to evaluate the single effect of each selected material parameter and to screen the most influent ones. Subsequently, a finite element method-response surface methodology-Monte Carlo simulation-integrated approach was implemented to quantify such effects. The proposed methodology provides the possibility to powerfully analyze material variability effect on the final process quality, assisting the designer in a subsequent process optimization.     

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。