A LOOP DRAWBEAD RESTRAINING FORCE MODEL IN SHEETMETAL DEEP DRAWING PROCESS

1. IntroductionIn the sheet metaJ fOrming process9 deep drawing is used frequently in the automotiveor packaging industry to manufacture products with comPlicated shapes and ctirvatures.In the deep drawing process, a sheet metal, the blank, is clamped between a die and a blankholder. The specific shape of the punch and the die is transferred to the blank during thedefor.atio.[1--4].In the deep drawing process, the material flow is restrained by both the friction con-dition and the blankholde…     

板料冲压成形数值模拟中等效拉延筋模型的建立与实现

设置拉延筋是板料拉深成形过程中控制材料流动的有效方法。在板料成形数值模拟中,为节省计算时间,常采用等效拉延筋模型。本文在参考国内外有关资料的基础上,建立了一种等效拉延筋模型。模型中考虑了拉延筋约束力、塑性厚向应变以及垂直于压料面的约束保持力的影响,并在程序中予以实现。文中给出了一个计算实例。     

拉深筋成形二维弹塑性有限元数值模拟

利用开发的拉深筋二维弹塑性有限元数值模拟软件 ,对圆形筋和矩形筋就压筋和成形的连续过程进行了数值模拟 ;分析了拉深筋主要几何参数对压筋力和拉深筋阻力的影响 ,研究了压筋和成形两个阶段板料在拉深筋作用下的变形规律与受力特点。模拟结果与实验结果吻合良好 ,为建立一种实用的等效拉深筋模型及进一步的三维拉深筋成形模拟奠定了基础。     

2D elasto-plastic FE simulation of the drawbead drawing process

The drawing process including the locking and pulling phase under a drawbead of circular and rectangular section shape is simulated by means of a static-implicit FE code developed by the authors for 2D elasto-plastic simulation of sheet metal forming. The influence of the main bead geometrical parameters on the binder hold down force (BHDF) and drawbead restraining force (DBRF) is analyzed. The deformation law and loading characteristics of the sheet around the drawbead are studied during the two sequential phases. The calculated results show a good agreement with the experimental data. The investigation lays a foundation for setting up an applied drawbead model in the future 3D simulation of drawbeads.     

汽车覆盖件成形中拉延筋约束力的模拟计算

通过拉延筋基本单元模拟试验，对板料在筋内变形机理、压边力和筋的几何参数对拉延筋约束力的影响规律，拉延筋约束力随模具包角变化的规律及板料拉过筋时的变形情况进行了研究，建立了拉延筋约束力计算模型。     

一种考虑包辛格效应的等效拉深筋模型

基于Voce各向同性硬化模型和Armstrong-Frederic随动硬化模型,建立了一个考虑包辛格效应影响的混合硬化模型,并通过CR4钢板的拉压循环实验验证了该混合硬化模型的准确性。将该混合硬化模型引入Stoughton等效拉深筋阻力模型,替换原有的各向同性硬化模型,考虑包辛格效应的影响对该等效拉深筋阻力模型进行了改进。利用专门设计的拉深筋阻力测定装置,针对矩形拉深筋和半圆形拉深筋,分别获取了不同几何结构参数下的拉深筋阻力,经实验验证,改进后的等效拉深筋模型能够有效地提高拉深筋阻力的计算精度。     

Analysis of an equivalent drawbead model for the finite element simulation of a stamping process

In order to facilitate the three-dimensional finite element analysis for the stamping process, an equivalent drawbead model was adopted to simulate the restraining effects produced by the real drawbead. In the present study, the restraining force exerted by the real drawbead was first computed by the finite element simulation, and the optimum pseudo drawing speed and mesh sizes for both the drawbead and sheet metal employed in the computation were determined through a systematic approach. The computed restraining force was then assigned to a regular mesh which replaced the mesh of the real drawbead. This constitutes the equivalent drawbead model, which avoids the extremely fine mesh required to describe the deformation of sheet blank in the drawbead area. In consequence, a huge amount of computation time can be saved. The accuracy of the finite element simulations using the equivalent drawbead model was validated by both the experimental data and the theoretical predictions.     

A simulation-based prediction model of the restraining and normal force of draw-beads with a normalization method

This paper proposes a simulation-based prediction model to predict the restraining and normal force of drawbeads for the sheet metal forming process. A reliable prediction model is constructed for the equivalent drawbead by a modified DOE (Design of Experiment) method, which consists of the Box-Behnken design and a simplified full factorial design. To construct prediction models of draw-bead forces, draw-bead forces are first calculated by finite element analysis and confirmed by experiments followed by an approximation with second order regression equations in various design cases. To increase the accuracy of prediction models, normalization of draw-bead forces is conducted based on the effectiveness ratio of design variables in a regression analysis. The normalized draw-bead forces are then approximated by second order regression equations again. The accuracy of the prediction models constructed is verified by comparing the prediction results with the simulation results in the entire design space.     

Drawbead design and performance

Experiments on drawbead restraining in sheet metal forming with several bead configurations were carried out. With the binder hold-down force as an independent variable, the magnitude of the restraining force, the amount of metal flow through the bead, and the sensitivity of these quantities with respect to lubrication were determined. Performance of these beads as viewed from shop floor practices was discussed.     

基于数值模拟的拉延筋约束阻力计算方法研究

在汽车覆盖件拉深成形中,拉延筋可以在较大范围内调节和控制板料的变形程度和变形分布,抑制多种成形质量问题的产生.其中,拉延筋几何参数起着重要的作用.本文以矩形拉延筋为例,建立了拉延筋约束阻力计算有限元模型,对拉延筋几何参数与约束阻力之间的关系进行分析研究.结果表明:拉延筋约束阻力与凹槽圆角半径和凸筋圆角半径成反比,与筋高成正比.结合某轿车B柱加强板实例,通过优化其拉延筋结构参数,得到当1号等效拉延筋高8mm、凸筋和凹槽圆弧半径3mm;2号等效拉延筋高4 mm、凸筋和凹槽圆弧半径6mm时,该制件成形质量达到最佳.     

基于迭代学习控制模型的覆盖件模具拉深筋优化算法

提出了基于迭代学习控制模型的覆盖件模具拉深筋优化算法,极大地提高了优化效率。利用成形状态函数,成形质量函数和学习律函数构建工艺参数优化的迭代控制模型。将该模型应用到拉深筋阻力值优化中,利用有限元模拟代替很难显示表达的状态函数,预测给定工艺参数方案下板料成形后的应力应变状态。根据单元的应变状态,定义拉深筋线段的局部缺陷程度为成形质量函数,评价拉深筋周围的成形质量好坏。学习律函数不仅参考拉深筋段周围的成形质量偏差确定拉深筋阻力值的改变量,同时还能智能更新学习增益修正拉深筋阻力值的改变幅度,加快了优化收敛速度。通过门内板的算例,证明了该拉深筋优化算法的快速性和实用性。     

左前门防撞梁冲压成形数值模拟研究

采用数值模拟技术可以在模具设计初期预测产品的成形质量,从而优化工艺参数以便获得高质量的成品。以eta／DYNAFORM有限元分析软件为平台,对某轿车左前门防撞梁不同工艺参数下的拉延成形过程进行了数值模拟,得出了相应的成形极限图。重点探讨了压边力和拉延筋的设置对起皱和未充分拉深区域的影响,得出了较好的解决方案。     

An analysis of drawbead restraining force in the stamping process

A theoretical model based on the virtual work principle was proposed to calculate the restraining force produced by the drawbead located on a stamping die surface. In the theoretical model the deformation of the sheet metal drawn over the groove shoulder or bead is assumed to be subjected to bending, sliding and unbending processes, and only the sliding process is responsible for the frictional force. The governing equations derived from the theoretical model were solved by a numerical procedure. In order to validate the proposed model, the finite element simulations were also performed to calculate the drawbead restraining forces for various steels. The simulated results together with the experimental data obtained from the published literature were compared with the predicted values calculated by using the numerical procedure. The good agreement between the simulated results, experimental data and the calculated values justifies the proposed theoretical model.     

拉延筋约束阻力的数值模拟研究

在覆盖件的数值模拟中,为提高等效拉延筋的模拟精度,需要建立合理有效的拉延筋约束阻力求解模型。文章根据平面应变假设,建立了合理的数值模拟研究模型。模拟结果表明,弯曲过程中存在鲍辛格效应和加工硬化等现象。将该模型提取的拉延筋阻力曲线用于模拟软件,模拟结果与真实拉延筋模拟结果及物理实验进行比较,验证了该模型的合理性与有效性。该模型为研究拉延筋约束阻力提供了一种有效可行方案。     

圆筒形件冲压成形中拉深筋的成形性分析

建立了圆筒形件的有限元模型,利用CAE专业软件DYNAFORM,模拟得到该零件的成形极限图,分析了不同压边力和拉深筋设置情况下,圆筒形件在拉深过程中的成形性能。研究表明,拉深筋对板材的摩擦阻力和变形阻力有显著的影响。拉深筋的使用能有效控制局部变形,使零件变形趋于平衡,从而保证零件的顺利成形。     

基于有限元分析的覆盖件拉延筋设计与优化

结合等效拉延筋模型，采用基于有限元逆算法的三维有限元分析软件，对汽车后窗内板的拉延成形进行模拟。在确定合理的等效拉延筋阻力后，通过适当的优化算法对拉延筋的真实几何结构进行优化设计。并通过UG二次开发技术，获取优化的拉延筋几何参数和位置，在拉延件上生成真实的拉延筋模型。     

梯形拉深筋等效约束阻力模型研究

对拉深成形过程中板料经过梯形拉深筋时的变形情况进行了分析,运用能量法建立了一种简单实用的梯形拉深筋等效约束阻力计算模型,利用Dynaform软件对梯形拉深筋的等效约束阻力进行了模拟,将计算结果与模拟结果进行了比较。分析结果表明:在拉深成形过程中,如拉深筋设置在圆弧部位,板料经过拉深筋后最终等效约束阻力是随拉深过程的进行而变化的;板料通过设在直线段的筋产生的等效约束阻力,在一定的压边力下,其值为恒定的值;理论计算与模拟值基本吻合,在数值模拟时,该模型可以作为等效拉深筋使用。     

汽车灯罩冲压工艺分析及有限元数值模拟优化

采用基于动力显式算法的板料成形非线性有限元分析软件Dvnaform对某轿车灯罩的拉深成形过程进行了数值模拟仿真.研究了不同坯料形状及应用实际拉延筋时压边力对零件冲压成形的影响,通过FLD和成形结果对比,对坯料形状和压边力大小进行了调整,并得到了优化的拉深件坯料尺寸和压边力,为同类零件的生产起到了指导作用.     

Equivalent drawbead models for sheet forming simulation

Equivalent drawbead models associated with drawbead types, with which the geometrical modeling of drawbeads can be replaced in a numerical simulation of the stamping process, are introduced. The accuracy of the equivalent drawbead models rapidly computing the drawbead restraining and opening forces, based on the hybrid membrane/bending method accommodating Barlat’s anisotropic yield function for the plane stress state and the modified Chaboche model considering the Bauschinger effect and transient behavior under the plane strain condition, is verified by comparing the equivalent drawbead forces with those obtained from the finite element simulation. Moreover, the drawbead forces computed by equivalent drawbead models are employed in a finite element simulation of the automotive fender stamping process, from which the effectiveness and applicability of equivalent drawbead models are observed by comparing strains and draw-ins with those measured in the tryout panel.     

板料成形拉延筋技术研究现状

拉延筋在汽车覆盖件拉深成形中起着十分重要的作用。利用拉延筋可以调节和控制板料的变形程度和变形分布,抑制破裂、起皱、面畸变等多种冲压质量问题的产生。在很多情况下,拉延筋的设置合理与否将决定覆盖件拉深的成败。较系统地总结了板料成形拉延筋技术以及拉延筋作用原理、阻力模型、影响因素等的研究现状。