S梁的拉深成形数值模拟

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,优化工艺参数,从而缩短模具设计周期,降低成本。基于Dynaform有限元分析软件,对S梁的拉深成形过程进行了数值模拟。针对起皱和未充分拉深等缺陷,提出了压边力和拉深筋工艺参数的改进方案并加以比较,得到了较好的成形模拟结果。试验结果表明：压边力为400kN（不加拉深筋）或300kN（加拉深筋）时成形质量较好。     

Form-accuracy analysis and prediction in computer-integrated manufacturing

The manufacturing of high-quality products at low costs is one of the greatest challenges of every company today. Form accuracy is among the quality parameters of machined parts and is directly related to functional performance. Control and improvement of form accuracy is to be performed under the computer-integrated manufacturing (CIM) concept. This paper investigates the form accuracy of mechanical machining and studies the essential aspects and procedures of form-accuracy simulation. The emphases are on the integration of form-accuracy analysis and the simulation into the CIM database construction and virtual manufacturing. Form-accuracy analysis in this paper reveals that the inherent drawbacks in design will directly affect the geometric quality of a workpiece, and proper process planning can enhance the manufacturability of parts with the required geometric quality. The simulation procedure implemented in this paper can be used at the design stage to predict the form accuracy of a machined part and functional performance. The procedure can also be used at the process planning stage to predict and control form accuracy during the machining process.     

应用JSTAMP／NV的管材液压成形案例仿真

为有效地预测管材液压成形过程中存在的问题,比如：制件在外侧过度减薄和内侧起皱,用JSTAMP／NV对汽车副车架液压成形工艺过程进行有限元模拟分析,得出各工序的仿真结果。应用逆向求解器Hystamp仅需直接指定管坯的尺寸参数、材料和弯曲工艺参数即可自动执行弯曲仿真计算并可在几秒内获取弯曲仿真的结果;应用LS—DYNA执行预成形和液压成形工序仿真的计算,需设定液压成形工序的工艺参数,包括液压加载的曲线和方向以及轴向进给位移。JSTAMP／NV能有效模拟管材液压成形工艺过程并预测成形过程中在变形区出现的屈曲、起皱和破裂等缺陷,可以为工艺试验提供指导。     

A review of the mechanics of metal spinning

This review presents a thorough survey of academic work on the analysis and application of the mechanics of spinning. It surveys most literature published in English and the most important publications in German and Japanese languages. The review aims to provide insight into the mechanics of the process and act as a guide for researchers working on both metal spinning and other modern flexible forming processes.The review of existing work has revealed several gaps in current knowledge of spinning mechanics: the evolution of the stress state and the strain history of the workpiece in both conventional and shear spinning is not well understood, mainly due to the very long solution times that would occur in modelling the process throughout its duration with a sufficiently fine mesh to capture detailed behaviour through the workpiece thickness; the evolution of microstructure, residual stress and hence springback, has not been examined—either numerically or by experiment; the failure mechanisms of spinning – fracture and wrinkling – are only partially understood, through analogy with other processes, and as yet models of the process have not made use of contemporary damage mechanics; the design of toolpaths required to make particular parts without failure remains an art, and cannot currently be performed automatically with confidence. Studies on novel process configurations in spinning have shown that great potential for innovation in spinning exists. The process has the potential to be more flexible, to produce a wider range of shapes, and to form more challenging materials.     

板料形状、压料筋的设置对汽车覆盖件成形中起皱和未充分拉深的影响

在汽车覆盖件成形工艺中,无论是对外观还是对功能的要求,起皱和未充分拉深问题是不允许出现的,因此对起皱和未充分拉深问题的预测和防止显得非常重要的。采用数值模拟技术可以在模具设计初期预测产品的几何形状,从而优化工艺参数以便获得高质量的成品。文章以eta/DYNAFORM有限元分析软件为平台,采用弹-塑性有限元法对DDQS钢进行数值模拟,得出相应的FLD曲线、起皱和未充分拉深区域。重点探讨了板料形状和压料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。     

Finite element analysis of the wrinkling initiation and growth in modified yoshida buckling test

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of wrinkles are influenced by many factors such as stress ratios, mechanical properties of the sheet material, geometry of the workpiece, contact condition, etc. In the study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. The wrinkling initiation is found by checking the determinent of the stiffness matrix at each iteration and the wrinkling behavior is analyzed by successive iteration with the perturbed guess along the eigenvector. The effept of magnitude of perturbation on the wrinkling behavior can be avoided by the Newton-type iteration method. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using the continuum-based resultant shell elements considering the planar anisotropy of the sheet metal. In order to investigate the effects of geometry and stress state on the wrinkling initiation and growth, a modified Yoshida buckling test is proposed as an effective buckling test. The finite element analysis are carried out for the modified Yoshida buckling test. The buckling behavior of the sheet is analyzed for various modified dimensions.     

Raising by spinning

Industrial metal spinning depends on costly trial-and-error when introducing new products. However, a recently developed flexible spinning setup allows a new form of process operation similar to raising by hammering: two rollers on either side of the rotating workpiece apply a couple to deform it locally whilst moving towards its edge. This paper presents this configuration for the first time and develops and verifies an upper bound yield-line model to design stable tool-paths that avoid wrinkling. Raising by spinning is shown to be feasible and more stable than conventional spinning, paving the way for automatic production of deep axisymmetric shapes.     

盒形件法兰皱曲失稳的临界条件

在盒形件拉深成形智能化控制过程中,为了防止法兰起皱的产生,必须认识起皱发生的机理,进而对起皱的发生进行控制.本文基于一点应力状态的C-B准则建立了应用与判断法兰起皱的判断准则,完善了起皱的预测方法,给出了获得起皱的临界行程与压边力关系曲线的方法,这为进一步实现法兰起皱的实时预测提供了依据.     

薄壁铝合金封头旋压成形工艺研究

应用ANSYS软件对薄壁铝合金封头冷旋压成形过程进行了弹塑性有限元数值模拟.通过对球冠部分和翻边部分第1道次各阶段的应力应变分析,揭示了其成形时的塑性变形流动规律,并分析了几种主要工艺参数对成形质量的影响规律及失效问题产生的原因.研究结果表明：薄壁铝合金封头冷旋压成形的主要失效形式是翻边部分的外缘起皱,控制皱纹产生的有效方法是采用弯边措施增加外缘法兰的刚度、选择合适的第1道次倾角和采用较小的进给比.     

An experimental evaluation of coefficients of static friction of common workpiece–fixture element pairs

Most machining fixtures utilize clamping forces and friction at fixture–workpiece joints to help prevent the workpiece from slipping out of the fixture during machining. The magnitudes of the clamping forces required are a direct function of the coefficients of static friction at the joints. Recently, analytical methods have been developed to predict minimum clamping forces. However, these methods require accurate estimates of the friction coefficients.One source of friction data are handbooks. However, these data are typically listed relative to the materials of the contacting elements and are otherwise completely generalized. This paper will illustrate that the coefficient of static friction for typical fixture–workpiece joints is not a simple function of the workpiece materials. Instead it is also a function of factors such as fixture element geometry, workpiece surface topography, clamping forces, the presence or absence of cutting fluids, and normal joint rigidity.     

电火花线切割加工工件厚度在线识别技术研究

通过理论分析方法推导得到工件厚度与放电间隙两端间的平均电压、平均电流、机床伺服进给速度、线切割缝宽等参数的关系式。采用田口试验方法分析不同加工参数下电火花线切割加工不同厚度工件时放电两极之间平均电压、平均电流、线切割缝宽及加工速度的影响规律,研究一种基于灰色理论的线切割缝宽预测模型,并基于该模型研究一种基于广义回归模型在线识别电火花线切割加工工件厚度的方法。工件厚度在线识别技术可实现电火花线切割加工时对工件厚度的预测,是电火花线切割自适应加工变厚度工件的前提和关键。     

端铣加工面尺寸误差预测

为了精确预测端铣加工面尺寸误差,利用铣削动态力卷积模型,引入表面生成窗概念,并考虑到工件与刀具的变形误差、机床空间误差与刀具偏摆的影响,建立了加工面尺寸误差预测模型。通过在铣床上进行实验,验证了该模型能够正确预测工件尺寸误差及其分布范围,且在铣刀轴向切深、主轴转速和进给速度一定的情况下,增加径向切深不会对工件尺寸误差产生显著影响。     

激光拼焊板制轿车门内板冲压成形的数值模拟

利用Dynaform软件对激光拼焊制轿车门内板进行了冲压成形数值模拟,分析了冲压成形过程中出现的拉裂、起皱、变形不充分和焊缝移动量过大等严重影响产品质量的成形缺陷产生的原因,采用正交实验法对拉深工艺参数和模面结构参数进行设计,提出选择最佳压边力、设置拉深筋高度合理、改善润滑条件等优化方案,可以改善成形质量;采用二次拉深成形工艺,能有效改善起皱、拉裂、焊缝移动和成形不充分等缺陷。实际的工艺设计和生产证明,成形过程与数值模拟实验结果吻合良好。     

自动装夹设计中支承位置与工件变形的几何推理方法

定位支承设计是装夹设计过程的核心部分。描述了一种自动装夹设计系统体系结构，并建立了初始装夹设计方案中工件最大变形的分析模型，应用有限元分析工具对工件最大变形进行定量分析；用3-2-1定位原理和定性分析方法提出了最佳定位支承点的调整规则和用几何推理方法求解最小变形定位支承位置推理机制。为自动装夹设计系统提供一种用3-2-1定位原理确定定位支承位置的一般算法，使工件在自动装夹设计过程中具有严格准确的位置。     

汽车钣金外观匹配小圆角成形工艺研究

针对某车型翼子板与前保险杆匹配处、侧围与后保险杆匹配处的钣金外观小圆角(R1.5 mm)工艺进行研究与验证,通过优化零件的冲压方向、过拉深工艺补充设计、CAE分析参数优化等方法,解决了圆角不顺、开裂、起皱等问题,并通过现场冲压验证了工艺方案的合理性,对R1.5 mm及以下匹配小圆角的成形和推广具有重要的意义。     

两厢轿车顶盖尾部冲压工艺优化设计

针对两厢轿车顶盖尾部在拉深、整形后出现起皱的问题,通过Autoform模拟及造型设计分析,对原工艺进行优化,设计了一种上、下模不同造型的工艺方案。该方案能有效增加材料流动性,消除制件起皱的缺陷,对同类制件的冲压工艺设计具有参考意义。     

大落差高强地板纵梁起皱问题解决方案

轻卡驾驶室高强地板纵梁的Z向落差大,该地板纵梁在成形过程中,材料流动易在落差面的中下部位形成积聚,导致制件起皱。在制件设计的初期,通过制件合理增加吸皱特征,并结合Autoform分析、优化工艺补充面,将起皱问题最大限度的得以解决。     

一种柔性变压边力的智能冲压过程研究

板料成形时易产生破裂、起皱以及尺寸和形状精度不良的倾向。在伺服压机的基础上,研究一种柔性可变压边力的独立加载闭环控制系统。选择圆筒形工件为模拟对象,利用有限元软件分析圆筒形工件在不同定值下及变压边力下冲压仿真结果。比较得到成形圆筒形工件的最优压边力曲线以及冲压载荷随时间变化的曲线,加载到装置的控制系统,使压边单元与板材始终处于贴合状态。该闭环系统通过压机变载、变行程等不同的运动模式协同柔性压边装置对冲压成形过程进行控制,柔性控制压边力和冲模载荷,来适合零件不同变形阶段的特点。实验证明:该系统可以最大限度提高金属板材成形性能,不仅防止了板材变薄在尾部产生褶皱以及工件拉裂的情况,而且可以提高板材拉深极限。     

A theoretical,numerical, and experimental investigation of plastic wrinkling of circular two-layer sheet metal in the deep drawing

In this paper, the wrinkling of two-layer (aluminum-stainless steel) sheets in the deep drawing process, is investigated through an analytical method, numerical simulations, and experiments. In a deep drawing process, wrinkling can always be eliminated with an increase in the blank holder force (BHF). Thus, the aim of this study is to obtain the minimum required BHF to prevent wrinkling. In the analytical model, energy method is used to predict the wrinkling. Also, FE simulations were performed to study the effect of forming parameters on wrinkling. Experiments have been conducted to verify the analytical model and FE simulations. The effects of parameters such as the material properties of aluminum layer and lay-up on BHF and forming force are investigated. Results demonstrate that the optimum BHF is dependent on the blank geometry, material properties and lay-up. It is shown that BHF is greater when aluminum is in contact with the punch. Results show a good agreement between analytical, FE, and experimental results.     

A hybrid method for accurate prediction of multiple instability modes in in-plane roll-bending of strip

The in-plane roll-bending of strip (IRS) is a flexible forming process to produce ring parts with advantages of low forming forces, low material waste and good flexibility. However, if deformation condition is inappropriate, it results in several instability modes including external wrinkling, internal wrinkling, turning-I and turning-II. Solely using pure analytical solution, implicit finite element method (FEM) or explicit FEM cannot predict all these instability modes of the strip. In this study, a new hybrid method is proposed to accurately predict all these instability modes in IRS. First, using two analytical models with two simple support conditions to simplify the actual roll-bending conditions, the eigenvalue buckling analysis and the analytical solution analysis are conducted to generate four kinds of buckling modes, respectively, and a series of imperfections are defined in the shapes of these buckling modes. Second, assigning these geometrical imperfections into the perfect geometry of strip, a series of hybrid FE models for IRS are established. Four specific case studies of external wrinkling, internal wrinkling, turning-I and turning-II are carried out. By comparing with corresponding experimental results, an appropriate imperfection and an optimal scaling factor A_i are obtained. Third, to validate our proposed method, the hybrid method is applied to five cases of arbitrary experimental condition. The comparisons between the predicted results and experiments show that the proposed method is reliable to accurately predict all instability modes in IRS.