Finite element simulation of the manufacturing process chain of a sheet metal assembly

An increasing number of components in automotive structures are today made from advanced high strength steel (AHSS). Since AHSS demonstrates more severe springback behaviour than ordinary mild steels, it requires more efforts to meet the design specification of the stamped parts. Consequently, the physical fine tuning of the die design and the stamping process can be time consuming. The trial-and-error development process may be shortened by replacing most of the physical try-outs with finite element (FE) simulations of the forming process, including the springback behaviour. Still it can be hard to identify when a stamped part will lead to an acceptable assembly with respect to the geometry and the residual stress state. In part since the assembling process itself will distort the components. To resolve this matter it is here proposed to extend the FE-simulation of the stamping process, to also include the first level sub-assembly stage. In this study a methodology of sequentially simulating each step in the manufacturing process of an assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparing with a physically manufactured assembly. The assembly is composed of three sheet metal components made from DP600 steel which are joined by spot welding. The components are designed to exhibit severe springback behaviour in order to put both the forming and subsequent assembling simulations to the test. The work presented here demonstrates that by using virtual prototyping it is possible to predict the final shape of an assembled structure.     

FE Simulation Models for Hot Stamping an Automobile Component with Tailor-Welded High-Strength Steels

Ultra-high-strength in sheet metal parts can be achieved with hot stamping process. To improve the crash performance and save vehicle weight, it is necessary to produce components with tailored properties. The use of tailor-welded high-strength steel is a relatively new hot stamping process for saving weight and obtaining desired local stiffness and crash performance. The simulation of hot stamping boron steel, especially tailor-welded blanks (TWBs) stamping, is more complex and challenging. Information about thermal/mechanical properties of tools and sheet materials, heat transfer, and friction between the deforming material and the tools is required in detail. In this study, the boron-manganese steel B1500HS and high-strength low-alloy steel B340LA are tailor welded and hot stamped. In order to precisely simulate the hot stamping process, modeling and simulation of hot stamping tailor-welded high-strength steels, including phase transformation modeling, thermal modeling, and thermal-mechanical modeling, is investigated. Meanwhile, the welding zone of tailor-welded blanks should be sufficiently accurate to describe thermal, mechanical, and metallurgical parameters. FE simulation model using TWBs with the thickness combination of 1.6 mm boron steel and 1.2 mm low-alloy steel is established. In order to evaluate the mechanical properties of the hot stamped automotive component (mini b-pillar), hardness and microstructure at each region are investigated. The comparisons between simulated results and experimental observations show the reliability of thermo-mechanical and metallurgical modeling strategies of TWBs hot stamping process.     

A comparative study of stamping and hydroforming processes for an automobile fuel tank using FEM

The use of sheet metal in the hydroforming process for hollow bodies is a new manufacturing technology for the automotive industry. In this paper, a comparison is made between the forming processes of sheet hydroforming and conventional stamping for production of an automobile fuel tank using a commercial explicit FEM code. A modeling methodology for correlation between stamping and hydroforming is proposed in order to obtain the optimal process parameters for producing a sound hydroformed fuel tank. The simulation model for a conventional stamping process is also verified by comparison with experiment. Finally, it is concluded that the hydroforming process can produce a fuel tank with a more uniform and sound thickness distribution than the stamping operation.     

高强钢板冲压回弹影响因素研究

基于ISO-CD24213/2006方法,以回弹角作为回弹值,运用Dynaform对高强钢板的冲压成形及回弹进行数值模拟,分析了板料厚度、板料宽度、压边力、拉延筋及材料性能等因素对回弹值的影响.研究发现:较小压边力下回弹值随板料厚度的增加而减小,较大压边力下则先增大、后减小,且随着压边力的增大回弹值显著减小;此外,减小板料宽度、合理布置拉延筋、选择屈服强度较小的材料均可减小回弹值.     

汽车覆盖件回弹试验及基于广义成形技术的回弹缺陷CAE分析方法

针对汽车外覆盖件冲压回弹缺陷,设计并制造4种不同的试验模具,在试验模具中包含了在汽车外覆盖件容易产生回弹的典型的反拉延特征。通过冲压试验,观察到表面回弹缺陷的产生,并搜集产生表面回弹缺陷处的最大和最小应力应变曲线图,及在回弹区域的位移偏移量云图。同时,以自主开发的商品化冲压成形CAE软件KMAS/UFT模块为平台,针对冲压过程中回弹缺陷进行精确预示,模拟计算结果与冲压试验结果基本一致。依据广义成形理论,提出针对回弹控制方案实施建议,对进一步修正冲压模具奠定基础。     

Modeling and FE Simulation of Quenchable High Strength Steels Sheet Metal Hot Forming Process

High strength steel (HSS) sheet metal hot forming process is investigated by means of numerical simulations. With regard to a reliable numerical process design, the knowledge of the thermal and thermo-mechanical properties is essential. In this article, tensile tests are performed to examine the flow stress of the material HSS 22MnB5 at different strains, strain rates, and temperatures. Constitutive model based on phenomenological approach is developed to describe the thermo-mechanical properties of the material 22MnB5 by fitting the experimental data. A 2D coupled thermo-mechanical finite element (FE) model is developed to simulate the HSS sheet metal hot forming process for U-channel part. The ABAQUS/explicit model is used conduct the hot forming stage simulations, and ABAQUS/implicit model is used for accurately predicting the springback which happens at the end of hot forming stage. Material modeling and FE numerical simulations are carried out to investigate the effect of the processing parameters on the hot forming process. The processing parameters have significant influence on the microstructure of U-channel part. The springback after hot forming stage is the main factor impairing the shape precision of hot-formed part. The mechanism of springback is advanced and verified through numerical simulations and tensile loading-unloading tests. Creep strain is found in the tensile loading-unloading test under isothermal condition and has a distinct effect on springback. According to the numerical and experimental results, it can be concluded that springback is mainly caused by different cooling rats and the nonhomogengeous shrink of material during hot forming process, the creep strain is the main factor influencing the amount of the springback.     

宽板U形弯曲的回弹试验研究

带状板材在受到冲压后,如果冲压工艺设计不合理,回弹会使板料的冲压结果达不到下一步安装工艺的要求。通过试验的方法,探求在无边压力的情况下板材的回弹问题,分别就板材性能、板料厚度、凸模圆角半径、凸凹模间隙、凹模跨度和摩擦因数等诸多因素对板料回弹的影响进行了分析,得出板材U形弯曲时回弹规律:凸凹模间隙越小,回弹就越小;随着凸凹模跨度的增大,回弹角增大;同一种板材,板材厚度越小,回弹就越大。研究结果有利于工业企业控制金属板材的回弹。     

Improvement of the drawability based on the surface friction stir process of AA5052-H32 automotive sheets

Based on the imperative social demand for lighter vehicles, lightweight materials such as aluminum alloys are expected to replace conventional steels in many automotive applications. In automotive parts manufacturing, most of the components produced in conventional stamping operations are geometrically complex as the blanks are subjected to both stretching and drawing deformations. However, aluminum alloys have intrinsic drawbacks, such as the inferior formability of these materials, although the effects of the weight reduction in terms of performance are highly promising. In an effort to improve the formability of aluminum alloy sheets, the surface friction stir process is proposed in this study. This process locally modifies the surface of automotive aluminum alloy sheets via stirring and advancing on the surface of the sheet, similar to the Friction Stir Welding (FSW) process that utilizes a probe without a pin. When the surface of the sheet is modified locally by stirring, dynamic recrystallization due to the severe shear deformation along with heat resulting from the friction occur due to changes in the micro-structure and mechanical properties in the stirred zone, while the dislocation density and grain size refinement are curtailed. In this work, the drawability performance of AA5052-H32 sheets (thickness 1.5 mm) that were welded using the surface friction stir process was experimentally and numerically investigated in cylindrical cup drawing tests. When applied to AA5052-H32 automotive sheets, the surface friction stir process improved the drawability of the entire aluminum alloy sheet. For numerical simulations, the non-quadratic anisotropic yield function Yld2000-2d was employed along with isotropic hardening, while the formability was evaluated by utilizing theoretical forming limit diagrams (FLD) based on Hill's bifurcation and M-K theories.     

筒形件磁脉冲辅助冲压成形数值模拟

针对磁脉冲辅助冲压成形过程,提出了基于ANSYS平台的有限元分析程式,通过编制用户子程序,采用重启动分析法,建立了冲压预成形过程显式求解和瞬态磁脉冲成形"松散"耦合分析之间的动态连接,并用于5052-O铝合金圆筒形拉深件磁脉冲辅助冲压成形过程的有限元仿真研究。结果表明,所建立的有限元分析方案,能实现圆筒形件磁脉冲辅助冲压成形连续变形过程的模拟,板坯变形信息体现了准静态冲压变形和高速率磁脉冲成形之间的耦合。有限元模拟结果与实验吻合较好。     

车用铝合金板材回弹规律研究

在车用铝合金材料的成形加工过程中,回弹是主要的成形缺陷之一并且较难控制。本文对车用6061铝合金板材进行了室温拉伸试验获得其应力-应变曲线并建立改进的Johnson-Cook本构模型。该模型被应用于V形弯曲试验的有限元仿真中,研究不同各向异性屈服准则对板料回弹预测精度的影响,仿真结果表明应用YLD2000-2d屈服准则时其预测精度较高,同时也验证了该模型用于回弹分析的有效性。进一步探究不同因素如变形程度,冲压速度,摩擦条件,压边力等对铝合金板材回弹行为的影响规律,并应用于铝合金发罩内板的冲压成形过程,能够有效减小工件的回弹。     

板料成形回弹模拟及补偿技术研究现状

板料冲压成形过程中的回弹是卸载过程产生的反向弹性变形,是一种普遍存在的物理现象.目前,越来越多的商业化CAE软件实现了金属薄板冲压成形过程中的回弹模拟,但是回弹模拟精度仍然是数值模拟的难点.本文详细分析了影响回弹模拟精度的主要因素,总结了回弹模拟及补偿技术国内外发展现状.这对制定合理的冲压工艺方案,并在模具设计过程中,考虑回弹的关键因素,以便修正模具尺寸,补偿回弹误差,具有重要的实际意义.     

Springback prediction of TWIP automotive sheets

In an effort to reduce the weight of vehicles, automotive companies are replacing conventional steel parts with light weight alloys and/or with advanced high strength steels (AHSS) such as dual-phase (DP), twinning induced plasticity (TWIP), and transformation induced plasticity (TRIP) steels. The main objective of this work is to experimentally and numerically evaluate the macro-performance of the automotive TWIP sheet in conjunction with springback. In order to characterize the mechanical properties, simple tension and tension-compression tests were performed to determine anisotropic properties, as well as the Bauschinger, transient, and permanent softening behaviors during reverse loading. For numerical simulations, the anisotropic yield function Yld2000-2d was utilized along with the combined isotropic-kinematic hardening law based on the modified Chaboche model. Springback verification was performed for the unconstrained cylindrical bending and 2D draw bending tests.     

薄板精密冲裁的变形过程和机理研究

本文构建了料厚为0.3mm的薄板精密冲裁变形有限元模型,运用该模型研究了薄板精密冲裁变形过程,分析结果显示冲裁断面质量与生产实际非常接近.论文分析了薄板精密冲裁变形过程中的静水应力的分布特征、影响机理.研究表明,强压边条件增加了静水压应力区域的范围和程度,从而延迟了裂纹的初始和发展,提高了冲裁断面的质量.     

Numerical modeling and deformation analysis for electromagnetically assisted deep drawing of AA5052 sheet

Electromagnetic forming(EMF) is a high-velocity manufacturing technique which uses electromagnetic (Lorentz) body forces to shape sheet metal parts. One of the several advantages of EMF is the considerable ductility increase observed in several metals, with aluminum featuring prominently among them. Electromagnetically assisted sheet metal stamping(EMAS) is an innovative hybrid sheet metal processing technique that combines EMF into traditional stamping. To evaluate the efficiency of this technique, an experimental scheme of EMAS was established according to the conventional stamping of cylindrical parts from aluminum and the formability encountered was discussed. Furthermore, a “multi-step, loose coupling” numerical scheme was proposed to investigate the deformation behaviors based on the ANSYS Multiphysics/LS-DYNA platform through establishing user-defined subroutines. The results show that electromagnetically assisted deep drawing can remarkably improve the formability of aluminum cylindrical parts. The proposed numerical scheme can successfully simulate the related Stamping-EMF process, and the deformation characteristics of sheet metal reflect experimental results. The predicted results are also validated with the profiles of the deformed sheets in experiments.     

Experimental investigations and numerical analysis for improving knowledge of incremental sheet forming process for sheet metal parts

The paper is related to the analysis of shape distortions and springback effects arising in single point incremental sheet forming in order to study the use of a FE model based on shell elements to perform simulation of the process. A comparison between numerical and experimental results is made to assess the suitability of the model. The measurements of geometrical profile of a truncated cone and springback of cut rings show that the FE model allows to predict accurate results for a set of well defined process parameters. The deformation mechanism of ISF is taken into consideration to determine the limits of the model studied.     

板料成形FE中网格节点重构参数曲面的方法研究

有限元模拟成形仿真的结果,可以帮助设计开发者正确选择冲压工艺参数和模具形状及材料特性等。在对模拟进行后处理过程中,往往必须了解由有限元节点构成的参数曲面的性质,为后续回弹分析及毛坯设计提供重要支持。如何应用变形后的节点阵构成光顺的几何曲面是问题的关键。文章给出了由节点序列散点构成非均匀B样条光顺曲面的实际算法,并开发了应用程序。对散乱点数据构成曲面进行了系统的阐述,所开发的方法已经用于板料成形仿真中FE网格节点重构曲面。     

Experimental springback evaluation in hydromechanical deep drawing (HDD) of large products

Springback is a really troublesome effect in sheet metal forming processes. In fact changes in geometry after springback are a big and costly problem in the automotive industry. In this paper the authors want to analyse the springback phenomenon experimentally in sheet metal hydroforming. Compared with conventional deep drawing, sheet hydroforming technology has many remarkable advantages, such as a higher drawing ratio, better surface quality, less springback, better dimensional freezing and capability to manufacture complicated shapes. The springback phenomenon has been extensively analysed in deep drawing processes but there are not many works in the literature about springback in sheet metal hydroforming. In order to study it, the authors have performed an accurate measuring phase on the chosen test cases through a coordinate measuring machine and the obtained measurements have been utilised for the determination of springback parameters, taking into account the method proposed by Makinouchi et al. The authors have focused their attention on the possibility of adopting a modified Makinouchi et al. approach in order to measure the springback of the large size considered test cases. Through the implemented methodology it has been possible to calculate the values of the springback parameters. The obtained results correspond to the observed experimental deformations. Analysing the springback parameter values of the different combinations investigated experimentally, the authors have also studied the pre-bulging influence on the springback amount.     

U形件拉深成形回弹影响因素的计算机仿真(英文)

回弹是板料冲压成形中的主要缺陷之一 ,控制回弹涉及到回弹量的准确预算。利用DANAFORM软件 ,对U形件拉深成形回弹影响因素进行了计算机仿真 ,得到了压边力、凸凹模间隙、摩擦系数、材料特性等参数对回弹影响的数值结果 ,并对模拟结果进行了分析。