Warm forming die design,Part II: Parting surface temperature response characterization of a novel thermal finite element modeling code

The majority of the research activities in the area of warm forming are concentrated on demonstrating or simulating the improved formability associated with forming lightweight materials such as aluminum alloys at elevated temperatures. However, the ability to design the proper thermal management system within the forming tool is a critical aspect to delivering this technology as a viable, stable production alternative to traditional stamping. This work begins to address the thermal stability issues of this process by examining the impact of process cycle time on the parting surface temperature response. Cycle times of 10, 15, 30, and 300 s were evaluated using a reciprocating surface and a self-heated experimental block of 1020 steel fitted with resistance cartridge heaters. The presented results indicate that cycle time does not significantly impact the steady-state temperature response at the parting surface for a well-insulated die that has proper thermal management. Parting surface experimental results were compared to values obtained numerically and through the use of the novel thermal finite element analysis software PASSAGE/Forming^®.     

有限元仿真技术在板材成形中的应用

有限元仿真技术具有很强的经济性和柔性，已广泛应用于汽车钢铁工业领域。文中论述了板材成形有限元仿真分析的关键技术及其研究进展，并采用动力显式有限元软件LS-DYNA对轻型车侧围后外板零件冲压成形过程进行了仿真计算，分析了变形过程的金属流动规律。     

薄板深拉延成形有限元仿真

板材成形有限元仿真采用虚拟制造技术反映模具与板材之间的相互作用以及板材实际变形的全过程,有助于推动生产的快速化和设计的智能化。汽车企业通过对板材成形过程的有限元仿真可确定钢板性能参数范围和冲压工艺参数范围,以保证生产的稳定性。采用动力显式有限元软件LS-DYNA,对上海宝钢St14-T冷轧薄板的深拉延成形过程进行了仿真计算,分析了变形过程的金属流动规律。     

半固态触变成形坯料感应加热的数值模拟

半固态触变成形技术以其降低宏观偏析、减少多孔性、成形力小和近终成形等优点受到广泛关注。在触变成形之前 ,使坯料具有均匀的固 液相分布和球状晶粒是很重要的 ,这就要求加热快而迅速。为满足这一要求 ,目前普遍采用电磁感应加热。文中对感应加热进行了有限元理论分析 ,采用商用有限元软件ANASYS对半固态触变成形坯料感应加热进行了数值模拟 ,模拟了频率、加热时间、线圈电流强度系数、坯料尺寸半径、线圈尺寸大小等参数对坯料温度的影响。     

LYl2半球形件拉深成形过程的动力显式有限元模拟

基于连续介质力学及有限变形理论 ,建立了用于三维板料成形过程模拟的有限元模型 ,开发了动力显式算法的板料成形过程模拟的有限元分析程序DESSFORMM3D。最后 ,用笔者新开发的动力显式弹粘塑性有限元程序对不同压边情况下半球形件的拉深过程进行分析 ,并把数值结果与实验进行对比 ,验证了软件的计算结果。     

LDR and hydroforming limit for deep drawing of AA5754 aluminum sheet

The goal of the research was to determine the limits and conditions in which the sheet hydroforming process provides a significant advantage over stamping in deep drawing of AA5754 aluminum sheets. Specifically, the maximum draw depth achievable by stamping, warm stamping (WF), sheet hydroforming (SHF), and sheet thermo-hydroforming (THF) of AA5754 aluminum alloy were quantified through experimental and computational modeling. A limited number of forming experiments were conducted with AA5754 aluminum sheets using a cylindrical punch and counteracting fluid at different temperatures and pressures. Several parameters, such as force–displacement, hydroforming pressure and temperature, and the maximum draw depth prior to wrinkling or tearing were measured during the forming process to make comparisons with simulations. The computational study included the simulation of stamping, WF, SHF and THF of AA5754 aluminum sheet with the LS-Dyna code, and the Barlat 2000-2d yield function with temperature-dependent coefficients. To predict the onset of wrinkling and tearing, the numerically generated, temperature-dependent forming limit diagrams (FLDs) based on the Barlat 2000-2d yield function were used. It was found that compared with stamping, SHF and THF can achieve more than 100% deeper draw depths with AA5754 aluminum sheet. The stamping simulations were used also to calculate the optimum blank size and die corner radii for the limiting draw ratio (LDR). The LDR was found to be very sensitive to the punch and die corner radii used in the experiments, which represent the curvature of character lines in an actual part. The LDR for AA5754 aluminum sheet was found to be 1.33 and 2.21 for sharp and round die corner radii, respectively. Overall, it was concluded that SHF is most ideal for deep drawing of aluminum sheets with sharp radii features. With the additional drawability provided by SHF, the automotive industry would be able to make difficult-to-form aluminum parts that cannot be stamped without product concessions such as increasing the die radii.     

金属板材成形的静力隐式有限元分析与程序设计

阐述了用于板材成形过程静力隐式数值模拟的弹塑性大变形有限元方法 ,基于给出的方法编制了板材成形过程数值模拟软件 ,并对矩形板的液压胀形进行了有限元分析 ,计算结果与典型的实验结果吻合很好。对球形模具拉伸成形过程进行了数值模拟 ,给出了计算结果     

面向对象板料成形有限元模拟软件的图形平台设计与实现

在板料成形有限元模拟软件系统中 ,图形平台是重要的组成部分。介绍了图形平台的设计与实现 ,并重点阐述了面向对象编程技术在软件开发中的实际应用 ,同时结合图形平台需要提供的功能 ,给出了图形平台各个类的继承关系和实现中的一些关键技术。实践表明 ,此平台具有较好的灵活性、可靠性和可扩展性     

多通管塑挤胀形关键技术的研究

多通管是工业上应用量大面广的一种基础件,但其传统的制造工艺目前还只限于铸造、焊接和机加工等,从经济或技术的角度讲都显得比较落后.此文讨论了利用聚氨酯橡胶棒为胀形介质,采用塑挤胀形的复合工艺把无缝管坯一次成形为成品的加工方法,分析了多通管塑挤胀形的过程,讨论了冲头作用于管坯的压力、聚氨酯橡胶棒产生的内压和平衡缸应提供的背压三者间应具备的合理的关系.以使变形区处于最有利于变形的强烈的三向压应力和合适的偏应力状态,获得尽可能长的支管.     

半球形件粘性介质压力成形的数值模拟研究

粘性压力成形技术是金属板材成形领域里新近出现的一种先进的加工工艺。对双面施放粘性介质的板材胀形进行了模拟研究 ,在双面施放介质的板材粘性介质胀形时 ,排放孔位置分布对毛坯成形过程有明显的影响。排放孔位置分布的不同造成模腔内介质的速度场不同 ,进而导致板材不同部位的流动速度的方向大小发生变化 ,最终使成形件的厚度分布不同     

冲模压力中心的快速确定

说明了基于VB6.0的冲模压力中心的开发过程 ;实现了冲模压力中心的快速、准确定位 ,即确定冲模压力中心与已知任意两点之间的距离     

材料结构参数对薄板冲压成形仿真结果的影响

采用不同材料屈服模型及参数对典型冲压过程进行了仿真 ,对仿真结果进行了分析。分析表明材料模型及参数对仿真结果影响至关重要 ,板料的厚度分布及成形极限图对结构参数n和r值很敏感。这对更好的了解不同材料在冲压时的力学行为和进行冲压仿真时怎样合理选择材料模型及参数提供了帮助     

板料成形模拟中压边力处理的研究

针对弹性压边建立了一个力学模型 ,用于板料成形的动力显式有限元模拟。以NU MISHEET’93方盒拉深标准考题为例 ,模拟了方盒在不同压边力情况下的起皱情况。数值计算结果表明该模型能有效地模拟弹性压边力 ,并预测工件法兰部位的起皱状况。     

采用薄膜模型模拟三维板料成形过程

此文基于有限变形理论建立了三维金属板料成形过程的弹塑性有限元数学模型。数学模型采用物质坐标系中的Total Lagrange描述、J_2型本构方程、等向强化假设,考虑了板料的厚向异性,对于金属板料与模具的摩擦采用近似的库仑摩擦定律以改善计算的收敛性。为简化计算采用薄膜单元。采用根据此模型编制的程序模拟了机油收集器基本件的成形过程,并与实验结果进行了对比。     

Determining work-brush interface temperature in magnetic abrasive finishing process

Magnetic abrasive finishing (MAF) is a process in which the work surface is finished by removing the material in the form of micro chips by magnetic abrasive particles (MAPs) in the presence of magnetic field in the finishing zone. During the MAF process, the frictional heat is generated at the workpiece surface due to the rubbing action of magnetic abrasive particles with the work surface. The order of temperature rise is important to study, as finishing mechanism and surface integrity of work materials depend upon it. The measurement of temperature distribution during MAF operation at the interface of work piece and flexible magnetic abrasive brush (FMAB) interface is difficult. In the present analysis, finite element based ANSYS software has been used to model and simulate magnetic field distribution, magnetic pressure and temperature distribution at work-brush interface during the process. In this work the maximum magnetic flux density has been simulated of the order of 0.223 T at 0.91 A of current in electromagnet coil. Magnetic pressure on MAPs due to magnetic field of electromagnetic coil has been calculated to evaluate the frictional heat flux generated at the work-brush interface. Transient thermal analysis of workpiece domain has been performed to predict the temperature rise due to frictional heat flux. The predicted temperature on work-brush interface was found in the range of 34–51 °C. The developed simulation results based on FEA have been validated with experimental findings.     

板料冲压成形和回弹分析过程的三维动态模拟

利用ANSYS/LS DYNA非线性动力有限元程序的显式 隐式连续求解功能 ,模拟了板料成形过程与卸载后板料回弹变形的全过程 ,得到了成形过程中任一时刻各处的应力和应变值及卸载后板料的回弹结果     

The development of a microscale strain measurement system applied to sheet bulge hydroforming

Micro and multiscale sheet metal forming processes represent new and attractive solutions to many manufacturing problems. However, evaluating the strains in these products is a difficult endeavor. Larger organizations are utilizing commercially available microscale digital image correlation systems to measure the strains in microscale parts or on macroscale parts with critical microscale features. The cost of these strain measurement systems is preventing smaller research and development organizations from entering this challenging area or they are forgoing the ability to determine strains. The present paper describes the development of a method for creating microscale grids and measuring strains on microscale parts or microscale locations on larger parts. The method developed was able to measure true strains up to 0.618 for square grids that are 127 μm measured from center-to-center. Microscale strains resulting from sheet bulge hydroforming experiments using 11 mm, 5 mm, and 1 mm diameter dies were evaluated and material properties of the sheet metal were estimated based upon the strains measured in conjunction with FEA simulations and compared to analytical solutions and microscale tension tests. The material properties determined using the strains and FEM approach were consistent with the other methods.     

电火花堆焊工艺在冲压模具维修上的应用

介绍了电火花堆焊设备及工艺在冲压模具维修中的使用情况,为大型冲压模具成形面拉伤修复探索出了一种新方法。     

Prediction of flange wrinkling in deep drawing process using bifurcation criterion

Surface distortions in the form of wrinkles are often observed in sheet metals during stamping and other forming operations. Because of the trend in recent years towards thinner, higher-strength sheet metals, wrinkling is increasingly becoming a more common and troublesome mode of failure in sheet metal forming. The prediction and prevention of wrinkling during a sheet forming process are important issues for the design of part geometry and processing parameters. This paper treats the phenomenon of flange wrinkling as a bifurcated solution of the equations governing the deep drawing problem when the flat position of the flange becomes unstable. Hill’s bifurcation criterion is used to predict the onset of flange wrinkling in circular and square cup drawing. In particular, the maximum cup height that can be drawn without the onset of flange wrinkling is predicted for the given set of process parameters. A parametric study of the maximum cup height is also carried out with respect to various geometric, material and process parameters. Finite element formulation, based on the updated Lagrangian approach, is employed for the analysis. The incremental logarithmic strain measure, which allows the use of a large incremental deformation, is used. The stresses are updated in a material frame. The material is assumed to be elastic–plastic, strain hardening, yielding according to an anisotropic yield criterion of Barlat et al. (2005) [23] (named as Yld2004-18p). Isotropic power law hardening is assumed. Inertia forces are neglected due to small accelerations. Modified Newton–Raphson iterative technique is used to solve the nonlinear incremental equations.     

大型车车身覆盖件冲压成形特征分析及选材研究

为满足大型车身覆盖件冲压成形要求并实现钢板与零件的对路供应 ,必须在深入解析零件成形特征的基础上 ,确定高应变部位的成形敏感材料参数。在材料力学性能测试和成形极限分析的基础上 ,对侧围外板的冲压成形特征和成形敏感参数进行了分析。结果表明 :侧围外板零件高应变部位的变形方式为胀形 深拉延变形 ,n值和r值为影响侧围外板零件成形的主要材料敏感参数