Investigation of active-elastic blank holder systems for high-pressure forming of metal sheets

Hydroforming constitutes a subgroup of sheet metal forming processes utilizing a pressurized forming medium. Besides the hydroforming of hollow sections, the high-pressure forming (HPF) of metal sheets is demonstrably one innovative method for the production of complex sheet metal components and offers high potentials to improve the properties and qualities of sheet metal parts. This report describes investigations of a newly developed active-elastic blank holder technology, which is used for HPF of metal sheets. Unlike the use of semi-rigid blank holder systems, the active-elastic blank holder system shows improvements with respect to the material flow in the flange area and reduced sheet thinning in critical corner regions of the work-piece. In addition to numerical analysis concerning the development and design of the active-elastic blank holder, current experimental examinations will be presented. The focus is on a comparative evaluation of the simulation and production of rectangular metal parts, by using conventional semi-rigid tools and active-elastic tools.     

叠层钢板成形模快速制造技术研究

研究了叠层制造工艺的分层处理技术,提出了一种基于EUCLID软件系统的CAD模型直接分层方法,采用等离子切割方法对板材进行切割,板件依序叠合起来后通过胶粘实现层间的粘接。实例表明该工艺为金属模具低成本快速制造提供了有益参考。     

Tribological measures for controlling material flow in sheet-bulk metal forming

Sheet-bulk metal forming (SBMF) is characterized by successive and/or simultaneous occurrence of quite different load conditions regarding stress and strain states. These conditions significantly influence the material flow and thus the geometrical accuracy of the components. To improve the product quality a control of the material flow is required. An appropriate approach is given by locally adapted tribological conditions due to surface modifications of tool and workpiece, so-called tailored surfaces. Within the present study different methods to adapt the surfaces are presented and investigated with respect to their tribological effectiveness in SBMF. In a first step, requirements regarding necessary adaptions of the friction values for two SBMF processes are numerically defined. Based on the requirements different tailored surfaces are presented and analyzed regarding their tribological influence. Finally, the potential of surface modifications to improve SBMF processes is shown.     

基于ABAQUS的汽车板材成形性能及变形规律研究

在板料液压成形过程中,由于流体压力的施加,对板材的受力状态会产生不同程度的影响,同时可以在一定范围内有效提高板材的成形性能。为了分析流体压力下板材成形性能的变化规律,基于有限元软件模拟软件ABAQUS,对不同流体压力条件下的2024铝合金的单向拉伸过程分别进行数值模拟研究,得出了流体压力对板材米塞斯应力分布、轴向应力分布、伸长率及颈缩区厚度的影响规律。研究结果表明,在流体压力作用下,板材的变形更加均匀;并随着流体压力的增大,板材表现出更大的变形潜力,可以达到更大的伸长量。     

超高精度表面的塑性加工技术

本文论述了用塑性加工技术成形高精度表面的原理及工艺条件,其结论为在最佳成形条件下,塑性加工技术完全可以生产出和精密机械加工技术同等的高精度表面。     

Prediction of surface topography in lubricated sheet metal forming

This study develops new model that is suitable for predicting the surface topography of the products of lubricated sheet metal forming. In the lubrication analysis, a finite element model is derived for the average Reynolds equation, no matter whether the tooling surface comes into contact with workpeice surface or not. With regard to the asperity contact theory and surface parameter analysis, a novel model takes account of the smoothing, roughening and tool elastic microwedge effects on the surface of the workpiece. A model was combined with a finite element membrane code of axisymmetric stretch forming to predict the contact area ratio and the surface roughness. Numerical results revealed that the new model is consistent with the experimental results. The superiority of the new model over the conventional model is that it predicts the surface roughness more accurately during the lubricated sheet metal forming process.     

A new joining by forming process to produce lap joints in metal sheets

This paper proposes a new joining by forming process to produce lap joints in metal sheets. The process combines partial cutting and bending with mechanical interlocking by sheet-bulk compression of tabs in the direction perpendicular to thickness. The lap joints are flat with all the plastically deforming material contained within the thickness of the two sheets partially placed over one another. The design of the lap joints is performed by a simple analytical model and the overall concept is validated by means of numerical modelling and experimentation. Destructive shear tests demonstrate the effectiveness and performance of the new proposed lap joints.     

Effect of the hot-rolling microstructure on texture and surface roughening of Al-Mg-Si series aluminum alloy sheets

This study investigates the effect of microstructural changes induced by hot rolling on the formation of the texture in high-strength aluminum alloy sheets used in automotive applications. Fully (S2) and partially (S1) re-crystallized samples were fabricated by controlling the final hot-rolling temperature. Optical microscopy (OM) was used to observe the microstructure of the transverse direction (TD)-plane of the hot-rolled strips, and the electron back-scattered diffraction (EBSD) technique was used to evaluate the texture of the normal direction (ND)-plane of the finished sheets that were subjected to hot rolling, followed by cold rolling and a solid-solution heat treatment (SSHT). The grains in S1 showed a low-angle grain boundary, and the concentrations of Cube {001}〈100〉 and Goss {011}〈100〉 orientations were detected at different sheet thicknesses. In contrast, a randomized texture was observed in S2. On the basis of the above results, this paper discusses how the microstructure and texture achieved after hot rolling can influence the final microstructure, texture and surface roughening behavior.     

板料成形中材料模型的研究进展

介绍了板料成形数值模拟中材料模型的研究进展。将材料模型的理论研究分为屈服准则、强化模型、流动法则、加卸载历史4个方面,并进行简要综述;对材料在循环加载条件下应力应变曲线的实验获取方法进行了探讨,重点介绍了板料压缩、三点弯曲实验确定材料反向加载应力应变曲线的原理和方法;对当前屈服准则、强化模型的研究热点和发展方向进行了分析。     

板料成形中考虑油膜厚度和滑动速度的摩擦模型

板料成形过程中,摩擦特性直接影响成形件的质量.通过分析边界润滑状态和流体润滑状态的金属镀层板料受力情况,建立了一个混合润滑状态下关于润滑油膜厚度和滑动速度的摩擦模型.采用平板滑动摩擦实验研究了润滑油膜厚度和滑动速度对镀锌钢板摩擦系数的影响,确定了实验条件下CR4镀锌板的摩擦模型参数,并验证了其准确性.研究表明:摩擦系数随着油膜厚度增加而减小并最终趋于稳定;随着滑动速度增加,摩擦系数减小.油膜厚度和滑动速度的增加都使得模具和板料镀层直接接触的面积在实际接触面积中的百分比降低,从而摩擦力下降.     

金属表面新型清理机

将高压水与砂粒从喷嘴喷出．在空中混合喷向金属表面而高效地 除鳞。这种方法除鳞彻底、效率高．比其它方法成本低而且无环境污染。     

Modified looping technique for remeshing of forming simulations with free surface folding

In finite element simulations of forming processes with a complex geometry, free surface folding phenomenon is likely during simulations when die design or the size of initial billet is inappropriately determined. In such cases, free surface geometry becomes so acute that mesh generation may be impossible with a conventional looping technique automatically. In order to solve this kind of problem, looping technique was modified to generate boundary elements for the acute geometry with a better mesh quality. The developed technique was implemented to the in-house bulk metal forming simulation program CAMPform and applied for forming simulations of ring gear forging and nosing in which surface folding defects occur. It was found that folding phenomenon was successfully handled with the currently developed algorithm and suitable process conditions to eliminate the free surface folding were determined through numerical simulations.     

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。     

Quantification of galling in sheet metal forming by surface topography characterisation

One of the major problems in forming of stainless steel sheet is galling due to lubricant film breakdown leading to scoring and bad surface quality. In a Danish research programme new lubricants substituting the normally applied chlorinated paraffin oils are being developed and tested for this purpose. In order to determine the limits of lubrication of these new lubricants, as well as commercial ones already available on the market, two sheet forming tests have been developed. Quantification of the degree of galling is done by roughness measurements on the workpiece surface. In a strip reduction test, this is done by 2D profilometry at strip locations corresponding to different sliding lengths, whereas a deep drawing test is based on 3D roughness mapping of local areas.     

有色金属板材若干温热加工成形技术的发展

介绍了有色金属材料加工先进新技术国内外发展和应用概况,包括近年来关于镁合金、钛合金、铝合金等典型有色金属材料领域出现的先进塑性成形技术,尤其温热加工成形技术。在镁合金板材冲压成形领域,介绍了镁合金板材温热冲压成形、差温冲压成形、温热液压成形和热冲锻成形以及镁合金型材温热拉弯成形等新工艺技术,为镁合金板材在汽车、电子、机车车辆等领域的应用奠定了技术基础。钛合金板材零件的热应力成形、热胀形成形、激光弯曲成形、高温蠕变成形技术都得到了发展和应用。随着铝合金的进一步应用和发展,一些低塑性难成形高强铝合金的用量在增加,应用领域在扩展。因此铝合金的温热液压成形、冲锻成形都有所发展。     

马鞍形板件冲压成形新工艺

曲面板件在冲压成形时常常发生起皱现象。从曲面板件的几种冲压成形方法出发,讨论了各自的特点,提出了一种新型的曲面板件冲压成形技术,其为多点压板成形冲压工艺与杆系柔性成形模具。杆系柔性成形模具由可重构的杆系组成,若干个可更换的冲压头构成模具冲压型面;冲压过程中模具对板料实施压边、压板与成形,板面压板力提升了板料的抗失稳能力,保证复杂曲面板件的顺利成形。     

板料成形几何尺寸光学检测精度评价的新方法研究

针对板料成形几何尺寸检测精度难以进行定量比较的问题,提出了一种板料成形几何尺寸光学检测精度评价的新方法.该方法基于统计学原理,结合三维光学测量技术的特点,引入统筹精度的概念来评价尺寸检测的精度,给出了统筹精度的计算方法和物理意义.采用该方法对某汽车后地板纵梁的回弹量检测精度进行评价.结果表明:后地板纵梁的三维空间几何量的统筹精度为0.512,x方向为0.059,y方向为0.363,z方向为0.539;其中z向的统筹精度数值大于三维空间值,三维空间量统筹精度的影响主要来自z向,y向次之,x向影响最小.     

Damage in metal forming

Physical mechanisms of ductile damage in metal forming, experimental characterization methods for damage, and models predicting the damage level in formed components are reviewed. Applications of damage analysis in metal forming processes reveal that damage in metal formed parts is not failure, but a product property that accumulates between processes. Various metal forming process designs demonstrate that damage in formed products can be reduced and their performance can be increased. Static and fatigue strength, impact toughness, stiffness, and formability are typical examples of performance indicators that can be improved by damage-based process design. Potential scientific and technological challenges are addressed to realize damage-controlled metal forming processes.