数字图像相关法测量板料成形应变

针对板料成形极限试验中传统应变测量方法的不足,提出并实现一种基于数字图像相关法的板料成形极限应变测量方法。对其中涉及的关键技术进行深入研究。针对板料成形中大变形测量的难题,根据系列变形图像相邻状态变形的连续性,提出一种大变形分步匹配算法,并介绍三维坐标重建和三维应变求解的方法。根据测得的试件表面应变分布,提出一种通过构建应变场截面线来拟合成形极限曲线的方法。基于Visual Studio 2010开发环境,开发用于板料成形极限应变测量的计算软件。为了验证方法的可行性,结合自研的图像采集装置和改进的板料成形试验机搭建成形极限测量试验平台。对SPCC钢板试件的测量结果显示所提出的方法能够快速、有效、直观地测量试件在整个成形过程中的表面应变分布,为建立成形极限图提供一种有效手段,且与传统的坐标网格等方法相比优势明显。     

基于激光冲击波的板料塑性成形新技术

提出利用激光冲击波技术实现板料的柔性塑性成形，分析了其成形机理、工艺过程和技术特点。利用脉冲能量为10－30J，脉宽为20ns的激光束，对SUS304薄钢板和40Cr进行了激光冲激波胀形实验，初步的实验结果表明，激光冲击波板料成形是一种冷塑性成形技术，具有超快速、高应变率等优点和较大的成形柔性。能适用于常规模具无法成形的结构钢和复合材料的成形，拓展了冷冲压成形的零件范围。     

成形板料表面的接触分形几何模型研究

提出一种新的方法用以描述板料与模具的接触问题。利用接触式轮廓仪对板料粗糙表面进行测量和分析，论证了成形板料表面的微观形貌可以用weierstrass—Mandelbrot分形函数来表征，所得到的参数是不依赖于测量尺度而变的“固有”参数。根据分形几何理论和接触力学理论，建立了板料与模具接触的接触面积与变形关系模型。     

板料拉深成形摩擦系数测量系统

建立了一套基于自主开发的探针式组合传感器的摩擦系数测量系统，并将此传感器耦合到拉深凹模结构中，以此来实时测量板料法兰平面测量点处所受到的垂向正向压力和径向切向拉力，并根据计算公式μ（摩探系数）=P（切向拉力）／F（正向压力）直接计算出该测量点处的实时摩擦系数大小，进而通过选择几个特征点来推导出整个板料法兰平面的摩擦分布情况及其变化规律。最后实际试验数据证明，该系统能够真实地反映板料拉深成形过程中法兰平面亡的实际摩擦分布情况。     

板料成形极限应力图研究

基于塑性应力应变关系,推导出极限应力与极限应变相互转换关系,针对分散性失稳、凹槽失稳和平面应变漂移失稳等准则,进行了双线性应变路径、曲线应变路径和复合应变路径下成形极限应力图的理论计算。结果表明,成形极限应力图不受应变路径影响,对于同一失稳准则,在不同加载应变路径下几乎为同一条曲线。因此,成形极限应力图作为复杂加载路径的成形极限判据更加方便和实用。     

板料数控柔性成形工艺在新品开发中的应用研究

板料柔性成形是基于产品的数字化信息,由产品的三维CAD模型直接驱动,通过高度可调的基本体构成包络面,实现三维曲面零件成形的技术。典型的板料柔性成形方法是增量成形与多点成形。增量成形通过一个成形工具头沿x、y轴方向的运动及z轴方向的进给,逐层形成零件的三维包络面,从而实现板料的渐进成形;多点成形的核心是规则排列的基本体阵列,通过控制基本体z方向的位置坐标使其构成所需包络面,进行板料快速成形。介绍了以数控多点柔性成形新工艺进行新产品开发试制的应用。     

板料成形极限应力图及其应用研究进展

简要介绍了板料成形极限判据的可靠性对于板料成形质量预测与控制的重要性;分析了传统的基于应变的成形极限(成形极限应变图)判据所存在的只适于在线性加载板料塑性成形中应用的缺陷;介绍了基于应力的成形极限判据(成形极限应力图)的应用前景;综述了国内外成形极限应力图的研究进展,并指出了目前成形极限应力图研究所面临的主要问题.     

板料成形坯料形状与应变分布的快速精确预测

采用有限元逆算法和四边形单元开发了板料冲压成形与模具设计快速分析软件FastAMP。模拟了比较典型的L形盒冲压件的坯料形状和厚向应变,并分别与实验结果和商业软件AutoForm的计算结果进行了比较,说明FastAMP软件可以精确地预测冲压件的坯料形状和应变分布规律,而且计算速度很快。     

板料的快速激光成形技术及其应用

介绍一种利用激光扫描金属薄板所导致的热应力来实现塑性变形的工艺方法，根据激光扫描时所形成的两类典型温度场，探讨激光成形的机理，在板料的几何参数，热物性，光束能量及分布等方面分析激光成形的技术要点，提出该技术所面临的问题，并展望其应用领域和前景。     

Finite element simulations of sheet metal forming under complex strain paths

Fracture is a common defect in sheet metal forming and it is essentially caused by tensile instability. This paper analyzes some experiments and theories for building forming limit diagrams of sheet metal and points out the advantages and disadvantages of current experiments and theories. According to this, a method that integrates the finite element simulation and experiment was used to research the forming limit diagrams of the sheet metal under complex strain paths. Taking the rear hanger that undergoes twice stamping as an example, the strain paths of the dangerous point of the rear hanger is investigated. Finally, the forming method of the rear hanger is confirmed. Results indicate that finite element method (FEM) can achieve the complex strain paths and different strain paths will have great impacts on the result of the sheet metal forming. __________ Translated from Journal of Jiangsu University (Natural Science Edition), 2005, 26(4): 289–293 [译自: 江苏大学学报 (自然科学版)]     

A new cyclic anisotropic model for plane strain sheet metal forming

A finite difference model was developed for sheet metal subjected to plane strain cyclic bending under tension. The model was used to describe the effects on the mechanics of the deformation of the sheet due to mixed isotropic-kinematic cyclic hardening curves. The analytical results were compared with experimental results obtained under testing conditions closely representative of the analytical model. Two tests were used: a pure bending moment device and a bending/unbending under tension device consisting of three cylindrical pins. The model was used to determine a constitutive curve that best characterize the cyclic behavior of the material tested, as compared with the experimental results. The significance of these results were discussed in relation to the prediction of the restraining forces in the sheet as it is drawn through the blank holder drawbeads.     

Characterisation of a measurement system for reproducible friction testing on sheet metal under plane strain

The testing equipment can compromise the quantification of the friction on sheet metal. This paper focuses on a systematic analysis of the testing equipment as a measurement system of the friction phenomena. It is shown that the mechanical response of the system may be responsible for significant variations on the quantification of frictional effects. Historical and inter-laboratory testing data show that, upon proper design of the measurement system, friction can be quantified, reproduced, and replicated with a significant degree of accuracy. This paper discusses the requirements and the controls of the test needed to maintain the uncertainty at its minimum level. The results show the feasibility of characterising friction in order to study the effects of the sheet, lubricant, and forming tools. This study is based on tests where cyclic bending under tension resulted in significant stretching and thinning of the sheet, but with the width remaining approximately constant. Friction research under other sheet forming modes may, however, benefit from the significance of the findings presented here.