一种基于时间戳认证的零水印方案设计

零水印方法是一种新的数字水印方法。本文介绍了零水印的概念及零水印技术的关键问题,提出了一种基于时间戳认证的零水印方案。该方案很好地解决了非零水印的不可见性与鲁棒性之间的矛盾,具有可行性和通用性。     

试论大型汽车覆盖件模具制造调试的途径

针对汽车大型覆盖件零件的工艺特点，采用先进的模拟仿真技术、测量技术、调试技术、逆向工程技术，探索出了一条汽车大型覆盖件模具制造调试的途径。     

冲压自动化的若干基本问题

本文分析讨论了冲压自动化领域中的若干基本问题，包括模具结构，工件上下料，毛坯开垛上料，工件码垛，安全问题等，文章介绍了一条先进的冲压自动化生产线，可供实际生产参考。     

刹车片背板弯挤成形工艺研究

针对刹车片背板传统成形工艺的缺陷，采用FEM方法对刹车片背板成形过程进行了数值模拟，确定了弯曲一挤压复合成形的工艺路线。根据有限元分析的结果，分析了不同尺寸的毛坯对工件成形过程及成形质量的影响，提出了刹车片背板弯挤毛坯尺寸的选择原则。设计了刹车片背板的弯挤成形模具，在一副模具中实现弯曲、挤压两种不同的变化。     

The effect of pre-straining on the mechanical behaviour of self-piercing riveted aluminium alloy sheets

Self-piercing riveting as an alternative joining method to spot-welding has attracted considerable interest from the automotive industry and has been widely used in aluminium intensive vehicles. Pressing and stamping are important processes in automotive production and result in additional straining on the vehicle body sheet material. It is therefore important to have knowledge of the effect of sheet pre-straining on the quality of the self-piercing riveted joints and on the mechanical behaviour of the riveted aluminium alloy sheets. This paper reports the influence of sheet pre-straining on the static and fatigue behaviour of self-piercing riveted aluminium alloy sheet. Wrought aluminium alloy sheet, NG5754 with a nominal thickness value of 2 mm was used to obtain pre-strained NG5754 sheets with pre-straining levels of 3%, 5% and 10%. Pairs of pre-strained NG5754 sheets were joined to create single-riveted lap joints which subsequently underwent lap-shear and fatigue testing. Microscopic inspection showed that the joint quality was satisfactory despite the increasing sheet straining levels. The results showed that by increasing the pre-straining level up to 10%, the shear and fatigue strength also increased. The rate of increase of the static and fatigue strength differed as the pre-straining levels varied.     

半球形厚壁封头冲压成形有限元分析及优化

在制造厚壁封头的过程中,经常由于锻造后的封头减薄量过大,最小壁厚值小于规定值,在强度方面不能满足要求;或者锻造后封头壁较厚,增加了机加工量。而厚壁封头冲压成形过程属于几何非线性和材料非线性的问题,很难用弹塑性力学理论的解析法进行研究。采用钢塑性有限元法,使用ANSYS有限元分析软件模拟了半球形厚壁封头冲压成形的整个过程,分析了成形后封头壁厚的变化规律。计算结果表明,封头心部的减薄量并非最大,减薄量最大值出现在靠近坯料中心的地方,边缘的直边部分增厚量最大,最大的减薄量或增厚量均达到坯料厚度的16%左右。通过优化坯料形状和尺寸,使封头易于成形且壁厚均匀。     

A numerical analysis of sheet metal formability for automotive stamping applications

A theoretical failure model is presented for the numerical prediction of the forming limit strains of automotive sheets. The model uses the Swift’s diffuse necking and Hill’s localized necking concepts in describing tearing-type sheet metal failures and a computational scheme is proposed in which the failure conditions are expressed in incremental forms. The Bauschinger effect is included properly in the deformation modeling using an additive backstress form of the nonlinear-kinematic hardening rule. The necking conditions and plasticity model are transformed into a set of algebraic equations that may be applied both for proportional and non-proportional strain-controlled loadings. An iterative approach is employed in the incremental solution of algebraic equations. The formability analyses are conducted using the proposed theoretical model and the forming limit strains of two new generation auto sheets (Trip600 1.4 mm, DP980 1.15 mm) are estimated. The numerically generated FLC are compared with the experimental data and the FLC calculated with the Keeler–Brazier equation. For both steels, the model produced conservative plain–strain intercept values, FLC₀, when compared with the predictions of Keeler–Brazier equation. Also the negative minor strain part of the experimental FLD’s is estimated with sufficient accuracy. For the positive minor strain side, however, the predictions are lower than both the experimental fit and the standard curve.     

冲压焊接多级离心泵叶轮内部流场的计算机辅助分析

基于时均N-S方程、标准κ-ε湍流模型和壁面函数法,在旋转坐标系中利用SIMPLE算法,对圆柱型、机翼型和堵塞流道型三种类型叶片的冲压焊接多级离心泵叶轮内部三维湍流流动进行数值计算与分析.研究冲压焊接多级离心泵叶轮叶型对流速分布、压力分布和泵性能的影响规律,揭示离心泵叶轮通道内部流动的主要特征.利用计算流体动力学(CFD)商用软件ANSYS CFX的数值计算结果,得到了三种类型叶片的叶轮在设计工况下的效率,并与相关的试验数据进行了比较.预测结果与相关的试验数据相吻合,验证了利用ANSYS CFX对冲压焊接多级离心泵叶轮内部流场进行数值模拟的可行性和有效性,减少了对试验数据和设计经验的依赖,为冲压焊接多级离心泵叶轮方案的优化和选择提供参考.     

汽车后桥横梁拉延工艺优化与回弹分析

针对汽车轻量化趋势,对某汽车后桥横梁的拉延成形和回弹问题进行了有限元数值模拟研究.首先建立零件的拉延模型,从冲压方向、工艺补充面、压料面、坯料初始形状等方面进行设计分析.利用Dynaform实现零件的成形和回弹模拟,重点对拉延筋的布置进行优化.通过对成形效果的比较,最终得到合理的拉延模型设计.     

模糊集合运算在冲压件工艺特征判断中的运用

针对目前的冲压工艺智能设计和特征识别的需要,提出了一种采用模糊集合运算的方法来进行冲压件工艺特征的判断。该方法适用于判断由多个因素的布尔关系决定的特征。运用本方法,首先将各个因素模糊化;然后选择合适的布尔运算和算子来进行模糊集合布尔运算;最后选择合适的λ进行λ截集,来实现工艺特征的判断。以悬臂和窄槽的判断为例,介绍了具体的计算过程。和以往的方法相比,该方法更加贴合工程实际,计算方便,灵活。