PREDICTION OF PATH-DEPENDENT FAILURE IN ALUMINUM SHEET METALS UNDER FORMING OPERATIONS

An approximate macroscopic yield criterion for anisotropic porous sheet metals is adopted in a failure prediction methodology that can be used to investigate the failure of sheet metals under forming operations. This failure prediction methodology is developed based on the Marciniak-Kuczynski approach by assuming a slightly higher void volume fraction inside randomly oriented imperfecte analysis. Here, a nonproportional deformation history including relative rotation of principal stretch directions is identified in a selected critical element of an aluminum sheet from a FEM fender forming simulation. Based on the failure prediction methodology, the failure of the critical sheet element is investigated under the non-proportional deformation history. The results show that thiven non-proportional deformation history.

Analysis of Sheet Metal Extrusion Process Using Finite Element Method

Sheet bulk metal forming processes have been widely developed to the facilitate manufacture of complicated 3D parts. However, there is still not enough know-how available. In this paper, as one of the typical sheet bulk metal forming processes, the sheet metal extrusion process was studied. A reasonable finite element method （FEM） model of sheet metal extrusion process taking the influence of flow-stress curve with wide range of plastic strain and ductile damage into consideration was established and simulated by an arbitrary Lagrangian-Eulerian （ALE） FEM implemented in MSC.Marc. Validated by comparing the results with experiment, some phenomenological characteristics, such as metal flow behavior, shrinkage cavity, and the influence of different combinations of diameter of punch, diameter of extrusion outlet, and diameter of pre-punched hole were analyzed and concluded, which can be used as theoretical fundamental for the design of the sheet metal extrusion process.

KEY TECHNOLOGY IN INTELLIGENT CONTROL FOR SHEET METAL DEEP DRAWING

Intellectualization of sheet metal in deep drawing is a new combined technology, which is concerned with control science and computer science and sheet metal forming theory. The intelligent control system for sheet metal deep drawing consists of four fundamental factors: real time measurement, identification, prediction and control. Real time identification of material properties and friction coefficient is the most important factor in the whole system. An artificial neural network model for identification of the material properties and friction coefficient was established according to deep drawing characteristics and more automation. The identification of the material properties and friction coefficient was realized.

A QUASI-FLOW CONSTITUTIVE MODEL WITH STRAIN-RATE DEPENDENCE

In this paper,the proposed is a quasi-flow constitutive model with strain-rate sen- sitivity for elastic plastic large deformation.The model is based on the Quasi-flow Corner theory, and is suitable for the sheet metal forming process simulation with a variable punch machine velocity. Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated.The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model.

Characterization of the asymmetric evolving yield and flow of 6016-T4 aluminum alloy and DP490 steel

6016-T4 aluminum alloy and DP490 steel were systematically tested under 24 proportional loading paths,including uniaxial tensile tests with a 15°increment,uniaxial compressive and simple shear tests with a 45°increment,and biaxial tensile tests using cruciform specimens.Cruciform specimens in the rolling/transverse and 45°/135°sampling directions were tested with seven and four different stress ra-tios,respectively.The normal and diagonal planes plastic work contours and the yield stresses under uniaxial tension and compression were measured to investigate the anisotropic yield.Meanwhile,the normal and diagonal planes directions of plastic strain rate and the rα-values under uniaxial tension and compression were characterized to confirm the plastic flow.Several existing asymmetric yield crite-ria under the associated and non-associated flow rules were comprehensively evaluated to describe the asymmetric plastic anisotropy of 6016-T4 aluminum alloy and DP490 steel.The results suggest that in the investigated yield criteria,the non-associated models can predict the tension and compression asym-metry of materials more accurately than the associated models,and the function of stress triaxiality can more effectively describe the asymmetric yield behavior than the first stress invariant.In addition,the pure shear stress states are helpful in assessing the validity and applicability of advanced asymmetric yield stress functions,and the inspection of diagonal plane plastic work contours containing more pure shear stress states should prioritized over that of normal plane plastic work contours.The evaluation of plastic potential functions should not only consider the prediction accuracy of the normal plane di-rections of plastic strain rate,but also further check the diagonal plane directions of plastic strain rate.Expressing mechanical properties as a function of equivalent plastic strain to calibrate parameters of the yield criterion allows the continuous capture of anisotropic evolution of the asymmetric yield surface and the changes in the asymmetric plastic potential surface.

Determination of Flow Curve and Plastic Anisotropy of Medium-thick Metal Plate:Experiments and Inverse Analysis

Sheet bulk metal forming is widely used for medium thick metal plate due to its convenience in the manu- facture of accurately finished 3D functional components. To obtain precise anisotropy and flow curve of metal plate is a prerequisite for correct simulation of sheet bulk metal forming processes. Inverse analysis of compression test was introduced here to evaluate the sensitivity of different flow curve models and geometric influence of compression test specimen. Besides, a methodology was proposed to compute plastic anisotropic coefficients of Hill quadratic yield cri- terion, which is based on the ratios of flow curves obtained by inverse analysis of compression tests using specimens cut in six directions on the medium-thick metal plate. The obtained flow curves and anisotropic coefficients were compared with those calculated from tensile tests. Flow curves based on inverse analysis of compression tests cover the curves of the tensile tests well, while the anisotropic coefficients are different, especially for the coefficient relat- ed to the RT45 direction. To estimate the effectiveness of the proposed method, the calculated material properties and those based on the traditional tensile tests were applied in a rim-hole process simulation. The simulation results based on the material properties from inverse analysis of compression tests accorded with the tested properties better.

基于模糊神经网络的压边力优化控制专家系统

说明了压边力优化控制模糊神经网络专家系统的总体结构框架及系统各模块的功能 ,对模糊神经元的选取、模糊神经网络的构造和模糊神经推理机制进行了深入的阐述 ,针对板料拉深过程中的变量选取了模糊神经网络的输入输出参数 .在板料拉深过程中 ,应用压边力优化控制模糊神经网络专家系统实现了冲压成形过程的智能化控制 .

多点成形控制系统总体设计及其关键技术

探讨了多点成形控制系统设计中的关键技术问题 ,研究了控制系统的硬件与软件结构。所研制的控制系统已在YAM 5及YAM 3型多点压力机开发中成功应用。

板材零件成对液压成形新技术

板材成对液压成形技术是一种新的板材成形技术 ,具有成形性好、制造工期短、费用低等优点 ,特别适用于批量小、形状复杂板材零件的生产 .介绍了板材成对液压成形技术的成形原理、成形过程、分类及研究现状 .

十字形试件双向拉深试验系统建立及加载精度分析

为了研究复杂加载路径下板料塑性变形行为 ,建立了十字形试件双向拉深试验硬件与软件系统 ,实现了同轴两夹头的位移同步控制 ,位移和载荷的比例加载与非比例加载控制 ,以及根据载荷变化判断加载停止的控制等关键技术。试验验证表明 ,所建系统具有较好的准确性和可靠性 ,为进一步研究提供了试验基础。

多点变压的压边力控制系统开发

总结了压边力控制技术的最新进展 ,重点分析了一种新型多点变压的压边力控制系统的工作原理 ,该压边控制系统的特点是能够提供随压制行程和随法兰位置变化的压边力。对斜侧壁盒形件进行了拉深实验 。

复杂钣金零件渐进成形方法

以复杂钣金零件-人面部模型零件为例,论述基于UG软件的建模及建模过程中应注意的问题、支撑模型的制作及其加工代码的生成、适用于渐进成形正成形过程的加工代码生成处理过程,给出加工代码的详细信息,成功加工出质量较高的人面部模型。人面部模型渐进成形试验结果表明,利用渐进成形正成形方法可以成形出形状复杂的钣金零件,生产小批量复杂零件可以节省时间与费用;UG生成的三轴数控加工代码需要通过处理才能应用于渐进成形正成形过程;复杂钣金件渐进成形过程中定位精度非常重要,定位精度高的零件厚度分布符合δ=δ0cosθ的规律,并可以成功成形出设计的零件,定位精度误差较大时零件厚度分布不均匀,成形工具头与板料的过度挤压侧板料厚度变薄急剧从而引起零件的过早破裂。

多点成形压力机及成形工艺的最新进展

多点成形技术是金属板材三维曲面成形的新技术 ,与传统的整体模具板材成形工艺相比 ,多点成形压力机有许多优点 ,可以实现三维板类件既经济又快速的柔性成形。本文介绍了多点成形压力机系列规格参数、设备构成原理及其成形工艺。重点论述了几个现有的多点成形压力机的技术参数、调形方式的重大改进及多点成形技术应用领域的不断扩大。

冲压冷锻成形工艺的模具设计及坯料计算方法研究

以车用空调用电磁线圈罩体零件为研究对象,研究了冲压冷锻成形工艺的模具设计以及适合此类工艺的坯料计算方法。工艺试验和批量试制表明:与传统的冷挤压成形、热锻制坯+机械加工等工艺比较,该工艺流程最短,成形力只有冷挤压的1/5,而效率提高了5倍,坯料计算方法的准确率达到100%。冲压冷锻成形的罩体零件,尺寸、形状和位置精度、表面粗糙度等质量指标达到了进口件的要求,合格率达到了99.8%,已成功应用于多家汽车空调生产企业。

新型多点变压的压边力控制系统研制

本文简要回顾了压边力控制技术的最新进展 ,重点分析了一种新型多点变压的压边力控制系统的工作原理 ,该压边控制系统的特点是能够提供随压制行程和随法兰位置变化的压边力。最后对铝合金阶梯盒形件进行了拉深实验 ,结果表明 ,该压边控制系统具有很好的变压效果。

板料成形压边力控制技术研究现状及发展趋势

首先从压边力的加载模式及加载位置等方面介绍了压边力的控制方式,其次对压边力的理论分析进行了总结,最后对以人工神经网络为代表的人工智能及与现代控制理论相结合的压边力控制技术进行了分析。在对国内压边力控制技术综述的基础上,指出了目前在压边力控制技术方面存在的问题;同时,探讨了压边力控制技术的发展趋势。

拉深工艺变压边力控制数值模拟研究

根据实际生产中压边力的控制状况和理论分析确定了几种压边力变化曲线 ,以非轴对称抛物面车灯反光罩的成形为例 ,采用 Dynaform软件对多种变压边力控制的成形工艺分别进行了数值模拟计算 ,分析了各种变压边力控制对成形的影响 。

三维曲面零件连续柔性成形技术的理论分析与回弹控制

对三维曲面零件连续柔性成形（CFF）新技术中的成形件形状控制、柔性辊轴线形状描述以及回弹等理论问题进行了研究。基于对连续成形过程中板料纵向与横向变形的分析，建立了成形纵向形状控制的理论与方法；结合多点控制的特点，给出了描述柔性辊辊形的样条插值公式；针对板料连续成形中的回弹补偿问题，基于对材料及变形方面的简化与假设，推导出横向与纵向回弹曲率半径的估算公式，给出了回弹修正方法。通过在CFF中的实际应用说明了这些理论与公式的有效性。

PEMFC薄金属流场板冲压成形有限元模拟

流场板是质子交换膜燃料电池(PEMFC)的重要元件之一。寻求一种操作成本低,容易批量生产的金属流场板加工方法,板料冲压成形是最佳候选。基于弹塑性有限元变形理论,采用有限元软件DYNAFORM建立质子交换膜燃料电池流场板冲压成形过程有限元模型。分析了变形过程中应变、厚度分布情况模拟结果验证了板料冲压成形应用在金属流场板加工上的可行性。

复合伺服驱动压边力控制执行机构建模与优化

将伺服电动机驱动与双滑块六杆机构复合,利用伺服电动机的可控性和六杆机构的速度特性,实现拉深过程的变压边力控制。在综合考虑机构输出位移中的弹性位移和刚性位移基础上,建立压边机构输入输出关系的数学模型。当机构几何参数一定时,可根据压边力与滑块位移的关系并考虑机构的变形,确定压边机构的输入速度。为优化杆系尺寸,在考虑压边工作行程和传动效果良好的基础上,以机构输出速度与压力机滑块速度相差最小(在压边力施加阶段),及机构总体尺寸最小为目标函数,优化确定了双滑块六杆机构的杆系尺寸。利用仿真软件,由前面建立的输入输出关系数学模型确定仿真输入速度,仿真结果表明,采用复合伺服驱动双滑块六杆执行机构实现压边力控制是可行的。