金属塑性成形过程CSPH无网格法数值模拟

应用微可压缩刚塑性材料的流动法则,采用修正的光滑粒子力学(Corrected smooth particle hydrodynamics, CSPH)无网格法,自行开发了求解金属方棒压缩和圆棒压缩等金属塑性成形过程应用程序。提出一种简单的求解体积应变速率的光滑技术,该技术使应力场计算结果能得到较好的改善。采用CSPH无网格法求解纯铝和Al6060铝合金材料压缩过程得到的速度场和应力场结果与有限元法计算结果以及试验数据进行了分析比较。结果表明, CSPH法能够较好地求解金属大变形过程,为今后进一步分析复杂金属变形问题提供了良好的研究手段。     

无网格法在金属成形模拟分析中的应用

利用无网格再生核质点法对金属塑性变形过程进行模拟仿真分析,讨论了无网格法的研究进展,无网格PKPM技术的基本原理和方法,以及应用无网格法进行金属成形过程仿真分析的关键技术,并通过塑性材料数值分析实例,验证无网格法框架下进行金属成形过程模拟分析的可行性和有效性。     

基于刚塑性流动理论的无网格伽辽金方法

为了对金属体积成形过程进行数值模拟，给出基于刚塑性流动理论的无网格伽辽金方法。由于移动最小二乘近似的非插值特征给无网格伽辽金方法的应用带来了一定的困难，将再生核质点法中的完全变换法与无网格伽辽金方法相结合，通过对速度场的移动最小二乘近似进行修正，实现速度边界条件的精确施加；采用罚函数法引入体积不可压缩条件，运用刚塑性材料的不完全广义变分原理，给出基于刚塑性流动理论的无网格伽辽金方法的离散控制方程以及收敛判据和收敛控制方法。数值计算结果表明方法的可行性及有效性。     

再生核质点法模拟金属镦粗过程

介绍再生核质点法的基本原理及其在刚塑性可压缩材料体积成形中的应用,采用罚函数法处理边界条件,为使结果收敛于精确值,对积分过程采用积分修正和稳定化技术,采用Newton-Raphson方法使非线性方程线性化,对下一时间步工件的形状可以用更新的节点坐标计算,模拟了二维平面镦粗过程,模拟结果与实际变形情况相符,说明该方法的有效性。     

基于配点型无网格法的金属体积成形过程数值模拟

基于配点型无网格法的基本原理，阐述了采用配点型无网格法求解偏微分方程的步骤和方法，推导了刚塑性二维轴对称问题的配点型无网格法求解公式。以汽车气门弹簧座冷挤压过程为例，对金属体积成形的塑性变形情况进行了模拟分析。算例表明，配点型无网格法不需要借助背景网格或有限元网格进行数值积分，解决了伽辽金型无网格法计算效率低的问题。计算结果与有限元法比较接近，说明配点型无网格法用于金属塑性大变形过程数值模拟是可行性的。     

金属塑性成形过程无网格伽辽金法数值模拟技术研究

将无网格伽辽金法与刚(粘)塑性流动理论相结合,对无网格伽辽金法在金属塑性成形过程数值模拟中的应用技术进行了研究,分别采用混合变换法和罚函数法实现速度边界条件和体积不变条件,提出了基于刚(粘)塑性力学流动理论的无网格伽辽金法,给出了金属塑性成形无网格伽辽金法数值模拟的关键算法,拓展了无网格方法在金属成形领域的应用范围。典型算例的数值计算结果表明了方法的可行性。     

刚(粘)塑性无网格伽辽金方法及其关键技术研究与应用

在国家杰出青年科学基金资助项目《塑性加工工艺及设备》(No.50425517)，以及国家自然科学基金资助项目《金属体积成形过程的刚(粘)塑性无网格伽辽金方法数值模拟理论及其关键技术研究》(No.50575125)支持下，开展刚(粘)塑性无网格伽辽金方法及其关键技术与应用的研究报告，对刚(粘)塑性无网格伽辽金方法的基础理论、数学模型建立方法、关键处理技术在金属塑性成形过程中应用研究的成果。 将无网格伽辽金方法引入塑性成形过程模拟，提出基于刚(粘)塑性理论的无网格伽辽金方法，推导刚度矩阵方程和求解列式。利用变换法施加本质边界条件，采用反正切摩擦模型描述摩擦力边界条件。对于模具边界任意的塑性成形过程，在局部坐标系下施加摩擦力边界条件，给出局部坐标系和整体坐标系的变换矩阵，解决了模具形状任意的二维塑性成形问题摩擦力边界条件的施加问题。采用直接迭代法获得初始速度场，利用Newton Raphson迭代方法求解刚度方程，给出模拟等温塑性成形问题的分析步骤。对于中高温条件下的塑性成形过程，推导出刚(粘)塑性无网格伽辽金方法热力耦合分析模型，给出热力     

金属塑性成形的求解方法

金属塑性成形是利用金属的塑性使金属在外力作用下成形的一种方法,具有效率高、金属损耗少和成本低等优点,因而在国民经济中,特别是在航空、汽车、电器、轻工和机械制造等工业部门得到广泛的应用.为了正确地进行工艺设计,使工件顺利成形,必须掌握塑性成形时金属的变形情况,包括应力、应变的分布,变形力的计算和金属流动规律等.在塑性理论的发展过程中,已经形成金属塑性成形的各种求解方法,如主应力法、能量法、滑移线法和上限法等.近年来,数值计算技术以及计算机的发展,使上述传统方法发生了巨大的变化;从上限法发展到上限元     

刚塑性无网格方法中体积闭锁问题的缓解算法

将无网格伽辽金方法引入金属塑性成形过程分析,在给出基于刚塑性理论的无网格伽辽金方法及其基本理论方程的基础上,重点研究应用无网格方法分析金属塑性成形问题时所面临体积闭锁问题的缓解算法,采用体积应变率映射方法,对能量速率泛函中的体积应变率进行修正处理,通过将速度场计算的体积应变率映射到低维空间,降低独立约束方程数目,从而建立体积闭锁现象的缓解算法。应用所建立的方法对典型锻造过程进行了无网格分析,结果表明,该算法能够有效解决体积闭锁问题。     

质点积分EFGM法在任意形状模具的塑性成形模拟中的应用

对任意形状模具型腔工况下的塑性大变形过程进行高效率的有效数值模拟有实际的工程指导意义,为此笔者将基于质点积分的无网格伽辽金法应用于该过程的分析。质点积分简化了无网格分析中最为耗时的积分运算,可在保证精度的前提下实现高效计算。文中使用有限元网格法描述模具型腔,处理接触界面时,用主从面法进行接触搜索,由罚函数法将接触约束引入变形控制方程,采用显式技术求解系统控制方程。使用上述方法分析带有球头凸模的反挤压铜块工件工艺过程,将计算结果与基于ANSYS/LS-DYNA环境的有限元法得到的结果进行比较,说明了笔者提出方法的正确性和可行性。     

Numerical simulation of three-dimensional bulk forming processes by the element-free Galerkin method

A new approach for simulating three-dimensional (3D) bulk metal forming processes is proposed by combining element-free Galerkin method (EFGM) with the flow theory of 3D rigid-plastic/viscoplastic mechanics. Different from the conventional rigid-plastic FEM, the velocity field is constructed by the moving least-squares (MLS) approximation. Special emphasis is placed on the treatments of essential boundary conditions, incompressibility constraint and friction boundaries. The stiffness equation for the analysis of 3D bulk metal forming using EFGM is derived and its key algorithms are given. To test the validity of the proposed meshless approach, a typical 3D upsetting forming process is analyzed and the numerical results are compared with those obtained by commercialized rigid-plastic FEM software Deform^3D. As results show, when handling 3D plastic deformations, the proposed approach eliminates the need of expensive meshing and remeshing procedures unavoidable in conventional FEM, and still provides results that are in good agreement with finite element predictions.     

金属体积成形过程的自适应无网格方法

采用动态显式自适应无网格RKPM方法的计算格式，在有效误差估计模型的基础上进行节点加密，采用区域分解思想确定新的计算模型中节点的影响域半径，对金属体积成形过程进行了全过程的计算机模拟。Taylor Bar冲击的自适应无网格计算结果与实验结果吻合良好，有效地验证了该方法的正确性和可行性。挤压算例的计算结果也表明该算法能提高计算精度和改善板内应变能误差。     

三辊楔横轧空心件成形机理的研究

利用刚塑性有限元,基于Deform-3D平台建立了三辊楔横轧空心件的有限元热力耦合模型.通过模拟计算,分析了轧制过程金属的流动规律,研究楔横轧轧件上每一点的应力、应变场分布以及轧辊的力能参数.研究结果对解决零件精确成形和提高轧件质量具有理论意义和实用价值.     

Study on multiple-step incremental air-bending forming of sheet metal with springback model and FEM simulation

A mathematical model of springback radius was developed with dimensional analysis and orthogonal test. With this model, the punch radius could be solved for forming high-precision semiellipse-shaped workpieces. With the punch radius and other geometrical parameters of a tool, a 2D ABAQUS finite-element model (FEM) was established. Then, the forming process of sheet metal multiple-step incremental air bending was simulated with the FEM. The result showed that average errors of the simulated workpiece were +0.68/?0.65 mm, and provided the process data consisting of sheet feed rate, punch displacement and springback angle in each step. A semiellipse-shaped workpiece, whose average errors are +0.68/?0.69 mm, was made with the simulation data. These results indicate that the punch design method is feasible with the mathematical model, and the means of FEM simulation is effective. It can be taken as a new approach for sheet metal multiple-step incremental air-bending forming and tool design.     

大棒材芯部疏松缺陷控制与负张力轧制工艺研究

以某厂直径150mm大棒材连轧机组为对象,将大规格连铸坯芯部疏松视为体积可压缩材料,利用刚塑性有限元方法,建立了非均质大棒材轧制过程三维热-力耦合非线性有限元模型,采用数值模拟方法研究了机架间张力对疏松缺陷致密压实的影响规律。结果表明,采用负张力轧制比自由轧制或微张力轧制能更有效地压实芯部疏松缺陷。从各道次孔型充满度和出口断面形状、轧制力能参数等方面探讨了实施负张力轧制工艺的可行性。     

On the prediction of side-wall wrinkling in sheet metal forming processes

Prediction and prevention of side-wall wrinkling are extremely important in the design of tooling and process parameters in sheet metal forming processes. The prediction methods can be broadly divided into two categories: an analytical approach and a numerical simulation using finite element method (FEM). In this paper, a modified energy approach utilizing energy equality and the effective dimensions of the region undergoing circumferential compression is proposed based on simplified flat or curved sheet models with approximate boundary conditions. The analytical model calculates the critical buckling stress as a function of material properties, geometry parameters and current in-plane stress ratio. Meanwhile, the sensitivities of various input parameters and integration methods of FEM models on the prediction of wrinkling phenomena are investigated. To validate our proposed method and to illustrate the sensitivity issue in the FEM simulation, comparisons with experimental results of the Yoshida buckling test, aluminum square cup forming and aluminum conical cup forming are presented. The results demonstrate excellent agreements between the proposed method and experiments. Our model provides a reliable and effective predictor for the onset of side-wall wrinkling in sheet metal forming processes.     

Analysis of plate rolling using the dual-stream function method and cylindrical coordinates

A mathematical model for plate rolling using the dual-stream function method and cylindrical coordinates has been proposed in this work to examine the plastic-deformation behavior of the plate at the roll gap. The velocity fields derived from this newly developed dual-stream function can automatically satisfy the volume constancy and the velocity boundary conditions within the roll gap. In the formulation, an inclined rigid-plastic boundary plane at the entrance of the roll gap is considered. Although this effect can be easily included in a finite element method, the demanding amount of memory and the computer time by an FEM approach makes it impractical as a personal computer routine. By this model, effects of various forming parameters such as the roll diameter, thickness of the plate, the friction factor, the aspect ratio of the plate, etc., upon the width spread of the product and the rolling power were discussed systematically. Furthermore, experiments on plate rolling using aluminum sheets were carried out. From the comparison between the analytical and experimental results, it is clear that this model can offer useful knowledge in designing the pass-schedule of plate rolling process.     

热带钢连轧多场耦合演变过程有限元分析

根据物理冶金组织演变规律和经验公式，开发了金属热变形过程耦合组织演变的计算模块。结合某厂2050热带钢连轧工艺过程，利用非线性刚塑性有限元法，建立热连轧过程热、力、组织的多参量耦合仿真模型。运用该模型对2050现场实际轧制过程进行模拟计算，分析了轧制过程轧件变形场、温度场及显微组织的演变规律。模拟得到的轧制力能参数、温度、组织分布与实测数据基本一致。     

材料参数对环件冷辗扩工艺的影响规律研究

基于ABAQUS软件环境,采用弹塑性动态显示有限元法,通过三维数值模拟研究揭示了几个重要的材料参数(硬化指数、屈服强度和弹性模量)对环件冷辗扩过程中环件端面质量、轴向宽展、辗扩力、辗扩力矩以及金属流动特性的影响规律,并从金属塑性成形原理和塑性加工力学等角度对这些规律进行了合理的解释,从而获得了何种材料性能适应冷辗扩成形的认识,为环件冷辗扩在实际应用中材料和设备的选择提供了依据,对揭示冷辗扩成形机理也具有十分重要的意义。