【作者】 王忠雷；

【导师】 赵国群；

【作者基本信息】 山东大学 ， 材料加工工程， 2011， 博士

【摘要】 金属体积成形工艺就是将金属材料,在锻压设备及安装在其上的模具作用下发生塑性变形,成形为所需形状和性能工件的工艺过程,金属体积成形工艺主要包括锻造、挤压、轧制、辊锻、楔横轧等。在工业生产中,金属体积成形制造技术是支撑国民经济发展与国防建设的主要技术之一,在汽车、航天航空、装备制造、兵器、能源、造船等行业具有广泛用途。金属体积成形技术具有产品机械性能好、生产效率高、节省原材料等优点,但是同时也具有模具成本高、生产周期长、浪费能源、污染环境等缺点。在全球“低碳经济”和“节能减排”的大形势下,如何扬长避短,适应新的发展形势,成为金属体积塑性加工技术研究新的任务和要求。金属体积成形过程是一个受多因素影响的复杂物理过程,材料性能、模具形状、毛坯形状、工艺参数、成形温度等对成形过程都有影响,这使其工艺和模具设计变得非常复杂,传统的经验设计方法,通常会带来设备、材料和时间浪费的弊端。对金属体积成形过程进行准确的数值模拟不但可以节省昂贵的实验费用,而且对合理确定成形工艺、保证模具设计的一次性成功具有重要的理论指导意义和工程实用价值。随着数值计算方法和计算机技术的发展,数值模拟分析方法已经成为解决工程问题的重要方法,其中有限元方法最为成熟,在金属体积成形过程数值模拟中发挥着重要的作用。近年来,随着体积成形工艺的快速发展,目前的体积成形有限元模拟软件存在网格再划分次数多、复杂运动条件加载困难、大型问题分析效率低等问题,已不能满足体积成形有限元分析的需要。为此本文对金属体积成形有限元模拟的理论、算法和具体实现技术进行了研究,并建立了基于刚粘塑性理论的体积成形有限元模拟软件平台。对三维有限元网格的划分方法进行了研究,为解决有限元网格模型精度与单元数量的矛盾,提出了自适应网格划分的方法,对常用的六面体网格模型、四面体网格模型的自适应生成方法进行了研究；为了兼顾两种网格模型的优点,研究了四面体、六面体混合网格模型的自适应生成方法；提出了不同网格划分方法的选择原则,建立了三维初次网格划分算法。对三维有限元网格的再划分方法进行了研究,研究了畸变网格几何形状提取和修复的方法,提出了新旧网格物理场量传递的算法。为了提高物理场量的插值精度,提出了基于几何特征和计算物理场量的双重自适应网格再划分方法。为了提高网格再划分的效率,提出了三维有限元网格局部再划分技术,针对干涉网格提出了局部网格加密法；针对畸变网格提出了局部网格优化法和局部网格剖分法。制定了不同网格再划分方法的选择标准和原则。分析了目前的体积成形有限元模拟的理论和方法,采用刚粘塑性理论作为体积成形有限元分析的基本理论；研究了基于六面体网格模型、四面体网格模型及四面体、六面体混合网格模型等不同网格模型的刚粘塑性有限元总体刚度方程的建立方法和求解方法。对三维金属体积成形有限元分析计算的关键技术进行了研究,提出了基于STL文件数据重构的模具三维几何形状的描述方法；提出了一种局部坐标系的建立方法,保证了接触模具和对称约束边界条件的正确施加；研究了模具复杂运动的处理方法,确定了模具运动的描述方法,给出了模具速度求解方法和模具位置更新方法；提出了三维动态边界条件的处理方法,采用相对位置法判断节点的触模情况,采用最短距离法处理触模节点的位置调整问题；为了提高分析计算的效率,减少存储空间的消耗,提出了总体刚度方程的压缩存储算法和总体刚度方程的高效求解方法。在关键技术研究的基础上,开发了三维金属体积成形有限元模拟分析计算系统。研究了三维温度场有限元分析的基本理论和关键技术,开发了三维温度场有限元分析系统；研究了热力耦合有限元模拟的基本理论及关键技术,如温度场震荡的处理、热热力学参数的处理、速度场和温度场相互影响的处理等关键技术；在理论基础和关键技术研究的基础上,将三维温度场有限元分析系统与三维金属体积成形有限元模拟分析计算系统相结合,应用间接耦合的方法建立了三维金属体积成形热力耦合有限元模拟计算系统。基于三维金属体积成形有限元模拟辅助子系统关键技术和实现方法的研究,开发了三维金属体积成形有限元模拟辅助子系统,主要包括：建立有限元模型的前处理系统,分析有限元计算结果的后处理系统,支撑系统运行的数据库系统。将这些辅助子系统与三维金属体积成形有限元计算系统相结合,构建了三维金属体积成形有限元模拟软件平台CASFORM-3D系统。通过典型的体积成形工程实例的模拟,将模拟结果与商业化软件DEFORM-3D的模拟结果进行了比较,二者吻合良好,验证了本文建立的关键技术和相关处理算法的准确性、可行性以及所构建系统的可靠性。更多还原

【Abstract】 Bulk metal forming technology is a process in which the metallic materials, with the help of forging equipments and corresponding molds mounted upon them, are formed into parts with the desired shapes and properties. Bulk metal forming includes mainly forging, extrusion, rolling, roll forging, cross wedge rolling and so on. In industrial production, bulk metal forming is one of key technologies supporting the development of the national economy and the construction of the national defense. It is widely used in branches such as automobile, aerospace and aviation, equipments manufacturing, weapons, energy, ship building etc. Bulk metal forming process has many advantages, such as high productivity, raw material saving and better mechanical properties of the formed products. It has also certain disadvantages, such as high cost of mold, long production cycle, waste of energy, environmental pollution etc. Under the global tendency of "low carbon economy" and "energy saving & emission reducing", new tasks and requirements in the bulk metal forming technology study are how to make full use of the advantages and avoid disadvantages to acclimatize itself to the new situation of development.Bulk metal forming is a complex physical process, which is influenced by many factors, such as the properties of material, the form of mold, the shape of blank, the process parameters and the temperature etc, so the planning of the process and the designing of the corresponding mold for the bulk metal forming process is quiet difficult, which with the traditional method often has certain malpractices like waste of equipments, material and time. An accurate simulation of the bulk metal forming process can not only reduce the high costs in the experiments, but also has significant theoretical guidance and realistic application value meaning for determining the reasonable forming process and ensuring successful mold design at the first time as well. With the development in calculation method and computer technology, numerical simulation and analysis method has become a powerful tool for the solution of engineering problems. Among them the finite element method (FEM) is the most matured and has played an important role in the numerical simulation of bulk metal forming processes. With the rapid development in the bulk metal forming technology in recent years, the existing finite element software for the bulk metal forming simulation has been unable to meet the requirements in finite element analysis for the bulk metal forming process any more, because of problems such as frequently remeshing, difficulty loading for complex motion and low efficiency in the analysis of large problems. In this paper finite element simulation theory and algorithms and the detailed implementation for bulk metal forming are studied and a finite element simulation software platform based on rigid viscoplastic theory is developed for bulk forming.The three-dimensional (3D) finite element meshing method has been studied. In order to solve the contradiction between precision and unit numbers of the finite element mesh model, a self-adaptive meshing method is proposed and the commonly used self-adaptive meshing method for hexahedral mesh model and tetrahedral mesh model is studied. In order to take the advantages of the two mesh models, a concept, hybrid mesh model of hexahedron and tetrahedron, is proposed and the adaptive generating method for hybrid meshing model is studied. Principles for choosing of the meshing methods are proposed and a matured algorithm for 3D finite element initial meshing is established. Method for 3D finite element mesh regenerating is studied. The method for geometrical form extraction and restoration in the distortion of mesh is researched and a method for transfer of physical field variables between new and old mesh is studied. In order to improve the interpolation precision of physical field variables, a double self-adaptive remeshing algorithm is proposed based on both geometrical characteristic and physical field variables. In order to improve the efficiency in remeshing, a technology for the local remeshing of the 3D finite element mesh is proposed. In view of the interference mesh a method for refinement of the local mesh is proposed. In view of the distortion mesh a method for optimization of the position of local nodes and a method for regeneration of the local mesh are proposed. Also the methods and principles for choosing remeshing method are recommended, and a systematic method for remeshing of three-dimensional mesh is established.The existing theories and methods in finite element simulation have been analyzed and compared and in this study the rigid viscoplastic theory is chosen as the basic theory for analyzing the bulk metal forming with finite element. Based on the rigid viscoplastic theory, the establishing methods and solutions of the whole stiffness equation for different mesh models are researched. The key technology for the finite element simulation in isothermal forming of the 3D bulk metal forming is researched. The description of 3D geometry of the reconstructed mold is presented based on data of STL files. A method to establish of a local coordinate system is proposed to ensure the correct exerting of the boundary conditions and the symmetrical constrained on the contacted mold. The handling methods for complex mold motion, including description method of mold movement, solving methods for mold velocity and location update method of mold, are studied. Handling methods for three-dimensional dynamic boundary conditions are proposed, which include judging of contact of the nodes with mold with the help of relative position method and adjusting of position of the nodes contacted with mold by using the shortest distance method. In order to improve the efficiency of analysis and calculation, reduce storage space consumption, storage compression algorithms and corresponding efficient solutions for the whole stiffness equation are proposed. Based on the research in key technologies, an isothermal simulation system for bulk metal forming with FEM is developed.Based on the isothermal simulation system with FEM, a thermal mechanical coupling simulation system for bulk metal forming with FEM is developed. The basic theory of FEM for 3D temperature field is studied and a system of FEM for 3D temperature field is developed. The basic theory and key technologies of a thermal mechanical coupling simulation with FEM are studied, such as treatment of temperature shock, thermal coupling boundary conditions, and treatment of thermodynamic parameters. In theory and key technologies research, based on the system of 3D temperature field simulation with FEM and the system of 3D isothermal simulation with FEM, the system of 3D thermal mechanical coupling simulation with FEM is developed by indirect coupling method.Based on key technologies and implementation method, supporting subsystems of 3D bulk metal forming simulation system with FEM is developed, including:the pre-treatment system of building finite element model, post-processing system of analysis finite element results, database system of supporting system. The combination of these auxiliary subsystems with the three-dimensional rigid viscoplastic finite element analysis system builds a software platform CASFORM-3D system of the 3D FEM for bulk metal forming. Through simulating with typical parts in practice, and comparing of the simulation results with those results with commercial software DEFORM-3D simulation, it shows a high identity between these two methods, therefore verifies the reliability of the key technologies and feasibility of the associated processing algorithms proposed in this paper.更多还原