金属波纹管焊接过程的应力及变形特性

针对焊接引起的变形及其所产生的残余应力和应变会影响金属波纹管正常使用的问题,用有限元法分析波纹管的焊接过程,研究焊接过程中金属波纹管的变形和应力.基于单元生死技术,考虑材料的性能随温度变化而非线性变化的影响,通过提取焊缝周边参考点和参考路径的应力和变形,重点研究热源移动对金属波纹管应力和变形分布、类型以及大小的影响.     

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.     

Dynamic analysis of structural deformation and metal forming

In the dynamic analysis of the deformation of bodies and structures it is often found that the duration of significant loads and high stresses is such that stress waves traverse the body and reflect from the surfaces many times in the period of interest for stress and deformation analysis. This circumstance can even apply in impact problems such as those arising in automobile collisions and hammer forging. In many problems, particularly when plastic flow occurs, numerical methods of solution must be utilized. The equations governing the dynamic deformation of a continuous medium are of wave type, but if dynamic elastic-plastic computer codes, such as those developed for ballistics problems which analyse wave propagation, are used for problems of the type considered here, excessive computing effort and round-off errors can be expected. Finite difference schemes for the wave equation are examined to select a scheme which is stable for long time steps and which adequately encompasses both wave analysis and long time solution, avoiding in the latter the complexity of the wave interactions. Economical computation is then achieved. This approach is applied to the study of dynamic deformation of a porous metal using the finite element method.     

Stress recovery procedure for discontinuous deformation analysis

The discontinuous deformation analysis (DDA) has been widely applied for rock engineering problems due to its special features in modeling the discontinuous rock mass. A linear polynomial function is often used in the standard DDA to ease the complex contact determination between the blocks. This linear displacement function generates a constant stress field within a block, which cannot be effectively used to model the stress variation within a block and across the block interface, especially in the region with a large stress gradient. In this paper, a stress recovery procedure is proposed for those DDA blocks which are glued together. Such a procedure can improve the stress accuracy along the block interface, and can be used for more accurate contact determination. Two numerical examples are presented to study the stress accuracy of the proposed method, and the results show that the proposed stress recovery method provides a better accuracy than the direct DDA and the averaging method.     

Flow of metal in high-temperature extrusion

The Rabotnov-Mileiko model of nonlinear viscosity is applied here to the problem of plastic flow of a metal. A theoretical solution, based on this model, is presented for stable flow in a circular tube and in a slit-type duct. The proposed algorithm (based on the Galerkin method) for axisymmetric cases is applicable to high-temperature extrusion. Computer results are presented for flow of a Newtonian liquid and of aluminium in a circular tube and at the outlet of a large reservoir.     

An analysis of metal forming processes using large deformation elastic-plastic formulations

A concise survey of the literature related to the large deformation elasto-plasticity problems including unilateral contact and friction is presented together with an extension of the friction law for large deformation analysis.Starting from the principle of virtual work, the so-called total Lagrangian and updated Lagrangian formulations are derived based on some fundamental assumptions in linearizing the nonlinear equations. By introducing the Zaremba-Jaumann (co-rotational) increment to the Cauchy stress tensor, the classical Prandtl-Reuss equations are generalized for describing the elastic-plastic material behavior. To allow a proper consideration of the contact conditions in the incremental analysis, a general friction law with an associated isotropic Coulomb sliding rule is obtained by the similarity between dry friction and plasticity. Finite element discretizations and approximations are applied to the resulting formulation of the updated Lagrangian approach.Four example problems are solved to test the formulations developed in this paper. The emphasis is made toward the numerical accuracy of the finite element solutions.     

An elasto-plastic rate-dependent finite element analysis of the metal forming process

An elasto-plastic rate-dependent finite element formulation is developed into the solution of the large strain and deformation problem. The formation is based on the power form constitutive equation for the stress-strain-strain rate relation of the material. A simple one-step Euler's time integration scheme is adopted to automatically control the time increment. After incorporating a force rate term which is due to the effect of the strain rate, the simulation is completed by modifying the updated Lagrangian formulation. The numerical results can be used as options in the selection of the adequate tool speed, die geometry, and die material.     

Control of a LDPE reactive extrusion process

A constrained model predictive control strategy is implemented to control the weight-average molecular weight and the high molecular weight end of the molecular weight distribution of a low-density polyethylene (LDPE) in a reactive extrusion process. To achieve simultaneous regulation of these properties, the amplitude and width of square wave-shaped pulses of a peroxide solution injected to the extruder are independently manipulated. The two polymer properties are inferred on-line from consistency and power-law index measurements obtained with an in-line wedge rheometer. Simulations and experimental results show that independent control of the polymer properties is feasible by this method, but only in a narrow range of operating conditions.     

金属冷挤压的闭塞复动成形模具研究

该文介绍了金属冷挤压的闭塞复动成形新技术的基本原理和特点,闭塞复动模具的基本结构形式.介绍了采用连杆、弹簧和液压的基本合模方式,芯轴同步运动的两种基本方法,对采用齿轮齿条传动和凸轮传动的同步运动结构和同步过程进行分析.同时也对模具的两种基本缓冲方式,采用弹簧缓冲和采用液压缓冲进行了分析.     

A model for the metal deposition process

In IC industry, the manufacturing technology trends toward more precision and more miniaturization, such as from 28 to 14 nm process. This nano-manufacturing, metal deposition process must be studied to improve higher quality and more reliability production rate of produce. Hence, a model for the metal deposition process is necessary. This model of a vacuum metal film deposition system for substrate application with normal metal material is considered. In this model, the finite difference method is employed to discretize the solution domain into meshes and nodes. The numerical solution of electric potential or electric intensity of the metal film sputtering system can be obtained by MATLAB numerical simulation software, and to solve these equations of the discrete nodes. Numerical analysis results indicate that this simulation model can be employed to study the coating quality of the metal deposition process system.

     

Neural network based modeling and optimization of deep drawing – extrusion combined process

A combined deep drawing–extrusion process is modeled with artificial neural networks (ANN’s). The process is used for manufacturing synchronizer rings and it combines sheet and bulk metal forming processes. Input–output data relevant to the process was collected. The inputs represent geometrical parameters of the synchronizer ring and the outputs are the total equivalent plastic strain (TEPS), contact ratio and forming force. This data is used to train the ANN which approximates the input-output relation well and therefore can be relied on in predicting the process input parameters that will result in desired outputs provided by the designer. The complex method constrained optimization is applied to the ANN model to find the inputs or geometrical parameters that will produce the desired or optimum values of TEPS, contact ratio and forming force. This information will be very hard to obtain by just looking at the available historical input–output data. Therefore, the presented technique is very useful for selection of process design parameters to obtain desired product properties.     

Soft computing applications in dynamic model identification of polymer extrusion process

This paper proposes the applications of soft computing to deal with the constraints in conventional modelling techniques of the dynamic extrusion process. The proposed technique increases the efficiency in utilising the available information during the model identification. The resultant model can be classified as a ‘grey-box model’ or has been termed as a ‘semi-physical model’ in the context. The extrusion process contains a number of parameters that are sensitive to the operating environment. Fuzzy rule-based system (FRBS) is introduced into the analytical model of extrusion by means of sub-models to approximate those operational-sensitive parameters. In drawing an optimal structure for each sub-model, a hybrid algorithm of genetic algorithm with fuzzy system (GA-fuzzy) has been implemented. The sub-models obtained show advantages such as linguistic interpretability, simpler rule-base and less membership functions (MFs). The developed model is adaptive with its learning ability through the steepest decent error back-propagation algorithm. This ability might help to minimise the deviation of the model prediction when the operational-sensitive parameters adapt to the changing operating environment in the real situation. The model is first evaluated through simulations on the consistency of model prediction with the theoretical analysis. Then, the usefulness of adaptive sub-models during the operation is further explored in existence of prediction error.     

Modeling,analysis and multi-objective optimization of twist extrusion process using predictive models and meta-heuristic approaches,based on finite element results

Recently, twist extrusion has found extensive applications as a novel method of severe plastic deformation for grain refining of materials. In this paper, two prominent predictive models, response surface method and artificial neural network (ANN) are employed together with results of finite element simulation to model twist extrusion process. Twist angle, friction factor and ram speed are selected as input variables and imposed effective plastic strain, strain homogeneity and maximum punch force are considered as output parameters. Comparison between results shows that ANN outperforms response surface method in modeling twist extrusion process. In addition, statistical analysis of response surface shows that twist extrusion and friction factor have the most and ram speed has the least effect on output parameters at room temperature. Also, optimization of twist extrusion process was carried out by a combination of neural network model and multi-objective meta-heuristic optimization algorithms. For this reason, three prominent multi-objective algorithms, non-dominated sorting genetic algorithm, strength pareto evolutionary algorithm and multi-objective particle swarm optimization (MOPSO) were utilized. Results showed that MOPSO algorithm has relative superiority over other algorithms to find the optimal points.     

直接金属快速成形中的变形测量系统研制

为了对直接金属快速成形中零件的变形规律进行研究,研制了一个变形测量系统。采用了电感调频式位移传感器,可对零件的变形进行在线或离线测量。通过消息传递机制实现了工作台运动进程与变形数据采集进程之间的通信。采集的数据根据不同分析需求进行输出,可以方便地对零件的变形进行分析研究。     

岩石材料变形破坏过程应用程序开发

为了研究岩石表面变形破坏过程的变化特征,设计了一个可视化应用程序.该应用程序以岩石常规力学性质试验视频作为研究对象,包括静态图像处理界面和视频图像处理界面.静态图像处理界面由图像类型转换、图像边缘检测、图像形态学处理、图像滤波处理4个模块组成.视频处理界面则提供试验视频帧数、历时、帧图像大小和维数等基本信息.通过在可视化界面上进行所需参数设置实现了单帧图像特征纹理参数计算和岩石试样表面位移场的计算.本文还以两个示例说明了使用该应用程序进行岩石材料变形破坏过程分析的方法.本文成果对分析岩石材料变形特点和破坏机制具有一定的参考价值.     

Integrated metal forming and vibration analysis of sheet metal parts

Modern software programs are routinely used by industries to study the characteristics of and to reduce the cost of sheet metal parts that are used in automotive and other applications. Virtual simulations that are based on complex math models and state-of-the-art computational tools play a very important role in reducing the high costs associated with prototypes and the time to market the product. Formability studies of a sheet metal part determine if a part is formable by changing the factors that affect its formability. Vibration (or modal) analysis is performed to determine the frequency and mode shapes of the component or the assemblies. A gauge optimization study is performed to determine the optimum gage thickness assigned to components of an assembly while constraining the frequency of specified modes to a desired level. Usually these studies are done separately by different engineering departments in a typical automotive industry. In this paper, a single component from an instrument panel (IP) reinforcement assembly is analyzed by integrating the three different studies mentioned above. It was found that the thickness of the bracket and the coefficient of friction in the stamping process should be kept as low as possible to reduce the chance of splits occurring in the bracket. An optimum thickness for the same bracket as part of an assembly can also be determined using a gauge optimization study so that the assembly was stiff enough while minimizing its mass. Thus, an integrated analysis using simulation tools helps in better design of the parts and subassemblies, which ultimately helps stay in competition to produce quality products.     

Modeling and optimization of cold extrusion process by using response surface methodology and metaheuristic approaches

Obtaining the optimal extrusion process parameters by integration of optimization techniques was crucial and continuous engineering task in which it attempted to minimize the tool load. The tool load should be minimized as higher extrusion forces required greater capacity and energy. It may lead to increase the chance of part defects, die wear and die breakage. Besides, optimization may help to save the time and cost of producing the final product, in addition to produce better formability of work material and better quality of the finishing product. In this regard, this study aimed to determine the optimal extrusion process parameters. The minimization of punch load was the main concern, in such a way that the structurally sound product at minimum load can be achieved. Minimization of punch load during the extrusion process was first formulated as a nonlinear programming model using response surface methodology in this study. The established extrusion force model was then taken as the fitness function. Subsequently, the analytical approach and metaheuristic algorithms, specifically the particle swarm optimization, cuckoo search algorithm (CSA) and flower pollination algorithm, were applied to optimize the extrusion process parameters. Performance assessment demonstrated the promising results of all presented techniques in minimizing the tool loading. The CSA, however, gave more persistent optimization results, which was validated through statistical analysis.

     

The vertex-to-vertex contact analysis in the two-dimensional discontinuous deformation analysis

In the two-dimensional discontinuous deformation analysis (DDA), contacts can be generalized into three types: vertex to edge, edge to edge, and vertex to vertex. In the vertex-edge contact, the contact reference edge is clearly and uniquely defined, while the contact reference edge for the vertex-vertex contact is not unique, which will lead to an indeterminate state. The indeterminacy of the vertex-vertex contact is a well-known problem in both the continuum-based methods and the discontinuum-based methods. The standard DDA employs the shortest path method to deal with the indeterminacy in the vertex-vertex contact, which is sensitive to the choice of analysis parameters, such as the time step size, the maximum displacement ratio and the contact spring stiffness. Two enhancements to the shortest path method are introduced in this paper. The first enhancement employs a temporary vertex-vertex contact spring to determine the moving tendency among two contact blocks. The second enhancement uses the trajectory of the vertex during a time step to find the entrance edge when the moving vertex invades into the target block. Examples show that these two enhancements to the standard DDA code work well.