Finite element analysis with deformation behavior modeling of globular microstructure in forming process of semi-solid materials

The behavior of alloys in a semi-solid state depends on the imposed stress state and on the morphology of the phase which can vary from dendritic to globular microstructure. An estimation of characteristic behavior in a compression simulation with semi-solid materials (SSMs) is made using the finite element method (FEM) and a proposed, new stress–strain relationship formulation with a separation coefficient. The proposed theoretical models for the compression forming process involve simultaneous calculations performed with solid-phase deformation and the liquid-phase flow saturating the interstitial space. A simulation process considering solidification phenomena is implemented with non-isothermal conditions in two-dimensions. To analyze the compression process of SSMs, a new stress–strain relationship is described, and the compression analysis is performed by using a compressible visco-plastic model for the solid phase and Darcy’s law of fluid flow through a porous medium for the liquid phase. The validity of the proposed models is investigated by comparing the calculated results with experimental data for the relationship between engineering stress and true strain, and the distributions of solid fraction, temperature effective strain, etc., are calculated.     

斜壁矩形盒件多点拉深成形的数值模拟

通过对斜壁矩形盒件多点拉深成形的有限元数值模拟,分析了成形过程中起皱与拉裂缺陷的产生,研究了四种不同压边力加载曲线即恒压边力、↘形压边力曲线、V形压边力曲线、■形压边力曲线对成形结果的影响。结果表明:斜壁矩形盒件在整个多点拉深成形过程中,在宽度方向的侧壁底部极易发生破裂缺陷,在法兰直边对称轴处起皱最严重;不同的压边力曲线对斜壁矩形盒件多点拉深最终成形结果的影响很大,其中■形状的压边力加载曲线最有利于斜壁矩形盒件的多点拉深成形。     

双层板汽车消声器外壳成形工艺分析及仿真

针对不锈钢双层板汽车消声器外壳成形中出现的起皱和破裂问题,从产品结构特点上详细地分析了可能产生问题的原因,提出了多种解决问题的成形工艺方案,并通过有限元数值仿真对其进行了模拟和对比分析.结果表明,对双层板采用点焊连接,并设置局部拉延筋和变压边力的成形工艺能够使得成形时材料流入均衡、改善凹筋弯曲处的受力状况,从而有效地解决汽车消声器外壳中凹筋弯曲处的起皱和拉伸深度过大端破裂的问题.     

Numerical simulation on the local stress and local deformation in multi-point stretch forming process

Multi-point stretch forming (MPSF) is a new flexible forming technique to form aircraft outer skin parts. The multi-point stretching die (MPSD) replaces the traditional fixed shape stretching die, and the sheet metal is formed over a MPSD composed by the punch element. The MPSD is a discontinuous surface of discrete stretching die, and the stress concentration and local strain occur on formed parts. These lead to generate dimples on the surface of formed part. In this paper, a series of numerical simulations on MPSF processes for stretching parabolic cylindrical, spherical, and saddle-shaped parts were carried out. The local stress and local strain in thickness distribution of MPSF part were analyzed by dispersed the blank into solid elements. The forming results of MPSF were compared with those that use traditional stretch forming, and the influences of thickness of elastic cushion and the size of punch element on the stress concentration and local strain were surveyed. The simulation results show the distribution of local stress and local deformation in different layers, and the elastic cushion and the small size of punch element can reduce the stress concentration and local deformation. The results may understand the stress distribution on the sheet and prevent the defect of dimple.     

基于数值模拟技术的吸塑模成型工艺优化

介绍了吸塑成型工艺过程,对吸塑成型的关键技术进行了阐述,包括运动函数的建立和成型时间的预测。基于Polyflow软件平台,以冰箱门体内胆吸塑模为例,通过对吸塑模成型过程的分析,对吸塑成型工艺过程进行了数值模拟分析。模拟结果表明:在整个真空吸塑成型过程中,吹泡时间的长短是控制制件成型质量的关键。吹泡时间过短会导致制件厚度局部变薄不均匀;而吹泡时间过长,则会出现局部折皱和折叠。结合数值模拟技术和运动函数,实现了吸塑成型工艺参数的优化。     

马鞍面件多道次多点模具成形数值模拟

通过对马鞍面件多道次多点模具成形的有限元数值模拟,阐述了多道次多点模具成形数值模拟的关键技术,并与单工步多点模具成形进行比较,分析了马鞍面件的成形过程,研究了不同曲率半径步长对成形结果的影响.结果表明:多道次多点模具成形与单工步多点模具成形相比改善了板材的受力状况,达到了消除变形集中的目的;多道次多点模具成形时,随着曲率半径步长的减小,板料厚度分布越来越均匀,不易形成集中失稳.     

激光拼焊板成形过程数值模拟技术现状及趋势

由于焊缝性能与母材存在较大的差异以及焊缝自身形状的特点,激光拼焊板在成形过程中的数值模拟分析可以采用不同的建模方法。介绍了国内外对激光拼焊板数值模拟采用的不同建模方法,比较了不同焊缝模型对计算结果的影响,并利用ABAQUS／Explicit动力显示积分模块分别采用忽略焊缝以及考虑焊缝采用壳单元时的建模方法对U形件的弯曲成形过程进行了数值仿真,结果显示焊缝模型对模拟结果影响较大,采用忽略焊缝的建模方法得到的焊缝移动量较小。     

锥齿轮冷挤压成形加工数值模拟研究

为了解决人工设计锥齿轮冷挤压模具过度依赖经验的问题,将数值模拟应用到锥齿轮模具设计中。设计了一套用于冷挤压加工锥齿轮的三层组合凹模,制定了相应的工艺措施,利用Deform-3D软件对锥齿轮的冷挤压加工过程进行了数值模拟,分析了加工过程中的载荷曲线、速度场、应力场和温度场,获得了有关锥齿轮变形规律的基本情况。研究结果表明,通过改善润滑条件、优化模具几何参数可以提高冷挤压加工锥齿轮的成形质量,并对锥齿轮冷挤压加工工艺流程定制、模具设计具有一定的指导意义。     

冷成形精密螺钉数值分析与工艺优化

利用有限元数值模拟仿真技术对精密微型螺钉的模具设计和成形工艺进行优化 ,对优化结果进行试验研究 ,并对成形缺陷进行金属学分析 ,讨论影响缺陷产生的因素 ,从理论上寻找缺陷产生的原因 ,从实践上印证理论分析和有限元模拟结果 ,最终得到可以消除裂纹和折叠缺陷的模具和工艺设计。     

Flow behavior of Plasticine used in physical modeling of metal forming processes

In this study, compression tests were conducted to determine the flow behavior of various types of Plasticine. True stress–true strain relations are presented in the form of a well-known power law equation. It is shown that the strength coefficient and the strain hardening exponent vary significantly among the Plasticine with different colors commercially available. Furthermore, since three dimensional simulations require arranging slabs of alternating colors to form a grid pattern, two different colors, exhibiting similar flow characteristics, are identified. The flow behavior of the composite model is usually not the same as that of the individual colors. The results presented in this paper allow selection of the type of Plasticine which most closely resembles the strain hardening characteristic of the actual metal, thereby satisfying the “similarity condition” of the Physical Modeling Technique.     

板料拉深成形数值模拟中动态边界条件的处理

针对板料拉深成形过程中工件与模具接触边界的动态变化,将模具表面离散为若干个三角形单元,并用参数方程来描述工件节点及模具三角形单元的运动情况,将工件与模具的接触问题转化为空间直线与平面的动态求交问题。在此基础上,通过实际的模拟分析,证明该处理方法的可行性。     

Numerical simulation of the electromagnetic sheet metal bulging process

Electromagnetic forming (EMF) is an uncommon metal working process that relies on the use of electromagnetic forces to deform metallic workpieces at high speeds. It is expected to overcome some formability barriers of materials. EMF process analysis is the foundation of theoretical analysis. However, the electromagnetic sheet metal process is very difficult to describe, because of the complexity of magnetic pressure distribution. In this paper, a numerical modeling of the electromagnetic sheet metal process is performed using a finite element method, and a series of simulations on free bulging are carried out using the FEA program ADINA. The dynamic deformation process of sheet metal is investigated. At last, some experiments are made and those simulations agree well with the experimental results.     

外凸台内齿圈精密成型有限元数值模拟

对外凸台内齿圈件及模具建立了弹塑性有限元模型,分析了零件加工工序过程。构建了相关有限元力学模型,采用数值模拟方法分析了外凸台内齿圈件冷挤压成型过程,研究了成型过程中的相关关键技术,得出了成形过程中的挤压力、速度、应变场及材料充填的变化规律。较好地预测了成形过程中可能产生的缺陷。通过试验研究发现仿真结果和实际符合很好。数值模拟研究成果对冷挤压成形仿真以及塑性成形工艺控制和模具结构优化设计具有指导意义。     

Generation and suppression of local severe plastic deformation in sectional multi-point forming

Sectional multi-point forming (SMPF) technology provides a new solution for forming large-size sheet metal. With this technique, large-size parts of sheet metal can be manufactured on a smaller multi-point forming press. But the force status and deformation of the workpiece are complicated in SMPF; the local severe plastic deformation will be produced easily in the transition region, and strain-hardening will be commonly produced subsequently. The hardening is difficult to eliminate in subsequent processes, which will largely affect the final deformation quality. In this paper, the generation of local severe plastic deformation was discussed; NURBS-based modeling method was used to construct the shape of the assortative region to suppress the defect. Experiments proved that the method is fairly effective. Finally, a plan was suggested to raise further the forming limit of materials and enhance the work efficiency by combining multi-point press forming with assortative region method.     

Applying forming simulation to process and tooling designs for minimizing springback in split dowel manufacturing

In this study, FEA simulations were conducted to analyze the forming and springback of a split dowel forming process. Through 96 simulations, the best dimensional quality product from the current production tooling was obtained. However, it still cannot meet the customer’s geometrical requirement, so a metal finish process (secondary operation) is required. In order to minimize manufacturing cost and time, the secondary operation is not desired. Therefore, a new forming process and die design were developed through many iterative FEA simulations. This new design adds a short coin bead on the seam line area of the split dowel. It has been found that the springback amount is almost eliminated and the product quality exceeds the customer’s geometry requirement. Through this real industry case study, it is shown that FEA simulation can be used to not only optimize the current process but also design a new process and tooling.     

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.     

Numerical study on characteristics of turbulent two-phase gas-particle flow using multi-fluid model

The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian method. A computer code is developed for the numerical study by using the k-ɛ-k _p two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is between 10⁻⁵ and 10⁻² for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number (St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number (St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected by the gas phase. A large particle volume fraction (α _p ≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction (α _p ≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and particle velocities.     

空心工字钢冷弯成型过程的数值模拟

空心工字钢是一种新型断面型材,它由铜板经冷弯成型机组在室温下冷弯成两块近似M形型钢后再焊接在一起而成.设计了一种冷弯成型孔型系统,并利用Pro/E软件建立了空心工字钢冷弯成型机的虚拟样机.采用三维有限元方法,利用ANSYS-LS/DYNA软件对冷弯成型过程中的弹塑性变形过程进行了数值模拟,系统地分析了成型过程中的应力变化规律.研究结果对于冷弯型钢产品的开发、孔型系统的设计具有参考价值.     

TA1板单点渐进成形壁厚变化规律的数值模拟研究

钛及其合金应用越来越广泛,目前单点渐进成形技术已经开始运用于钛及其合金的成形加工,但仍存在成形件壁厚过度减薄的问题,严重影响了成形件的成形质量。文章以TA1钛合金板材成形方锥形件为研究对象,运用Abaqus有限元仿真软件,依据单一变量原则,分别探究工具头直径、底面边长、板材原始厚度和螺距等工艺参数对成形件平均壁厚减薄率与最大壁厚减薄率的影响规律。结果显示:增大工具头直径,平均壁厚减薄率随之增大,最大壁厚减薄率随之减小;平均壁厚减薄率和最大壁厚减薄率都随着底面边长的增加而增加;板材原始厚度增加,平均壁厚减薄率与最大壁厚减薄率都随之减小;随着螺距的增加,平均壁厚减薄率逐渐减小,最大壁厚减薄率逐渐增大。     

固体颗粒介质成形新工艺试验研究与应力分析

自行设计制造了固体颗粒介质传压性能试验与测试装置,通过试验测得到了固体颗粒的传压规律.建立了板料在拉深力作用下的两种力学模型:线性分布载荷和二次函数分布载荷的力学模型.自行设计制造了板料成形试验模具与装置,通过对成形试验件的测量与分析,建立了自由变形抛物线函数变形模型.对固体颗粒介质板料拉胀成形未贴模时塑性变形阶段进行了塑性变形分析,推导出了自由变形区的应力分布计算公式,为固体颗粒介质板料拉胀成形塑性理论研究奠定了基础.