基于离散单元法的粉末高速压制流动过程模拟

将离散单元法应用于粉末高速压制流动过程研究,以模拟粉体流动的非连续特性。将粉末视为粘弹性的离散颗粒,推导了力与位移表达的粉末高速压制粘弹性本构关系,建立了粉末高速压制成形颗粒流动的离散单元法控制方程;并给出了该模型的动态松弛法求解过程。基于离散单元法求解器PFC软件,对粉末高速压制成形过程颗粒流动情况及密度分布进行了模拟,模拟结果与实验结果较吻合。分析了阻尼系数变化对求解过程的敛散性和压坯密度分布的影响     

Improved model and 3D simulation of densification process for iron powder

A new model for describing the compaction process of iron powder was proposed based on the continuum hypothesis and elliptical yield criterion. To simulate the densification behaviour, the constitutive model was implemented in Marc computer program. For the relationship between load and displacement, different models were compared and the influence of the parameters in the constitutive equations was determined by means of simulation and experiments. The density distribution of a balancer was measured and simulated. The results show that the parameter η adopted plays a modification role for the load-displacement curve, and compared with other models the present model fits better with the experimental data in the later stage of the compaction process mainly due to the different parameters A and B. The friction on the contact surface contributes to the inhomogeneous density distribution under large deformation of the workpiece. The comparison between the simulation and experimental data indicates that this model can be used to predict the powder compact process precisely and effectively.     

Numerical simulation of warm compacted synchronous pulley

A new mechanical model for warm powder compaction was presented. Warm compaction process of iron-based powder was investigated to deal with the existence of elastic, plastic and thermal strains. A coupled mechanical and thermal model was developed based on ellipsoidal yield criterion and continuum theory. The constitutive equations were integrated into the constitutive integral arithmetic and solved employing incremental iterative solution strategy. The flow stress model of iron powder was nonlinearly fitted according to uniaxial warm compaction. The constitutive model was implemented into user-subroutines of MSC.Marc. With the equations, algorithms and programs developed, the compaction procedures of a complex synchronous pulley were simulated. Two different compaction schemes with different punch displacements were tested and the relative density distribution was obtained. Comparison with experimental data shows that the homogeneity of green compact is greatly affected by the compaction mode. The simulation results agree with the experiments very well.     

高速压制成形粉末流动过程的格子Boltzmann方法数值模拟

根据高速压制工艺过程的特点,底部和侧面边界采用反弹与反射的混合格式,顶部通过改变分布函数构造能模拟动态压制过程的边界格式。利用粉体的初始密度和压制最大理想密度建立一个动态的松弛函数来代替格子Boltzmann方法的固定松弛时间。对圆柱体及单级台阶的圆柱体模具的高速压制成形过程进行二维数值模拟,直观显示压制过程中粉末的流动以及应力波的形成与传播过程。模拟结果表明:模具形状对应力波的波形有较大影响;压制完成后,圆柱体压坯最大密度差为12 mg/cm3,密度分布均匀且左右对称,压坯顶部和底部密度较中间部分密度稍大,与实验结果基本相似;圆柱体压坯中存在密度较低的横向窄带区域,揭示成形坯有可能形成分层或断裂。     

基于修正Drucker-Prager Cap模型的金属粉末压坯残余应力数值分析

基于修正的 Drucker?Prager Cap模型建立弹塑性本构模型,采用三维有限元模型对粉末压制过程及压制脱模后压坯的残余应力进行仿真分析。利用几个典型的力学性能测试实验确定粉末Distaloy AE的模型参数。模型通过用户子程序USDFLD实现,对粉末Distaloy AE的模压过程及脱模后压坯(d20 mm×5 mm)的残余应力进行预测分析。有限元分析结果与模压实验和X衍射实验结果基本吻合,验证了模型的有效性。结果表明,压坯的侧表面存在一层显著的残余压应力,而压坯上表面和下表面的残余应力值则很小。     

RESEARCH AND SIMULATION OF THE INFLUENCE OF THREE-AXIAL COMPACTION ON POWDER METALLURGIC PRODUCT PROPERTIES

The warm powder compaction process is simulated by the finite element analysis software, MSC/MARC. The thermal mechanically coupled analysis method is applied on the basis of the updated Lagrangian Method, to simulate the warm powder compaction process. The warm powder compaction process is simulated, and the influence of friction condition and pressing styles are researched on the density of powder green and the mechanics behavior at certain temperature. The results indicate that for cylindrical compacts, with the improvement of the friction condition, the uniformity of distribution of green relative density is largely improved, the pressing force and stress decrease, and the nonconforming pressing processes influence the distribution of green density to some degree. The status of stress distribution of the process that punches firstly press and die finally press is different from the other three processes, and presents the figure of 'flume'.     

Research and Simulation of Influence of Three-Axial Compaction on Powder Metallurgic Products Properties

The warm powder compaction process is simulated by the finite element analysis software, MSCJMARC. The thermal mechanically coupled analysis method is applied on the basis of the updated Lagrangian Method, to simulate the warm powder compaction process. The warm powder compaction process is simulated, and the influence of friction condition and pressing styles are researched on the density of powder green and the mechanics behavior at certain temperature. The results indicate that for cylindrical compacts, with the improvement of the friction condition, the uniformity of distribution of green relative density is largely improved, the pressing force and stress decrease, and the nonconforming pressing processes influence the distribution of green density to some degree. The status of stress distribution of the process that punches firstly press and die finally press is different from the other three processes, and presents the figure of ＇flume ＇.     

Simulation of die wall friction‘s effect on density distribution in metallic powder compaction

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Densification modelling for nanocrystalline metallic powders

A model for densification of metallic powders is proposed. It involves viscoplastic constitutive equations based on dislocation density evolution and also accounts for effects of porosity using a pressure-dependent critical density yield criterion. The model was applied to the case of cold compaction of nanocrystalline copper under uniaxial compression conditions. Densification behaviour during powder compaction was simulated using an explicit integration method as applied to the dislocation density evolution and the variation of the relative density of the compact. The model was gauged by comparing the experimental data generated by cylindrical die compaction tests on Cu powder with the simulation results. The model accounts for the grain size and the deformation rate dependence on the densification process. The proposed densification model was implemented into a finite element code. The finite element method was applied to simulating room temperature die compaction of nanocrystalline Cu powder in order to investigate the densification behaviour.     

Prediction of fracture generated by elastic recoveries of tools in multi-level powder compaction using finite element simulation

Fracture initiated in a compact by the difference between the amounts of elastic recovery of tools during the unloading process of multi-level powder compaction is predicted from calculated results by finite element simulation. The loading and unloading processes in the compaction are simulated by the rigid-plastic and elastic finite element methods, respectively. In these simulations, elastic tools are modelled as springs connected with the nodal points on the interfaces between the powder material and tools. This modelling leads to simple treatment of coupling of the tools and compact. The initiation of fracture is evaluated from the maximum principal stress, and the critical stress is measured by means of bending and shearing tests. Two-level compaction operations are simulated by the finite element methods to predict the initiation of fracture. The predicted critical values of relative density for the occurrence of fracture are in good agreement with the experimental ones for iron powder compacts.     

基于有限元模拟的钼粉末温压成形分析

为了研究钼粉末温压成形过程,用有限元分析软件建立了钼粉末温压成形的有限元模型,对三维圆柱等截面粉柱温压成形过程进行了有限元数值模拟,从模拟结果得到了最终坯体内部密度和应力等参量的分布情况以及钼粉末颗粒轴向和径向流动规律.实验验证了所建立有限元模型的可靠性,并分析了部分工艺和材料性能参数对钼粉末成形的影响.结果表明:在钼粉末的温压成形过程中,压坯顶部半端面、轴截面和侧壁的相对密度分布等值线和其应力分布等值线非常接近.     

Investigation of Die Stress Profiles During Powder Compaction Using Instrumented Die

The die stress profiles during compaction of commercially pure titanium (Ti) and commercial lubricated iron (Fe) powders were experimentally investigated using an instrumented die. The die was designed to simulate double-action pressing, and a detailed stress profile was measured along the height of the die using multiple custom-made strain gage pins. The stress history shows that residual stress remained in the die in the radial direction after the axial compaction stress was removed from the powder. Also, the stress profile at the maximum axial stress and the residual stress profile were observed to be symmetric across the height of the compact for both powders, but both have a unique shape for each powder. For both the stress profile at the maximum axial stress and the residual stress profile, the unlubricated Ti powder produced a much higher radial stress at the center of the compact with a steep pressure gradient on both top and bottom of the compact, while the lubricated Fe powder produced a rather uniform radial stress distribution along the height of the compact. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16–20, 2007, in Detroit, MI.     

An analysis of the powdered metal compaction process in solid cylind cal parts

In this study, the friction effect on the powdered metal compaction process has been analyzed by applying finite element methods. A plasticity theory applicable to powdered metal compaction is summarized and a variational form for finite element analysis is described. The compaction processes of the axisymmetric solid cylinder are simulated for different compact geometries in single-action pressing. Efforts are focused on the pressure transmitted between the upper and lower punches through the compact and density distributions within the compacts. The numerical results show that: (1) the friction condition between the metal powder and the dies can be determined simply from the force data transmitted by a single such action compaction test and the simulation results; (2) the density variations within the compacts rely on such compact geometry as the height to diameter ratio and the frictional conditions between powder and dies; the (3) additional useful information obtained includes the Min/Max density ratio within the compacts.     

Using finite difference method to simulate casting thermal stress

Thermal stress simulation can provide a scientific reference to eliminate defects such as crack,residual stress centralization and deformation etc., caused by thermal stress during casting solidification. To study the thermal stress distribution during casting process, a unilateral thermal-stress coupling model was employed to simulate 3D casting stress using Finite Difference Method (FDM), namely all the traditional thermal-elastic-plastic equations are numerically and differentially discrete. A FDM/FDM numerical simulation system was developed to analyze temperature and stress fields during casting solidification process. Two practical verifications were carried out, and the results from simulation basically coincided with practical cases. The results indicated that the FDM/FDM stress simulation system can be used to simulate the formation of residual stress, and to predict the occurrence of hot tearing. Because heat transfer and stress analysis are all based on FDM, they can use the same FD model, which can avoid the matching process between different models, and hence reduce temperature-load transferring errors. This approach makes the simulation of fluid flow, heat transfer and stress analysis unify into one single model.     

高速列车制动盘盘毂锻造工艺数值模拟

基于实测的40CrA钢高温应力-应变曲线和热物性参数,建立了高速列车制动盘盘毂毛坯在模锻过程的有限元模型。运用DEFORM-3D软件,对该盘毂的多步骤锻造过程进行热力耦合模拟,得到了应力、应变和温度随时间的变化规律;研究盘毂成形过程的金属流动机制,模拟了产生折叠缺陷的位置;预测了盘毂完全成形所需的锻锤打击次数;对终锻模具的最大主应力进行分析,预测了模具在实际生产中可能产生的塌陷、开裂缺陷及其位置。根据模拟结果进行了生产试制,验证了工艺的可行性和模拟的准确性。     

钼粉末温压成形过程的数值模拟研究

运用MSC.MARC有限元分析软件,采用热-机耦合方法,对钼粉末温压成形过程进行了有限元数值模拟,获得了粉末体形变、应力场和相对密度分布等相关数据,为改善钼粉温压成形工艺及优化工艺参数提供了理论依据.     

6061铝合金轮毂的力学性能与锻造工艺的计算机模拟

分别采用树枝晶和非树枝晶6061铝合金锻造生产汽车轮毂,并应用CMT5305电子万能实验机对轮毂不同位置取样进行力学性能测试,用三维有限元软件Deform-3D模拟6061铝合金轮毂的锻压过程,分析对比轮毂不同位置的应力应变状态以及与力学性能之间的关系.结果显示,经过电磁搅拌处理的非树枝晶材料生产的轮毂,其力学性能较普通材料整体上有较大改善;轮毂中累积应力应变越大的位置,其力学性能相对应力应变小的位置更佳.     

Application of the finite element method to powdered metal compaction processes of multi-level flanged parts

A plasticity theory applicable to powdered metal compaction is summarized and its discretization for the finite element analysis is briefly described. The compaction processes of axisymmetric flanged components are simulated. For the analysis of compaction of two-level components, the investigations were performed for different compact geometries and various compacting methods. Highlights of the results for a given part geometry with two compaction methods are reported in terms of relative density distributions within the compact and pressure distributions along the dies and punches. The compaction process of three-level flanged components was also analyzed for two compacting methods. General conclusions from these simulation results are: (1) the compaction process is more effective with increased relative motions within the compact; and (2) the effect of various compaction schemes of combination of punch motions is not significant for the pressure distribution on punches and energy consumption in compaction processes. However, the variation of the punch forces in three-level component compaction, due to punch operating schemes, may be an important consideration in the critical design of compaction tooling system.     

Numerical modeling and simulation of metal powder compaction of balancer

1 Introduction “Cold” compaction, which is operated at room temperature, is currently the most generally used compacting method in powder metallurgy industry. Under this circumstance, metal powder is often considered a kind of time-independent, elasto-…     

粉末烧结体镦粗致密与成形的有限元分析

选择典型的镦粗工艺对粉末烧结坯的致密与成形行为和规律进行了研究，提出了多孔材料的致密模型并简要介绍了多孔材料的塑性理论。然后，采用有限元法模拟了不同镦粗压下量的烧结坯的致密与成形过程。密度与等效应变分布的一致性表明，烧结坯的致密强烈依赖于材料的塑性变形。