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.     

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-…     

Numerical simulation in powder compaction of metallurgy component

1Introduction Forming multi-level component in die compaction,the density is more or less inhomogeneous depending onthe part geometry,the tool design and the frictionbetween powder and die wall[1?3].The productdistortions are result of inhomogeneous densi…     

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     

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.     

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

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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。     

Coupled mechanical and thermal simulation of warm compaction

1 Introduction Powder metallurgy is an advanced manufactural technology widely used for volume-producing mechanical parts with high performance and high precision[1?3]. Warm compaction is a low cost and effective technique to produce green compact with de…     

置氢TC21合金粉末压制方程研究

为建立置氢TC21钛合金粉末的压制性能评价体系,和置氢TC21合金粉末室温模压成形过程压制方程,测定了置氢TC21合金粉末外加压力、压坯密度及压坯强度与合金粉末置氢量的关系,将试验数据代入推导的置氢TC21钛合金粉末的压制方程之中,采用VB求解超限定方程组,计算出方程中所含的3个参数的值,并最终定量研究了这3个参数与置氢量的关系,确定了占主导地位的成形机制,最终得到了置氢TC21合金粉末压制性能及压制方程,从而为精确控制置氢钛合金粉末模压成形提供了依据。     

Numerical simulation and experimental validation of powder flux distribution in coaxial laser cladding

In this research work a numerical model which simulates the powder flux distribution on a coaxial nozzle is presented. CFD fluent code was used to solve the model equations. The geometry of the domain was obtained using a reverse engineering process of a coaxial nozzle. The model required a deep study of the powder size distribution and feed rate because of their importance as input parameters. The simulation for the discrete phase model was carried out using both, the turbulence k–? model and the Euler–Lagrange approximation. During the model validation a technique based on the selective weight measuring on planes perpendicular to the nozzle axis was used. The powder flux model validation results showed coherence between the estimated and measured particle flux values, particularly when the powder stream presents a Gaussian profile. A simple geometrical model was presented as an application example of the flux distribution model to estimate the clad height.     

热成形TA32钛合金薄壁件的形状控制与性能优化

为了优化TA32钛合金薄壁件的热成形工艺,对其热流动行为、显微组织演变和断口形貌进行研究.根据实验数据建立一套基于合金显微组织的本构方程,描述高温流动应力与相体积分数、位错密度、晶粒尺寸和损伤演化之间的关系.将本构模型嵌入ABAQUS 6.14中模拟典型薄壁件的热成形过程,预测不同工艺参数下成形件的等效应变、位错密度、...     

爆炸压涂钨铜覆层到铜表面的研究

采用爆炸烧结将钨铜合金覆层烧结到纯铜表面的方法,即将钨铜合金粉末预压到铜板的表面后,进行通氢烧结,然后通过爆炸压实将混合粉末进一步压实在铜板表面,最后扩散烧结成为钨铜复合材料。先采用AUTODYN软件模拟了爆炸压实过程中粉末与铜板中的压力分布,确定了一套可以使覆层粉末中压力分布均匀,有利于钨铜合金粉末均匀致密化的参数。而后进行爆炸压实试验,制出的试样覆层密度达到了理论密度的99.3%。对爆炸后的试件进行电子探针检测,检测结果表明钨铜粉混合均匀,钨颗粒的尺寸比铜颗粒要大的多。断口分析结果显示,钨铜覆层的断口形貌不同于传统的断口形貌。钨铜结合面的形貌分析表明,钨铜合金密实的烧结在了铜基体的表面。     

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.     

Effects of foaming parameters on microstructure and compressive properties of aluminum foams produced by powder metallurgy method

Semi open-cell aluminum foams having channels between individual cells were produced using low cost CaCO₃ foaming agent and applying the powder compact melting process. To this end, the aluminum and CaCO₃ powder mixtures were cold compacted into dense cylindrical precursors for foaming at specific temperatures under air atmosphere. The effects of several parameters including precursor compaction pressure, foaming agent content as well as temperature and time of the foaming process on the cell microstructure, linear expansion, relative density and compressive properties were investigated. A uniform distribution of cells with sizes less than 100 μm, which form semi open-cell structures with relative densities in the range of 55.4%–84.4%, was obtained. The elevation of compaction pressure between 127–318 MPa and blowing agent up to 15% (mass fraction) led to an increase in the linear expansion, compressive strength and densification strain. By varying the foaming temperature from 800 to 1000 °C, all of the investigated parameters increased except compressive strength and relative density. The results indicated the optimal foaming temperature and time as 900 °C and 10–25 min, respectively.     

应用本构模型和神经网络模型预测铝/镁基纳米复合材料的高温流变行为(英文)

为了预测Al/Mg基纳米复合材料的高温流变行为,在不同的应变速率(0.01-1.0s-)和温度(523,623和1723K)的条件下进行热压缩试验,利用所得到的应力-应变数据,开发了本构模型,比如一般流动方程。阿累尼乌斯双曲模型、Johnson-Cook(JC)和改性的Zerilli-Armstrong(ZA)模型及人工神经网络(ANN)模型。通过使用统计参数,例如均方根误差(RMSE)、回归系数(R2)、平均相对误差(MRE)和分散指数(Is),比较了人工神经网络和不同的本构模型。结果表明,人工神经网络模型对AA5083-2%TiC复合材料的热变形流动应力的评估准确性更高。     

W-Cu复合药型罩EFP的形成及其聚能破甲效应研究

在爆炸压实技术中,粉体中激波和稀疏波的强度及作用时间直接影响压实体的质量。为探究爆炸压实中不同因素对粉体中压力变化的影响,基于AUTODYN有限元程序,建立了爆炸压实W-Cu粉末的有限元模型,通过流固耦合算法实现炸药、盛粉管和W-Cu粉末的相互作用。建立与现有试验对应的有限元模型,模拟结果和试验结果具有较好的吻合性,验证了模型和材料参数的可靠性。通过对爆炸压实过程的数值模拟,分析了装药厚度和盛粉管厚度对爆炸压实压力的影响。结果表明,装药厚度越厚,激波压力的作用时间越长,对粉末的压实越有利;随着装药厚度的增加,作用时间的增长减缓。盛粉管厚度越厚,粉体中稀疏波的强度越低,对压实体的影响越小;但随着管厚增加,粉体中心压力将会降低,粉末的压实质量下降;故选择盛粉管厚度时,需综合考量粉体中心压力和稀疏波强度对爆炸压实体的影响。

     

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.     

Hybrid forming processes for production of lightweight high strength automotive panel parts

Abstract

The research concentrates on a heat treatable AA 6082 aluminium alloy. A set of unified constitutive equations has been developed and determined from experimental data. In addition to modelling viscoplastic flow of the material at different temperatures, the equations contain other two specific features. One is to predict the failure of the material under various deformation conditions based on continuum damage mechanics theories. The other is to model the precipitation formation and growth under straining and aging conditions; thus, the strength distribution of formed parts can be predicted via process modelling. The determined unified constitutive equations are then implemented into the commercial finite element code ABAQUS/Explicit via the user defined subroutine, VUMAT. A finite element process simulation model and numerical procedures are established for the modelling of a hot stamping and cold die quenching processes for a spherical part with a central hole. To validate the simulation results, a test programme is developed, a test rig has been designed and manufactured and tests have been carried out under different forming rates. It has been found that very close agreements between experimental and numerical process simulation results are obtained for the range of forming rates carried out.     

Explosive compaction of tungsten powder using a converging underwater shock wave

Tungsten and tungsten-based alloys have wide applications in industries. Powder metallurgy is one of the major processes for production of tungsten parts, but tungsten parts with high density cannot be produced by this method. Two explosive compaction processes using converging underwater and no-water shock wave, were applied to compact tungsten powder in the present investigation. C4 as an explosive material with a detonation velocity of 8.2 km/s applied to consolidate amorphous powder with a mean grain size of 5 μm. The density and hardness of consolidated tungsten parts were determined and by scanning electron microscope (SEM) analyzed their fragment surfaces. In addition to explosion experiments, a numerical simulation of compaction processes conducted by use of LS-DYNA program. Finally, the experimental results of two processes and numerical simulation results of the same processes compared. The results indicated that the tungsten parts without cracks and with a hardness equal to 570 Vickers and a density equal to 18.5 g/cm³ can be obtained by underwater shock wave compaction method.     

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.