数值模拟在粉末冶金中的应用概况

简介数值模拟应用在粉末冶金中的一些基本模型和方法以及近来在粉末压制、注射成形、热等静压成形等领域的研究应用情况     

Effect of friction between powder and a mandrel on densification of iron powder during cold isostatic pressing

The effects of friction between the powder and the mandrel on densification behavior of metal powder were investigated under cold isostatic pressing. The friction coefficients between the powder and the mandrels with different surface roughness were determined from the relationship between the compaction pressure and the ejection pressure of the mandrel from powder compacts. The elastoplastic constitutive equations based on the yield function of Shima and Oyane were implemented into a finite element program (ABAQUS) to simulate compaction responses of metal powders during cold isostatic pressing. Finite element results were compared with experimental data for pure iron powder under cold isostatic pressing.     

Model for compaction of metal powders

A new yield criterion for metal powder compaction based on continuum mechanics has been proposed. It includes three parameters to characterize the geometric hardening of powder compact and strain hardening of incompressible metal matrix. The elasto-plastic finite element method to describe compaction of metal powders has been formulated using the new yield criterion. The values of parameters in the yield criterion could be determined through cold isostatic pressing (CIP). The finite-element method was used to simulate compaction behaviour of copper powders of different shape and mean particle size.     

Numerical simulation and experimental investigation on densification,shape deformation,and stress distribution of Ti6Al4V compacts during hot isostatic pressing

Hot isostatic pressing of metal powders involves a complex thermal and mechanical coupling process. A constitutive model based on Perzyna’s elastic-viscoplasticity equation was proposed, and a Lagrangian finite element method was applied to analyze the large deformation, nonlinear friction, powder flow, and densification behavior during hot isostatic pressing. The mechanical behavior of the powders was analyzed in terms of stress distribution. For comparison to the simulation results, the density, shape deformation, and residual stress of the specimens were evaluated using Archimedes’ principle, 3D measuring technology, and Empyrean X-ray diffractometer.     

Densification of mixed metal powder at high temperature

Densification behaviors of mixed metal powder under high temperature were investigated. Experimental data of mixed copper and tool steel powder with various volume fractions of Cu powder were obtained under hot isostatic pressing and hot pressing. By mixing the creep potentials of McMeeking and co-workers and of Abouaf and co-workers originally for pure powder, the mixed creep potentials with various volume fractions of Cu powder were employed in the constitutive models. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data for densification of mixed powder under hot isostatic pressing and hot pressing. Finite element calculations by using the creep potentials of Abouaf and co-workers agreed reasonably well with experimental data, however, those by the model of McMeeking and co-workers underestimate experimental data as observed in the case of pure metal powders.     

Modeling the powder compaction process using the finite element method and inverse optimization

This paper focuses on studying and adapting modeling techniques using the finite element method to simulate the rigid die compaction of metal powders. First, it presents the implementation of the cap constitutive model into ABAQUS FE software using the closest point projection algorithm. Then, an inverse modeling procedure was proposed to alleviate the problems raised by the interpretation of the experimental tests and to more accurately determine the material parameters. The objective function is formed, based on the discrepancy in density data between the numerical model prediction and the experiment. Minimization of the objective function with respect to the material parameters was performed using an in-house optimization software shell built on a modified Levenberg?CMarquardt method. Thus, an integrated simulation module consisting of an inverse optimization method and a finite element method was developed for modeling the powder compaction process as a whole. The simulation and identification module developed was applied to simulate the compaction of some industrial parts. The results reveal that the maximum absolute error between densities is 2.3%. It corresponds to the precision of the experimental method.     

Wear resistance of in situ MMC produced by supersolidus liquid phase sintering (SLPS)

The resistance to abrasive wear can be effectively raised by hard particles embedded in a metal matrix. Powder metallurgy allows to admix larger particles than those precipitated from the matrix. To save costs ferrotitanium (FeTi) particles are admixed to a tool steel powder and are transformed in situ into titanium carbonitrides during compaction by supersolidus liquid phase sintering (SLPS) instead of hot isostatic pressing. Pin-on-abrasive paper-tests as well as scratch tests reveal an increase in wear resistance of in situ SLPS–metal-matrix-composites (MMC) over hot isostatic pressing (HIP)–MMC, which is linked to the large size of precipitated hard particles in the former. The application of these laboratory results is seen in reinforcing inserts of wear parts.     

A single cone-cap plasticity with an isotropic hardening rule for powder materials

In this paper, a new single cone-cap plasticity with an isotropic hardening rule is presented for powder materials. A general form is developed for the cap plasticity, which can be compared with some common double-surface plasticity models proposed for powders in literature. The constitutive elasto-plastic matrix and its components are derived based on the definition of yield surface, hardening parameter and nonlinear elastic behavior, as a function of relative density of powder. Different aspects of the model are illustrated and the procedure for determination of powder parameters is described. Finally, the applicability of the proposed model is demonstrated in numerical simulation of triaxial and confining pressure tests.     

Experimental based finite element simulation of cold isostatic pressing of metal powders

The present work addresses the various ingredients required for reliable finite element simulations of cold isostatic pressing (CIP) of metal powders. A plastic constitutive model for finite deformation is presented and implemented into an explicit finite element (FE) code. The FE implementation is verified so that numerical errors (both temporal and spatial errors) are kept under control. Thereafter, uniaxial die compaction experiments are performed required for determining the material parameters in the constitutive model. Subsequently they are applied for the simulation of a “complex” CIP process. The experimental observations of the complex CIP process were used to validate the overall method by comparing the FE results (final dimensions and average relative density) to the experimental observations. The numerical results (final dimensions and relative density) are in good agreement with the experimental observations.     

Creep densification of copper powder compact

Densification of metal powder under high temperature processing was investigated. Experimental data were obtained for copper powder under hot isostatic pressing, hot pressing and uniaxial creep compression. Theoretical calculations from the constitutive models by McMeeking and co-workers were compared with the experimental data. The agreements between experimental data and theoretical calculations are reasonably good when hydrostatic stress is dominant, but not as good when deviatoric stress increases.     

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing was investigated. Hot isostatic pressing was carried out for a bundle of copper-coated tungsten fibers in copper powder. Due to tungsten-fibers and copper coating layers, the densification rate of a tungsten-fiber-reinforced copper powder compact was slower than that of pure copper powder. The constitutive equations by McMeeking and co-workers and by Abouaf and co-workers were implemented into a finite element program (ABAQUS) to analyze densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing. Finite element calculations were compared with experimental results for the variation of relative density with time for copper powder compacts during hot isostatic pressing. Density distributions in copper powder compacts were also investigated by comparing experimental results with finite element calculations.     

Near-net-shape forming of alumina powder under hot pressing and hot isostatic pressing

Densification and deformation of alumina powder under hot pressing and hot isostatic pressing were investigated. Finite element calculations were performed by implementing constitutive equations for grain growth, power law creep and diffusional creep in the user defined subroutine CREEP of ABAQUS. An alumina compact of valve head shape was produced under hot pressing and its forming process was predicted by the finite element calculation. Densification behavior of an alumina powder compact encapsulated by a stainless steel container was also investigated under hot isostatic pressing. Inhomogeneous deformations of an alumina powder compact due to the shield effect of a container during hot isostatic pressing were observed experimentally and predicted by the finite element analysis.     

冲压件成形计算机模拟工艺参数优化方法研究

分析了常规有限元金属板料成形模拟的不足，提出了参数化有限元分析的概念，在对人工神经网络、遗传算法进行深入分析研究的基础上，采用参数化有限元分析方法进行分析，得到了训练样本。提出了采用人工神经网络技术建立冲压件成形多参数映射关系模型，采用遗传算法进行多参数组合优化，实现冲压件成形计算机模拟工艺参数优化的方法。实际应用结果表明，优化结果与试验结果基本吻合，该优化方案实用可行。     

Densification behavior of aluminum alloy powder under cold compaction

Densification behavior of aluminum alloy (Al6061) powder was investigated under cold compaction. Experimental data were obtained under triaxial compression with various loading conditions. A special form of the Cap model was proposed from experimental data of Al6061 powder under triaxial compression. The proposed yield function and several other yield functions in the literature were implemented into a finite element program (ABAQUS) to compare with experimental data for densification behavior of Al6061 powder under cold isostatic pressing and die compaction. The agreement between finite element calculations from the proposed yield function and experimental data is very good under cold isostatic pressing and die compaction.     

采用GPS+HIP生产工艺制造Al2O3基陶瓷刀片

介绍了采用GPS +HIP生产工艺制造Al2 O3 基陶瓷刀片所涉及的混料、压制、排胶、气氛保护烧结(GPS)、热等静压 (HIP)处理、刀片刃磨等主要生产工序     

Synthesis of silicon carbide ceramics from a polysilastyrene at low temperatures

The conventional route for preparation of silicon carbide ceramics is by the use of pressureless sintering, hot pressing, or hot isostatic pressing of silicon carbide starting powders. High sintering temperatures (2073–2473 K) and the addition of sintering additives are normally used to enhance densification. These sintering additives, however, form second phases at grain boundaries which impair the mechanical properties of the material, particularly at high temperatures. It is therefore desirable that new processing routes are developed that overcome these difficulties. A proposed route is to use a polymeric pressure which can provide a Silicon carbide matrix as binding agent for silicon carbide powders, thus making the requirement for high temperatures and sintering additives unnecessary. This paper reports observations of the direct transformation of a polymeric precursor into amorphous Si–C, and crystalline SiC at low temperatures, and the use of this precursor as a binder for the production of SiC powder/ex-precursor SiC composites.     

基于粉末本构模型和多体力学仿真的模架集成式粉末成形设备的设计

研制出一种新型的低成本、小体积、高精度的专用模架集成式粉末成形设备。以MSC.Marc与MSC.Adams软件相结合提出基于数值模拟的1 MN压机设计方法,即根据粉末压制试验构建末材料流动应力本构模型;通过该模型在MSC.Marc软件数值计算出所设计压机压制过程的模冲载荷;在分析模架集成式粉末成形设备各个模板在压制工过程运动特点的基础上,建立多体运动学数学方程;将所得模冲载荷作为边界条件加载到对模架集成式粉末成形设备在压制过程的模拟仿真;并在MSC.Adams软件中分析各个模板在压制过程中力学状态,从中分析该设备在实际工况下的可靠性。研制出电液比例阀和光栅尺相结合的控制系统,实现对缸同时驱动,解决不同模板之间的动作协调的问题,所研制试验样机实现零件轴向压制精度为±0.02 mm。实际压制过程所得各模冲载荷与模拟结果相一致,从而验证粉末成形设备设计所采用的本构模型是准确的,基于数值模拟进行粉末成形设备设计的方法的正确性。     

The analysis of shape change during isostatic pressing

To improve the design of optimum consolidation cycles for powder processing, it is important to be able to predict the final shape of the product. When components are solidified from metal powders by isostatic pressing, substantial shape changes can occur due to the constraint of the can. This effect can be modelled in terms of a new constitutive law for the plastic yielding of powder aggregates. It is found that in the early stages of consolidation, the shape is controlled by the container and the powder has no influence. The container deforms into shapes it would achieve if it were empty. This suggests that the initial design of a container can be carried out with an empty can under external pressure.     

Densification behaviour of ceramic powder

A three-dimensional compaction device has been developed to carry out compaction of a ceramic powder. The details of the device, which provides compaction with various stress ratios, are described. A densification criterion for the powder is proposed; this is similar to that for the case for metal powders, but the role of the hydrostatic stress component appears to be different. Stress-strain rate relations are then derived using the concept of plastic potential; experimental results show that the normality of the strain rate vector to the surface which corresponds to the criterion almost holds.     

A densification model for mixed metal powder under cold compaction

Densification behavior of mixed copper and tool steel powder under cold compaction was investigated. By mixing the yield functions proposed by Fleck et al. and by Gurson for pure powder in terms of volume fractions of Cu powder and the fraction of contact, a new mixed yield function was employed for densification of powder composites under cold compaction. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data and with results from the model of Kim et al. for densification of mixed powder under cold isostatic pressing and die compaction. Finite element calculations by using the yield functions mixed by the fraction of contact agreed better than those by volume fractions of Cu powder with experimental data.