Simulation Of Powder Compaction Research Articles

Inverse Identification of Drucker–Prager Cap Model for Ti-6Al-4V Powder Compaction Considering the Shear Stress State

Numerical simulation is an important method to investigate powder-compacting processes. The Drucker–Prager cap constitutive model is often utilized in the numerical simulation of powder compaction. The model contains a number of parameters and it requires a series of mechanical experiments to determine the parameters. The inverse identification methods are time-saving alternatives, but most procedures use a flat punch during the powder-compacting process. It does not reflect the densification behavior under a shearing stress state. Here, an inverse identification approach for the Drucker–Prager cap model parameters is developed by using a hemispherical punch for the powder-compacting experiment. The error between the numerical and experimental displacement–load curves was minimized to identify the Drucker–Prager cap model of titanium alloy powder. The identified model was then verified by powder-compacting experiments with the flat punch. The displacement–load curves acquired by numerical simulation were compared to the displacement–load curves obtained through experiments. The two curves are found to be in good agreement. Meanwhile, the relative density distribution of the powders is similar to the experimental results.

On the use of HCP and FCC RVE structures in the simulation of powder compaction

Use of hexagonal close packed and face centered cubic structures to simulate powder compaction reveals that plastic deformation is effective in reducing porosity until a relative density of 0.96, beyond which a drastic rise in pressure is required. The compaction process can be divided into three phases demarcated by relative densities of 0.8 and 0.92, characterized, respectively, by local yielding around the initial contact point, coalescence of locally yielded zones and full plastic flow to reduce pores. The macroscopic yield behaviour of the powder assembly in the present work agrees reasonably with analytical and numerical models such as the Storåkers-Fleck-McMeeking model and multi-particle finite element model. It is found that for rate-dependent powder materials, the compaction process is noticeably rate dependent from a relative density of 0.85. Although a regular packing of powders is unrealistic, the understanding gained from a regular packing model provides insight into the role that plastic deformation plays during powder compaction.

Discrete element simulation of powder compaction in cold uniaxial pressing with low pressure

This paper presents numerical studies of powder compaction in cold uniaxial pressing. The powder compaction in this work is considered as an initial stage of a hot pressing process so it is realized with relatively low pressure (up to 50 MPa). Hence the attention has been focused on the densification mechanisms at this range of pressure and models suitable for these conditions. The discrete element method employing spherical particles has been used in the numerical studies. Numerical simulations have been performed for two different contact models—the elastic Hertz–Mindlin–Deresiewicz model and the plastic Storakers model. Numerical results have been compared with the results of laboratory tests of the die compaction of the NiAl powder. Comparisons have shown that the discrete element method is capable to represent properly the densification mechanisms by the particle rearrangement and particle deformation.

316L Metal Powder Compaction Simulation with Assisted Friction

Friction plays a major role in powder compaction and there is a large energy loss in trying to overcome its negative effects. It is therefore rational to use the friction to assist metal flows and reducing the amount of lubricant and its negative effects. The appropriate use of friction in practice involves the solving of complex engineering problems. The paper approach will mainly focus upon issues concerning the conversion of the friction force and simulation in PM compaction processes and improving density gradient in the powder compaction process of AISI 316L austenitic powder.

Determination of the constants of cap model for compaction of three metal powders

Cap model is a well-known model for defining the yield surface of porous materials. In this work, the constants of the model are determined by a combined experimental/numerical/optimization technique for aluminum 7075, iron and copper powder. The compaction of powder is conducted using Instron testing machine. The numerical simulation of powder compaction is performed using the Ls-Dyna hydrocode. Optimization is carried out using genetic algorithm. The objective function is defined as the difference between the experimental and numerical load–displacement curves of the compaction. The constants of the model correspond to the case when this difference is optimized. A second order Maclaurin polynomial is assumed for the objective function. The results indicate that the cap model can reasonably predict the powder compaction of iron and aluminum. The model however, proves not to be accurate for copper powder. The results also show dependency of the model’s constants on strain rate.

A constitutive formulation and numerical procedure to model rate effects on porous materials at finite strains

A constitutive formulation for viscoplastic porous materials subjected to finite deformations is developed. To account for porosity effects on the viscous response it is proposed an apparent viscosity, that is, it is assumed that the viscosity depends on the relative density evolution. Using an associative Perzyna-type formulation the constitutive equations as well as the density-corrected consistent tangent modulus are obtained from a suitable extension of the elastoplastic porous model. The proposed constitutive formulation is implemented inside the Finite Element Method context and it is numerically assessed by the analysis of some classical examples, as the isostatic compression, simple shear, and die pressing testing. In addition, a more complex simulation is presented. It is shown that in a relaxation test the viscoplastic porous material recovers the rate-independent response as an asymptotic limit only when some conditions are satisfied. Numerical results show that the proposed constitutive formulation is able to capture the rate effects when porous materials are subjected to high deformation speeds. This type of constitutive formulation is convenient for high-velocity metal powder compaction simulation, where rate effects play an important role on the material response and final properties.

Genetic algorithm-based numerical optimization of powder compaction process with temperature-dependent cap plasticity model

In this paper, a shape optimization technique is presented for the cold and hot isostatic pressing of metal powders based on the genetic algorithm (GA) approach. The GA technique is used to obtain the desired optimal compacted component by changing the boundaries of component and verifying the prescribed constraints. The coupled thermomechanical analysis of hot isostatic pressing is employed for metal powders during densification process. The numerical modeling of hot powder compaction simulation is performed based on the large deformation formulation, temperature-dependent cap plasticity model, and frictional contact algorithm. The modified cap plasticity takes the temperature effects into the numerical simulation of highly nonlinear behavior of metal powder. Finally, numerical examples are analyzed to demonstrate the feasibility of proposed optimization algorithm for designing powder components in the cold- and hot-forming processes of powder compaction.

Modeling of hot isostatic pressing of metal powder with temperature–dependent cap plasticity model

In this paper, the coupled thermo–mechanical simulation of hot isostatic pressing (HIPing) is presented for metal powders during densification process. The densification of powder is assumed to occur due to plastic hardening of metal particles. The constitutive model developed is used to describe the nonlinear behavior of metal powder. The numerical modeling of hot powder compaction simulation is performed based on the large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for the large powder deformations. A modified cap plasticity model considering temperature effects is used in numerical simulation of nonlinear powder behavior. The influence of powder-tool friction is simulated by the use of penalty approach in which a plasticity theory of friction is incorporated to model sliding resistance at the powder-tool interface. Finally, numerical examples are analyzed to demonstrate the feasibility of the proposed thermo–mechanical simulation using the modified cap plasticity model in the hot isostatic forming process of powder compaction.

Optimal design of powder compaction processes via genetic algorithm technique

In this paper, an optimal design is performed for powder die-pressing process based on the genetic algorithm approach. It includes the shape optimization of powder component, the optimal design of punch movements, and the friction optimization of powder–tool interface. The genetic algorithm is employed to perform an optimal design based on a fixed-length vector of design variables. The technique is used to obtain the desired optimal compacted component by verifying the prescribed constraints. The numerical modeling of powder compaction simulation is applied based on a large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for large powder deformations. A cap plasticity model is used in numerical simulation of nonlinear powder behavior. The influence of powder–tool friction is simulated by a plasticity theory of friction to model sliding resistance at the powder–tool interface. Finally, numerical examples are analyzed to demonstrate the feasibility of the proposed optimization algorithm for designing powder components in the forming process of powder compaction.

The genetic algorithm approach for shape optimization of powder compaction processes considering contact friction and cap plasticity models

PurposeThe purpose of this paper is to present a shape optimization technique for powder forming processes based on the genetic algorithm approach. The genetic algorithm is employed to optimize the geometry of component based on a fixed‐length vector of design variables representing the changes in nodal coordinates. The technique is used to obtain the desired optimal compacted component by changing the boundaries of component and verifying the prescribed constraints.Design/methodology/approachThe numerical modeling of powder compaction simulation is applied based on a large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for large powder deformations. A cap plasticity model is used in numerical simulation of nonlinear powder behavior. The influence of powder‐tool friction is simulated by the use of penalty approach in which a plasticity theory of friction is incorporated to model sliding resistance at the powder‐tool interface.FindingsFinally, numerical examples are analyzed to demonstrate the feasibility of the proposed optimization algorithm for designing powder components in the forming process of powder compaction.Originality/valueA shape optimization technique is presented for powder forming processes based on the genetic algorithm approach.

Finite Element Simulation of Powder Compaction with Rubber Punch and Sintering of Tiles Having Two Layers

A compaction process of tiles consisting of two layers of powders with a rubber punch was discussed. The densification behaviors during compaction and sintering were simulated by the viscoplastic finite element method. In this method, both rubber punch and powder during the compaction were modeled as rigid porous materials. Using the rubber punch, the density distribution in the compact became more uniform, and thus the occurrence of fracture during the sintering could be prevented. The compaction process with a rubber punch is applicable to practical operations because of its easy applicability.

Numerical simulation of powder compaction for two multilevel ferrous parts, including powder characterisation and experimental validation

The paper presents a summary of two case studies that were carried out by the scientific team in the Thematic Network PM Modnet. During the life of this project, the compaction of complex multilevel ferrous components was investigated. These formed a vehicle to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results. Density comparisons were made with results from Archimedes, quantitative metallography, and computerised tomography and force levels were compared with recordings from the pressing trials. The results highlight differences between equipment and experimental techniques used in characterising powders. They also show that hardness, metallographic analysis, and computerised tomography may be used to measure density variations throughout the compact. The prediction of density variation was reasonably consistent when using different simulations, whereas punch force prediction showed good consistency. It was found that predicted and measured density distributions agree within 0·05 to 0·5 g cm-3 and that punch force levels may be predicted within 10 to 30%. The study effectively establishes a benchmark with which to compare and improve future simulations.

Modelling and numerical simulation of powder compaction

Recent progress in modelling and numerical simulation of powder compaction is reviewed, drawing on work presented in the Dienet Workshop and modelling sessions of Euro PM2001.

Model Simulation of Powder Compaction by Complex Mold Based on Deformation Behavior of Free Particles Measured by Compression Test

ABSTRACTDiscrete element method (DEM) is one of the excellent procedures for model simulation of behavior of granular assemblies. A two-dimensional DEM simulation of powder compaction by a complex mold was conducted by considering the deformation behavior of individual particles measured by a compression test of free particles. Spherical copper particles were used as a model material in this study. The particles (particle size ranges from 38 to 125microns) were individually compressed between parallel platens to measure compressive load and displacement in the loading direction. From the measured load and displacement data, force-displacement relations at contacts between the particles, and between the particles and mold wall were determined. In the simulation, the two-dimensional complex mold consisting of three stages (upper stage:3-mm wide and 1-mm deep, middle stage:2-mm wide and 1-mm deep, lower stage:1-mm wide and 1-mm deep) was charged with the copper powder consisting of spherical particles with size range of 50 to 200microns and was pressed under four press conditions. Forces at all contacts were calculated by using the determined force-displacement relations and each particle's position was traced by solving equations of motion for each particle. Pressure at each wall of the mold and density distribution in the powder compact were calculated as results of the simulation. It was found that the increase in the pressure at each wall corresponds to the increase in the density of the powder near the wall.

Modeling of the metal powder compaction process using the cap model. Part I. Experimental material characterization and validation

Abstract In order to produce crack free metal powder compacts that respect both the dimensional tolerances and the mechanical strength requirements, both tooling design and compaction sequence have to be adequately determined. The finite element method, through the use of an appropriate constitutive model of the powder medium, has recently been used as an efficient design tool. The accuracy of this method highly depends on the faithfulness of the constitutive model and the quality of the material parameter set. Furthermore, in order for the simulation results to be reliable, they should be experimentally validated on real parts featuring density variations. Hence, the main concerns of this paper are the development of a standard calibration procedure for the cap material model as well as the development of a reliable technique for the experimental validation of the powder compaction simulation results. The developed calibration procedure, applied for the case of 316L stainless steel powders, is based on a series of isostatic, triaxial and uniaxial compaction tests as well as resonant frequency tests. In addition, a sensitivity study was performed in order to determine the relative importance of each factor and basic simulations served to validate the parameter set extraction procedure. On the other hand, a local density measurement technique was developed for the experimental validation of the model results. This technique is based on correlation with Vickers macro-hardness. Finally, an application featuring the compaction of a 316L stainless steel cylindrical component is presented to illustrate the predictive capabilities of the cap material model as well as the accuracy of the acquired material parameter set.

1622 多段形状圧粉体の金型成形プロセスのシミュレーション

Simulation of powder compaction in closed die is carried out by the elastic-plastic FEM. The study is focused to investigate the effect of toll kinematics in die-compaction on density variation in a multi-stepped part. Based on the simulation results, it is shown that there is an appropriate tool kinematics that provides a small variation in density in the obtained compact. It is also shown by the simulation that a slip crack-like defect can occur depending on the tool kinematics.

Simulation of the particle misalignment of hard magnets after compaction

The simulation of powder compaction for Nd–Fe–B, Sm–Co, and barium ferrite shows the influence of different static field strengths and different mold filling on particle misalignment. The final magnetization differs up to 20%. The processing determines the pressure activated processes in which the particle overcomes a volume barrier, characterized by elastic energy fluctuations. Isostatic compaction shows less pressure activated processes as compared to uniaxial mold pressing. However, an improved magnetization of about 10% owing to isostatic pressing was observed only for spherical particles. The pressure activated processes determine particle density defects such as cracks and pores, misalignment of c axes at the punch side, at corners and at particle density defects, and internal stress areas with cold plastic flow.

Computer simulation of powder compaction of spherical particles

The authors have developed an algorithm for simulating the isostatic compaction of powders with dispersed spherical particles. This algorithm can be classified to the collective relocation model, and can be used for powders of rigid spherical particles of any given size distributions.

Predictive capabilities of cap material model for powder compaction simulation : H.Chtourou et al. (Laval University, Canada.)

Predictive capabilities of cap material model for powder compaction simulation : H.Chtourou et al. (Laval University, Canada.)

常圧及び加圧焼結のメカニズムとニヤネットシェイプ制御 粉体成形・粉末治金のプロセス解析のための粉粒体モデル開発とその応用

The granular modeling has been developed not only to make direct simulation of powder compaction and forming for parts and members but also to consider the coupling between magnetic fields and powder flow for hard copy and powder compaction in the magnetic field. Through those successful analyses, our developed granular modeling is found to be an effective tool to describe powder flow and compaction behavior in actual powder forming. One of the most preferable features to this modeling should be its rational extention to fine-grained particle modeling through our developing averaging; this mesoscopic modeling on the basis of the granular modeling can be expected to be available to micro-rheological analysis of aggregated fine particles, various compounds and suspensions.