• Journal of Powder Materials
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• v.11 no.4
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• pp.301-307
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• 2004

Successful implementation of the powder forming process requires a detailed understanding of several interacting phenomena. The aim is to better control the process variables and to optimize the design parameters. A number of studies were carried out using various constitutive models that take the density change during powder forming into account. Most of them were developed for powders and sintered porous metals, but few of them can describe powder agglomerates, whose behaviour is different from that of uniformly arranged powders. The modification is needed to account for the effect of agglomeration on densification behaviour. Incorporating powder agglomeration into a constitutive model is of considerable importance, as it provides a possibility of relating the powder densification response to microstructural characteristics of powder particles, especially in case of nano powders. In this paper, we proposed a new powder agglomerate model in order to describe the unique densification behaviour of nano powders. The proposed model was applied to the densification of powder agglomerates during cold isostatic pressing.

• Journal of the Korean Ceramic Society
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• v.29 no.2
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• pp.136-142
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• 1992

The effects of cyclic stress, frequency and bias-pressure on densification of Al2O3 powder cyclic compaction are investigated. The effect of frequency was not significant on densification of Al2O3 powder under cyclic compaction. The higher the cyclic stress and the lower the bias pressure, the higher densification was achieved. To obtain a higher densification, cyclic compaction was more efficient than 1 stroke compaction. A densification equation was proposed to describe an cyclic time dependent pressure-volume relation for Al2O3 powder under cyclic compaction. This equation was obtained empirically, based on the pressure-volume equation proposed by Cooper and Eaton, the time dependent densification equation by Kim and Suh and experimental data for Al2O3 powder under cyclic compaction. The agreement between the proposed equation and experimental data for Al2O3 powder under cyclic compaction was very good.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2749-2761
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing. Finite element results by using the proposed model also well predicted experimental data in the literature for densification behavior of nanocrystalline zirconia powder during pressureless sintering and sinter forging.

• Journal of Powder Materials
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• v.16 no.1
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• pp.50-55
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• 2009

Numerical simulations of the powder extrusion need an appropriate pressure-dependent constitutive model for densification modeling of the magnesium powders. The present research investigated the effect of representative powder yield function of the critical relative density model. We could obtain reasonable physical properties of pure magnesium powders using cold isostatic pressing. The proposed densification model was implemented into the finite element code. The finite element analysis was applied to simulation of powder extrusion of pure magnesium powder in order to investigate the densification and processing load at room temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.333-339
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• 2008

Densification behavior of copper powder was investigated to study the effect of an aluminum mold under warm pressing. The low flow stress of an aluminum mold is appropriate to apply hydrostatic stress to powder compacts during compaction under high temperature. The suggested powder metallurgy process is very useful under high temperature since copper powder compacts have higher relative density over axial stress of 100 MPa and show more homogeneity as compared with conventional warm pressing. Elastoplastic constitutive equation proposed by Shima and Oyane was implemented into a finite element program (ABAQUS) for densification behavior under warn pressing by using a metal mold. Finite element results agreed well with experimental data for densification and deformation of copper powder compacts in the mold.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.282-283
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• 2006

Densification behavior of nano-agglomerate powder during pressureless sintering of Fe-Ni nanopowder was investigated in terms of diffusion kinetics and microstructural development. To understand the role of agglomerate boundary for sintering process, densification kinetics of Fe-Ni nano-agglomerate powder with different agglomerate size was investigated. It was found that activation energy for densification was lower in the small-sized agglomerate powder. The increase in the volume fraction of inter-agglomerate boundary acting as high diffusion path might be responsible for the enhanced diffusion process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.112-118
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• 2000

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 and contact numbers of Cu powder new mixed yield functions were 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 for densificatiojn of mixed powder under cold isostatic pressing and cold die compaction. finite element calculations by using the yield functions mixed by contact numbers of Cu powder agreed better with experimental data than those by volume fractions of Cu powder.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.930-939
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• 2004

Constitutive models for final stage densification of metal powder compacts with power-law creep deformation were investigated. The constitutive models were implemented into a finite element program (ABAQUS) by using user subroutine CREEP and, from FEM results, useful densification curves were obtained when hydrostatic and uniaxial stress were applied to the powder compacts at various pressures and temperatures. Because the densification behavior varied as the constitutive models, the equivalent stress surface on each constitutive equation was investigated to analyze the difference of densification behavior.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.393-398
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• 2000

Densification behavior of mixed copper and tool steel powder under cold compaction was investigated. By mixing the yield functions originally proposed by Fleck-Gurson for pure powder, a new mixed yield functions In terms of volume fractions and contact numbers 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. and with calculated results from the model of Kim et at. for densification of mixed powder under cold isostatic pressing and cold die compaction. Finite element calculations by using the yield functions mixed by contact numbers of Cu powder agreed better with experimental data than those by volume fractions of Cu powder.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.5
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• pp.379-386
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• 2008

Densification behavior of dissimilar material powder (copper and pure iron powder) under die compaction was investigated. Experimental data were obtained for copper and pure iron powder compacts with various volume ratios under die compaction. Dissimilar material powder was simultaneously compacted into a jointed cylindrical compact with different powder materials in inner and outer part, respectively. To simulate densification behavior of dissimilar material powder, elastoplastic constitutive equation proposed by Shima and Oyane was implemented into a finite element program (ABAQUS) under die compaction. Finite element results were compared with experimental data for densification, deformed geometry and density distribution of powder compacts under die compaction.