• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.853-854
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• 2006

Warm compaction powder metallurgy was used to produce a $Ti_3SiC_2$ particulate reinforced Cu matrix composite. Fabrication parameters and warm compaction behaviors of Cu powder were studied. Based on the optimized fabrication parameters a Cu-based electrical contact material was prepared. Results showed that in expend of some electrical conductivity, addition of $Ti_3SiC_2$ particulate increased the hardness, wear resistivity and anti-friction ability of the sintered Cu-base material.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.851-852
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• 2006

The introduction of ceramic particulate into metallic powder will unavoidably lower the compressibility and formability of the mixed powder. In this study, warm compaction, which is a simple and low cost technique to produce high density PM parts, was introduced in preparing composite. The aim of this paper is to prepare the warm compacted NbC particulate reinforced Fe-based composite, then study its tribological behavior and application in the valve-guide cup. A 15 wt.% NbC reinforced iron-based composite was prepared. It possesses a relative density of 98%, a tensile strength of 515 MPa, a hardness of HRC 58 and a remarkable tribological behavior.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.201-202
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• 2006

An apparatus measuring changes of various forces directly and continuously was developed by a way of direct touch between powders and transmitting force component, which can be used to study forces state of powders during warm compaction. Using the apparatus, warm compaction processes of iron-based powder materials containing different lubricants at different temperatures were studied. Results show that densification of the iron-based powder materials can be divided into four stages, in which powder movement changes from robustness to weakness, while its degree of plastic deformation changes from weakness to robustness.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.377-380
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• 2005

In this study, the experiments of warm deep drawing were done with heated die, and with heated die and cooled punch in order to investigate the formability of ZA31 magnesium sheet alloy of warm deep drawing. For this, warm deep drawing experiments were executed under various temperature, punch velocity and blankholder force. The results of warm deep drawing with heated die showed that fracture occurred punch part at punch velocity of 75mm/min and punch stroke of 10mm under temperature of $100^{\circ}C\~250^{\circ}C$, but did not occure under temperature of $275^{\circ}C\~400^{\circ}C$. And fracture at punch stroke of 25mm did not occurre at punch part under punch velocity of 30mm/min and $250^{\circ}C$, but occured under punch velocity of 75 and 125 mm/min. Also the results of warm deep drawing with heated die and cooled punch showed that the temperature happening maximum height under punch velocity of 10-100mm/min was $225-250^{\circ}C$. And necking occurred at punch shoulder under $20\~150^{\circ}C$, but at die wall under $200\~300^{\circ}C$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.138-141
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• 2001

The evolution of lectures and microstructure during the warm-rolling and subsequent annealing in aluminum 3004 alloy sheets was investigated by employing X-ray texture measurements and microstructure observations. Whereas the typical $\beta$-fiber orientations with the strong Bs-orientation $\{112\}<110>$ formed in the normally cold-rolled specimen, the warm-rolling at $250^{\circ}C$ led to the development of a strong through thickness texture gradient which was characterized by shear texture at the surface layer and rolling textures at the center layer After warm rolling, ultra-fine grains formed in the thickness layer with shear texture components. Upon recrystallization annealing, the $\{001\}<100>$ Cube-texture developed at the expense of normal rolling texture components the rise to the formation of corase recrystallized grains. However, in the layer with shear texture components the continuous recrystallization took place and the fine grain size persisted even after recrystallization annealing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.215-217
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• 2004

In order to obtain the initial starting sample having a random texture and fine grains, aluminum alloy 3103 sheets were repeatedly deformed by CCSS up to six passages and subsequently annealed at $300^{\circ}C$ for 1h. These samples were cold rolled at room temperature and also warm rolled at $250^{\circ}C$. Changes in rolling temperature gave rise to the different texture evolution. Warm rolling led to the pronounced texture gradients comprising the shear texture at the surface and the rolling texture at the sheet center. The formation of the rolling texture components, i.e., the ${\beta}$-fiber, was promoted by cold rolling than warm rolling.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.288-292
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• 2007

This study focuses on the warm forging of a magnesium alloy impeller used for the fuel cell. The impeller has the very complicated shape with sharply twisted blade and thus is generally produced by mechanical machining or casting process. However, since these technologies give the high manufacturing cost or poor mechanical properties, the forging technology is required to make the high-quality impeller with the lower manufacturing cost. In order for production of the impeller by warm forging technology, the parametric studies using finite element analyses were carried out to find the optimal perform shape of impeller. Based on the FE simulation results, dies for impeller forging were designed and the resultant forged impeller was shown.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.49-52
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• 1999

In the present study the tensile test was carried out for steel sheets to offer the database for the material characteristics at various temperature condition. The results are constructed with tensile strength total elongation Lankford vale and the flow curve and these can be employed usefully into the analyzing program as input data for the sheet metal forming processes at warm condition.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.152-157
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• 2003

A typical die-set for enclosed-die forging of half axle gears in double action hydraulic press is presented, the important factors those influence on precision forming of half axle gears are analyzed, warm forming process of half axle gears is simulated by FEM software $DEFORM\_3D$. The results show, that proper die structure and dimension, suitable web thickness and position can improve material filling, ensure full filling of tooth cavity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.63-66
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• 2006

The effect of warm rolling under various conditions on the microstructure and mechanical property was investigated using an AZ31 Mg alloy sheet. Several processing parameters such as initial thickness, thickness reduction by a single pass rolling, rolling temperature, roll speed, and roll temperature were varied to elicit an optimum condition for the warm rolling process of AZ31 Mg alloy. Microstructure and mechanical properties were measured for specimens subjected to rolling experiments of various conditions. Warm rolling of 30% thickness reduction per pass was possible without any side-crack at temperatures as low as $200^{\circ}C$ under the roll speed of 30 m/min. The initial microstructure before rolling was the mixed one consisting of partially recrystallized and cast structures. Grain refinement was found to occur actively during the warm rolling, producing a very fine grain size of 7 mm after 50% reduction in single pass rolling at $200^{\circ}C$. Yield strength of 204MPa, tensile strength of 330MPa and uniform elongation of 32% have been obtained in warm rolled sheets.