• 소성∙가공
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• 제14권7호
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• pp.619-623
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• 2005

Lubrication and cooling characteristics are the most important factors of elevated temperature forging lubricants. Usually adopted lubricants in warm forging processes are graphite, synthetic and emulsion lubricants. Most widely and effectively applied lubricants are graphite lubricants, but these have a lot of problems like tool corrosion and dusty environment. In this research, boronite lubricant is considered, because it is able to substitute for graphite. Hot ring compression test, cooling test and mass production test are performed to check the validity of new lubrication pigment.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.198-201
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• 2004

Aluminum alloys have high potential for weight reduction in automotive and other applications. But aluminum alloys have relatively low tubular hydroformability which can be enhanced by conducting the hydroforming at elevated temperatures. Hot working processes are commonly used in bulk forming such as forging and rolling, but still is rare in sheet metal forming like hydroforming. In this study hydroforming test at elevated temperatures is performed by special designed induction heating system to investigate the hydroformability of aluminum alloys. The high temperature formability characteristrics are obtained by 1?fitting forming test and circular bulging test and the effects of the process parameters such as feeding amount, internal pressure and temperatures on the tubular forming limits are mainly investigated.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.43-47
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• 2006

Since the sheet metal forming of Mg alloy is performing at elevated temperature, the effect of process conditions related with the forming temperature is very important factor. Therefore, the investigation for process variables is necessary to design the tools and process conditions. In this study, the effects of process variables were studied by the experimental and FE analysis using the square cup deep drawing. The temperature, forming speed, and lubricant condition were investigated. When forming temperature was $250^{\circ}C$, speed forming was low, and teflon sheet was used as lubricant, the formed parts were good without defects.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.409-412
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• 2006

Bulk metallic glass (BMG) strips of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ were produced by warm rolling of the amorphous powder canned with copper. Controlling of temperatures of the rolled sample and rolls was essential for the successive rolling process. Because improper controlling of the sample temperature gave rise to the crystallization of BMG loading to the catastrophic fracture of BMG strips, the temperature of rolls should be properly controlled for achieving successful powder rolling of BMG. The variations of the strain state and temperature in the roll gap was simulated by the finite element method(FEM) using various roll temperatures.

• 소성∙가공
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• 제16권5호통권95호
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• pp.401-405
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• 2007

Due to the low densities and high specific strength and stiffness, magnesium alloy sheets are very attractive lightweight materials for automotive and electrical products. However, the magnesium alloy sheets should be usually formed at elevated temperature because of their poor formability at room temperature. For the use of the magnesium alloy sheets for an industrial, their mechanical properties at elevated temperature and appropriate forming process conditions have to be developed. In this study, non-isothermal simulation of a square cup drawing of magnesium alloy sheets have been conducted to evaluate a proper forming process conditions such as the tool temperature, the tool shoulder radius, friction between the blank and the tools. According to this study, appropriate forming process conditions of square cup drawing at elevated temperature from magnesium alloy sheets are suggested.

• 소성∙가공
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• 제16권5호통권95호
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• pp.364-369
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• 2007

The effect of temperature on the forming limit diagram was investigated for AZ31B magnesium alloy sheet through the limit dome height test in the range from room temperature to $300^{\circ}C$. The formability of AZ31B sheet was improved significantly according to the increasing temperature. Also we studied the springback characteristics through the 2D draw bending test with different blank holding forces at elevated temperatures. Springback quantity was considerably reduced as temperature went up. The blank holding force in the range used, however, had little influence on springback. Experimental results obtained in this study may provide a material database for AZ31B sheet.

• 소성∙가공
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• 제21권2호
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• pp.113-118
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• 2012

Magnesium sheet alloys possess limited plastic formability at room temperature but their formability is substantially improved at elevated temperatures and optimum strain rates. In the present paper, three different types of failure criteria, namely, strain-based, stress-based, and work-based criteria, are compared for their applicability to warm press forming of magnesium sheet alloys. Warm deep-drawing experiments were conducted on AZ31 alloy sheet, and the results were used to assess the strength and weakness of the failure criteria.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.63-70
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• 1999

Some deep drawing characteristics to the elevated temperatures were investigated for the SCP1 steel sheets by using the Cr-coated die. For this investigations six steps of temperature ranges from room temperature to 25$0^{\circ}C$ and six kinds of drawing ratio from 2.4 to 2.9 were adopted. As a result the limiting drawing ration maximum drawing force and the maximum drawing depth were sensitively affected by the elevated temperatures and the more stable thickness strain distribution was observed to the elevated temperatures, Some experimental results were compared with analytical results using the DYNA-3D code.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 제2회 단조심포지엄 단조기술의 진보
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• pp.100-123
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• 1995

The relationship between plastic deformation and crystal grain change in warm forging processes of SM100 carbon steel is studied. If the carbon steel is deformed in warm forging temperature (about recrystallization range), the crystal grain and cementite of the internal part are changed, so material properties are changed. Some experimental values, such as the elliptic degree of cementite, the grain size of cementitie and ferrite grain size, are investigated. When the plastic deformation proceeds, the elliptic degree of cementite becomes large, the grain size of cementite particle is small, and the size of ferrite grain appears fine by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging is calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result. At effective strain 0.3 dynamic recovery and dynamic recrystallization begin, over 2.5 the organization of material has better quality that is suitable for the following cold forming.

• 소성∙가공
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• 제15권8호
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• pp.597-602
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• 2006

Bulk plastic forming characteristics were studied for the magnesium alloy, AZ31 in warm backward extrusion. Effects of process conditions such as extrusion ratio, forming temperature, and punching speed were investigated respectively. Variation of microstructure induced by the warm backward extrusion process was observed. Microstructure of the work piece showed evidences of recrystallization under the experiment conditions. It is estimated that in specific punch speed region fast stroke accelerates recrystllization and reduces the forming load.