• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.183-185
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• 2008

Forming Limit Diagram(FLD) is a representative tool for evaluating formability of sheet metals. This paper presents a methodology to determine the FLD using Finite Element Method. For predicting the forming limits numerically. Previous methods such as using the thickness strain or the ductile fracture criterion are limited at plane strain domain. These results suggest that behavior of the void growth in sheet metals is different from real one. In contrast to previous methods, a more exact model which takes void growth into account is used. This result agrees with the experimental result qualitatively.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.117-120
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• 2003

Warm deep drawing which is one of the new forming technologies to improve formability of sheet metal is applied to the cylindrical cup drawing of Mg-alloy sheet metal. In experiments the temperature of die and blank holder is varied from room temperature to $300^{\circ}C$, while the punch is cooled by circulation of coolant to increase the fracture strength of workpiece on the punch corner area. Test material chosen for experiments is AZ31 magnesium sheet metal. Teflon film as a lubricant is used on both sides of a workpiece. The limit drawing ratio as well as thickness distributions of drawn cups are investigated and validity of warm deep drawing process is also discussed.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.429-434
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• 2010

The material used is a commercial magnesium based alloy AZ31(Mg-3Al-1Zn) sheet with a thickness of 0.8 mm. Friction tests at various temperatures(R.T. to $200^{\circ}C$) and at various holding forces in the 4 type molds were carried out to investigate the coefficient of friction. A warm drawing process with a local heating and cooling technique was developed in the Mg alloy sheet forming to improve formability because it is very difficult for Mg alloy to deform at room temperature by the conventional method. So, the coefficient of friction at various mold surface treatment conditions in this study was needed to develop the Mg alloy sheet forming technology.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.118-121
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• 2005

The square cup drawing of magnesium alloy AZ31 $(aluminum\;3\%,\;Zinc\;1\%)$ sheets was studied by experimental approach in various temperatures (200, 250, 300, 350, $400^{\circ}C$) when blank holding force (BHF) was controlled in real-time. And so on, the drawability was measured with the different die and punch coating. The square cup drawing test was performed by three different coated punches (CrN, TiCN, Non-coated). BHF was set about 2.0 KN, forming speed was 50 mm/min, blank thickness were 0.5, 1.0mm and the cup size was 40 mm by 60 mm after forming. The experimental data of square cup drawing test show that the tools coating and temperature were effect on the drawbility.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.69-72
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• 2005

The crystal structure of magnesium is hexagonal close-packed (HCP), so its formability is poor at room temperature. But formability is improved in high temperature with increasing of the slip planes. Purpose of this paper is to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature is increased, yield${\cdot}$ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) are decreased. But strain rate sensitivity (m) is increased. As strain-rate increased, yield${\cdot}$ultimate strength, K-value, and work hardening exponent (n) are increased. Also, microstructures of grains fine away at high strain-rate. These results will be used in simulations and manufacturing factor for warm and hot forming process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.413-413
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• 2009

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.374-377
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• 2008

Magnesium alloy sheets are usually formed at temperatures between $150^{\circ}C$and $300^{\circ}C$ because of their poor formability at room temperature. In the present study, the formability of AZ31B magnesium alloy sheets was investigated by the analytical and experimental approaches. First, tensile tests and the limit dome height test were carried out at elevated temperatures to get the mechanical properties and forming limit diagram, respectively. And then deep drawing of cross shaped die was tried to get the minimum corner radius and forming limit at specific temperature. Blank shape, punch velocity, minimum corner radius, fillet size, etc, were determined by finite element analysis physical try-outs. Especially, optimum punch and die temperature were suggested through the temperature-deformation analysis using Pam-stamp.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.398-400
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• 2008

In this work, an air-bending test using magnesium alloy ZK60 sheet was carried out at the various temperatures from room temperature to $300^{\circ}C$ in order to investigate the effect of grain size on the spring-back characteristic. It was found out from experiments that the amount of spring-back was nearly zero at all temperature range when the specimens with grain sizes of 14.66 and $60.71{\mu}m$ were bent by $90^{\circ}$. On the other hand, the spring-back amount dramatically increased at room temperature and phenomenon of spring-go was observed at high temperature when the specimen with submicro grain size of $0.98{\mu}m$ was bent by $90^{\circ}$. From this kind of different spring-back characteristics according to the grain size, it was confirmed that the grain size of material is one of the important factors which have an effect on the spring-back.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.55-62
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• 2004

In this study, the effects of Ca content and processing variables on hot rolling properties of gravity cast AZ31-xCa alloys were evaluated systematically. The number and length of side crack were decreased with increasing preheating temperature and decreasing reduction ratio per pass and Ca content. The UTS and YS were not strongly dependent on the Ca content but the elongation decreased with increasing Ca content. The decrease of elongation in Ca containing alloys was least when the sheets were fabricated under preheating temperature of $400^{\circ}C$ and reduction ratio per pass of $15\%$. The sheets had the sound external features with little side cracks by homogenization of gravity cast AZ31-xCa alloys before hot rolling. In the cases of AZ31-xCa alloys containing under $1wt.\%$ Ca, the annealed sheets after homogenization and hot rolling had the similar tensile properties to those of AZ31 sheet.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.53-56
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• 2006

Magnesium alloy AZ31, which processed by conventional rolling or extrusion, has high anisotropy of mechanical properties in its strength and elongation at room temperature. We compared the influence of differential speed rolling with conventional rolling process on microstructure and mechanical properties of commercial AZ31 sheet. Commercial AZ31 alloy sheets were processed with conventional and differential speed rolling with thickness reduction ratio of 30% at a various temperature. The elongation of AZ31 alloy, warm-rolled by differential speed rolling is larger than those rolled by conventional rolling. Besides, grain size and distribution on microstructure of the conventional rolled materials were coarse and inhomogeneous, on the contrary, those of the differential speed rolled were fine and homogeneous.