• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.06a
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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.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.178-185
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• 1995

Warm deep drawing for optimum forming conditions to give the maximum drawing depth is investigated and compared with the results at room temperature. Experiments which draw square cups of STS 304 stainless steel sheet under the constant lubrication condition of teflon film made both in a crank and hydrqulic press for two kinds of specimens . The maximum drawing depth at warm forming condition reaches 1.4 times the drawing depth at room temperature in a crank press, whereas 1.6 times in a hydrqulic press, and also more uniform distribution of thickness in case of warm deep drawn cup is observed. The effects of other factors on formability , such as forming temperature, speed of press and cooling of punch are examinnied and discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.203-210
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• 1995

The rapid progress of automobile industry has led to a demand for sheet metal products and the new forming technology for complex product is required. In Deep Drawing process of steel sheet, especially stainless steel sheet at room temperture, some intermediate annealing need to be added to lessen strain hardening effect. The present study is concerned with the wram deep drawing of stainless steel sheet. In order to reduce the number of working process. the limit drawing ration is considered as main parameter. In this study, the effect of process variables such a sblank holder force, working temperature and lubricant on limit drawing ration is investigated . Experiments are carried out for the hemisherical and sqare shape at room and warm temperature respectively. The drawing loads and thickness deviation accoring to process variables measured . As the result of apploying those experimental data to the commerical butt product, the number of process can be reduced and good quality of products can be obtained.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.67-70
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• 2000

The tool life is not long enough under sever forming condition in warm forging. The tool life is affected by wear heat fatigue plastic deformation and so on. Especially wear is one of the most serious factors for tool life. To increase tool life we should consider various factors like processing design die design die materials lubrication and cooling system This study design to obtain the steady state temperature of die by FEM analysis under several conditions of cooling. There are four cooling conditions in this study no cooling internal cooling external cooling and both internal and external cooling. With above obtained temperatures tool life is predicted using Archard's model that is considered softening of die. The effect of internal cooling system is better than that of externally cooled die. To predict the die life the steady state temperature is calculated by using mean temperature of die. Considering only wear the die life much longer as the cooling effect is bigger. The more accurate die life will be predicted if we consider heat crack as well as wear.

• Transactions of Materials Processing
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• v.17 no.5
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• pp.373-379
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• 2008

A fundamental study on warm incremental forming of a magnesium alloy sheet has been carried out. In order to enhance the incremental formability of the magnesium alloy sheet, a local heating device was newly designed and manufactured. Through the incremental forming tests of AZ31 under various forming conditions, the effects of process parameters such as the temperature, feeding depth per cycle, and inclination angle on the incremental formability of AZ31 were investigated. In addition, conventional FLDs at elevated temperatures were constructed experimentally and applied to predict the forming failure.

• Transactions of Materials Processing
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• v.27 no.3
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• pp.160-164
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• 2018

The success of warm forming of Mg alloy sheets is very dependent on its frictional behavior at elevated temperatures. The effects of contact pressure and sliding length on the frictional characteristics of AZ31B Mg alloy sheet were investigated at elevated temperature and at room temperature. The contact pressure range for the friction test was determined through FE analysis of the roof panel which is a candidate for Mg alloy application. According to the experimental results, the frictional behavior of the Mg alloy sheet is equally highly influenced by both sliding length and contact pressure at room temperature. At elevated temperatures, however, the sliding length has a more dominant influence on the frictional characteristics of the Mg alloy sheet than the contact pressure, if the contact pressure is lower than a certain level.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.4
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• pp.44-49
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• 2008

The characteristic of magnesium alloy is the most light in utility metal, the effect of electromagnetic wave interception, excellent specific strength and absorptiveness of vibration. Although magnesium alloy with above characteristic is a subject matter which is suitable in world-wide tendency of electrical component frame, sheet magnesium alloy is difficult to process. Therefore, forming analysis of sheet magnesium alloy and applying warm-working to process are indispensable. Among Finite element method, the static implicit finite element method is applied effectively to analyze sheet magnesium alloy stamping process, which include the forming stage. In this study, it was focused on the crack, wrinkling and spring back on sheet magnesium alloy stamping by the static implicit analysis. According to this study, the result of simulation will give engineers good information to access the forming technique on sheet magnesium alloy. And its application is being increased especially in the production of electrical component frame for the cost reduction, saving of defective ratio, and improvement of Productivity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.23-26
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• 2004

The deformation behaviors of fully annealed or T6-treated 6061 and 7075 aluminum tubes are investigated at elevated temperature using uniaxial tensile test. Fully annealed 6061 and 7075 tube, and T6-treated 7075 tube do not show sharp local necking with an elongation of $50\%$ at tensile temperature of $300^{\circ}C$, accordingly, it is expected that warm hydroforming process can be applied. The increase of tensile temperature does not significantly affect the total elongation of T6-treated 6061 tube.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.256-259
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• 2004

In the present study, AZ31B sheets has a bad formability in room temperature, but the formability is improved significantly as increasing the temperature because of rolled magnesium alloy sheet has a hexagonal closed packed structure (HCP) and a plastic anisotropy. In this paper, after tensile test in various temperatures, strain rate, show the tensile mechanical properties, yield and ultimate strength, K-value, work hardening exponent(n), strain rate sensitivity(m). As temperature increased, yield, ultimate strength and K-value, work hardening exponent(n) are decreased but strain rate sensitivity(m) is increased. As cross-head-speed increased, yield, ultimate strength and K-value, work hardening exponent(n) are increased. And according to the temperature, how change the plastic anisotropy factor R. In addition, we observed how temperatures and cross-head-speed effect on microstructure.