• Transactions of Materials Processing
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• v.21 no.3
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• pp.186-194
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• 2012

Hot stamping is a forming method that offers various advantages such as superior mechanical properties, good formability, and very small springback. However, relatively large-sized parts, such as front pillars, exhibit poor formability when hot stamped due to the limited material flow and thickness reduction imparted by the process. This reduction in thickness can also lead to cracks. One of the reasons is the relatively high friction between the sheet and the die. In this study, in order to obtain the optimal conditions for hot stamping of front pillars, various process parameters were studied and analyzed using the sheet forming software, J-STAMP. The effects of various parameters such as the die structure, blank shape, blank holding force, punch speed, clearance(upper and lower dies) and distance block were analyzed and compared.

• Korean Journal of Materials Research
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• v.18 no.9
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• pp.492-496
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• 2008

The through-thickness variations of strain and microstructure of high-speed hot rolled 1050 pure aluminum sheet were investigated. The specimens of 1050 aluminum were rolled at temperatures ranging from 410 to $560^{\circ}C$ at a rolling speed of 15 m/s without lubrication and quenched in water at an interval of 30ms after rolling. The redundant shear strain induced by high friction between rolls and the aluminum sheet was increased largely beneath the surface at a rolling reduction above 50%. Recrystallization occurred in the surface regions of the specimen rolled to reduction of 65% at $510^{\circ}C$, while only recovery occurred in the other regions.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1073-1074
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• 2011

The loss is most important problems for the practical applications of permanent magnet synchronous motor(PMSM). In this paper, rotor sleeve and stator shape design of high speed permanent magnet motor for loss reduction. First, this paper found optimum sleeve thickness for calculation eddy current loss on the basis of analytical method, because eddy current is influenced by conductivity of material and area. Then, stator shape design is changed as maintain same slot area for reducing stator core loss. Finally, this paper compared analytical result with optimum sleeve thickness obtained from finite element(FE) method, and stator core loss is calculated from FE method.

• Water Engineering Research
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• v.5 no.1
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• pp.37-45
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• 2004

As one alternative to alleviate damages caused by stormwater runoff, the effects of runoff quantity reduction are analyzed when porous pavement is used. Porous pavements with various depths, general pavement and an artificial rainfall generator are installed for laboratory experiments. Runoff changes are analyzed according to the various rainfall durations. The rainfall intensity of 150 mm/hr is generated for 30 minutes, 60 minutes, and 120 minutes. For porous pavements with 80 cm thickness, 100%, 93%, 56% of discharge is infiltrated through soil, respectively. For porous pavements with 20 cm thickness, 81%, 32%, 28% of discharge is infiltrated through soil, respectively. It is found that the porous pavements are able to decrease the runoff.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.639-642
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• 2001

The possibility of weight reduction of rotor part in gas-gas geater(GGH) is studied from the viewpoint of allowable stress. In this work, finite element analysis(FEA) is performed with original model and three weight-reduced models with different diaphragm thickness, respectively. Stress concentrations at rotor diaphragm happen due to the dead weight, pressure difference between treated gas and untreated gas and thermal distribution in the rotor. As the thickness of diaphragm is decreased, the stress level is increased. The direction of treated gas and untreated gas flow may affect the stress level. Fatigue life assessment is not considered because pressure difference, the only cyclic load, can be ignored. The possible weight-reduced model is presented.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1124-1128
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• 2008

Thin-wall injection molding is associated with many advantages, including increased portability, the conserving of materials, and the reduction of the molding cycle times. In the application of the thin-wall molding, a considerable reduction of the effective flow thickness results in filling difficulty. High-frequency induction is an efficient way to overcome this filling difficulty by means of heating the mold surface by electromagnetic induction. The present study applies the induction heating to the injection molding of thinwalled micro structures with high aspect ratio. The feasibility of the proposed heating method is investigated through a numerical analysis. The estimated filling characteristics of the micro-features are investigated with variations of mold temperature and part thickness, of which results are also compared with experimental measurements.

• Transactions of Materials Processing
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• v.22 no.8
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• pp.486-491
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• 2013

A numerical investigation of the butting process for an AZ31B magnesium alloy tube at elevated temperatures was conducted to develop a double-butted magnesium alloy tube. As a result of the current study, it was found that the amount of doming of the tube end, prior ironing-extrusion to obtain high wall thickness reduction are important factors for the butting process of magnesium alloy tubes. There is also a limitation of the thickness profile of butted tube due to buckling of tube wall during the stripping stage.

• 전기의세계
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• v.30 no.4
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• pp.227-230
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• 1981

The variation of sheet resistance and the reduction of masking oxide thickness with the flow rate of nitrogen gas has been measured in Boron predeposition process with Planar Diffusion source, BN-975. At 900.deg. C, the sheet resistance varied as much as 75% when the nitrogen flow rate was changed from 0.4 liters/min to 2.0 liters/min. At 975.deg. C, however, only 12% of sheet resistance variation was observed under the same flow rate change. The reduction of masking oxide thickness at 975.deg. C for a 5 min predeposition was 600 nm when the nitrogen flow rate was 0.4 liters/min. When the flow rate incresased to 1.9 liters/min, however, only 100nm of masking oxide was consumed in a similar predeposition process.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1213-1214
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• 2006

The synthesis of silver coated iron base alloy (Sendust : Fe-Si-Al) powder having the both effects of shielding and suppressing of electromagnetic wave was studied. Depending on thickness of silver coating layer, the electromagnetic properties of the dispersed particles complexed with organic binder were examined. It is proposed that the silver coated sendust flake powders with controlled electrical properties and thickness can be used as thin microwave absorbers in quasi-microwave frequency band.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.9
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• pp.397-407
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• 2002

A new simulator which predicts the quantum effect in NMOSFET structure is developed. Using the self-consistent method by numerical method, this simulator accurately predicts the carrier distribution due to improved calculation precision of potential in the inversion layer. However, previous simulator uses analytical potential distribution or analytic function based fitting parameter Using the developed simulator, threshold voltage increment and gate capacitance reduction due to the quantum effect are analyzed in NMOS. Especially, as oxide thickness and channel doping dependence of quantum effect is analyzed, and the property analysis for the next generation device is carried out.