• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.65-71
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• 1997

Computer simulations and test trials are carried out to get the optimal conditions about the stamping die design of the tailor laser welded automotive door inner. Firstly, the stamping process including gravity deflection, bead calibration, binder wrap, forming and spring back, are analyzed by the computer simulation. The results of simulation shows good correspondance with those of test trial under the same conditions. The variables of parametric study which will be investigated in the simulation and test trials, are determined form the results of the first run. The formability under the various conditions is evaluated, which are the initial postion of blank, blank holding force, corner radius and the shape of drawbead. Finally, well controled sound product without fracture, wrinkling and excessive weldline movement is obtained.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.53-56
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• 2007

Magnesium sheet used in electrical device due to mobility and EMF shielding characteristics. Magnesium case by press forming was advantageous compare with conventional die casting process, because of its thin gauge of wall and surface quality. But it need to makes the boss to fix inner part or assemble the case. CD stud welding was effective way for joining the boss to the thin gauge case of the electrical devices. In this study, we investigated the performances of the magnesium boss welder To measure the process parameters such as the force and the weld current, we design the monitoring system for CD stud welding. We test the characteristics of CD stud welding for AZ31 sheets at some variables. Finally we select the optimum welding range of magnesium sheets in CD stud welding process.

• Laser Solutions
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• v.12 no.2
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• pp.7-10
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• 2009

In this paper, we study experimentally the local polishing of $SiO_2$ surface using the $CO_2$ laser. For laser local polishing, we polished to remove the grooves or to be reformed the surface of grooves after forming the grooves on the material surface. We measured the reflectance, transmittance, and beam profile in order to measure the roughness of polished surface. The Atom Force Microscope (AFM) is used to measure roughness of local polishing surface. We can predict that the laser polishing contribute to the removal of generated debris and surface roughness on the micro processing.

• Design & Manufacturing
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• v.12 no.1
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• pp.26-30
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• 2018

The aluminum chassis drive gear manufacturing process improvement has been very effective in both technical and economic aspects. Technology for Shear mold design technology, mold material selection and processing technology, and press molding technology has improved greatly overall. In the meantime, it is necessary to clarify the causes of defects that occur frequently due to lack of technology, Based on this, it is meaningful that it has secured the ability to respond to new product development and molding in the future. By applying these technologies, we plan to expand not only the drive gear chassis, but also various types of press forming such as frame, handle, various fastening parts of system window. In addition, the ability to develop precision products in the future is expected to become a driving force in further enhancing the competitiveness of companies.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.86-91
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• 2006

Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good castability in spite of hexgonal closed-packed crystal structure of pure magnesium. In this paper, FE analysis was executed about the formability of AZ3l magnesium alloy on press forging process. For this, the variation of sheet temperature, distribution of punch force and the effect of heat transfer and friction between punch and sheet on the forming characteristics during press forging of AZ31 has been analyzed by finite element analysis. In order to obtain temperature dependence of material characteristics, uniaxial tension tests at elevated temperature were done under temperature of $100^{\circ}C\~ 500^{\circ}C$.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.243-248
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• 2004

Disk galaxies abound with intermediate-scale structures such as OB star complexes, giant clouds, and dust spurs in a close geometrical association with spiral arms. Various mechanisms have been proposed as candidates for their origin, but a comprehensive theory should encompass fundamental physical agents such as self-gravity, magnetic fields, galactic differential rotation, and spiral arms, all of which are known to exist in disk galaxies. Recent numerical simulations incorporating all these physical processes show that magneto-Jeans instability (MJI), in which magnetic tension resists the stabilizing Coriolis force of galaxy rotation, is much more powerful than swing-amplification or the Parker instability in forming self-gravitating intermediate-scale structures. The MJI occurring in shearing and expanding flows off spiral arms rapidly forms structures elongated along the direction perpendicular to the arms, remarkably similar to dust spurs seen in HST images of spiral galaxies. In highly nonlinear stages, these spurs fragment to form bound clumps, possibly evolving into bright arm and interarm H II regions, suggesting that all these intermediate-scale structures in spiral galaxies probably share a common dynamical origin.

• International Journal of Air-Conditioning and Refrigeration
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• v.14 no.2
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• pp.66-75
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• 2006

The effect of antifreeze solution liquid film on the frost prevention is experimentally investigated. It is desirable that the antifreeze solution spreads widely on the heat exchanger surface forming thin liquid film to prevent frost nucleation while having small thermal resistance across the film. A porous layer coating technique is adopted to improve the wettability of the antifreeze solution on a parallel plate heat exchanger. The antifreeze solution spreads widely on the heat exchanger surface with $100{\mu}m$ thickness by the capillary force resulted from the porous structure. It is observed that the antifreeze solution liquid film prevents a parallel plate heat exchanger from frosting. The reductions of heat and mass transfer rate caused by the thin liquid film are only $1{\sim}2%$ compared with those for non-liquid film surface.

• BMB Reports
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• v.33 no.6
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• pp.476-482
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• 2000

In this paper, we report a new cationic lipid composed of L-lysinamide and cholesterol as a potent gene delivery vector. $3{\beta}$[L-Lysinamide-carbamoyl] cholesterol could self-assemble with plasmid DNA forming discrete lipoplexes. From atomic force microscopic images of the complexes, the size distribution was observed to range from 100 to 150 nm in diameter. The transfection efficiency of this amphiphile on different cell lines was evaluated as a micellar solution in the absence of the fusogenic helper lipid, dioleoyl phosphatidyletbanolamine (DOPE). Transfection experiments were performed as a function of charge ratio (lipid/DNA) and transfection time. Cytotoxicity and in vitro transfection efficiency of the amphiphile was demonstrated and compared with those of commercially available Lipofectin and polyethylenimine (PEI).

• Steel and Composite Structures
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• v.8 no.4
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• pp.281-296
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• 2008

Visco-elastic material and thin metals were adhered to plate structures, forming the composite components that are similar to the sandwich plates, called constrained layered damped (CLD) plates. Constrained layer damping has been utilized for years to reduce vibration, and advances in computation and finite element analysis software have enabled various problems to be solved by computer. However, some problems consume much calculation time. The vibration equation for a constrained layered damped plate with simple supports and an impact force is obtained theoretically herein. Then, the results of the vibration equation are compared with those obtained using the finite element method (FEM) software, ABAQUS, to verify the accuracy of the theory. Finally, the 3M constrained layer damper SJ-2052 was attached to plates to form constrained layered damped plates, and the vibration equation was used to elucidate the damping effects and vibration characteristics.

• Journal of the Korean Society of Safety
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• v.24 no.4
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• pp.82-89
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• 2009

Unlike concrete bridge, steel bridge resists external force by forming thin plate. Thus, because steel girder bridge has big slenderness ratio, buckling is a major design factor. Plate girder consists of flange and web plate. Because of economic views, web plate that resists shear forces is made by more thinner plate. Thus, web plate has much risk for buckling. The objective of this study is to analyze the buckling behaviors of plate girder and to present the proper reinforcement location of longitudinal stiffeners. Various parametric study according to the change of web height, transverse stiffeners and load condition are examined.