• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.50-53
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• 2001

Hydroforming process has become an effective manufacturing process because it can be adaptable to forming of complex structural components. Tube hydroforming has been successfully developed in the real industrial field by many researchers. However, there still remains the constraint about shape which can be manufactured by tube hydroforming. In order to improve this constraint of shape and formability of conventional sheet metal forming, hydroforming process of sheet metal pairs becomes an important technology. In the present work, the finite element analysis of hydroforming process of sheet metal pairs is presented. After basic study about experimental parameters based on numerical analysis, hydroforming process of sheet metal pairs is developed which uses hydraulic pressure as a main forming source.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.611-618
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• 2011

Flow forming is an incremental forming process in which rollers are used to form cylindrical parts with repeated turning of both roller and starting material. Both sheet and tube can be used as the starting material. The process is highly useful for producing hollow shaped parts from a tube, with the benefit of the average strain in the final shape being significantly lower than that from a sheet material. In the present study, the flow forming process was studied and optimized for producing a hollow shaped part from seamless steel tube by both experiment and numerical analysis. Upon considering the difficulty of forming seamless steel sheet, the thickness reduction was distributed over several tool paths. In the end, an optimum process condition was attained, and the experiment verified the simulation results.

• Transactions of Materials Processing
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• v.10 no.1
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• pp.3-14
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• 2001

Hydroforming is the technology using hydraulic pressure and forming sheet or tube metals to desired shape in a die cavity. lt can be characterized as tube hydroforming and sheet hydroforming depending on the shape of used blank. Due to its prcess-related benefits, this production technology has been remarkably noticed for great potential for feasible applications and recently gained great attraction from many industrials including automotive and non-automotive. This Paper analyzed the tube and the welded blank hydroforming process and compared formability of the processes for automotive engine mount bracket. The mathematical analysis was performed by using the dynamic explicit finite element code, PAM-STAMP. In tube hydroforming, bending, springback, and forming analysis were carried out and the effect of mandrel and axial feeding were examined. In welded blank hydroforming, pressure curve history is determined and the results of forming analysis were evaluated by the comparison of experimental results in the aspects of deformed shape and thickness distribution.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.1
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• pp.29-38
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• 2001

In this paper, the defrosting characteristics of a PTC heating sheet is investigated by means of a defrosting heat source for the fin-tube heat exchanger in a refrigerator The defrosting characteristics of the PTC heating sheet are examined and compared with those of a conventional electric heater experimentally. It is found that the characteristics of the water draining rate with the defrosting time show a smoothly oscillating pattern when the PTC heating sheet Is used, and the drained water is completely melted. The defrosting efficiency of the PTC heating sheet is found to be about 75%, which is about 25% higher than that of the electric heater. Also, the reduction of the defrosting time and the increment of the defrosting efficiency may be obtained by improving the arrangement of the heating elements of the healing sheet. It is shown that the defrosting time of the PTC heating sheet increases linearly with the amount of frost, whereas the defrosting efficiency is nearly constant. When applying the PTC heating sheet to the refrigerating system, one should notice the fact that the defrosting performance of the PTC heating sheet may be degraded due to the repetitive operations.

• Transactions of Materials Processing
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• v.16 no.8
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• pp.621-628
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• 2007

Nowadays, Exhaust Gas Recirculation(EGR) Cooler is one of the most favorite systems for reducing the generation amount of $NO_x$ and other particle materials from vehicles burning diesel as fuel. Efficiency of the system is mainly dependent on its heat transfer efficiency and this ability is affected by net heat transferring area of the system. For that reason, several types of heat transfer tube such as dimple, wrinkle and spiral types that have large net area are used. However, it is difficult to manufacture the rectangular tube with dimpled type structure because it experiences too much strain around the rectangular tube surface during the forming process. For that reason, in this study, numerical simulation for forming process of non-symmetric dimple shape on a thin sheet metal was carried out. Furthermore, theoretical forming limit curves(forming limit diagram, forming limit stress diagram) were proposed as criteria of formability evaluation. From the results of finite element simulation in view of stress and strain distribution, it is found that the designed process has robustness and feasibility to safely manufacture the dimpled rectangular tube.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.141-146
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• 2003

An experimental investigation was conducted to estimate the flexural behavior of circular concrete beams confined by carbon sheet tube under the loading and unloading cycles. Six specimens were produced with different layers of carbon sheets and with or without corrugations inside of tubes. The experimental results represented that the load and displacement capacity are increased in the specimens which have increased layers of tube and have installed corrugations inside of tubes. In order to obtain enough capacity, tubes have to keep tubes at proper layers but it can not affect positively more than certain layers to increase the layers of tube. Therefore, appropriate estimation of structural member is needed to obtain enough capacity and displacement by means of proper carbon sheet direction and layers of tube.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.136-144
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• 2004

Optimal process and system to produce the laser welded tube for one body formed bumper beam are studied. The calculated size of tube is a thickness of 1.4mm, diameter of 105.4mm and length of 2000mm. The tube is shaped from a cold rolled high strength steel sheet(tensile strength: 60kgf/$\textrm{mm}^2$ grade). Two roll bending method is the optimal tube shaping process compared to UO-bending, bending on press brake, multi-step continuous roll forming and 3 roll bending methods. Weld quality monitoring and seam tracking along the butt-joint lengthwise to the tube axis are also studied. The longitudinal butt-joint is welded by the $CO_2$ laser welding system equipped with a seam tracker and plasma sensor. The constructed $CO_2$laser tube welding system can be used for the precision seam tracking and the real-time monitoring of weld quality. Finally, the obtained laser welded tube can be used for one-body formed automobile bumper beam.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.1
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• pp.147-155
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• 1999

In this work, the defrosting characteristics of PTC heating sheet used as a defrosting heat source of fin-tube heat exchanger in a refrigerator have been experimentally compared with those of conventional electric heater. It is found that the characteristics of water draining rate with defrosting time show smoothly oscillating pattern when PTC heating sheet is used, and the drained water is completely melted. The defrosting efficiency of the PTC heating sheet is about 75%, which represents about 25% higher than that of the electric heater. A reduction of defrosting time and an increase of defrosting efficiency may be obtained by improving the arrangement of heating elements of the heating sheet. It is shown that the defrosting time of PTC heating sheet increases linearly with the amount of frost, however the defrosting efficiency is nearly constant. In the application to the refrigerating system, one should notice the fact that the defrosting performance of PTC heating sheet may be defraded due to the repeated operations.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.18-20
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• 2003

Optimal processing and system to produce the laser welded tube for one body formed bumper beam are studied. The calculated size of tube is a thickness of 1.4mm, diameter of 105.4mm and length of 2000mm. The tube is shaped from cool rolled high strength steel sheet(tensile strength: 60kgf/$\textrm{mm}^2$ grade). Two roll bending method is the optimal tube shaping process compared to UO-bending, bending on press brake, multi-step continuous roll forming and 3 roll bending methods. Weld quality monitoring and seam tracking along the butt-joint lengthwise to the tube axis are also studied. The longitudinal butt-joint is welded by the $CO_2$ laser welding system equipped with a seam tracker and plasma sensor. The constructed $CO_2$ laser tube welding system can be used for the precision seam tracking and the real-time monitoring of weld quality. Finally, the obtained laser welded tube can be used for one-body formed automobile bumper beam.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.147-154
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• 2003

The purpose of this study is to investigate analytically the flexural behavior characteristics of Circular concrete beams confined by carbon sheet. Nonlinear analysis method is presented to simulate the structural behavior beam models. The proposed analytical hardening models were considered the confinement effect of concrete and the tensile effect of carbon sheet in tensile region of concrete. Prandtl-Reuss numerical formula was used to nonlinear analysis of finite element models. Comparisons analytical models with experimental data obtained from flexural testing in the laboratory were presented. Analytical and experimental models show similar behavior.