• Transactions of Materials Processing
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• v.23 no.1
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• pp.29-34
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• 2014

The damage level of the die surface was predicted by estimating the surface roughness with a finite element analysis and the wear characteristics. Wear and friction tests were conducted to compare the wear characteristics for three kinds of surface treatments - CrN, TiAlN and AlCrN coatings. A prediction model was derived from the surface roughness results with respect to contact pressure and sliding speed which were obtained from the wear test. Surface roughness values for the damage regions of the die surface were compared between the experiments and the prediction model, which shows fairly good agreement with each other.

• Journal of Information Display
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• v.6 no.1
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• pp.1-7
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• 2005

We propose new fabrication methods of a pixel-isolated liquid crystal (LC) structure for flexible display applications. In the LC structure fabricated through the proposed method, the patterned interpixel walls for sustaining the cell thickness are supported by the solidified polymer layer through anisotropic phase separation of LC/polymer composite, causing the alignment of the LC molecules to have very good mechanical stability against external pressure. In addition, we show that such pixel-isolating walls can be made by the stamping method which can be applied to fabricate large size plastic LCDs by roll-to-roll processing.

• Transactions of Materials Processing
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• v.19 no.2
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• pp.113-119
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• 2010

Hydroforming is the technology that utilizes hydraulic pressure to form tube or sheet materials into desired shapes inside die cavities. Tube hydroforming provides a number of advantages over the conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength. In many case, hydroformed parts have to be structurally joined at some point. Therefore it is useful if the hydroformed automotive parts can be given a localized attachment flange. In this study for the numerical process design FE analysis was performed with DYNAFORM 5.5. Die parting angle and circumferential expansion ratio was optimized. With optimized condition, bulge and hydroforming experiments to form flange were performed. Forming characteristic at various pressure conditions was analyzed and optimized internal pressure condition was evaluated. The results show that flanged parts can be successfully produced by tube hydroforming process.

• Textile Coloration and Finishing
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• v.34 no.1
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• pp.58-67
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• 2022

In this study, self-reinforced composite(SRC) was prepared using HDPE(High density polyethylene) fabric(2×2 plain) and LDPE(Low density polyethylene) film. The optimal conditions were derived by manufacturing specimens according to the temperature of 100 ~ 140℃ using a hot stamping at a pressure of 100bar for 10 minutes in order to find the optimal conditions for the SRC. The manufactured SRC was analyzed for tensile properties, compressive strength and shear strength through a universal testing machine(UTM). As a result of the measurement, the P3 specimen prepared by hot stamping at a temperature of 130℃ and a pressure of 100bar for 10 minutes was found to be higher than other specimens with tensile strength and tensile modulus of 210MPa and 19GPa, compressive strength 69MPa and shear strength 13MPa and it was considered to be optimal condition. Finally, the composite material according to the fabric structure was modeled using experimental values and the physical properties of the composite material according to the fabric structure were predicted using GeoDict and Digimat.

• Transactions of Materials Processing
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• v.3 no.1
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• pp.51-62
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• 1994

Cup drawing test and U-bending test were performed to evaluate the friction characteristics of sheet materials for the different deformation modes involved in stamping process. The coefficient of friction calculated from the each test was compared to that obtained from the draw bead friction test. It was clarified that the cup drawing test could be simply used for evaluating the friction characteristic of sheet material in deep drawing process with high contacting pressure. However the U-bending test is suitable to evaluate the frictional characteristic of sheet material in bending process with low contacting pressure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.269-272
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• 2006

The hydroforming processing is a relatively new technology in comparison with conventional stamping process. The hydroforming processing makes torsion beam in rear suspension of automobile. The durability of torsion beam is very important characteristic that operate in an automobile. In order to optimize the hydroforming process and satisfy the durability, the hydroforming simulation which could control an axial compression and high internal pressure with computer simulation has to be operated. This paper is about an optimum design to improve the kinematic and compliance characteristics of a torsion-beam of suspension system. The result from finite element analysis shows that the forming and the durability are optimized. If there is effect of First pressure in hydroforming processing that gap is in the die tool, the prototype of tube is not satisfied on the durability test.

• Transactions of Materials Processing
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• v.21 no.1
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• pp.5-12
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• 2012

The weight of the bipolar plate is one of the crucial aspects of improving power density in PEMFC stacks. Aluminum alloys have good mechanical properties such as density, electrical resistivity, and thermal conductivity. Furthermore, using aluminum in a bipolar plate instead of graphite reduces the bipolar plate cost and makes machining easier. Therefore in this study, an aluminum alloy was selected as the appropriate material for a bipolar plate. Results from feasibility experiments with the aim of developing fuel cells consisting of Al bipolar plates with multiple channels are presented. Dynamic loading was applied and the formability of micro channels was estimated as a function of punch pressure and die radius. Sheets of Al5052 with a thickness of 0.3mm were used. For a die radius of 0.1mm the formability was optimized with a sine wave dynamic load of 90kN at maximum pressure and 5 cycles of a sine wave punch travel. The experimental results demonstrate the feasibility of the proposed manufacturing technique for producing bipolar plates.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.202-205
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• 2009

Tubular torsion beam of high strength steel is going about in an automotive rear axle due to the advantages of light weight and efficient rear packaging capability. High strength tubular beam can be manufactured by the hydroforming in order to ensure dimensional accuracy, while a conventional stamping has been used for steel tubular beam. Internal pressure, feeding and their combination are the key factors of controlling the process. Based on the numerical simulation and try-outs, the optimized hydroforming process conditions for the high strength tubular beam were suggested.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.616-620
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• 2001

The wrinkling in the flange and wall of a part is a predominent failure mode in stamping of sheet metal parts. In many cases this wrinkling may be eliminated by appropriate control of the blank holding force(BHF), but BHF affects the draw depth. Although the wrinkles of flange have been made in the incipient stage of drawing, if the height of wrinkles is maintained under a prescribed limit by decrease or extinction of wrinkles in the course of drawing, small BHP can be allowed so that the depth of drawing could be increased. Authors research the variation of the wrinkles in flange in the course of square cup drawing by using aluminium A1015 and aluminium alloy A5052.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.146-149
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• 2007

The 2-step manufacturing method consisting of preforming and stamping processes was developed to manufacture composite bipolar plates for PEMFCs. The preform was composed of expanded graphite, graphite flake and phenol resin. Precuring conditions were optimized by checking the electrical conductivity, flexural strength and microstructure. Precuring temperature ($100^{\circ}C$) slightly above the melting point of phenol powders ($90^{\circ}C$) induced moderate curing, but also prevented excessive curing. Preforms utilizing the tangled structure of expanded graphite were easily fabricated at low pressure of 0.07-0.28MPa. The proper precuring time, 5min, was determined to fabricate the preform stably because insufficient and excessive precuring deteriorated the flexural strength of composite bipolar plates.