• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.381-385
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• 2007

In order to examine the effect of the blank holding force on the friction behavior in the sheet metal forming, a sheet metal friction tester is designed and manufactured, which can measure friction forces in various forming conditions such as lubrication, die roughness, drawing speed, radius of die corner, blank holding force, etc., and the friction tests are performed, in which friction coefficients in various blank holding forces and pulling speeds are calculated using Coulomb's friction law. The friction test reveals that friction coefficient decreases as the blank holding force, the drawing speed and lubricant viscosity increase together or individually.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.175-178
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• 1997

A modified Mukerjee's model considering the microstructural evolution was developed to study the superplastic bulge forming process of Ti-6Al-4V alloy. Through the microstructual observation after deformation, it was found that the grain growth rate of uniaxially tested specimens was different from that of biaxially deformed specimens. From this result, bulge forming experiments with and without back pressure were performed to examine the grain growth behavior and to compare the results of biaxial test with those of triaxial test. Good agreement between the prediction by a modified Mukerjee's model and the experimental measurements was obtained for bulge profile and thickness distribution.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.54-57
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• 2002

In order to find the effect of lubricant viscosity, sheet surface roughness, tool geometry, and forming speed on the frictional characteristics in sheet metal forming, a sheet metal friction tester was designed and manufactured and friction tests of various sheets were performed. Friction test results showed that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extreme1y low or high, the friction coefficient is high. As punch comer radius and punch speed are bigger, the value of friction coefficient is smaller. The sensitivity of friction coefficient is mainly governed by lubricant viscosity and sheet surface roughness.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.450-453
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• 2009

In order to overcome drawbacks of the advanced high strength steel such as inferior formability and large springback, the hot press forming process(HPF) has been being applied for forming of automotive sheet parts. Good formability and dimensional accuracy without springback as well as good crash performance of final products are the advantages of the HPF process. In this work, a method to characterize the mechanical properties of the HPF steel was developed based on the simple tension test at high temperatures and its finite element analysis, while it was applied to obtain strain rate and temperature dependent flow curves of the HPF steel. The final flow curves were represented by utilizing the Johnson-Cook type equation both in uniform and post-uniform deformation regions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.222-225
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• 1997

This paper describes experimental investigation on the forming limit for mash-seam welded sheets. The uniaxial tensile test was conducted to evaluate the mechanical properties of weld bead. Experimental forming limit diagrams were investigated for the different thicknesses and properties of welded sheets.

• Transactions of Materials Processing
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• v.10 no.2
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• pp.137-143
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• 2001

The change of flow stress due to dynamic recrystallization during hot forming process is investigated. A series of mechanical tests has been conducted at various temperatures, and constitutive relations and recrystallization kinetics were formulated from the test results. The effect of dynamic recrystallization to the flow stress was implemented to a commercial FEM code by conditioned remapping of state variables. The datum strain of stress compensation was optimized to minimize the overestimation of forming loads. Suggested datum was formulated as an exclusive function of critical strain for recrystallizalion and validated by mechanical tests and microstructural observations.

• Transactions of Materials Processing
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• v.19 no.3
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• pp.167-172
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• 2010

Roll-to-roll forming process is one of important metal processing technology because the process is simple and economical. These days, with these merits, roll-to-roll forming process is tried to be employed in manufacturing the circuit board, barrier ribs and solar cell plate. However, it is difficult to apply to the forming of micro scale or sub-micro scale pattern. In this study, the roll forming processing for the micro scale is designed and analyzed. The forming of micro pattern for small electric device such as LCD panel by incremental roll forming process is analyzed. Firstly, the optimum analysis conditions are found by several analyses. And then, formability is analyzed for various protrusion shapes at various forming temperatures. The formability is evaluated in terms of filling ratio and damage value. The filling ratio is defined from the tool geometry and critical damage is determined from the analysis of uniaxial tensile test. Finally, optimum forming conditions that guarantee the successful forming are found.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.293-295
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• 2007

The thixoforming process become important for forming automobile parts. But, the thixoforming process cannot still prevent to forming defects such as pores and shrinkage which reduce mechanical properties of automobile parts. Therefore, it is necessary to analyze the correlation between forming defects and mechanical properties. However, it is difficult to get data about relations between mechanical properties and forming defects in thixoformed aluminum alloy parts. In this study, three parts of aluminum thixoformed knuckle have been analyzed using tensile test and computer tomography(CT scan). Experimental results showed that the elongation properties of thixoformed aluminum parts were significantly dependent on size and number of forming defects.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.9-15
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• 2012

Vibrational film has been more employed in ear-phones or small type of speakers along with a wide use of portable multi-media equipments such as MP3 and MP4. However, the current hand work production process of diaphragms is inefficient. In this study, a die-and-mold and a single production forming machine are developed, and they result in a multi-production forming machine. The multi-production forming machine consists primarily of a film feeding unit and an unwinding unit. A vacuum suction device provides the film feeding unit, while the unwinding unit is obtained using an appropriate damper. The advantage of the developed single production forming machine is shown according to a proper voice test.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.5
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• pp.519-524
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• 2014

The use of light weight magnesium alloy offers significant potential towards improvement of the automotive fuel efficiency. However, the application of formed magnesium alloy components in auto-body structures is restricted due to the low formability at room temperature and lack of knowledge for processing magnesium alloys at elevated temperatures. In this study, a warm tensile test of magnesium alloys was performed to measure tensile strength and elongation. An improvement in formability was confirmed at increased temperatures above about $250^{\circ}C$. Car body warm forming technology was conducted for forming forming reinforced dash components of the magnesium alloy AZ31B sheet at elevated temperatures.