• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.164-170
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• 1998

Hemi-spheroidal punch stretching test was developed to evaluate the press formability of sheet materials. In the plane strain stretching tests, our specially designed hemi-spheroidal head punch, hemi-cylindrical head punch(RIST type) and hemi-spherical head punch were used, respectively. In this experiment, the circular sheet blanks with parallel edge sides are uniformly stretched up to fracture by raising these punches to assure plane strain stretching deformation along the longitudinal direction of the specimens. The press formability was evaluated by limit punch height(LPH) and minor strain measurement around the fracture area. Compared with the hemi-spherical punch and the hemi-cylindrical one, our hemi-spheroidal punch was more useful in the experimental reproduction and reliance for press formability test.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.539-544
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• 1998

Hemi-spheroidal punch stretching test was developed to evaluate the press formability of sheet materials. In the plane strain stretching tests our specially designed hemi-spheroidal head punch were used. In the experiment the circular sheet blanks with parallel edge sides are uniformly stretched up to fracture by raising these punches to assure plane strain stretching deformation along the longitudinal direction of the specimens. The press formability was evaluated by limit punch height(LPH) and minor strain mea-surement around the fracture area. Compared with the hemi-spherical punch and the hemi-cylindrical one our hemi-spheroidal punch was more useful in the experimental reproduction and reliance for press formability test.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.670-680
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• 2000

The purpose of this study is to provide the database of forming limit diagram applicable to the warm forming of oil pan. The test materials are SCP1 and SCP3C with the thickness of 1.4mm which is used for the oil pan of automobile. The testing temperature is 5$^{\circ}C$~15$0^{\circ}C$ which is In the range of practical usage. The results are the forming limit diagram limiting dome height and the maximum punch load at each temperature such as 5$^{\circ}C$, $25^{\circ}C$, 6$0^{\circ}C$, 9$0^{\circ}C$, 12$0^{\circ}C$ and 15$0^{\circ}C$. From these results, we can see that the forming limit curves are translated depending upon the temperature and that FLC at low temperature is higher than at high temperature. Both of limiting dome height and maximum punch load also decrease as the temperature increases. Present results can be useful for die trial and forming analysis as a tool of evaluating the forming severity for the sheet metal forming processes at the warm working condition by comparing the practical strains with FLC.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.295-299
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• 2006

The inner-structure bonded(ISB) sheet metal is defined as a composite sheet metal which has middle layer of truss-structure between two skin sheets. The characteristics such as ultra-light weight, high rigidity, high strength, etc are required especially for automobile parts. The characteristic of ISB sheet metal depends on inner-structure pattern or method of bonding. Pyramid type of crimped expanded metal is used for inner-structure and both of resistance welding and adhesive bonding are applied to make a specimen. As a result of compression test, it is appeared that forming limit is 10% reduction in thickness under a load of 8kgf per unit element(one inner-structure). In case of uniaxial tensile test the non-uniform surface integrity rather than the buckling of inner-structure happened at a load of 450kgf, which indicates elongation of 7.2% and thickness reduction of 13%. The eye-inspection method was applied to examine the defects occurring on the specimen during stretch forming. In case of biaxial stretch forming only the non-uniform deformation on the surface of a skin sheet could be observed. The forming limit in stretching of ISB sheet metal with the hemi-spherical punch of 150mm in diameter was 3mm in forming depth and 5% reduction in thickness.