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Anisotropy at high temperatures
Y.T.Keum,B.Y.Ghoo' 한양대학교 세라믹연구소 2002 Journal of Ceramic Processing Research Vol.3 No.3
In this study, special attention is paid to the definition of planar anisotropy of non-ferrous sheets at high temperatures. Barlats strain potential is employed for depicting the yield behavior. A smoothing function with a third order polynomial is introduced for non-isothermal Barlats anisotropy coefficients. The predicted Barlats coefficients are compared with experimentally obtained coefficients. As a crucial result, the smoothing function provides a big advantage in evaluating non-isothermal Barlats anisotropy coefficients: there is no necessity to carry out tensile tests in high temperatures.
Springback of FCC sheet in warm forming
Y.T.Keum,B.Y.Han 한양대학교 세라믹연구소 2002 Journal of Ceramic Processing Research Vol.3 No.3
These days, automobile industry tends to use aluminum alloy sheets to reduce weight of auto-body. However, aluminum alloy sheets have the drawback that they have tremendous springback in press forming operations. Springback deteriorates accuracy of the product as well as causes difficulties in assembling the parts such that technical plans for springback reduction before pressing have to be prepared. In this paper, the warm forming method, which changes material properties, is proposed to decrease springback. In order to suggest the warm forming method, first, the material properties of aluminum alloy sheets, AL1050 and AL5052, in high temperatures such as yield stress, plastic strain ratio, Young's modulus, true stress-strain curve, etc. are obtained from tensile tests. Next, the bending and draw bending tests in various forming temperatures are performed to measure the springback in various forming temperatures. Two kinds of experiment show that the springback tremendously reduces in warm forming, specially in the forming temperatures of above 150oC.
Numerical Design of Drawbeads for Advanced High Strength Steel Sheets
Y.T. Keum,D.J. Kim,G.S. Kim 한국소성가공학회 2010 기타자료 Vol.2010 No.6
The map for designing the drawbeads used in the stamping dies for advanced high strength steel (AHSS) sheets is numerically investigated and its application is introduced. The bending limit of AHSS sheet is determined from the extreme R/t’s obtained simulating numerically the plane-strain process formed by the cylindrical punches and dies with various radii. In addition, the forming allowance defined by the difference between FLC? and the strain after passing the drawbead, which is observed by the numerical simulation of drawbead pulling test, is computed. Based on the bending limit and forming allowance, the design map for determining the height, width, and shoulder radius of the drawbead which are key parameters in the drawbead design and depend on the restraining force is constructed by aid of the equivalent drawbead model. A drawbead of the stamping die for forming a channel-typed panel is designed by using the design map, and the formability and springback of the panel to be formed are numerically evaluated, from which the availability of the design map is demonstrated.