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서오석(Oh Suk Seo),김헌영(Heon Young Kim),박종규(Jong kyu Park),서창희(Chang Hee Suh) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5
A hot stamping process can be divided into two types, direct process and indirect process, according to the sequence of heating, forming and quenching. In this study, the indirect hot stamping of boron steel tube was adopted to be numerically analyzed. The whole process including forming at room temperature, heating and cooling process with phase transformation was analyzed and simulated by the implicit code DEFORM. From the analyses, it was found that different heat transfer coefficients should be used at different zones of the model in order to ensure the accuracy of the heating and cooling analysis. Therefore, the heat transfer coefficients applied in the analysis were measured at various positions in the tube, e.g., outside, inside, bending area by using heat cartridges. Finally, these coefficients were determined through a correlation of values in the real tests and those from the numerically backward traced analysis. Comparison between experiments and analysis of the final deformed shape and the distribution of the temperature shows good agreement. Hot stamping process consists of forming at the elevated temperature and rapid quenching, which induces phase transformation and results in the press hardening of steel parts. In this study, the hot stamping process of boron steel tube was analyzed by applying different heat transfer coefficients which had been experimentally measured and numerically backward traced.
핫스템핑 공정시 소재의 두께 변화에 따른 냉각채널 설계
서오석(O. S. Seo),박종규(J. K. Park),이명규(M. G. Lee),김헌영(H. Y. Kim) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
Recently, ultra high strength products can be manufactured by the hot stamping process in automotive industry. In the hot stamping process, cooling rate of quenching process is key factor to get the high strength, which is closely related to the design of cooling system such as the diameter, the position and the arrangement of the cooling channels. In this study, the quenching process was analyzed including phase trasnformation by finite element analysis(FEA) and the developed FE procedure was applied to the optimization of new cooling channel design with different gage thickness.
Yoshida-Uemori 모델을 이용한 Al 판재의 스프링백 예측
서오석(O. S. Seo),이은국(E. G. Lee),홍석무(S. M. Hong),최선철(S. C. Choi),유수열(S. Y. Ryu),이명규(M. G. Lee),김헌영(Heon Young Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
Springback is caused by the recovery of elasticity of a flat-rolled metal, which occurs when the forming force is released from a flat-rolled metal. Springback takes place in a large degree when a high strength steel plate or AI alloy sheet is processed. It has been known that hardening model is the most efficient for the prediction of springback. Recently, various researches have been carried out. In particular, Yoshida-Uemori model has been proved to be the most suitable for forecasting the springback of a high strength steel plate. In this paper, Uniaxial tension tests and cyclic loading tests(T-C-T, C-T-C) were conducted on the 1050 Al alloy sheet, 3003, and 5052 series. And based on the test results, coefficients required for Yoshida-Uemori model have been figured out. In addition, the test results were put into commercial finite element program PAM-STAMP to predict the springback of Al Alloy sheet and the outcome has been proved to be quite accurate.