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한영현(Y. H. Han),이경훈(K. Lee),서창희(C.H. Suh),이재진(J.J. Lee),임용희(Y.H. Lim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
An approach of design improvement for uniform cooling of cooling channels of hot press forming (HPF) dies is presented. The approach is based on CFD simulation and analysis of relative velocity of sectional velocity profiles. Potential problematic regions in cooling channels that can potentially cause irregular cooling can be quickly identified merely through velocity simulation of cooling channels. Two types of widely-used HRF dies that are really used in shop flows are investigated and suggestions of design improvements for them are illustrated with some examples.
이승열(S. Y. Lee),이경훈(K. Lee),임용희(Y. H. Lim),정우창(W. C. Jeong) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.5
The heat transfer characteristics between die and sheet and between die and coolant are major processing parameters in hot press forming process. The determination of quenching time to guarantee full martensitic transformation requires proper understanding of these heat transfer characteristics. The contact area changes drastically during the quenching process due to the volume change of both die and sheet by temperature drop and also phase transformation. Several different type of modeling method is tested and proposed proper method. The effect of martensitic transformation with respect to the quenching time is investigated and compared to the experiment. The influence of heat conductivity of die material is also considered.
형상정밀도 예측을 위한 780MPa급 차체부품의 스프링백 해석
최현준(H. J. Choi),전용준(Y. J. Jun),김세호(S. H. Kim),김기풍(K. P. Kim),김동환(D. H. Kim),임용희(Y. H. Lim) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
Finite element stamping analysis is carried out for the side sill inner member of an auto-body with a 780 MPa-grade high strength steel sheet in order to predict the spring-back phenomena accurately. The springback mechanism is investigated in the cross section of the stamped product quantitatively and the amount of the compensation angle is predicted to correct the unexpected shape inaccuracy. Parameters for the accuracy measurement such as gap and flush are calculated in the simulation and it is confirmed that the simulation result shows good agreement with the experimental one within ±1 mm tolerance.
DP780이 적용된 자동차용 계단형 사이드실의 성형공정 연구
서창희(서평자),신효동(H. D. Shin),정윤철(Y-C. Jung),박춘달(C. D. Park),임용희(Y. H. Lim),김영석(Y. S. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
High strength steels are widely used for lightweight automobile parts and the control of springback is very important in sheet metal forming. The object of this study is to develop the forming process for stair type side sill made of high strength steel, DP780. Stair type side sill with local formed area and geometry change area can improve stiffiness and design freedom but there are a few studies for forming process. The forming technology considered in this paper is form type process, which have many advantages for forming of high strength steel compared with draw type process. Finite element analysis is carried out to predict formability and springback. It is shown that angle calibration of die is essential for reducing springback, and local forming involving bead is effective to control springback also. The effectiveness of local forming and angle calibration is verified by experimental.