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송정훈,박종진,Song, Jung-Hoon,Park, Jong-Jin 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.11
Compared to a full three dimensional FEM, the Slab-FEM hybrid method reduces the required computation time distinctly and it can be applied to the analysis of a shape rolling process. However, the method is somewhat approximate and predictions by the method contain certain inaccuracies. In the present investigation a parameter called T-factor was introduced to compensate the inaccuracies of the method and proper values of the parameter were estimated for different widths of bars and reduction ratios. Then, the method was applied to analyze cold and hot rollings of rectangular bars and predicted results were compared to those of experiments. Nonuniform distributions of temperature in the bars were predicted by utilizing the temperature equation obtained for a semi-infinite solid under radiation and convection boundary conditions. It was found out that accuracies of spread and roll separating force predictions could be enhanced by using proper values of the T-factor.
공형압연에서 롤의 비대칭 배치로 인한 소재단면형상의 변화
김성기,이동윤,이석의,정원태,남규한,나두현,이영석 대한기계학회 2024 大韓機械學會論文集A Vol.48 No.5
공형압연에서 롤을 지지하는 부품의 강성부족으로 발생한 롤의 비대칭 배치로 인해 압연된 소재의 FSP(free surface profile)가 대칭이 되지 않는다. 본 연구는 이런 점을 역이용하여 롤의 비대칭 배치가 압연된 소재단면의 FSP에 미치는 영향을 분석하였다. 롤의 비대칭 배치는 상/하부 롤이 수평방향으로 서로 어긋나 약간 평행 이동한 경우, 상/하부 롤의 좌/우측 롤 갭이 다른 경우 그리고 상/하부 롤이 압연방향으로 상반되게 약간 회전한 경우이다. 상기 세 가지 비대칭 압연조건에서 3종류의 티타늄 소재(Ti-Gr.4, Gr.19, Gr.23)를 압연하였다. 같은 압연조건에서 FE 해석을 수행하였고, 계산과 측정결과를 비교 분석하였다. 결과적으로 상기에서 언급된 3가지 비대칭 압연조건 중에서 상/하부 롤이 압연방향으로 상반되게 약간 회전한 경우가 FSP 변화에 가장 큰 영향을 주었다. In groove (or caliber) rolling, the free surface profile (FSP) of the rolled material is not symmetrical owing to the asymmetric arrangement of rolls caused by the insufficient stiffness of the components supporting the roll. This study utilizes this aspect to analyze the effect of the asymmetric arrangement of rolls on the FSP of materials departing from the rolls. The asymmetric arrangement of rolls is reflected in cases where the upper/lower rolls propagate parallel to the horizontal direction (x-direction), the left/right roll gaps of the upper/lower rolls are different, and the upper/lower rolls rotate in opposite directions along the rolling direction. Titanium of three grades (Ti-Gr.4, Gr.19, and Gr.23) are rolled under the abovementioned three asymmetric rolling conditions. We perform three-dimensional finite-element analysis under the asymmetric rolling conditions mentioned above and compare the predictions with the measurements. The results show that among the three asymmetric rolling conditions, the case where the upper/lower rolls rotate in opposite directions along the rolling direction exerts the most significant effect on variations in the FSP.
허종욱(Jonguk Her),이형직(Hyung Jik Lee),이영석(Youngseog Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Experimental and numerical studies were performed to examine the effect of material temperature and reduction ratio on friction coefficient during hot flat rolling. We carried out a single pass pilot flat rolling test at the temperatures range of 900~1200℃ and measured the width spread of deformed material while reduction ratio varies from 20% to 40%. Material used in this study is a high carbon steel, POSCORD80M and its dimension is 50㎜×50㎜×300㎜. To investigate the effect of material temperature and reduction ratio on Coulomb friction coefficient during hot flat rolling, we performed a series of finite element simulation of the rolling process as Coulomb friction coefficient is changed from 0.3 to 0.5. To guarantee high accuracy of FE analysis, we performed high temperature tensile testing as well. Results show that friction coefficient is dependent on reduction ratio in a non-linear manner. Friction coefficient is highest in case where reduction ratio is 40% at the temperature of 1200℃.