This paper is concerned with a simulation-based process design for the tension levelling of metallic strips based on the elasto-plastic finite element analysis with reduced integration and hourglass control. The tension levelling process is performed to elongate the strip plastically in combination of tensile and bending strain by a controlled manner so that all longitudinal fibers in the strip have an approximately equal amount of length and undesirable strip shapes are corrected to the flat shape. The analysis deals with a method for calculating the quantitative level of the curl to investigate the roll arrangements and intermesh suitable to elimination of the curl. The analysis provides the information about the intermesh effect on the amount, the tension effect and distribution of the strain as well as the stress in order to determine the amount of elongation for correction of the irregular shape. The desired elongation is referred to determine the number of work rolls and the value of tension. For the first time, the analysis investigates the effect of the mesh size in the non-steady state finite element analysis on the amount and distribution of the strain and the mesh size is selected to perform the finite element analysis for the tension levelling process with the consideration of the time and economic probability of the analysis.
We select several kinds of unit models which is actually used in the tension levelling process line and look into strain and stress history at the designated point along the thickness of the strip, levelled strain, residual strain and the deformed shape of the strip after the levelling and the springback with respect to the variation of the intermesh and the tension for each of the unit model. We also examine the down force at the down roll and the tension of the right of the strip with respect to the variation of the intermesh and the tension for each of the unit model. This finite element analysis is performed is two cases; the one is the smooth strip without the shape defects, the other is the strip with the shape defects.
On the basis of this fundamental analysis for each of the designed unit model, we design the total tension leveller and carry out the finite element analysis on this total tension leveller. In the similar to the unit model, we look into strain and stress history at the designated point along the thickness of the strip, levelled strain, residual strain and the deformed shape of the strip after the levelling and the springback with respect to the variation of the intermesh and the tension in the smooth strip and the strip with the shape defects. These shape defects often can be appeared after the actual cold and hot rolling process. We will find the process parameter to minimize the curvature of the deformed shape of the strip after the levelling and the springback for the designed tension leveller.
인장교정기술은 굽힘과 인장을 반복적으로 가해서 불량한 판재의 형상을 교정하는 기술로 압연 후의 판재의 평탄도 개선에 널리 사용되고 있는 공정이다. 본 연구에서는 금속판재에 대한 인장교정 공정을 정확하게 수치 모사할 수 있는 탄소성 유한요소법을 도입하여 인장교정기의 단일 유닛들에 대하여 압하량과 인장력의 변화에 따른 변형률과 응력의 분포를 찾아내고 압하중을 계산하고 인장교정 후 스프링백에 의한 판재의 최종 성형형상을 살펴보고 판재의 잔류곡률을 밝혀내서 이를 최소화 할 수 있는 공정변수의 설계 방안을 제시한다. 즉, 여러 개의 유닛을 롤의 크기와 롤피치를 고려하여 선정한 후에 형상결함이 없는 판재에 관한 유한요소 해석을 수행하고 또한 형상결함이 있는 판재에 대해서도 유한요소 해석을 수행한다. 이를 바탕으로 하여 여러 개의 유닛을 조합하여 인장교정 공정 전체 과정을 나타낸 인장교정기를 구성한 다음 이 교정기에 대하여 교정 후 판재의 최종형상에서 잔류곡률을 최소화 할 수 있는 공정변수의 설계 방안을 제시한다.
