• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.88-94
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• 2000

A winding bend rig for measurement of springback ratio is made. It measures the bending angles before and after release of bending load which bends specimens with keeping a constant curvature. Thus the springback ratio can be obtained by using this bend rig. Analytical explanations for the spring back are tried by employing simple beam theory. For the analytical calculations with the theory, Young's modulus, fracture strain and stress-strain curve are necessary and these data are obtained from a tensile test. Using both of the beam theory and the results of tensile test, the springback ratio is also calculated. Comparisons of the two springback ratios, one is obtained from bending test and the other from tensile test, show a good agreement.

• Proceedings of the Korean Society for Quality Management Conference
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• 2006.04a
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• pp.80-85
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• 2006

HSS (high strength steel) is widely applied to reduce the weight but improve the strength in automobiles. This research has been peformed to secure a methodology to accurately predict the springback of HSS for successful tool and process designs in sheet stamping operations. We first peformed U-draw bending test to evaluate the springback characteristic. We then evaluated forming and springback processes using the 1-row model of the finite element method. Based on the peformance measure and parameters selected, extensive analyses of the factor effects on the springback have been made using experimental design concepts. We specifically selected Taguchi's orthogonal array, $L_{18}(2^1{\times}3^7)$, and the optimal level combination of the factors have been drawn from the analysis.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.95-101
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• 2000

To measure springback ratio of thin sheet or plate, winding bend rig is made. It bends a specimen with keeping its curvature constant and measures the bending angles before and after release of bending load. To check the performance of the bend rig, we calculated the bending moment by two ways which are based on simple beam theory. One is that the bending moment is calculated by using the results of bending test, and the other is that the moment is calculated by using the results of tensile tests. The former may entails the effect of the friction between bending pin of the rig and the surface of specimen, but the latter does not contain any effects of the friction since the bending moment is obtained by using tensile tests. Nevertheless, the values of the two bending moment shows the same level of bending moment, which implies that the friction does not influence on the value of springback ratio in spite of the presence of friction within the cope of the test performed in this experiment.

• Transactions of Materials Processing
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• v.3 no.4
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• pp.401-414
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• 1994

Springback for the three point bending is anlayzed and experimented. Neutral axis is assumed to remain at the midthickness for large ratio of radius of curvature to thickness. Pure bending theory is used to be extended to the analysis of the springback for three point bending. The specimen is thought to be divided into numerous small elements. The theory for pure bending is then adopted for analysis of each element to obtain springback in terms of the relationship between initial and final deflections. the boundary conditions between neighborhood elements are the deflection and slope which should be the same. Deflection is calculated by summing up the deflections of each element. Experiments have been performed for different conditions which are punch radius, span length, and initial deflections. Comparisons between the analytical solution and experimental results show the same trends.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.106-109
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• 2005

Springback is a common phenomenon in sheet metal forming, caused by the elastic recovery of the internal stresses after removal of the tooling. Recently, advanced high strength steels (AHSS) such as TRIP and DP are finding acceptance in the automotive industry because their superior strength to weight ratio can lead to improved fuel efficiency and assessed crashworthiness of vehicles. The major troubles of the automotive structural members stamped with high strength steel sheets are the tendency of the large amount of springback due to the high yield strength and the tensile strength. The amount of springback is mainly influenced by the type of the yield function and anisotropic model induced by rolling. The discrepancy of the deep drawn product comparing the data of from the product design induced by springback must be compensated at the tool design stage in order to guarantee its function and assembly with other parts. The methodology of compensation of the low shape accuracy induced by large amount of springback is developed by the expert engineer in the industry. Recently, the numerical analysis is introduced in order to predict the amount of springback and to improve the shape accuracy prior to tryout stage of press working. In this paper, the tendency of springback is evaluated with respect to the blank material. The stamping process is analyzed fur the front side member formed with AHSS sheets such as TRIP60 and DP60. The analysis procedure fully covers the binderwrap, stamping, trimming and springback process with the commercial elasto-plastic finite element code LS-DYNA3D.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.410-415
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• 2002

A winding bend rig is designed to overcome the drawbacks of the conventional bend rig for measuring springback ratio of a strip or plate. Using the present bend rig, springback ratios are measured and they are compared with ones that obtained by using simple beam theory and tensile test. Theoretically, there should be no difference between the two values as far as the simple beam theory holds true for the bending test. But, within the scope of our tests, there is a difference of 5% between the two values since the specimen under bend test is subjected to a transverse shear force and friction force on the surface of the specimen.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.2
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• pp.1-9
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• 2001

To measure springback ratio of thin sheet or plate, winding bend rig is made. It bends a specimen with keeping its curva-ture constant and measure the bending angles before and after release of bending load. To check the performance of the bend rig, we calculated the bending moment by two ways which are based on simple beam theory. One is that the bending moment is calculated by using the results of bending test, and the other is that the moment is calculated by using the results of tensile tests. The former may entails the effect of the other is that the moment is calculated by using the results of tensile tests. The former may entails the effect of the friction between bending pin of the rig and surface of specimen, but the latter does not contain any effects of the friction since the bending moment is obtained by using tensile tests. Never-theless, the values of the two bending moments shows the same level of bending moment, which implies that the friction does not influence on the presence of friction within the scope of the test performed in this experiment. This phenomenon is explained theoretically by using moment equilibrium.

• Journal of Korean Society for Quality Management
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• v.36 no.4
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• pp.29-36
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• 2008

최근 자동차 경량화를 위한 부단한 노력이 진행되고 있다. 이 목적에서, HSS (high strength steel)는 전통적인 연강 (mild steel)의 대안으로 널리 사용되고 있다. 본 연구의 목적은 판금의 형단조에 있어서의 공구와 공정설계를 위하여 HSS의 스프링백(springback)을 정확히 예측하기 위한 성공적인 방법론을 추구하고자 함이다. 연구를 위하여 먼저 스프링백의 개념과 그의 측정치들을 설명했으며 U-draw bending 시험을 수행하였다. 시험 결과 및 선정된 파라메터들 중심의 수행평가기준에 근거하여, 주어진 파라메터 조합들을 중심으로 유한요소 해석을 수행하였다. 직교배열을 통하여 스프링백에 대한 인자 효과들을 포괄적으로 분석하였으며 최적 인자 조합들을 도출하였다. 이 과정에서 직교배열상의 한 조합 전체의 데이터가 가용하지 않는 문제가 수반되었으며, 반복적으로 signal-to-noise 비(ratio)를 개선해가는 기법을 적용하여 해결하였다.

• Transactions of Materials Processing
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• v.12 no.3
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• pp.202-207
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• 2003

In order to examine the springback amount and material properties of aluminum alloy sheets (AL1050 and AL5052) in the warm forming which forms the sheet above the room temperature, the stretch bending and draw bending tests and tensile test in various high temperatures are carried out. The warm forming temperature 15$0^{\circ}C$ is a transition in terms of the material properties: over the forming temperature 15$0^{\circ}C$, them $\sigma$$_{YS}$ , $\sigma$$_{TS}$ , E, K, n, etc. are bigger but $\varepsilon$ and plastic strain ratio are smaller. Below the forming temperature 15$0^{\circ}C$, there are no big differences in material properties as the forming temperature changes. AL5052 sheet has more springback effect than AL1050 sheet. While the springbacks of AL5052 and AL1050 sheets show a big reduction over the warm forming temperature 15$0^{\circ}C$ in the stretch bending test, the springback rapidly reduces in the warm forming temperature 15$0^{\circ}C$-20$0^{\circ}C$ for AL5052 sheet and 20$0^{\circ}C$-25$0^{\circ}C$ for AL1050 sheet in the draw bending test.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.302-307
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• 2016

The technology of multistage deep drawing has been widely applied in the metal forming industry, in order to reduce both the manufacturing cost and time. A battery can used for mobile phone production is a well-known example of multistage deep drawing. It is very difficult to manufacture a battery can, however, because of its large thickness to height aspect ratio. Furthermore, the production of the final parts may result in assembly failure due to springback after multistage deep drawing. In industry, empirical methods such as over bending, corner setting and ironing have been used to reduce springback. In this study, a bottoming approach using the finite element method is proposed as a practical and scientific method of reducing springback. Bottoming induces compression stress in the deformed blank at the final stroke of the punch and, thus, has the effect of reducing springback. Different cases of the bottoming process are studied using the finite element program, DYNAFORM, to determine the optimal die design. The results of the springback simulation after bottoming were found to be in good agreement with the experimental results. In conclusion, the proposed bottoming method is expected to be widely used as a practical method of reducing springback in industry.