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판재 점진 성형 공정의 정밀도 향상을 위한 다이 구조 개선에 대한 연구
이원준,김민석,선민호,유제형,이창환,LEE, Won-Joon,KIM, Min-Seok,Seon, Min-Ho,YU, ․Jae-Hyeong,Lee, Chang-Whan 한국금형공학회 2022 한국금형공학회지 Vol.16 No.2
Unlike other press forming processes, ISF (Incremental sheet forming) doesn't require a punch and die set. However, during the ISF processes unwanted bending deformation occurred around the target geometry. This paper is aimed to analyze the effect of the die structure, which is supported by bolts, on the geometric accuracy of the ISF processes. In this research, the ISF processes with Al5052 sheet of 0.5 mm, the tool diameter of 6 mm and the stepdown of 0.4 mm was employed. L-shaped, step-shaped, relief-shaped geometry were employed in experiments. Sectional view and the plastic strain were compared. From this research we find out that the bolt supported ISF processes increases the geometric accuracy of products very effectively.
마그네슘 합금 판재의 평면 DIC 측정을 위한 지그 개발과 이를 활용한 단축 변형 특성 분석
강정은,유지윤,최인규,유제형,이창환,Kang, Jeong-Eun,Yoo, Ji-Yoon,Choi, In-Kyu,YU, Jae Hyeong,Lee, Chang-Whan 한국금형공학회 2021 한국금형공학회지 Vol.15 No.2
The specific strength of magnesium alloy is four times that of iron and 1.5 times that of aluminum. For this reason, its use is increasing in the transportation industry which is promoting weight reduction. At room temperature, magnesium alloy has low formability due to Hexagonal closed packed (HCP) structure with relatively little slip plane. However, as the molding temperature increases, the formability of the magnesium alloy is greatly improved due to the activation of other additional slip systems, and the flow stress and elongation vary greatly depending on the temperature. In addition, magnesium alloys exhibit asymmetrical behavior, which is different from tensile and compression behavior. In this study, a jig was developed that can measure the plane deformation behavior on the surface of a material in tensile and compression tests of magnesium alloys in warm temperature. A jig was designed to prevent buckling occurring in the compression test by applying a certain pressure to apply it to the tensile and compression tests. And the tensile and compressive behavior of magnesium at each temperature was investigated with the developed jig and DIC equipment. In each experiment, the strain rate condition was set to a quasi-static strain rate of 0.01/s. The transformation temperature is room temperature, 100℃. 150℃, 200℃, 250℃. As a result of the experiment, the flow stress tended to decrease as the temperature increased. The maximum stress decreased by 60% at 250 degrees compared to room temperature. Particularly, work softening occurred above 150 degrees, which is the recrystallization temperature of the magnesium alloy. The elongation also tended to increase as the deformation temperature increased and increased by 60% at 250 degrees compared to room temperature. In the compression experiment, it was confirmed that the maximum stress decreased as the temperature increased.
정규석(Kyu-Seok Jung),유제형(Jae-Hyeong Yu),정완진(Wan-Jin Chung),이창환(Chang-Whan Lee) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.9
Incremental sheet metal forming can be used to manufacture various products without the punch and die set. However, it is difficult to manufacture the desired shape due to section deflection and springback of the sheet. Section deflection is caused by the force of the blank holder for fixing the sheet and the tool for forming the sheet. In this study, we analyzed the characteristics of the section deflection according to the geometries of the circular cup shapes in the sheet incremental forming process. The section deflection increased with an increase in the entering radius and forming angle in the section deflection region. However, section deflection was constant according to the exit radius. In addition, the secondary forming process for reducing the shape error was introduced. The secondary incremental forming process was conducted in the opposite direction. Characteristics of the shape error according to the entering depth of the tool among the forming parameters for reducing the shape error of the cup shape were analyzed. The springback in the cup-shape was reduced by the additional forming process with an optimum entering depth of the tool.
Optimization Design of Penetrator Geometry Using Artificial Neural Network and Genetic Algorithm
정규석(Kyu-Seok Jung),조성민(Sung-Min Cho),유제형(Jae-Hyeong Yu),유요한(Yo-Han Yoo),김종봉(Jong-Bong Kim),정완진(Wan-Jin Chung),이창환(Chang-Whan Lee) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.6
When the penetrator collides with the target, the penetrator has different penetrating characteristics and residual velocity after penetration, according to the geometry of the penetrator. In this study, we optimized the geometry of the penetrator using the artificial neural network and the genetic algorithm to derive the best penetration performance. The Latin hypercube sampling method was used to collect the sample data, Simulation for predicting the behavior of the penetrator was conducted with the finite cavity pressure method to generate the training data for the artificial neural network. Also, the optimal hyper parameter was derived by using the Latin hypercube sampling method and the artificial neural network was used as the fitness function of the genetic algorithm to optimize the geometry of the penetrator. The optimized geometry presented the deepest penetration depth.