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Blank optimization for free bulging of Inconel 718 to maximize bulged height at high temperatures
유준태,윤종훈,이호성,윤성기 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.8
Thickness profiled blank is designed via the optimization technique to maximize the bulged height in free bulging for Inconel 718. Thethickness of the blank is described by the Bezier curve by using four control points. The location of each control points is used for thedesign variables of optimization. The material parameters for the flow stress equation of Inconel 718 are obtained from the free bulgingtest at constant pressure condition by using a flat blank and verified via numerical analysis. The objective function and constraints foroptimization are the maximization of the bulged height within a limited strain range. The equivalent static load method for non-linearstatic response structural optimization with a move limit scheme is used for optimization. The result of optimization shows 21.95% increasedbulged height and uniformly distributed strain after bulging. The free bulging test using blank with optimized profile is conductedto verify the optimization process. The results of bulged height and deformed shape are compared with those from numerical analysis,and the comparison shows good agreement.
가스압력을 이용한 자유벌징에서 성형양 최대화를 위한 두께 분포 최적화
유준태,윤종훈,이호성,윤성기 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.8
자유벌징에 있어서 성형 높이를 최대화하기 위하여 블랭크의 두께 분포를 최적화 하였으며, 등가정하중을 이용한 구조최적화법을 사용하였다. 두께형상은 부드러운 곡선으로 나타내기 위하여 베지어곡선을 사용하였고 제어점의 위치가 설계변수이며, 최대 변형률을 일정 값으로 제한하였다. 사용된 소재는 인코넬 718 이며 최적화된 두께분포로 가공된 블랭크를 이용한 자유벌징 시험을 수행하여 평판형 블랭크를 사용한 결과보다 22% 더 높은 성형 높이를 얻었다. 최적화결과에서 예측된 변형형상, 정점에서의 변형 경향, 두께분포가 실험에서 얻은 결과와 유사하여 최적화 과정의 유효성을 입증하였고, 최적화 결과가 실제 구현될 수 있음을 검증하였다.
고온 성형을 이용한 인코넬 718 샌드위치 코어 구조 성형
유준태(Joon-Tae Yoo),윤종훈(Jong-Hoon Yoon),이호성(Ho-Sung Lee) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
In this study, flat core structure is formed using alloy 718 by hot gas forming at 980C. Initial blank is composed of 2 sheets which are welded by electron beam welding to get core pattern. To prevent the separation at welding joint during forming, welding width is increased by multi-pass welding. Maximum forming pressure is limited 48 bar considering the strength of die and capacity of pressurization system. Forming process is analyzed by numerical method. Flow stress equation is determined by free bulging test and it is a function of strain-rate sensitivity and strength coefficient. 2D and 3D models are used for analysis and its results are compared with experimental results in deformed shape. Analysis using 3D model shows good agreement. In case of 2D model, it has a little difference because model is considered as plane strain. But it will be more useful using 2D model to save computational cost and to find the response in various boundary conditions.
접합툴의 형상에 따른 Al-Li합금의 마찰교반용접특성 고찰
유준태(Joon-Tae Yoo),윤종훈(Jong-Hoon Yoon),이호성(Ho-Sung Lee) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
Al-Li alloys show extraordinary specific strength and have been used in Space Shuttle SLWT(Super Lightweight Tank) with application of Friction stir welding (FSW). FSW has many advantages like the absence of porosity, distortion and residual stresses which are typical defects of the fusion welding processes. The process uses a rotating tool with a profiled pin that penetrates the parts to be joined; the tool then starts to travel along the joint line. By keeping the tool rotating and moving it along the joint line to be welded, the softened material due to the frictional heat is stirred and mechanically mixed together by the rotating pin forming a weld in solid state without melting. The present work is to investigate the effect of tool configuration on the microstructure and mechanical properties of friction stir welded AA2195. Since the mechanical properties of the joint are related with development of microstructure evolution during FSW, microstructure and mechanical properties of joints were investigated for different tool configuration.