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이혜경(Hyae Kyung Yi),이건엽(Gun Yeop Lee),이성문(Sung Mun Lee),이영선(Young Seon Lee),문영훈(Young Hoon Moon) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.11
In this study, the characteristics of aluminum tube hydroformed products at different extrusion type and heat treatment conditions were investigated. For the investigation, as-extruded, full annealed and T6-treated Al 6061 tubes at different extrusion type were prepared. To evaluate the hydroformability, free bulge test was performed at room temperature to 300℃. Also mechanical properties of hydroformed products at various pre- and post-heat treatments were estimated by hexagonal prototype hydroforming test at 250℃. And the tensile test specimens were obtained from hexagonal prototype hydroformed tube. As a results, hydroformability of full annealed tube is 5~8% higher than that of extruded and T6-treated tube. The tensile strength and elongation of T6-post heat treated indirect extrusion tube were more than 330㎫ and 12%, respectively. However, T6 pre treated hydroformed product represents high strength, 330㎫ and low elongation, 8%. Therefore, Hydroformability of Al6061 tube showed similar value for both extrusion types. However flow stress of direct tube showed 20~50㎫ lower value than indirect tube.
냉간단조 공정을 적용한 크랭크 샤프트 스프로켓의 기계적 특성 연구
임홍섭(Hong sup Yim),이혜경(Hyae Kyung Yi),이성문(Sung Mun Lee),문영훈(Young Hoon Moon) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Recently, it is attempted to automotive parts by various cold forging methods to meet requirements of mass production and qualities. Compared to hot forged products, cold forged products reveal higher strength and better mechanical properties. In this study, the properties according to forging process type are analyzed for crank shaft sprocket. Cold forged crank shaft sprocket was evaluated surface hardness, micro structure and surface residual stress. Analyzed micro structures and mechanical properties of cold forged crank shaft sprocket were compared with that of conventional hot forging process.
주병돈(Byeong Don Joo),이혜경(Hyae Kyung Yi),장정환(Jeong Hwan Jang),권승오(Seung O Kwon),문영훈(Young Hoon Moon) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.6
Hydroforming is one of the useful processes in the automotive industry and recently for to improve the fuel efficiency, automotive industry focus on weight reduction. Aluminum alloys are light and has high structural rigidity, the need for hydroforming of aluminum alloy is increased. In this study, hydroformability and fracture criteria of FE analysis based on ductile fracture were investigated in warm hydro forming of Al 6061 tube and to evaluate the hydroformability, un i-axial tensile test and bulge test were performed at room temperature and 200℃. The measured flow stresses were used as input parameters for FE analysis, the damage values were calculated by FE analysis based on ductile fracture criteria at maximum radius of free bulged tubes, and damage values were compared of hexagonal shaped hydroformed parts.
박현규(Hyun Kyu Park),임홍섭(Hong Sup Im),이혜경(Hyae Kyung Yi),김광순(Kwang Soon Kim),문영훈(Young Hoon Moon) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In recent years, developments of light weight vehicle are one of the most important issues in automotive industry. It is important to know the variations of the mechanical properties in the hydro forming process for the safe and durable design purposes. Generally, tube hydro forming process consists of three main processes such as bending, preforming, and hydro forming. It means that the strain hardening histories of final products are nonlinear. In this study, strain hardening behavior during hydro forming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and strength were used as an index of strain hardening during respective processes. The correlationship between strength and hardness obtained from tensile test at various pre-strain conditions has been equivalently converted into correlation between hardness and pre- strain.
이재호(Jae Ho Lee),장정환(Jeong Hwan Jang),이혜경(Hyae Kyung Yi),권승오(Seung O Kwon),문영훈(Young Hoon Moon) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.6
Sheet or plate bending is one of the most important industrial metal forming processes. And considerable attention has been focused on gaining a better understanding of many bending characteristics. One of default in bending process is springback. In this study, the springback characteristics of cold rolled steel in U-bending process was investigated. The cold rolled strips were consisted of 3types of thickness(1.2t, 1.4t, 1.8t) combination SPFC780 sheet to obtain the effect of different thickness combination on the springback and three different material strips, (SPFC590, SPFC780, SPFC980), to investigate the influence of different mechanics properties on springback. Three punch profile radii of 3, 9 and l2㎜ were used. As results, the springgo aspect could be observed experimentally in the small punch profile radius. And suggested analytical model results were compared with experimental results.
Cu-Ca 합금을 이용한 고효율 로터의 반용융성형 공적 적용에 관한 연구
이상용 ( Sang Yong Lee ),문영훈 ( Young Hoon Moon ),이혜경 ( Hyae Kyung Yi ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 대한금속·재료학회지 Vol.45 No.5
The melting range, electrical conductivity, and microstructure of Cu-Ca alloys and thixoforming process design of developed Cu-Ca alloy were investigated. High purity calcium was added to molten copper up to 1.4% by weight. SIMA(Strain induced melting activated) process has been carried out to modify the copper dendrites to spherical shapes. The semisolid range, grain size and electrical conductivity of Cu-Ca alloy were significantly influenced by the content of calcium and prestrain. Thixoforming experiment of developed Cu-Ca alloy were performed. Efficiency of rotor was negative influenced by internal defects. Thixoformed Cu-Ca rotor shows high efficiency to that of die cast Al rotor by optimization of forming process.