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임학진(Hak Jin Lim),오정규(Jeong Kyu Oh),김평호(Pyeong Ho Kim),이종환(Jong Hwan Lee),김정석(Jeong Suk Kim) 한국생산제조학회 2013 한국생산제조학회지 Vol.22 No.5
In recent years, aluminum processing has been increasing in the aerospace, vehicle, airplane industries etc.,because aluminum has abundant resources and has a high specific strength. Aluminum alloys have a high coefficient of thermal expansion therefore, it is necessary to consider the temperature problem in the cutting process. The objective of this research is to investigate the machinability of a hardened aluminum alloy Al7075-T6 by using cryogenic heat treatment. The machining test is conducted by comparing the cutting force and surface roughness, corresponding to various cutting conditions of depth of cut, cutting speed, and feed rate, with those of Al7075-T0.
강-소성 유한요소법의 역추적기법을 이용한 정밀정형 쉘 노우징 부품의 성형공정 개발과 실험적 증명
김상현,이진희,임학진,Kim, Sang-Hyeon,Lee, Jin-Hui,Im, Hak-Jin 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.7
A preform is designed by the backward tracing scheme of the rigid-plastic finite element method(FEM) for net-shape shell nosing components without machining after forming. The current process of the shell nosing requires cost-consuming machining to produce final products. Here, the backward tracing scheme of the rigid-plastic FEM, a novel method for preform design of metal forming processes, derives a sound preform for net-shape shell nosing product. The current process is simulated by the rigid-plastic finite element analysis to check the metal flow involved in the forming with a trial preform and its modified preform. The two preforms are found to be inadequate for net-shape shell nosing product. The first application of the back ward tracing scheme derives a preform producing a not-shape shell nosing product. The first application of the backward tracing scheme derives a preform producing a net-shape product numerically, but it is difficult to be formed economically as a preform. Thus an improved preform is designed by the badkward tracing scheme, which is suitable for net-shape manufacturing of the shell nosing components in view of economy of production and forming characteristics of the product. The preform in the current process and a modified preform are confirmed by a series of experiments and the results give the same deformation with the numerical ones. Finally the newly designed preform by the FEM was experimentally proved to be adequate in obtaining net-shape products.
선반 가공조건에 따른 경화처리된 A17075-T6 소재의 가공특성 변화에 관한 연구
이희덕,김정석,정지훈,임학진,Lee, Hee-Deok,Kim, Jeong-Suk,Jeong, Ji-Hoon,Im, Hak-Jin 한국생산제조학회 2012 한국생산제조학회지 Vol.21 No.1
The cutting characteristics of hardened aluminum alloy A17075-T6 were investigated during turning processing. Under variation conditions of cutting speed, depth of cut, and feed rate, the characteristics of cutting force, surface roughness, and machined texture were investigated. Surface roughness became worse in proportion to the increase of the feed rate. The thickness of material alteration layer which is derived from the effect of cutting force was the biggest when feed rate 0.148mm/rev. This research confirmed that the deformed layer is dominantly dependent on the variation of feed rate.
선반 가공조건에 따른 경화처리된 Al7075-T6 소재의 가공특성 변화에 관한 연구
이희덕(Hee-Deok Lee),김정석(Jeong-Suk Kim),정지훈(Ji-Hoon Jeong),임학진(Hak-Jin Im) 한국생산제조학회 2012 한국생산제조학회지 Vol.21 No.1
The cutting characteristics of hardened aluminum alloy Al7075-T6 were investigated during turning processing. Under variation conditions of cutting speed, depth of cut, and feed rate, the characteristics of cutting force, surface roughness, and machined texture were investigated. Surface roughness became worse in proportion to the increase of the feed rate. The thickness of material alteration layer which is derived from the effect of cutting force was the biggest when feed rate 0.148mm/rev. This research confirmed that the deformed layer is dominantly dependent on the variation of feed rate.
열처리된 대직경 알루미늄 튜브선삭에서 콜릿지그를 통한 진원도 향상에 관한 연구
김평호(Pyeong Ho Kim),임학진(Hak Jin Lim),이정민(Jung Min Lee),이종환(Jong Hwan Lee),김정석(Jung Suk Kim) 한국생산제조학회 2012 한국생산제조학회지 Vol.21 No.5
The purpose of this study is to evaluate the proposed jig for turning process of large-scale aluminum tube of D500mm through Finite Element Analysis (FEA). Also, a machining evaluation is conducted with general heat-treated and cryogenic heat-treated tubes. Dimensions of the specimens are determined to be suitable for collet appearance. The characteristics of equivalent stress and strain according to the expansion of the collet are evaluated by FEA. The aluminum tubes which are heat-treated by T4/T6 condition and cryogenic condition are machined by using a large-scale lathe machine and the roundness of machined tube is evaluated by using a 3D measuring machine. Through the results of this study, effects of each heat treatment and residual stress on the roundness are established.
Al6061-T6 열처리 잔류응력의 유한요소해석 및 측정
고대훈(Dae Hoon Ko),김태정(Tae Jung Kim),임학진(Hak Jin Lim),이정민(Jung Min Lee),김병민(Byung Min Kim) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.7
본 연구의 목적은 Al6061 의 T6 열처리 시 발생되는 잔류응력의 변화를 예측하는 것이다. Al6061-T6 의 일반적인 열처리 조건인 용체화처리(530℃, 2hr)와 인공시효(175℃, 9hr)에서 인공시효 시간에 따라 잔류응력 변화를 고려하였다. 잔류응력 예측은 열처리 실험을 수행하여 대류 열전달계수를 확보하고, 탄소성 모델로 가정한 유한요소해석을 적용하였다. 또한 인공시효와 같이 재료가 고온에서 장시간 유지되는 경우의 Zener-Wert-Avrami 함수를 적용하여 잔류응력 변화를 확인하였다. 잔류응력의 측정은 X 선 회절법으로 측정하고 측정결과는 예측된 유한요소해석 결과와 비교하여 해석의 신뢰성을 확보하고 해석기법을 확립하였다. The purpose of this study is to predict the residual stress in Al6061 during T6 heat treatment. In this study, the variable residual stress in case of the solid solution(530℃, 2h) and artificial ageing(175℃, 9h) of Al6061 subjected to T6 heat treatment is determined at different ageing times. A heat treatment experiment is conducted to determine the heat transfer coefficient, on the basis of which the residual stress during the T6 heat treatment is predicted. In order to take into account the relaxation of residual stress during artificial ageing, a Zener?Wert?Avrami function is used and elasto-plastic nonlinear analysis is conducted through FE-simulation. Further, the residual stress is measured by using the X-ray diffraction(XRD) method, and the result is compared with the result from the FE-simulation. It is found that the residual stress predicted form the FE-simulation is in good agreement with the residual stress measured by using the XRD method.
극저온 열처리에 의한 Al6061 합금의 잔류응력 제거 및 열처리 특성 평가
고대훈(Dae Hoon Ko),박기정(Ki Jung Park),조영래(Young Rae Cho),임학진(Hak Jin Lim),이정민(Jung Min Lee),김병민(Min Byung Kim) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.10
본 연구의 목적은 극저온 열처리를 통해 Al6061 의 열처리 잔류응력을 제거하는 것이다. 이를 위해 유한요소해석을 이용하여 열처리 잔류응력을 예측하였으며, 열처리 조건에 따른 각 단계별 대류 열전달계수를 T6 와 극저온 열처리 실험을 수행하여 결정하였다. 예측된 잔류응력 결과는 X 선 회절법(XRD)으로 측정된 잔류응력 결과와 비교하여 유한요소해석 결과의 타당성을 확인하였다. 또한 T6 와 극저온 열처리에 대해 각각 전기 전도도와 경도를 측정하여 기계적 특성을 평가하고 TEM 관찰과 XRD 회절 분석을 통해 석출물의 크기 및 성분을 파악하였다. 이를 통해 Al6061 의 T6 열처리와 비교하여 극저온 열처리를 적용함에 따른 잔류응력, 기계적 특성 및 미세조직변화를 조사하였다. The purpose of this study is to relieve the residual stress of Al6061 using cryogenic heat treatment. Experimental T6 and cryogenic heat treatments were carried out to define the convective heat-transfer coefficient, which was then applied in the finite-element method (FEM) to predict the residual stress. The predicted residual stress was compared with the residual stress measured by X-ray diffraction (XRD), and the results were in good agreement. The mechanical properties were estimated by measuring the electrical conductivity and hardness. In addition, the size and formation of the precipitations were observed by TEM and XRD analysis for both T6 and cryogenic heat treatments. The effects of the cryogenic heat treatment on the residual stress, mechanical properties, and precipitation of Al6061 alloys were thus confirmed.
극저온 열처리 공정이 6061 알루미늄 합금의 잔류응력과 인장특성에 미치는 영향
박기정 ( Ki Jung Park ),고대훈 ( Dea Hoon Ko ),김병민 ( Byung Min Kim ),임학진 ( Hak Jin Lim ),이정민 ( Jung Min Lee ),조영래 ( Young Rae Cho ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
To develop a 6061 aluminum alloy with low residual stress and high tensile strength, a cryogenic treatment process was investigated. Compared to the conventional heat treatment process for precipitation hardening with artificial aging, the cryogenic treatment process has two additional steps. The first step is cryogenic quenching of the sample into liquid nitrogen, the second step is up-hill quenching of the sample into boiling water. The residual stress for the sample was measured by the sin2 ψ method with X-ray diffraction. The 6061 aluminum alloy sample showed 67% relief in stress at the cryogenic treatment process with artificial aging at 175℃. From this study, it was found that the optimum cryogenic treatment process for a sample with low residual stress and high tensile strength is relatively low cooling speed in the cryogenic quenching step and a very high heating speed in the up-hill quenching step.
고대훈(Dae Hoon Ko),김태정(Tae Jung Kim),이봉상(Bong Sang Lee),임학진(Hak Jin Lim),이정민(Jung Min Lee),김병민(Byung Min Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
The purpose of this study predicts the residual stress of Al6061 during T6 heat treatment according to conditions of solid solution and ageing time. The General T6 heat treatment of AI6061 is composed of solid solution(530℃, 2hr) and artificial ageing(175℃, 9hr) process. This study conducts the prediction and measurement of residual stress during T6 heat treatment. The prediction of residual is analyzed by elasto-plastic nonlinear FE-simulation and the residual stress relaxation of artificial ageing is investigated by applying a Zener-Wert-Avrami function. In order to consider the relaxation of residual stress during artificial ageing, FE-simulation is used in DEORM-3D V6.0 with USER SUBROUTINE. Also, residual stress is measured by X-ray diffraction(XRD) which is conducted to confirm the result of FE-simulation. Residual stress predicted by FE-simulation is in good agreement of with measured residual stress.