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TMCP강을 적용한 해상용 풍력타워의 용접 공정에 따른 기계적 물성 평가
지창욱,최철영,남대근,김형찬,장재호,김기혁,박영도,Ji, Changwook,Choi, Chul Young,Nam, Dae-Geun,Kim, Hyoung Chan,Jang, Jae Ho,Kim, Ki Hyuk,Park, Yeong-Do 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.1
FCAW(Flux Cored Arc Welding), SAW(Submerged Arc Welding), EGW(Electro Gas Welding), and three-pole SAW are applicable in manufacturing the offshore wind tower. In this paper, mechanical properties of these welded-joints for TMCP steels were evaluated in all above welding processes. The tensile strength of welded-joints for all the welding methods satisfied the standard guideline (KS D 3515). No cracking on weldment was found after the bending test. Changes of weldedments hardness with welding processes were observed. In a weld HAZ (heat-affected zone), a softened HAZ-zone was formed with high heat input welding processes (SAW and EGW). However, the welded-joint fractures were found in the base metal for all cases and small decrease in welded-joint strength was caused by a softened zone. The multi-pole SAW welds exhibited similar mechanical properties comparing to the one with one-pole SAW process.
440 ㎫급 도금강판의 저항 점 용접 시 AC 및 MFDC전원에 따른 가용전류구간 비교 연구
지창욱(Changwook Ji),박찬수(Chansu Park),김치호(Chiho Kim),조용준(Yongjoon Cho),오동진(Dongjin Oh),김명현(Myung-Hyun Kim),김양도(Yang-Do Kim),박영도(Yeong-Do Park) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.1
This paper presents a comparative study of the AC and MFDC resistance spot welding process with consideration of sheet thickness. The previous studies have confirmed that there is difference in the optimum welding current and expulsion current with AC and MFDC. The aim of this study was revealing the effect of sheet thickness on weldable current range and expulsion behavior for AC and MFDC welding processes. The optimum welding current of AC was lower (1.6 ㎄) than MFDC welding process in 0.8 mm sheet thickness. Early nugget growth being caused by the peak current of AC developed weld interface deformation, which resulted in suppressing the growth of corona bond and occurrence of low current expulsion. The resistance spot welding for thicker sheet (1.4 ㎜) required lower current of 0.6 ㎄ for the expulsion on the MFDC welding process. The growth of contact diameter (size of corona bond) and button diameter was linear up to the expulsion current with MFDC welding process. Therefore, more attention is required when the AC and MFDC resistance spot welding process is applied for different thickness of steel sheet combination for automotive application.
원자력간 현미경을 이용한 TRIP강 저항 점용접부의 미세조직 분석에 관한 연구
최철영,지창욱,남대근,장재호,김순국,박영도,Choi, Chul Young,Ji, ChangWook,Nam, Dae-Geun,Jang, Jaeho,Kim, Soon Kook,Park, Yeong-Do 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.1
The spot welds of Transformation Induced Plasticity (TRIP) steels are prone to interfacial failure and narrow welding current range. Hard microstructures in weld metal and heat affected zone arenormally considered as one of the main reason to accelerate the interfacial failure mode. There fore, detailed observation of weld microstructure for TRIP steels should be made to ensure better weld quality. However, it is difficult to characterize the microstructure, which has similar color, size, and shape using the optical or electron microscopy. The atomic force microscope (AFM) can help to analyze microstructure by using different energy levels for different surface roughness. In this study, the microstructures of resistance spot welds for AHSS are analyzed by using AFM with measuring the differences in average surface roughness. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy in resistance spot weld TRIP steels. The systematic topographic study for each region of weldments confirmed the presence of different microstructures with height of 350nm for martensite, 250nm for bainite, and 150nm for ferrite, respectively.
용융아연도금 강판 저항 점 용접 시 정전류 및 적응제어 적용에 따른 연속타점 특성 평가 및 고찰
서정철,최일동,손홍래,지창욱,김치호,서성부,서진석,박영도,Seo, Jeong-Chul,Choi, Il-Dong,Son, Hong-Rea,Ji, Changwook,Kim, Chiho,Suh, Sung-Bu,Seo, Jinseok,Park, Yeong-Do 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.2
With using adaptive control of the resistance spot welding machine, the advantage on electrode life time for galvanized steels has been addressed. This study was aimed to evaluate the electrode life time of galvanized steels with applying the constant current control and the adaptive control resistance spot welding process for a comparison purpose. The growth in diameter of electrode face was similar for both the constant current and the adaptive control up to 2000 welds. The button diameter was decreased with weld numbers, however, sudden increase in button diameter with use of the adaptive control after 1500 welds was observed. The peak load was continuously decreased with increasing number of welds for both the constant current and the adaptive control. The current compensation during a weld was observed with using the adaptive control after 1800 welds since the ${\beta}$-peak on dynamic resistance curve was detected at later weld time. The current compensation with adaptive control during resistance spot welding enhanced the nugget diameter at the faying interface of steel sheets and improved the penetration to thinner steel sheet.
Al 5052 합금의 저항 점 용접 시 가압력 제어에 따른 용접부 특성 비교
김원호(Wonho Kim),김재훈(JaeHun Kim),전현욱(HyunUk Jun),천주용(JooYong Cheon),이은경(Eunkyung Lee),지창욱(Changwook Ji) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
자동차의 배기가스 및 연비 규제가 심화됨에 따라 자동차 연료의 효율 증대 및 배출 가스 저감 등을 목적으로 자동차의 경량화가 지속적으로 요구되고 있다. 자동차에 적용되는 경량 소재는 알루미늄 합금, CFRP(Carbon Fiber Reinforced Plastic), 마그네슘 합금이 존재하며, 그중 알루미늄 합금은 높은 신뢰성과 효율성으로 자동차의 차체에 광범위하게 적용되어 사용되는 추세이다. 그러나 알루미늄 합금의 저항 점 용접 시, 알루미늄 표면에 분포하는 Al2O3 산화층 및 높은 열전도도와 전기전도도, 660 °C의 낮은 융점과 같은 고유한 소재 특성으로 인해 용접부 내부의 기공과 수축공으로 인한 용접품질을 열화 시키는 문제가 지속적으로 초래되고 있다. 이와 관련되어 예비 통전, 용접 시간에 따른 용접성 평가, 전극 표면 가공을 통한 품질향상 연구들이 활발하게 이뤄지고 있으나, 가압력 제어를 통한 용접성 특성 및 영향에 대해서는 연구가 미진한 실정이다. 따라서 본 연구에서는 용접부 내부에 발생되는 결함 감소 및 용접품질 향상을 목적으로 용접 가압력에 변수를 두고 선 가압(Pre-force) 및 후 가압(Post-force), 선 가압과 후 가압을 결합한 다단 가압(Multi-force) 등을 적용하여 너겟경의 크기와 용접부 내부에 발생되는 결함 분포 양상을 비교·고찰해보았다.
Hyun-Uk Jun(전현욱),Jae Won Kim(김재원),Jae-Hun Kim(김재훈),Kwang-Weon Lee(이광원),Jooyong Cheon(천주용),Changwook Ji(지창욱) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.1
This study investigate the effect of weld mechanical properties and the failure mode on the distance of misalignment that occurs during resistance element welding (REW) when the base sheet (steel plate) overlaps the cover sheet (aluminum plate). Differences exist in the tensile shear strength, cross tension strength, ductility ratio, and failure mode based on the distance of misalignment. The length of the nugget diameter is a major factor that influences the mechanical properties and failure mode in the REW. In addition, it is necessary to consider, the asymmetrical nugget shape derived from the abnormal current path which itself results from an increase in the misalignment distance, as well as the stress concentration generating mechanism resulting from the gap between the cover sheet and base material.