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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.
Acute Pulmonary Coccidioidomycosis and Review of Published Cases with Lung Involvement in Korea
Ji Hyun Oh,Hyo Shik Kim,Kyu-Tae Yoon,Yena Kang,Changwook Min,So-My Koo,Jung-Hwa Hwang,Ki-Up Kim 순천향대학교 순천향의학연구소 2015 Journal of Soonchunhyang Medical Science Vol.21 No.2
Coccidioidomycosis is a fungal infection caused by Coccidioides immitis. The endemic area is mostly south-western United States. As increasing in overseas travel to endemic areas, the incidence rate has been recently increased in non-endemic areas. The diagnosis may be delayed in non-endemic area. It is important to elicit traveling histories and to differentiate lung consolidation with eosinophilia, for timely diagnosis of coccidioidomycosis. Recently, we experienced a case with pulmonary coccidioidomycosis in a Korean American who visited Korea showed consolidation in right lower lobe on chest X-ray and prolonged eosinophilia. In the case, a confirmatory diagnostic method was percutaneous transthoracic needle biopsy of lung. We report acute pulomonary coccidioidomycosis case and review previous published reports with pulmonary manifestation in Korea.
( Maksudur Rahman ),( Siva Prasad Murugan ),( Changwook Ji ),( Yong Jin Cho ),( Joo-yong Cheon ),( Yeong-do Park ) 한국부식방식학회(구 한국부식학회) 2018 Corrosion Science and Technology Vol.17 No.3
Electrical Resistance Welding (ERW) on a longitudinal seam-welded pipe has been extensively used in oil and gas pipelines. It is well known that the weld zone commonly suffers from grooving corrosion in ERW pipes. In this paper, the grooving corrosion performances of API X65 grade non-sour service (steel-A) and API X70 grade sour gas resistant (steel-B) steel electrical resistance welding pipelines were evaluated. The microstructure of the bondline is composed of coarse polygonal ferrite grains and several elongated pearlites. The elongated pattern is mainly concentrated in the center of the welded area. The grooving corrosion test and electrochemical polarization test were conducted to study the corrosion behavior of the given materials. A V-shaped corrosion groove was found at the center of the fusion zone in both the steel-A and steel-B ERW pipes, as the corrosion rate of the bondlines is higher than that of the base metal. Furthermore, the higher volume fraction of pearlite at the bondline was responsible for the higher corrosion rate at the bondline of both types of steel.
The Resistance Spot Weldability of a Stainless Steel/Aluminium/Low Carbon Steel 3-Ply Clad Sheet
Siva Prasad Murugan,Muralimohan Cheepu,Vijeesh Vijayan,Changwook Ji,Yeong-Do Park 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.1
The present paper is aimed at investigating the resistance spot weldability of a 3-ply clad sheet comprised of stainless steel (SS), aluminium (Al) and low carbon steel (LCS). The weldability was assessed with the help of the weldable current range (WCR), the current range between the minimum current required to produce 4√t nugget diameter and a maximum current at which expulsion occurs. However, electrode-sheet sticking was found as the limiting factor instead of expulsion. It was observed that the introduction of aluminium to the SS/LCS clad increased the weld current range by shifting the expulsion to higher current, but resulted in melting of the electrode and subsequent electrode-sheet sticking.
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.
Review on the Wire Arc Additive Manufacturing Process and Trends in Non-ferrous Alloys
Jae-Deuk Kim,Joo Yong Cheon,Changwook Ji 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.6
Owing to global trends, automation with the fourth industrial revolution, and environmentally friendly policies owing to certified emission reduction, wire arc additive manufacturing (WAAM) is attracting attention in various industrial fields. In addition, the demands of non-ferrous metals such as aluminum and magnesium alloys are attracting attention from industries that require lightweight, large, and complex metallic parts that can be fabricated through WAAM. In this study, additive manufacturing (AM), WAAM, and current issues on the WAAM of non-ferrous metals particularly aluminum and magnesium alloys are discussed.
Nazmul Huda,Jae Won Kim,Changwook Ji,Dae-Geun Nam,Yeong-Do Park 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.1
The optimal parameters for joining two different titanium alloys were determined by the Taguchi method and applied in similar and dissimilar joining of conventional Ti-6Al-4V and newly developed Ti-3Al-2.5V alloys. The microstructures of the two alloys and their mechanical properties were comparatively evaluated at the optimal parameters. The Ti-6Al-4V alloy showed a larger back bead width than that of Ti-3Al-2.5V under similar heat input, because of its lower thermal conductivity and higher specific heat capacity. The welded zone of Ti-3Al-2.5V contained a retained beta phase, which was absent in that of Ti-6Al-4V. This indicates that the transformation of the Ti-3Al-2.5V weld metal starts above the martensite temperature, while it starts below the martensite temperature for Ti-6Al-4V. The failure of the welded specimen occurred in the base metal for both the titanium alloys, which indicates the superior weld quality. However, the welded Ti-6Al-4V showed superior tensile strength to that of the Ti-3Al-2.5V weld under optimal conditions, owing the high beta phase fraction in its base metal. Meanwhile, it showed inferior ductility to that of Ti-3Al-2.5V because of its coarser beta phase.
Decreased Maximal Tongue Protrusion Length May Predict the Presence of Dysphagia in Stroke Patients
Hyunchul Cho,Jeong Se Noh,Junwon Park,Changwook Park,No Dam Park,Jun Young Ahn,Ji Woong Park,최윤희,천성민 대한재활의학회 2021 Annals of Rehabilitation Medicine Vol.45 No.6
Objective To investigate the relationship between maximal tongue protrusion length (MTPL) and dysphagia in post-stroke patients.Methods Free tongue length (FTL) was measured using the quick tongue-tie assessment tool and MTPL was measured using a transparent plastic ruler in 47 post-stroke patients. The MTPL-to-FTL (RMF) ratio was calculated. Swallowing function in all patients was evaluated via videofluoroscopic swallowing study (VFSS), Penetration-Aspiration Scale (PAS), Functional Oral Intake Scale (FOIS), and Videofluoroscopic Dysphagia Scale (VDS).Results The MTPL and RMF values were significantly higher in the non-aspirator group than in the aspirator group (MTPL, p=0.0049; RMF, p<0.001). MTPL and RMF showed significant correlations with PAS, FOIS and VDS scores. The cut-off value in RMF for the prediction of aspiration was 1.56, with a sensitivity of 84% and a specificity of 86%.Conclusion There is a relationship between MTPL and dysphagia in post-stroke patients. MTPL and RMF can be useful for detecting aspiration in post-stroke patients.