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440 MPa급 도금강판의 저항 점 용접 시 AC 및 MFDC전원에 따른 가용전류구간 비교 연구
지창욱,박찬수,김치호,조용준,오동진,김명현,김양도,박영도 대한용접접합학회 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 kA) 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 mm) required lower current of 0.6 kA 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.
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.
Effects of surface coating on weld growth of resistance spot-welded hot-stamped boron steels
지창욱,조일국,이현주,최일동,김양도,박영도 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.11
Aluminum-silicon-based and zinc-based metallic coatings have been widely used for hot-stamped boron steel in automotive applications. In this study, resistance spot weldability was explored by investigating the effects of the properties of metallic coating layers onheat development and nugget growth during resistance spot welding. In the case of the aluminum-silicon-coated hot-stamped boron steel,the intermetallic coating transformed into a liquid film that covered the faying interface. A wide, weldable current range was obtainedwith slow heat development because of low contact resistance and large current passage. In the case of the zinc-coated hot-stamped boronsteel, a buildup of liquid and vapor formation under large vapor pressure was observed at the faying interface because of the high contactresistance and low vaporization temperature of the intermetallic layers. With rapid heat development, the current passage was narrowbecause of the limited continuous layer at the faying interface. A more significant change in nugget growth was observed in the zinccoatedhot-stamped boron steel than in the aluminum-silicon-coated hot-stamped boron steel.
고융점 금속의 미소형상 정밀주조를 위한 탄소몰드의 적용성에 관한 연구
지창욱,이은주,김양도,임영목,Ji, Chang-Wook,Yi, Eun-Ju,Kim, Yang-Do,Rhyim, Young-Mok 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.2
Carbon material shows relatively high strength at high temperature in vacuum atmosphere and can be easily removed as CO or $CO_2$ gas in oxidation atmosphere. Using these characteristics, we have investigated the applicability of carbon mold for precision casting of high melting point metal such as nickel. Disc shape carbon mold with cylindrical pores was prepared and Ni-base super alloy (CM247LC) was used as casting material. The effects of electroless Nickel plating on wettability and cast parameters such as temperature and pressure on castability were investigated. Furthermore, the proper condition for removal of carbon mold by evaporation in oxidation atmosphere was also examined. The SEM observation of the interface between carbon mold and casting materials (CM247LC), which was infiltrated at temperature up to $1600^{\circ}C$, revealed that there was no particular product at the interface. Carbon mold was effectively eliminated by exposure in oxygen rich atmosphere at $705^{\circ}C$ for 3 hours and oxidation of casting materials was restrained during raising and lowering the temperature by using inert gas. It means that the carbon can be applicable to precision casting as mold material.
자동차 차체용 1.8기가급 핫스탬핑 강판 도금층 및 용접특성분석
지창욱,김재훈,전현욱,김재원 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
최근 연비 및 C02배출저감으로 인하여 자동차 산업에서 연비와 안정성을 동시에 향상시키기 위하여 차체의 경량화가 요구되어, 특히 보론강과 같은 초고강도강 (Ultra High Strength Steel)의 적용이 급격히 증가하고 있다. 핫스탬핑 보론강 (hot stamping boron steel)은 1500 MPa 급 이상의 초고강도 소재로 스프링백 및 두께 감소로 인한 경량화를 동시에 만족하는 장점을 지니고 있다. 또한 Al-Si 도금된 핫스탬핑 보론강은 자동차 차체 부품 중 충격 특성을 필요로 하는 범퍼 빔, A-필러(pillar)와 B-필러 등 부품 소재에 흔히 적용되고 있다. 또한 경량화율을 높이기 위해 1800 MPa급의 Al-Si 도금의 핫스탬핑 보론강판의 개발이 진행되고 있는 중이다. Al-Si 도금된 핫스탬핑 보론강은 고온의 열처리 공정을 거치기 때문에 도금층 두께 및 구조, 물성은 기존의 아연 도금 강판의 특성과는 차이가 존재한다. 복잡한 합금화층 및 소재의 높은 강성으로 인하여 도금층이 용접부에 혼입될 경우 용접부 물성에 좋지 않은 영향을 미친다. 본 연구는 1.8기가급 핫스탬핑 보론강판의 도금층에 대해서 분석하였고, 저항용접과 레이저 용접의 특성에 대하여 비교·분석해보았다.