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전기선폭발법으로 제조된 텅스텐 분말의 산소 조성이 방전플라즈마소결 거동에 미치는 영향
김철희,이성,김병기,김지순,Kim, Cheol-Hee,Lee, Seong,Kim, Byung-Kee,Kim, Ji Soon 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.6
Effect of oxygen content in the ultrafine tungsten powder fabricated by electrical explosion of wire method on the behvior of spark plasma sintering was investigated. The initial oxygen content of 6.5 wt% of as-fabricated tungsten powder was reduced to 2.3 and 0.7 wt% for the powders which were reduction-treated at $400^{\circ}C$ for 2 hour and at $500^{\circ}C$ for 1h in hydrogen atmosphere, respectively. The reduction-treated tungsten powders were spark-plasma sintered at $1200-1600^{\circ}C$ for 100-3600 sec. with applied pressure of 50 MPa under vacuum of 0.133 Pa. Maximun sindered density of 97% relative density was obtained under the condition of $1600^{\circ}C$ for 1h from the tungsten powder with 0.7 wt% oxygen. Sintering activation energy of $95.85kJ/mol^{-1}$ was obtained, which is remarkably smaller than the reported ones of $380{\sim}460kJ/mol^{-1}$ for pressureless sintering of micron-scale tungsten powders.
아연도금 강판의 $CO_2$ 레이저-TIG 하이브리드 용접에 관한 연구 Part 2 : 공정변수와 용접성과의 관계
김철희,최웅용,채현병,김정한,이세헌,Kim, Cheol-Hee,Choi, Woong-Yong,Chae, Hyun-Byung,Kim, Jeong-Han,Rhee, Se-Hun 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.4
Optimization of process parameters for laser-arc hybrid welding process is intrinsically sophisticated because the process has three kinds of parameters-arc, laser and hybrid welding parameters. In this paper, the relationship between weldability and several process parameters such as laser beam-arc distance, electrode height, welding current and welding speed, were investigated by the full factorial experimental design. Weld quality was evaluated by using weight of spatters which is related with the pore area. It was found that the weld quality was increased with the increases in laser beam-arc distance and welding current, and decreased with the increases in electrode height and welding speed.
김철희,채현병,이창우,김정한,이세헌,Kim, Cheol-Hee,Chae, Hyun-Byung,Lee, Chang-Woo,Kim, Jeong-Han,Rhee, Se-Hun 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.1
Laser-rotating arc hybrid welding was introduced by combining $CO_2$ laser and rotating gas metal arc welding. While the arc rotation enhances the weld pool motion, it reduces the undercut formation which is one of most critical weld defects in the conventional laser-arc hybrid welding. This research investigated the bead characteristics according to the welding parameters such as frequency of rotation, welding voltage, shielding gas composition and interspacing distance between laser and we. The welding parameters were selected to reduce spatter generation and ensure sound weld beads fur bead welding and butt welding with various joint gaps. Gap bridging ability was improved, such that the sound weld beads were achieved for butt joint with up to 2mm joint sap, with no adjustment of CTWD(Contact tip-to-workpiece distance) and electrode diameter.
아연도금 강판의 $CO_2$ 레이저-TIG 하이브리드 용접에 관한 연구 Part 1 : 용접현상분석
김철희,최웅용,채현병,김정한,이세헌,Kim, Cheol-Hee,Choi, Woong-Yong,Chae, Hyun-Byung,Kim, Jeong-Han,Rhee, Se-Hun 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.4
In lap welding of zinc-coated steel, porosity formation is one of most significant weld defects, which is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past years but development of more effective method is a worthwhile subject to be investigated. In this study, autogenous laser welding and laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without gap, and weld pool behaviors were observed by using high speed camera and the porosity generation mechanism was analyzed. The weld defects were successfully eliminated by laser-TIG hybrid welding. This is because the leading TIG arc partially melted the upper sheet and vaporized/oxidized the coated zinc on the lapped surfaces prior to the trailing laser illuminating the specimen.
Al 5052, 6061합금에 대한 플라즈마-GMA 용접공정특성 평가
김철희,안영남,최진강,이세헌,Kim, Cheol-Hee,Ahn, Young-Nam,Choi, Jin-Kang,Rhee, Se-Hun 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.6
In this study, the bead-on-plate welding were conducted by using GMA welding and plasma-GMA welding on Al 5052 and, Al 6061 plates. For these processes, the maximum welding speeds for full penetration were compared, and various weld qualities such as bead appearance, cross-section, cracks and porosities were examined. Faster welding speed, cleaner bead surface and more stable drop transfer could be achieved by plasma-GMA welding, compared with GMA welding.