고생산성 TIG용접에서 C형 단면 용가재의 금속이행현상에 관한 연구

Abstract

TIG (Tungsten Inert Gas) welding is used industry-wide as it is able to secure outstanding welding quality on almost all materials. Additionally, the welding method helps maintain clean work environment without spatter, fume, and slag. Furthermore it shows excellent qualities in terms of health, safety, and environment or HSE compared with other welding processes. However, despite all the advantages, TIG welding has one issue: lower welding productivity. In typical TIG welding, increased filler metal feeding enables productivity improvement. Consequently, melting filler metal necessitates higher welding current. In the process, the molten pool depression caused by high arc pressure occurs giving rise to defects such as undercut, humping bead which results in difficulties in improving productivity. The study suggests a filler metal type appropriate to high-productivity TIG welding by providing a new perspective on arc for the purpose of improving productivity of TIG welding. To attain the goal, the author measured the diameter of arc by recording the arc zone after changing arc length, welding current, and shielding gas. Afterwards, by defining effective arc diameter, it presents C type filler metal. To observe what happens when newly designed C type filler metal is applied to TIG welding with high current, recording and monitoring for the voltage were carried out. Depending on the feed height of filler metal the fluctuation of bead surface, transfer, and voltage was researched. Transfer modes are divided into continuous bridging transfer and intermittent bridging transfer followed by their modelling. To figure out the problem arising from the nickle-based alloy welding, surface tension and specific resistance affecting the metal transfer were reviewed by observing nickel-based alloy GMAW droplet transfer. To address the issue, the study applies TIG welding with high current using C type filler metal to nickel-based alloy butt welding, the result of which is a good macro section. In butt welding of thick plates, improving productivity and reducing welding cost are possible by decreasing cross-sectional area by developing a manufacturing process for narrow gap welding. Several welding experiments were conducted on carbon steel, STS316L, 9Cr1Mo steel, alloy 625 materials, resulting in seamless bead appearance and flawless macro section. The effectiveness of developed manufacturing process was validated by measuring the average melting depth, the length from groove face to fusion line, and standard deviation.