チタンMIG(Metal Inert Gas)溶接におけるコンタクトチップ融着に及ぼす諸因子の影響について

概要

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A noble titanium welding wire for Metal Inert Gas Welding has been developed. The wire has oxygen-enriched surface layer which contributes to improve the arc stability and the regular droplet transfer in pure argon shielding gas. The shape and appearance of weld bead are excellent and the spattering is very few. However the meltback of contact tip is concerned during MIG welding process for titanium, because of the higher electric resistance of titanium. The effects of oxygen content of oxygen-enriched layer of welding wire, contact tip temperature, mean arc voltage and contact tip to work distance (CTWD) on meltback were investigated, while phenomenon of meltback was observed by digital high speed camera (4000 frames/sec). Meltback phenomenon was occurred along the following steps. a) Sparking was generated between titanium welding wire and inner surface of contact tip. b) Feeding of welding was stopped. c) The length of welding arc was increased very rapidly and finally the contact tip was burned off. The welding wire with higher oxygen content in oxygen-enriched layer showed stable arc voltage and did not generate meltback, although the welding wire with lower oxygen content in oxygen-enriched layer arc voltage was unstable and meltback was sometimes observed. The lower mean arc voltage and longer CTWD can provide stable arc and improve meltback phenomenon.