Fujii, Hidetoshi

Lu, Shanping

Nogi, Kiyoshi

Sato, Toyoyuki

A new type of TIG welding has been developed, in which an ultra-deep penetration (10mm for one pass) is obtained. In order to control the Marangoni convection induced by the surface tension gradient on the molten pool, He gas containing a small amount of oxidizing gas was used. The effect of the concentration of O₂ and CO₂ in the shielding gas on the weld shape was studied for the bead-on-plate TIG welding of SUS304 stainless under He-O₂ and He-CO₂ mixed shielding gases. Because oxygen is a surface active element for stainless steel, the addition of oxygen to the molten pool can control the Marangoni convection from the outward to inward direction on the liquid pool surface. When the oxygen content in the liquid pool is over a critical value, around 70ppm, the weld shape suddenly changes from a wide shallow shape to a deep narrow shape due to the change in the direction of the Marangoni convection. Also, for He based shielding gas, a high welding current will strengthen both the inward Marangoni convection on the pool surface and the inward electromagnetic convection in the liquid pool. Accordingly, at a welding speed of 0.75mm/s, the welding current of 160A and the electrode gap of 1mm under the He-0.4%O₂ shielding, the depth/width ratio reaches 1.8, which is much larger than for Ar-O₂ shielding gas (0.7) and Ar shielding gas (0.2). The effects of the welding parameters, such as welding speed and welding current, were also systematically investigated. In addition, a double shielding gas method has been developed to prevent any consumption of the tungsten electrode. along the heating line, the inherent deformation of smaller plates, with the same thickness and formed under the same heating and cooling conditions, can be accurately and easily predicted

Osaka University Knowledge Archive

Effect of Oxygen Content in He-O₂ Shielding Gas on Weld Shape in Ultra Deep Penetration TIG

https://ir.library.osaka-u.ac.jp/repo/ouka/all/6051/jwri37_01_019.pdf

Effect of Oxygen Content in He-O₂ Shielding Gas on Weld Shape in Ultra Deep Penetration TIG

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