African Fusion November 2017

Figure 7: The depth of sidewall fusion for different helium content. arc lengthdecreases, the arc root on the sidewall decreases and the heat of the arc at the sidewall reduces, therefore the sidewall fusion depth drops slightly. The change seen in sidewall penetration is consistent with that of the arc shape. The depth is the largest when the helium content is 25%, but undercutting defects occur. Conclusions 1. With increasing helium content, the arc core expands and the welding voltage increases if the current and arc length are held constant. 2. For constant voltage welding, the current decreases as helium con- tent increases. When the shielding gas composition used for welding changes, the arc works at a new equilibrium position to keep the wire-melting rate equal to the wire feed speed. 3. Theweldbeadprofile transforms fromfinger-shaped tobowl-shaped, and the depth of sidewall fusion increases as the helium content increases. Helium can, therefore be added to the shielding gas used for narrow gap welding to ensure sidewall penetration. References 1. MTanaka, STashiro, TSatoh, ABMurphy, JJ Lowke: Influenceof shielding gas composition on arc properties in TIGwelding. Science and Technol- ogy of Welding and Joining, 13, 225-231 (2008). 2. J Zähr, U Fussel, MHertel, M Lohse, M Sende, M Schnick: Numerical and experimental studies of the influence of process gases in TIG welding. Weld in The World, 56, 85-92 (2012). 3. HY Huang: Effects of shielding gas composition and activating flux on GTAW weldments. Materials Design, 30, 2404-2409 (2008). 4. LL Wang, FG Hu, HP Wang, AB Murphy, XH Tang: Effects of shielding gas composition on arc profile and molten pool dynamics in gas metal arc welding of steels. Journal of Physics D: Applied Physics, 47: 465202 (2014). 5. ZH Rao, J Hu, SM Liao, HL Tsai: Modelling of the transport phenomena in GMAW using argon-helium mixtures. Part I - The arc. International Journal of Heat and Mass Transfer, 53, 5707-5721(2010). 6. ZH Rao, J Hu, SM Liao, HL Tsai: Modelling of the transport phenomena in GMAWusing argon-heliummixtures. Part II - Themetal. International Journal of Heat and Mass Transfer, 53, 5722-5732 (2010). 7. SA Urmston: Effect of shielding gas composition on transfer and fusion characteristics in P-GMAW of carbon steels. Cranfield University, Cran- field (1985). 8. L Theocharis: Tandemgasmetal arc pipelinewelding. CranfieldUniver- sity, Cranfield (2007). 9. AB Murphy, M Tanaka, S Tashiro, T Sato, JJ Lowke: A computational investigation of the effectiveness of different shielding gas mixtures for arc welding. Journal of Physics D: Applied Physics, 42, 115205 (2009).

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November 2017

AFRICAN FUSION