| Summary: | A new welding method, flux bands constricting arc (FBCA) welding, is proposed to compensate for the shortage of insufficient weld width of laser welding T-joints in high steel sandwich panels. The arc behavior (arc burning position, arc shape, arc heat, and arc stability) before and after sticking the flux bands (GMAW and FBCA welding) to the ultra-narrow gap groove was tested. Results indicate that flux bands have solid-wall constricting effect (SWCE) and thermo-compression effect (TCE) on the arc and self-producing slag and gas function in FBCA welding. In ultra-narrow gap groove, the arc burning position climbing up phenomenon (APCP) occurs without flux bands. The SWCE of flux bands on the arc effectively suppresses the APCP because of the insulation of flux bands. In the FBCA welding process, the effective heating area of the arc is increased by at least 5 mm<sup>2</sup> compared with that in GMAW. When the groove gap decreases, flux bands not only compress the arc from an inverted bell shape to a rectangular shape, but also make the 660 °C isotherm on the core-plate to increase from 3 mm to 8 mm. In the end, the proportion of unstable arc burning time is reduced by 86.85%, the fluctuation of arc voltage and welding current are also significantly reduced by the flux bands because of their SWCE on the arc.
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