Shielding gas

About: Shielding gas is a research topic. Over the lifetime, 6697 publications have been published within this topic receiving 58668 citations.

Monopulse investigation of drop detachment in pulsed gas metal arc welding

Abstract: The drop detachment process in pulsed welding was investigated by a novel, non-continuous method. A pendent drop was formed on a fixed electrode by a low-current arc. The drop was then detached by a single high-current pulse. The detachment process was studied by high-speed filming and by current and voltage measurements. The shielding gas was Ar with various amounts of CO2, O2, H2 and He. Comparative experiments with ordinary pulsed welding were also done. The authors found ample evidence for an upward force on the pendent drop, most likely caused by the recoil force of evaporating metal. The force increases with CO2 concentration, base current and base current duration. The recoil force gives rise to a critical concentration of the molecular additive, above which it is impossible to detach the drop almost regardless of pulse width. This critical concentration decreases with increasing base current and base current duration. It also seems to decrease with increasing dissociation energy of the molecular additive. The drop velocity decreases with increasing CO2 concentration. For 95Ar5CO2 they also present results on the effect of drop mass and pulse current on drop velocity, minimum pulse width for detachment, and shortest detachment time (tdmin). They find evidence for a minimum detachable drop mass being smallest for large pulse currents. In the pulse current range 210-350 A they observe Ip1.7 tdmin=43, and in the range 350-600 A, Ip1.2 tdmin=2.4 (basic SI-units).

Marangoni convection and weld shape variations in He–CO 2 shielded gas tungsten arc welding on SUS304 stainless steel

Abstract: Bead-on-plate GTA welding (gas tungsten arc welding) on a SUS304 substrate is carried out to investigate the effect of carbon dioxide gas in the helium base shielding on the oxygen content in the weld pool and the weld shape variations. Experimental results show that small addition of carbon dioxide to the shielding gas can precisely adjust the weld metal oxygen content and change the weld shape from wide shallow type to narrow deep one when the weld pool oxygen content is over the critical value, which is from 68 to 82 ppm, due to the Marangoni convection reversal from the outward to inward mode on the pool surface. The weld depth/width ratio increases two times suddenly when the carbon dioxide content in the torch gas is over 0.4 or 0.2% for 1 mm or 3 mm arc length, respectively. The GTA weld shape depends to a large extent on the pattern and magnitude of the Marangoni convection on the pool surface, which is influenced by the active element oxygen content in the SUS304 pool, temperature coefficient of the surface tension (dσ/dT), and the temperature gradient on the pool surface (dT/dr, r is the radius of the weld pool surface). Changing the welding parameters will alter the temperature distribution and gradient on the pool surface, and thus, affect the magnitude of the Marangoni convection and the final weld shape.