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Tuesday, June 3, 2008 - 9:05 AM

Mechanism of Metal Transfer in Double-Electrode GMAW

K. Li, ESAB North America, Florence, SC; C. Wu, Institute of Materials Joining, Shandong, China

Double-Electrode GMAW (DE-GMAW) is a novel welding process targeting at high welding productivity. DE-GMAW was formed by adding another TIG torch (called bypass torch) to a conventional GMAW system. Except for the high productivity and low heat input, experiments also revealed that the critical current in DE-GMAW is decreased such that spray metal transfer can be obtained at a lower current level. This paper proposes a mechanism to explain the change on the metal transfer in DE-GMAW.

 

The metal transfer phenomena in DE-GMAW were studied with high speed camera. By adjusting the welding current, the critical current for spray metal transfer to occur in DE-GMAW was recorded and analyzed. Comprehensive experiments verified that the critical current in DE-GMAW was decreased. The arc forces including electromagnetic force, surface tension, gravity force, and plasma stream force, etc, are mathematically analyzed and compared. It was found the bypass arc in DE-GMAW not only provides a second loop for the welding current, but also increases the angle of the current conduction zone in the anode. The enlarged angle significantly increases the electromagnetic force, which plays a very important role in metal transfer. Because of this increased electromagnetic force, the spray metal transfer can be achieve with a low welding current, at the same time, the dissymmetric electromagnetic force acts on the arc root and pushes the droplets away from the axis of the welding wire.


Summary: Double-Electrode GMAW (DE-GMAW) is a novel welding process targeting at high welding productivity. DE-GMAW was formed by adding another TIG torch (called bypass torch) to a conventional GMAW system. Except for the high productivity and low heat input, experiments also revealed that the critical current in DE-GMAW is decreased such that spray metal transfer can be obtained at a lower current level. This paper proposes a mechanism to explain the change on the metal transfer in DE-GMAW.