Abstract
Arc efficiencies of gas tungsten arc welding (GTAW) were measured using two different methods, liquid nitrogen calorimetry and water-cooled copper anode calorimetry, across a range of welding currents from 98 A to 302 A. Arc efficiencies determined with water-cooled copper anode calorimetry remained constant throughout the entire current range, while those measured with liquid nitrogen calorimetry exhibited a concave curve. A hypothesis was proposed to explain the changes in arc efficiency with varying welding currents. Accordingly, a decrease in arc efficiency at 149 A welding current was caused by reduced Joule heating due to increased electrical conduction from iron-vapor contamination in an arc. For welding currents above 227 A, a decrease in arc efficiency was attributed to increased penetration depth, leading to more uniform heating in the base metal beneath the arc column, thereby preventing heat conduction within the metal. Thereafter, the relationship between penetration depth and arc efficiency was experimentally confirmed. Comparing with the arc efficiency of gas metal arc welding (GMAW), it was found that the mechanism in which arc efficiency changes with welding current in GTAW was different from that in GMAW.
