Numerical Simulation of Heat Source Characteristics in Arc Spot Welding with Constricted Nozzle

** , TANAKA Manabu *** , MURATA Akihisa **** and MURATA Tadasuke **** Two-dimensional axisymmetric simulation was carried out to investigate heat source characteristics during an arc spot welding with a constricted nozzle. As a result, it was clarified that a part of the welding current flowed from a cooling nozzle which was an anode to a tungsten cathode directly. The temperature increase of the cathode tip was suppressed by the decrease of the Joule heating at the tip because of this separation of the current path. Comparing temperature and heat input density distributions on a base metal surface with a conventional tungsten inert gas (TIG) welding, there was no difference in the temperature on the central axis of the tungsten cathode, but the peak of the heat input density during the arc spot welding was lower than that in the TIG welding. In addition, the heat input range was narrower than that in the TIG welding by a cooling nozzle contacting the base metal. It was also clarified that the heat input to the base metal surface and the temperature increase of the tungsten electrode were suppressed by the nozzle. Inner gas flowing from the constricted nozzle cooled the outer edge of the arc plasma, suggesting that it contributed to the long lifetime of the tungsten electrode.