The temperature of metal droplets is essential for clarifying the phenomenon of metal droplet transfer and the melting behavior of wire; also, it governs the emission of fumes. On the other hand, in-situ measurement of the temperature of a metal droplet formed at the tip of a wire during welding was difficult. Hence, this temperature was obtained in many experiences of measurements by such a way that several numbers of metal droplets were collected in a calorimeter to measure the amount of heat content of metal droplet and the heat was converted to temperature. With this way, however, the reliability of the measurement is not necessarily high because the heat loss of the metal droplet during the time when detaching from the wire tip and entering into the calorimeter has to be estimated properly. In this research, two-color pyrometry has been conducted to obtain the temperature of metal droplets, in which metal droplets have been photographed by high speed camera during arc welding, two wave lengths (950 and 980 nm) of light in the infrared range have been selected from the thermal radiation light emitted from the metal droplet at the instant of arc extinguishment by using an imaging spectroscope, and the temperature has been obtained from the intensity ratio of the two waves of light. Consequently, in CO2 arc welding, it has been revealed that the constricted arc causes high heat input density locally at the arc root portion of a metal droplet and thereby the arc root portion exhibits a higher temperature. By contrast, in MAG (80%Ar-20%CO2) arc welding, it has been disclosed that because the arc covers metal droplets, the temperature distribution in a metal droplet is relatively uniform and the average temperature is lower than in CO2 arc welding.
