Shielding gas in GMAW has significant effects on the metal transfer, the arc stability, the wetting of the base metal, the amount of surface slag and spatter. Pure Ar and mixture of Ar and $CO_2$ gas are used to obtain the spray transter and to increase the arc stability. AMAG(Auxiliary Metal Active Gas) torch system is proposed in this thesis to save Ar gas and to enhance the arc stability. The performance of AMAG torch is compared with that of DMAG(Double Metal Active Gas) and conventional GMA torch. Numerical calculation was performed to obtain Ar composition around electrode tip in DMAG. The calculated results showed similar trends with the experimental data using gas chromatography. Gas composition of AMAG is also measured and Ar composition of AMAG is found to be higher than that of DMAG. Weld quality of AMAG using 30% Ar is also enhanced compared with that of DMAG.
