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Abstract.A new technology of MIG MAG welding control is developed. Authors introduce use of power AC and pulse feed of welding wire in the arc zone, that downsizes the heat affected zone, stabilizes formation of electrode metal droplets, as external magnetic field's effect on the arc is reduced. Principal criteria for electrode metal transfer control, when powered by AC sources, are specified. IntroductionConditions of the arc, if power AC supply, differ from conditions of the arc, if DC power supply. The active spot on the cathode changes voltage hundred times per second when a sinusoidal voltage frequency is 50 Hz. At the end of each half-cycle, sinusoidal voltage drops to zero; this diminishes the intensity of arc distance's electrical field. Consequently the gas ionization in the arc column diminishes and near-electrode spatial charge diffuses; that does not comply with the terms of arc stability [1]. However, alternating current arc welding has several advantages, i.e. absence of external magnetic field effect on the arc ensures its spatial stability; cathode's sputtering degrades the oxide layer during half-cycles when a product becomes the cathode. AC arc gives the best temperature fields distribution, which affects quality of microstructure and residual stresses of welded joints. In world practice, AC is used only when non-consumable electrode welding of aluminum metals and alloys, as well as arc welding with special purpose electrodes. The authors present a new technology of mechanized gas metal arc AC welding with a pulse wire feed for welding of steel structures in different spatial positions. This problem was considered by Paton B.E., Lebedev V.A., Mikitin Ya.I.