SHIELDED METAL ARC WELDING (SMAW)
It also known as Manual Metal Arc Welding (MMAW). The heat required for welding is generated by the electric arc formed between metallic electrode and base metal. When the welder touches the plate to be welded with the electrode, immediately a high starting current flows which melts the tip of the electrode, thus initiating the welding arc. If the welder maintains the arc gap, the arc continues to remain stable and the arc heat melts the plate, electrode and the flux coating. The flux covering of the electrode melts in the arc heat and produces a large volume of gases and the slag. The gases cover the arc and shield it from reacting with the atmospheric air. The slag covers the molten metal pool until it solidifies. The slag can be removed after welding. The flux also provides filler metal with alloying elements to increase the strength of the weld joint. The electrode is consumed in the arc during welding. In SMAW, the electrode polarity i s chosen depending on the manufacturers recommendation, which is printed on the cover of the electrode pocket.
Shielded metal arc welding is the most common, versatile and least expensive one and accounts for nearly 25 % of total welding in developed countries and nearly 65 % of total welding in India. The electrode diameter varying from 1.6 mm to 6.3 mm and length varying from 250 mm to 450 mm. The power supply required for welding may be either a transformer or motor- generator or transformer - rectifier supplying AC or DC power. For achieving high quality welding, thyristor controlled or transistor controlled or inverter based power sources are employed. These latest solid state type of power sources is having feedback controls to deliver the controlled amount of voltage and current to the welding arc to achieve desired weld quality. The inverter power supplies are the latest technology and upto date power source. The main advantage of this power supply is the portability, lightweight and robust design. It can give required characteristics so that we can do SMAW, GTAW, GMAW, FCAW and gouging with the same power supply.