Shielded Metal-arc Welding (SMAW) is the simplest and used for many joining processes. More than 50% of industrial and maintenance welding currently is performed by this welding process. In this welding operation electric arc is generated by touching the tip of a coated electrode against the workpiece and withdrawing it quickly to a distance sufficient to maintain the arc as shown in picture below. The electrodes are in the shapes of thin, long rods that are held manually. The heat generated melts a portion of the electrode tip, its coating and the base metal in the immediate arc area. The molten metal consists of a mixture of the base metal, the electrode metal, and substances from the coating on the electrode, this mixture forms the weld when it solidifies. The electrode coating de-oxidizes the weld area and provides a shielding gas to protect it from oxygen in the surroundings. A bare section at the end of the electrode is clamped to one terminal of the power source, while the other terminal is connected to the workpiece being welded. The current may be either DC or AC usually in the range of 50 to 300 A.
For sheet-metal welding, DC is suitable because of the steady arc it produces. Power requirement is generally less than 10 kW.
The shield Metal-arc welding process has the advantages of being relatively simple and requiring a smaller variety of electrodes. The equipment consists of a power supply, cables, and an electrode holder. The shield metal-arc welding process commonly is used in general construction, shipbuilding, pipelines and other maintenance work. It is mainly useful for work in remote areas where a portable fuel-powered generator can be used as the power supply. shield metal-arc welding is best suited for work piece of thickness 3 to 19 mm, although this range can be extended easily by skilled operators using multiple-pass techniques as shown in picture. The multiple-pass approach requires that the slag be removed after each weld bead. Unless removed fully, the solidified slag can cause severe corrosion of the weld area and lead to failure of the weld but it also prevents the fusion of welded layers. Before applying another weld, the slag should be removed completely by using wire brushing or weld chipping.