Shielded Metal Arc (SMA) Welding
• Shielded Metal Arc Welding (SMAW) is a welding process in which coalescence of metals is produced by heat from an electric arc maintained between the tip of a consumable electrode and the surface of the base metal in the joint being welded.
• This is the most commonly used arc welding process, the equipment is cheap, welder has more freedom of movements, and it is possible to weld a wide variety of metals by changing only the electrode type.
4.1 PRINCIPLE OF OPERATION
• The electrode and the work are part of an electric circuit. Two cables come out from the power source. One is connected to the workpiece and the other to the electrode holder. Welding commences as an arc is struck between the tip of a consumable electrode and the workpiece region where welding is needed. Arc temperature is of the order of 5000°C. Melting of the workpiece and electrode tip occurs instantaneously. Process requires sufficient electrical energy to melt the electrode and proper amount of base metal. Metal droplets from the electrode are transferred to the weld pool and the electrode moves along the line of welding and is fed to the pool at a rate at which it is consumed to maintain a consistent arc length. Electrode melting rate depends upon the welding parameters used, electrode size, covering ingredients, polarity used etc. Shielded metal arc welding operating variables will now be discussed.