Principles of Operation:

Shielded Metal Arc welding is by far the most broadly used of the several arc welding procedure. It employs the heat of the arc to melt the base metal and the tip of a consumable covered electrode. The electrode & the work are part of an electric circuit shown in Figure 3. This circuit start with the electric power source and includes the welding cables, a workpiece connection, an electrode holder,  the workpiece (weldment), and an arc welding electrode. One of the two cables through the power source is associated to the work. The other is assiciated to the electrode holder.

Welding commences while an arc is struck among the tip of the work and the electrode. The intense heat of the arc melts the tip of the electrode and the surface of the work close to the arc. Tiny globules of molten metal quickly form on the tip of the electrode, then transfer from the arc stream into the molten weld pool. In this, filler metal is deposited as the electrode is progressively consumed. The arc is moved on the work at a suitable arc length and travel speed, melting and fusing a part of the base metal and constantly adding filler metal. As the arc is one of the hottest of the commercial sources of heat (temperatures above 5000ºC have been calculated at its centre), melting of the base metal occur almost instantaneously upon arc initiation. If welds are build in either the flat or the horizontal location, metal transfer is induced by the force of gravity, electric , gas expansion, electromagnetic forces and surface tension. For welds in other location, gravity works against the other forces.

The process needs sufficient electric current to melt both the electrode and a correct amount of base metal. It also needs an suitable gap between the tip of the electrode and the base metal or the molten weld pool. These requirements are essintial to set the stage for coalescence. The sizes & types of electrodes for shielded metal arc welding describe the arc voltage requirements (within the total range of 16 to 40 V) and the amperage requirements (within the total range of 20 to 550 A). The current might be either alternating or direct, based upon the electrode being utilized, but the power source might be able to control the level of current in a reasonable range in order to respond to the complex variables of the welding procedure itself.