1.3.1 Arc Efficiency
The welding arc provides the intense heat needed to locally melt the workpiece and the filler metal. In
fact, all the electrical energy supplied by the power source is converted into heat (current x voltage).
Some energy is lost in the electrical leads, and therefore the energy available for welding is the product
of the current (I) and voltage drop between the electrode where the current enters it and the weld pool
(V). For example, with 400 A current and 25 V drop from the contact tip to the weld pool, the arc
energy is 10,000 Joules/second. This arc energy is partly used up in heating the electrode, melting the
consumable electrode or the separately added filler metal in a nonconsumable electrode process, and
heating and locally melting the workpiece. The rest of the heat is lost by conduction, convection,
radiation, spatter, etc. The proportion of the energy that is available to melt the electrode/filler metal and
the workpiece is termed the arc efficiency.
The arc efficiency for some of the commonly used arc welding processes varies between 20% and 90%.
For a given process, factors like welding in a deep groove, arc length, etc. also influence the arc
efficiency. Higher arc efficiency usually means that for a given arc energy, a greater amount of weld
metal is deposited and the workpiece cools at a comparatively slower rate.