For a given wire diameter, the deposition rate and depth of penetration both increase with increasing welding current. Excessive current causes the electrode wire to overheat causing arc instability, a deterioration in weld profile and, sometimes, undercutting. Below a minimum current level, arc instability will also occur giving arc wander and poor penetration.
The figure shows the welding current range for mild steel wires of diameter 1.6-6.0mm, together with deposition rates in kg/hr at the maximum and minimum welding currents using DCEP (Direct Current Electrode Positive) polarity. On DCEN (Direct Current Electrode Negative) polarity deposition rates are approximately 35% greater at any particular current. Welding current should be selected to give the penetration required.
For single pass procedures (and one pass either side procedures), the current should be sufficient to achieve the required depth of penetration without burnthrough. For multipass welding, the current should be selected to give the required weld bead size whilst also ensuring adequate fusion to the underlying material. In the case of circumferential joints, the selection of welding current will also be affected by the diameter of the workpiece.