The magnetic field introduced by the current flowing in the electrode also plays a role in metal transfer.
When the tip of the electrode melts, there are several forces that act at the molten tip. These include
surface tension, gravity, plasma jet and electromagnetic pinch force. Surface tensions tends to prevent
the detachment of the liquid drop at the electrode tip, irrespective of the welding position. Gravity
supports droplet detachment when welding in the flat (downhand) position and attempts to prevent it in
the overhead position. The plasma jet in most situations tries to detach and propel the molten drop
across the arc column to the workpiece.
The electromagnetic pinch force helps in the process of detaching the molten metal drops from the
electrode tip. Generally, when there is some necking between the molten tip and the unmelted
electrode, the magnetic field introduces a pinch force acting in both directions away from the neck
(Figure 1.8). This helps to separate the drop from the electrode. Since this pinch force increases as
the square of the current, smaller and smaller drops are detached as the current increases.