Have you ever thought why weld bead shape/geometry varies with change in certain parameter?
Today, in very brief, mechanism of generation of arc force is explained.
Electrical current flow generates magnetic fields that interact with current carriers and produce body Lorentz forces. These forces have only a radial component for a cylindrical arc, inducing higher pressure in the arc. If the arc has a variable radius, as welding arcs do, the pressure will have a gradient along the arc axis. Since the diameter of the arc column increases toward the workpiece, the pressure decreases along the length of the arc. The arc plasma flows from the high-pressure region to the adjacent low-pressure regions. High current will likely result in a more intense plasma jet and a higher arc force. This plasma jet impinges on the weld pool, and at high welding currents may produce a depressed pool surface.
In GTAW process Arc force and its distribution depend on electrode tip angle, arc length, and shielding gas type as well, so the threshold arc current (means where weld pool depression is observed maximum) for pool depression varies for different welding conditions and materials. As current increases, the pool surface depresses with greater arc forces.
Reference: A Study of Arc Force, Pool Depression, and Weld Penetration During Gas Tungsten Arc Welding
Keep reading, Happy welding