The current in electric resistance welding can be regulated by Changing the primary turns of the transformer.

The electrodes are one of the most important factors in the resistance welding process but often the most abused. It is important to consider the electrode material, shape, size, tip profile and cooling.
The electrodes used in spot welding have a tip of Copper.

Seam welding is a Continuous spot welding process.
seam welding is a variant of the basic resistance spot welding process.
In seam welding a series of overlapping nuggets is produced, usually by replacing the conventional spot welding electrodes by wheels that turn as the parts to be welded are fed between them.

Projection welding is a modification of spot welding.
In this process, the weld is localized by means of raised sections, or projections, on one or both of the workpieces to be joined.