This is a drawing of the welding electrodes used for resistance spot welding. These assemblies consist of a hollow shank, with water tubes inside, and a welding cap on the end.

Two of these are used to clamp the sheet metal with 600-1200 pounds of force. Then 8,000-12,000 amps of electricity is forced through the metal. Click here to view a simulation. This develops only about one volt across the metal, but it generates 10,000 watts of power, which melts the metal. Aluminum welding may use twice this current.

The upper one is the "old fashoned" kind, which has better cooling flow, whereas the lower one is the "heavy duty" type, with more copper at the taper that holds the cap. Many people drill out the new type, as the old type are not easily available. This gives better water cooling, which is very important in the welding process.

This is best viewed at 800 x 600 resolution, but if you want to see it at 640 x 480 click here.

Scroll the text upward to get a better view.