Here's how the different welding processes work:
Two stationary pieces of metal overlap. A magnetic field forces the molecules to mash into each other, creating a metallurgical bond.
One piece of metal is stationary. The other piece spins. The two are brought together, and the friction creates intense heat, which joins them. It is comparable to a forging process.
Metal inert gas welding
Two pieces of similar metal are brought together. Electricity is passed through a wire, made of the same metal, that is put between the two parts to be joined. A spark melts the wire and joins the pieces.