Cold welding uses pressure applied to the workpieces in dies or rolls. It is important that both surfaces are mutually soluble, that intermetallic compounds do not weaken the joint. When pressure is applied through rolls the process is called roll bonding. This is the technique used to manufacture the U.S. quarter. Here two outer layers of 75% copper-25% nickel are bonded to an inner layer of pure copper. To obtain the desired bond strength, the mating surfaces are chemically cleaned and wire-brushed a common requirement.
And Furthermore . . .
Explosive Welding Forge Welding