Cold welding is the process of bonding two objects together without heat and without any melting taking place. It is totally opposite of traditional welding as the two objects do not change state as they combine into one. Objects that are cold welded combine through the application of intense pressure of a vacuum force.
Many people are unfamiliar with cold welding. This is not surprising because it is no at widely used method. There is good reason for this. Oxygen is the nemesis of the cold welding process. Objects that have any layers containing oxygen or that are exposed to an oxygen-rich environment will not bond together with cold welding or if they do, the cold weld will not hold for long. Because of this, welding involving intense heat is generally the preferred method for items within the oxygen-rich environment of the Earth's atmosphere.
Cold welding does have its place though. It is often applied as a part of the process of bonding materials together to form objects that are designed to operate in space, outside of Earth's atmosphere, such as satellites and crafts used to travel through space. These objects will not be exposed to an oxygen-rich environment and a cold weld will likely help them last longer than a traditional heat weld. The process of cold welding can also be applied to certain types of electrical connections with success as well and is utilized in this manner to some extent.
In reality though, there are few metals that respond to a cold weld. These metals must be nonferrous in nature and contain no carbon. The most common metals that are cold welded are aluminum and copper, although there are others that respond successfully to the process as well. Cold pressure welding has been discovered to be the best method for joining copper to aluminum without brittle inter-metallic compounds forming as occurs with traditional heat welds. The quality of the weld created by cold pressure creates a superb bond because it produces a worked structure as opposed to the cast structure obtained in fusion welding. Additionally, there is no area on the object that has been negatively affected by heat. However, it is very important to keep in mind that care has to be taken to keep items that are cold welded protected until they are able to be placed into space or their functional environment.