Cold welding involves joining two pieces of metal together using intense pressure and without the application of heat. Cold welding is a solid state process in which pressure at ambient temperature initiates coalescence between two metals. The pressure produces deformation until a desired state is reached. Cold welding is especially suitable for plastic materials (plastics and resins) and metals such as aluminum, copper, silver, nickel and iron. The most common application is with aluminum and aluminum with dissimilar metals, such as aluminum-copper. Cold welding is widely used in the aviation industry and electrical engineering, among other fields.
The first demonstration of cold welding was performed in 1724 when Reverend J L Desaguliers demonstrated that if two lead balls of approximately 25 mm (0.9 inches) were pressed and twisted together, they would form a bond. The joint results were erratic; however, the bonds were as strong as the original material from which they were made. It was not until the 1940’s that the phenomenon was studied with more detail. It was learned that if an initial intense force could be applied to two pieces of similar material inside a vacuum, they would join together. Permanent welding occurs on the atomic level and the bonds are much stronger than what could be achieved by other methods.
Scientists have discovered that cold welding can also be accomplished without the use of excessive pressure. Through the application of low pressure over longer periods of time, the same outcomes can be achieved. In practice, the bonding of two materials results almost impossible due to surface irregularities. In order to achieve the maximum cold welding results, any form of contamination must be reduced, while the area to be welded has to be amplified as much as possible. Another method involves accelerating the molecules of two materials by increasing their surface temperature.
In the 1950’s, General electric company (GEC) developed a simple way to join two pieces of non-ferrous together. The welding occurs by merely squeezing them together. The pressure alone is sufficient to produce homogenous bonds in copper, aluminum, zinc, lead, nickel and cadmium. The industrial potentials of cold pressure welding made it possible to produce armature conductors, wire joints, cable sheaths, airtight cans, among many others useful items without the use of ho-welding techniques. In addition, cold pressure welding made it possible to make metal unions which could not be possible by electrical welding.
Cold welding can be used to join together most non-ferrous wire, including copper and aluminum. Most ferrous materials contain carbon, which prevents the cold welding process to take place. Tests have been practiced using low carbon steel wire; however, heat has to be introduced for the cold weld to occur. Due to the costs and safety implications of this technique, it is more practical to use hot welding to join ferrous materials. Other cold pressure alloys can be made using brass, nickel, silver, zinc, gold and many others. Plated wire, such as nickel plate, silver plated and thinned copper can be welded to themselves or to plain copper.
Unlike macro-scale cold welding which usually requires the application of enormous pressures, a new technology involving nanowires with diameters of less than 10 nm can be used to cold-weld together by mechanical contact and low applied pressures. Through transmission microscopy (TEM), it has been demonstrated that the bonds at the Nano-scale are nearly perfect, with similar crystal orientation, strength and conductivity as the nanowire employed. Cold welding at the Nano-scale, performed between silver and gold and silver and silver, suggest that the technique can be generally applicable at the macroscopic cold welding scale.
Presently, cold welding has numerous applications in various industries, including electrical engineering, electronics and aerospace engineering. Cold welding is used for joining many metal objects, including wires, strips, rods, thin-walled pipes and non-metallic materials of sufficient plasticity, including plastics, resins and glass. Cold welding is favorably considered for use in space. According to nextbigfuture.com, cold welding of metals at the Nano-scale will play an important role in the in the manufacture of electrical and mechanical Nano devices.