Cold welding is a bonding process where two items are combined into one through means of intense pressure that is applied by dies and rolls. As the name implies, this technique does not rely on heat to change the state of the items being bonded—these substances remain in a solid state throughout the procedure. Not all metals make ideal candidates for cold welding due to the oxygen content within their outer layers, and even after extended brushing and cleaning, the metals will not bond if one of them is not malleable. Likewise, if the two bonded pieces are later exposed to an oxygen-rich environment or certain other reactive compounds, the cold weld will fail. Due to these limitations, the process of cold welding is most suitable for objects that will be deployed outside of the earth’s atmosphere, such as satellites or spacecrafts.
Cold welding was initially discovered by modern societies in the early 1940s and thought of as a new phenomenon, but this process has actually been in existence for thousands of years. It was learned that two pieces of similar metals will bond together inside a vacuum as long as they possess clean, flattened surfaces and a strong initial force can be applied. During the process, deformities occur across 60 to 80% of the bonding surface, and this allows pure, clean metals to come in contact. Permanent bonding then takes place on the atomic level, with welds much stronger than what could be accomplished by other means. Another advantage is that there are absolutely no intermediary materials used as a type of solder, so as long as oxides are not allowed to reform across the metal’s surface, it should last for decades.
Since the initial discovery period, researchers have shown that cold welding can also be accomplished without excessive force. By applying less pressure over a longer period of time, similar results can be achieved. Another method is to increase the surface temperature of the two materials being bonded for a short period of time to accelerate the molecules.
Modern uses for cold welding are numerous, but it is still definitely considered a situational process due to the aforementioned limitations. The technique makes it possible, however, to work in many hostile environments that were previously impossible, like welding underground pipelines that carry flammable gasses. Another setback is that since the weld takes place quickly and is considered permanent, it is very difficult to verify the integrity of the weld, especially in thicker metals.