Although welding is usually associated with hot orange sparks and molten metal, several welding processes do not match this visual effect. One of the most remarkable welding processes is cold welding. It has been used at the industrial level for nearly a century and has several advantages over other welding processes.
Cold welding is a solid state welding process that joins two or more metals together with little or no heat. Instead, the energy used to hold the materials together takes the form of pressure. During cold welding, no metal is liquefied, even heated to a significant degree.
Cold welding binds two metals together without heating because the oxide layer is removed from the surface of the material being joined.
Under normal conditions, almost all metals have some type of oxide layer on them, although it may not be visible to the naked eye. These metal oxides form a barrier that prevents the metal atoms in the material from being pressed together and bonding to each other. Once the oxide layer is removed, however, the metal atoms are able to bond to each other under enough pressure.
Various mechanical and chemical methods are used to remove the oxide layer. Use wire brushes, degreasing and other techniques to ensure that the metal surface is free of oxides. Metals also have to have some toughness. Industrial machinery is then used to create the massive pressure required to produce metallurgical bonding.
One of the most common examples of cold welding is when joining dissimilar metals. That’s because when different metals melt together, they don’t stick together very well. This can cause metals to fail to join together, or lead to weak or cracked welds. Cold welding avoids this problem because it relies entirely on atomic bonds formed through free electrons.
Typically, cold welding is used to create butt or lap joints. Industries include aerospace, automotive, advanced manufacturing applications, and laboratory experiments typically use cold welding. It is also often used to join wires together.
Since ductile materials are usually required, metals commonly used for cold welding include:
Aluminum (including 7XXX series and other non-welding grades)
Carbon-based metals cannot be cold welded.
One of the biggest advantages of cold welding is that there is no heat affected zone. This reduces the risk of negative chemical and mechanical changes to the base material during the welding process. Another key advantage is the ability to join dissimilar metals, as mentioned above. Also, if cold welding is performed correctly it creates a weld at least as strong as the weakest parent material.
The primary disadvantage of using cold welding is that the materials must be extremely clean and oxide free to create a satisfactory weld. This can be difficult to do, and it can also be expensive and hard to implement in a high-volume scenario. Since at least one of the metals must be ductile, cold welding is also limited by what alloys can be joined together.