Introduction to Cold Welding
Cold welding does not rely on the heat or thermal power associated with other forms of welding. Most welding processes work when we heat the metals to their melting point to affix them together. Heat or thermal techniques include ultrasonic welding, friction welding, laser welding, or arc welding.
Not all metals need heat or fusion for the welding process to take place. Cold welding is a process where metals are joined without heat. The method uses solid-state welding, where no molten or liquid phase is present in the joining process. Cold welding is also called contact welding or cold pressure welding.
Cold Welding is Frequently Used to Weld Electrical Parts. It is Particularly Useful When Joining Wires in Space
History
Cold welding has centuries of history. Researchers have found that cold welding was even present in the Bronze Age. The first official experiment with cold welding was done in 1724 by Reverend J I Desaguliers. In his experiment, he observed that when he pressed and twisted two lead balls of the same diameter together, they get attached. Further, his testing showed that, sometimes, the strength of this bond is as similar as to the parent metal.
Many theories and experiments tried to describe this phenomenon, such as the energy hypothesis and recrystallization. But, all of them got rejected.
The accepted explanation of this phenomenon is that when two metals or materials are pressed together with force, the interaction between electrons and free ions occurs, which causes the creation of a metallic bond between both metals. Thus, both the metals get joined to each other. Cold welded metals can be as strong as the parent metals.
Cold Welding Definition
Cold welding is the joining of two nonferrous metals without the use of heat.
How does Cold Welding work?
In creating a typical weld, heat softens metal. This process causes the diffusion of atoms which results in the bond between two metals.
Cold welding is also known as cold pressure or contact welding. It uses pressure to affix two metals or materials. Scientifically, the process of using pressure is called solid-state diffusion. Whenever two metals are pressed together, generally, they do not affix to each other. The reason behind this thing is that there is a layer of oxide on the surface of the metal. This oxide layer on the metal surface is like a barrier that does not allow them to diffuse into each other. Pressure needs to produce 35% to 90% deformation at the joint in order to expose fresh metal by breaking through the oxide layer.
The cold welding technique addresses this issue by preparing the metal before being welded. The process of preparation involves brushing and cleaning the metals to remove the oxide layer or barrier. This can be achieved through de-greasing and then wire-brushing it. Once the surface is prepared, both metals are pressed together with a certain amount of mechanical force. The required amount of force depends on the metals. As some metals only weld at higher pressure, more force might be required.
Cold welding has some other conditions as well. One is that cold welding will work only on metals that have not gone through any hardening procedure and are ductile or soft.
Cold welding can be used to produce a wide array of joints. Some common joints that can be made through this process are:
- Butt Joints
- Lap Joints
In the Butt Joint, removal of oxide or barrier layer is not necessarily required. You can easily break the oxide layer or the barrier by applying pressure.
Lap Joints require that you clean and brush the surface.
Advantages:
The most important and notable advantage of cold welding is that it can carry the same bond strength as the parent metal or material.
Creating appropriate circumstances or surfaces for cold welding might be hard to achieve.
Cold welding can be beneficial for welding metals such as Indium and the Aluminum 2xxx and 7xxx series. There is no other metal welding technique that can weld the Aluminum 2xxx and 7xxx series together.
Cold welding is also used for welding Aluminum and Copper together. Both of these metals are extremely hard to weld together with alternative techniques.
Limitations:
While welders use this technique, it is still not a go-to welding technique because of its limitations.
To start, achieving a perfect cold weld is difficult. The joint or weld acquired through cold welding will be strong as the parent metal only if the cold welding techniques used are correctly applied.
The lack of flawlessness and the hassle to achieve it is usually due to:
- inadequate preparation, such as the presence of an oxide layer on the metal surface
- surface irregularities
- surface contamination
The oxide layer is hard to remove, even if you vigorously clean and brush it. Further, it can be hard for the metals to affix together due to irregularities on the surfaces, even after the cleaning process. The perfect cold weld can only be achieved if both of the metal surfaces are clean. The flatter the surface, the easier it will be for you to form a perfect weld and achieve full strength.
Metals that have gone through any severe hardening process will not weld properly with cold welding. Even if you try to weld them through cold welding, you will not get a strong bond. Softer metals, such as Aluminum and Copper, are the two most common metals that can be welded easily by cold welding technique. Metals that contain any kind of carbon cannot be welded through cold welding.
Applications
While cold welding is not common, it is still used for electrical applications such as wire welding. Alternatives such as thermal energy or heating can damage wires.
Cold welding is also suitable for joining unlike metals such as Aluminum and Copper.
FAQ
Is cold welding strong?
Cold welding is strong when welding nonferrous metals together such as brass alloys (70/30), copper, aluminum, zinc, gold, or silver alloys. The process works extremely well when metals being welded have a similar material composition.
What causes cold welding?
When two nonferrous metals such as copper, gold, or aluminum are pressed together, atoms from each metal touch and attract to each other forming a strong weld.
Can cold welding join stainless steel?
Cold welding can be used to join two flat pieces of stainless steel.
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