Cold Welding: Joining Metals Without Heat
When we think of welding procedures, the first thing that comes to mind is the use of heat. Heating metals to their melting point and fusing them together is how most welding techniques work.
Technologies such as arc welding, friction welding, ultrasonic welding and laser welding all involve heat in some way. In fact, heat is considered synonymous with welding and is indispensable for combining two materials.
But this is far from fact, cold welding is the obvious proof. Cold welding is the process of joining two metals without heating.
It may sound impossible, but this is one of the most popular welding methods.
How can we add metal without heat?
The heat in the welding process is used to make the parts have sufficient plasticity so that atomic diffusion can be carried out between the two workpieces or using different media in between.
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However, it is not mandatory to use heat to connect materials. Cold welding can be displayed in real time.
Cold welding (also called cold pressure welding and contact welding) uses pressure to join two materials. Scientifically speaking, this process is called solid-state diffusion, which uses pressure to create welds.
When two materials are pressed together, they usually do not weld to each other. This is mainly due to the presence of an oxide layer or a thin barrier layer on the surface of the material.
If you take metal as an example, the oxide layer on the surface acts like a barrier, not allowing it to diffuse with another metal.
Cold welding solves this problem by preparing the metal before welding. The preparation process includes cleaning or brushing the metal to the extent that the top oxide or barrier layer is removed and a cold welding machine.
This can be achieved by degreasing the metal and then wire brushing it.
Once the required surface cleanliness is achieved, the two materials are mechanically pressed together with the appropriate force. The amount of force depends on the material itself, because some materials can only be welded under high pressure.
One of the conditions required for cold welding is that at least one of the materials must be ductile and must not undergo a rigorous hardening treatment.
Obviously, this narrows the range of materials that can be used for cold welding. Soft metal is the best choice for cold welding.
The history of cold welding
Cold welding has a history of hundreds of years. The excavator discovered that the cold welder dates back to the Bronze Age.
Reverend J I Desaguliers completed the first scientific cold welding experiment in 1724.
Observation found that when he pressed and screwed two shot balls of the same diameter together, they would stick to each other, which provided motivation for his experiment. Further testing showed that sometimes the bond strength is almost similar to the parent metal.
There are many theories trying to explain this phenomenon, including recrystallization and energy assumptions. However, they were all refuted.
Currently, the accepted explanation is the creation of metal bonds, which are caused by the interaction between free ions and electrons when two metals are pressed together.
If cold welding is performed according to the correct procedures and materials, the result is usually as strong as the base metal.
Limitations of cold welding
Perfect cold welding is difficult to achieve. This is caused by many reasons, such as the oxide layer formed on top of the metal under atmospheric conditions, uneven surface, and surface contamination.
Optimal cold welding only occurs when the two surfaces that are pressed together are clean and free of any form of contamination. Moreover, the smoother and regular the surface, the easier the weld seam will be uniform.
In addition, the types of metals that can be added to cold welding are also limited. Non-ferrous soft metals are the only candidate materials suitable for cold welding. Copper and aluminum are the two most commonly used cold weld metals. Metals containing carbon cannot be cold welded.
Advantages of using cold welding
The most significant advantage of cold welding is that the resulting weld has the same bonding strength as the base metal. It is difficult to reproduce this feat in metal processing. In the industry, cold welding is known for its ability to weld aluminum and copper together, and aluminum and copper are often difficult to weld with other forms of welding techniques. However, the bond formed by cold welding between the two materials is very strong.