What is Cold Welding, and How Does It Work?
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Welding is supposed to be hot, right? Lots of sparks, maybe a rag or pant leg catching fire – this is what we think of when we hear ‘welding.’ So how can welding be cold? Cold welding, or contact welding, is a solid-state welding process. We don’t normally think of welding in this way, but arc welding processes technically are liquid state. That is, the arc liquefies the metal so that it can fuse.
How can metal fuse any other way? One way is by cold welding. Cold welding consists of removing the oxide layer on pieces of metal by removing grease and wire brushing the metal. The metal is then pressed together hard enough to cause it to bond.
There is some confusion with the terminology which we will cover. Oftentimes welders when they hear the term ‘cold welding,’ either think of cold metal transfer welding or JB weld. Part of this is because of the disconnect that happens between what the engineers do ‘upstairs,’ and what the welders and fabricators do on the ground level of the shop. So, let’s try to bring both worlds together and get a holistic view of what ‘cold welding’ can mean.
How does it work?
When metal is formed in a steel mill, oxidization is not necessarily a part of the production design. Instead, after cooling, oxidization (exposure to oxygen) begins to occur. This occurs at different rates depending on the type of metal. For example, potassium, which is an extremely soft metal (you can cut it with a paring knife), oxidizes within seconds of being exposed to the air. Other ferrous (high in iron content) metals oxidize more slowly.
In any case, before cold welding can take place, this oxide layer needs to be removed from any type of metal because it prevents bonding. Why? When the bare, unoxidized metal is exposed the two joint members can bond under enough pressure. This is because the overall crystalline shape of metals has a molecular structure that has a lattice structure. In between the atoms of the lattices, there are electrons which, when not covered by oxidization can flow freely causing both of the joint members to bond at the surface. This is all done without heat or electricity of any kind, induced into the material.
What are the different types of Cold Welding?
As we have already mentioned, when people hear ‘cold welding,’ they usually think of things other than what we have been talking about thus far, meaning contact welding. So, we will cover a couple of other types of ‘cold welding’ as well.
Where Is It Used?
Advantages of Cold Welding
Disadvantages of Cold Welding
Frequently Asked Questions (FAQs)
What is a Cold Weld?
Yet again, another understanding of the term cold weld gets thrown into the mix. A cold weld is a weld defect in arc welding. It is also described as a lack of fusion. This is where the travel speed of the electrode is too slow. The weld starts to pile up and not fuse properly. The weld metal can also get in front of the arc while traveling. This is not related to the contact welding process.
Do you need gas for Cold Welding?
No shielding gas is required for contact welding since it only utilizes pressure after the oxide layer of the metals has been removed. However, CMT requires shielding gas since it is a MIG welding process.
Is Cold Welding strong?
Though no fusion or heat is used in order to bond the two joint members, Cold Welding can be extremely strong. Essentially what is occurring is creating a new piece of metal. In this sense, it is not a joint per se. The bond will have the same strength as the parent material since it has been bonded molecularly.
Cold is a confusing term when it comes to welding. Part of this is due to the lack of communication between engineers. People on the ground floor of a fab shop have not likely encountered contact welding. But they are well familiar with a machine ‘running cold’ or JB Weld. All of these processes have tremendous value. It’s just a matter of what is more appropriate for the project.
Featured image credit: Manuel Trinidad Mesa, Shutterstock