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.

  • Contact Welding
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    Credit: Robert Bertold, Shutterstock

We have spoken about cold welding as contact welding. The oxide layer of metals is removed so that the electrons in the molecular structure of each metal can flow freely to the other joint member. But how is this done? The bond can even begin by pressing manually. But usually, a variety of presses are used, most often pressure welding machines. They are specifically designed to induce enough force to cause the crystalline grain of the material to link.

  • Cold Metal Transfer
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    Credit: Photo Love, Shutterstock

When people hear ‘cold welding,’ they often think of a fusion welding process that utilizes an electrical arc. In this case, cold is a much more relative term. Cold metal transfer (CMT) is a MIG welding process that emits about 90% less heat than conventional MIG welding. The essential difference between this process and contact welding is that this is an arc welding process whereas contact welding uses pressure. Since CMT is an arc welding process it uses an electrode wire fed into a molten weld pool. This is controlled by electronics that register the short-circuiting of the arc so that the wire retracts. This causes the heat input to be so much less than standard MIG welding.

There is also a TIG welding process, which is also known as cold welding. Sometimes a TIG machine that includes direct current and alternating current will have a setting called ‘cold.’ This is a manual process where each time the arc is initiated with the TIG gun, it has a ‘zapping’ effect. That is, it is only introduced for a fraction of a second. This is hardly enough time to melt any filler metal, but if you do, softer metals such as aluminum are preferred. The cold setting is usually used to fuse two pieces of metal that could oxidize or melt under too much heat.

  • JB Weld

JB Weld is a brand name for an epoxy bonding system. This is touted as the “original cold weld.” Properly speaking, it is not welding at all. There is no molten weld pool since it uses no electricity, neither is there any molecular contact between the pieces to be welded. Instead, it is a mixture of two components, an activator, and a base. You mix both of these and apply them to the area to be bonded. The parts are then secured with clamps or something else that will stabilize them while the epoxy cures.

Where Is It Used?

  • Contact Welding

You are not likely to see this used in your average steel fabrication shop. It is for very specific applications that have to be preapproved by the engineer. The engineer might designate contact welding because too much heat introduced into the material might cause warping or weakening of the material. Contact welding is most often used for welding wires that need to be suitable for welding alloys. For example, nickel and mild steel wire can be cold-welded.

  • Cold Metal Transfer

CMT is often used in applications where the metal cannot afford to be warped, much like contact welding. The automobile and sheet metal industries use CMT a lot.

  • JB Weld

JB Weld has been a favorite of professionals and DIYers for decades. When cured, the bond can be as strong as steel. It can be used on anything from trailer hitches to old bar stools. It’s extremely user-friendly.

Advantages of Cold Welding

  • The obvious advantage of cold welding is that heat is not introduced into the material. This reduces the chances of warping or weakening the material. It also allows you to join metals of different types without having to have as much skill or dexterity as arc welding.

Disadvantages of Cold Welding

  • Of course, JB weld and certain ‘cold’ settings on TIG welders are widely available for even home use. But contact welding is a niche in its own right. Pressure welding machines can be expensive and hard to come by.

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.


Conclusion

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

Aaron Rice
 

Aaron is a Pacific Northwest native. He worked in landscaping from a young age which eventually led him to start his own small-scale business. He then turned his attention to welding. He has worked as a welder and fitter on Portland and Tacoma waterfronts building railcars, bridges, and marine structures. Bringing together the theoretical aspects of fabrication with the nitty-gritty is something he's enthusiastic about. In his free time, he enjoys coffee, playing guitar, and playing cribbage with his wife. He is currently a graduate student in Boston, Massachusetts.