What is Cold Welding?

Whenever we think or talk about welding, we consider it in the same lens as heating. The very first thing that comes to mind in a discussion over welding is the use of thermal energy to heat and weld metal objects together.

Most welding techniques work by heating metals to their melting point and then joining them together to create a fusion that doesn’t just last longer but is also more durable and functional.

All welding techniques such as friction welding, arc welding, laser welding, and ultrasonic welding involve heat in one way or the other. Heat is considered a necessary addition to the welding process and makes the process easier to follow.

However, what we perceive and believe about welding is far from the truth. Cold welding is one very popular form of welding that works without the need or the presence of heat.

To simplify the process, cold welding is the rather effective procedure of joining two metals without the use of thermal or heat energy. To the naked, untrained eye this entire procedure might sound a bit too unbelievable to be true.

But, cold welding is a big part of the welding industry and there is no way to deny that.

How do we join metals without heat?

To understand just how metals can be joined together without heat, we first need to understand just how the process works when you are performing it using thermal energy. The presence of heat within a welding process helps you in making the metal parts plastic enough.

Once the parts have become plastic and flexible, the welding process jumps towards diffusing the atoms. The diffusion process either involved the two workpieces you are working with or a completely different medium placed in between.

However, contrary to popular belief, you don’t really need heat energy to perform a welding job. Cold welding, using the energy generated through free ions and electrons, is the living proof of how welding can be done without thermal energy.

Cold welding demonstrates a real-time example of how welding can be done without the need for thermal energy. Cold welding, which is also popularly known as contact welding or cold pressure welding, makes use of pressure to join and diffuse the atoms for two materials together.

This process is scientifically acclaimed and is known as solid-state diffusion in the science circles. It is scientifically possible to weld two pieces of metal together using the forces of pressure.

When you press two metal surfaces or materials against each other, they generally wouldn’t weld together. Regardless of the force you apply to the materials, the pressure solely wouldn’t help in creating a weld.

This hindrance is particularly faced due to the additional oxide layer present on the surface of both these materials. This oxide layer works as a barrier, preventing the layers to be attached together just through the application of pressure.

Since welding is most frequently practiced on metals, let us take up their example. Almost all metals come with an additional surface oxide layer on the surface that acts as a barrier of sorts.

The surface layer prevents the metals from being weld together just through the application of force or pressure. You cannot weld the two pieces together, because the surface oxide layer does not allow both the metals to diffuse atoms with each other.

Cold welding takes this issue and the possibilities of pressure welding into perspective and prepares both these metal surfaces for what is to come. The preparation process is extensive and includes the cleaning and brushing of all metal surfaces, to an extent that the top-most layer of oxide is removed.

Since the oxide isn’t present anymore, you are easily able to weld substances together through the use of pressure. No thermal energy is needed, and you can add a completely new definition to welding through cold welding.

The cleaning and brushing process, however, requires thorough application without leaving any untouched bits on the surface. The process involves the de-greasing of all metal surfaces involved in the process.

Once the de-greasing is done, you carefully wire brush the entire surface of the metals.

Once you have completed the desired cleanliness of both surfaces involved, you can get to the all-important process of pressure application. Remember to not rush into the process, as it is necessary that you brush and clean the surface with all necessary adjustments.

Moving to the pressure application step, you need to make sure that the materials are pressed together and the right amount of force is applied to them. The amount of force isn’t the same for all metals.

Different materials come with different properties, which is why it is best to understand their welding properties and weld them at the high pressures they require.

Cold welding has its own conditions as well, which should also be studied before you start the project. For one, cold welding will only work on materials that haven’t undergone any extensive hardening procedure and are ductile in nature.

The process cannot be practiced on objects that have undergone severe hardening procedures and those that happen to be ductile in nature.

Once you apply this condition, a lot of materials will be cut off. This will eventually narrow down the list for materials that can be possible candidates for the cold welding procedure.

To make your decision-making process easier, cold welding should be your go-to option for welding soft metals together.

Cold welding can be used to manufacture a wide array of joints, but the most common joints that can possibly be made through this process include:

  • Lap joints
  • Butt joints

In butt joints, it isn’t necessary for you to clean the surface layer of the metals being welded together. In this joint, you can easily break up the additional layer on the surface through the pressure that is applied to it.

This will save you the extra time and effort you would have otherwise spent on cleaning and brushing.

Lap joints, on the other hand, require special cleaning and brushing of the surface, as the metals would not adhere or stick with each other without the cleaning. These joints require you to put additional efforts into the process.

History of cold welding

Cold welding might sound like a relatively new concept to you, but it has centuries of history behind it. Excavators studying relics and extracts from the past have found out utensils that were weld together through cold welding techniques.

Some of these utensils date back to the Bronze Age, lending proof to just how old the concept of cold welding it.

While cold welding has been practiced by citizens of the world since a long time ago, the first scientific experiment on this technique was conducted by Reverent J I Desaguliers in the year 1724. This experiment was the first of its kind and helped propel further research in this regard.

Desaguliers tested the concept of cold welding through the use of two lead balls. Both the lead balls came with the same diameter and were observed carefully.

What Desaguliers did was to hold both these lead balls together and then exert pressure while twisting them. When he did this, Desaguliers noticed that the balls would stick together.

This was the first scientific test of its kind and opened the doors towards the science of cold welding.

Further testing in this regard went on to prove that the bond formed after the pressure was applied, had the same strength as that of the parent metal. Hence, the bond formed between the lead balls had the same strength as that of the lead balls themselves.

This proved that the weld could be trusted and wouldn’t just fall apart abruptly.

Cold welding has been an interesting subject of science, and many budding scientists and researchers have shed light on it. We now have over a dozen theories looking behind the formation of this bond.

Some of these theories pinpoint and focus on recrystallization, while others have also credited the energy hypothesis for the weld. However, all of these researches have been discredited and disproved due to a lack of sufficient evidence.

The only acceptable explanation for the creation of the weld through cold welding is the formation of a metallic bond.

The metallic bond carries the same characteristics and strength of the parent metals, because it is formed due to the interaction between the free electrons and ions of both metals when they are pressed together, and a certain force is applied to exert pressure.

Cold welding, when done with the right material treatment and procedures, can help create a significant weld that sticks for a long time. This, however, can only happen when the weld in between the metals is just as strong as the parent metal itself.

This strength and sturdiness can only be achieved if all due procedures and treatment methods are religiously followed.

Limitations of cold welding

Considering just we have explained the positive side of the picture to you, you might wonder why cold welding isn’t an industry mainstream by now. Fair enough, it is used by many individual welders, but it still isn’t the go-to welding method in the industry.

This is because cold welding comes with a few limitations.

To begin with, perfect cold welding is extremely hard to achieve. The weld achieved through cold welding will only be as strong as the parent metals if the cold welding techniques used are perfect.

The lack of perfection, and the difficulty to obtain it, usually comes down to different reasons, such as the presence of the oxide layers on the surface of the metal, surface contamination, surface irregularities, and a lot more.

The oxide layer is often hard to remove, even if you brush and clean it to the best of your knowledge. Moreover, irregularities on the surface of the metals can make it hard for the metals to stick together even if the surface is cleaned and brushed.

The perfect cold welds can only be made if both the surfaces you are working with are clean, free from all different contaminants, have a regular shape, and have no irregularities in the surface. It is also significant to know that the more flat and regular your surface is, the easier it would be for you to form a uniform weld.

If your final weld isn’t uniform or flat, it wouldn’t have the strength you desire.

Also, cold welding isn’t an industry-standard because of the limitations on the number of metals that you can weld together through cold welding techniques. As we have discussed above, non-ductile metals or metals that have undergone severe hardening procedures wouldn’t react effectively to the processes of cold welding.

Even if you are able to form a cold weld on them, it wouldn’t stick for long. If you narrow down your options, you will realize that non-ferrous soft metals can only be welded together through cold welding.

To give you examples, aluminum and copper are the two most common metals to be welded together through cold welding procedures. Also, metals containing any form of carbon cannot be welded together through cold welding.

These limitations make it hard for industries and individual welders to adapt this welding method as a primary source for welding. Of course, cold welding can prove beneficial in certain scenarios, but in a majority of all scenarios, you will find the process to be excruciatingly long and ineffective.

Advantages of cold welding

Just as we have discussed the limitations of cold welding, there are some advantages of the procedure as well, which require special mention. The most significant and noteworthy advantage of cold welding is that it carries the same bond strength of the parent material.

While creating the feasible circumstances for cold welding can be hard, you will be pleased to know that once you have created the right circumstances, the weld you create will be pretty strong. This feat is extremely difficult to recreate within other metal welding methods.

Cold welding techniques can prove to be extremely beneficial for welding Aluminum 2xxx and 7xxx series. As we have mentioned above, cold welding techniques are perfect for aluminum and copper surfaces.

No other metal welding option can weld together aluminum 2xxx and 7xxx material series.

Cold welding also comes across as a decent option for welding both aluminum and copper together. Aluminum and copper are known to be extremely hard to weld together by other forms of welding.

Cold welding simplifies the procedure and makes it easy for you to weld both of them together. Also, the ultimate bond you create between these two metals, through cold welding is fairly strong and will last a long time.

Finally, cold welding gives you a simple solution to creating strong and clean welds on surfaces that support the procedure. The welding procedure helps create a strong bond without forming any intermetallic compounds of a brittle nature.

Applications of cold welding

While cold welding is not a common procedure in the industry, it still is used significantly for welding wires. The procedure is applied for welding wires, because of the crisp weld it forms and also because there is no heat involved.

Thermal energy can be detrimental for wires, which is why a cold weld is the call of the day.

Cold welding gives a long-lasting and perfect weld to wires, mainly made from 70/30 brass, zinc, copper, aluminum, silver alloys, silver, gold and nickel, and gold. Interestingly, you can also buy easy to use, handheld tools for working on cold welding wires.

These tools are extremely portable and are easy to carry around with you. They can help save time and effort.

Cold welding is also a possible option when it comes to joining dissimilar metals like copper and aluminum together. We have already discussed how cold welding can form a strong bond between copper and aluminum.

This weld is stronger than what can be created between these metals through any other method.

Is cold welding strong?

As we have already discussed through the course of this article, cold welding can create a strong bond when the conditions and the metals are feasible for its use. If conditions are perfectly suited for cold welding, the weld created between the metals would be just as strong as the parent metals themselves.

However, creating the perfect conditions can be hard, as the technique cannot be applied to non-ductile and severely hardened surfaces. Also, the brushing and cleaning process requires significant effort and the metals need to be regular in shape.

However, the bottom line still stands that cold welding can create some of the hardest and strongest welds if the conditions around are suitable for its use.

Summary

There you have it – basically everything you need to know about cold welding. By understanding how to do it, the advantages, and the limitations, you’re only beefing up your welding knowledge.

Remember, though, you can always take it to the next level with some extra reading material 🙂

About Pierre Young

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Hey, I'm Pierre Young a qualified AWS Certified Welder. I got into welding in 2009 as a side hustle. Ever since then, I've been doing all kinds of welds - both for business and pleasure. While immersing myself in this wonderful hobby, I've learned from hands-on experience what welding gear works and what doesn't. Welding Headquarters is the site where I share everything I've learned.

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