Molten metals, people in safety gears, bright red and orange sparks- that’s our first impression when we hear the word “welding”. After all, this picture came to be as we perceive it that way.
Because most welding techniques involve heating two or more pieces of metal and joining it, we’ve conditioned ourselves to think that welding is synonymous with heat. But the truth can’t be any farther and cold welding is a testament to that.
Simply, cold welding is a process where you’d remove the oxide top-layer and join metals by using pressure. You don’t need heat to bind these metals together.
In the aftermath, the metal is not heated or liquified.
Can’t believe it? You can read more below and see for yourself!
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A brief history of cold welding
Industries have been using cold welding for decades. But, the first use of it dates back to a time when metal wasn’t as dominant as it is now, the 18th century.
In 1724 Mr. Desaguliers, a reverend, explored it while experimenting with similar-sized lead balls. He pressed and twisted them and saw them sticking together.
He noticed the joint piece had the same strength as the lead balls, coming to the conclusion that the resulting build is as strong as the parent metals.
Soon after, many scientists tried their hands on it and came up with a few theories. First, people assumed recrystallization was the reason it happened, then came the energy hypothesis and many more theories.
Although these got debunked later for lack of satisfactory evidence.
Now we accept the idea that free ions are what causes these metals to bond together.
Isn’t it interesting how the most groundbreaking innovations are born in a little corner of the world?
How cold welding works?
Here, I will explain to you in-depth about the secrets of cold welding and why it is so lucrative.
Let’s clear the welding process first so that it would be easy to understand the cold welding process later on.
From there, I’ll go on and cover every matter step by step:
1.1. Working principle for cold welding
In an orthodox welding method, we use heat to raise the metal’s temperature to the boiling point so that the metal starts to show plasticity.
Afterwards, atoms start to diffuse, and the metals slowly begin to join together. Heat plays an important part here, which is why people start to think it’s a must-have.
But, unlike popular welding techniques [like arc welding, laser welding or friction welding], cold welding doesn’t use any kind of heat at all. Instead, this method relies on free ions.
The energy that you need to join two or more pieces of a metal comes from pressure, that diffuses the atoms and makes the welding possible. That is why this approach is also known as contact welding or cold pressure welding.
Still bemused? Don’t worry; it is a scientifically proven method that centers its approach around the solid-state diffusion process.
Now that you understand how the process works, we can look at how you need to prepare the necessary materials to do it smoothly.
1.2. Things you need before welding
Cold welding is more than just making two metal pieces hug each other. You need to be methodological; otherwise, it won’t work.
If you still don’t believe we can join metals using pressure instead of heat, let me clarify where your confusion is coming from- you’ve never seen two pieces of metal get joint just by pressing, right?
That’s because, albeit pressure is a big player in this game, it’s not the only catalyst. A layer of oxide on both metals’ top surface prevents them from getting stuck to one another.
No matter how much pressure you apply, the oxide layer will act as a barrier so that the atoms don’t get to bond with one another and prevents you from joining the metals.
In cold welding, we prepare the metal keeping that in mind, and clean them accordingly until the top layer’s oxide is almost non-existent.
The cleaning is pretty extensive, by the way.
First, we need to de-grease the metal, and then we have to follow it up by scrubbing with a wire brush. No need to rush it; take as much as time you need. When you’re done with cleaning, you’ll be ready to start applying pressure.
1.3. The actual procedure
Different metals have different tolerance to pressure, so you can use regular stuff for some metals, while for others, you need industrial-grade machinery.
For putting pressure on the metals, you need to make sure of the following things:
- The metals are pressed together
- You’re applying the right amount of pressure
- Pick metals that haven’t experienced the hardening process
- At Least one metal has to be ductile
Following these considerations shortens the list a lot, so that’s one less headache for you.
A pro tip from me: go for soft metals. Aluminum and Copper are the two most common metals that get cold-welded. Gold, Silver, and Nickel are great choices too!
As for the procedure- generally people use punch presses to apply pressure on these metals. Rolling stands are also a common choice for this.
Aluminum needs 1400-2800 KPa [kilopascal] to get joint, most of the others need even more pressure. When you reach the necessary pressure, the metals start to deform.
After a while you’ll see the metals stretching and before long you’ll have a one truly similar joint that will match the toughness of the parent materials.
Since there is no heat involved and the joint is vacuum tight, you don’t have to wait for it to cool down or seal it.
What is cold welding used for?
While cold welding might be new to you, it has been used in industrial work for ages. From automotive to aerospace, labs to the workspace- it has a WIDE range of situations where you could use it.
You’ll see cold welding used in joining wires as heat is not used at all [it’s a big no-no for wires] for this method, and it’s done relatively quickly.
The most common application for cold welding is making joints, there are a lot of them but it is popular mainly for lap and butts joints.
For butt joints, there is no need for you to clean the surface layer; you can just press it hard, and that layer will break by itself. This way, you get to save some time.
However, lap joints need that investment of time and effort because metals won’t stick to each other otherwise. So, it’s best if you give it a special cleaning treatment.
You can see an interesting application of cold welding in joining dissimilar metals. These don’t have any affinity at the initial phase of the melting process, so any welding that includes heat isn’t much efficient; there still will be cracks, weak spots, or the worst case – it won’t be joint at all.
Cold welding is best suited to deal with this situation as it depends on free electrons to build atomic bonds for the welding process.
Advantages of cold welding
- No heat
- Less risk of chemical changes
- Join dissimilar material
- Strong finish
- Only method that can weld aluminum 2xxx and 7xxx
- Simple method
Disadvantages of cold welding
- Metals must be fully cleaned
- Expensive on a large scale
- Hard to perfect
- Oxide layer is hard to remove, might need professional help
- Can fail in oxygen rich area
Is cold welding strong?
The results of a cold weld actively depend on the metals you will be using. If you’ve used sturdy metals that are durable, the product you get from cold welding will be just as strong, at the very least.
If the durable base metal you’re using is designed correctly and you’ve followed everything religiously, it is safe to assume your weld will be strong enough.
Well, that was a brief introduction to the world of cold welding. I’m hopeful you were as amazed as me when I first found out about this unique way of welding metals.
Watching it and writing about it only reinforced the opinion I had: Cold welding is nothing short of an art.
So, now that you’ve stumbled upon it, why don’t you try indulging in it? Who knows, you could be the next master of cold welding!
Last Updated on February 9, 2021 by Gary Hargrave