Cold Welding – The Art of Joining Metals without Heat!

Cold Welding - The Art of Joining Metals without Heat!

What is Cold Welding?

Most of the welding processes involve heat transfer and metal fusion. Let me surprise you by saying that there is a popular welding technique that is independent of heat. Yes, you read correctly; there is no need for any thermal energy during the process. That’s why it is termed ‘cold welding’.

To understand the working principle of cold welding, let’s recap the core idea of the most common welding processes. The high voltage or amperage produces a strong arc to provide enough heat that causes metal atoms to diffuse into one another.

The molten metal globules form a weld or joint on cooling. Contrary to this, cold welding involves applying high pressure in the range of several mega bars to force metals to join. Because of the pressure application on metals in solid-state, this welding type is also referred to as cold pressure welding or solid-state welding or, sometimes, contact welding.

Conditions of Cold Welding:

You may have held metals together many times in your welding career or might have applied pressure as well, but how come the metals didn’t join? Firstly, the pressure was not enough, and secondly, the preventive oxide coating on metals restricts them from doing so.

As you know, the oxide layer hinders contact welding of metals; hence the preprocessing of metals is a necessary step. The metals are gone through brushing and cleaning until the oxide layer peels off. For better results, metal de-greasing techniques are also useful before wire brushing of the surface. Once the cleaning process is done, the pressure is applied uniformly on the metals. Flat surfaced metals result in better welding.

Apart from cleaning, the metal ductility also affects its welding. This pressure welding is suitable for nonferrous ductile metals like aluminium, copper, lead, gold, etc.

Joints Welded Through Cold Welding:

Welders use this welding technique for many joints. But, most commonly, cold welding fits for butt and lap joints.

For butt joints, you won’t have to put extra effort and time into cleaning the surface. The process will do it for you. Contrary to butt joints, lap joints will cost you an extra step of rubbing metal.

Cold-Welding-Butt-joint

 Cold Metal Transfer Welding:

Cold Metal Transfer, abbreviated as CMT, is a smart welding process controlled by a welding robot. It is a modified MIG short circuit metal transfer process where a signal is triggered when the filler wire comes in contact with the base metal.

Moreover, this short-circuit occurs at low current input, and hence, less spatter is observed. The generated impulse signal retracts the filler wire and allows the weld pool with an offset to cool. Therefore, the droplet formed sets in place to create an aesthetically enhanced and durable weld. The best thing about this welding method is the controlled metal deposition rate with low thermal input.

Cold metal transfer process

Nano-Scale Cold Welding:

Cold welding is the only welding method that can be used to weld materials on the Nano level. Can you imagine welding gold wires with a diameter of up to 10 microns? Wow, wouldn’t it be amazing to make extremely small welds that are not visible to unaided eyes? Plus, these nanowires require a low-pressure application for weld formation. Such Nano- welds produced with greater inspection give perfect joints with commendable features like conductivity and strength. 

Mostly, solid-state welding at a Nano-scale is done with gold and silver wires in Nano-fabrication processes.

Bullet Cold Welding:

We all want to have a collection of our favorite things. For example, women love makeup, and their hearts still want more even if you buy them all shades of lipsticks! Similarly, some adventurous people are interested in collecting bullets.

Bullets also undergo ‘cold welding’ due to high neck tension with their brass case. This fusion usually happens when bullets are kept for a year or more. To avoid this type of unwanted welding, you can try imperial dry graphite as interior neck lube.

Cold Welding in Space:

Did you know that cold welding occurs in space as well? When metal pieces come in contact in a vacuum, they collapse to diffuse together permanently. But this happens only when there is no rust or oxide layer on that metals. This phenomenon causes defects in satellites and is termed a hazard in space studies.

To avoid metal fusion in space, aerospace engineers devise equipment with material that has low contact adhesion. Other preventive measures include the usage of coated or lubricated surfaces and reduced actuator dependency.

Cold Welding Machines:

Cold welding machines come in a wide range depending upon the diameter of the wire they can weld. Generally, two wires are fed in the machine, and pressure is applied through the lever. The internal mechanism amplifies that input pressure to form permanent welds stronger than the original material of the wire.

An HP180 small welding machine can weld wire strips with a diameter ranging from 0.3mm to 1.8mm. You can find other TIG machines which are capable of cold welding. On a healthy budget, you can buy cold welders for wire diameters up to 15 mm.

Cold Mode of TIG Welders:

Usually, TIG welding machines operate on two modes. One is for TIG welding, while the other labeled as ‘cold welding mode’. The TIG welding mode works conventionally, i.e., the trigger is continuously pressed to produce arc, and filler wire is fed that joins the base metals. But the other mode uses electro spark technology for welding. There is no need for filler wire, and you have to press the trigger at quick regular intervals. There is a sudden spark that forces metals to melt and join.

Are you pondering why is this still called a ‘cold welding’ because there is spark and heat involvement? The logic is that you can touch the gun with bare hands right after welding and feel the warmth.

Advantages of Cold Welding:

  • The admirable perk of cold welding is that no heat is consumed in its process. Welders do not need to deal with high temperature and hence ultimately, no spatter and hence no mess at the work area.
  • Secondly, the other welding techniques are less suitable for joining different metals. Cold welding serves best for welding aluminium and copper together without the formation of brittle intermetallic compounds. Moreover, the welds formed are eye-catching and strong at the same time.
  • Welders recommend welding nonferrous malleable metals like gold, copper, silver, aluminium and brass with this technique, especially when the wire diameter is thin.
  • It is also a time-efficient method because no time is wasted in heating and cooling base metal.
  • Aluminium 2xxx and 7xxx series can be cold-welded only. They cannot be welded with MIG or TIG because of aluminium’s tendency for hot cracking.
  • Cold pressure welding doesn’t produce heat affected zone (HAZ). Instead, it leaves a mechanically affected zone (MAZ) due to strain and pressure on the bonded region.

Limitations of Cold Welding:

So far, we have discussed many aspects of contact welding. It is time to show you the other side of the picture. There are a few limitations or disadvantages of cold welding that need to be addressed.

As an experienced welder, I would say cold welding is hard to achieve. If the technique is not applied perfectly, you will have to compromise on the joint/weld strength. The unexpected results are mainly because of contaminated surface or surface irregularities.

Only nonferrous ductile metals are suitable for cold welding, making it a limited method. You have to ensure that these metals have not gone through any other hardening processes earlier. Metal hardening processes usually result in the addition of carbon to metal, and hence metal is prone to break under high pressure.

 Applications of Cold Welding

  • Commercially, this welding finds its applications in the aerospace, nano-fabrication, and automotive industries. The hydraulic, electric, or pneumatic sources produce enormous pressures capable of solid-state welding.
  • Contact welding is also applicable information of assembly of small transistors where heat can be risky.
  • Whenever wires break during the process, they are joined through cold welding as it is quick, and the tools are also portable

Frequently Asked Questions FAQ’S

Is cold welding strong?

Yes, cold welding produces strong joints if all conditions are met perfectly. It only works best for ductile and nonferrous metals. Welders consider it hard to perform a perfect cold-welding process. But if done professionally, it results in welds stronger than the base metals.

What causes cold welding?

The attractive forces among the metal atoms are the main cause of cold welding. The application of high-pressure results in higher attraction among the metal atoms, and they are likely to fuse to form metallic bonds.

Conclusion

To conclude, cold welding is a process of joining metal under pressure. It is a quick and cleaner welding technique that produces joints stronger than the original metals. Plus point of cold welding is it can be used for welding dissimilar metals or nonferrous ductile metals. But cold welding is limited to metals without oxide layers and is useful for lap joints or butt joints only.

Hello Everyone, I am James from Kentucky and been into this welding fiasco for 13 years in that time I have worked as a private welder and did most of the auto restoration work. In this recent, COVID-19 outbreak I decided to start a welding blog and share welding tips along with product reviews.

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