What is cold welding? What’s it used for?

Last Updated on Jan 18, 2022

When we recall the word welding, we probably think of fusing and heating, but, with cold welding, the fusing of two metal components takes place at room temperature but under pressure, even as names indicate.

Cold welding of malleable metals like aluminum, copper, lead, and others are fairly common. This article will cover what cold welding is, how it works, its advantages, applications, and limitations. Let’s have a look!

Cold Welding – High Level Explanation

In simple words, Cold welding is a kind of welding that joins metals in the solid phase, and it is performed at room temperature. Other types of solid-phase welding take place at high temperatures.

Cold welding is a joining technique in which two solid objects are pressed together to create a single piece. In other words, cold welding is a welding procedure including solid metal objects that involves combining metals without using heat and fusion at the junction of two pieces to be bonded. 

Contact welding is another name for cold welding. There is no molten or liquid phase at the junction during the fusion-welding process. Metals are welded firmly without the need for a spark in cold welding.

Parts are welded using exceptionally high pressure or collision in a high vacuum condition without heat. At low temperatures, pressure is applied on metal sites to be welded. The particles on the welded interface are brought into certain intimate interactions by the applied pressure as they disperse over the contact surface, resulting in a cold pressure weld. Metallic bonds hold the atoms of metals together. As a result of attraction forces, the metallic bond can be represented as a ‘cloud’ of freely and negative charge atoms forming a unit.

The outer surface layer (oxide) surrounds all metals that must be dislodged when awarded. Cold welding at room temperature requires a high pressure of between 1400 and 2800 Newton per millimeter square for aluminum metal and at least twice as for copper. It causes inter-facial permanent deformation of 60percent to 80 percent, breaking the oxide layers and allowing fresh, purified metal to maintain contact. Under this stage, the weld is produced by inter-atomic interactions.


Cold welding prerequisites

The essential requirement for cold welding would be that the metal being fused be ductile and that the interface is smooth and clean. Cold welding is possible with non-ferrous metals such as aluminum, copper,  gold, etc. Let’s have a look at the characteristics of Cold welding;

Characteristics of Cold welding

  • There is no warmth applied at all.
  • Proper surface preparation is essential.
  • All metal workpieces must be thoroughly clean and flat.
  • Metal Workpieces should have short parts sheared out.
  • The metals used for both workpieces can be comparable or dissimilar.
  • At least a few of the metals should be ductile and not have been overworked.
  • A cold weld is usually stronger which has the same electrical characteristics as the original material.

History

The phenomenon of cold welding was first discovered in the 1940s using Bronze Age techniques. However, the history of cold welding methods dates back much longer.

Until 1724, there was no discovery of the cold welding concept. But, Once John Theophilus Desaguliers utilized two lead balls to evaluate the idea by keeping them together again and twisting them, were at the juncture, he started to notice how they had wedged together. Additional testing revealed that the created bond had the same hardness as the parent metal.

After then, several tests were conducted to elucidate the physics behind cold welding; nonetheless, the most common explanation would be that cold welding occurs when two metals form a magnetic link. Using the prescribed processes, such as having a completely level and clear surface and applying adequate pressure, can increase the mechanical properties of the weld. Owing to the unrestricted passage of electrons between both metals, a metallic connection is established.


Machines for cold welding

The cold welding equipment can cold weld all non-ferrous malleable metals. Such machines can manage wires or rods as small as 0.5 millimeters and as large as 15 mm in size. You can also use a custom cold welding machine for lower diameter wires, and for larger diameter wires, you can still use electric pneumatically powered devices. 

Such cold welding machines are usually small and can work with wire and strip. Individual dies must be fitted to the cold welding machine to handle wires or strips. Thus, the dies are adaptable to accommodate a slight difference in wire thicknesses and strip sizes.


How does Cold Welding Work?

The first essential thing is to remove the oxide coatings on the interfaces of the materials before cold welding can link two or even more metals around each other. Some metals get an oxide coating on their surface that acts as a buffer during normal circumstances, stopping metal atoms from joining.

These metals can then be pushed with each other at high pressures to form metallurgical bonding that once oxide film has been removed. Wire cleaning, degreasing, and other mechanical or chemical treatments can eliminate the oxide coating.

These metals can also be forced together once cleaned, but they must be ductile and haven’t been severely hardened. As a result, during cold welding, softer metals are frequently chosen.

Because the cold welding procedure does not eliminate relative movement among surfaces to be bonded, it has produced mechanical issues in earlier satellites and other spacecraft. It implies that adherence, galling, fretting, and clinging can occur simultaneously, allowing cold fusing and fretting about running in parallel. On the bright side, the ability to fuse metals without the need for a liquid or melted phase allows astronauts to operate efficiently and precisely other than in a spacecraft to perform any needed repairs.

Cold welding may also be done at the nano. It’s possible to link single-crystalline extremely thin gold nanowires as their diameters are less than 10 nm mechanically in seconds. The outcomes were nearly flawless, with about the same crystal alignment, electrical strength, and conductivity,  as the remainder of the nanowire.

Its nanoscale sample size, dynamically aided surface diffusion, and orientated attachment processes are all factors that contribute to this greater welding. Nanoscale cold welding has now been established for attaching silver to gold and gold to silver.

“The explanation for this surprising phenomenon is significant. As if the atoms in interaction are most of the same type, there is still no means to understand separate pieces of copper. In his “Feynman Lessons,” Richard Feynman wrote while describing cold welding functions. If additional atoms are present, such as in greases and  oxides, as well as more complex thin surface coatings of impurities somewhere between, the atoms ‘understand’ when there not even on the similar section.”


Advantages of Cold Welding

Cold welding has numerous advantages over all other welding methods, such as the following:

1. Joining Materials That Aren’t the Same

Cold welding can combine dissimilar metals that seem hard to join using conventional methods, such as copper and aluminum.

2. Welds that are both strong and clean

Cold welding can produce neat welds and be as effective as the original materials’ worst component. The cold welding method does not produce brittle intermetallic complexes at the joint.

3. There is no HAZ (Heat Affected Zone)

Because cold welding does not form a heat-affected zone, the risk of mechanical or chemical alterations to the materials needed to be connected is considerably reduced.

4. Welding of Aluminum

Cold welding’s advantages aren’t limited to attaching copper with aluminum; the process is also used to join aluminum 2xxx or 7xxx types, which is impossible with any alternative metal welding procedure.

Disadvantages of Cold welding

Although cold welding has certain distinct advantages, it does have significant drawbacks. Because of these disadvantages, cold welding is rarely used as a primary joining process for most cases. On the other hand, cold welding might be useful in specific situations, as indicated above. The following are some of the problems and obstacles associated with cold welding:

1. Metal Purity

The fundamental issue with cold welding would be that the metals must be clean and clear of oxide to produce a good weld. It can be hard to achieve in a large production setting and costly and complex to regulate.

2. Shape of the Material

Though all other precautions have been performed, imperfections in metal surfaces could make joining them problematic. Cold welding necessitates materials with a consistent form and no surface imperfections. Flat, uniform surfaces result in the toughest cold welds.

3. Types of Materials

The materials that can be cold-welded together are limited since the metals should be malleable but have not experienced any significant stiffening procedures. Furthermore, this process cannot link metals that include any carbon.


Applications of Cold Welding

Copper and Aluminium Welding

Cold pressure welding is commonly used to join aluminum and copper wires/rods with diameters 0.5 mm – 12 mm or above, with a butt weld type. Cold welding could also join wire metals such as aluminum and copper. This technique proves useful while laying underground wire lines, wherein welding with heating is problematic due to the likelihood of exploding gases.

Sealing container

The cold welding method is preferred for sealing heat-sensitive containers (those containers that contain explosives for detonating).

Heat-Sensitive Semi-Conductors

Cold welding is utilized to make heat-sensitive semiconductor materials within the electronic sector.

Post-weld drawing to small diameter

To allow for post-weld bending to small diameters, rod coils are usually joined by a butt weld.

Magnets Welding

It is used to attach components that cannot be heated, such as magnets.

Electronics Industry

Cold welding procedures are used in consumer electronics to weld tin-plated steel crystalline cans and copper packaging for high-temperature semiconductors.


Frequently Asked Questions

What Metals Are Suitable for Cold Welding?

Cold welding is widely used to weld aluminum, even unweldable types like the 7XXX series, 70:30 brass alloys, zinc, copper, silver & silver alloys, gold, and nickel, notably wires. Cold welding is also used to connect metals under high pressure, including stainless steel. In addition, Cold welding is not possible with carbon-containing metals.

Is Cold Welding a Long-Term Solution?

Under the right circumstances, cold welding can produce lasting welds. The connection can be undone with disruption to the workpiece if executed right. On the other hand, the joints are prone to failure if the cold welding isn’t performed under the appropriate conditions.

Is it possible to do cold welding in space?

Don’t panic; cold-welding in space is rare despite its seeming simplicity. Due to interaction with the Earth’s atmosphere, most metals shot into space usually have a small oxidation layer. Cold-welding is impossible because the covering is frequently still there once in space.

Is TIG welding and cold welding the same method?

The main distinction between this and contact welding is an arc welding procedure, while cold welding employs pressure. A Tungsten gas welding (TIG welding) procedure is available, often known as cold welding.


Now let’s conclude by summarizing the main points mentioned. Owing to solid-state dispersion, two separate pieces of ductile metal with clean and straight surfaces interact under pressure and thus are connected or cold-welded altogether. However, cold welding is Thus, also called cold pressure welding or contact welding.

Cold welding allows for both lap and butt joints. Butt joints are commonly utilized for cold welding aluminum and copper wires with diameters ranging from 0.5-10 mm or above. Events that occurred while the spacecraft had been in orbit prompted space researchers to think about cold welding problems when designing the spacecraft, primarily to prevent undesirable cold welding.

Cold welding provides numerous advantages, such as cold weld aluminum with copper, which was previously impossible using traditional procedures. Moreover, Contact welding has constraints, such as the difficulty of keeping a clean and flat surface on the pieces to be fused and the use of non-ferrous ductile materials.

In addition, it is commonly used to combine aluminum wires & rods and aluminum appropriately with copper, seal dynamite containers, and build heat-sensitive semiconductor materials.

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