What is Cold Welding & how it is done?


What is Cold Welding?

Cold welding is a solid state joining technique that works on no heat or fusion for making a weld joint. Cold welding is also known as contact welding. In the cold welding process, the energy (which is usually heat in fusion welding processes) used for making a weld is applied in the form of pressure. During the welding state, there is no molten pool form as we observe in fusion welding processes such as SMAW or TIG or friction welding even, a type of solid state welding.

In cold welding, as the name is given, the welding or joining of two metal parts takes place at room temperature and under pressure.

How Cold Welding works?

The principle of cold welding to create a bond between two metals is based on cleanliness and closeness. Two metals are bonded without heat is because of the removal of the oxide layers on the surfaces of the materials being joined. Thus meeting the per-condition of cleanliness.

Almost all metals in their natural states have some type of oxide layer on them (e.g. on stainless steel & aluminum). These metal oxides form a barrier that prevents the metal atoms on the materials from being pressed together and bonding with one another. However, once the oxide layer is removed, the metal atoms are able to join with one another with enough pressure. This applied pressure help to create the necessary metallurgical bond in the cold welding.

The oxide layer before the welding can be removed by wire brushing, grinding, vapor degreasing, and other chemical and mechanical means. As a pre-condition to cold welding, the material to be welded needs to be ductile to avoid fracture during the pressure stage.

Uses of Cold Welding

The cold welding technique is highly beneficial for dissimilar metals. As when dissimilar materials are fused during welding, they don’t produce any joint because of metallurgical reasons. This can result in the metals not joining together or can lead to weak welds or welds with cracks. Contact welding mitigates this issue as it is based primarily on the atomic bonds created by the atomic closeness between two parts.

Generally, cold welding is used to join butt or lap joints. Cold welding is used in automobiles, lab research works, aerospace & advanced science experiments where conventional welding techniques can not be applied.

Challenges in Cold Welding

1. Cleanliness

The first pre-condition for cold welding is the material surface condition. The materials to be welded shall be free from the oxide layer and other surface contamination. Which is a highly time taking a job and an expensive one.

2. Type of metals

Metals that are not brittle and possess adequate elongation can only be joined using cold welding. Also, metals or alloys with carbon and those that get strain hardening are not advised to be joined with cold welding.

3. Geomtry of the material

This welding technique works best with regular shape components. For example, the joining of wire is a good example of cold welding of uniform and regular part shape. An irregular product shape will reduce the weld joint strength.

4. Closeness

The other main challenge is to bring the closeness between the two parts so the atomic force can make a joint take place. To achieve this, high pressure is mandatory.

Which material can be joined with Cold Welding

As you understand cold welding apply high pressure to produce a joint so only ductile metals can be joined with cold welding. Cold welding is successfully used to join aluminum, Al (even 7XXX series which is generally lack weldability), Ni alloys, copper, and its alloys such as brass, silver, and silver alloys, especially as wires.

Material with carbon lacks weldability with this welding technique.

Strength of Cold Welded Joint

Cold welding produces similar strength joint as produced by other welding processes such as SMAW, TIG, Laser, etc. subject to welding takes place in right conditions. As stated earlier pre-conditions of welding such as oxide-free surface, right pressure, ductile metals, carbon free metals & ideally a regular surface at the joining area.

Advantages of Cold Welding

1. Heat affected zone free weld

Contact welded joints have no heat-affected zone (HAZ) as there is no heat is involved.

2. Sound and neat weld joints

As there are no metallurgical changes in the weld metal and HAZ, Cold welding produces quite strong weld joints.

3. Welding of Dissimilar Metals

Cold welding product sound weld joint for dissimilar materials. Weld joint of copper to aluminum can be made with cold welding which is otherwise not possible to join.

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