What comes to your mind when you think of a welding procedure? If you are like the rest of us, it is going to be the use of heat for melting the metals and thus fusing them. That is how most of the welding techniques work except for cold welding. When it comes to cold welding, two metals are joined without making use of heat.
Yes, we know it sounds impossible, but it is the truth. NASA has had quite a run with it, and you can read about cold welding in space as well.
Welding Metals Without Heat? What Is Cold Welding?
Let’s start with the obvious purpose of heat when it comes to welding metals together. Heat is utilized for making the metals plastic enough to allow for diffusion of atoms. This can be achieved by using two workpieces or making use of a different medium in the middle for fusing them together.
Cold welding, however, works a bit differently. It is also known as cold pressure welding and contact welding. It relies on pressure for joining two materials. The process is scientifically known as solid-state diffusion. When you press two metals together, they will not weld together. Why? Because of an oxide layer that acts as a thin barrier on the surface of the materials.
Cold welding tackles this issue by preparing the metals before they undergo welding. The preparation involves brushing or cleaning the metals to the extent that the top oxide layer or any barrier layer is removed. Generally, this is achieved by first de-greasing the metal and then wire brushing it.
As soon as the required cleanliness of the surface is achieved, both materials are pressed together mechanically with sufficient force. The amount of force will be based on the kind of material that is being used. Another condition for cold welding is that at least one of the materials must be ductile and should not have undergone severe hardening. This leads to a narrowing of the list of materials that can actually be used for cold welding. Soft metals perform the best when it comes to cold welding, and the most common joints that can be achieved with cold welding are Butt joint and Lap joint.
For the Butt joint, often, the barrier layer doesn’t have to be removed since plastic deformation takes place during the joining process and removes the barrier automatically. On the other hand, lap joints do need special care since otherwise, the materials won’t adhere properly to one another. Cold welding has been in use since the bronze age. However, the very first scientifically made cold weld experiment was carried out in 1724 by Reverend J I Desaguliers.
The currently accepted explanation of cold welding is that it creates a metallic bond that is formed as a result of interaction between electrons and free ions when two metals are pressed against one another. When cold welding is executed properly and with the right material treatment, the resulting metal is actually as strong as the parent metal.
The Limitations Of Cold Welding
Despite the said benefits and ease, the perfect cold welding is not easy to achieve. This is because of a number of reasons; oxide layers, surface irregularities, surface contamination, and more. Ideal cold welds only come into existence when two surfaces that are being pressed together are clean and free from any kind of contamination.
Benefits Of Cold Welding
Some of the benefits of cold welding include the fact that it creates the same bond strength as that of the parent material. Welding using other means won’t help you achieve such a strength. Cold welding can be used for welding Aluminum 2xxx and 7xxx series that is generally doable with other kinds of welding.
Cold welding can help you achieve clean and strong welds without the formation of any kind of brittle intermetallic compounds.
