Welding is a process of fabrication that applies heat to two or more metal parts to melt and fuse them together. Cooling the metal parts form a secure bond. Cold welding seems like an anomaly, and it can happen in unwanted circumstances. How do you stop cold welding?
You can prevent cold welding by selecting the right materials, lubricating and coating surfaces with materials that prevent adhesion and fusion, and securing structures that could otherwise join if left loose.
This article delves into the mechanism of cold welding and how to stop it from happening. It also describes the advantages of cold welding and whether it is a bad welding process.
What Is the Mechanism of Cold Welding?
Even though welding is almost always synonymous with applying heat, not all fabrication processes need to use heat. Cold welding is an alternative fabrication process that works without heat, and it is also the only fabrication method that works at room temperature or close to it.
Cold welding is also called cold pressure welding or contact welding, and it uses pressure under vacuum conditions rather than heat. The metal atoms within the metal parts come together to fuse the pieces through solid-state diffusion.
It differs from laser welding, arc welding, and friction, as it has no molten or liquid phase in the joint. You can also join plastics using cold welding, and all bonds cold welding forms are as strong as those of the parent metals.
Most metals usually contain a surface oxide layer, whether visible or negligible. The oxide layer is a thin barrier that prevents two metal parts’ atoms from forming metallurgical bonds, and eliminating this thin barrier allows the metals to fuse.
However, removing the oxide layer does not guarantee that cold welding will occur. Another condition is that at least one of the metal parts must be free from severe hardening, carbon, and ductile or malleable.
This second requirement limits the choices of metals you can use for cold welding. Copper and aluminum are soft metals you can weld using this process.
You can also weld “unweldable” grades of aluminum like the 7xxx series and 2xxx series, as well as copper, zinc, silver, silver alloys, stainless steel (under great pressure), nickel, and gold, especially in wire form.
How Do You Stop Cold Welding?
Unwanted cold welding is a problem early satellites faced, and current spacecraft also contend with it. There is a vacuum in space, and orbiting materials without an oxide layer can easily stick together to form cold welding bonds. To prevent accidental cold welding, here’s what you can do:
- Select the right materials
You could choose materials with contact surfaces that do not allow cold welding or use dissimilar metals—with low contact adhesion. A Cold Weld Database listing material combinations and their adhesion is available via the Aerospace & Advanced Composites site.
- Coat the surfaces of selected materials
You can oxidize, paint, anodize, or coat surfaces with a chemical film to reduce contact adhesion. However, fretting and impact damage can reduce the effectiveness of the coating.
- Cleanliness
Clean the assembly before deployment and during use by flushing or purging it with inert gases or liquids. You can also perform environmental sealing.
Cleanliness reduces the molecular and particle contamination of the assembly, which reduces wear, corrosion, and abrasion of the coated materials.
- Reduce the actuator dependency or the number of moving parts.
- You can also apply a lubricant between two moving or contacting surfaces or use the specific material surface properties they have.
- Reduce environmental exposure by shielding against radiation, electrostatic charge, micrometeorite, chemical interaction, and thermally insulated parts exposed to thermal cycling. They introduce contaminants and damage coating.
- Secure passive structures like locks, fasteners, latches, etc., to prevent abrasive particle contaminants from coming in between other moving parts and wear.
With these measures, you will limit the risk of unwanted cold welding occurring.
What Are the Advantages of Cold Welding?
This unique fabrication process provides several benefits due to the absence of heat and other opportunities it offers. The advantages are:
- Cold welding does not produce a heat-affected zone (HAZ), which reduces the risk of negative mechanical or chemical changes to the fusing parent materials.
- It offers clean welds with joints as strong as the parent material. The absence of brittle intermetallic compounds at the join also ensures a clean weld.
- You can join dissimilar metals that don’t join with other welding processes, like aluminum and copper.
- Besides the advantage it provides when joining aluminum to copper, cold welding also allows the welding of aluminum 2xxx and 7xxx series that does not respond to other metal welding processes.
- Other welding processes require heat energy to run, which can be expensive for manufacturing companies.
Although the initial setup for cold welding is more costly compared to heat welding, cold welding is cheaper to perform in the long run because it requires less energy.
Applications of Cold Welding
Cold welding has a range of applications across various industries, including:
- Electrical engineering and aviation—cold welding is a common welding technique here, and operators consider it one of the best ways to bond metals and other materials.
- It makes up the issues thermal energy poses in welding wires, which is perhaps the most common application of cold welding. It forms strong and fast joints on wires.
- The automotive and aerospace industries also use cold welding to create lap or butt joints.
Is Cold Welding Bad?
When Galileo arrived at Jupiter in 1991, NASA scientists could not launch the spacecraft’s antenna completely, and several studies led them to conclude that cold welding had fused the antenna’s main mobile structure.
Cold welding is almost always a terrible occurrence in space exploration without appropriate preventive measures. Other limitations and disadvantages of cold welding are:
- The cost of cleaning materials and ensuring they are oxide-free. Cleaning can also be hard to manage in an environment of high-volume production.
- There is a limit to the materials you can join using cold welding because the materials must be ductile and free from carbon.
- Any irregularities on the surfaces of the workpieces can also pose a problem when joining. Cold welding requires the materials to be of normal shape and have no surface irregularities.
Cold welding is still a valuable asset in the fabrication process across many industries, despite these drawbacks.
