Most of us associate welding with an electrical arc or an open flame as the energy source. The metal is heated to a liquid or molten state in the joint, and it can be connected with or without filler material.
However, cold welding is not the same. No flame, no electrical arc, and no molten phase exist as an energy source.
In this article, you will learn about the basics of cold welding, including how it works, its advantages and disadvantages, and its various applications. We will also explore the history of cold welding, from its discovery in the 1940s to its modern-day uses in pressure welding machines, laser welding, and ultrasonic welding.
How Does Cold Welding Work
Cold welding is a solid-state welding process that joins two metal surfaces together without the need for heat or electrical current flow. It works by pressing two metal surfaces together, which brings the surfaces as close as possible. As the space between surfaces becomes extremely narrow, the nanoscale distance becomes irrelevant, making the atoms jump from one surface to another. The formed joint has the same characteristics as the base metals, and the two pieces become a homogeneous mass, making it difficult to find the joint line and differentiate between the two original pieces.
Preparing the Metal For Cold Welding
To achieve perfect cold pressure welding, it is necessary to clean the surfaces and prepare the joint's geometry. If cold welding wires together, there is no special attention needed in the preparing phase other than making a clean cut on the ends of both wires before applying pressure. However, if welding more complex sections, it is necessary to prepare the metal accordingly.
The Joint Surface
Whether you are welding pipes, wires, or another kind of section, the recommended surface is a simple flat area between two metals. The surface irregularities and roughness make it more difficult for interatomic attraction to form a homogeneous mass. So, you should flatten the joint surface area as much as possible before attempting to achieve a cold weld.
Cleaning The Surfaces For Cold Pressure Welding
The most vital step is cleaning the surface of the two metals from the oxide layer, oils, grease, and any other contaminants. There is zero tolerance for contamination if you wish to achieve a perfect cold welding joint. While every metal has oxides on its surface, removing the oxide layer is not the first step. The grease and oil are also present on the surface, even if not visible to the naked eye. Attempting to remove the oxide layer first with abrasives like wire brush wheels or similar can push grease and other contaminants deeper into the metal surface. Soft metals like gold, copper, silver, and aluminum are most susceptible to getting impurities embedded under the surface. This will make cold welding difficult because the metal part will now have impurities within itself. If you attempt a cold weld, those impurities may not get squeezed out and cause a certain part of the joining area not to achieve interatomic bonds because the contaminants will stand in the way.
So, it is necessary to first clean the surface thoroughly from oils using a cleaning solution appropriate for the metal you are welding. Afterward, the oxide layer is removed by a wire brush, wire wheel, flapper wheel, or other abrasive suitable for the welded metal.
How Strong Are Cold Welded Joints
If you successfully prepare the metal surfaces and clean them perfectly, the cold welded joint will be as strong as the parent metal. With other welding processes, it is possible for the joint's strength and other mechanical properties to outperform the parent metal because the added filler metal may be of a different alloy, or the thermal treatment may influence the material in the weld zone, changing its characteristics. However, the cold welded joints cannot achieve better joint characteristics than the metal itself. It is easiest to achieve near-perfect bonds when cold welding wires. But when welding other metal shapes, improper preparation can compromise the joint strength.
Cold Welding Advantages
- The most significant advantage of the cold welding process is the absence of heat-affected zone ("HAZ") responsible for many welding problems. Since there is no arc or concentrated heat, there is no HAZ either.
- If correctly performed, cold welding makes perfect welds without brittle intermetallic compounds, micro-cracks, porosion, contamination, and other joint weaknesses.
- It is relatively easy to perform because most of the work is actually related to metal preparation.
- The cold welding process is perfect for welding aluminum, especially when joining it to copper. Achieving such a bond is very challenging with other welding processes.
- Welds a wide variety of metals, and it's especially suitable for joining dissimilar metals.
- It is faster than many other welding methods.
Cold Welding Disadvantages
- The metal must be perfectly cleaned to achieve high-quality cold welding bonds.
- It is very challenging to use the cold welding method in industrial applications because of contaminants in the air like metal dust, sparks from grinding in fab shops, and other cross-contamination sources.
- Nanoscale molecular irregularities can weaken the resulting metal parts joint.
- Cold welding works best with flat surfaces, while irregular shapes are difficult to achieve.
- Cold welding procedures cannot join metals with carbon content like carbon steel. It is possible to achieve cold-welded bonds only with ductile, non-ferrous metals like copper, aluminum, silver alloys, lead, gold, etc.
What is Cold Welding Used For
Cold welding is a solid-state welding process that is used in various industries, including dentistry, electronics, automotive, production, and aerospace, to join two or more metals together without the need for heat or fusion. This process is particularly useful when working with flammable or explosive substances, as it is a safe method for joining metals. It is also commonly used when laying underground wires where there is a hazard of flammable gases, as arc welding or similar processes may cause these gases to ignite.
What Materials Can Be Cold Welded
Cold welding is limited to non-carbon and non-ferrous materials, but most other softer metals are suitable for cold welding. These materials include copper, aluminum, gold, silver, and its alloys, nickel, 70/30 brass, zinc, and even alloys like Aldrey, Tripple E, and Constantan. The cold welding process can also achieve strong welds with 2xxx and 7xxx aluminum series, which is impossible using any arc welding process.
One of the most significant advantages of cold welding is its ability to join dissimilar metals. For example, it significantly outperforms the bond quality achieved between copper and aluminum compared to processes like friction welding, flame brazing, or resistance welding. The cold welding process solves the issue of fusion welding failure when joining aluminum and copper by squeezing out the oxides and air spaces and achieving a near-perfect bond without any heat that can affect the metallurgical characteristics of these metals.
Possible Weld Joints
The butt and lap joints work the best when cold welding because this process relies on the contact surface. For welding wires and pipes, the butt joints are used. It's easy to prepare the ends by trimming the wires or cutting the pipes, which brings out a shiny, clean metal surface to the contact area between two pieces, allowing you to achieve a strong bond.
When cold welding with a lap joint, you have to consider the reduction in metal thickness that occurs due to applied pressure. Your welded part could lose up to 50% of its original thickness, depending on the material. This should be calculated in advance because your finished product may not meet your expectations.
In summary, cold welding is a useful process for joining metals together without the need for heat or fusion and is used in various industries, including dentistry, electronics, automotive, production, and aerospace. The materials that can be cold welded include copper, aluminum, gold, silver, and its alloys, nickel, 70/30 brass, zinc, and even alloys like Aldrey, Tripple E, and Constantan. The butt and lap joints work the best when cold welding, and the cold welding process can achieve strong welds with dissimilar metals.
Conclusion
In conclusion, cold welding is a solid-state welding process that has been around since the Bronze Age but has only recently gained popularity in the industry. With the help of modern cold welding machines, butt weld joints can be completed in seconds. Cold welding is a process that requires no heat energy, making it a practical option when arc welding is not feasible. Unlike MIG welding or laser welding, cold welding requires only a clean surface and powerful pressure. Although it may seem odd to rookie welders, cold welding is definitely possible and has many practical applications in the industry.
Frequently Asked Questions
How does cold welding differ from traditional welding methods?
Cold welding is a solid-state welding process that does not require heat or fusion to join two or more metals together. Instead, the energy used for creating a weld comes in the form of pressure. In traditional welding methods such as arc welding, the metal is liquefied to create a bond. Cold welding is a non-thermal welding process that results in a strong bond without altering the metal's properties.
What are the applications of cold welding in various industries?
Cold welding has various applications in different industries. It is commonly used in the electronic and aerospace industries for joining wires and small parts. It is also used in the automotive industry for repairing engine components, such as cracked cylinder heads. Cold welding is also used in the medical industry for orthopedic surgery, where it is used to fuse bone fragments together.
Can cold welding be used for joining dissimilar metals?
Yes, cold welding can be used for joining dissimilar metals. However, the metals need to be compatible for a successful bond. Cold welding is most effective when joining metals with similar properties.
What are the primary benefits and limitations of cold welding?
The primary benefit of cold welding is that it does not alter the metal's properties, resulting in a strong bond without compromising the metal's integrity. Cold welding is also a non-thermal process, which means that it does not require heat, making it a safer alternative to traditional welding methods. However, cold welding has some limitations, it is not suitable for all metals, and it requires a clean and precise surface for a successful bond.
How does cold welding technology apply to space equipment?
Cold welding technology is essential in the aerospace industry, where it is used to join small components such as wires, connectors, and sensors. In space, traditional welding methods are not practical due to the absence of gravity, making cold welding the preferred method for joining components.
What considerations are needed for successful cold welding in orthopedic surgery?
In orthopedic surgery, successful cold welding requires precise alignment of the bone fragments and a clean surface to ensure a strong bond. The surgeon needs to have a good understanding of the properties of the metal and the appropriate pressure to apply to create a successful bond. Cold welding is a non-invasive procedure, making it a safer alternative to traditional surgical methods.