We all have an idea of what welding is right? It’s simply the process of joining two or more materials by applying pressure, filler material, or heat. Of course there are a number of different welding processes, each of which are given titles that match the method they use to meld the materials together. For instance if base materials along with a filler material are melted down to join materials together, the process will be called fusion welding. If melting of this kind doesn’t happen, the process will be titled solid state welding.
Basically, any welding process that doesn’t require materials to be melted together is titled solid state welding. You won’t find yourself requiring heat to be applied when you perform the solid state welding process. You will however, need to apply heat in order to get a solid joint, which is why this process is also sometimes called pressure welding. So it’s important to keep in mind that the base materials are typically raised to a higher temperature when being joined-but, they are never raised to a temperature considered the melting point.
What are the Solid-State Welding Processes?
Welding processes that don’t require melting to take place are titled solid state welding processes. A more scientific way to describe these processes is a group of welding processes that require heat below the melting point of the metal, without adding brazing filler metal to the equation. Inside of the umbrella of solid state welding are:
- Forge Welding
- Ultrasonic Welding
- Friction Welding
- Roll Welding
- Cold Welding
- Explosion Welding
- Diffusion Welding
Solid-State welding processes are some of the oldest welding processes on the planet.
What are the advantages of Solid State welding?
- You don’t have to worry about a wide HAZ.
- The appearance of your weld is more sumptuous
- You don’t have to worry about as much distortion due to the lack of heat in your welds.
- It’s easier to join different types of metals
What are the disadvantages to Solid State welding?
- You would need to have a special joint design, surface finish, or edge preparation
- The shape of the components is important to pay attention to.
- You can’t use filler material which means that you can’t fill a wide root gap.
Roll Welding
What is Roll Welding?
Roll welding is a process that joins together a stack of sheets or plates. The stack of sheets is fed through a cold rolling mill under sufficient pressure to produce enough deformation. Metals used in roll welding should be ductile such as:
- Aluminum Alloys
- Copper
- Copper Alloys
- Nickel
- Low Carbon or Mild Steel
- Aluminum
There are a few types of roll welding including Pack Roll-Welding and Laser Roll-Welding.
Cold Welding
What is Cold Welding?
Cold Welding (aka contact welding) is a bonding process that doesn’t require heat or fusion at the point where the two metals are joined. There is no molten/liquid point in these two welding processes. Cold welding was discovered in the 1940s it was found that two similar, clean metals would bond if brought into contact in a vacuum.
Video credits to Audiopedia. It explains what cold welding is and it’s applications.
It can be a challenge to achieve a perfect cold weld for a few reasons due to the oxide layers that form on the top of metals in most conditions, irregularities, surface contamination, etc.
What are the types of cold welding?
There are 2 recently discovered forms of cold welding called micro-scale cold welding and nano-scale cold welding.
What is cold welding used for?
Cold welding is considered the best welding process for joining metals and creating a parent metal like bond. It’s great for joining metals and creating a parent metal like bond with metals. Non-ferrous metals are the perfect candidates for cold welds. The two most commonly cold-welded metals are Aluminum and Copper. Carbon is a metal that is impossible to cold weld.
Diffusion Welding
What is Diffusion Welding?
Diffusion bonding is a form of solid-state welding that is capable of joining both dissimilar and similar metals. A principle commonly seen in solid-state welding wherein the atoms of two metallic surfaces intersperse over time. Diffusion welding is typically done at a temperature between 50 and 70 percent of the absolute melting temperature of the materials being welded.
Video credits to TWI Ltd. It talks about the diffusion welding process.
What are the characteristics of Diffusion Welding?
Diffusion welding doesn’t require the metals to go through a liquid phase and often doesn’t require a filler metal. The weld itself has no added weight and the weld itself will often show the temperature resistance and strength of the metals being welded. There is also very little (to no) plastic deformation among the weld.
When is Diffusion Welding used?
Diffusion welding is used for fusing reactive and refractory metals, similar and dissimilar metals, as well as pieces of metal of varying thickness. It’s typically used for welding jobs that are impossible or incredibly difficult to weld by other means only because of how ridiculously expensive it is to perform the process.
How is Diffusion Welding performed?
When you join metals with a similar structure diffusion bonding is done by clamping both metals together with their surface abutting one another. Before you weld you must machine both surfaces to as smooth a finish as possible. Not only that but you must also keep contaminants away from the weld.
Once you clamp the two metals both heat and pressure must be applied for several hours. One can heat both surfaces using either electrical resistance or in a furnace. Pressure can be applied to the weld using a hydraulic press at temperature, which allows for exact measurements of load on both pieces of metal.
Diffusion bonding must be done in either an inert-gas or a vacuum when you’re using metals that have a high oxide layer.
What are the benefits of Diffusion Welding?
Diffusion welding offers several benefits including:
- Diffusion welding offers high quality joints and takes away from the possibility of porosity or discontinuity occurring.
- Diffusion welding allows materials to be manufactured that have a complex shape.
- The cost to perform Diffusion welding isn’t incredibly high.
- The process can be used on both dissimilar and similar metals alike.
Forge Welding
What is Forge Welding?
Forge welding is a welding process that joins two pieces of metal together through heating and hammering them together. Forge welding can also consist of both heating and forcing the metals together by using a means to create enough pressure to cause plastic deformation. This is considered both one of the oldest and simplest methods of joining metals together.
Video credits to Black Bear Forge. It gives a basic introduction to what Forge welding is and the process of doing it.
What are Forge Welding processes?
The most well-known forge welding process is the manual hammering method. The manual hammering forge welding process is done by doing the following:
- Heat metal to a proper temperature
- Coat the metal with flux
- Overlap the weld surface
- Strike the joint with a hand-held hammer
The weld joint in this occasion is typically formed to allow the flux some space to flow out (by beveling / rounding the surface a bit and subsequently hammering the metal in an outward fashion so it can be squeezed out).
What temperature is needed to forge weld?
The temperature necessary to forge weld is around 50 to 90 percent of the metal’s melting temperature. One can weld iron when it passes it’s A4 temperature where it’s allotrope changes from gamma iron to delta iron. Steel welds at a lower temperature than iron because it’s critical temperatures are affected by alloying agents such as carbon. When the carbon content in steel increases, the welding temperature decreases. As long as their carbon content is similar Iron, cast-iron, and different steels can be welded to one another. For a more detailed understanding of the temperatures look below:
- Pure Iron can be welded at temperatures between 2,500 degrees Fahrenheit and 2,700 degrees Fahrenheit.
- When Steel has a Carbon content of 2 percent it can be welded at a degree of 1,700 degrees Fahrenheit and 2,000 degrees Fahrenheit.
- Common Steel can be welded when it’s between 1,600 degrees Fahrenheit and 1,800 degrees Fahrenheit.
Friction Stir Welding
What is friction stir welding?
Friction stir welding is a welding process that requires a non-consumable tool to join two facing work-pieces without causing the two metals to actually melt. The heat generated in friction stir welding is generated by friction that stems from friction generated by both the work-piece and the rotating tool – this heat then turn into a softened metal near the friction stir welding tool.
Video credits to NASA Video. It explains what friction stir welding is and it’s uses.
What are the advantages of friction stir welding?
Friction stir welding yields several advantages over fusion welding processes. One major benefit / advantage that friction stir welding has is that since it doesn’t cause the metal to go through a liquid phase issues dealing with porosity, solidification, liquation cracking, and a few other welding defects can be ignored. Aside from that benefit friction stir welding works well with a number of materials and parameters.
Other advantages of friction stir welding are:
- It has good mechanical properties in the as-welded condition
- No consumables are needed
- It yields improved safety because of the lack of spatter and toxic fumes
- One can use thinner materials with the same joint strength
- It has a low environmental impact
- It typically produces a good weld appearance and has minimal thickness over/under matching, which takes away the need for expensive machining after welding
- It offers both performance and cost benefits when you switch from fusion to friction welding.
What are the limitations of friction stir welding?
If friction welding is performed improperly it can yield certain, unique welding defects. When you weld with lower than necessary temperatures due to either low rotational speeds/ high traverse speeds the weld material won’t be able to handle extensive deformation while it’s being performed. This can result in tunnel-like defects appearing on the either the subsurface or surface of the weld. One such defect is one called the “kissing bond”. This welding defect is considered troublesome only because it’s difficult to detect using methods such as ultrasonic testing or x-rays.
Examples of other disadvantages in friction stir welding are:
- An exit hole is left when the FSW tool is withdrawn
- Friction stir welding processes are less flexible than both manual and arc welding processes.
- Friction stir welding often has a slower traverse rate than other fusion welding techniques.
- Large down forces are required with heavy duty clamping necessary to hold plates together.
Explosion Welding
What is Explosion Welding?
Explosion welding is a solid-state welding process that uses acceleration at high velocity and chemical explosives to weld materials together. Explosion welding is done when a compression force is created via detonation of explosives and is used to join overlapping metal sheets.
Video credits to NobelClad. It goes over the explosion welding process.
What is Explosion Welding used for?
Explosion welding is usually used to clad carbon steel, stainless steel, titanium, and copper with aluminum. In essence, explosion welding can be used to weld nearly any metal and alloy that allows more than 5% of strain.
What are the advantages of Explosion Welding?
An advantage of explosion welding is that it produces bond between metals that typically wont occur with regular welding processes. Explosion welding doesn’t melt either surface metals but it does plasticize the surface of the metals which causes them to become intimate enough to weld together. Another advantage of using explosion welding is:
- They weld a wide array of both non-compatible and compatible metals that can be welded using explosion welding. In total there are 260 possible metal combinations.
- Explosion welding produces a permanent bond.
- Explosion welding produces a bond at the molecular level.
What are the disadvantages of Explosion Welding?
A major disadvantage of explosion welding is that extensive knowledge of explosives is required to be good enough at it to weld safely.
Ultrasonic Welding
What is Ultrasonic welding?
Ultrasonic welding is an industrial welding technique that uses high frequency acoustic vibrations to create solid weld (among-st pieces that’re held together using pressure). Ultrasonic welding is typically used to weld plastics and dissimilar metals. There are no nails, soldering materials, connective bolts, or adhesives used during ultrasonic welding to bind the metals together.
While ultrasonic welding is a good welding process for welding both hard and soft plastics, it is also a decent welding process for welding metals, such as:
- Nickel
- Copper
- Aluminum
What industries are Ultrasonic welding used in?
Ultrasonic welding is performed in various industries, including but not limited to:
Automotive / Aerospace
When used in either the automotive or aerospace industries Ultrasonic welding produces engine components, steering wheels, flash drives, and microcircuits
Computer / Electrical
When used in the electrical and computer industries Ultrasonic welding produces computer disks, microcircuits, flash drives, field coils, wired connections, and capacitors.
Packaging
When used in the packaging industry Ultrasonic welding produces items such as frozen food packages, candy bars, beverage containers, and containers for sensitive materials such as fireworks and ammunition.
What are the benefits of Ultrasonic welding?
Ultrasonic welding offers a few benefits as well. Listed below are the benefits one can expect to receive while Ultrasonic welding.
- Since very little time is needed for curing and drying Ultrasonic welding saves time.
- Ultrasonic welding joins materials without using any adhesives, soldering materials, or screws which translates into lower production costs.
- Ultrasonic welding doesn’t need heat or filler materials which means that neither thermal distortion nor the introduction of contaminants into the weld. There are no visible seams where part being welded are joined which results in the weld having a visually appealing finish and durable bond.
- The bonding process for Ultrasonic welding is considered sanitary which makes it well-suited for medical and food products.
