Welcome back to the Spinweld blog! In our last couple of posts, we’ve shown you just what friction welding does and why it’s useful. In this post we’ll dig into the number one reason for using friction welding: Joining dissimilar metals.
Joining two metals may sound unusual, but in the fabrication world, the process is a lot more common and desirable than you’d think. Many industries have embraced the advantages of friction welding, and you probably have used products that made use of it.
What exactly qualifies two metals as different from each other?
The composition of metals is overly complex. Though their outer appearance may seem similar, the true makeup of the metal goes deep beneath the surface.
The main trait of metals is their nobility. The nobility of metal indicates how sensitive it is to corrosion, which occurs when electrons are given away. Basic metals let their electrons go easily; noble metals make you work for it!
Metals that are closer to each other on the galvanic scale tend to be the best for pairing. However, with friction welding, you can join metals further apart on the scale, and the more noble metals will help prevent corrosion from the less noble metals.
What is the reason to join dissimilar metals?
The strength, savings, and flexibility of joining dissimilar metals are the main reasons it appeals to manufacturers. When you use two different types of metals, you:- Save on material costs by combining materials you already have or being able to purchase materials that don’t cost as much.
- Increase joint strength in your project. When you use two dissimilar metals, a process occurs creating a new phase of composition, properties, and crystal structure, which makes the item stronger.
- Reduce the weight of your item by using a pipe/tube body that is solid at the ends but not in the interior.
- Save on machine costs and use by using weldments that are closer to the final size needed.
- Form and function – In some applications there is just no other way to make it.
What kinds of projects use dissimilar metals?
The core purpose of joining two dissimilar metals is to create more efficient tubes, shafts, and industrial rollers. These key parts of manufacturing are used frequently in vehicles, from the automobile you might drive to planes and even in ships. They are also found in industrial printers and in various equipment in the oil industry. Without the use of dissimilar metals, the items built would cost more and possibly even run less efficiently.
Most common bi-metallic friction welds:- Aluminum to steel
- Copper to aluminum
- Titanium to copper
- Nickel alloy to steel
Are there certain metals that can’t be joined?
While friction welding is quite magical, it can’t join everything together. Because of their electrochemistry, certain materials just can’t be joined.
Dry bearing and non-forgeable materials cannot be welded by a friction welding process. Dry bearing (polymers, carbon-graphite’s, solid film lubricants and composites, and ceramics-cermet’s). Non-forgeable (ductile cast iron, materials with carbon content over 2%).
In general, if it can be welded by mig or tig or other conventional welding techniques, it can be friction welded with increased value. Most materials can be welded to themselves. Bi-metallic welds are common, but some combinations are not possible or produce a less than full strength or brittle weld.
