Friction welding is a type of welding that uses the heat created from rubbing one object against another to fuse the two together. Pressure is applied to the two objects to help this fusion take place. The heat is created from the friction of the objects, so it occurs directly in the area being fused together and has little effect on the surrounding areas. This process is ideal for two objects that have very different melting points. It creates a bond between the two surfaces through fusion, but is not literally melting the materials during the process.
Since melting typically does not occur during the actual procedure, this process is technically a type of forging rather than a type of welding. The process is much like that of welding, however, and it is classified as such. Within friction welding exist two categories of welding techniques. The first technique fuses together different metals while the second is used with thermoplastics.
Metals can be fused through friction welding techniques such as spin welding or linear friction welding, both similar processes. Spin welding, also known as inertia welding, rotates one piece while the other remains stationary. Pressure is applied and the rotating piece gradually comes to a stop. The heat and pressure cause a bond to form between the two materials. Linear welding follows the same process, but the piece is rubbed up and down instead of rotated.
In thermoplastics, friction welding can join together a plastic and a metal. This is a useful way to connect materials that cannot be joined through traditional welding methods. Eyeglasses are an everyday example of the benefits of welding thermoplastics. The plastic glasses frames can connect with the metal hinges through a friction welding process. This would be harder to achieve without friction welding due to the fact that the metal and the plastic have such different melting points.
Orbital friction welding and linear vibration welding are techniques used on thermoplastics. Linear vibration welding uses vibrations and pressure to rub the pieces together to create fusion, while orbital friction welding rotates points of one material against the surface of the other. Since plastics begin to melt under heat, the process continues until the plastic has softened. Then the process is stopped, and as the plastic cools it forms a bond. These processes help easily bond together a variety of different materials without requiring extra materials or nuts and bolts.