Friction welding techniques are generally melt-free, which mitigates grain growth in engineered materials, such as high-strength heat-treated steels. Another advantage is that the motion tends to “clean” the surface between the materials being welded, which means they can be joined with less upset forging process pdf. It is believed that the flash carries away debris and dirt.
Another advantage of friction welding is that it allows dissimilar materials to be joined. Normally the wide difference in melting points of the two materials would make it impossible to weld using traditional techniques, and would require some sort of mechanical connection. Friction welding provides a “full strength” bond with no additional weight. Friction welding is also used with thermoplastics, which act in a fashion analogous to metals under heat and pressure.
The heat and pressure used on these materials is much lower than metals, but the technique can be used to join metals to plastics with the metal interface being machined. For instance, the technique can be used to join eyeglass frames to the pins in their hinges. The lower energies and pressures used allows for a wider variety of techniques to be used. Friction welding was first developed in the Soviet Union, with first experiments taking place in 1956.
The American companies Caterpillar, Rockwell International, and American Manufacturing Foundry all developed machines for this process. Patents were also issued throughout Europe and the former Soviet Union. The piece is then spun up to a high rate of rotation to store the required energy in the flywheel. Once spinning at the proper speed, the motor is removed and the pieces forced together under pressure.