Friction welding technology has developed from several traditional forms to more than 20 kinds, which greatly expands the application field of friction welding. The shape of welded parts extends from typical circular cross-section to non-circular cross-section (linear friction welding) and plate (friction stir welding). The welded materials are broadened from traditional metal materials to new materials such as powder-free alloy, composite materials, functional materials, refractory materials, ceramics-metal and other heterogeneous materials.