Rotary friction welding Rotary friction is a solid-state process joining two metal objects by applying rotational motion and forging pressure to the objects. High temperatures generated by friction, transform the point of contact into a plasticized state. This area is known as the weld interface. The pressure is applied to forge a metallic bond between the atoms of the objects. The overall molecular integrity of the original objects remains intact due to the narrow heat-affected zone of this tec