Friction welding method and friction welding apparatus

A friction welding apparatus that causes relative rotation of an end surface of a first workpiece and an end surface of a second workpiece while the end surfaces are in mutual contact as a compressive load is applied thereto so as to generate heat due to friction at a joint interface between the workpieces, thereafter causing the relative rotation of the workpieces to stop, and then causing application of an upset process pressure to the workpieces, the friction welding apparatus comprising:

• a pair of holding devices each having a chuck unit holding a workpiece and arranged with the chuck parts facing each other;
• a movement drive source associated in a drivable manner with at least one of the paired holding devices and moving the workpieces respectively held by the chuck parts of the pair of holding devices in a relatively approaching direction;
• a rotary drive source associated in a rotationally drivable manner with at least one of the chuck parts of the pair of holding devices and relatively rotating the workpieces held by the chuck parts;
• a compressive load detecting unit detecting a compressive load acting between the end surfaces of the workpieces held by the chuck parts of the pair of holding devices which press against each other;
• and
• a control unit programmed to control the movement drive source and the rotary drive source based on information from the compressive load detecting unit when the end surfaces of the workpieces held by the chuck parts of the pair of holding devices are brought into contact with each other, so that the compressive load acting between the end surfaces of the workpieces which press against each other is less than a lower threshold of a bend-producing compressive load domain that would cause bending of the workpieces but the compressive load and the relative rotational speed between the workpieces are such as will cause the heat due to friction which is generated between the workpiece end surfaces to be capable of causing plastic deformation between the workpiece end surfaces, wherein
• the control unit includes
• a storage unit storing as setting information the rotational speed of the rotary drive source and the compressive load at the time of contact between the end surfaces of the workpieces, and
• a controller controlling the movement drive source and the rotary drive source based on the information from the compressive load detecting unit and the setting information stored in the storage unit when the end surfaces of the workpieces held by the chuck parts of the pair of holding devices are brought into contact with each other, so as to cause the end surfaces of the workpieces to press against each other with a compressive load that is less than the lower threshold of the bend-producing compressive load domain and so as to cause the compressive load and the relative rotational speed between the workpieces to be such as will generate heat due to friction between the workpiece end surfaces that is capable of causing plastic deformation to occur between the workpiece end surfaces as a result of that heat due to friction.