Abstract: A cylindrical portion of a motor yoke has a securing portion to secure a stator core at an axial section except the axial ends of the cylindrical portion. When manufacturing the yoke, at first, a work is prepared that corresponds to the yoke before the securing portion is formed. A mandrel, which includes a forming portion, is then inserted into the work. The forming portion has an outer diameter smaller than the inner diameters of the axial ends of the cylindrical portion. Subsequently, the axial section of the cylindrical portion on which the securing portion is to be formed is pressed with dies from radially outside of the cylindrical portion toward the forming portion, thereby displacing the pressed section of the cylindrical portion radially inward and forming the securing portion on the work. As a result, the motor yoke with high accuracy is manufactured while reducing a waste of machining.

Abstract: A cylindrical portion of a motor yoke has a securing portion to secure a stator core at an axial section except the axial ends of the cylindrical portion. When manufacturing the yoke, at first, a work is prepared that corresponds to the yoke before the securing portion is formed. A mandrel, which includes a forming portion, is then inserted into the work. The forming portion has an outer diameter smaller than the inner diameters of the axial ends of the cylindrical portion. Subsequently, the axial section of the cylindrical portion on which the securing portion is to be formed is pressed with dies from radially outside of the cylindrical portion toward the forming portion, thereby displacing the pressed section of the cylindrical portion radially inward and forming the securing portion on the work. As a result, the motor yoke with high accuracy is manufactured while reducing a waste of machining.