Disk drive motor, and method of manufacturing its rotor

摘要

A motor rotor 10 is formed as follows: First, in a first forging step, a hum manufacturing primary block 6A is formed. Next, a second forging step B is effected to form the primary blank 6A into a secondary blank 6B. In this step, a forging die is used to secure an annular yoke 34 to the inner cylindrical surface 61a of a hub cylindrical portion 61 by punching, in such a manner that both whole edges of the annular yoke are sealingly closed thereby. In the second forging step B, by drawing the inner cylindrical surface 34a of the annular yoke, its circularity is improved. The annular yoke can be secured to the hub cylindrical portion with use of an adhesive agent. Moreover, the annular yoke can be fixed in such a manner that it is accurately coaxial with the hub cylindrical portion. In addition, the gap between the annular yoke and the hub cylindrical portion can be eliminated.