Assembly Process of Rotor, Electric Motor
The rotor assembly is formed when a shaft is interference fitted into a rotor core. The fitting characteristics are very important for reliable operation of motor and for secure transmission of torque. A wrong designed intereference fitting can lead to detachment of rotor core from the shaft. One test to be performed here after final assembly of rotor, shaft and the necessary parts is a dynamic balancing method.
Two main types of interference fit are known for this application:
- shrink fit
- press fit
Usually press fit is used for small rotors. For large rotors the force required for assembly can be large and special attention is needed here for abnormalities such as shaft bend, overstressed rotor cores, etc..
Shrink fit is performed by heating the rotor cores with induction heating, while keeping the shaft at room temperature. When the rotor core reaches a specific temperature the internal diameter expands and becomes slightly larger than the outer diameter of the shaft, thus allowing the shaft to be inserted inside the rotor core without significant force. At the final step the assembly is allowed to cool down. In addition, rotor packages are compressed with a special tool.
The diagram below illustrates one example of rotor manufacturing process for electric motors.
The rotor core is formed from thin lamination materials. The lamination sheets are punched by stamping mamchines or cut by laser to form the desired lamination patterns. The stamped laminations are then passed from a heat treatment process to stabilize their various properties such as electromagnetic, thermal, mechanical, etc. Finally these lamination sheets are packed together to form the rotor lamination pack or rotor core