Controlling end ring balance in pre-balancing spinning process

1. A method comprising:

assembling rotor bars so that they are at least partially enclosed in a core of a rotor;

connecting an end ring to ends of the rotor bars;

inserting a shaft into the core;

balancing the end ring around the shaft in a pre-balancing spinning process that involves spinning the rotor by assembling a conical wedge onto the shaft before the pre-balancing spinning process, the conical wedge placing a pre-load on the end ring; and

spinning the rotor in the pre-balancing spinning process.

2. The method of claim 1 , wherein the shaft is inserted into the core before the end ring is connected to the ends of the rotor bars.

3. The method of claim 1 further comprising machining the shaft to create the conical wedge.

4. The method of claim 1 , wherein balancing the end ring around the shaft comprises assembling an inner bracket inside the end ring, the inner bracket having an interference fit to the end ring and to the shaft.

5. The method of claim 4 , wherein the inner bracket is annular with a cylindrical inner surface toward the shaft, and a cylindrical outer surface toward the end ring, and an annular groove between the cylindrical inner and outer surfaces.

6. The method of claim 5 , further comprising using a chamfer on the shaft in assembling the end ring and the inner bracket onto the shaft.

7. The method of claim 1 , further comprising assembling the rotor into a stator to form an electric motor.

8. The method of claim 1 , further comprising balancing the rotor.

9. A method comprising:

assembling rotor bars so that they are at least partially enclosed in a core of a rotor;

connecting an end ring to ends of the rotor bars;

inserting a shaft into the core; and

balancing the end ring around the shaft in a pre-balancing spinning process that includes:

assembling an outer bracket onto the shaft with an interference fit, wherein one of the outer bracket and the end ring has a protrusion, and another of the outer bracket and the end ring has a slot corresponding to the protrusion; and

spinning the rotor.

10. The method of claim 1 , further comprising determining, after the pre-balancing spinning process, whether the rotor is imbalanced, and, if so, balancing the rotor by adding or removing material on the end ring.

11. The method of claim 9 , wherein the shaft is inserted into the core before the end ring is connected to the ends of the rotor bars.

12. The method of claim 9 , further comprising machining the shaft to create a conical wedge.

13. The method of claim 9 , wherein the step of balancing the end ring around the shaft in the pre-balancing spinning process comprises assembling an inner bracket inside the end ring, the inner bracket having an interference fit to the end ring and to the shaft.

14. The method of claim 13 , wherein the inner bracket is annular with a cylindrical inner surface toward the shaft, and a cylindrical outer surface toward the end ring, and an annular groove between the cylindrical inner and outer surfaces.

15. The method of claim 14 , further comprising using a chamfer on the shaft in assembling the end ring and the inner bracket onto the shaft.

16. The method of claim 9 , further comprising determining, after the pre-balancing spinning process, whether the rotor is imbalanced, and, if so, balancing the rotor by adding or removing material on the end ring.

17. The method of claim 9 , further comprising assembling the rotor into a stator to form an electric motor.

18. The method of claim 9 , further comprising further comprising balancing the rotor.