Lamination Sheets

As noted on previous post, rotor and stator core consists of thin lamination sheets. These lamination sheets are packed together to form the stator/rotor lamination package. The rotor lamination package is then interference fitted to the shaft with either shrink fit or press-fit.

Below is a picture that illustrates the rotor core and the thin lamination sheets placed together:

In general, various Key parameters of lamination material of rotor core are important such as

  • magnetic flux density
  • low coercivity
  • low core-loss characteristics

 

Furthermore, the selection of lamination sheets depends on various factors such as:

  • mechanical
  • electromagnetic
  • thermal
  • material cost
  • etc

The majority of the applications use electrical steel variants. One variant of electrical steel that is used very common is silicon steel

Another step in the process of creating rotor/stator cores is the direction of the rolling process and the annealing method, since it affects significantly the material properties of the core. Common approach here is to roll the lamination sheets on specific degrees and then to place them in directions which enhance for example the strength characteristics of the package. Thus the material usually exhibits orthotropic behavior.

An additional step in the process of forming rotor-stator cores is the step of insulating the lamination steels so eddy current losses can be minimized between them

Various grades of thin lamination sheets are available with information such as thickness, permeability, losses, other properties. The cold rolled lamination sheet is the cheapest and the most common for not so demanding motors.

Finally, the rotor core is assembled on the shaft by an interference fit. The value of the interference fit is selected having in mind various technical specifications such as, mechanical properties of mating parts, max speed of rotor, spin stresses, etc.