The most common method used by manufacturers is to anneal the electrical steel after the lamination has been punched to its final shape (e.g. the diameters are fixed, the slot geometry is complete, and any "retaining" geometry is complete). Due to the temperatures involved (750 C or so), it is something that is done at the end of the process whereby the lamination is created - well before any actual construction (e.g. stacking) of the stator or rotor begins.
Generally speaking, the laminations are "rotated" through several iterations around the circumference. How many different orientations result is dependent on the number of laminations per circle (for large machines) and the manner of fixing the laminations to the stack (for smaller, single-circle, laminations).
The anneal process is used to relieve the magnetic changes induced by the mechanical action of the punch shearing the edge of the steel. It is not to "de-burr" the edge, where the shearing action has created a small upset.
There are couple of points regard to the rotations of laminations while stacking:
1. Laminations should be rotated every 90degrees with reference to the notch of the previous axial section for every 0.25" or 0.5" stack. This actually helps in
- (i) randomizing the grain directions (the idea to use CRNGO steel) and
- (ii) to reduce the ovality of the stator ID along the stack length which would otherwise give rise to uneven airgap, unbalanced magnetic pull, require higher ampere turns and increased electrical noise and vibration.
2. The burr side of every lam should be in the same direction so as to maximize the stacking factor.
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