Abstract: Complementary packs of laminations (41, 43) are provided for use in an electromagnetic device, the laminations in different layers having legs of length that alternates according to a predetermined pattern. The lamination of one pack (41) can fit into the laminations of another pack (43) which has legs alternating according to a complementary pattern. The packs (41, 43) can be push-fitted together about a bobbin (45) to form an interleaved stack of laminations for a transformer or other electromagnetic device. A method and apparatus for forming the stacks are also described.

Abstract: In one embodiment, the pack is torsionally flexible. Pack of laminations comprises laminations which are connected one to another by only a single connection. The single connection is provided by a projection which projects into a depression. The projection has a height which is greater than 50% of the thickness of the lamination and the depression has a depth which is greater than 50% of the thickness of the lamination. The depression and projection are produced by a projection punch which cooperates with a die. The die has a lip which is either radiused (r) or conical (C) and the punch causes the metal of the lamination to be extruded past the lip into the die while the depression is being formed. The radiused or conical lip allows the height of the projection and the depth of the depression to be greater than the normal 50% shear stress fracture depth/height.

Abstract: Packs of laminations and a method of assembling the packs of laminations to make a core of an electromagnetic device such as a transformer or motor are described. First and second packs of complementary laminations (12, 14) are provided that fit relatively freely together and have interfitting formations e.g. dovetail formations (16) and projections (18). Preferably adjacent laminations of each pack are attached. The first and second packs of laminations (12, 14) are held positively together in mechanical contact e.g. in a jig. The formations (18) on one or both of the laminations are then deformed to engage the formations (16) of the other lamination to clamp the first and second packs of laminations (12, 14) together. In an alternative form the first and second packs of laminations clip together.