To understand how
laminations are made, it helps to first understand how they
work. The above drawing shows a lamination with magnetic flux
ø dividing equally through what is known as the "back iron" or
"back leg" of the lamination.
The dimension of the
back iron and the side legs (W1) are chosen to be
exactly half of the center leg width (W2) to keep
the flux density equal throughout the
lamination.
Scrapless lamination stamping
Here we see a method of
stamping a steel strip which prevents waste of material by
stamping the center leg of one "E" from the space between the
center leg and the side leg of another lamination.
This method can be used
only when the center leg dimension is equal to the "window
area" of the transformer coil. The result is a side-leg
dimension exactly one-eighth that of the length of the back
iron. The width of the back leg is usually (but not always)
the same as the side leg width to equalize flux
density.
When an air gap is
desired, the lamination tool is modified to shorten the length
of the entire leg. This causes the width of the back iron of
one half of the lamination to be larger by the amount of the
gap.
Most lamination tools
are set up such that only one half of the lamination set
contains the air gap. This reduces tolerance buildup of the
air gap dimension, improving electrical
consistency.
The gapped half may in
some cases be identified by adding punches to the corners of
the laminations.
Another tell-tale sign of a
scrapless lamination die is a small bump which occurs at the
separation point between outer legs of adjacent
laminations.
