Oil canning is a complex phenomenon to measure and determine the source of, mainly because it has numerous causes that could come into play.
One of the most prominent reasons metal warps to form oil canning is because metal inherently wants to return to its original shape.
So when it’s getting processed and roll formed, the metal takes on a new form, but may attempt to revert back to how it was before.
Such movement can form the wavy bumpiness characteristics of oil canning.