[Sidponcho]

Originally Posted by north

The problem you are describing about the center and corners is classic “springing”. When you stamp steel you don’t just hit it hard enough to make it take the shape you want but you hit it with even more force so that you tear the fibers in the steel to “teach” it that this new shape is its natural shape. The way you do this is press size and the number of stamping steps to get the final shape. The classic problem with all repop stamping is those Asian mills are using much lighter presses so even though they can completely press the dies together the pressure is insufficient to prevent the steel from “springing” back a bit to the flat sheet it used to be.

Anyone who’s had experience fixing damaged factory sheet metal knows what I’m talking about that when you “help” a crumpled panel with heat, pulling and pressure it “wants” to find its way back to the way it was stamped.

Actually, nitrogen is often used in the lower die to control the form. If the Chinese used QC fixtures and were held to standards you'd have better repops. Often times it's the same amount of work to make it right.