Myth 3 - Anytime you put compound contours in sheet metal, the costs go out of sight

Pure nonsense!

It is a tooling issue, typically relating to fuselage skins. The photos below show a skin stretch die machined out of laminated lumber yard particle board.

The cost was less than $4,000 and is used to form a New Meyers fuselage skin.

It has reversals in the contours (compound contours) and with a little maintenance from time to time, would be good for a couple of thousand parts.

There are probably two to three dozen shops around the country that could stretch these skins.
Click on image to see enlargement.

Machining particle board stretch die with compound contours.
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Laminated particle board stretch die used to form compound contoured aluminum skins.
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Stretching 2024-0 aluminum over particle board. The top of the die shows the reversals or compound curves.