Why a thin aluminium disc warped, and how to stop it

The part is a machined aluminium disc with a 1.2 mm web and a 5 mm boss. Parts were coming out of flat after machining and anodising, and a web that thin has very little stiffness to resist internal stress.

Scrapping or straightening parts was no long-term answer. The client needed the cause, so the process could be changed at source.

The most likely cause was residual stress in the plate, released unevenly as more material came off one side of the part than the other. With so little material left in the web, even a small imbalance bends it, and heat from anodising and sealing adds to the effect.

We set out practical changes across the whole route: stress-relieved plate, such as T651 temper or cast aluminium tooling plate; machining sequences that take material evenly from both faces; vacuum fixturing that holds the part without clamping distortion; and changes to the sealing step to reduce its thermal effect.