Grinding thin aluminum to obtain .02 flatness

I’m currently working on a project where the print requires .09 thick 6061-T6 aluminum with a .02 flatness callout. The print also requires a few thousand small holes to be drilled in it, all the same size.
The problem is this: the material seems to be moving around a lot after the holes are drilled, specifically, it goes in and out of the .02 flatness requirement. Some parts are way out of flat, some are in. We can’t seem to control the process enough to get a consistent part.

I was considering starting with .125 thick material and fly cutting it. Would this be advantageous?? Any other suggestions for an aluminum to use where it will be easier to hold the flatness??? Any other suggestions that would make holding the flatness on this part easier??


I wonder if maybe a completely different solution is in order. With the thickness-diameter ratio of your plate, along with a ~1/32" grid of holes, it doesn’t sound like this is intended to support significant loads. This leads me to think it might be some kind of diffuser plate or flow control for a low-viscosity liquid or a gas.

Would it be possible to substitute a semi-permeable material for this highly machined plate? Something like an air bearing - maybe a pressed & sintered powdered metal.

If you need to stick with the solid aluminum plate, I’d try drilling the .09" material in T6 condition (you could drill a stack of plates if it is cost-effective), then clamp a stack together in a fixture (with spring preloading) to send through a full solution anneal & artificial aging cycle. This would stress-relieve the plates, re-flatten them, and put them into a dimensionally-stable condition. The spring preloading will ensure that the clamp force is maintained as the plates flatten.

Above is a snippet.

In the original thread, the plate is a disk 15" in diameter and there are 5000 holes 0.05 diameter (with 0.0005" tolerance). This could be something like an air table pressure pad (needing extreme flatness to function) or a particle filter (not needing much flatness at all).

Did anybody think of checking how much pressure is required to produce the deflection tolerance?
Would it be acceptable to flatten the part in a hydraulic press to re-flatten it?

With 6061 you really are at the mercy of the internal stresses in the plate - as noted elsewhere, it’s not uniform enough to trust the plate to respond to the hole drilling process consistently.

1 Like