Grinding thin aluminum to obtain .02 flatness

[bwoody33]

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??
Thanks...

 

[israelkk]

Aluminum warps after massive machinning. The multiple holes change the internal stress balance in the plate. causing the warp of the plate.

The only solution is to machime the two sides after drilling the holes. However, you have to stress relieve the plate after the drillings before machining the two sides. Two options are given . First, is to let the plates rest for two weeks after drilling and then machine both sides. Second to stress relieve the plates in an oven and then macjine both sides.

You didn't mention the size of the plate which is very important, as larger the plate the worst the problem.

 

[bwoody33]

Thanks for the reply, that was helpful. The OD of the part is 14.940, so it's a pretty good size.
If we end up grinding after drilling the holes, we're going to have a heck of a time deburring the thousands of holes. Any ideas for how to easily deburr these holes after grinding?

Thanks!

 

[unclesyd]

Try the following website for deburring.

http://www.surftran.com/

There are a lot of other ways to get holes in metal.

What are the size of you holes and how many?
What type edge doe you have to have at the hole?

 

[israelkk]

What is the holes diameter?

I would try to drill the holes in a such a way that the internal stresses will be relieved equally. Similar to the way you tight the bolts of a car wheel or in a motor head, you tight each time the two bolts which are most far away from each other. In the same way I would try to drill the holes such a way that it will always be in a symetrical way with respect to center of the plate.

One other way is to clamp the plate or few plates between two thicker plates and then drill the whole stack togeter. When the drilling is finished stress relieve the whole stack together and then diassemble the stack. This can be done if the hole diameter is large enough.

 

[bwoody33]

The holes range from .0465-.0492 and are all toleranced at +/-.0005, so drilling is pretty much the only option. Even with drilling the cycle time is long, about 15 hours, as there are approximately 5000 holes. The edges of the holes only need the burr removed, and they don't need to be countersunk or shaped in any way.
Currently, a 3/4" bottom plate is being used and a top plate isn't. But mounting a top plate wouldn't work because the cycle time would be way too long, especially since the current cycle time is already 15 hours.

 

[unclesyd]

Take a look at this technology.

http://www.lourdessystems.com/home.htm

 

[grinderguy]

Just a few thoughts. Stress relieving may change your material from t6 to t0. I use vacuum chucks, which we make, to hold parts like this when we grind them, even when there are holes in the part. I would use the longest, closest to the part tool holder for the drill. 12 seconds per hole, sounds like it could be faster. The finish on the cutting edge of the drill could change the burr and feed rate.

Robert Setree

http://www.advanced-grinding.com

 

[funnelguy]

bwoody33,
I really don't have an answer for you. Just an observation and maybe something to try.

You said, "Some parts are way out of flat, some are in. We can't seem to control the process enough to get a consistent part." It seems as though the only part of the process that would give this type of inconsistency is the raw material. I'd look into having blanks premachined, stress relieved and ground in an unrestrained condition to lower the internal stresses in the material and improve the consistency, lot to lot.

For something to try, how about hording a few of the scrapped parts and making them available to a really good vacuum heat treat operation. Perhaps they can bring them back into flatness? I realize this is a "Hail Mary" suggestion, but these are high value parts that are currently only useful as paperweights or wind chimes. I will recommend a company off forum if requested. Just a thought. There is the possibility that any form of thermal processing coupled with restraining the part back into the flat condition will screw up other features, but hey, what have you got to lose?

 

[bvasa]

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.

Good luck!
-exploring the cutting edge of old technology-

 

[willeng]

bwoody33
Have you considered laser profiling--very accurate, no burs minimum distortion.
Apart from increasing production from the time saving this may give desired results.

 

[dvadams]

Another possibility is Wire-EDM. You could have a tool made that forms multiple holes simultaneously.