making a 'flat' aluminum plate

[bnrg]

Hello all,
I have an application that requires an aluminum plate to be flat when mounted within a certain amount. It is approximately 70 inches x 18 inches x .50 inch. Taking out the deflection due to bending leaves me with an allowance for flatness of the plate of about .010 inch. In the past with stainless steel parts I have had problems when machining off the 'skin' on one or 2 sides and the part turned into a potatoe chip shape. Does anyone have any recommendations on machining/thermal processes to machine the part to required thickness and flatness?
Thanks,
Bob

 

[MintJulep]

Can you use cast aluminum jig plate? Should meet your .010 flatness requirement as purchased.

 

[unclesyd]

Here is the websites of two people we have used to provide tooling plate (jig plate) in our manufacturing area. The tolerances listed for Alcoa are lower than we experienced in real life you might give them a call.

Interlakes Bases can give you a better tolerance and were nice people to work with.

http://www.alcoa.com/global/en/products/product.asp?prod_id=605&Business=&Product=&Region=

http://www.interlakesbases.com/productsindex.htm

I was about to forgot the best one..

http://www.tciprecision.com/index2.shtml

 

[MikeHalloran]

That's a relatively thin part in aluminum.

As suggested, prefinished jig plate is your best bet. Thicker jig plate would be better yet.

I don't know what happened to your stainless parts, but cold working is part of the mill process for many aluminum tempers, especially in the 'high strength' alloys. If you take the skin off a cold- worked aluminum plate, you release some of the locked-in cold work strain that bestows apparent strength. The remaining strain should be _expected_ to warp the part, badly.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[tbuelna]

bnrg:

Some aluminum alloys are more suceptible to machining induced distortion than others. Talk to a metalurgist at your supplier. The alloys marketed as "tooling plate" are usually the most dimensionally stable.

 

[unclesyd]

If you will look at this site and click on the titles "Grinding" or "Sawing" you can see what is possible with different metal removal processes. As you bring up either one of the above use the slider to get more information.
Also your part could be mechanically straightened or flattened.

http://www.tciprecision.com/index2.shtml

 

[IFRs]

Try 6061-T651 alloy.
Standard mill thickness tolerance on the 18" width is +/- 0.023" while standard mill allowable deviation from flat for sawed or sheard plate is 0.1875 in any 6 feet longitudinal and 0.375 transverse.
On the other hand, I have never seen 1/2" plate any where near that bad. You'll ahve to measure it and get it ground as needed.

 

[ProEpro]

Cast plate will give you better results.

http://www.designnews.com/article/CA270744.html

ProEpro

http://www.whitelightdesign.com

Pro/E FAQ

http://www.whitelightdesign.com/servicestips.htm

 

[surfdog]

You could try stress relieving the piece. Take a cut on both side to get the "skin" off. Then stress relief (call a Heat Treater)...then finish machine the thickness....do you have a vacuum chuck (it would be a big one)?

 

[SuperStress]

Check with your aluminum supplier about getting "MRS" plate (minimum residual stress). It is flat-rolled product specifically intended for applications where material is removed off of one side only (usually chem-milling in aerospace applications). It is chemically identical to other product forms of the same alloy, only the processing has changed. I know Alcoa offers MRS, and I'm pretty sure Kaiser does too. Don't know if it is available in .5 inch stock.

The goal is reducing the delflections from unequal residual stresses after machining or chem-milling.

I don't have a lot of personal experience with this material, but have heard a lot of good things.

SuperStress

 

[Tmoose]

"an aluminum plate to be flat when mounted......."

The mounting sub-strate may boss the plate around. Depending upon the flatness of the sub-structure, the mount detail (2 inch diameter metal standoff?) and the number and location mounts, I'd anticipate I might have to shim to keep the plate neutral/flat at assembly. Or, even use the mounts to flatten/true the plate.

 

[bellman]

Cast jig plate would be the way to go. First, it is cast, second, it has been ground to remove the "skin" and flattened and leveled. I have worked with this many times and always had good results. But a piece that size, you need to pay alot of attention to what you are mounting it to and how. A thicker plate would be recommended.