Internal Stress?

[gutboy17]

I just received back a flat panel from our chemical milling facility and it is warped. The panel is 7075-T6 .080" thick aluminum alloy and measures 46"x24" roughly. The panel deflects almost 6" mid-span of the 46" length. The bow is in the direction of the chemical milled side. The chemical mill is to a depth of .03" and represents about 80% of the total surface area of the panel. I was told that the reason the panel warped was due to internal stresses in the material were not relieved and when the chemical milling took place it created an asymmetric stress loading on the panel causing it to warp. Is this a possibility or is there some other reason? Supposedly, when we purchased the material for the project we selected aircraft grade aluminum (QQ-A-250/12). Shouldn't the aluminum be stress relieved? Lastly, is there any hope in saving this panel for use? Reverse roll the warp out of the panel, stress relieve, etc?

 

[swall]

Can you live with T73 properties instead of T6? If so, you may be able to straighten the panel by clamping it or weighting it and applying the T73 thermal treatment.

 

[unclesyd]

If you can live with a little surface modification on the concave side you can very easily flatten the sheet with peen forming. I have straightened similar thickness panels using a set up that used our bead blasting apparatus. I think you can find one off shops that can straighten the panel.

Here are two companies that provide the machinery to do this and will probably provide you the name of a shop that can do the job.

http://www.metalimprovement.com/shot_peen_forming.php

http://www.wheelabratorgroup.com/xq/aspx/f.3/c.49/pt.1/qx/equipment.htm