Controlling flatness of welded aluminum plate.

[fordfan485]

I'm currently designing a platform that has an 18ft outer diameter plate with a cutout in the center (roughly 100” x 130”) for the equipment it interfaces with. The plate is made out of 1/4" aluminum 5086. To get the required size the plate will be seam welded from multiple smaller plates and have the welds grounded smooth. To avoid this thing looking like a potato chip after it is welded up I was thinking of applying flatness to the bottom of the plate.
Now you are probably saying to yourself why bother doing this on a weldment. In the past we have had problems with our shops welding up thin aluminum plate. Numerous times we have had assemblies delivered (they were not very big about 48 in diameter had stiffeners and handles welded to them using 1/8 fillet welds) that really did look like Pringles after they where welded up (It seems like all our stuff is built by 3rd shift apprentices.)
I was thinking of applying flatness 1/4" over the whole surface and 1/16" over any 6 in dia area. Does this seem reasonable to achieve or does anyone have any suggestions? I’m not looking for this thing to be machined but if it were be out of spec after welding to either have the shop bend, flame straighten ,or any other means to get it flat.

 

[Tmoose]

If I read this right 3/4 inch over any 10 feet x 4 foot section would be the commercial tolerance for flatness of a brand new plate.

http://www.fergusonperf.com/pdfs/tolerances-options_flatness.pdf

Is the finished 18 foot plate going to be shipped as one piece someplace?

 

[MintJulep]

You can put it on the drawing.

That doesn't mean anyone can achieve it.

 

[MikeHalloran]

Since you can't stand on a plate that big without buckling it, you will probably need some reinforcement. The most logical way to do that is to make it like pieces of a pie, with the radial edges folded down, and bolted to each other. You can probably fold the inner edges, too. That leaves an arcuate weld to a slightly bent strip at the outer edge, and four corner welds per section.



Mike Halloran
Pembroke Pines, FL, USA