Advice re: warping sheet steel
- I am NOT a welder. I need advice regarding a project that involves
welding some 14 ga. HRPO steel.
I'm having a cabinet fabricated. After the four sides are fabricated,
I need to have a top and a bottom applied. They need to be watertight
(but not pressure tested).
The base and top of the cabinet are roughly 26 x 20. I'm having the
base and top formed by cutting a sheet an inch oversize (27 x 21),
then notching a 1/2" out of each corner, and bending the four sides
up. This essentially forms a tray that's 26 x 20, with a 1/2 inch
lip. This tray is slipped over (or under) the four sides, and then
welded (MIG) to the sides.
I need the bottom of this cabinet to be pretty flat. When my welder
attaches this bottom 'tray' to the four sides of the cabinet, the 20 x
26 bottom warps. Everyone thought that the bottom was expanding; I
think that the 1/2" vertical lip is shrinking. The force that it
applies warps the bottom.
We did an experiment today with a 'tray' with a bigger lip (~3/4").
We formed the tray, then welded its corners closed. Then we put the
cabinet sides into the tray, and substantially filled the tray with
water. Then we welded. The result was the best we've seen of all the
many experiments we've tried. The'tray' warped, but not too badly.
The sides warped pretty bad, but they were dummies -- only 5" tall,
where the real cabinet sides are about 30-something inches tall.
We have tried forming only 2 lips on the tray and butting the other
two edges. We have formed the tray to fit both inside and outside the
cabinet. We have tried making the bottom out of 10 ga. We've never
tried running a single bead across an entire side; we just do an inch
or two here, and inch of two there, over to the third side, then to
the fourth, back to the first to continue, and so forth. So far, all
have warped. The best result has been with the cooling water.
So: I have two questions. 1) What's really happening here? Why am I
getting this warpage? 2) What can I do about it.
Thanks in advance for any insight,