Need advice regarding forcing metal into curve and welding to hold shape, and warping

[1911guy]

Sheet metal is .105" and was bent on edges and rolled at the back end where they couldnt roll/radius it due to the side folds.
I had pcs waterjet cut that will become the curved folded edges.
I'm building a wood and steel form to lay the main piece over and then screw the edges down onto it, holding it in the correct curve and then welding the add-on edge pieces on.
Im using a MIG with mild steel .030 wire and tacking it every 2 inches or so to start to avoid warping.
So, as I've never done this before.....how do I minimize and warping or puckering at the joint? I will be going on the backside and tacking the inside 90 degee joint too after the outside is fully welded and all gaps are filled.
Will the forced curve want to rebound and crack the welded joint (see side view "gap exaggerated" pic) on the side?
I'm probably overthinking theis whole proceedure but want it right the first time.
Thanks

 

[Sergei Slovenija]

Did something similar. Thickness 4 and 3 mm. Welded with dots, then with an intermittent seam. And welding gaps, alternately on both sides. Filling and leveling seams with acrylic sealant.

 

[mike 109444]

Maybe use a pair of ratchet straps to "set" and "hold" the curve while welding.
And welcome BTW

 

[1911guy]

Yes had thought of the straps meadthod to get it there but then hold it securely with screws.
Thanks

 

[maroon]

If u got a compressor handy. Blow air onto it. To keep it cool. I wouldn't adviser running water around a mig. But a bit of air/water running are ways to cool it. Although looking at that you shouldn't need it. I'd alternate the tacking doing the two sides together. Starting at the butting on the side working outwards to the end. It will bend around with more ease the closer you get. But do the two sides together alternating to stop it warping/going on a wonk getting strength/rigidity (less warp flex) coming from the opposite side as you go on. Not finish one side, then do the other. Pull it evenly out over.
That's how I'd approach it.
Meet it together as you go on type of thing, push it together with your knees.

It's quite bizarre that if you were doing that with gas you would be pointing your gun in the complete opposite direction of where you were welding.

 

[Barking Mat]

Oxy acetylene and clamps, then tack welds ?