How to keep plate straight when welding

[spressomon]

Ok...I have a little project I'm working on. 1/4" flat stock 6"x10". To that I tacked a piece of 1/4"wall 3.5"x3.5" square tube (10" tall; open end to the flat stock). I tacked all 4 sides of the square tube to the 1/4" flat stock then I burned it in. But then I got heat curl at the ends of the 1/4" flat stock after the bead run.

So: What's the best way to get the two pieces welded (MIG) together without distorting the 1/4" flat stock?

 

[PAToyota]

Short segments of weld alternating around the weld and letting things cool between welds so that you don't get extreme heat buildup in any one area.

 

[chet]

that is a tricky one to weld without getting pull. try tacking the flat plate down to a metal table first.

 

[madinal]

PATOYOTA is right. Patience and lots of cool ventilation. Weld a little here and a little there and then go do something else while the metal relaxes and cools off. Then repeat until done. Don't try and turn down the heat you'll just get bad welds.

 

[spressomon]

Thanks to all for your input. Its tough being patient enough to stop in the middle of pushing that puddle...

 

[KLF]

I have several pieces of W-shapes and some scrap lengths of 4"X4" heavy tube, I use lots of clamps to keep it flat while welding and cooling.

 

[Dirtsquirt]

depending on the severity

you can sometimes salvage the part by welding on the crown of the curve which will make the metal pull towards the weld side.
and grind flush.

This a last ditch hail mary its better to never have to do this.

 

[Walton]

No matter what, you are going to shrink metal when you weld. Get a dead blow hammer, and stretch it back flat. Clamping it down will help also.

The Space Needle legs were straight until they flame bent them. You can do wonders with a torch, and a water hose.

 

[OregonLC]

could you tack the 6x10 plate to some larger 1/2" stock and then cut it off and dress it after the square tube was welded on?

 

[Pin_Head]

could you tack the 6x10 plate to some larger 1/2" stock and then cut it off and dress it after the square tube was welded on?

No. It will shrink and bend when you cut it off due to accumulated stress.

Metal always shrinks when welded. You can minimize it by minimizing the amount of heat input, but you can't eliminate it. You either have to engineer the welded part to be the proper dimension after welding or you have to straighten it post welding.

 

[ojaij40]

No. It will shrink and bend when you cut it off due to accumulated stress.

Metal always shrinks when welded. You can minimize it by minimizing the amount of heat input, but you can't eliminate it. You either have to engineer the welded part to be the proper dimension after welding or you have to straighten it post welding.

'
You could try "stress relieving" the plate before you cut the tacks,..by heating the plate with a rosebud,..and letting it relax

 

[Pin_Head]

Stress relieving works by shrinking the surrounding metal to match. If you heat the larger plate to a high enough temperature it will also shrink and relieve the overall stress. Steel always shrinks when heated above the phase transition temperature (approximately cherry red). Below the transition temperature, the steel will expand with increasing temp, but will return to its original dimensions when cooled.

 

[tgreening]

Pre-tension your flat stock.

Cut a couple square shaped pieces of flat stock, stack them up, and place them under the piece of flat stock you will be welding, positioned under the spot your tube will be.

Put a clamp on each end of your flat stock and draw it down into a bow shape. Based on the amount of warping you experienced the first time you should have a good idea of how much to pre-tension it.

Place your tube in position and weld away. Still a good idea to jump around when welding without putting too much heat into any one spot.

Release your clamps and do the happy dance.