Welding heat distortion

[warrenpfo]

Hey chaps thought i would ask those here in case i am missing a trick.

I am making up a gate from some 40x20mm stock tubing with a 2mm wall thickness and across the width which it 1200mm i am welding some 10mm sqaure bar every 150mm.

For the life of me i cant get the square bar to not twist. Clamping it or holding it in a vice works great but as soon as you release the vice or clamps it twists.

I am using good old stick welding with 2mm rods and 50Amps. Much higher and i blow a hole in the tubing.

Any tips appreciated.

 

[Shayne]

I'm no welder but i would be looking for the lowest amps that still melted the stick .

 

[frank rabbets]

Put a tack on all the corners to force it to stay where you want. In fact I would have thought to tack the whole job up first and then weld together randomly. Jon will know.

 

[silvercruiser]

Pretty much what Frank said, tack it all square and work small areas at a time. Ive seen some thick plate curl up when welding and getting to much heat in one go.

Do you know anyone with a mig?

 

[BRE Fabrications LTD]

As others have said. Tack it up and then weld small sections at a time. Once you have completed one weld move to the opposite side of the gate and then weld a section there and then onto another and make sure the welds hve cooled before you move back into an area. Keep checking everything is square and flat as you work your way through all of the welds. If you see anything starting to Pull out of shape you may pick it up early enough so that it is localised. I would also avoid any quenching as this will make the distortion worst.

When you are welding the tube to the box section, don't weld fully around the tube in one go. Also do small sections (90') and then weld on the opposite side. When you weld the tube it will have a tendancy to pull towards the side welded. If you have enough decent tacks this will help minimise this.

Lastly, 2mm wall for stick welding is pretty thin, maybe up it to a 3.2mm wall tube? Or rent a MIG...

Pics?

 

[Jon Wildsmith]

I'm not sure what you mean by the bar is twisting? Bending or pulling to one side I can understand but I can't think what you'd be doing to twist the 10mm bar? The tube you're welding it to will distort every time you weld onto it, is that a factor? I don't think I'd be doing any tack welds for a 10mm bar for lack of space for the real weld, I'd clamp it well at both ends, weld 2 opposite sides at one end, weld the same opposite sides at the other end, then back to the 1st end do the other 2 sides, then the remaining 2 sides at the other end. When you weld, as the metal cools you get shrinkage, so you try to do your welds in an order that will even out the shrinkage.

 

[frank rabbets]

I took twisting as in torsion bar even though I could not understand that.

 

[Pat]

Last year I went to an auction at an engineering shop that handled big jobs.What amazed me were the huge welding platforms which were approx 50mm plate to which the jobs were welded to.I spoke to the supervisor and he told me that was the only way to keep the weld jobs correct in their dimensions.

 

[warrenpfo]

Thanks guys I will give all the advice a go and post a few pictures.

 

[StarCruiser]

Last year I went to an auction at an engineering shop that handled big jobs.What amazed me were the huge welding platforms which were approx 50mm plate to which the jobs were welded to.I spoke to the supervisor and he told me that was the only way to keep the weld jobs correct in their dimensions.

Yep, seen this myself. sometimes it's how the metal is cut that makes the difference. For instance cutting a corner at 45 degrees is likely to pull whereas doing a square cut and butting together pulls less.