Distortion for long welds

I have to extend the rear of my cattle crate down 2 inches as its a bit to high for most cattle loading ramps and i also have now got a trailer to pull and its also to high for that as well. The crate is not permanently attached to the truck tray and only clamped on. The existing "bumper" is 125mm x 75mm RHS (rectangular hollow section) mild steel (don't know what thickness) which has been fully welded to a piece of 75x75 (6 or 7mm) angle. My extension is a piece of 100x50 RHS fully welded to a piece of 30x30 RHS (both 3mm wall) I made the extension this shape as i wanted to bumper to butt against the crate when backing against the ramp, so the tray takes the force rather than the clamped on crate. My question is around the distortion which is going to be caused by fully welding the extension on. I believe fully welding the entire join is necessary because it will be living its entire life is cattle feces and urine and every crate ive ever seen with stitch welds and either no caulking or even with caulking it soon fails and allows liquids in which rusts out. I fully welded my extension and got a bend as expected but was also able to press it out also as planned. However welding the extension in, if it warps i wont be able to press it out. I have stick and mig available (both gas and gasless), but am entirely self taught so probably by professional standards pretty ordinary, but things usually stayed glued together when im finished. Don't really want to hire it out to be tig'd, but if its the only way well so be it. I fabricated the other crate you can see in the background in one of the photos and every join in that was fully welded and apart from surface rust due to my crappy paint job it is rust free after 15yrs. However none of the rhs was off the same size im going to use now, i don't know if having the welds further apart will cause more or less distortion? My extension will be welded along the long side, so 130mm apart, both ends welded and 2470mm (8ft) of weld. Previously kept my welds to about an inch and skipped along keeping both sides even and keeping the voltage down to reduce heat input. Was using gas mig. In the photos, white steel is tray, maroon is crate and unpainted is my extension. I know it will distort to some extent, a few mm i can live with, looking like a banana, probably not. Any better way? Or other advice? Thanks

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you're not welding up pipe for an x-ray or pressure test, so stitch weld it. Get it tacked and then 50MM here and there give it time to settle. It won't pull it out of shape if you don't lean on it in one go.

Weld it up like SK1 posted. Then if you want it completely welded for corrosion, which I understand, take a couple of days to finish it. If you get a bigger bow than you like, come back with pictures and we will tell you how to heat straighten it (assuming you have an OA torch).

Beating the bejasus out of each weld with a needle gun as soon as you finish laying down each pass of a particular stitch will also help to reduce any stress in the weld bead that might want to cause a bow in the finished job.

Just move around and try not to put too much heat in one area. MiG with gas would be the best.

yes I love stitching with a MIG. Easy. and @Nige was right about peening too. I don't have a needle gun but the point of a slag hammer does wonders.

skyking1 said: yes I love stitching with a MIG. Easy. and @Nige was right about peening too. I don't have a needle gun but the point of a slag hammer does wonders. Click to expand... I would suggest to @Pony that if he doesn't already posses a needle gun then buy, beg, borrow, or steal one before starting the job......

Thanks all for the replies. Yes, I have a needle scaler, I refurb a bit of of rusty old stuff now a now and again, very handy bit of gear. Never used it in this context before though, will do now. Also have oxy/acetylene, although I'd rather try to keep it from warping to any significant extent, rather than trying to remove said warp with heat if possible. The crate is steel frame with aluminium riveted for the panels (Huck riveted?) There also appears to be some sort of sealant tape between the two metals. While welding should be far enough away not to effect the tape, would like to keep the oxy away if possible. I'll be in an open sided shed to weld, so will need to set up some tarps to keep the wind out, they're forecasting storms soon, so might be a few days before I get it done. Will update with results, thanks again.

Pony said: Never used it in this context before though, will do now. Click to expand... If you have an offsider to run the needle gun while you weld it would make the process really easy.

I am not convinced about the need to peen the weld. Looks to me the bit it is getting glued to will hold it pretty straight. Weld 6 inches, skip 18 inches, weld six inches and rinse and repeat. Have to keep an eye on it in the future, the constant slamming into ramps might cracks develop years down the track. One of our trucks the rear bumper section is bolted to the tray as well, just as well as it is always getting cracks where it is attached to the crate.

I agree with RC. Weld even 4 inches at a time spread out and then back step weld. After you do the first welds and come back to the first weld (hopefully it has cooled sufficiently) do the next weld coming back to the first weld instead of continuing the first weld. Back step welding is common for reducing warpage. Have never seen or heard a needle scaler reducing warping. Stress relief yes but warping is caused by too much heat input and the subsequent cooling. Large I-beams can be curved just by using a rosebud(s). Some don't think about warping and will weld either a full rod/long weld at a time or just keep welding from one side to the other. Short welds and back stepping is the most common for reducing warpage.

Still haven't gotten around to welding this in, had to go and work elsewhere. Hopefully this week. Related question. I built a stockcrate for another smaller truck approx 15yrs ago, by chance this crate will fit perfectly on my new trailer (actually new, not just new to me) for length and width. Just to add context which will become clear later on, I built this crate on the flat bed of the truck. Bolted the angle iron to the combing rails and welded everything else on from there. Truck was 10yrs old at that time and purchased 2nd hand. I had to cut out 2 spreader bars acoss the floor to allow the crate to sit flat on the combing rail of the trailer However the crate will not sit flat on trailer, on one side the middle of the crate is bowed down, so there is a 10mm gap at one end and a 4mm gap at the other. The other side is bowed slightly up, so there is a 4mm gap approx 2/3 way along. I went and got the other truck and yes the flat deck is not flat, it must have previously featured in "Overload of the Day" and the tray is slightly bent. So i built the crate to have the bows in it, as its fits the tray. I put some lashing straps over the crate and was able to pull some, but not all of bows out with it sitting on the trailer. With tension, one side is flat with the trailer, the other side has a 5mm gap front and rear. Crate is 6400mm (21ft) long, 2490mm (8ft) wide and 2100mm (7ft) high. 50x50x5mm angle iron base, 40x40x2.5 rhs bows and crosspieces with 1.6mm gal sheeting, top rail is 25x25x5 angle on which the sliding divider runs, every join welded, inner and outer. The only way i can see this becoming flat is to cut it in half across the middle, bolt it onto the trailer and re-weld it back together. Then i still have to fab up a front sliding gate and fill the rest of the front. If i drill the trailer combing rail, bolts would probably pull it enough to conform to the flat trailer but would be setting up a lot of stress and risk cracking with the roads we have. Other point against brute force is the these crates are supposed to be quick and simple to remove and reinstall, left as is, it wouldn't be either. Other option is put the crate back on the other truck, weld the bottom spreader bars back in and sell it as a truck and crate. Then get a new crate built for the trailer. New crate = $25k Don't have the time to do it myself again. Plan was to sell the smaller truck anyway, just not with the crate. Apart from the paint, existing crate is in perfect condition and i know how strong it is. Wont get an extra 25k selling other truck with crate, so financially worse off, but don't know if its worth the effort to make my crate fit? Opinions?

Your pics. don't show the warping and gaps well enough. You might be able to clamp everything flat and then apply heat to the curved members and leave the clamps on until everything cools off. Welding a heavier straight section on the curved pieces could help as well.

Thanks Dave, I wasn't trying to show the gaps, figured telling was enough. Pictures were more to show the structure of crate to give some idea of rigidity. I just put it back on the smaller truck, to confirm that cutting the spreader bars out hadn't compromised the structure and introduced a warp. It fits back on the tray perfectly, so the bows are simply built into the crate. Clamps won't bend it flat, tried that, i had more luck with the transport straps over the top, but they still wouldn't bend it enough. There's 6 separate longitudinal crossmembers along with over 4ft of sheet metal that has to bend, like I said, I just can't see it happening without cutting it in half. But again, I'm only a hack, so could well be wrong.

Can you tack a few shims under to level up the raised bits, maybe at points where it bolts down or whatever? Seems like it's strong enough and good enough, just needs shimming. Edit. I guess you wanted continuous welds earlier for rust prevention, so you might not like shims.

If it's mostly the bottom you want flat, could you weld angle iron to the bottom tube so it sits flat?

Just cut off the entire bottom or just along where you want to pull it down with a plasma cutter or cut off disc or something like that and reweld it back on. I doubt it would take that long to do.

Went and had a look and, bugger. Another job to do. Out of interest its stitched welded.

Ahh another crappy TWE crate. Ours is cracked far worse then that. Have already welded it up twice. Needs doing again.