Welding Stainless Frame without doing curve.

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Hi, i am currently out of idea for my problem. I am making a metal detector convoyeur for my job all in stainless 304 square tubing 1 1/2''. I am using Tig welder about 150amp with a pedal and 8-10 cfm with pure argon. So when i finish welding 2 tubing together it make an arc, curve wich i cant allow for later strap ajustement. I tried several thing like put in water to cold it fast, tack small at once and let it cold slower,clamp and remove it after its cold, i even tried to purge the tubing but always the same. I know some people can weld a frame without any curve in it but how !
Reply:Have you ever welded anything?Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:It happens because the inside of the miter shrinks more than the outside, the main cause is just the shape of the square tube and difference in strength at the inside point vs. the outside point. I've dealt with this problem before and found two solutions.1. Go with the flow. Cut the miter slightly obtuse, so that when it shrinks it will be square. This requires a little experimentation.2. Fight the power. Build a fixture that will hold the material in the correct position during and after the weld. This fixture must be extremely rigid and strong. This method is pretty much the same as building a rig that can bend the weldment into the right shape after it's cooled. Which way you choose depends on a few things like position, accessibility, and the desired surface finish.Ian TannerKawasaki KX450 and many other fine tools
Reply:Yes i weld almost everyday, mostly stainless sheet gauge 16-20 without problem but now i need max 1/32" curve because my ajustement for my strap will be very minimal. Now im having like 1/4'' to 3/8''
Reply:Originally Posted by fortyonethirtyIt happens because the inside of the miter shrinks more than the outside, the main cause is just the shape of the square tube and difference in strength at the inside point vs. the outside point. I've dealt with this problem before and found two solutions.1. Go with the flow. Cut the miter slightly obtuse, so that when it shrinks it will be square. This requires a little experimentation.2. Fight the power. Build a fixture that will hold the material in the correct position during and after the weld. This fixture must be extremely rigid and strong. This method is pretty much the same as building a rig that can bend the weldment into the right shape after it's cooled. Which way you choose depends on a few things like position, accessibility, and the desired surface finish.
Reply:Can you make the frame without doing a miter? Attached ImagesIan TannerKawasaki KX450 and many other fine tools
Reply:Your right picture frame is ok, but left one on the top and bottom is there i have problem like my picture. I want to be like left one and now im having problem like the right side of the picture. I have about 1 feet long between top and middle tubing. Attached Images
Reply:That is my frame with detector on it, i wish i was at the job to give you a more detailled plan. But you can see the frame. On the top of the tubing i have my side plate with bearing for the roller. Attached Images
Reply:Why dont you make two rectangular frames and then make the uprights out of Angle and just weld (or bolt) them  where they meet the frames on the corners, finally bolting on the outside plates?  Personally I'd make the whole thing from angle, it'll be better for bolting onto, look tidier,  and have less places for dirt to hide, especiallly if it's for a food factory.Oh, and to answer your question, try heating the opposite side to the weld with oxy/acet, go easy though, a little heat goes a long way with Stainless (and make sure you've got some pickeling paste to clean the heat marks off afterwards).Last edited by Baila La Pinza; 05-27-2011 at 04:15 PM.
Reply:cant do that because you missing something that is not on my plan the side tubing one is at 11inch and the other at 7inch. And we had a sample of Ceia Metal detector conveyor at 13k$ wich is why we are making ourself for like 2-3k$ they are the same design and they got no curve at their welding tubing, i guess they are using gabarit or something. And yes i tried to heat up with oxy/ace torch the opposite it work a little when its hot but it come back slowly when its cold. Maybe i should heat the opposite before welding then weld it or heat all the zone and weld when its red hot lol.
Reply:Can you skip the vertical weld? If so, you will eliminate a lot of the warping. Attached ImagesIan TannerKawasaki KX450 and many other fine tools
Reply:I could but i dont think so it would be a good idea because the machine will be wash down completly so if i dont weld bacteria could store inside tubing and for food industry we dont want that. Maybe i could put some stainless magic potty !
Reply:Run a bead down the back side of the tubing that is bending inwards. The cooling effect will pull the material straight.Or gusset the tube on the two sides to fight the cooling of the fillet weld that is causing your movement.Like stated above, your two options are to restrain the material prior to welding or straighten it after welding. Attached Images
Reply:Yeah thats a good idea my friend would like that would be better ? Maybe i would tack it temporary with clamp maybe Attached ImagesLast edited by srgess; 05-27-2011 at 07:08 PM.Reason: forgot text
Reply:After I modeled that up, I thought about a temporary strut to fight the movement. Tack it in, weld, tack it back out.You could also force it outward in preparation for the movement. Holding it square will solve a lot of your problem, but it will move a little after you take the strut off.Peening a weld can relieve the stresses that cause movement. You could peen the weld face while pushing the bent leg out and it might allow the bent leg to push out.I made a drill guide fixture for work. I milled a flat on one side, then welded on the other side. After welding I put a .120" bow in the plate (about 14" long). I had really good success peening the welded side to relieve the stress. Took about 5 minutes with a pnuematic chisel and it was flat as could be. It was the bosses idea and he claimed that's how they used to lower their drag cars back in the 50's. Peen the leaf springs to flatten them out.
Reply:After research on web ive found that, i think that may be interesting, not the same as the picture but same technique if i take a beam back on my tubing with an other piece of metal in the intersection of my welding area and clamp opposite side to like bow the tubing so when welding i think this will help a bit. What you think ?
Reply:Anticipate the movement. Intentionally bend the part in the wrong direction, weld it and let it pull back. Problem with this is you have to tune the process and follow the same procedure. Heat input, weld size and fit up will all influence the movement.The strut or gusset is probably your easiest choice.
Reply:so im back to my shop and nothing worked beside taking a 20 ton press cric and put it in between tubing on a table and move up the part. It went straight back without deforming anything.
Reply:Originally Posted by SundownIIIHave you ever welded anything?
Reply:Yes i never welded Stainless tubing, all i welded was shaft, and stainless sheet, wich did not really twist as tubing did to me since i was needing 1/32 max over mesure.
Reply:Well I just got caught up here...If the thing "bows" where you weld and need it straight...seeing as you already have a "test piece" how much is it out from the center of the weld to the outside edge?Should be about even on both ends...That measurement say it's 1/16"..FIRST!Tack the piece together all 4 corners..Take a piece of 1/16" tig wire and place it where the middle of the weld will be and clamp the part down to a bench real good..Weld and let it sit before letting off the clamps..Here is the same thing but different..http://weldingweb.com/vbb/showthread.php...ight=Bend+weldYou will get the idea.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Yeah i will try that on my next frame, if it bend ill just press it like i did on my first one. But still i did not have problem on anything else beside tubing wich i believe its the worst think to weld with max precision. thank you man.
Reply:Zap beat me to it.  Everything should be tacked with as small a tack as you can get by with until the whole thing is connected.  Then go back and weld a joint here and there skipping around so you don't build up too much heat at any one location.  If it warps too much doing it that way, I would be surprised.  The idea of welding the joints crooked hoping they pull-in at just the right angle later is something NASA could probably do, but I would never get it right.PS:  Sundown always comes up with some comment which brightens my day and makes me smile.... although I wouldn't want to be on the receiving end of one.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:Here a little update, I used a 20 tons jack to bend over, so i can weld full weld so after i can get it back straight. I had 3/8''-1/2'' off after welding and with the jack i can pull it straight to 1/64'' or less. Here picture of my projet, almost finished one just need to strap wich the guy need to come over to weld it after my roller are plated. Attached Images