back to direct shape after welding for bended plate

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hi my dears!my question is that we have L shape product that weld to tube .after welding we see a deformation in bend of product .how can we solve this problem and prevent change of bending and back to direct shape after welding for bended platetanx
Reply:When the piece is bent cold it has stresses.  The heat from welding releases some of the stress and the item opens up.  A similar thing can happen if you take your bent piece and drop it on a concrete floor.  You could reduce the amount of welding heat, overbend the item before assembly, bend it back to 90 degrees after welding, or tack weld braces across the bend and remove after welding.  I have a feeling that the braces would not hold the bend and it would spring open when they are removed.
Reply:Yep, exactly what lotech says. You couldn't get a better example of how to straighten steel with a tiny bit of heat. The inside of the bent piece is under tremendous compression. The outer side was stretched but still holds the inside in place and in compression because it is in the 'cold' rigid state. That quick heat on the outer edge of the bend allows the outer to expand, become slightly more porous at the micro level (active molecules) for a short time and the inside easily comes out of compression and re compresses the outside to some degree. Probably the shrinking of the bead does a little of the straightening but mostly the rapid surface heat to the outside."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:What alloys?? How critical?? Could you not just heat the plate with a rosebud and bend it back (shrug)?Semper FiJesus may have been a Carpenter, but his dad was a Millwright" A grinder and a can of paint, will make a welder what he aint' "I've done so much, with so little, for so long, that now I can do anything with nothing!
Reply:tanx for your answers. the material of plate is st37 and we can't bend it more than 90 degree .how we can reduce the heat of welding ???
Reply:St37 is carbon plate if memory servers me correctly.Heat and bend it back to 90 degrees after the weld or look at your welding procedure.What process are you using to weld with? Stick; Tig or Mig?Does it have excessive weld? Size/alloy of tube?Do you have a WPS for this?Use copper heatsinks maybe.Would be simple enough just to heat and bend back to 90Semper FiJesus may have been a Carpenter, but his dad was a Millwright" A grinder and a can of paint, will make a welder what he aint' "I've done so much, with so little, for so long, that now I can do anything with nothing!
Reply:A bit more info about the job would be nice...Do they have the same 90 degree bend at both ends? If so, try tacking 2 of them back to back, tack as many bits as needed down the length of them, then weld with MAG for low heat input (if WPS allows), welding stringers on opposing sides to keep the heat equal between the 2 pieces.If that don't work, then apart from what the other posters have already mentioned, could you put them back in the press after welding (Might need to make special tooling and depends on the length of them), or maybe make a jig on a suitably sized bench and if you've got enough leverage bend them back by hand to avoid heating them(again, depends on the length and material thickness)?Last edited by Baila La Pinza; 09-24-2011 at 05:56 PM.
Reply:Mechanics,one other method that may reduce the weld bend influence is to bevel the tube end especially along the side were the bend is located.A fillet weld between the face of the bent part and the tube end will draw or pull the bend back because of the weld's contraction across the fillet face. If the weld were less face distance along the bent part's curved surface, then the weld contraction will be reduced somewhat.So if a bevel were cut/ground/formed on the end of the tube piece, especially nearest the curved end of the bent part, then welding contraction will be minimized by forming the fillet inside and underneath the flatter surface of the bent part instead of outside where a greater face of contraction can deform the finished part.Cheers,Kevin Morin
Reply:clamp a piece of heavy wall square tube to the 'L' piece before welding, leave it on until cool.
Reply:Myself..I don't see how that could bend where it is bending in relation to where the weld goes..Just tack a piece from one end to the other (Top to bottom)Weld tube..Let cool..Remove brace piece and call it a day....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:It's probably china steel, gonna have problems with it no matter what you try Semper FiJesus may have been a Carpenter, but his dad was a Millwright" A grinder and a can of paint, will make a welder what he aint' "I've done so much, with so little, for so long, that now I can do anything with nothing!