How To De-Warp These Flat Bars?

admin

Please take a look at the following video: I tig butt welded some 1 1/4" X 1/8" flat bar to the edge of some 1/4" plate.  I have some warpage on the longer sections.What is happening is as I weld, it is heating up the steel, which is expanding the steel, and when the weld freezes it locks it in it's expanded state, therefore causing the flat stock to bow out (aka warpage).Are there any tricks to de-warp these bars?Normally I heat it up with a torch and hammer it back down which compresses the steel in the heated area. While this removes the warp, it somewhat deforms the area where heat has been applied. This has especially become true with these thin 1/8" flat bars which is more susceptible to deformation than thicker stock.Any Idea?
Reply:Use a torch and apply heat to the opposite side of the warp, do a little bit at a time and it should pull back without the need to do any hammering.
Reply:Savfil,Please clarify. Do I heat the entire bar?  Do I heat it red hot?
Reply:If that is an out doors railing, then they will warp again because of heat from sunlight......Had same thing happen the day I built a cutting table for plasma/gas torch. All thin members were cut exactly the same length but warped as I installed/welded them in the welded frame.
Reply:Your cutting them too long  leave about a 1/16th to 1/8th" shorter then weld them in try leaving an equal gap on each end. When they cool you will have a little tension on them.Klutch 220si mig , stick, and dc tigHobart 140 AHP ALPHA 200X 2016Lotos LTP5000DSmith O/P
Reply:Try to heat some spots on the bars, then cool with water to get them to contract.  You may need to shorten the last one or two.  It will be a balancing act like tensioning cable in a guardrail.  Typically you get more contraction than expansion after heating metal, thus the cross bars are probably bowed some amount. You may also try heating the edge on the 1/4" so it will pull.
Reply:I have always been under the impression that larger gaps require slower welding and therefore more heat is applied to the workpiece which is why I tried to make the gaps tight.Heating the bars and cooling quickly with water is good, I have done that with limited success on 3/16" flat bar in the past. It might be more effective on this 1/8" material. I think the heating of the 1/4" plate is a fantastic idea because it can tolerate the heat way more and is less likely to further bow out the flat stock. With the heating and then cooling with a wet rag technique do I heat the metal red hot or just hot without much color change?
Reply:I would do cherry red.  And heat spots opposite the weld.  Ironically, The last garden gate I built using 11g flat bar, I intentionally bowed the bars, by cutting longer than needed and welded them in place.  They were very rigid and uniformed.  Functional sold as modernesque. I actually them til the arc center was  .25" off my table .Last edited by tapwelder; 05-04-2016 at 12:55 PM.
Reply:The weld will shrink as it cools. If there is a gap it will pull on your slats and tension them. This is a double edged sword. It may tension some more than others making some appear loose.Eventual master of the obvious, practitioner of "stream of consciousness fabrication".  P.S. I edit almost every post because because I'm posting from my phone and my fingers sometimes move faster than my brain.
Reply:there is NOTHING you can do for that, especially putting more heat into it. The flaw is the design, not heat from warping. bottomline, you needed to choose thicker slats given that span. but hey, you saved money.Last edited by Jimmy_pop; 05-04-2016 at 02:06 PM.
Reply:jumpinjoe,There are MANY excellent threads/posts on the forum regarding correcting warpage.  Suggest you do a bit of searching...lots of good info here.
Reply:I agree also with leaving a little bit of a gap, as the shrinks it will add tension to the member. I had a large structural project (platform) warp one time, and we went along with the rosebud at each crossmember weld, and just less than cherry red heat it pulled straight... and then too much, learned to be conservative with our heat input that day.
Reply:deleteLast edited by Kelvin; 05-07-2016 at 12:00 AM.
Reply:The Seattle Space Needle, built for the 1962 World's Fair (oh, we were so proud of our little city then!):http://static.seattletimes.com/wp-co...8-1020x670.jpgLook at the three legs, each leg being two beams with webbing between.  Note that each beam is straight at the top and at the bottom, but curved in the middle.  Those beams were made from three sections from top to bottom, welded end to end. Here's the part that pertains to this thread: the beam sections that are curved  .  .  .  started out straight! They got their curve by heat-bending.  A section of straight beam was laid out horizontally, and two guys with torches applied heat to them in a very precisely engineered sequence and created the curve.The engineer in charge of this operation was U of Washington Professor of Mechanical Engineering Richard Holt. Professor Holt's father had been a blacksmith, and had developed considerable skill with this technique.  When the blacksmith's son became an engineer, he began doing the science and working out the mathematical formulas for heat input and heating patterns for heat bending, and for avoidance of welding distortion. As a UW student, majoring in History but with more interest in things mechanical, I managed to get into the Engineering Department's 1-credit introductory welding course, taught by Prof. Holt.  A big tip and red-hot is a lot hotter than necessary if you do this right. Practice on some thinnish steel, say 1/8-3/16", and look very closely as you apply heat with a medium size welding tip.  You should be able to detect a point at which the metal takes on a faint silver hue. That heat, when it has penetrated the thickness of the metal, is enough. What you're doing is trying to create a particular temperature gradient between hot and cold, meaning you try to apply just enough heat, in the right place, rather quickly, as opposed to continuing to add heat until the metal starts glowing red and the heat is spreading all over. This takes practice, like most welding skills. But I have used this to heat-bend trailer frame rails that had been bent into a downward curve by repeated overloading. There are particular patterns and sequences in which you apply the heat in order to "pull" the metal in the desired direction, and you try to figure out ways to apply some mechanical pressure or loading that helps move things farther and faster. As mentioned above, autobody men know how to apply a wet rag to quick-cool the heated spot before the heat spreads and wipes out the sharp heat gradient needed to shrink the steel. This subject is not covered in a paragraph (Richard Holt spent a career developing it). I don't do drawings, so if I can find a good article or book on it, I'll come back with a link.Last edited by old jupiter; 05-09-2016 at 01:10 PM.
Reply:These flat bars are done. Way to thin for a gate or anything. Cut them out of there and use some stiffer steel.Less welds is better on these kind of project.
Reply:To keep them from flopping, they all need to be in tension.  A balancing act.  You could try to heat shrink the real floppy ones by heating all the way across somewhere in the middle of the piece.My name's not Jim....
Reply:So I dewarped them. At first I heated the 1/4" steel where the flat bars were welded and I hammered the flat bars down which compressed the steel enough to flatten them out. The problem I had with this however is all the heat on the 1/4" plate began to cause dishing and other warping issues. So I abandoned that idea quickly.I ended up cutting the warped flat bars out. Preheated them with a propane torch to get them all expanded out. And tack welded them progressively until they were completely welded. That did the trick. I should have known to preheat first, I just forgot this time. Thanks for all your help!
Reply:Let's see the results.
Reply:I've done a fair bit of line heating over the last 10years or more and unless they are tied in fairly rigidly which they don't appear to be you'll only make that wavy by heating it. I would suggest as others have said if possible use thicker flatbar if not consider adding some square or round stock as a crossmember on the back side to tie it in. Sent from my HTC_PN071 using Tapatalk
Reply:Square or round stock on the back is a good idea.