oil canning

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We make weldments for the mining industry. We have problems with oil canning with sheeting on parts that we weld.  We weld 11 and 12 ga. sheeting to 1/8" and 1/4" tubing.  We have tried welding on lower voltage and still we have the oil canning. The structure has open spots underneath the sheeting where there is no support for the sheeting.  Everything is nice and flat when we start but even with skip welding and moving around on the decks they still oil can. The decks are somewhat big 7' wide  and 15 foot long. The customer will not let us use stiffners between the gaps saying that it will add to much wieght. If anyone has any ideas of how to fix or minimize this problem I would greatly appreciate it.
Reply:That is a difficult problem. I believe the best advice is if they can live with it. The most obvious joining method that I can think of that won't produce oil canning in large flat thin materials is friction stir welding but I doubt the people would approve the budget when they see how much it costs.
Reply:temporary stiffeners, backing blocks, heat sinks are options. So is preheat; it will keep the warping minimized, but adds cost, time, and it's harder to work on a big piece that is smoking hot all over. Any pics to show us to make it easier to understand exactly what you're up against??And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Originally Posted by Rojodiablotemporary stiffeners, backing blocks, heat sinks are options. So is preheat; it will keep the warping minimized, but adds cost, time, and it's harder to work on a big piece that is smoking hot all over. Any pics to show us to make it easier to understand exactly what you're up against??
Reply:Just in case I'm mistaken, when you say 'oil-canning', I'm guessing your describing the sheet material curling or curving, such that it pops in and out with a little pressure.  What you want instead is a smooth, taught sheet that doesn't move.  Have I got the right idea?There's a big article on distortion in shipyard welding in January 2010 issue of the Welding Journal.  Most shipyards deal with distortion by shrinking the material using heat after the welding is done.  This is most often done with an oxy-fuel torch; by someone with lots of practical experience.  But several companies are selling induction heating machines for taking the distortion out of welded sheet and plate.  the induction machines are very fast, accurate, and don't require a lot of cleanup after use.  Downside is that they are expensive.I've seen high end induction equipment used in a shipyard and it really does work like a charm.  I don't know if your operation has the money or if the project would support the cost of the equipment, but it might be worth your time to investigate...Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:A seven foot long by fifteen foot wide span without some warp even when installed is almost impossible.  Any steel supplier I know would have buckled or marked the sheet when delivering.  It seems to me that the panels should be "cross braked"  Often you will see this done to  panel doors on tool boxes and service boxes on electrical equipment.  The panel is set in a press brake and bent slightly putting a crease in it from corner to corner.  In the case of a 15 foot there would be two X creases put in it before installation.  Your stitching should be done at around 18 volts with .035 wire and no longer than an inch at each location, say a stitch every 18 inches.  Leave no craters even though the bead is small.  It is amazing what customers want sometimes.  It reminds me of the finish work I helped with on oil rig cabs.  In a week of service after delivery any perfection was not even noticed under mud and boot prints everywhere.
Reply:Rivets...MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by DesertRider33Rivets...
Reply:Please post the pictures if you can. I'm having a hard time visualizing what you're doing. If the weld is causing the warpage, have you considered peining after you each weld?
Reply:The weld bead shrinking as it cools could possibly be used to help prevent rather than cause the oil canning effect. Too much random skipping around could actually make thin worse at times more so than others. Think like you were stapling screen material to a wooden frame, pull and staple completely at random and you'll have a mess. Some kind of a predesignated pattern (scheme) might work. It's worth some thought anyway.
Reply:For a cost vs quality aspect i would say a cross break is your best bet.   if your trying to keep it flat as flat can be, good luck.Vantage 500's LN-25's, VI-400's, cobramatics, Miller migs, synch 350 LX, Powcon inverters, XMT's, 250 Ton Acurrpress 12' brake, 1/4" 10' Atlantic shear,Koikie plasma table W/ esab plasmas. marvel & hyd-mech saws, pirrana & metal muncher punches.
Reply:Start in the middle and work towards the corners.  The shrinking welds pull the sheet tight like stretching canvas.  I use this method with expanded and sheets on my trailers.  It will cause the frame to bow if it is not stiff enough though.My name's not Jim....
Reply:What are you building for mines and what kind of mines? They usually arent that picky except my old boss used to say "weave and die mother****er" Coal mines will not except weaved cover passes here. I used to build and repair all kinds of **** for coal mines and we had oil canning problems with 5/16 plate and no one cared. They beat the ever loving **** out of everything anyway.  With the gauges and unsupported areas you are talking about I don't see there being an answer to this problem other than them living with it. The post about the heat from the sun causing warpage pretty much sums it up.
Reply:Here are some pictures of the finished product. We did not have any oil canning on them. Attached Images
Reply:So what did you do/change to correct the problem?My name's not Jim....
Reply:when we used to build tail gates foe a local truck body co, they would warp when welding the braces.     we built a tubing structure for behind it with compressed air in the tubing tubing every 16 inches holes every 6 inches it worked   kept it cool from behind   i dont know if this will help or not   good luck
Reply:i dont think i was verry clear on my pre. reply  keep the tubung back about 6 inches and the air coming out of the holes kept the metal we were working with cool    good luck
Reply:Have you tried spray arc.  That should also help with the HAZ.I am tired of Ketchup, I want the Gravy...
Reply:It looks like you kept your stitches nice and small.  The next problem that will surface will be in about a year or two when moisture between the tubes and the sheet will cause rust and bleeding rust stains everywhere.  The best solution I have seen is to caulk all the joints between the beads.  If done right it will look like part of the weld.  A coat of paint on top and the finish will last a long time.
Reply:Originally Posted by lotechmanIt looks like you kept your stitches nice and small.  The next problem that will surface will be in about a year or two when moisture between the tubes and the sheet will cause rust and bleeding rust stains everywhere.  The best solution I have seen is to caulk all the joints between the beads.  If done right it will look like part of the weld.  A coat of paint on top and the finish will last a long time.
Reply:Originally Posted by BoostinjdmI've never seen the caulking trick work like it's supposed to.  I've seen it make the rust problem worse and I've seen it make repairs a real pain in the ***, but I've never seen it work like people say.
Reply:Marine stores sell Sikaflex. Sikaflex is a very light  almost whipped consistency compared to stuff like Pl urethane caulk found in most store like Home Depot, Lowe's or your local hardware store. When you use it on the trailer make  sure the area where it well be applied is clean of slag, oil, grease. The weld area should be painted & dry before applying the chaulk. When you apply the chaulk with the chaulk gun do the most important thing!! Force  the bead of chaulk into the joint. Moisten your finger in Napha and the chaulk will flow better while pushing it into the joint. Plus with the Napha your finger will clean up easier.Co-Own CNC shop:Miller :1251 plasma cutter, MaxStar 700 TIG/Stick, & XMT 456 Multiprocess Welder.&  2 Hypertherm HPR260's Plasma CutterSorry I had a bad stroke but now I am back.
Reply:Originally Posted by BoostinjdmSo what did you do/change to correct the problem?
Reply:Originally Posted by lotechmanIt looks like you kept your stitches nice and small.  The next problem that will surface will be in about a year or two when moisture between the tubes and the sheet will cause rust and bleeding rust stains everywhere.  The best solution I have seen is to caulk all the joints between the beads.  If done right it will look like part of the weld.  A coat of paint on top and the finish will last a long time.
Reply:welding on one side of the sheet is going to cause problems anyway, it pulls the material as the weld coolsI wonder if the ones that came thru without any problems had the bow in the plate on the opposite side of the welds.  You say the sheet comes distorted to some degree when delivered.  Just handling with a forklift causes some bow in the material even though it appears to lay flat."Any day above ground is a good day"http://www.farmersamm.com/