Oil canning - need to stop

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I am welding a pc that has to be seam welded on all sides. When I do this I get distortion on the back side of the pc. Do I need to fixture the entire pc with a heat sink to displace the heat or is there another way?
Reply:pc ????DennisThermal Arc 185-TSWMillermatic Challenger 172VictorO/AAtlas Craftsman 12 by 24 LatheEsab PCM-875Wholesalem Tool Mill-Drill
Reply:He probably means piece.  That distortion or canning takes place because the welding area shrinks and pulls and the thinner the metal the more oil canning.  It is hard to get it all out but if you lay your piece on a metal surface and tap with a small hammer next to the seam the full length of the weld you can take a lot of it out.  Don't bogart it, but just a little bit at a time.
Reply:You can also try to do it in 1 inch lengths, staggered opposite the previous weld.When the weld cools it contracts and pull the metal in, so try to plan the weld sements to counteract the last one. And ,as Riley said, light hammering on the weld will flatten the weld and expand the weld joint. Some car guys do it hot others do it cold. they call it hammerwelding.good luck!
Reply:I appreciate the input...I will try the hammering idea. The item I am welding is an enclosed box so it may be a little difficult to accomplish the hammering on the last few welds. I have also thought if clamping a piece of copper bar along the back side of the seam to remove some of the heat. Let me know what you think.
Reply:Also, if the part is small say cube 6x6x6 for example. leave a vent space in the seam that will relieve pressure. After it is welded completely and cooled; seal the vent space quickly and it won't blow the puddle out leaving a hole. Less than 1/2" long should do it.That way you don't have to drill holes you don't want. Post a pic.Weldtek
Reply:When I used to work in a shop that did a lot of antique car work, we used to heat up the center of the "oilcanned" area so it's cherry-red then immediately slap a soaking wet rag on the cherry. It always shrunk it every time.
Reply:Okay, all of these suggestions are good ones. My only issue is that this is a production environmentand the fix to this problem has to be something that can be consistent and worked into the already existing process. The piece I am working with has studs and standoffs close to the outside edge of it which prohibits me from using a large piece for backing. We are tig welding these items and that, I think, is where alot of my heat is coming from. What does anyone think about changing to mig.