Keeping the metal Flat after Welding??

admin

Guys this is my first post here and its a basic question which shows that I'm newbie at welding.I have a Lincoln 180 Mig and have it setup for the mig feature using the gas.(Helps me look like I know how to weld)(take more than just gas)Anyway,I am restoring a table saw that has alot of screw holes,knockout holes that I am repairing in the cabinet of the table saw.While doing this,there is a seam on the front where the cabinets two halfs come togeather,on the inside of the cabinet its spot welded in several places to hold the halfs togeather.I thought that I could fill the seam on the outside of the cabinet using my little mig welder and make the seam disappear will the help of alittle bondo.What happen is now the front of the cabinet has a bow in it of about 1/2".I can pull it out straight by hand but it just goes back being bowed towards the inside of the cabinet.I did spot weld the seam (outside on the cabinet)about every inch or so then weld again every 1/2 then fill in.Guys so this rookie mistake won't go to waste,what did I do wrong and what should I have done?Thanks and don't laugh to loud-----Carroll
Reply:It's called "oil canning". The area needs heated and rapid cooled to shrink back into place.[ame="http://www.youtube.com/watch?v=mptiiRLEJs0"]YouTube Video: Shrinking Sheet Metal[/ame]In your case, I would heat up the entire seam and cool with a very wet rag or a weed sprayer full of water (this works the best).  Good Luck.Millermatic 200Hobart Handler 120Victor O/A & Ramco BandsawLincoln 225 ACSnapOn AD HoodMiller XMT304/22AHypertherm Powermax 1650 G3Lincoln Idealarc DC600 w/Extreme 12 VSMiller Digital Elite "Joker"
Reply:It's from shrinkage. The only way to straighten it out is to plannish the area. Being a corner joint you are SOL. Call it a learning experience.Two turn tables and a microphone.
Reply:Air compressor will cool it down as well.I was always told not to let it get bright red.  At some point, you will get some hardening (even low carbon steel - just not a lot).  Dull cherry red maybe low cherry.... assuming low carbon steel. (Just over 1000F)If its just oil canning, sometimes hitting it with a DA sander and 60 or 80 grit will put enough heat into it.  If you have to sand it anyway to paint, might give that a shot.Basically, if you heat it, it will expand, but it will thicken as well.  When you rapidly cool it, you are freezing the outside edge and the insides will cool a bit slower and suck everything in - effectively shrinking more than it expanded when heated.Oh and some autobody companies make hammers and dollies that help shrink and expand metal.  Personally I find heat-shrinking easier.  With heat shrinking you are essentially making things tighter - like the strings on a guitar.  The tighter, the straighter (to a point).Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX