Tig - welding 20gauge to 3/16" steel

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Boy did I make a mess of it ! Trying to reproduce a battery box for my old car and originally, it was 20gauge sheet metal spot welded to a 3/16" steel bar, so I reproduced everything and to "simulate" the spot welding what I tried to do was drill a 3/16" hole in the sheet metal and I planned to create a puddle in the 3/16" steel through the hole in the sheet metal and just a touch of filler would hold it all together. Lincoln 185 Tig and I at first I had the amps too high,I thought I needed it to create the puddle in the 3/16" but melted a nice big hole in the sheet metal before a puddle in the thicker steel ever showed up, then tried very low amps and succeeded, one light wack with a hammer and it all fell apart, the weld was cold and I never got penetration.  I tried some silcon-bronze rod that I have and it helped but still made a mess. So how does one weld very thin metal to thick metal ? Was my idea of drilling a hole in the sheet metal and welding it to the thicker metal something that can be done and I am just not good enough yet, I thought that would somewhat replicate the look of a spot weld, especially after paint/etc.
Reply:Mikey,  Well personally I like your idea...but im lazy  I never would have bothered.   Id have just burned it in good iwth the tig no filler  heh  but still I like your idea.  The technique of thin to now thats a challenge.  You only learn it with practice so. I will say that starting out with Silicon bronze would have helped you...but again hindsight is always 20/20.  Dont kick yourself too hard.  Go have a beer...see if you can grind it up as best as possible and put it your box of "Things you learned the hard way"  it gets easier    goodluckIF it Catches...Let it Burn
Reply:Its a good idea and it can be done but I dont think a tig is the best choice. I'd probably mig it.
Reply:I would have not thought of migging that,  my friends always told me I did not need a plasma cutter after they saw me use my mig on sheet metal. Anyway, with the silicon bronze rod, I did get it to hold together but i had lots of grinding to do to clean it up, and it was not pretty at all, the sheet metal burned up in nothing flat.  I was just disappointed because while this will never be seen by anyone when the car is assembled, I have similar parts to make that will be visible, guess i need to practice this a LOT more before I get to the visible parts.   Mike
Reply:Try drilling through the sheet and slightly into the  3/16.  This will create corners and allow you to use less amperage.
Reply:I do that frequently with the MIG, try a bigger hole in the sheet, so that the arc could be focused more to the bar stock then when the metal flows fill in the puddle.Millermatic 251Century 180 migSpectrum 625 Syncrowave 250DX
Reply:Thanks for the suggestions, I am going to go drill myself a 100 holes (ok not that many) and practice.  The drilling slightly into the 3/16" idea sounds good, it makes sense and I will try that. I will also try the mig since I still have my mig but I never and I mean never got the hang of mig on thin sheet metal. The only reason I purchased the tig was because I could never mig sheet metal, I kept the mig however for all the other things it can do very well.  I will try it on this also today and report back. Thanks, I knew I was just in-experienced and I should be able to do this.
Reply:When welding thick to thin use the weld settings appropriate for the thin stuff.  The trick is wetting out the thick stuff.  For what you're describing, I'd agree with the suggestion to drill a larger hole such that you can get a pool going on the thicker part and then wet out the thinner part.-Heath
Reply:It just takes practice to tig this stuff.  You have to keep your heat in the thicker metal and only let your puddle touch the thinner metal.  If the thin metal starts to burn away, you can't chase it with the arc, you have to add filler and work the puddle over to it.
Reply:Mike,Maybe a preheat on the bar stock will help too.ClayWhat's up with all the icons on this board? They jump around enough that my screen flickers?
Reply:If I understand this correctly you are just making plug welds. Run the mig just a little hotter than usual, point the wire straight up and down in the center of the drilled hole and give it a quick shot. As soon as the puddle forms let off the trigger. A fast, hot shot is all you need. With the 3/16 holes it might be a little hard so you might go with a little bigger, maybe even 5/16. Make sure you have a tight fit. (no gap between thick and thin pcs) If there is a gap then the thin has a tendency(sp?) to melt first and that makes it hard to chase. Short hot shots, like a spot welder.
Reply:A heavy positioning magnet should help close a gap.
Reply:Thanks to everyone who replied, luckily this was not a structural thing just cosmetics.  I kept trying to TIG it and could not get the thicker steel to form a puddle without melting the thin stuff and no mater how hard I tried, I could not help myself chasing the melting away thin stuff.  I need to practice this as it shows one oh my many weaknesses in TIG. I did get it done with my MIG, as "TEK" suggested, hotter than usual and slower wire feed than usual and got nearly perfect welds.  Strong enough to not fall apart when smacked with a hammer and cosmetically close enough to a "spot weld" that after paint,etc. it will look fine.  Odd part is that after buying my TIG a few months ago I was going to sell the MIG and the guy at the welding shop said to keep it, guess he was right, I was looking forward to the cash from the MIG but I will keep it now.Last edited by mikeyr; 01-03-2006 at 01:15 AM.
Reply:Someting I do,  I get that arc a little extra hot for the thicker...then that way it will melt that thicker so much quicker I doint have as much time to heat up the thin.  Just what Ido....good luck thoughIF it Catches...Let it Burn