Penetration on a MIG weld?

[Guest TegRacer324]

Alright so I finally got a MIG. Unfortunately my class that I took did pretty much mostly arc on stuff that was like 1/8"+ steel mostly probably 1/4+. This really doesn't help me for MIG welding on stuff under 1/10. Well just running some beads I'm having trouble getting the heat down just right. I had some .030 thick steel and I went to the factory recomended settings. I'm just wondering should I be seeing the bead pretty much all the way through the back of the metal just running a bead on it? It seemed awfully easy to burn a hole through. So how much should be penetrating exactly?

[OlderThanMe]

well that is realy thin steel. What size wire are you using? you should probably use .023 wire for something that thin. What company made your MIG? Miller, Hobart(same as Miller), or a Lincoln?

[Guest TegRacer324]

It's a Lincoln SP-135 Plus. I hade .025 in there.

 

Wait, it may have been .08. Crap I'll have to check when I go home this weekend.

[johnc]

.030 sheet metal is about 22 gauge and is thinner then what you find on a 240Z. You should not see any drop through on the backside. You should see discoloration.

[Guest TegRacer324]

Alright that's what I thought. I guess I had the heat up a bit too high. What about something like a butt-weld? You should be able to see a little coming through the back right?

[331CI 280z]

Maybe a little. Go buy the Welder's handbook at Border's or Barnes and Noble. It will give you some good starting points and tips

[SSflyer]

I found the easiest way to weld the sheetmetal on these cars is to use a backing plate where ever possible, especially on a butt weld.

[boodlefoof]

You probably don't want to run a continuous bead at all on such thin metal with a MIG. You will warp it. Also, blow through is a problem as you've described. For such thin metal, you would probably be better served to lay a series of spot welds and small (less than 1'' long) beads.

 

It can be done... I've welded 24ga. with my 175 amp welder with no trouble using this method. Just a little time consuming.

 

If you must run a bead, lay a copper backing plate behind it. The copper will act as a heat sink, and your welding wire won't stick to it.

[JMortensen]

I can run a bead on the Datsun sheet metal just fine. If you try to run a long continuous bead the metal will warp from the heat as boodlefoof says, but if you get the heat and wire feed settings right blowing thru isn't an issue. The copper is a good tip. The other thing I've noticed is that if the nozzle is pointed directly at the work you're more likely to blow a hole in it. Keep it at an angle when you can, but sometimes you just can't.

 

I don't know what your settings are like on the Lincoln, but with the miller I run the voltage at 3 and the wire speed at 25-30. Works like a charm. I generally tend to run the voltage hotter than the welder recommends and the wire speed a tad slower FWIW, your mileage may vary.

[Guest TegRacer324]

Alright thanks guys. I thought it did look a bit odd with the weld dropping all the way through almost. I'll have to play around with the heat to get it right I guess. I do have that book, but I read it so long ago now that it's kinda fuzzy and it didn't help welding stick on 1/4" plate most of the time.