welding sheet metal.

-
dukeboy440

dukeboy440

FABO Gold Member
FABO Gold Member
Joined
Jan 19, 2007
Messages
56,966
Reaction score
34,141
Location
No
Ok. I've got a little training in welding and been doing it since highschool off and on, most arc/stick, not career wise. I can weld a stack of dimes very well with a stick. Mig, not so much but not bad on thicker stuff but I've never done much with sheetmetal. My question is this. I have a new Lincoln 240 V Mig, using 75/25 gas as recommend for sheet metal by my local shop. Also using .024 wire and turning my settings as low as they will go, I'm still getting either burn through or not enough penetration. I'll get some pics up later but any suggestions?
 
Is the material clean? Mig work on sheetmetal usually requires a bit more care in surface prep than stick-welding 1/4" plate together, since you don't have the high amperage to rely on to jump past the debris.
 
Sometimes I'll back off the gas just enough to raise the heat a little on that lower setting that isn't penetrating.
 
BobK said:
Is the material clean? Mig work on sheetmetal usually requires a bit more care in surface prep than stick-welding 1/4" plate together, since you don't have the high amperage to rely on to jump past the debris.
Click to expand...

As best I can tell. I wiped the sheets down with brake clean before hand.
 
stitch is on and off the trigger allowing a short cool period between welds...running a bead is a continuous weld
 
I'm currently butt welding a patch panel in my trunk for the first time with almost no welding experience. I have a hobart 140 with gas. Voltage set to 2 and wire speed around 30 (can't remember the exact wire speed). I'm basically just holding the mig gun at a slight angle and pulling the trigger for a second without moving the gun at all. When the metal is clean on both sides (and back) the welds look great and get good penetration. There's a part of the patch where I'm forced to weld to chewed up metal that had surface rust and that's been a lot tougher. I took a copper coupler and flattened it out in a vice and I tape it to the bottom. Seems to help a ton when it comes to blowing through. I'll do a few spots here and there around the panel and then the next go round I'll put the welds right next to where I previously welded. This seems to help with distributing heat and not burning through.

Also make sure your cable is plugged all the way into the machine. Mine was backed out about 1/8" which allowed the gas to escape before it ever got to the tip. Made the welds look terrible and was blowing through left and right.
 
Also make sure you have swapped polarity of your leads for thin sheet metal. It puts the heat in the wire instead of in the metal.
 
I've always used .035 on everything I do. That's just my personal preference. Use a scrap piece to dial in your settings. I've always ran my welder a bit hot and adjust my technique to fit what I'm doing. Make sure you space your stitches far enough apart so you don't warp the hell out of the metal.
 
Just a thought.... Have you checked the polarity? Maybe welded some aluminum and didn't switch back?
 
grimreaper said:
Also make sure you have swapped polarity of your leads for thin sheet metal. It puts the heat in the wire instead of in the metal.
Click to expand...

This I did not know. so basically switch the polarity to that of what it would be if i was running it as flux core?
 
Try running electrode negative instead of electrode positive like you use for normal welding of unshielded wire. It puts heat into the wire instead of in the metal. You get slightly less wire attraction but it can help burnthrough. Run short beads spaced far apart.
 
clean metal, if maybe greasey, with oil/grease/wax remover, (paint store stuff,) or laquer thinner, BUT be sure the laquer thinner has evaporated or it will NOT be nice IE fire, boom etc.....!!!!!!), .be sure the metal is making good contact if lap welding. I like to screw it all together before welding, and go back and weld the holes shut. if trying to butt weld and you have NEVER mig welded sheet metal,, , I would practice somewhere first!!???? look at chart on your welder, to see what it recommends for heat/ speed, and tip distance from metal / always weld a stitch maybe 1/2 in long,and them move to another area if the metal might worp from heat. floor pans should not be a problem, but patches on qtr etc, YES a problem.......
takes some practice, setting up the welding right, eye/hand coordination
 
dukeboy_318 said:
This I did not know. so basically switch the polarity to that of what it would be if i was running it as flux core?
Click to expand...
No the polarity for gas shielded is opposite that of flux core.
Cleaner is not enough for good, easy puddling; take a sander or grinder and grind lightly to clean bright metal at least 1/8" back from the edges. The normal gray coating on steel is not pure, clean steel.
It is not easy to do so keep practicing.
 
barbee6043 said:
clean metal, if maybe greasey, with oil/grease/wax remover, (paint store stuff,) or laquer thinner, BUT be sure the laquer thinner has evaporated or it will NOT be nice IE fire, boom etc.....!!!!!!), .be sure the metal is making good contact if lap welding. I like to screw it all together before welding, and go back and weld the holes shut. if trying to butt weld and you have NEVER mig welded sheet metal,, , I would practice somewhere first!!???? look at chart on your welder, to see what it recommends for heat/ speed, and tip distance from metal / always weld a stitch maybe 1/2 in long,and them move to another area if the metal might worp from heat. floor pans should not be a problem, but patches on qtr etc, YES a problem.......
takes some practice, setting up the welding right, eye/hand coordination
Click to expand...


This is practice. I'm practicing on 22 gauge sheet, which is what I believe the replacement panels are made from. It's lap welding.
 
Pushing or pulling? I find pushing works better on sheet. Keep the gun closer to a 90 degree angle, close to metal so the arc doesn't blow as much and since your getting penetration, move faster.
 
fklskv said:
Pushing or pulling? I find pushing works better on sheet. Keep the gun closer to a 90 degree angle, close to metal so the arc doesn't blow as much and since your getting penetration, move faster.
Click to expand...

ill try pushing, ive been pulling. thanks
 
nm9stheham said:
No the polarity for gas shielded is opposite that of flux core.
Cleaner is not enough for good, easy puddling; take a sander or grinder and grind lightly to clean bright metal at least 1/8" back from the edges. The normal gray coating on steel is not pure, clean steel.
It is not easy to do so keep practicing.
Click to expand...

true. grind the metal to be bright clean!!! if already ground down and any oily contaminants present, clean that. also note that mig does not like any rust!
pushing, pulling, angle, distance from tip to metal. condition of liner, the friction of wire on roller, roller set for wire size??? polarity? mig wire that has NOT rusted sitting around, so many variables. I use on size larger tip than the wire i'm welding. good ground is a must.
and some welders just weld a lot better than others.
learn these skills and forget paying someone else to do it!!!!
 
And if you're like me and welding skills are marginal at best, be patient, go slow, and get good with your grinder! Grind slow and don't create too much heat... I use a cutting disc and just nip slowly at the boogered weld sideways. Not perfect but it turns most 'mistakes' into something acceptable.
 
dukeboy_318 said:
This is practice. I'm practicing on 22 gauge sheet, which is what I believe the replacement panels are made from. It's lap welding.
Click to expand...
Original metal gauge was more like 18-19 ga. The quarter we just got from Layson's is around .045, which is in the 18-19 ga range. If you can get good with 22 ga, then standard replacement panels will be a snap.

When you do a lap weld, you would like to focus more time with the heat on the underlying metal; the exposed edge will gain heat MUCH faster than the underlying piece. With a constant filler speed of the MIG process, it is harder to do this compared to oxy or TIG, where you can put heat into the underlying metal to get it to puddle without adding filler for a short time, then direct heat into the edge and add filler to complete the weld. But the total heat of the MIG process is lower...important for sheet. I am getting ready to work some MIG sheet metal welds, so I'll let you know any breakthroughs.
 
You must log in or register to reply here.
-

Back
Top