Mig welding sheet metal

[FoFittyFoSS]

Have done this with succes before but the current ride is thinner than most it seems. Weld, burn through, build up, grind down, start over. Replacing a rusty battery tray with flat metal. Using a Lincoln Pro-Mig 180 with .025" wire and Unamix, turned all the way down ( setting A, wire speed 2). Would .035" wire be more forgiving? What about shielded wire and no gas? Any advice would be appreciated.

[Ron Ward]

Re: Mig welding sheet metal

Learn to trigger the welds. On sheetmetal, especially something this thin, don't try to lay down a contiuous bead. Tack a spot, move a few inches away and tack another spot. Don't get the area too hot or it will warp. Make 3-4 tacks, take a drink. Make 3-4 more tacks, smoke a cig, make 3-4 more tacks, take a whizz, etc. It takes a lot of time and a lot of patience, but it is worth the effort.


Ron

[std]

Re: Mig welding sheet metal

When you're trying to weld new metal to old metal it's really important to get the old metal as clean as you can, and the thinner the metal the cleaner it needs to be. It takes more amps to melt into the rusty metal so you tend to burn thru.

Also don't try to weld a continuos bead. Put down a bunch of tack welds and the just click on the trigger insted of holding it. It will keep it from overheating. I'm not sure that was a good description of what I do.

[FoFittyFoSS]

Re: Mig welding sheet metal

It's working and looking ok for a battery tray. Moving on to a piece of rocker panel next though. Seems the spot welding is working ok. Should I spotweld the entire piece eventually or just some and the on to the bodywork? I but welded the last pice. Should I butweld the rocker or overlap slightly? Thanks.

[Ron Ward]

Re: Mig welding sheet metal

A series of tack welds is the proper method. Space them out and let them cool before coming back to that area. Eventually, you will have closed the entire seam with tack welds. Doing it this way will help to keep from warping the material.

When you grind the welds, remember you are applying heat with the grinding wheel, too. Do it slowly and let the grinder do the work. Don't put a lot of pressure on it. Don't get the metal hot and it won't warp as badly.


Ron

[68 Valiant]

Re: Mig welding sheet metal

When you grind the welds, remember you are applying heat with the grinding wheel, too. Do it slowly and let the grinder do the work. Don't put a lot of pressure on it. Don't get the metal hot and it won't warp as badly.


Ron

The really talented ( I'm not one of them) use an oxy/acytele welding torch and then there will be no grinding. This will reduce the work hardening of the steel.I maybe shouldn't say the "really talented" The motions are similar to TIG welding.

[Mr.WFO]

Re: Mig welding sheet metal

torch.

better yet,
use rivets.

[DanStokes]

Re: Mig welding sheet metal

Ron and Dave (std) have steered you right, from my experience. I used to torch weld everything when I had better vision and didn't have a MIG - it works great, too. You can braze it, too.

A butt weld gives a better result if you want the repair to look as OEM as possible. It you're going to lap it you might as well bond the seam with adhesive - I use the Lord Fusor system. Very strong and no chance of warping. Hold the seam together with Clecos or pop rivets until it sets (I give it overnight). Remove the rivets/Clecos and use Bondo Hair or similar for the first coat to fill the holes. Another trick is to sink the holes slightly so the hairy filler has a broader base to adhere to.

Dan

[SuperBuickGuy]

Re: Mig welding sheet metal

torch.

better yet,
use rivets.

x2 - trying to weld too thin metal with a mig is frustrating and (if anyone sees it) completely embarrassing.... torch/braze it. (then it's pretty too).

[CTX-SLPR]

Re: Mig welding sheet metal

I've become addicted to the harbor freight butt weld clamps. These things are great, heck I even use them on tubing. On 16Ga metal weld for no more than 1/4-3/8in at a time and let air cool, quenching it will make it shrink more.

[DanStokes]

Re: Mig welding sheet metal

Good point, CTX. Quenching sheet metal is bad ju-ju - unless you WANT to shrink the area.

Dan

I've become addicted to the harbor freight butt weld clamps. These things are great, heck I even use them on tubing. On 16Ga metal weld for no more than 1/4-3/8in at a time and let air cool, quenching it will make it shrink more.

[malc]

Re: Mig welding sheet metal

I just got me a nice little MIG welder, have?nt been able to plug it in for three weeks due to power fluctuations.

The last time I welded with one of these was waaaay back, twenty years old, an apprentice at the time.
My first welds on Sunday looked like chicken doo doo but diddling the power and wire feed I was getting the hang of it again.
Luckily there is help online.
http://www.mig-welding.co.uk/
http://www.thefabricator.com/ArcWeld...le.cfm?ID=1083
http://www.millerwelds.com/resources...tips/MIG_tips/

I also got one of those nifty self darkening face shields, Summit again, they cost too much here
in Spain.

[Barry Donovan]

Re: Mig welding sheet metal

Learn to trigger the welds. On sheetmetal, especially something this thin, don't try to lay down a contiuous bead. Tack a spot, move a few inches away and tack another spot. Don't get the area too hot or it will warp. Make 3-4 tacks, take a drink. Make 3-4 more tacks, smoke a cig, make 3-4 more tacks, take a whizz, etc. It takes a lot of time and a lot of patience, but it is worth the effort.


Ron

works for me too. the thinner it is, the quicker you go. sometimes it is a couple of feet in hours, but the cooldown, exponential gain in strength, you could type writer it to whatever thickness. make beam beads, whatever nicknames of home engineering you prefer
I dove right in thinking it would be quick. over 120 hours later....
the cooldown is months.