patch panel with MIG?

[73-charger-383]

I'm not really familiar with doing bodywork, but was wondering can a person use a mig welder for replacing/repairing panels?  I'm pretty competent with a welder and was just thinking if i went along and just tack welded along along the seam it would work fine.  (if you can do this, how low do you usually run for voltage/speed/inductance in order to keep the panel from pulling too hard.) -- i'm used to using copper core wire (.035) with C25 shielding gas.  --should i use thiner wire? How bout the gas?  Does it matter at all if you use c10 or c25??  --as far as penetration??

thanx guys

[Drop Top]

I'm an old timer so I use a gas torch most of the time or a tig. But when I do use a wire feed or mig. I use the smallest wire that I can get. With it on the lowest setings possable. I can't remember the size wire I use. Its been so long sense I had to buy it. This will allow fast penetration with out allot of heat build up. I use argon for my gas. Its a much cleaner weld with it. Like you said keep the tacks about an inch apart after you have tacked it in place. Don't allow the metal to get too hot. If you can't touch the metal then its too hot. Jump around a bit to keep it cool. If you need to cool the metal let it cool naturally. DON"T use water in any form. It crystallizes the metal and weekens it. If you use anything use compressed air to cool it down. The reason I don't like using a mig is the weld itself is harder then the sheet metal you are welding with it. This makes it much harder to grind away the weld without taking off to much of the surrounding metal. But if its the only welder you have and you know what your doing It can be done. Just take your time and don't rush the job. Practice on some scrap first. The more you do it the easier it will become. Keep the welds as flat as you can. This will cut down your grinding time and less heat bild up wile grinding. Grinding will worp metal just as bad as welding it.

I'm sure someone will chime in on the size wire and heat settings. Sorry but I just don't use a wire feed much for body work. I use it for my frame work.

[69hemi]

I used the cheapest MIG welder Century makes with a gas kit.  For the majority of my car I used .30 wire with an argon blend gas and got good, solid, clean welds.  There is a picture of it at my website www.69hemi.com in the tools section. 

As far as heat goes, use the highest setting without getting burn through as you can to ensure a good solid penetration.  I used a blow gun to blow air across the welds to cool them and it works well.  Just take your time and keep feeling the panel and if it too hot to touch it is too hot to weld on anymore.  Take a break, light a smoke, go to the john, have a beer, whatever, but let the entire panel relax and cool down before you start again.  It takes a little longer this way but you will have less work on the bodywork side with less things to dolly, shrink and fill.

[Mike DC]

MIG is used for panel replacement constantly in the bodyworking industry.  

I could tell you a bunch of warnings: "Oh, you should always get the utmost penetration whenever you join two peices of steel on a car, and blah, blah, blah . . ."
But you sound like you don't intend to booger the welds on & have panels falling off the car so I'll spare you the speech.   The important issues are mainly hanging the panel correctly and creating a seam that can be finished invisibly.

When people are doing bodywork on the outer skin of a car they are interested in the cosmetic aspects of it just as much as the metallurgy.   A "great weld" is not a great weld when you also warp the surrounding metal to do it and the car needs hours of finish work just to look right. Some people still like to butt-weld a sheetmetal seam for the ultimate in quality, but realistically most people in the bodywork world are okay with a decent "step" flange job to join the sheetmetal.   Of course the panels need to be safely joined with decent penetration but you're not building a rollcage either.   You need to be able to make good solid zaps with the welder that get good penetration within only a few seconds each time, but don't start laying 3-inch-long beads or you'll never hide the warping when you're done.

So hang the panel on the car with clamps.   When you get it fit perfectly, give it a half-dozen scattered small tacks with the MIG all over the perimeter of the panel just to hold it in place before you get busy.   Then start adding tacks, moving around constantly so that you don't ever heat up too much in one single area . . .

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And try using a light coating of "weld-thru" spray paint on the areas where the metal will be overlapping when you're done.   This will help prevent rust getting between the layers.   3M makes some good weld-thru primer.   It's not cheap but it works.

.

[is_it_EVER_done?]

Try this wire   http://www.jwharris.com/images/twentygauge.pdf.   It really makes sheetmetal work easy, even for a novice like me. The link also lists recommended settings for most welders.

Another tremendous help is to use a piece of copper to back the area your welding, it stops most burn throughs and draws much of the excess heat away from the surrounding metal which helps reduce warpage. A piece of copper plumbing pipe hammered flat, or to the shape of the area being welded, works as well as any commercially produced copper spoon.

[73-charger-383]

thanx guys.......maybe i'll get this dang car back on the road yet....

[wetfeetmi]

I have tried .020 gauge wire and went back to .035. The thin wire would melt to quickly no matter what heat setting I tried. I might have been the welder (Miller 225), but the thicker wire worked better. It was alot easier to fill gaps with it!

[wetfeetmi]

By the way, I always butt weld and try to push the weld away from you as you go. Short, hot zaps (heat setting at 10-12 range and wire speed near 5 on Miller). You won't be able to get a spoon in place behind most panels, but use one where you can.  Lots of clamps and patience! I will post a few pics of plug install soon on clone.

[terrible one]

This sure is a good topic, really good information here guys, very helpful!

[clausoe]

I'm an old timer so I use a gas torch most of the time or a tig. But when I do use a wire feed or mig. I use the smallest wire that I can get. With it on the lowest setings possable. I can't remember the size wire I use. Its been so long sense I had to buy it. This will allow fast penetration with out allot of heat build up. I use argon for my gas. Its a much cleaner weld with it. Like you said keep the tacks about an inch apart after you have tacked it in place. Don't allow the metal to get too hot. If you can't touch the metal then its too hot. Jump around a bit to keep it cool. If you need to cool the metal let it cool naturally. DON"T use water in any form. It crystallizes the metal and weekens it. If you use anything use compressed air to cool it down. The reason I don't like using a mig is the weld itself is harder then the sheet metal you are welding with it. This makes it much harder to grind away the weld without taking off to much of the surrounding metal. But if its the only welder you have and you know what your doing It can be done. Just take your time and don't rush the job. Practice on some scrap first. The more you do it the easier it will become. Keep the welds as flat as you can. This will cut down your grinding time and less heat bild up wile grinding. Grinding will worp metal just as bad as welding it.

I'm sure someone will chime in on the size wire and heat settings. Sorry but I just don't use a wire feed much for body work. I use it for my frame work.

Does it really matter if you use water to cool the spots when you're welding really low carbon steel? I know that rapid cooling will cause small crystals and a bit more brittle metal but isn't this hardening more of an issue if it was a high carbon steel. I've been told that replacement panels and the welding material used for bodywork was really low carbon to prevent hardening and brittle metal from welding/cooling and hammering.

Hope I used the word brittle correctly, meaning that it will break or crack easily.

[Drop Top]

The best way is to let the metal cool naturally. Allot of people use water all the time. I don't recommend it. The metal will crack eventually, right next to the weld if its cooled off to quick. If you really need to cool the metal faster then use compressed air. The best way to do it with a mig, would be to tack it in first. Then move around so the heat doesn't warp the panel. If you feel any heat at all the metal will start to move. Keep a hammer and dolly handy to keep it all straight as you weld. But the best advise I can give you is. When the panel gets too hot to touch. STOP and have a soda or ice tea and let it cool naturally. The bigger the panel the more likely it will distort.

[plum500]

This sure is a good topic, really good information here guys, very helpful!

I second that. Thanks for all the posts.

Cheers,
fred.

[1973_WP29P]

3M's Weld Thru primer # 05917.



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