tig rod for patch panels

[57barnwagon]

what is your recommended tig rod for patch panel replacements on the 57 fenders and doors?

[Rick_L]

Almost everything you do with mild steel (or even alloy steel) should be welded with ER70S6 rod. Which is the most common alloy available in rod form.

That is the only rod I keep on hand for steel. Obviously you need something different for stainless (309 is the most common choice) or for aluminum.

ER70S6 is also the most common mig wire, and you can spool off mig wire if you need wire that small.

[57barnwagon]

Thank you

[chevynut]

One thing I've found is that TIG welding patch panels isn't easy. It's a lot easier to do with MIG than TIG. I have found TIG to "volcano" a lot more due to contamination. If the metal isn't perfectly clean on both sides, it can drive you crazy trying to weld it. I have welded new metal to new metal with no problems, but for some reason I had big problems TIG welding old body panels.

I'm not sure why you would prefer TIG over MIG. Some guys say the MIG weld is harder but that's never made sense to me. It's the exact same alloy rod/wire. I also think you get less distortion with MIG because the heat is lower and the HAZ is smaller. When TIG welding you tend to heat the metal more than you need to. IMO.

[LEE T]

Once upon a time, several guys who were well educated in metallurgy got together on one forum to discuss what makes mig welds harder than tig welds. They came up with the answer to that, and much more good information about mig and tig. Its a lot of reading, but worth it for welders.

Reasons for mig weld being harder
http://www.allmetalshaping.com/showthread.php?t=1287


close up of mig process
http://www.youtube.com/watch?v=UFFSJ1G4vsg&feature=related

[chevynut]

Well if this guy is a metallurgist, I think he's FOS:

"Mig welds are "harder" because the temps mig run at superheat the metal, effectivley above the boiling point, commonly around 10,000 degrees. Add to that the superfast air quench, and that results in a very large grain structure.

It has nada to do with the gas used, or the wire, or the deoxidizers in the wire. Arc welding is not nearly as hot, although deeper penetration is achieved.

Tig welding gets it well above melting temperatures, but well below the boiling point, and gas welding brings it generaly to just a few hundred degrees above melting. Also, the cooling rate is slower for each process listed.

Marty"

First of all, I doubt MIG welding is any hotter than TIG. If the metal boiled, it would go away. Secondly, large grain structure makes metal SOFTER, not harder. And cooling rate isn't affected by welding process, unless the surrounding metal is absorbing more heat. But once you reach a certain temperature on cooling, nothing changes.

I think the carbon addition from the CO2 makes much more sense than anything else. I always wondered why they use CO2/Argon mix with MIG and not with TIG.

"Marty" goes on to say this, which is pure BS imo:

"The rockwell test I done showd that it was harder but only by a few points. It IS harder, but by not much. It is not harder because of added carbon like tool steel, rather the larger crystaline structure."

"The carbon involved is a mechanical bond, not chemical."

I've always speculated that the MIG weld "appears" harder because there's more metal deposited, not because it is actually harder. If "Marty's" Rockwell tests really say there's not much of a difference in hardness, then that's probably the case.

I had a hard time believing the cooling rate is much of a factor, but this guy named "DanGunit" seems to know what he's talking about. But MIG isn't "supercooled" either as one poster (a supposed metallurgist) tried to claim. IMO.

http://www.allmetalshaping.com/showthread.php?t=1287&page=7

[Rick_L]

This is always coming up.

For me, I am not good at tig welding except at the bench. Maybe someday I can master the use of a torch mounted control as opposed to the foot pedal. So I usually use mig for on the car welding. For finishing butt welds, I find that the amount of weld bead to grind or planish makes tig desirable over mig, not the hardness. The grinder doesn't care about small differences in hardness, but it does matter how much material is to be removed. Likewise, when planishing, more metal = more work, I don't care how hard.

I also agree with Chevynut on mig being a bit less sensitive to contamination and rust. The other thing about tig, at least the way I do it, it's slower.