Having Fun Learning to Gas Weld with a new Cobra 2000 torch!

[55 Rescue Dog]

An acetylene flame is an acetylene flame. All you need is the same size orifice and the same gas flow rate and you'll get the same flame. There's no magic going on there.

Glad you guys like it, but I'll stick with my MIG, TIG, and plasma cutter. The only thing I use my oxy-acetylene torch for is heating stuff to bend or shrink it.

That's awesome you have a TIG and plasma cutter. This is just a alternative addition to having just a MIG. I would love to justify having those too, but I think this is a another need to learn technique, that has some benefits of it's own, for a couple grand less or more.

[LEE T]

I tried the Henrod many years ago for just a couple of minutes, and wasn't impressed at the time. I had been using o/a torch and wanted less heat distortion, so I bought a tig welder, and was immediately impressed.

This floor patch was welded with o/a torch using 5# pressure with a small smith torch and low pressure regulators
I don't do much welding but I always want to have the best equipment and do the best job I can with do in what ever I'm doing.







This floor patch on the same car was done with a tig welder, and the difference in heat is obvious.







As far as planishing a tig weld, this quarter panel was taken off the car for good access and finished without any filler.



There was actually two long welds



The next pictures were wiped with reducer to add gloss.







That took a lot of planishing with no cracking, and I would not want to try it with a mig.

I'm not a metal shaper and seldom visit those sites, but that is the place to get the correct answers.
Here are some very knowledgeable people discussing mig weld hardness.

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

[chevynut]

That's awesome you have a TIG and plasma cutter. This is just a alternative addition to having just a MIG. I would love to justify having those too, but I think this is a another need to learn technique, that has some benefits of it's own, for a couple grand less or more.

I guess my point is I can't see why anyone would spend $500 on an acetylene torch when you can buy a decent MIG welder for $600 or so. Even a more versatile TIG can be had for not too much more, especially if you buy used.

[chevynut]

That took a lot of planishing with no cracking, and I would not want to try it with a mig.

I'm not a metal shaper and seldom visit those sites, but that is the place to get the correct answers.
Here are some very knowledgeable people discussing mig weld hardness.
http://www.allmetalshaping.com/showthread.php?t=1287

Thanks for the great pics Lee. That TIG welding is pretty impressive. My problem with TIG welding sheet metal has been cleanliness. It's hard to clean a used panel and not get "volcanoing" from my experience. In fact, for some reason I have trouble trying to use 1/16" TIG rod at all and not get the "volcanoing" typical of a contaminated weld. I don't know why, unless my rod is bad. I typically use 3/32" and it works well on 1/8" steel.

I read some of the stuff on that site you linked, and to me the most convincing argument for a harder MIG weld is the CO2 in the gas. If it adds carbon to the metal, it will be come harder. Everything else is essentially the same as TIG welding, just a different process and technique.

And this guy on that link is totally FOS imo:

"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 "

MIG and TIG are both electric arc welds, and I don't see why MIG would be any hotter than TIG at the same settings. Also, when you ANNEAL (soften) metals you get grain growth, so the "very large grains" he says makes a MIG weld harder is BS. Cooling rate is not substantially different either...why would it be? In fact, a larger bead would tend to cool slower.

And his comment that "arc welding is not nearly as hot" as MIG is also BS. How do you get "deeper penetration" then? TIG welding temperature is around 11,000 degrees F and MIG temperature is similar since they're both arc welding processes. The boiling point of steel is around 6,000F.

Here's some pretty good stuff on metallurgy and how it relates to welding:

http://www.gowelding.com/met/carbon.htm

[chevynut]

Ok this is the best explanation I've seen for why a MIG weld is harder than a TIG weld. Watch the video...

"The biggest factor influencing the weld integrity is the polarity used in the Mig welding process, electrode positive, this means that the electrons flow out of the base metal toward the torch and concentrate the majority of the heat there. This polarity is required by the Mig process to melt the constant addition of filler wire from the torch, but it leaves the base metal colder.

By contrast, the Tig process uses the electrode negative polarity, where the electrons flow from the torch to the base metal, concentrating the heat in the base metal and mimicing the function of the oxy-fuel torch process.

The biggest functional difference is that the Tig and oxy-fuel processes allow you to melt the base metal and filler metal together completely as you progress, whereas the Mig process progresses regardless of weld fusion. The Mig process heats the base metal to a lesser extent, sometimes barely melting the edge of the work pieces, but it melts the filler wire completely until a ball of fluid molten metal falls to the workpiece.

Since the base metal is much colder than the molten ball of filler, the filler is quenched on contact until the base metal reaches sufficient heat to allow proper fusion to occur. Since most sheet metal welding is done in short bursts the base metal doesn't reach sufficient temperatures for proper fusion.

In this video you can see the short circuit welding action and it is plainly evident that the filler is radically heated while the base metal remains relatively cold and the filler piles up on top of it.

http://www.youtube.com/watch?v=UFFSJ...eature=related

It is possible to get more complete fusion with Mig, but it involves running a short wire stickout and a long arc to generate sufficient heat, but the risks are blowouts, burn back to the contactor tip, and drastically increased spatter due to the longer distance the molten metal has to travel to the base metal.

There are certain processes that allow you finer control over Mig welding parameters, such as those developed by Fronius;

http://www.youtube.com/watch?v=_WrhW...eature=related

This process is called CMT (Cold Metal Transfer) and is especially usefull for things like additive manufacturing and cladding where they boast low weld dilution. This is an exaggerated example of the above assertion, low weld dilution means that there is very little base metal melting and mixing with the filler metal. This is important if you want to build up lots of weld metal without heating the base metal very much, or welding dissimilar metals like steel and aluminum where the dilution would cause reactions, but it is the opposite of what we are looking for in welding sheet metal with complete fusion and resulting ductile joint.

Cheers,
Daniel "

[LEE T]

My problem with TIG welding sheet metal has been cleanliness. It's hard to clean a used panel and not get "volcanoing" from my experience. In fact, for some reason I have trouble trying to use 1/16" TIG rod at all and not get the "volcanoing" typical of a contaminated weld. I don't know why, unless my rod is bad. I typically use 3/32" and it works well on 1/8" steel.

I don't put that much effort in cleanliness as shown in the first tig weld picture, it was just lightly blasted then welded, all 1956 GM metal. I have parts cars and try to use original metal whenever possible. You might need to look elsewhere for the problems you are having.

All the 1957 quarter panel parts were acid dipped. The lower side of the quarter patch panel was rusted out so I used an old rocker panel for the bottom patch panel, and it was one gage thicker than the quarter panel. The rocker panel was welded on the donor quarter panel before cutting the patch panel out.

[55 Rescue Dog]

Funny, most people that say the Cobra doesn't have any merit are the ones that don't own one, or actually spent time to learn how to use it. What I've found out after using it a few times is, that it is so much better than my 2 previous torches that I will probably never use them again, because for one the set-up on this torch is as easy as it gets for a perfect neutral flame. Just set both regulators to a balanced 4 psi, attach the appropriate tip and go. The weird pistol grip is actually really easy to manipulate after you get the hang of it. No, it's not a TIG or MIG , but another great tool in the toolbox. It can do things you can't do with TIG/MIG, and vice versus. Short of a plasma, it cuts narrower/cleaner with single ports instead of the multi-port conventional cutting torch. It can weld dirty metal for one. I just used it to weld some not clean 1/8 angle pieces together for a torch holder. Got it welded just fine, but I will definitely be using my Miller 200 MIG on 1/8th, or thicker for sure. Takes a ton of heat on heavy metals, and the gloves get hot too. Everything was a hot orange, but nothing distorted. Thinner stuff, it will work great even with no gloves. No, I'm not ready yet to try and make a 7 foot O/A weld on a new 55 quarter panel yet, but it would work great in the right hands. Hell yeah I want a TIG too, but learning to weld with 2 hands with a torch will make that transition much easier.The good old gas torch is nothing to poo-poo, as it is still a preferred method for sheet metal, and even on aircraft, of which some of those welders probably use the Dillon/Henrob/Cobra/DHC2000. May the flame be with you.

[55 Rescue Dog]

Thanks LEE T for that thread! It surely makes you think about the magic involved. I haven't looked at the other links in the thread, but I will, and it will probably lead to some other stuff I never thought of. I love leaning new shit, and wow, I wish the internet was around 50 years ago.

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

[Rick_L]

Part of this deal is economics as already mentioned. I have a mig and a tig, and also a standard Victor torch. About all I use the torch for is to heat and bend. Even at that I had to borrow a rosebud tip one time to do a good job with that.

As for tig welding sheet metal, I have had no problems unless I was really weak on the prep. I can butt weld new 20 gauge sheet metal on the bench with no filler. For me, a lot tougher on the car.

As for mig welding sheet metal and the hardness of the weld - I don't think that's really the problem, but it doesn't matter - the main problem with butt welding and metal finishing mig welded sheet metal is just the amount of filler. There will be a lot and it will have to be dressed down before you can planish.

If you do a lot of O/A welding, having a Henrob or Cobra torch may be worth it. I would see a learning adjustment would be needed just to learn to hold the torch and manipulate it if you already had some skill with standard torch.

I don't think the torch competes with tig in other areas like welding aluminum. Or welding thin pieces to thick pieces, aluminum or steel.

Having good tools makes you a better welder. Having too many probably makes you broke. And while it doesn't have to be a situation, open flames are probably a bigger safety risk.

[55 Rescue Dog]

I've oftened wondered, what does a master metal worker like MP&C have to say about any of this???

[LEE T]

Ok this is the best explanation I've seen for why a MIG weld is harder than a TIG weld. Watch the video...

"The biggest factor influencing the weld integrity is the polarity used in the Mig welding process, electrode positive, this means that the electrons flow out of the base metal toward the torch and concentrate the majority of the heat there. This polarity is required by the Mig process to melt the constant addition of filler wire from the torch, but it leaves the base metal colder.

By contrast, the Tig process uses the electrode negative polarity, where the electrons flow from the torch to the base metal, concentrating the heat in the base metal and mimicing the function of the oxy-fuel torch process.

The biggest functional difference is that the Tig and oxy-fuel processes allow you to melt the base metal and filler metal together completely as you progress, whereas the Mig process progresses regardless of weld fusion. The Mig process heats the base metal to a lesser extent, sometimes barely melting the edge of the work pieces, but it melts the filler wire completely until a ball of fluid molten metal falls to the workpiece.

Since the base metal is much colder than the molten ball of filler, the filler is quenched on contact until the base metal reaches sufficient heat to allow proper fusion to occur. Since most sheet metal welding is done in short bursts the base metal doesn't reach sufficient temperatures for proper fusion.

In this video you can see the short circuit welding action and it is plainly evident that the filler is radically heated while the base metal remains relatively cold and the filler piles up on top of it.

http://www.youtube.com/watch?v=UFFSJ...eature=related

Exactly! That is what finally came up in the link I posted. I have read about some companies pre heating the metal under controlled conditions for mig welding.

[MP&C]

Here's a good video on torch welding. Note he doesn't do any "hammer welding" while the panel is hot. Premise is that striking the metal in its expanded state is just hammering the bulge back into itself, or shrinking the spot. The heat from welding is already shrinking, why add more? Let the panel cool...

https://www.youtube.com/watch?v=fkNtUjxSf7Q

I started with a MIG and like many people went through the trial and error of blowing holes, weld blobs, etc. Finally got my method down to single weld dots, extra heat for full weld penetration, and planishing. I surely can't be the one who invented this process, but I have shared it quite a bit that others with MIG only could perhaps have better consistency in results in using a MIG on sheet metal.. The detractors to using the MIG is that by welding only one dot or short burst at a time, the panel is heating and cooling in that one spot, each and every time we weld a dot. This essentially gives us the most shrinking of the various processes we could use. Weld a burst of 5 successive dots, let it cool, weld five more, let it cool, etc. This may get the job done more quickly, but now notice the buckling/panel distortion at each start and stop point. This is what causes the majority of distortion, starting and stopping, differing forces, their cause and effect will all have an outcome on panel distortion. Another detractor is that the welds are harder than other processes (try using snips to cut through a MIG weld seam that's been ground flush, you'll know exactly where it is) and there is considerable grinding and dressing of the panel afterward, then all the planishing and panel bumping afterward to try and remove all the distortion...

For TIG or O/A, I find both to be similar processes, where the TIG is somewhat cleaner of a process. For both of these, a non-stop continuous weld is the best for keeping distortion to a minimum. You will need to tack the panel together first to hold things in place. Note in Peter's video above, each tack starts at the edge of the last HAZ, so when you have completed tacks from one end to the other you have a fairly consistent HAZ from one end to the other. With TIG, I have shown tack welds before that had no HAZ whatsoever, but this would require absolutely tight joints. SO in that case, HAZ would be a non factor in tacking, so choose the spacing you wish. Again, consistency here helps keep any distortion to a minimum. I have both a TIG machine as well as a HENROB (so you can see how old it is). In my view the Henrob torch is very capable but is also cumbersome. In many cases (working on a bench) your arm is up in the air and wrist all contorted to be able to properly aim the torch. If you can't hold your wrist straight, you are going to add fatigue. A standard style torch IMO is more comfortable, so my Henrob normally comes out when I need a torch for heating something. I lean towards the TIG for welding based on a cleaner process. At our last Tommasini class at the shop, Peter had recently purchased one of the MECO torches from Kent White (www.TinManTech.com) as he said it was one of the best designs he has used, nice and compact, and comfortable to use. Aluminum gas welding usually requires more heat, and Peter said it has plenty of balls for that as well.. He prefers gas welding aluminum as he says it provides a softer weld that can be put right into the english wheel.


Regardless of the process you are using, be it MIG, TIG, or OA, the weld process begins with panel fitup and trimming. Consistency is key throughout. Tight, accurate joints are needed, size of weld, width of HAZ, all affect amount of planishing needed, and all these factors have an effect on panel distortion. Unlike the MIG, in welding a continuous seam from one end to the other with TIG or OA, you have a gradual heating and a gradual cooling as you travel across the panel with the torch. This keeps any shrinking effects more balanced/consistent, where the circumferential shrink of the MIG weld dot is pulling at the panel with each and every weld dot. So a non-stop weld using TIG or OA should give us less linear shrink than the MIG.

At the end of the day, the method to use comes down to one's ability or lack thereof. Use what works for you. Someone who can't walk, talk, and chew gum at the same time likely doesn't have the dexterity and coordination of heat and feed needed for TIG or OA. So sure, they could use the MIG as an alternative. More planishing, more grinding, more cleanup, more panel bumping will be needed, but you can still get acceptable results. Did I mention consistency?

[55 Rescue Dog]

Thanks Robert, that clears up a few questions for sure. Could a quarter panel be tacked with a MIG, and then gas welded in between?

[MP&C]

There are guys that use that method, but IMO you are using one method over others for a reason, why not use that method throughout? David Gardiner (Classic Metalshaping, UK) will hold the patch in one hand, align and tack using OA torch in the other, then realign, tack, realign, tack, etc, never using a clamp. I'm nowhere near his badassery..

[LEE T]

I don't see any advantage to using a mig for tack welding either.
As for the so called hammer welding---I have never been quick enough or safe enough with the torch for that. And after several inches of welding, its not all red hot anyway. I wouldn't mind going all the way across the panel, but I loose site of the seam due to my worn out eyes.