The Stovebolt Site Forums The Shop Area The Tool Chest mig welder vs. oxy acet. pro's & con's

That's where I am right now. I have the MIG thing down and feel confident my welds are strong, but TIG looks intriguing. My local welding shop tells me TIG is hotter. Hotter isnt something that floats my boat! Warpage is already a very clear and present danger. Yet I can see that welds would be prettier with TIG since the rod would be easier to control? I want to take a class though, because there is DC TIG, AC TIG, and many settings new to me.

You will win a welding race with your MIG, but I will win the prettiest weld contest with my TIG. One thing about the TIG which I like is that there is no splatter, no burnt down "busy" shop.
Carl

I know. Very intriguing. I want one. I hear they are a little pickier about starting with a clean surface, but I am already very meticulous about that. I actually put up a 8 foot by 10 foot galvanized wall at my welding setup so the weld spatter wouldnt be messing up the walls. I use Argon/C02. I cant imagine what MIG with flux core wire would do, but I have seen the end result. The gas IS a different mix between MIG and TIG right? I want to do stainless, alum, and mild steel but changing over takes so much time AND money since each alloy requires a different setup.

TIG uses pure Argon. I can't believe that you don't have a TIG yet Deve. If you get one, I'll bet your MIG will then start collecting dust. Do you have steady hands? If not, you can cheat by making sure you can support the heels of your hands as you go. The pedal takes a while to get used to, but it is what gives you finesse which other welding techniques lack.
Carl

Everyone goes nuts for the 'stack of dimes' look.. but in all honesty a good weld is a good weld and poor penetration is poor penetration no matter how pretty it looks.

Touching any airframe component on a certified airframe needs an A&P ticket. Experimental aircraft not so much.

FAA recommends post weld tempering for all TiG welds. I'd want to see that in a log book if TiG was used on an airframe I owned.

Not wanting to debate FAA rules.. they are what they are. My post was that the FAA RECOMMENDED post TiG weld tempering.

AMT Handbook 2012:

"However, do not eliminate the postweld heat
treatment as doing so could severely limit the fatigue life of
the weldment due to the formed martensitic grain structure."

Even Gas welds are to be tempered:
"When the weld is complete and still in the red heat,
circle the outer envelope of the torch around the entire
weldment to bring it evenly to a dull red. Slowly back
the torch away from the weldment to ensure a slow
cooling rate."

If it ain't in the log book, it didn't happen.

You can bet they'll look at the process after a crash. I'm sure it's happening to Larry Dixon after his car split in half a few weeks ago. Top fuel crash

I retired from the FAA a few years back, and yeah, it is what it is! I am sure they have pretty clear guidelines on what type of welds they want on just about everything. We have the safest air traffic system in the world so they must be doing something right.

No sense arguing with one who knows it all.
dg

I have had a Trailblazer 440 with a water cooled tig for many years. A few years ago I bought a Miller 350 with a water cooled torch because I was frustrated with getting bird nests in my Millermatic 251 with push pull. But tig is just too slow to suit me. I bought a Millermatic 212 with a spoolgun last December and I think this is the way for me to weld aluminum. I use ER5356 alloy. Cornhusker 800 builds hopper trailers with a trip dump that I designed back in 1992 for me. The prototype is still in daily service and I added 3 more to the fleet last year. Cornhusker does all of their welds with wire. If they use wire to build them, I see nothing wrong with wire to repair them. I am beginning to think I wasted about $8,000 on buying the tig equipment because all it has done is collect dust since I bought my last spool gun. I don't fix airplanes, but I have owned and maintained a fleet of trucks for over 50 years.

Embry-Riddle taught me well. So yeah.. education and all that.

Also you seem to miss that its not REQUIRED, only RECOMMENDED that post weld stress relief be done. Do you have a copy of the AMT?

In your haste to claim to be smarter than everyone else in the world you missed the fact that

1. I did not say you made a mistake.
2. Didn't clearly read, but ASSumed something never said.
3. Made an ad hominem attack when there was nothing to cry about.

Deleting posts to cover tracks.. hmmm....

Before y'all get this thread deleted, give me some time to write down about half of it. I'm still slow. Make every comment as if you were within knuckle reach- that's a good rule to follow.

I only brought the thread out of hibernation because I saw the welder trainer at work (doing software updates) & remembered smith talking about wanting to use it. Someone before that saw the Aviation units using it.

Brad

Brad, come on up to the farm and bring some 1" wide strips of 12-16 gauge mild steel if you can locate some. We can have a little training session on OAW techniques, and I promise the atmosphere will be a LOT more cordial! I've got a new toy to play with, at least temporarily, too!
Jerry

Easy fella's. Let's get back on topic.

To the OP, it sounds like you are primarily looking at automotive sheet metal work, a lot of your machine choice will be determined by how well you do in panel fitup. Mig is a bit more forgiving in wider and inconsistent panel gaps, as it is constantly adding feed wire. Let's call it a point and shoot. Tig is more of a manual dexterity challenge, as your feed hand needs to keep up with the torch hand, in coordination with the foot pedal. Now add a little excess panel gap and not enough feed and the heat will burn away at the parent metal, easily blowing a hole.


Given the limited panel thickness in welding sheet metal, heat control is a must. In using a Mig, it is nearly impossible to try a full pass weld with any semblance of consistency. Your start may be a little cold, showing little to no weld penetration on the back side, a little further along and you'll be getting a nice bead with full weld penetration, a little further once the panel has heated up and the weld will likely blow through. For this reason, and to try and have any consistency with the welds, Mig welding sheet metal is usually welded one dot at a time with the welder set hotter than normal to insure full weld penetration, wire feed a bit faster to help prevent any blowout, and weld size controlled by the length of the "zap".

Unfortunately, every time you weld one of these dots, the weld and HAZ (heat affected zone) shrink, pulling the surrounding panel in toward the center of the weld from all sides. This is best corrected by planishing each weld dot individually, and then grinding down to get it out of the way for the next set...

Example:

http://www.garagejournal.com/forum/showpost.php?p=2924553&postcount=53


The ER70S-6 wire that typically comes with all Mig machines is a bit troublesome for sheet metal welding in that it hardens up a bit as it cools. This makes it more difficult to planish, and more of a chore to grind and sand down flush. There are other options to make this easier, EZ-Grind wire is softer making it easier to planish and grind, ER70S-7, in addition to those features, has more manganese in it's formulation for better wetting properties, which means better flowout to the parent metal and less proud on the weld. This helps to limit the amount of cleanup work afterward, and make what does need done easier. Still not as clean as a TIG, but it helps.


Tig. Welds are typically softer than the -6 Mig wire for an easier job of planishing the sheet metal, easier grinding/sanding the panel smooth. Full penetration Tig weld beads are typically less "proud" than their Mig counterpart, for less cleanup. Tig welding a continuous bead (as on a panel that has been tacked together) will have less shrinking and thus distortion issues than Mig. The continuous weld bead heats up and cools down progressively across the panel, so the shrinking effects are comparatively less than that of the shrink that occurs around each weld dot in Mig welding. For those really skilled at panel fitup, Tig also adds the option of fusion welding, ie: using no filler at all. This is beneficial on all aspects as there is virtually no grinding afterward, just a bit of planishing..:

http://www.garagejournal.com/forum/showpost.php?p=2809607&postcount=301

Most of the details above discussing the TIG apply equally to the O/A torch.

Back in the early 1970's I watched a body man on Okinawa fusion-weld a patch about 3" square into the middle of a door panel on a 57 Chevy sedan with a torch, with virtually no distortion. He used a tiny, needle-sharp flame and worked very quickly. He was good, to say the least! Later on, I used a similar technique to patch the front fenders on my M-151 Jeep where I had removed the turn signal mounts, with almost as good results. I needed to do a little metal finishing and shrinking afterwards, but no Bondo.
Jerry