MIG vs. TIG welding

[ggdad1951]

So, spent more time welding on TODD this weekend...posted a few pics on FB...a buddy of mine messaged me that since I'm using MIG, once the cab sits in the sun, I'm gonna start to see issues regardless of the body work after welding....

 

So, on that note, I'd like to hear from the guru's of welding....

 

Will I have issues since a MIG weld is so much harder?  

 

Then there is the finish grinding, etc..

 

Sould long welds really be TIG'd?

 

Etc.

 

Discuss....and thanks

[Dave72dt]

I have heard of flanged panels being visible in the sun because of the different expansion rates from metal thickness and I suppose the same could be true from weld seams. I haven't seen either happen. I could theorize that once the expansion has equalized anything that might have been visible goes away and I would expect the same from exposure to cold. Have you been able to outline any patches or repairs on FEF from sitting in the sun? All of those were MIG welded.

I try to finish off both sides of a weld when I can. Not only looks better but feels better to anyone looking for repairs and I want both sides sealed against moisture. TODD won't have that many welded panels exposed on both sides and some won't see direct sunlight either sand as tall as TODD is, it'll be tough for anyone to see how the roof reacts.

Tig is always preferred on sheetmetal. It's a different skill set than MIg, requires very clean metal, very good and consistant gaps between panels and is easier to planish the welds after. I don't have a TIG so all my welds are Mig and you can do long panel welds successfully with one.

This ugly hood came to me cut up and partially welded. Four seams down the length of the hood plus a bunch across the nose. All MIG, single panel thickness, exposed both sides, skim coats of filler only and no signs of welds visible when exposed to sunlight.

Edited April 25, 2016 by Dave72dt

[Dave72dt]

A few more of the extensive welds required.

[ggdad1951]

no, I've never seen a patch point on FEF, I'm dressing the welds on the weld side with a cuttoff wheel, not a big old grinder tryign to keep things cool as I go, just like welding, I hop around.

[wayfarer]

Excessive heat is the problem regardless of weld platform. As with your grinding, skip around and limit the bead length.  I would also recommend some practice work to find the lowest voltage vs wire speed setting that you can effectively work with.

Where possible, use a heavier block of 'something' as a back-up/heatsink.

[Fargone]

I've got to do the bottoms of my doors and the fender mounts on both sides. Those areas are in rough shape, but surprisingly the rest of the truck is pretty solid. The doors pose the biggest challenge as both the exterior panel and the base inside structure are rotted away to nothing. I've got donor doors for patterns but only 1 of them is straight and true. I'd hoped to just install them as a swap but the drivers door has a lot of damage. I can't use just one of the because the 1950 has a different interior look than my 1951.... I grabbed all the sheet metal I could from the 1950 to aid in repairs of my truck and if anyone needs a complete hood for a 1 ton let me know I have one.

[Dave72dt]

Be very careful with the discs when grinding with them. A bit too much side pressure or flexing of the disc can make them explode and it hurts when the pieces make contact- a lot!

[ggdad1951]

Be very careful with the discs when grinding with them. A bit too much side pressure or flexing of the disc can make them explode and it hurts when the pieces make contact- a lot!

 

no real side pressure....already had one go explodey when working on FEF...smashed a face shield!  I tend to not look down the blade now because of that, but rather off from the side.

[NiftyFifty]

You guys use flapper discs? Their way way better then the old grinding discs of past...their very very coarse sandpaper very tightly packed together..they will grind welds just about as fast and way less heat. As for tig vs mig....tig in reality is for new sheet metal, or very very clean old, and yes...it takes a lot of talent. I'm good friends with a custom hot rod builder who has built some beauties...all mig welds and no signs even on his gloss black cars. I'd recommend gas only welds tho, flux core wire is messy and doesn't weld sheet metal worth a darn...

[ptwothree]

Anyone try ESAB's Easy Grind mig wire?  Supposed to be easier to grind and hammer weld as it is a softer wire then regular mig wire.  Made just for sheet metal work.  Not good for structural stuff.

[DJ194950]

Checked it out online sounds good but expensive not sure. Cheapest price after a little time spent was $ 80 shipped for a 11lb. spool of .023 wire. Have not bought any  mig wire for several years so I'm not up with current prices but that does seem about 3 times what I spent locally for .023 11lb. spool then.

 

Maybe it is worth more if it does save enough grinding time and grinding wheels, but how much more. Supposedly as strong as normal mig wire-general use type. es70 I think?.

 

Also interested if anyone has tried it.

 

DJ

[Dave72dt]

You guys use flapper discs? Their way way better then the old grinding discs of past...their very very coarse sandpaper very tightly packed together..they will grind welds just about as fast and way less heat.

I use them as well as regular grinding disc and the cut off wheels.  I prefer to use them for finishing the grind as opposed to general  grinding.  They're so much pricier than a regular disc I use them somewhat sparingly and since you can't see where you're grinding as well, it's easy to take metal off the surrounding area  as well..  After the flap wheel I either leave them as is or hit them with  a roloc disc or 80 grit on the DA.

[jeffsunzeri]

All popular welding methods can be used to stitch together automotive sheetmetal successfully. Oxy-acetylene has worked beautifully for decades, TIG works just fine, and MIG is very successful. The only method that is not usually recommended is stick-arc. It is very difficult to get satisfactory welds on thin gauge material with this process, but it has been done.

The key to a good bond and final appearance has much more to do with the body man than the welding method. Some notes:

* Both TIG and MIG require the same amount of cleanliness of the base material before welding as both use burning inert gas to keep the weld area clean.

* In order to keep warping to a minimum, the Heat Affected Zone must be kept to a minimum. Operator skill is key here.

* MIG requires less skill to operate than either TIG or Oxy-Acetylene.

* Welders are trained on Oxy-Acetylene process first, then move on to MIG and TIG to build skill in understanding how the weld process works.

* No matter the process, hammer welding skills are necessary to get a satisfactory seam.

* Cleaning the weld area AFTER welding is extremely important to a final finish that adheres and appears properly.

The final word is that it is the skill of the operator, not the weld process type that determines the goodness of the end result.

NOTE: I've excluded flux-core automatic wire welding and brazing methods as outside the scope of this little discussion.

Edited April 26, 2016 by jeffsunzeri

[1952B3b23]

All popular welding methods can be used to stitch together automotive sheetmetal successfully. Oxy-acetylene has worked beautifully for decades, TIG works just fine, and MIG is very successful. The only method that is not usually recommended is stick-arc. It is very difficult to get satisfactory welds on thin gauge material with this process, but it has been done.

The key to a good bond and final appearance has much more to do with the body man than the welding method. Some notes:

* Both TIG and MIG require the same amount of cleanliness of the base material before welding as both use burning inert gas to keep the weld area clean.

* In order to keep warping to a minimum, the Heat Affected Zone must be kept to a minimum. Operator skill is key here.

* MIG requires less skill to operate than either TIG or Oxy-Acetylene.

* Welders are trained on Oxy-Acetylene process first, then move on to MIG and TIG to build skill in understanding how the weld process works.

* No matter the process, hammer welding skills are necessary to get a satisfactory seam.

* Cleaning the weld area AFTER welding is extremely important to a final finish that adheres and appears properly.

The final word is that it is the skill of the operator, not the weld process type that determines the goodness of the end result.

NOTE: I've excluded flux-core automatic wire welding and brazing methods as outside the scope of this little discussion.

 

I agree with what's said above. I'd have to say though, MIG is slightly more forgiving with the material cleanliness. TIG is notorious for requiring extremely clean material for welding. Regardless of what process you use, MIG or TIG they both need clean metal. I prefer tig welding my sheet metal when ever possible. It gives you better control over the heat input to the panel and the welds are easier to dress. As Jeff stated above it's really the technique not the weld process!! Theres guys out there who do beautiful metal work and all they use is oxy-acetylene welding. Which to me gives you very little control of the heat input, at least not on the fly like tig. It's really important to use the least amount of heat as possible when welding sheet metal. Excessive heat causes more distortion (shrinkage), which then needs to removed by hammer and dolly work. Thats why i like tig so much, i can control the heat on the fly with the foot pedal. The techniques you use as you go along during the welding process is also real important. I like to weld a little bit (with tig i weld a few inches), then stop and grind down both sides of the weld. I use a 1/4" air die grinder with a 40 grit Roloc disc. I leave the weld just a few thousandths proud on both sides. Then i go to town with the hammer and dolly, this stretches the weld back out and helps to cold forge the weld into itself. Then i grind it flush on both sides and do a bit more hammer and dolly work. The goal here is to raise up any low spots. A neat trick that i use to find the highs and lows is to use a Sharpie marker and highlight the entire weld area. Then take a dulled file and pass it across the surface that you have inked. The file will scrape the marker off where it is a high spot and leave the marker behind where it's low. You now use this as your road map to finding the lows and bump those areas up with the hammer and dolly. Once the surface feels pretty good and you make sure it isnt all out of whack you can continue welding and repeating this process. At the end is when you can go back over the entire area and do the metal finishing. This requires more time with the sharpie, file, hammer, and dolly. In conjunction with the hammer and dolly i also use a shrinking disc. This is used to shrink any of the high spots down to give you a super smooth finish. If i was using mig i would do the same approach except instead of welding a few inches at a time, id jump around with a bunch of spot welds in various places. This helps keep the heat input to a minimum. Then just continue filling in with more spot welds till the seam is welded. Make sure to stretch the weld area as you go (hammer and dolly). I've attached some pics of fender repairs that i did on my '39 Plymouth Coupe. They where done with TIG and metal finished with the method described above.

 

Regardless of the weld method i would definitely make sure you don't have any pinholes in your welds. This is where people run into issues, they coat with bondo and forget about the small pin holes that continue to let the moisture in. This will cause the patched area to show down the road. They make a filler called "All Metal" which is supposed to be really good and fill any of the pin holes and lock out all moisture. Heres the link:

 

http://www.amazon.com/USC-14060-All-Metal-Specialty-Filler/dp/B0082LFAI6

 

So to answer the original posters question, i don't think you need to tig your panels to have them turn out quality. If you just take your time and pay attention to what the panels are telling you, how they are moving and reacting to the heat (hopefully not much) you'll be alright. If you're up for learning a new skill then maybe try out TIG. It's not as hard as it seems and the welders really aren't all that expensive any more. Plus you dont need anything big to weld sheet metal. If you want more info on the process or have any questions feel free to send me a PM. 

 

Good Luck,

 

-Chris 

[NiftyFifty]

Biggest mistakes I made when I was learning mig on sheet metal was tacking one edge on a patch panel then welding away and not taking the middle and opposite edge before I did...better be ready for some big gaps when you do it the wrong way. I did some real bad work even on this go round, thatnI had to go back and repair..but a dirty regulator was giving me argon issues and causing bad welds. I would rather do 100 small welds, then burn through on one clean line...so I move around a lot and sometimes use a chunk of old copper as a heat sink if I can.

[1952B3b23]

Biggest mistakes I made when I was learning mig on sheet metal was tacking one edge on a patch panel then welding away and not taking the middle and opposite edge before I did...better be ready for some big gaps when you do it the wrong way. I did some real bad work even on this go round, thatnI had to go back and repair..but a dirty regulator was giving me argon issues and causing bad welds. I would rather do 100 small welds, then burn through on one clean line...so I move around a lot and sometimes use a chunk of old copper as a heat sink if I can.

 

Thats a really good point you bring up. Its really important to tack the panel in A LOT of places before starting to weld. I usually try to put my tacks about 3/8" apart. The backing with a piece of copper is also a good idea on areas with less than ideal gaps. When TIG welding i always try to back the weld area with copper, it helps to purge the back of the puddle with argon. Sometimes though its just not possible to get the copper back there.

 

-Chris

[JBNeal]

I have done some emergency patchwork with oxy-acetylene and with stick welds, and tho stick welding is very difficult, it can be done, better results with DC neg.electrode...clean metal and a good ground are paramount. The best sheet metal welds I have seen have had many tacks before several seams are welded...kinda like stitching the metal, to minimize warpage. Another issue is the composition of the metals welded...differing carbon composition in panels will have different thermal expansion rates. I have seen old steel patched with new, and in the TX summer heat, the patch panels stick out like tumors to the trained eye. At any rate, the stitching approach is not fool-proof, as excessive heat can cause wrinkling at the weld seam.

[NiftyFifty]

Not using enough heat is bad too..poor penetration means weak welds...I've taken stuff apart welded by others that literally just need a small hammer tap..sometime important structural welds. I would never claim to be anything but a backyard dabbler, but I've always worked hard to make sure what I stick together, stays that way. My father was a welder for many years including high pressure, and ran a welding shop on a military base up here, so I had a pretty good teacher...although he never did much mig or any tig..he was a true pro at the old fashioned oxy welding sheet metal.

[48Dodger]

Welding is a danger sport. Its fun and rewarding, but it can kill. Its grouped into what's sometimes referred to as "hot work".

 

•  Tank Manifold explosion (not putting your stuff away right)

•  Unskilled welds used on important areas of a vehicle/trailer

•  Trying to weld rims with the tire still on it (equal delayed tire explosion)

•  Cleaning metals prior to welding with the wrong cleaner (ie brake cleaner...mixed with argon makes phosgene...its deadly)

•  Creating heat in the presence of a undiscovered fuel source (resulting in fire or explosion)

 

Not to mention minor injuries due to improper clothing protection (yea...you can set your tennis shoes and hair on fire!)

 

I post on the Pilot House forum a lot...and I mean A LOT......but this is where I go for welding.  

 

 http://www.allmetalshaping.com/  great place to get educated without a classroom.

 

http://www.weldingtipsandtricks.com/   best place for the novice to get the right answers the first time. Jody's Youtube videos rock.

 

http://www.millerwelds.com/resources/communities/mboard    Miller welding forum...simple and to the point....a good site to be constantly reminded of being safe while welding.

 

48D

[Jeff Balazs]

Tim I couldn't disagree with you more. I spent more than 30 years around some of the most highly skilled welders on the planet. Cross country pipeline welders, Offshore platform welders and precision manufacturing welders. One thing I know for certain is that it is not a sport. If anything it is a fine art form in the hands of real talent. The things I saw these guys build or repair just boggles the mind. Years of watching these guys work left a couple of lasting impressions. First and foremost was that most top tier welders work instinctively. They know exactly what they are doing and how to get the results they need. And they are always in control of the situation at hand. Sadly the second impression is a little less positive. Like real musicians good welders have a gift. Just because someone goes out and buys the instruments and takes all the classes doesn't really mean a lot without this gift. It truly is an art form that only a small segment of the population ever master. No matter what we all think about our capabilities we can't all be good at everything. Quite a bit of automotive welding IMO belongs in the gifted hands of a real pro.

 

Jeff