What is stronger and why? Mig or Tig

[mikegyver1]

What is stronger and why? Mig or Tig
I have two different buddies that are both certified welders claim Mig welding is stronger then Tig welding. If so why would you Tig weld a cage then....

[bajaviking]

I think this sums it up pretty well.

Weld 'strength'... need to look at the complete picture (rather than just weld size for exmaple), a chain is only as strong as it's weakest link and all that. Assuming welds have proper fusion most metal/weld failures are the result of fatigue rather than lack of outright strength- a sharp edge, notch, bump etc concentrates stress in one area and with time a crack forms, grows and then (when the section has been weakened sufficiently) fails. An oversize weld can be a stress riser as can an undersized weld.

In the wrong hands... MIG is more prone to lack of fusion defects (that big weld's just sitting on the surface) and stress risers at the weld toes (sharp bump). TIG is more prone to undercutting (sharp notch and a reduction in section thickness at the same spot) from nervous hands and a desire to get a small, pretty weld!

A good MIG weld will be 'stronger' than a bad TIG weld and visa versa. It's quite hard to produce a lousy but good looking TIG weld, MIG on the other hand...

TIG is the most versatile process there is with regards to materials that can be welded- if it's metal and weldable it can be done with an AC/DC TIG, press a couple of buttons grab the correct filler and you're good to go. No changing of gas mixes or swapping out wire reels. Downsides would be initial equipment costs and weld deposition rates. MIG is typically faster, especially on heavier sections that require larger welds.

[David D]

A properly done weld with no defects is only as strong as the filler material that you use. When welding mild steel with either a mig or tig the most common filler is a er-70, which means that both welds would have a tensile strength of 70,000 psi. So neither is stronger per say they just are used at different times.

[machinisttx]

Originally Posted by David D

A properly done weld with no defects is only as strong as the filler material that you use. When welding mild steel with either a mig or tig the most common filler is a er-70, which means that both welds would have a tensile strength of 70,000 psi. So neither is stronger per say they just are used at different times.

Yep.

[mechanicalmongoose20]

Originally Posted by David D

A properly done weld with no defects is only as strong as the filler material that you use. When welding mild steel with either a mig or tig the most common filler is a er-70, which means that both welds would have a tensile strength of 70,000 psi. So neither is stronger per say they just are used at different times.

This.


Personally, I think a TIG is used at times for the prettiness. They can make a great looking weld, but as far as strength goes it is apple to apples.

[AggieTJ2007]

Most of the high end chassis you see that are TIG welded are TIG welded because they are made from chromoly tubing.

The both have their place but on 1020 CR steel a proper Mig weld may tend to be stronger because of higher penetration.

[red racer]

It mainly depends on who"s doing the welding . Both are about equal.......I say smaw is better on thick material and more versatile and less prep required.

[Invert'D]

Originally Posted by AggieTJ2007

Most of the high end chassis you see that are TIG welded are TIG welded because they are made from chromoly tubing.

The both have their place but on 1020 CR steel a proper Mig weld may tend to be stronger because of higher penetration.

MIG doesn't have higher penetration than TIG, it has higher deposition: it lays down filler material much more quickly. If anything that feature makes the penetration at any given moment more difficult to ascertain. If you're putting more heat into the filler material, you've got less going into your base material, which is why MIG is highly prone to cold lap, even for experienced weldors.

TIG gives you far better control of penetration and fusion than does MIG, and gives you much better control of deposition as well. It is more prone to undercutting, but that's easier to detect and fix than cold lap.

TIGs main disadvantages compared to MIG are that it's much slower, more sensitive to contamination and poor fitup, and tends to heat up the workpiece more (may be good or bad).

To the OP, TIG welding is better for roll cages for the reasons I mentioned above. Especially when so many MIG fabricators feel the need to make a bead out of tack welds so that it looks pretty--which pretty much guarantees cold lap.

Please ask your two friends to explain exactly wtf they're talking about and fill the rest of us in. Stronger in what way? For what applications? Jet turbines, maybe?

[AggieTJ2007]

Have you ever acid etched a Mig weld vs a Tig weld of the same size?

The Mig weld has more penetration because the wire "drives" the penetration into the base metal. Tig welding does give you more control over weld size and heat input though which tends to make it a better choice for welding intricate roll cages if you have the skill.

[Jeepman14wheel]

Originally Posted by Invert'D

Stronger in what way? For what applications? Jet turbines, maybe?

I work with 7 gas turbines everyday and there is no mig on any part....

Four LM2500 GE
Three Rolls Royce K34

NO MIG....

[mikegyver1]

Originally Posted by Invert'D

Please ask your two friends to explain exactly wtf they're talking about and fill the rest of us in. Stronger in what way? For what applications? Jet turbines, maybe?

I did ask... that's when one buddy spat out a bunch of info about how TIG Argon gas changes the steels molecular structure (brittle in front and behind the weld) differently then MIG Mix gas (flexable in front and behind the weld).
Any truth to that?

[Invert'D]

Originally Posted by AggieTJ2007

Have you ever acid etched a Mig weld vs a Tig weld of the same size?

The Mig weld has more penetration because the wire "drives" the penetration into the base metal.

No offense, but I think you're confused. For starters, comparing weld sizes between MIG and TIG is like comparing apples and oranges. If anything, you have that completely backwards. TIG welds are characteristically smaller than MIG welds. If you were to join two pieces of metal of a given thickness, a proper TIG weld is going to be smaller and flatter than a proper MIG weld. This is because unlike MIG, TIG does not use filler material to achieve penetration, it uses the application of heat. Filler is added as needed.

I think a more useful comparison would be based on amperage. Let's use a concrete, useful example for DIY motorsports fabrication. Take a vanilla 175 amp MIG: it's capable of getting full penetration on a single pass weld on about 1/8" (.125") thick carbon steel--if the base metal isn't too cold and it isn't Tuesday. Now take a vanilla 175 amp DC TIG welder: at 175 amps, you'd better go fast on that 1/8" material, or you will blow a big hole right through it. A better setting would be something like 120 amps give or take.

What you describe above is a good, simple explanation of of how short circuit MIG welding works, but that doesn't give it better penetration than TIG. Spray transfer MIG doesn't work the way you described and it gets better penetration than short circuit MIG, because, like TIG, it's hotter and puts more heat into the base metal (to put it simply).

[Invert'D]

Originally Posted by Jeepman14wheel

I work with 7 gas turbines everyday and there is no mig on any part....

Four LM2500 GE
Three Rolls Royce K34

NO MIG....

Well no wonder--none of those were made in China, now were they??

Originally Posted by mikegyver1

I did ask... that's when one buddy spat out a bunch of info about how TIG Argon gas changes the steels molecular structure (brittle in front and behind the weld) differently then MIG Mix gas (flexable in front and behind the weld).
Any truth to that?

Well, that's something I can address, because saying that MIG welds are stronger than TIG welds is just complete B.S.--where to even start? Both processes can make joints of comparable strength when done properly.

Are you sure this guy is your friend? TIG welds are not more brittle than MIG welds, in fact, just the opposite is true--TIG welds generally are more ductile than MIG. This is because TIG creates a larger HAZ (heat affected zone) than MIG. TIG also tends to mix the filler material with the base material better than MIG.

Now if you want to talk about a process that is more ductile than TIG (it sure as hell isn't MIG), lets talk about oxy-acetylene welding. A lot of airframe weldors won't use anything else, but if they did, it sure as hell wouldn't be MIG.

By the way, an argon mix is typically used for MIG welding, although plain argon can be used. Argon is a non-reactive, "noble" gas, meaning it is chemically inert. CO2, which is the second ingredient in a typical MIG mix, is a reactive gas, meaning it is chemically reactive. It can and will bind with other materials and effect changes in molecular structures. It's used in MIG welding steel (again, usually mixed with argon, but sometimes straight).

[wheelerpeeler]

Originally Posted by Invert'D

Well no wonder--none of those were made in China, now were they??



Well, that's something I can address, because saying that MIG welds are stronger than TIG welds is just complete B.S.--where to even start? Both processes can make joints of comparable strength when done properly.

Are you sure this guy is your friend? TIG welds are not more brittle than MIG welds, in fact, just the opposite is true--TIG welds generally are more ductile than MIG. This is because TIG creates a larger HAZ (heat affected zone) than MIG. TIG also tends to mix the filler material with the base material better than MIG.

Now if you want to talk about a process that is more ductile than TIG (it sure as hell isn't MIG), lets talk about oxy-acetylene welding. A lot of airframe weldors won't use anything else, but if they did, it sure as hell wouldn't be MIG.

By the way, an argon mix is typically used for MIG welding, although plain argon can be used. Argon is a non-reactive, "noble" gas, meaning it is chemically inert. CO2, which is the second ingredient in a typical MIG mix, is a reactive gas, meaning it is chemically reactive. It can and will bind with other materials and effect changes in molecular structures. It's used in MIG welding steel (again, usually mixed with argon, but sometimes straight).

So if I am hearing you correct why do they MIG or Stick weld structural steel then if Tig is so strong? Just so I am clear I am talking in the shop and not in the field! One other thing have you seen a Tig torch put a hole in 1" plate? I have not, but I have seen a MIG do it!

[David D]

Originally Posted by wheelerpeeler

So if I am hearing you correct why do they MIG or Stick weld structural steel then if Tig is so strong?

Speed. GMAW and SMAW both are much faster than GTAW, strength as I stated earlier depends on the filler used. All three process are capable of laying down a weld of the same strength, you just take a different path getting there. GTAW welding is also more expensive which is another reason not to use it if not necessary.

[BIGBEN68]

You can never say that one process is stronger than another.

Nor can you say that one process is better than the others.


Each welding process has advantages and disadvantages, as well as suitable applications and non-suitable applications.

And the different gases used can change the bead profile and penetration of a weld, but not as much the strength of a weld. That still comes down to what base metal and what filler metals are being joined together.

[Invert'D]

Originally Posted by wheelerpeeler

So if I am hearing you correct why do they MIG or Stick weld structural steel then if Tig is so strong? Just so I am clear I am talking in the shop and not in the field!

Originally Posted by David D

Speed.

This ^^^. Or perhaps more to the point, Economy. That question has already been answered several times in this thread for the thinking reader. Time is money. TIG will require more work to fit up and prepare joints, and once you're actually welding, it's slower. Add the fact that TIG is considered to require more training and skill than MIG, and labor costs per hour go up.

TIG is used for structural work, but MIG and stick are usually good enough, so why go broke? If Joe's Structural Steel is bidding on a job based on MIG and/or stick, and you're bidding on it based on TIG, you won't be the low bidder.

TIG is capable of producing higher-quality, more consistent welds than either MIG or stick. Is that level of quality necessary? Do codes or specifications require it? If not are there other reasons that people would pay extra for it? Those are the questions that determine whether TIG is commercially viable.

Originally Posted by wheelerpeeler

One other thing have you seen a Tig torch put a hole in 1" plate? I have not, but I have seen a MIG do it!

No, I can't say I have, and if I had done it, I wouldn't admit it. So at what point in this minor MIG catastrophe did the blowout occur? The root pass of a v- or u-groove joint? At the tail end of the joint/ weld bead? Don't try to tell me that someone was MIG welding 1" steel single pass and had a blowout.

Just for the record, I MIG, stick, and TIG weld, and am likely to do any or all of those in any given week. They each have their advantages. I know I've chosen the right process for the job when I find myself wondering why I would ever use anything else. As far as peace of mind goes when it comes to the thought of joint failure, I rank TIG or Oxy-Acetylene, stick, and MIG in that order.

One final thought: all else being equal, is a bigger weld bead stronger than a a smaller one? Of course, but how much stronger than the base metal does a weldment have to be? Under stress would it be better for a larger area to deform, or for the base metal to crack or tear beside the weld bead?

[hockeyaddict_6]

Arc welding is unfortunately a dying art (unless you are working on gas lines or something similar) which is a shame. It is so simple, economical, and versatile. Plus (in my opinion) it takes more skill to lay down a good stick weld than MIG weld, which is also appealing to me. Part of being a craftsman is being able to do things well that other people can't.

On the other hand, I prefer MIG welding thick aluminum (over .25 in) over TIG, mostly because my shop has a small TIG torch hooked up to the machine all the time which can't handle enough amperage to weld the thick stuff, and it's time consuming to hook up the bigger torch.

Anyone ever stick welded aluminum?

[Yeager1]

MIG and stick can typically do much thicker materials (not too many high amp TIGs out there- I do have a 300 amp tig, and I've seen bigger, so they are out there- just not very common) so many welders think the others are stronger.
But as others have said, IF done properly they should be comprable. However, for the hobbiest you will probably get a stronger weld with a MIG due to its ease of use.

[rockcrawlncj5]

At my work we do have stick aluminum rod wich being one of the only stick tig welders we have I get the job of using that crap rod.IT burns really fast a nightmare to make it look decent.The rod attracks moisture really bad and fast.But it can produce a weld that holds I have proven that many times.

[miguelitojeep]

WWJD.... nuff said

[mikegyver1]

Very interesting read guys, thank you for setting the record straight. For my project I chose to Tig weld the structural parts of the cage and Mig the rest. Maybe stick weld the shock hoops.

[Deadman 94 xj]

Dumb question from somebody who's actually new to welding in general - I've always been under the impression that tig is used where heat transfer might be an issue. In other words, tig produces less heat so warping is less of a worry on more "sensitive" projects. Am I way off base in thinking this?

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[Invert'D]

Originally Posted by Deadman 94 xj

Dumb question from somebody who's actually new to welding in general - I've always been under the impression that tig is used where heat transfer might be an issue. In other words, tig produces less heat so warping is less of a worry on more "sensitive" projects. Am I way off base in thinking this?

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It's not that TIG produces less heat. As I mentioned earlier, the HAZ tends to be larger in TIG than in MIG. The difference is, TIG with a foot pedal or finger control gives you better control of the heat. You set the machine to a maximum amperage setting a, and your foot pedal controls the heat from 0 to a. You can use just enough heat at any given moment to get the bead you want. If you play that game with MIG, you're begging for cold lap.

MIG is often preferred for auto body work because it's relatively easy to make an acceptable weld that doesn't warp the thin sheet. These are not critical welds and will often be ground flat. If one wanted to work the sheetmetal (e.g. stretching, shrinking) after welding, MIG would be a poor choice, since, again, it tends to produce a more brittle weld. Working/ peening the bead makes it more brittle. Oxy-acetylene or TIG would be much better choices.

[Deadman 94 xj]

Okay, that puts it into perspective, thanks.

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