MIG vs. TIG again

[Carbaholic]

Most of the arguments I've heard that TIG is better than MIG say thing like: "It's just better" or "It looks better" or "Carrol Smith Says it's better" Does anyone have any numbers that quantify how much stronger a TIG weld is, how much lighter they are, and/or how much longer they take?

Thanks in advance

[Carbaholic]

Most of the arguments I've heard that TIG is better than MIG say thing like: "It's just better" or "It looks better" or "Carrol Smith Says it's better" Does anyone have any numbers that quantify how much stronger a TIG weld is, how much lighter they are, and/or how much longer they take?

Thanks in advance

[Garlic]

Have you read ALL OF THIS?

[SeanM]

it's not always about numbers being proof. Tig welding is more accurate then mig welding is with mig you have less control over the arc you simply touch the tip to the metal and pull the trigger tig you can stike an arch and then go from there. for an example of just how accurate tig welding is look at F1 a-arms the inserts or the rod-ends are tig welded in and that would not be possible to do with a mig welder.

[RiNaZ]

and i think MIG is faster and sloppier whereas TIG is slower and accurate (im talking about welding time).

Just started using TIG, been using MIG ... so i wouldnt know the difference yet, still learning on TIG. And i think i like MIG better ... more forgiving i guess ...

[erny]

i have just learnt both, as i see it mig just adds a bridge between the two metals, it adds rod contstantly . Tig seems to be more about getting the two metals to fuse then add a little rod when it gets thin, much more emphasis on fusing the two together.

I was told by a good teacher that with tig you aim for 2/3 penetration and when i look at my welds i see that the welds almost show on the inside of the tubes.

I have just started and my tig welds are much neater than any mig i have seen. the level of penetration must mean they are stronger

[Garlic]

Any weld done properly will be stronger than the material around it, so there's no way to compare that case.

TIG will always have less heat affected area. So the material aurrounding the weld will be stronger. If you MIG, you have to heat treat to regain strength. If you TIG, it's not always neccessary. Although it might be to have the best stiffness.

[Boston]

I thought only strength would be affected, not stiffness (steels have the same stiffness regardless of heat treat)

[DaveC]

First off, I'd only MIG mild steel, so having to heat treat a mig vs a tig weld isnt an issue. Stress relieving alloys is a good idea regardless of process, if you don't the HAZ will be a lot weaker, as we all probably know. I'm not sure how much this matters in an FSAE car, though. Hopefully you wont hit anything hard enough to find out what part of your frame failed first.


I owned a MIG machine for years before I bought a TIG, my mig welds are superior to my tig welds so far. You can get good at mig much faster, tig takes a while before you'll want to weld anything structural, or that requires some finesse. You can get good penetration with a mig, but it does operate like a caulk gun, making it hard to get a feel for whats happening.

Erny, I want to see pics of those tig welds youre proud of. A beginning tig welder making welds nicer than ANY mig weld? Thats great if you can, though... I'd be jealous

[Perry Harrington]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Garlic:
Any weld done properly will be stronger than the material around it, so there's no way to compare that case.

TIG will always have less heat affected area. So the material aurrounding the weld will be stronger. If you MIG, you have to heat treat to regain strength. If you TIG, it's not always neccessary. Although it might be to have the best stiffness. </div></BLOCKQUOTE>

You've got that backwards. MIG has a smaller heat affected zone than TIG, which is why it's preferred for some types of welding, such as autobody. TIG is the electric analog of gas welding, the operation is nearly identical. In gas welding a carburizing flame provides your "gas shield" to keep oxidation away from the weld zone. TIG uses argon for the shield.

With TIG, you can more easily see your penetration and have more confidence in a weld. MAny chassis are welded with MIG simply because it takes 1/3rd to 1/5th the time to weld. However, MIG welding a chassis is best done when you have experience with the voltage and amperage settings on your welder. MIG has the problem of not penetrating the surface and simply building up a fat bead that doesn't really do anything. Any weld is only as good as the tangenital line across the arc of the bead, convex or concave.

MIG welds are more brittle than TIG welds because the HAZ is so small. The area affected by the arc is so small that it has very great variations in stress in a very small area. TIG has the advantage that it's heat is more even, assuming constant current. The TIG weld's stresses trail off more gradually from the weld zone, leaving a less stressed piece. It's not possible to always heat treat a chassis, so living with an as welded stress is better with TIG. Coincidentally, there are a few rods that are useful for untreated, unrelieved CrMo welds, thos are 309 stainless and 3SMW "Super Missle Weld". SMW has a higher tensile strength than the base metal, so you are guaranteed that the base material will tear first. 309 is a compromise because it's cheaper (SMW is $27 per lb) and it relies on the chrome-nickel content to do the bond, but many saturday night racers use it. I only use SMW on CrMo because I don't like to gamble on my welds.

FWIW, 308L is also an excellent general purpose rod for chrome-nickel reliant welding. I've welded cast iron with the TIG using that rod and it's very hard when done. 316L is also a nice rod, mainly used for body jewelry by artisans.

--Perry