Where does the received wisdom that MIG is inferior to Arc for welding thick material come from?

[Jelly_Sheffield]

I often hear it stated that "Arc is better than MIG for welding thick material"... But I've never seen a comprehensive justification for that statement.


My personal experience is that:

- If you can position a weldment in a way that let a you use MIG in Spray Transfer, it's normally the best option.

- Welding out of position, like on pipe spools that can't be done on a rotator or field fit and weld applications, an all positions Dual Shield (in the workshop) or Flux Core (in the field) wire, gives both the higher productivity of wire-feed welding, and the practical advantages of Arc using rods with a fast-freezing slag.

- Arc only really comes into its own for field applications where you're working around restrictions on the input power supply, or physical size of welding plant that you can get to the job. Those applications are when the comparatively greater "heat" and arc force for a given amperage, offered by Arc will allow you to get deep penetration in a situation where Wire-Feed processes wouldn't.

I also know sweet FA about pipeline welding (as distinct from pipefitting) apart from the fact that Arc is still widely used in that discipline, in spite of semi-automatic or automatic SAW processes gaining ground.


Having trained up to pass a C&G L3 Diploma, and BS 4872 assessment, I like to think I have a reasonable basic knowledge of welding...

But at the same time I've never worked full time as a welder, and there's bound to be on-the job knowledge I've missed out on as a result of that.

(See recent threads where I got my **** kicked welding 1mm sheet, teaching myself auto-body repair, for examples of a skills gap.)

So what am I missing?

 

[Jack Ryan]

I often hear it stated that "Arc is better than MIG for welding thick material"... But I've never seen a comprehensive justification for that statement.


My personal experience is that:

- If you can position a weldment in a way that let a you use MIG in Spray Transfer, it's normally the best option.

- Welding out of position, like on pipe spools that can't be done on a rotator or field fit and weld applications, an all positions Dual Shield (in the workshop) or Flux Core (in the field) wire, gives both the higher productivity of wire-feed welding, and the practical advantages of Arc using rods with a fast-freezing slag.

- Arc only really comes into its own for field applications where you're working around restrictions on the input power supply, or physical size of welding plant that you can get to the job. Those applications are when the comparatively greater "heat" and arc force for a given amperage, offered by Arc will allow you to get deep penetration in a situation where Wire-Feed processes wouldn't.

I also know sweet FA about pipeline welding (as distinct from pipefitting) apart from the fact that Arc is still widely used in that discipline, in spite of semi-automatic or automatic SAW processes gaining ground.


Having trained up to pass a C&G L3 Diploma, and BS 4872 assessment, I like to think I have a reasonable basic knowledge of welding...

But at the same time I've never worked full time as a welder, and there's bound to be on-the job knowledge I've missed out on as a result of that.

(See recent threads where I got my **** kicked welding 1mm sheet, teaching myself auto-body repair, for examples of a skills gap.)

So what am I missing?

You are missing context.

The statement, by itself, is rubbish.

If you have a 130A "MIG" and a 130A ARC welder, the arc welder will likely be better for anything thicker that 3mm. Most "MIG" is done using short circuit transfer, a cold process, so it will not be good on thick material. That is generally where those statements come from.

Flux core is often better (on thicker material) - particularly with out of position work and, if using FCAW-S, out in the open.

"Better" can only be applied if the complete context is known.

Jack

 

[chrismac]

You are missing context.

The statement, by itself, is rubbish.

If you have a 130A "MIG" and a 130A ARC welder, the arc welder will likely be better for anything thicker that 3mm. Most "MIG" is done using short circuit transfer, a cold process, so it will not be good on thick material. That is generally where those statements come from.

Flux core is often better (on thicker material) - particularly with out of position work and, if using FCAW-S, out in the open.

"Better" can only be applied if the complete context is known.

Jack

Totally agree with Jack, its not its better maybe just more manageable with lesser equipment for smaller volume tasks. where the expense of shelling out for an all singing all dancing mig/flux core setup where you could get by with MMA.

 

[Jelly_Sheffield]

You are missing context.

The statement, by itself, is rubbish.

If you have a 130A "MIG" and a 130A ARC welder, the arc welder will likely be better for anything thicker that 3mm. Most "MIG" is done using short circuit transfer, a cold process, so it will not be good on thick material. That is generally where those statements come from.

Flux core is often better (on thicker material) - particularly with out of position work and, if using FCAW-S, out in the open.

"Better" can only be applied if the complete context is known.

Jack

That makes complete sense.

I have been very fortunate that because of how I learned, access to a wide range of gear has been a given ever since I started welding... A context that makes processes that aren't so universally available seem entirely familiar and obvious.

I guess my puzzlement is why a statement we both agree is rather flawed is still so widely and frequently stated as fact, rather than something more informative (but with the same practical upshot) like:

"Arc requires less [power/Amps] than MIG to achieve adequate penetration in thick material, Flux-Core can often give the best of both worlds".

 

[Jack Ryan]

That makes complete sense.

I have been very fortunate that because of how I learned, access to a wide range of gear has been a given ever since I started welding... A context that makes processes that aren't so universally available seem entirely familiar and obvious.

I guess my puzzlement is why a statement we both agree is rather flawed is still so widely and frequently stated as fact, rather than something more informative (but with the same practical upshot) like:

"Arc requires less [power/Amps] than MIG to achieve adequate penetration in thick material, Flux-Core can often give the best of both worlds".

It's the way many people are, they assume that their context should be obvious to everyone.

It's why you get questions like "X is not working - what could be the problem?"

Jack

 

[bletchmonster]

I think it's partly because everyone only looks at the amps.
You can have equal amp mig and arc welders, but the arc welder will be working at a higher voltage so more welding power.

 

[minimutly]

Maybe it's because at lower amps mig can give you cold lap - stick welding gives an obvious visual indication of this - mig does not.

 

[hotponyshoes]

I think it's generally regarded as 'better on forums because you get a lot of people asking questions like:

"What is the best way to weld 10mm thick steel plate, I have a 13amp socket and a £200 budget"

 

[8ob]

I dont think there is anything in it in the hands of the competent. I have seen prefabbed mig welded manifolds on a pipeline job pass on site xray's.

Bob

 

[Morris]

Having built seriously heavy duty low loaders in the past using mig I would say it's not an issue. For box beams we used submerged arc.

 

[Erie Fred]

As above, some people equate MIG with only short arc.

 

[Dutch Welder]

Horses for courses.
For production work in a wind free environment MIG/MAG/Dshield will always be king of the hill, if the equipment is man enough for the job.

 

[zzr1200]

Stick out performs mig out on site, mainly because it's easily portable (well it is within the range of your leads up to 150+ft-ish) for a site welder, or a mma inverter shoe box, in a workshop mig, the only real restriction is the welding position and depending on short arc or spray.

 

[Jelly_Sheffield]

Stick out performs mig out on site, mainly because it's easily portable (well it is within the range of your leads up to 150+ft-ish) for a site welder, or a mma inverter shoe box, in a workshop mig, the only real restriction is the welding position and depending on short arc or spray.

I can see how that would be the case...

The SWF on my big MIG has a 20M umbilical to the power supply, but just that connection (Current, Earth, Remote Control, Coolant Feed, Coolant Return, Gas) without the feeder or wire reel is about 3-4 times the weight of a modern arc Inverter.

Fine in a shipyard or something where you're slowly progressing along a massive weldment, but a load of extra work to manage if you're doing lots of separate "small" weldments at height for structural or pipework.

 

[hotponyshoes]

Lot faster setup with arc as well,
Seconds to change from a 1.6mm rod to a 4mm one and twiddle the power knob.

With mig, at least 5mins to change the wire over and change the tip. Possibly have to swap the torch or liner as well.
Feed the wire through..
Then maybe a different gas..
At maybe a different flow rate..
Adjust power and wire feed speed..

 

[Munkul]

I think there are two things that contribute to the "Arc is better than MIG for welding thick material" theory that the OP has heard (we've all heard it I'm sure)

1. the number of people trying to weld heavy metal with a sub 200 amp machine, in short-circuit transfer, or JUST being into spray but piling metal up to give bead size and not getting a good root penetration
2. the number of badly trained mig monkeys in the 90's who mistook the voltage knob for the the "power" knob, turned the voltage way up, wirespeed down, and got weld defects left right and centre.

I certainly used to hear it all the time growing up from engineers in my family.

The best thing for MIG welding heavy metal in general has been synergic machines - yes I know, all operators should be "trained welders" but the reality is, a lot of them are just mig monkeys there to put a shift in pulling a trigger. The less brain power you need to set a welder correctly, the better it goes.

This is a vast generalization and I am well aware there are lots of outliers to this theory

 

[Screwdriver]

2. the number of badly trained mig monkeys in the 90's who mistook the voltage knob for the the "power" knob, turned the voltage way up, wirespeed down, and got weld defects left right and centre.

What? You mean that's NOT how it's done??

 

[Robotstar5]

2. the number of badly trained mig monkeys in the 90's who mistook the voltage knob for the the "power" knob, turned the voltage way up, wirespeed down, and got weld defects left right and centre.

Always been the same with production welders (tackers) turn everything up to max to get the job finished early so they can sit around 'til the end of shift

 

[premmington]

I think there are two things that contribute to the "Arc is better than MIG for welding thick material" theory that the OP has heard (we've all heard it I'm sure)

1. the number of people trying to weld heavy metal with a sub 200 amp machine, in short-circuit transfer, or JUST being into spray but piling metal up to give bead size and not getting a good root penetration
2. the number of badly trained mig monkeys in the 90's who mistook the voltage knob for the the "power" knob, turned the voltage way up, wirespeed down, and got weld defects left right and centre.

I certainly used to hear it all the time growing up from engineers in my family.

The best thing for MIG welding heavy metal in general has been synergic machines - yes I know, all operators should be "trained welders" but the reality is, a lot of them are just mig monkeys there to put a shift in pulling a trigger. The less brain power you need to set a welder correctly, the better it goes.

This is a vast generalization and I am well aware there are lots of outliers to this theory

I would agree - I am car mechanic - I have never done MIG spray transfer only dip transfer. I have never owned or used a MIG welder over 200amp.

I always use an MMA welder on thick stuff...

 

[Munkul]

I would agree - I am car mechanic - I have never done MIG spray transfer only dip transfer. I have never owned or used a MIG welder over 200amp.

I always use an MMA welder on thick stuff...

you can do it on MIG successfully... but getting penetration is hit and miss, unless you know what you're looking for...

Somehow, when we were in our teens, like 15-16, we built a tractor transport box with 60x60x60 angle, 100x50x5 RHS and 100x10 plate. We used a 180 amp clarke MIG welder, and I'm absolutely positive it wasn't turned to max. We didn't know much back then other than "don't weld downhill". We just wanted good looking welds.
Somehow, that box has done 20 years without falling apart... getting rattled across fields every day every summer. I don't know what we did right, but we got a "hit" with those welds

On the other hand, very little else we welded back then has survived... most of it "miss"

These days, I'd know to look for the arc digging into metal, keep the wire on leading edge of puddle, or weld uphill.