No mulitpass in MIG?

[J Tiers]

X2 what JTiers said -- you need a lot of machine to run flux core generally and the homeowner sized ones ain't it. Commercial sized machines have no problem with it, it is an approved process for very heavy stuff -- my experience is that it goes best with a spray-transfer (very hot and smooth) mode. They build skyscrapers and bridges with flux core nowadays BUT they are using 600-amp machines with .072 diameter wire. And engineers -- actual engineers with degrees design those weld joints and get it approved.

And a 110v machine isn't capable of that. They sell these machines because they are at a good price point and don't necessarily need gas. But it is best to be aware of their limitations. I find them useful to do exhaust work on cars, but thats about it.

Those little machines are not trash. They CAN do decent work. And they can weld 1/8" material just fine.

I have welded 1/8" thick square tubing with the very same machine that faied so badly with 1/4" material. Yes, I DO know that it was getting heat into the material, because I blew holes in the material and had to fill them in. By definition, it melted the base material.

I think much of the problem is that folks never get told about that thing known as the "puddle". If you get a decent puddle going, odds are that you are melting base material. Not a guarantee, but........

At the very least, if you have no puddle, you ain't "welding", as far as I know.

[Willy]

Yes you do need the puddle but you also need to have the arc force or extra heat to drive that puddle into the parent metal.
Without that extra heat input all you end up with is a pretty weld that lays on top and lacks the penetration.required to make a sound fusion weld.
If you can blow holes in the .125 inch tubing you obviously have more than enough heat input, but all too often a lot of folks just focus an a nice bead without considering the complete fusion process underneath.
Probably the single biggest factor that has given the GMAW process an unjustified black eye.

[nickel-city-fab]

Yes you do need the puddle but you also need to have the arc force or extra heat to drive that puddle into the parent metal.
Without that extra heat input all you end up with is a pretty weld that lays on top and lacks the penetration.required to make a sound fusion weld.
If you can blow holes in the .125 inch tubing you obviously have more than enough heat input, but all too often a lot of folks just focus an a nice bead without considering the complete fusion process underneath.
Probably the single biggest factor that has given the GMAW process an unjustified black eye.

Arc force is another name for voltage, and the smaller machines are limited in that regard. Lincoln electric calls it "dig". Its the voltage that drives penetration, and current that dictates how much material you can melt in a given time. JTiers has probably found the limit of them, he understands their capabilities and uses it to the full extent.

MIG gets a bad rep on two different fronts:
One, the untrained not knowing about the puddle (and being too nervous to carry one)
and two, the thermal gradient causes problems.
You get a very narrow and sharp HAZ while the rest of the mass of metal acts to quench the weld. The end result is that even though MIG wire is rated for the same tensile as 7018, it completely lacks the ductility and elongation. So the part snaps instead of stretching. In contrast to the 7018 where the flux coating acts as an annealing oven to protect the weld while it cools, and the HAZ is 4x wider than the equivalent MIG weld with a much gentler thermal slope.

MIG is able to do good work, but its important to actually learn to weld and what the limits of your machine are. Which is why I would rather that the amateur just starting out could have access to real industrial equipment. Because its much easier to learn on the good stuff.

[nickel-city-fab]

Those little machines are not trash. They CAN do decent work. And they can weld 1/8" material just fine.

I have welded 1/8" thick square tubing with the very same machine that faied so badly with 1/4" material. Yes, I DO know that it was getting heat into the material, because I blew holes in the material and had to fill them in. By definition, it melted the base material.

I think much of the problem is that folks never get told about that thing known as the "puddle". If you get a decent puddle going, odds are that you are melting base material. Not a guarantee, but........

At the very least, if you have no puddle, you ain't "welding", as far as I know.

True enough, I have to concede that -- see my reply to Willy above. I do wish that folks could have access to the industrial machines more than the homeowner ones. Because it is much easier to learn on one of them.

[Willy]

Arc force is another name for voltage, and the smaller machines are limited in that regard. Lincoln electric calls it "dig". Its the voltage that drives penetration, and current that dictates how much material you can melt in a given time. JTiers has probably found the limit of them, he understands their capabilities and uses it to the full extent.

MIG gets a bad rep on two different fronts:
One, the untrained not knowing about the puddle (and being too nervous to carry one)
and two, the thermal gradient causes problems.
You get a very narrow and sharp HAZ while the rest of the mass of metal acts to quench the weld. The end result is that even though MIG wire is rated for the same tensile as 7018, it completely lacks the ductility and elongation. So the part snaps instead of stretching. In contrast to the 7018 where the flux coating acts as an annealing oven to protect the weld while it cools, and the HAZ is 4x wider than the equivalent MIG weld with a much gentler thermal slope.

MIG is able to do good work, but its important to actually learn to weld and what the limits of your machine are. Which is why I would rather that the amateur just starting out could have access to real industrial equipment. Because its much easier to learn on the good stuff.

Two very good points, thank you for elaborating on them.

And as you say, much easier to learn the fundamentals on good equipment but then one gets spoiled and frustrated because it often it is not in the budget.
Much like machine tools.LOL

[J Tiers]

OK, I agree about using good machines to learn on. I took a welding course, and the learning machines were Miller 250 something or others (don't recall exact model).

With a good powerful machine, you can see what a "real puddle" is, and more importantly, what it does. You get to move it between the parts and watch it "bite into" the metal at both sides.

I shold have mentioned that point about driving the puddle into the metal, having it "bite into" it visibly. But of course, that was no issue with the big miller machine. I guess I just do that without thinking about it.

There is a question, though........... I flat don;t understand how to have a "puddle" that somehow floats on top of the base material without melting in. It seems that to HAVE a puddle, you must be melting base material, or the melted wire material would be laying there like bird poop.

I've been soldering for many many decades, and even with solder, the appearance of what is going on is different if there is no bonding. The "puddle" does not look right.

I've never actually seen a welding puddle that would lay down and look right without having melted-in somewhat.

The point about weak welds due to narrow HAZ is a new one to me, but makes sense, if the materials have enough carbon to harden. With low carbon base material, and compatible wire, it seems like that would not be much of an issue.

Edit:

I suppose it could depend a bit on the weld type. Maybe a fillet weld could look "sort-of" good without penetrating, dunno.

But when there is no melting of the base material, it always seems to look like blobs of bird crap sitting on the surface. That would seem like it should still look like it is a string laying in the angle, without "wetting out".

[nickel-city-fab]

There is a question, though........... I flat don;t understand how to have a "puddle" that somehow floats on top of the base material without melting in. It seems that to HAVE a puddle, you must be melting base material, or the melted wire material would be laying there like bird poop.

.......
But when there is no melting of the base material, it always seems to look like blobs of bird crap sitting on the surface. That would seem like it should still look like it is a string laying in the angle, without "wetting out".

Actually it is possible to have a MIG weld that looks great and doesn't have any penetration to speak of. I've seen a few like that, I have even made a few like that. Using industrial machines no less. Especially when using a short arc or globular transfer technique -- They had a few entire discussion threads about this over on welding web. What I got from those discussions is that it is possible to have the wire burn perfectly without affecting the base metal at all (relatively speaking) if there is too great of a size mismatch between the base metal and the machines ability to create heat. For example using 030 wire on 1" thick plate with no preheat -- you could get a beautiful bead that has almost no penetration because looks can be very deceiving. I tend to favor a spray transfer mode to avoid the whole situation and get a "guaranteed good" weld -- but that requires a bit of beefy machine.

At work they have some smaller 220v "pro-sumer" machines that are good for lighter jobs and yet they can still go into spray mode. Such machines usually go for around $1500 - $2000 retail, and these 220v MIGs are the ones I usually recommend for homeowners and hobbyists -- the fill a good "in-between" niche. Miller has their 210 mig, and Lincoln has the 210 PowerMIg MP.

[Willy]

Improper gun or electrode angle and insufficient amperage allow the puddle to roll on the surface while creating very little in the way of fusion.
The weld bead by all appearances looks great but lacks penetration and or complete fusion.
I've had to repair a few of these and it is very evident once you grind or air-arc out the weld.. You can't always judge a book by looking at the cover.

This is exactly why non destructive testing is done on critical welds. Mind you the guys who get their welding inspected like this routinely are usually pretty good to start with but it is a safeguard just in case. It only takes one small defect in a 36" diameter pipeline to create havoc.

[J Tiers]

Ok, you are talking about something different.

Basically, you are describing a weld where there IS FUSION, just not ENOUGH of it.

I can totslly understand and appreciate that. And can see how it looks good, but does not have the strength that the appearance promises. But it is NOT a case of "no fusion", it is a case of "not enough", not penetrating enough, vs not penetrating "at all", which is what I thought you were saying.

[dons]

Several previous posters are dead on in talking about required heat and fusion for multipass welding with GMAW or "hard wire".

GMAW has two different "power levels" if you will. In welding codes these are referred to as transfer modes.

The smaller machines run in what is called short circuit transfer mode ( short arc ). The electrode makes contact with the base metal, and the resulting arc melts a very small bit of the base metal and a dab of the electrode. Short Arc does not give deep penetration and is usually not allowed in structural welding codes without some special testing. You could probably lay a multi pass bead in short arc, but root pass fusion to base metal is dicey as is fusion between passes.
Short arc is very useful in out of position welds ( vertical ) or on thinner materials.

In our shop we do a lot of structural and multi-pass welding. We use mostly GMAW. We use the second transfer mode known as spray transfer ( Spray ). Spray is required in these applications by code. Spray requires a lot more amperage in the power source. Spray also requires and argon content in the shielding gas of at least 85%. This is hot, fast welding. As the electrode gets close to the base metal, the arc jumps across the gap. In the process, it melts the electrode and caries the filler metal across the gap as a molten spray. The argon rich atmosphere facilitates this. Spray does a great job in multipass welding. Most of us ain't got the electrical service in a home setting to run it. Spray can easily blow the heck out of thinner base metal if one is not careful and is usually reserved for flat and horizontal only ( we won't get into pulse here).

Forgive the long-winded post. As a CWI I work with this stuff all day long. Couldn't help myself.

[nickel-city-fab]

Several previous posters are dead on in talking about required heat and fusion for multipass welding with GMAW or "hard wire".

.......

In our shop we do a lot of structural and multi-pass welding. We use mostly GMAW. We use the second transfer mode known as spray transfer ( Spray ). Spray is required in these applications by code. Spray requires a lot more amperage in the power source. Spray also requires and argon content in the shielding gas of at least 85%. This is hot, fast welding. As the electrode gets close to the base metal, the arc jumps across the gap. In the process, it melts the electrode and caries the filler metal across the gap as a molten spray. The argon rich atmosphere facilitates this. Spray does a great job in multipass welding. Most of us ain't got the electrical service in a home setting to run it. Spray can easily blow the heck out of thinner base metal if one is not careful and is usually reserved for flat and horizontal only ( we won't get into pulse here).

X2 on the spray mode, when I need perfection from a MIG weld that is my go-to. Usually with at least 045 wire and a 350-amp machine. Usually I'll run it around 28 to 30 volts and just crank the wire right up there. I used to do that a lot on impact mills/hammer mills with 1" thick plate parts.

My current employer doesn't have any machines like that, and for sure most homeowners don't have the electrical service for that.
Nowadays I'm doing more stick than anything tho, doing mobile heavy equip't repair.

[SVS]

I’m often fooled by tack welds when piecing things together. One zap here will hold like grim death, and the next lets loose before you set the stinger down.

Illustrates two things I think-One:It’s easy to be fooled by superficially “good” mig beads.

Two:The general perversity of the universe….The “grim death tacks” are invariably in the wrong place.

[J Tiers]

I am aware of spray mode (had to learn about it in class) but I do not think I have ever used it, as the largest welder I have used is a miller 250A, used in class, and they were not running at full capacity.

Knowing "of" it is not the same as knowing "about" it, so question time......

It takes high current, 25 to 30 volts, and the right gas, but does it take special conditions other than that to occur?

Or is it generally something that just occurs if you do have the current capacity, voltage, and gas? (seems to be per internet sources like ESAB, etc)

I am not at home, or I'd look it up in my old class text.

Also:

Many home-shop folks use a flux core machine. While tons of them are low current, and it is often dissed in amateur forums as "a worthless process, only for babies", I understand that flux core is also used at much higher currents for outdoor structural work where gas shielding just won't work. My understanding is that it allows considerably better penetration than standard short-circuiting transfer.

Comments?

[BigMike782]

The subject of spray transfer is not as cut and dried as it sounds. It can be achieved with a 200 amp machine but with smaller(.030) wire and for short periods of time.
As stated it is a VERY hot process and will overheat even a 300 amp mig gun quickly.
High concentration argon is text book to achieve it but…..
with a high enough voltage it can be achieved with 75/25 argon co2.
The higher the argon content the faster spray is achieved. With 95/5 argon oxygen it’s instantaneous. With tri mix, argon/co2/oxygen it short arcs for a split second and then transitions.
Voltage varies, text book is 26-26.5. With non traditional spray gases I start at 27.
Wire speed feed seems happy at 450ipm.
How do I know this?….. experimentation.
It helps when you have access to multiple shielding gases and would be even better if I could find a gas mixer

[nickel-city-fab]

It takes high current, 25 to 30 volts, and the right gas, but does it take special conditions other than that to occur?

Or is it generally something that just occurs if you do have the current capacity, voltage, and gas? (seems to be per internet sources like ESAB, etc)

Mostly correct -- it takes high current and volts between 25 to 30 as you say. The gas is a matter of some debate still. Certain dual-shield flux cored wires are more particular about this, but for regular solid wire I don't worry about the gas type. In a nutshell: spray transfer will occur under the right conditions of voltage and current capacity. Whether you have enough machine to do it depends on the diameter and speed of the wire -- if your machine won't go into spray, you could try a thinner wire at a higher speed. The 250-amp machines should be able to do it with (say) .030 wire no problem. Maybe even 035. The machine settings will be near max or "wide open" . The arc will give a smooth hissing sound.

Also:

Many home-shop folks use a flux core machine. While tons of them are low current, and it is often dissed in amateur forums as "a worthless process, only for babies", I understand that flux core is also used at much higher currents for outdoor structural work where gas shielding just won't work. My understanding is that it allows considerably better penetration than standard short-circuiting transfer.

Comments?

Flux core is an established and accepted practice under several different codes. It does indeed get a bad reputation from the uninformed bottom end of the market, where there is a flood of under-powered cheap machines aimed at the weekend welders. Flux core needs LOTS of volts and amps compared to other processes, and a 110v machine just ain't got it, the physics are against it.

Flux core was used to build the crane my employer just bought. I used it to build boilers back in the day, that was certified work (ASME). Many pros use it for structural work such as docks, pilings, stairs and railings(AWS, DOT). Be aware that the guys that run gasless outdoors are often running on a 400-amp generator or something similar -- not a cheap rig.

Flux core does indeed have better penetration and often has better weld chemistry due to the spray mode and the flux. Also, not all flux core is gasless -- there is the dual-shield variety which usually wants CO2 shield. It gives quite pure welds, and is favored for production work on small and mid-size contracts. Only drawback when running flux core is to be sure to clean all the flux out between passes. Like any other welding, it needs to be absolutely clean in between passes.