Flux Core Welding Vs MIG Title Image

Deciding to use Flux Core welding rather than MIG depends on:

What you’re welding.

Where you’re welding.

And the finish you’d like for your weld.

After that.

Which welding method you choose comes down to your personal own preferences.

Take a walk through some key points and differences.

​Flux Core V MIG What Does The Terms Mean

First things first.

Flux core welding’s official title is FCAW – Flux Core Arc Welding.

And MIG welding’s official title is GMAW – Gas Metal Arc Welding.

Both are electrical welding methods and use an electrical arc to weld.

​Welding Wire In Flux Core Welding VS MIG Welding

What’s the Same?

When you look at flux core welding and MIG welding.

They use a spool of welding wire to weld with. And both welding systems use your welding wire as an electrode.

What does that mean?

The end of your wire is where your arc is.

And your welding wire delivers your filler metal to your weld.

Ok you say. Sounds like they are the same so far. Yes. In these ways both welding methods are the same.

What’s Different?

In MIG welding you use a solid wire.

Lincoln Electric Solid MIG Wire for Mild Steel
Lincoln Electric Solid MIG Wire for Mild Steel

In contrast flux core welding has tubular wire.

What’s that?

The best way to understand this is.

Think of your flux core welding wire like a filled straw.

The outside part of your flux core wire is metal. It’s your filler metal.

But the center of your wire has something called flux inside.

And this is what gives flux core welding its name.

Inside Flux Core Wire
Inside Flux Core Wire

This difference in the makeup of the two welding wires. Means the wires behave electrically different.

More on that later.

The above is a brief overview of flux core wire welding. When you’re ready to go into more detail on flux core wire. Take a look at the article here all about it. What is Flux Core Wire.

​A YouTube Video Comparing Flux Core Welding And MIG

Here’s a great 14 minutes 20 second video from weld.com. It covers at a high level the difference between flux core and MIG welding.

Worth watching.

MIG vs Flux Cored Welding and When to Use Each

Video Credit: weld.com

​MIG Welding Shielding Gas Compared To Flux Core

MIG Welding With Shielding Gas

Here’s an area where the two welding systems are different.

You weld solid MIG wire with external shielding gas.

Why’s that?

Hot metal needs protecting from normal air. Or the weld fails. Shielding gas gives this protection.

And this means you’ll need a high pressure tank of gas for MIG weld welding.

You connect up your tank of gas to a regulator or flow meter.

It’s how you control how fast your shielding gas comes out of your high pressure tank.

And then you’ve a hose running from your tank and into your MIG welder.

Argon/CO2 Shieding Gas Cylinder
Argon/CO2 Shieding Gas Cylinder and Regulator

This need for external shielding gas means your welding machine must feed the gas.

MIG welding uses;

  • Argon gas
  • Argon and Carbon Dioxide gas mixes
  • Pure Carbon Dioxide
  • Tri-Mix (a mix of Helium, Argon and Carbon Dioxide) to weld Stainless Steel.

Some Flux Core Welding Uses No External Gas

In contrast. Self Shielded Flux Core wire makes the protective gasses for your weld at the weld point.

You say what?

The flux inside your flux core wire melts. And when it melts in the arc. Creating gas is one of the things the flux does.

This gas covers your weld pool. And protects it from the air around.

There’s a real advantage of this way of welding.

It means you won’t need to buy or transport a cylinder of gas.

This is why self shielded flux core welding is so popular.

Flux Core Welding That Does Need External Gas

There’s a form of flux core welding that does need a tank of external gas.

This type of flux core welding uses dual shielded flux core wire.

Dual shielded flux core wire is tubular wire. Just like self-shielded flux core wire. It has flux in its center.

It’s like MIG welding because you’ll need a cylinder with gas in it. A regulator and a hose from your high pressure gas. And a MIG welder that can feed gas.

Dual shielded flux core welding has two types of shielding.

Your weld pool is shielded by the gasses made by the flux core as you weld.

And the external shielding gas you use.  

Dual shielded flux core wire uses similar gas mixes as MIG welding.

The gases are;

  • Argon
  • Argon Carbon Dioxide mixes and
  • Pure Carbon Dioxide
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​Flux Core Vs MIG Welding: Strength Of Your Weld

Some swear that MIG welding gives a stronger weld.

Others argue that flux core welding does.

The truth is.

Both methods using this narrow measurement are the same.

Looking at the weld strength point of view.

They both make a weld that will hold. Be strong. – When welded well.

Let’s take a look at the welding wires.

Solid mild steel welding wire for MIG welding compared to mild steel flux core wire. Both conform to the American Welding Society standard. You’ll get at least of 70 ksi tensile strength.

Assuming the amps, wire feed speed and gas coverage (in the case of MIG or gas shielded flux core). Is set right for the wire. And the skill of the person welding is the same.

All things being equal. No one wire will make the stronger weld.

The weld strength would be the same.

It’s not here you’ll see a difference.

Example of A MIG Weld
Example of A MIG Weld

​Looking At MIG Welding Metal Penetration V Flux Core

Flux core welding has the reputation of better metal penetration than MIG welding.

Is it true?

Again, the answer is. It depends.

Because both welding methods used effectively give great metal penetration.

The truth of this argument lies in the amps or volts you’ve available to weld with. And the metal thickness you’re welding.

Or put another way.

What can you weld for the electrical input you put into your weld.

Flux core allows you to weld thicker metal for less amps.

 – Electrical power sent down your wire to form your arc.

A Worked Example Flux Core Welding v MIG

Let me take you through an example.

The Hobart 140 using flux core mild steel wire 0.030″ diameter – link to 030 vs .035 flux core wire doc

will weld 3/16th of an inch (4.8 mm) thick base metal. You set your Hobart at setting number 4. And use 45 wire feed setting.

When you compare the same welder.

Hobart 140 MIG welding with mild steel solid wire. Using the same sized welding wire 0.030″ diameter with C25 shielding gas. Your Hobart 140 will weld 1/8 of an inch (3.2 mm) thick base metal. At it’s number 4 setting and 40 wire feed speed.

You see.

For the same welding setting on the Hobart 140 you can weld 3/16th flux core compared to 1/8 with MIG.

You’ll find the same is true on any welder, Hobart, Lincoln, Everlast. …

You can use less amperage for the wire size and gauge of metal welded with flux core welding.

Or think of it this way

Flux core welding gives more weld for your electrical buck.

When you’re welding at the welding limit of your welder. Use flux core wire welding and you can weld thicker metal.

And when taking your flux core welder to a weld site. You’ll not need as big a generator to support your welding compared to MIG welding.

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​Flux Core Welding Compared To MIG: Thickness Of Metal Welded

Following on from the better penetration argument. …

You’ll see a difference in the two welding methods in the thickness of metal each can weld.

Flux core as the ‘hotter’ process has a minimum of 20 gauge metal as the thinnest metal welded. Or you risk blowing holes through your metal.

Versus MIG welding with solid wire and gas can weld down to 24 gauge.

Note: Bigger number gauges mean thinner metal.

MIG welding’s ability to weld thinner is partly helped by smaller diameter wire. You can buy solid MIG wire in smaller sizes. Plus, the ‘cooler’ MIG welding process is best for thinner gauges of metal.

At the other end of the spectrum.

When you’ve a powerful enough welder. And gas shielded flux core wire to weld with. You can zip through welding half inch thick steel in a single pass with flux core wire.

Flux core wins when you’re looking at thick gauges of metal.

And it’s why the construction. And ship building industries have used flux core welding for many years.

​Weld Polarity Of Flux Core And MIG Welding

Another difference you’ll find is in your weld polarity.

Self shielded flux core welding demands a DCEN. This means Direct Current Electrode Negative setting when you weld.

When you’re flux core welding. You set your electrical current to your welding gun. To the negative terminal.

And your ground clamp. – Attached to your welding project or the welding table. To the positive terminal.

MIG welding needs DCEP (Direct Current Electrode Positive).

The polar opposite. You set your MIG gun set to the positive terminal.

MIG welders that also weld flux core have terminals you change from one to the other.

Example of MIG Polarity Terminals
Example of MIG Polarity Terminals

It’s important for your weld that you’ve the right setting for your welding.

If not. You’ll find your weld arc fails to form. Or you’ve a really poor weld when you’ve finished welding.

Flux core only welders only use self shielded flux core welding wire. And are DCEN set when you buy.

There’s an exception to the above.

Not all Flux core wire you weld with a DCEN setting.

Self shielded flux core wire for welding stainless steel needs a DCEP setting. And that means you can only use in a welder that allows you to change to this polarity.

Dual shielded flux core wire also called gas shielded. You weld with separate shielding gas, just like MIG welding. This wire also needs a DCEP setting.

Types Of Metals You Can Weld With Flux Core Vs MIG

When you compare MIG welding and flux core welding there’s some overlap with metals welded.

And differences to note are.

You use Flux core welding for galvanized steel. It’s the process that copes with that steel covering. ​

Flux Core Welding
Flux Core Welding Galvanized Steel

When you MIG weld you need to grind off all the galvanization before you weld.

Both MIG welding and flux core welding will weld mild steel and low alloy steel.

You can buy flux core wire to weld stainless steel.

But stainless steel is more often MIG welded. As the end results are more consistent.

MIG welding is the welding process of choice for welding Aluminum. As there is no flux core wire that’ll weld Aluminum.

​MIG Versus Flux Core For Weld Quality

MIG is often claimed to produce the better quality weld. Is this true?

To answer to this question depends on your definition of quality.

When the strength of the weld is the quality factor. Then both flux core and MIG welding can make strong welds.

When the look of the finished weld is your measurement. With skilled hands both processes will produce good looking welds.

MIG welding seems on the surface easier to produce a quality weld.

But in novice hands you can make a great looking weld. But have little metal penetration. In truth the filler metal sits on top of the weld joint and doesn’t penetrate at all. Leading to your ‘good looking’ weld failing over time.

So where does this argument come from?

​Slag And Spatter Of Flux Core And MIG

The argument that says MIG produces better quality welds. Is normally down to the production of slag and spatter in flux core welding.

Flux core welding as part of its welding process makes welding slag.

Welding slag? – A covering over the hot weld pool that needs to cool before you take it off to reveal the underlying weld.

picture of flux core weld slag on

The flux in the flux core welding wire also removes impurities from the weld into the slag.

The covering called ‘slag’ in MIG welding is lighter and more easily brushed away.

Dual Shielded flux core welding is even better than MIG welding. When you look at light weld coverage after welding. You’ll find a document that goes into welding slag on the site. Click on the link text to know more.

Example Of A Flux Core Weld Slag On
Example Of A Flux Core Weld Slag On

MIG And Flux Core Spatter

So what about Spatter?

Welding wire makes Spatter. It’s spots of molten metal sent up in the air around your weld area.

Both flux core welding and MIG welding produce spatter.

And the amount of spatter made by MIG welding depends on the shielding gas you use.

Like MIG welding with Carbon Dioxide gas. It’s well known for spatter production. Yet people expect flux core welding to result in more spatter.

With the right weld settings you can keep spatter to a minimum in flux core welding.

Plus you can buy products to reduce spatter’s effect.

The truth is. With the right settings in your flux core welding the slag can pretty much peel itself off. Welding spatter minimized and brushed away using Anti Spatter products.

It’s largely true that when you flux core weld you’re in for more clean up at the end.

If you dual shield flux core weld you largely get low spatter. Of course with the correct settings and gas used.

Want to know more about welding spatter? Head over to this article on the site and have a read.

​Flux Core And MIG Compared Welding ‘Dirty Steel’

There’s no doubt. MIG welding is intolerant of ‘dirty steel’.

And this means any steel that is rusty, or covered in mill scale or has paint or galvanization on it. Needs thorough cleaning down to the base metal. Or a poor weld with porosity within the weld. And the weld rusting and failing will be your result.

Versus Flux core welding which is much more tolerant of ‘dirty steel’.

Because of a feature of flux core welding wire. It has inside scavenger compounds. And these scavengers lift impurities from the base metal into the slag where you chip it off at the end.

Both MIG welding and flux core welding needs any oil removed from your weld point.

And it’s always advised to have your metal as clean as possible before welding.

But flux core welding is the method of choice where you need to weld galvanized steel. Or metal you can’t get totally clean because of where it is.

Example Of Flux Core Weld Slag Removed
Example Of Flux Core Weld Slag Removed

​Using Flux Core For Car Body Panels

You pick MIG or indeed TIG welding for the visible parts of car body repairs.

Because MIG welding’s best for the thinner steel used in car panels.

Plus once you’ve made your weld you need to prime and paint your weld for the best finish.

Using flux core welding for body panels is firstly a problem as the metal is often thinner. And flux core welding is just not suited to thin metals.

An inexperienced welder thinking little cleaning of their weld is needed. May well find their flux core weld spreads impurities through their weld area. Because they’re welding quickly to prevent blowing through the metal,

Or using short tack welds to prevent blowing holes in the metal.

But flux core welding needs good slag coverage. Because its welding slag takes up the impurities from the weld pool.

And good slag needs heat and enough time to form.

The rush to not blow through the metal. Or a lot of short tack welds with flux core welding results in bad slag coverage. And impurities and slag within the weld.

And no amount of grinding of your weld surface is going to cure that.

Then when you put on body filler. And or primer on top. It won’t work on a surface with impurities. Never mind the weld itself holding over time.

Because of this. You’ll find a complete clean of the surface. And then MIG welding is the way to go.

And when you’re pushing the envelope of MIG welding on thin metal body panels. Some tack welds on thinner material is only really workable with a MIG welder.

​Flux Core VS MIG Welding Which Is Cheaper

Some say MIG welding is the cheaper welding method compared to flux core welding. Because the solid welding wire of MIG welding is cheaper to buy pound per pound. Compared to flux core welding wire.

This is true.

But the argument is not quite as straight forward as that.

Flux core only welders tend to be cheaper to buy than a MIG welder that can also weld with flux core wire. Though of course you do have more flexibility with a welder that can weld with both methods. You can choose the method you want to use.

What’s missing from the ‘flux core welding is more expensive’ discussion is;

  • MIG wire needs shielding gas.
  • You need to buy a tank of gas. With the implications of needing different tanks filled with different gasses. Because you need a certain type of gas for each type of metal you weld.
  • Size of tank. Transportation of your tank of gas to and from where you refill it.
  • Safe storage of the gas cylinder. Including safe lifting and moving it to where you weld.
  • ​Buying the gas itself.

When you take all these costs into account. You may well find the cost versus convenience of flux wire is much closer than you thought.

Flux Core Welding Outside
Flux Core Welding Outside

​Where You Can Weld: Flux Core VS MIG

MIG welding and gas shielded flux core welding are inside processes. Meaning you’ll need a work shop, garage or work space to weld in.

As MIG welding and dual shielded flux core welding uses a tank of shielding gas. This gas is sensitive to wind. And can blow away, leaving your hot welded metal unprotected outdoors.

Yes, you can put up wind shields to protect your weld area when you need to MIG weld out in a field. But it’s yet more stuff needed at your weld site. And to transport to your weld site.

Self shielded flux core welding is the process of choice when welding outside. Self shielded flux core welding is tolerant of quite windy conditions. And there is less equipment to take to an outdoor location.

Take your welder filled with welding wire. A means of getting electricity and your safety wear. And you’re ready to weld.

​YouTube Video Demonstrating Flux Core Welding In High Winds

​Here’s a 8 minute 38 second video for you. When you watch the first few minutes you’ll get the idea. You’ll see a flux core weld outdoors. And in pretty windy conditions. 

It shows well the benefits of flux core for outdoors.

Flux Core Welding Thin Tubing

Video Credit: TheToolReview

​MIG VS Flux Core Other Considerations When Choosing Where To Weld

Just because MIG welding is an indoor process this doesn’t mean you don’t need ventilation. It doesn’t matter if you’re MIG welding or flux core welding.


MIG welding and dual shielded flux core welding use gas that could suffocate you when leaked.

And those gasses have no smell.

Flux core welding makes more smoke and fumes when you weld. And can make it difficult to see the weld puddle.

Flux Core Welding Fumes
Flux Core Welding Fumes

​And some of these fumes are noxious and you shouldn’t breath them in.

​A Round Up Of Other MIG VS Flux Core Differences

1. Flux core welding is more often used for out of position welding. This is where you’re welding at any angle other than a flat or horizontal angle. For vertical, uphill and particularly for overhead welding flux core welding wins.

2. Both welding methods need a contact tip of the right size for your welding wire. MIG needs a nozzle over the contact tip to direct your shielding gas to cover your weld pool.

3. Flux core welding needs a longer welding wire stickout length. Around twice the stickout compared to MIG welding.

Welding Wire Stickout
Welding Wire Stickout

But always check your manufacturer stickout recommendations for your welding wire.

4. Flux core wire needs knurled drive rolls installed inside the welder to feed the flux core wire over. The grooves in knurled drive rolls are U shaped and notched to gently grip the more delicate flux core wire.

MIG welder drive rolls have V shaped grooves to feed the solid MIG wire.

Knurled Drive Roll
Knurled Drive Roll

​5. The welding gun angle for flux core welding is a drag angle generally. This means you angle your welding wire and gun along the weld pool. This is because this angle helps build the right slag cover for flux core welding. 

For MIG welding you use the opposite. You use a push angle.

​What To Do Now

Did you enjoy this head to head assessment of flux core welding vs MIG welding? And now you know that the welding method you choose to use depends on what you’re welding.

The type of metal, the kind of object you’re welding. When you can’t clean well. Or bring in to MIG weld. Then your option when comparing the two is to flux core weld.

How about taking a look at some of the related articles on the site.

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