Flux-Core vs. MIG Welding: Differences Explained

Flux-core and MIG welding are among the most popular welding techniques. They have a lot of similarities, as they’re both easy to learn and provide automatic feed to the welding torch.

The main difference between flux-core and MIG welding is that MIG requires a gas tank, while flux-core does not. Because of this, many people call flux-core welding the gasless MIG.

However, these processes have more differences which we’ll unpack throughout the article.

Summary of MIG and Flux-Cored Welding

If you’re short on time, here’s a quick comparison of the flux-core and MIG welding processes:

	Flux-Cored	MIG
Learning Curve	Moderate	Moderate
Wire Cost	More expensive	Affordable
Operating Cost	Moderately priced	Moderately priced
Gas Tank Requirement	Not required	Required
Surface Prep	Works through dirt, rust and paint	Best for bright white metal
Wind	Up to 35 MPH (outdoors)	Less than 5 MPH (indoors)
Bead Appearance	Spatter and slag	Little spatter without slag
Post Clean Up	Cleaning the slag and spatter	Little need for cleaning
Thin Stock	⅛ or thicker	Down to 24 ga.
Thick Stock	Good penetration up to ⅜ inches	Acceptable with enough power
Aluminum	Possible although messy	Cleaner than stick welding
Cast Iron	Stronger than MIG, with better penetration	Possible, but the weld will be weak
Mobility	Easier — no tank	Harder — has a tank

Flux-Core Vs. MIG Welding – The Similarities

Both techniques are easy to learn and handle as they provide continuous wire feed since both wires act as electrodes.

Also, MIG and flux-core welding provide an automatic feed to the torch. That makes the whole welding process much faster, as it’s continuous and uninterrupted. These welding methods are a much better option for beginners compared to stick welding, where you constantly need to feed the electrodes to the welding machine.

Another similarity between flux-core and MIG is while flux-core uses only flux-cored wires, MIG can use either a solid MIG wire or a flux-cored wire. 

When it comes to wires, both are equally good and allow you to weld in multiple positions. 

They’re also versatile as they can weld various materials, including:

• Aluminum
• Steel
• Stainless steel

However, there are situations where one will be a better choice than the other!

Below is an illustration showcasing the process of flux-cored arc welding (FCAW).

Below is an illustration showcasing the basic setup for metal inert gas (MIG) welding or gas metal arc welding (GMAW.)

Flux-Core Vs. MIG Welding – The Differences

One of the most important differences is that flux-core welding doesn’t require gas, meaning there’s also no need for a tank. Therefore, flux-cored welding is more portable, provides more mobility, and makes a better choice for outdoor conditions. Read on!

Wire

Both flux-core and MIG welding use a spool of wire which provides the filler metal to the weld. However, these processes use different wires, which sets them apart.

Flux-cored welding uses a tubular wire with flux inside, while MIG welding uses a solid wire.

Wire Construction

The section above shows the main differences between the wires that welders use for MIG and flux-core welding. However, another important detail you should be aware of is the wire construction.

Flux-cored wires function differently than solid wires because of their flux. That said, when using flux-cored wires, you must purchase the right type based on the weld you need and the material you’re working on. Because you need multiple different wires for each welding project, flux-core welding can become overwhelming. 

Also, in some cases, your flux-cored wires will require specialized storage conditions. Otherwise, they would go bad. That also makes these wires harder to store compared to solid wires. 

Shielding Gas

As we mentioned earlier, the most significant difference between flux-cored and MIG welding is that MIG welding requires a shielding gas, whereas flux-cored welding doesn’t. 

The gas tank is essential for performing a proper MIG weld, as its primary purpose is to shield and protect the weld from the air. Otherwise, there would be defects, and your weld wouldn’t be as strong as supposed to be. 

Flux-cored welding does experience the same problem but has a different resolution. Instead of needing a gas tank, flux-cored welding relies on the flux inside the wire to protect the weld.

Because of this feature, people often refer to flux-cored welding as gasless MIG welding. 

While that makes flux-cored welding more convenient, it also increases the work after welding. The flux-cored wire also produces slag, which requires more cleanup afterward.

You should also remember that there are two types of flux-cored wires based on the kind of shield they provide. They can be:

• Self-shielded: The most common type of flux-cored wires. 
• Dual-shielded: These flux-cored wires have protection from their flux but also need additional shielding from gas tanks.

Polarity

Flux-cored and MIG welding have different polarities on their torch, which also sets them apart.

MIG welding requires you to set the wire to the positive terminal, following the direct current electrode positive (DCEP) settings.

On the other hand, for flux-core welding, you need to follow the direct current electrode negative (DCEN) settings and connect the wire to a negative terminal. 

However, some flux-cored wires require a positive electrode arrangement, which is something to remember when setting your polarity during flux-core welding.

Also, if a MIG welder uses a flux-cored wire, it can switch between the terminals.

Filler Material

MIG wires are solid, making them suitable for most passes as they contain purer filler materials than flux-cored wires. Also, their alloy is commonly the same as the material you’re welding. 

Flux-cored wires contain additives along with their flux, making them significantly different from solid MIG wires. 

The term flux-cored wire is quite broad as flux-cored wires are designed to work with a particular metal, which will affect the flux and alloy mixture inside the wire. That requires you to check whether the flux-cored wire makes the weld suitable for multiple passes.

It’s best to verify the rate of your flux-cored wire to ensure it will function for your needs.

Strength

The strength differences between flux-cored and MIG welding are insignificant and almost unnoticeable. Both welds will be good as long as you do them right. If you’re using the proper wires, settings, and welding technique, there won’t be distinctions between the welds.

However, there is a slight difference when welding cast iron, which you can also see in the chart at the beginning of our article.

Flux-cored welding is a better option for welding cast iron as it provides better penetration and stronger welds. It’s not impossible to use MIG welding to weld cast iron, but the weld would be weak. 

Penetration

Both types of wires (flux-cored and solid MIG) penetrate well. However, there are differences in the way they penetrate.

The flux-core electrode provides heat with more focus, differentiating flux-core arc welding from gas metal arc welding. Therefore, flux-cored welding makes a better choice for thick materials.

Which Is Better?

There’s no right or wrong answer to which welding technique is better, as both flux-core and MIG welding are excellent options. 

However, in some cases, one is preferable to the other.

Surface Preparation

When it comes to surface preparation, flux-cored welding is much easier than MIG welding because it can handle dirt, rust, and paint. It can cut through contaminated material areas, removing all the dirt and metal oxides.

On the contrary, MIG welding is unsuitable unless the surface is bright white metal and doesn’t handle dirt, paint, or rust. Because of that, flux-cored welding is a more suitable choice when the metal you’re working on is not pristine white. 

Appearance

The final product and the appearance of the weld are much sleeker when using the MIG welding process. MIG welding produces almost no spatter, while flux-cored produces slag, spatter, and spitting. 

That makes MIG a better choice when you want a cleaner weld and less need for cleaning after you finish welding. 

Outdoor Work

Flux-cored welding is a much better option when welding outdoors, which you can also see in the chart at the start of our article. As flux-cored wires get protection from the flux inside the wire, their welds can withstand winds up to 35 MPH. 

MIG welding gets protection from the gas tank, which would get blown away if the wind reaches 5 MPH. 

Thin Stock

The MIG process becomes a better option when welding thin stock than flux-cored welding. Because it has a penetration down to 24 ga, MIG welding typically won’t burn through the material. 

Also, it’s not uncommon for thin stock to need painting after the welding is finished, which will be much easier with cleaner MIG welds. 

Costs

The cost comparison between these two welding processes can be somewhat complicated as people have clashing opinions. Most people consider MIG welding more affordable because solid MIG wires cost less than flux-cored wires.

However, MIG welding requires higher upfront costs as you also need a gas tank and additional components like a flow meter and a regulator. 

Cast Iron  

As we already discussed, flux-cored welding is a much better option when welding cast iron. It provides better penetration and welds than MIG, which can weld cast iron, but the welds would be weak. 

Aluminum

MIG is the clear winner when welding aluminum, but you’ll probably need a spool gun. It provides clean welds, which work great for aluminum considering most parts remain exposed. 

Galvanized Steel

Flux-cored welding is more suitable when welding galvanized steel as it can penetrate through the galvanization and form a decent weld. 

On the contrary, if you wanted to use MIG welding for galvanized steel, you would need to grind off the galvanization, which requires more time and complicates the process. 

Related: How To MIG Weld Stainless Steel

Pros vs. Cons Summarized

Flux-Cored Wire

Solid MIG Wire

FAQs

Wrapping It Up

There’s no need to say that both flux-core and MIG welding are excellent welding techniques with their benefits and disadvantages.

However, as a beginner welder, it’s helpful to learn more about each welding process and determine when one makes a better choice than the other. 

Once you learn how to use each technique to achieve a good weld properly, you’ll become a better welder and enhance your welding skills.