What is the Difference Between a MIG and a Flux Welder?

Both Metal Inert Gas (MIG) and Flux-Cored Arc Welding (FCAW) are popular welding techniques that are used in a wide range of applications. 

Each method comes with its own set of pros and cons, and one cannot be just called superior to the other.

In this article, I will be sharing some valuable insights into the key differences between MIG and flux welding. 

By understanding the basics of these two welding processes and understanding their differences, you will be able to better judge which method suits the specific needs of your welding project. 

So, without any further ado, let’s jump to the in-depth comparison of these two popular welding methods. 

MIG / GMAW vs FCAW: Uncovering the Differences

Both GMAW and FCAW involve feeding a spool of wire into the welding gun. Although the nature of the wire is different, the general process is the same. The wire is fed into the weld pool to create the weld and the wire is consumable. 

You might be surprised to know that many MIG welder units have the ability to use both MIG wire and Flux-core welding wire. So, you don’t need to purchase a separate welding unit for FCAW. 

There are plenty of differences between these two welding methods. Let’s discuss some of the most prominent of these differences. 

The Core Difference: Shielding Gas vs Flux Core

The most prominent difference between MIG and Flux-Cored welding lies in the way they shield the weld puddle from atmospheric contamination. 

MIG welding, also known as Gas Metal Arc Welding (GMAW) uses an electric arc generated from a consumable wire electrode to weld the base metal. The shielding gas that protects the weld pool comes out of the nozzle.

The process uses a solid wire electrode that gets consumed in the weld pool to create the weld. 

The welding gun has a gas delivery system that is attached to the shielding gas cylinder. 

So, you will have to adjust the gas flow from the cylinder and replace or refill the cylinders when required. Inert gasses are quite expensive, which makes this an expensive process.

The shielding gas in MIG welding is not only responsible for protecting the weld pool but also for preventing oxidation and porosity, preserving the weld integrity, and improving the appearance and quality of the weld. 

On the other hand, in Flux-Core Arc Welding (FCAW), the process uses a consumable tubular wire filled with flux, unlike MIG welding. 

The flux generates the shielding gas when heated, which removes the need for a shielding gas cylinder, gas delivery system, regulator, securing connections, and all that hassle. 

The ability to produce its own shielding gas also got this welding method a unique name “Gasless MIG Welding”. 

However, when we go into the details, we come to know that the process is not entirely gasless but does use gas. 

FCAW generates shielding gas of its own directly from the flux wire. The flux reacts with heat and releases vapor. The gas forms a protective barrier that protects the weld pool and the slag layer on the weld protects the cooling weld afterwards. 

Differences in Weld Quality and Appearance

Each welding method is unique and so is the resulting weld quality you get with it. Both GMAW and FCAW techniques produce distinct weld qualities and appearances. 

This difference can impact the final aesthetics and functionality of the welds. 

MIG welding provides clean and visually appealing welds that have minimum spatter and slag. Yes, you will require some cleaning, but it won’t be much if you have done the job right. 

Yes, the aesthetics won’t be as top-notch as you would get from a TIG welder, but the process is still much cleaner as compared to stick welding. 

Hence, you will have a smooth weld surface with less post-weld cleaning and grinding required. 

Also, you get a neat and consistent weld-bead appearance which makes the method an efficient choice for visible welds where appearance matters. 

In short, with MIG welding, you get professional-looking results and it’s a good choice where aesthetics are important. 

On the other hand, FCAW is responsible for producing robust welds with much better penetration. 

But, as you might have already guessed, the welds may not be as aesthetically pleasing due to the presence of slag and spatter. 

On the positive side, unlike MIG welding, FCAW can handle rust, paint, and minor surface contaminants. It requires much less pre-weld preparation and is ideal for outdoor or dirty environments. 

The deeper penetration provides you with much stronger welds and makes it a good choice for thicker materials. Also, this distinct property makes FCAW a better choice for structural applications. 

Areas of Applications

Both GMAW and FCAW can be used in a wide range of applications. You have to understand their basic suitability for various tasks to decide which area they can be used for. 

MIG welding, generally, is well-suited for precision work on thin and medium gauge material. Hence, it is a popular choice in the automotive and aerospace industry. 

It comes with a variable heat and wire feed speed control that allows you to gain precise control over the welding process. 

The lower heat input reduces the distortion in thin materials and minimizes the burn-out risk, which makes it a good alternative to TIG welding, as it has better productivity and faster weld speeds. 

Hence, MIG welding is widely used in the automotive and aerospace industry to make high-quality and visually appealing welds. It is also used for precision welding of critical components, especially lightweight materials such as aluminum. 

On the other hand, Flux-cored arc welding is primarily used for heavy-duty tasks and thicker material. 

Hence, it is a popular choice in the construction and manufacturing industry where high productivity is required regardless of weld appearance. 

It has a much higher heat input, which makes it unsuitable for thinner materials, but on the bright side, makes it perfect for thicker materials. The higher heat input provides much better penetration. 

The process is ideal for welding steel beams and heavy equipment where a strong weld is required. The robust welds provide better structural integrity and stronger tolerance for contaminants. Hence, FCAW is perfect for outdoor and harsh environments. 

Related: What Can You Weld with a MIG Welder?

Welding Speed and Efficiency

MIG and Flux-cored arc welding are known to have different levels of speed and efficiency, which can impact the overall productivity of the welding methods and also the turnaround times. 

MIG welding is considered faster and more reliable for large-scale production. The welding method has a higher deposition rate which makes it a more efficient process for many welding applications. 

Adding to this, the GMAW has a higher overall efficiency which also means minimal spatter and slag, requiring less post-weld cleanup. So, you will be able to finish your project much faster.

Compared to this, Flux-cored welding is a bit slower but much more versatile. The process isn’t as slow as TIG welding, but when compared with MIG, it does get work done a bit late. 

However, the versatility and adaptability of FCAW compensate for this drawback which makes FCAW a valuable choice. The best part is that the technique can be used in various positions including vertical and overhead welding positions. 

Hence, you will have more position flexibility and you will be able to weld in hard-to-reach areas. 

But there is a downside. You get much more spatter and slag, which means you will have to spend a lot of time on post-weld cleanup. 

The cleaning, grinding, and finishing take up plenty of time which makes the overall project completion slower and hence makes flux-cored welding slower indeed.

Related: What is a MIG Welder Used For? Applications of MIG Welding

Ease of Use and Learning Curve – Which One is Better for Beginners? 

Both of these methods come with different learning curves and their ease may vary from person to person. 

MIG welding is considered more beginner-friendly due to its straightforward process and easier-to-control welding gun. 

Hence, one can argue that it is easier for beginners to learn, and they can quickly master the basic skills. Also, there is less room for error in MIG welding. 

You can practice on a piece of scrap metal to perfect your craft and fine-tune your settings. Also, you can experiment with different settings to learn which one works best for you. 

But the ease of use does depend on the environment as well. MIG welding, no matter how efficient and easy, cannot be used in outdoor windy situations. 

Also, the shielding gas tank does bring another advantage of ease, when you are required to change the materials being welded. 

In MIG welding, you can simply swap the gas tank with a different one. While gas tanks are heavy and need to be handled carefully, the process is pretty straightforward. 

You simply need to swap the tank with a different or required one. Yes, removing the hose connections and regulator and then replacing it will be a hassle, but it is nothing compared to what you have to do with FCAW. 

However, FCAW is considered a bit more advanced, with much higher power which requires higher skill and a bit more experience to master. 

The process isn’t complex, to be honest, but the higher heat of the system makes it a bit difficult to control which means you will require more practice. 

But, on the positive side, it can be used in outdoor windy situations even for air up to 35 miles per hour. 

As for the tank changing, as I have discussed above, you don’t need to do it with the Flux-cored welding technique. 

However, you will need the right type of alloy wire and flux-core mixture and you will need to keep various of them at hand if you deal with different metals in your welding projects. 

Storing all of these wires and organizing them can become a hassle. Also, some of these wires require specific conditions for storage. They might need low humidity, or they will go bad which makes them unusable. 

Polarity

MIG and FCAW also differ in their polarities, which is another distinct feature that makes them different from each other. 

When you are using the MIG welding technique on a MIG welder, you will have to connect the wire electrode to the Direct Current Electrode Positive (DCEP) and the workpiece to the negative electrode. 

This is known as reversed polarity which means the current will be flowing from the workpiece to the wire. The process concentrates more heat in the workpiece. 

On the other hand, the flux-cored welding, the electrode is set to the negative terminal while the workpiece is set to the positive terminal. 

So, in this process, the current will jump from the wire electrode to the workpiece, which is in the opposite direction as compared to the above process. 

This arrangement is known as Direct Current Electrode Negative (DCEN) also known as straight polarity. 

The process generates more heat in the electrode, instead of the workpiece. 

You must keep in mind that some flux-cored wires require DCEP arrangement instead of DCEN. 

The current flow decides where the heat will be concentrated most during the welding. DCEP ensures more heat in the workpiece while DCEN ensures more heat in the electrode. 

So, with higher heat on the workpiece, you will get deeper penetration which means better welds with thicker material. 

On the other hand, DCEN polarity provides lighter penetration, with more heat on the electrode, the welds are usually wider and shallower. 

But, with flux-cored welding, a lot of this heat is released onto the base metal which provides high heat for the flux to work. 

While the flux-cored wire can be used with MIG welders, not all welders support them. You have to make sure that the MIG welder comes with polarity swapping capability. 

Filler Material

MIG welding is quite efficient because it uses pure filler material that is of the same nature as the base material. Hence, you can use the material for multiple passes as well during the welding to make the welds stronger. 

However, that is not the case with flux-cored wire. Flux-cored wires have a lot of differences from solid wires, as they not only contain the flux but also some additives in addition to the flux. 

The wire shell alloy along with the flux is filled in the follow of the flux-cored wire that is designed to work with specific metal. 

These additives allow the reacted flux to reside on the surface and cover the bead which makes the bead an alloy to the base metal being welded. However, the bead is not the same as the base metal. 

Also, some flux-cored wires have higher manganese, which means, you cannot make multiple passes on the weld. 

The manganese strengthens the weld, but multiple passes can make it hard and brittle which can lead to cracking. 

Hence, you must ensure that the flux-cored wire is rated for multiple passes before you do the process. Each flux-cored wire is rated for single or multiple passes. 

Cost Comparison

Another factor that can help you make an informed decision about the two is the cost associated with welders and their consumables. 

MIG welding requires a higher initial investment due to the need for specialized equipment. I mean, you need to purchase a MIG welder, a gas regulator, a shielding gas cylinder, and welding accessories.

Also, there will be ongoing expenses for shielding gas and the wire feed. The storage and maintenance of gas cylinders can be added to the overall cost.  

On the other hand, flux-cored welding has a lower upfront cost, as it doesn’t require shielding gas, regulator, gas delivery system, and all of its gas-related accessories. 

So, you will have to make a comparatively lower initial investment, which makes it a bit simpler. Also, you don’t have the ongoing cost of gas refill which also reduces the maintenance and storage cost. 

However, when it comes to wire costs, FCAW beats MIG welding because the flux wire is much more expensive than the normal MIG welding wire. 

Related: How to Use a MIG Welder?—Ultimate Guide & Expert Tips

Frequently Asked Questions

Is Flux-Cored welding stronger than MIG welding?

Neither of the processes can be called stronger than the other because each one comes with its own set of pros and cons. If done the right way, both MIG and flux-cored welding produce strong and reliable welds. 

MIG vs Flux-cored, which one penetrates better?

While you might have heard that flux-cored arc welding provides deeper penetration, when you look at the polarity, you think MIG has more penetration. In truth, both techniques have fairly good penetration, but flux-cored has rapid heat input. 

Is MIG welding better than flux-cored welding?

One method cannot be named better than the other without considering a specific scenario. Each method comes with its own advantages and drawbacks. MIG welding is generally considered better because it has more advantages than drawbacks. 

Can you use flux-cored wire in a MIG welder?

Yes, MIG welders do support flux-cored arc welding as well. So, you can use the flux-cored wire in a MIG welder with some minor tweaks. However, some flux-cored wires require DCEP polarity, which means your MIG welder will be required to have it. 

What is flux welding best for?

The greatest advantage of flux-cored welding is its ability to deal with dirty, rusted, or contaminated metals. You don’t require as much surface preparation as you would require in MIG welding. 

Can I use flux-cored welding for thin metal sheets?

It is not recommended generally because of the higher and rapid heat input of FCAW. Flux-cored welding has a higher risk of burning through the thin metal sheet, so professionals recommend not using it. 

Is flux-cored welding gasless?

Well, technically it is not gasless. The reason FCAW is considered gasless is that it doesn’t require a shielding gas cylinder. The gas is generated from the flux inside the wire, so in a way, it is a type of gasless welding. 

Wrapping Up!

To sum it all up, there are plenty of differences between MIG welding and FCAW. Both methods come with their own set of pros and cons. 

Although MIG welding is generally considered better than Flux-cored welding, in truth, FCAW does come with its own set of advantages. 

So, it is safe to say that in certain situations FCAW can beat MIG welding and is a better choice. 

The best part is that you can use both Flux-Cored and MIG wire on the same welder if it comes with swappable polarity. 

So, with the right MIG welder, you can use both welding methods and enhance your welding applications. 

If you still have any doubts, feel free to drop them in the comments section below and I will get back to you as soon as I can.