Flux Core Welding vs. MIG Welding – The Main Difference Explained

Last Updated on May 2022


We all have different views when it comes to which welding method is preferable over another. Some of us think that flux core welding should be considered over MIG welding. Others may say MIG welding is better than flux core. Everyone has a reason behind whatever welding method they choose.

But both of these welding methods have things that differentiate them, features that make them equal, and several things that make each better than the other. For those who are new to welding, choosing the best among the two may not be an easy task.

Through comparison, there are three significant facts that are important to consider when choosing between these two welding methods: the material which you are going to use, the welding area, and lastly, the exterior finish surface.

Other factors you need to consider when making your decision are discussed below.

Flux Core Welding

This is a welding process denoted by FCAW. It is one of the earliest welding processes and used in only the flux core welder. There can also be a MIG welder set to feed this process with shielding gas or a solid gas. Flux core is an alternative to shielding arc welding.

There are two types of these processes, which are self-shielding and gas shielding. The difference between the two is that in gas shielding, a gas supply is required to protect the weld, whereas self-shielding requires no external shielding gas.

MIG Welding

MIG welding is a semi-automatic process where a wire is connected to direct current from the source. The wire acts as an electrode, and its primary purpose is to connect the two metals as it is passed through a welding gun.

During this process, both inert gas and wire electrodes are simultaneously passed through a welding gun. The purpose of the inert gas is to shield or keep off airborne contaminants from the weld area. This, therefore, makes it ideal in welding non-ferrous metals and different kinds of aluminum.

Generally, both of these processes will give you worthy grounding, but there are some differences you are likely to encounter.

Ways to Use Flux Core Welding

Use of Shielding Gas

This is one difference you are going to come across when comparing the two processes. Shielding gas is necessary when welding a MIG wire. Therefore, you will need to purchase a separate pressure gas tank connected to a flow meter or a regulator to the MIG welder through a running hose.

The hose supplies the welder with the gas. There are several gases that can be used as protection in MIG welding, and they include argon, carbon dioxide, and a mixture of carbon dioxide and argon. A combination of carbon dioxide, argon, and helium is used for stainless steel.

As mentioned earlier, there are two flux core welding process, the self-shield and a dual shield flux core. In the self-shield flux core, the wire produces its own protection gases at the point of the weld. The flux in the wire melts on heating, producing gas, which then covers the weld pool.

This is economical since you don’t need to purchase or transport a welding gas wherever you are working. However, a dual shield flux core wire needs to be used together with a shielding gas, just like in MIG welding. For more information on Argon welding tanks and gas [Read our Full Guide].

The Kind of Wire to Use

First of all, both methods use a barrel of wire as a welding electrode, so it is essential to know the type of welding wire to be used in each process. Among the differences, this is the main one. The MIG welding process uses a solid wire electrode while, on the other hand, Flux Core uses a tubular welding wire.

The difference between the two is that a tubular welding wire is hollow. It is made of metal on the outside and flux at the center. The flux material gives rise to the welding mechanism’s name. The difference between the wires means they all behave in a different way. You cannot use a solid wire to weld with flux core welders.

Comparing the Weld Polarity 

There is a sharp difference between the polarities of flux core and MIG welding. Starting from the setting, each of the processes should be fitted with the right applicable wire.

In-depth, you need DCEN setting when welding with self-shielded flux. This means that the wire contained in the welding wire should strictly be aligned to the negative terminal. On the other hand, a ground clamp needs to be attached to the welding table or welding projector and shot directly to the positive terminal.

In MIG welding DCEP is used. This is the direct current electrode positive, where the MIG gun uses the positive terminal. Some MIG welders use a flux core to weld. These can be switched from one terminal to the other.

It is important to know the exact settings to use. More so, not all flux core wires need a DCEP setup for welding. With stainless steel, you need a self-shielded flux that can be used with a welder that allows the user to change to a DCEP polarity. Gas shielded flux core uses a separate shielding gas for welding, and its wire requires a DCEP setting.

Does Flux Core Offer Better Metal Penetration than MIG?

Most people have the opinion that flux core gives a better penetration compared to that of MIG welding. But how do you differentiate between the two? Metal penetration may vary due to different factors.

The voltage and the amperage to which you set your welder is the first determinant of how much the welding will penetrate the metal. The second aspect is metal thickness; how thick the metal is will determine how deep the welding will go. Therefore it is how effective the welding method is used that determines how deep the penetration will be.

For instance, you can weld a 4.8mm steel by using a .030 flux core wire by using 140v. This is different from the results you get when you use the same diameter of a solid MIG wire, which will give you a 1/8 inch welded steel.

This same principle is certain when you use Hobart, Lincoln or Everlast among other metals. However, by using flux core, you are in a better position to weld thicker metals with less amperage to that of MIG. Therefore the argument that flux core offers better metal penetration is equally valid.

Welding Quality: Flux Core Weld vs. MIG 

Just as with all other aspects, quality needs to be considered in determining the best welding process between the two. MIG welding is considered to offer better quality, but this will depend on how you define ‘quality.’

In most cases, strength measures the weld quality. If this is true, then both methods provide a strong weld. In other instances, texture and looks may be a quality determinant to many; therefore, if that is so, MIG welding produces a great looking metal.

How is this achieved? Filler metal is set to sit up the joint weld. This gives you an excellent looking weld joint.

Slag and Spatter Produced

There are different results when it comes to how much slag and spatter is produced when welding metal with either MIG or Flux Core. Flux core wire contains a flux at the center of the wire which results in some slag production during welding. This slag cover forms a welded pool, and it is later scrubbed off once the metal cools.

Slag is the host of impurities removed by flux; therefore, there the chances are high of finding slag when using flux core welding. MIG welding is not exempt from this, as it is also known to produce some residue. The difference between the two is that the slag produced by MIG welding is easier to clean than that of Flux Core.

Spatter is produced when the molten metal spots are sent around the welding zone by the welding wire. Like slag, spatter is also formed by both welding processes, but how much spatter is produced will depend on which shielding gas is used.

Carbon dioxide shielding gas produces more spatter. Overall, Flux core welding is said to generate more spatter, which can easily be removed by the use of anti-spatter products.

Comparison of Flux Core and MIG on Dirty Steel

All metals that may be galvanized have paint or are covered in scale do not favor MIG welding. To get perfect results, you need to clean the metal to weld thoroughly from top to the base. In case this is ignored, the results will be a poor weld, weld rusting, and even failure.

Flux core welding is tolerant to dirt. This is because flux wire contains scavengers that get rid of impurities from the base into the slag. This slag is chipped out simultaneously until the welding stops. All metals need to be oil-free for both MIG and flux core.

Despite flux being tolerant of dirt, it is always advised to have your metal cleaned before welding. In case you are dealing with a galvanized metal, flux core is the best choice for you.

Which One is Cheaper?

Some views are that MIG welding is cheaper compared to that of flux core. This is because MIG uses a solid welding wire, which is less expensive than that used by flux core welding wire. But this may not be true since, despite its welding wire being cheap, it needs additional equipment, which increases the cost.

For starters, you will need to buy a gas pressure tank and all the components that comes with it — a flow meter, a hose, and a regulator. Considering all aspects needed, MIG is more costly than flux core.

Where to Weld

There is a slight difference when it comes to where these machines are used. MIG welding and dual shielded gas are an indoor activity. This means that you need to have a workspace or garage to weld in.

Both use shielding gas, which is sensitive to the wind, therefore, quickly blown away. In case you have to use a MIG or dual shielded flux core outdoors, it is advisable to use a windshield. Since the self-shielded flux core requires no gas tank, it is best to use it when doing outdoor welding.

More so, the self-shield flux core has less equipment to carry around, thus making it more manageable. Caution should be emphasized above all in every place of welding.

Flux Core Welding Advantages

  • It is known to be highly stable under vicious atmospheric conditions
  • Preferable in welding thick pieces
  • Simple set up when welding
  • No external gas needed for self-shielded welding
  • It is slightly cheaper compared to MIG welding

Disadvantages of Flux Core

  • Not ideal for thinner materials, that is, metals under 20 gauge are unsuitable with flux core
  • Critical gun position more so for new welders

Advantages of MIG Welding

  • It is known to offer less spatter and a soft arc making it best for appearance
  • Maintenance, the setup process, and operation are easy
  • Beginners may find it more comfortable compared to that of Flux core
  • Cleaning of slag and spatter is easier and fast

Disadvantages of MIG Welding

  • Unsuitable when welding thicker metals
  • On purchase, you need additional tools which include, gas tank, electric valve, a hose among others to complete the setup
  • Said to mar the surface area


In a nutshell, this assessment proves that both flux core welding and MIG welding each have some advantages over the other. Both have specifications that make them suitable in different welding applications.

When choosing between the two, it is important to evaluate your needs first. Think of what metal you are going to weld, what you would like the results to be, the environment, and how much you need to spend for the entire setup.

Whatever process you choose to use, choose the right quality of the machine, follow the manual, and handle the machine with care. With that done, it should serve you efficiently.

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