Flux-cored welding is very similar to MIG welding, and like MIG welding, it is one of the easier types to set up and learn. But what is flux-cored welding, its common use cases and what makes it such a versatile welding method?  

What Is Flux-Cored Welding?

Flux-cored welding is an arc welding process where a tubular (hollow) wire electrode is continuously fed through a welding gun into a weld pool. An arc is formed between the wire electrode and base metal, melting the base material while consumable filler wire is deposited, creating the weld.

Flux-cored welding doesn’t require a shielding gas. Instead, as the wire melts and deposits metal, the flux compound in the wire dissolves and releases vapours (gases). These gases rise to the surface of the weld pool, where they solidify and create a protective slag layer over the weld.

Flux-cored welding is also known as Flux-Cored Arc Welding (FCAW) and gasless MIG.

How Does Flux-Cored Welding Work?

Flux-cored welding uses a direct current (DC) and requires a completed electric circuit running on a constant voltage power source. The components of the welder all work together to form this circuit.

 
To form the circuit, a wire spool is loaded into the machine. This wire is fed through the knurled driver rollers, into the torch liner and out of the contact tip. The wire will start feeding continuously when the torch trigger/button is pressed and stop when it’s released.

The wire does two things: it’s the heat source and filler material. When the wire passes through the copper contact tip, it becomes electrically charged with the welding current. The wire comes out of the torch and touches the base metal, creating an arc between the two.

The arc melts both metals, depositing filler metal into the molten base metal to form a weld. At the same time, the flux inside the wire also melts, providing a shielding gas to protect the weld from atmospheric contaminants.

The earth clamp completes the electric circuit that runs from the machine, through the torch, into the base metal, then back up the earth clamp to the machine. Without it, your machine won’t arc. You can still pull the trigger and feed the wire through your torch, but it won’t weld.

On top of that, getting a proper grounding is important because a bad earth can cause issues like burnback or a wandering arc.

Flux-cored welding works very similarly to MIG welding, and most MIG welders are capable of both MIG welding and flux-cored welding. It’s also a semi-automatic process, as the wire feeding is done automatically, but the torch movement is still done manually.

Types of Flux-Cored Welding

There are two types of flux-cored welding: self-shielded and gas-shielded. The main difference between them is whether an external gas is needed.

Self-Shielded Flux-Core

As the name implies, self-shielded flux-core (FCAW-S) does not need a shielding gas. Only the flux in the wire is used to protect the weld pool from atmospheric contaminants.

Gas-Shielded Flux-Core

Gas-shielded flux-core (FCAW-G), also known as dual-shielded flux-core, does need a shielding gas. The flux in these wires doesn’t fully shield the weld pool, so an additional shielding gas is needed to stop it from becoming contaminated.    

Gas-shielded flux-core welding is a more specialised type of welding with some very specific use cases. The ‘dual shielding’ makes it great for structural welding, with increased weld deposition rates, high penetration and a doubly protected weld.

Both of these processes work the same way, with the only difference being the addition of a gas bottle (often CO2) when using gas-shielded wire.

What the Flux in Flux-Cored Welding Does

Like MIG welding, the wire used for flux-core welding works as both the electrode and filler material. The difference is that flux-cored wire is ‘hollow’: the centre is filled with flux and sheathed in a metal sleeve.

The flux core in the wire does several things:

• Shields the weld

The main role of the flux is to shield the weld from contaminants. The flux melts and dissolves, releasing its own gases that keep any external atmospheric gases like oxygen out of the weld.

Dual-shielded flux-cored wires also do this, but they still require an external shielding gas.

• Forms a protective slag

The gases produced by the flux rise to the surface of the weld pool, where they solidify and create a protective slag layer over the weld. This slag, like the slag on stick electrodes, protects the weld as it cools.

• Adds alloying elements

Alloying elements are added to steel to change the physical properties of the metal, like its strength, hardness and corrosion resistance. The flux adds these extra alloys, like manganese or nickel, to the steel, as they’re not present in the metal sheath. It also adds deoxidisers to the weld pool to keep it from oxidising.

• Stabilises the arc 

The flux contains additional compounds that work to help stabilise the arc while welding.

There are various types of flux, with differing makeups to suit different material types and grades. 

Metals

Flux-cored welding is not the most versatile when it comes to the different materials it can weld. It can be used to weld:

• Mild steel
• Stainless steel
• Hard facing 

Wire Selection

Because of the addition of flux and the different range of compound makeups, flux-cored wires come with a classification code.

Depending on the type of wire, there are mandatory and optional designators, as not every designator applies to every type of wire. Using our HYPERSHIELD 71T flux-cored wire as an example, its classification code reads E71T-1M/C. Here’s how that breaks down:

• The first digit ‘E’ stands for electrode. Every wire will start with E.
• The second digit (7) represents its minimum tensile strength x10 ksi. This wire has a tensile strength of 70ksi or 70,000psi.
• The third digit (1) indicates the welding positions it can be used in. This number has two variations: 0 (flat & horizontal only) and 1 (all positions).
• The fourth digit ‘T’ indicates that it’s a flux-cored tubular electrode.
• The dash (-) and fifth digit refer to the usability and performance capabilities, including polarity requirements and general operating characteristics. The usability designator also indicates whether a wire is self-shielded or gas-shielded.

Self-Shielded Designators	Gas-Shielded Designators
T-3	T-1
T-4	T-2
T-6	T-5
T-7	T-9
T-8	T-12
T-10	T-G
T-11	T-GS
T-13
T-14
T-G
T-GS

These designators are used to generally group electrodes that contain similar characteristics with the exceptions ‘G (general)’ and ‘GS (general single pass)’.

• The sixth digit ‘M/C’ refers to the shielding gas type. There are three variations of this: M = 75%-80% Ar/20%-25% CO2, C = 100% CO2, and blank = no shielding gas. The HYPERCORE T-11 (E71T-11) only uses internal flux, so its classification ends with its usability designator.

These six digits are the mandatory designations used to classify flux-cored wires. The following designations are optional: 

• Improved toughness: this is represented by a ‘J’, and it indicates that the flux-cored wire will produce a weld with Charpy V-notch (CVN) values of at least 20 ft·lbf @ -40°F (27 J @ -40°C).  

Note

The Charpy V-notch test is a high strain rate test that determines a material’s toughness.

• Supplemental mechanical property requirements: this is represented by a ‘D’ or ‘Q’, indicating that the deposited weld metal will meet the requirements when welded with high heat input, slow cooling rate and low heat input, fast cooling rate procedures.  
• Diffusible hydrogen levels: this is represented by an ‘H4’, ‘H8’, or ‘H16’, and it indicates the maximum diffusible hydrogen amount in every 100 grams of deposited weld metal. A H4 designation means there is a maximum of 4mL of hydrogen, H8 would mean 8mL, and H16 is 16mL.  

Settings (Voltage & Wire Feed Speed)

Generally speaking, because flux-cored welding is done using a MIG machine, the settings for both are the same: voltage and wire feed speed. The voltage determines how much heat is in the weld. Turning it up or down will adjust how much welding current is added to the weld.

The wire feed speed determines how much wire per minute is added to the weld. The more wire added, the cooler the weld will be, and vice versa.

Your voltage and wire feed speed generally work in harmony together. If you turn your wire feeding to the max but leave your volts too low, the wire won’t burn. You need enough heat to melt the wire but not so much heat that it gets sprayed everywhere except in the weld.

What you want to set them to depends on a few things. The metal thickness, the metal type, filler wire thickness, weld position and joint type will all impact the settings.

If you’re not sure where to start, almost every UNIMIG MIG welder comes with a Setup Guide on the inside of the machine’s door. It provides recommended settings for different metal types, metal thicknesses and wire sizes as a starting point. It also includes the gas flow and polarity recommended for each application.

Polarity

Flux-cored welding is done on electrode negative polarity. That means the current is negatively charged and runs from the positive to the negative. It’s also known as straight polarity or DCEN (Direct Current Electrode Negative).

To set up a UNIMIG welder for DCEN, plug the polarity cable into the negative (-) panel mount and the earth clamp into the positive (+) panel mount.

The polarity cable acts as the torch because all UNIMIG MIG torches come with a Euro quick-connect plug.

The exception to this is when running gas-shielded flux-core wire. The polarity you’ll need to run your wire may depend on the type of wire used. Some dual-shielded wires will call for DCEP (Direct Current Electrode Positive).

That means you’ll plug your torch/polarity cable into the positive (+) panel mount and the earth clamp into the negative (-) panel mount.

Common Flux-Cored Fabrications & Applications

Flux-cored welding can be used on a range of metals and is one of the fastest ways to weld, making it a popular choice for several industries. Common FCAW uses include:

• Home hobby and DIY projects – the ease of use and relatively low setup costs of flux-cored welding (no need for a gas bottle!) make it an excellent choice for beginners and jobs around the house.
• Outdoor use – flux-cored is the first choice for any kind of outdoor welding where wind blowing away your gas coverage would be an issue.  
• General fabrication – though it’s not recommended for very thin metal, flux-cored works well for frames, fences, trailers, repair jobs, etc. 
• Construction – its speed, the ability to weld thick metal, and without the need for gas, it’s ideal for construction work.  
• Manufacturing – its ease of use and high deposition rates with aesthetic-looking welds when using a dual-shielded flux-cored wire make it a top choice for manufacturing and heavy equipment production or maintenance.

Advantages of Flux-Cored

Many things make flux-cored welding a popular choice, not just that it (generally) doesn’t need a gas bottle.

• It has a high deposition rate. The flux core in the wire provides a more stable arc, so you get faster welding speeds and a higher weld deposit rate. 
• It provides good penetration. It achieves great penetration into the base metal, giving you stronger welds with fewer passes.
• It can weld in every position. Flux-cored welding works regardless of whether you’re in a flat, horizontal, vertical or overhead position. 
• It’s versatile. It can be used to weld a range of metals and alloys with different variations in the flux. Plus, it can weld quite thick material as well. 
• It’s excellent for outdoor welding. It doesn’t (for the most part) use gas, so you can work on any outdoor application without worrying about having your shielding gas blown away.
• It can be used anywhere. Because you don’t need a gas bottle, flux-cored welding is one of the most portable. So long as you have access to a power supply, you can use it.
• It’s easy to learn. As a semi-automatic process that’s relatively point-and-weld, it’s easy for beginners to learn.

Disadvantages of Flux-Cored

While there are many reasons to choose it, flux-cored welding still has some downsides.

• The initial cost. Though you won’t need to purchase gas, the cost of the machine and consumables is still more expensive than stick welding. The filler wire is usually more expensive than solid MIG wire.
• It produces fumes and smoke. As the flux evaporates, it produces a lot of toxic fumes and smoke, more than the other welding processes do. 
• It’s subject to flux and gas welding defects. If the gases get trapped as the slag hardens, it can cause porosity, and there is a chance of getting wormholes or slag inclusions.
• It can’t weld sheet metal. Because flux-cored welding runs hotter than MIG welding, it’s unsuitable for welding sheet metal or anything thinner than 1mm. 
• There’s extra downtime. Once you’re done with the weld, the slag still needs to be removed before it’s finished, and another weld can be done.
• It needs extra storage considerations. The flux inside the wire absorbs moisture faster, so it needs to be stored properly. Moisture in the flux will cause weld defects. 

In summary, flux-cored welding is easy to learn and use and is a good place to start if you’re getting into welding. It can be used for a wide range of applications, including niche ones that require a gas-shielded flux-cored wire.