Flux-Cored Arc Welding (FCAW): Learning the Basics

Have you wondered, "What is flux core welding?" or "What is a flux core welder?" Flux core welding, also known as flux-cored arc welding (FCAW), is a type of welding that uses a continuous hollow wire electrode to meld metals and other materials together. Flux core welding is suitable for materials contaminated with dirt and rust, making it ideal for outdoor and contaminated environments.

There are two types of flux-cored arc welding: gas-shielded and self-shielded. Gas-shielded FCAW is similar to gas metal arc welding (GMAW), while self-shielded FCAW does not require an external shielding gas.

FCAW is commonly used in the construction industry due to its high welding speed, portability and ability to be used outdoors. Flux core welding has advantages such as increased mobility, high deposition rate and versatility, but also has disadvantages such as fumes, cleanup and higher equipment costs.

Keep reading to learn more about flux core welding basics and processes.

What is Flux Core Welding

Flux core welding (FCW) is a type of arc welding that uses a continuous wire electrode with a flux core to create the weld. This method is similar to MIG welding, but instead of relying on a separate shielding gas, the flux within the wire provides the necessary protection from contaminants in the air. This makes flux core welding ideal for outdoor use or in environments where shielding gas might be difficult to maintain. It's commonly used for thicker materials and in industries like construction and heavy equipment repair.

What Is Flux Core Welding Used for?

Flux-cored arc welding is a good technique to use on materials that are no thinner than 20 gauge, including carbon steel, low-alloy steels, high-nickel alloys, cast iron and stainless steels. The flux-cored wire is powerful and able to penetrate thick weld joints. For this reason, it can also prove more productive than other types of welding.

FCAW is often used in the construction industry, since this semiautomatic type of welding can be used outdoors, has a high welding speed and is easily portable.

FCAW can be used for projects like:

• Shipbuilding
• Construction
• Water tank repairs

When a welder needs to work outdoors, especially in extreme conditions like scorching hot days or freezing cold temperatures, FCAW can be a game-changer. This welding process is particularly useful when working on contaminated materials or in less-than-ideal environments. Its ability to produce high-quality welds quickly can help welders stay efficient—even when the weather makes the job feel even more challenging. However, FCAW isn’t ideal for everyone or every project. Let’s discuss the advantages and disadvantages of flux core welding.

Pros & Cons of Flux Core Welding

Pros

Increased mobility

Since flux-cored welding contains its own shielding method, it doesn’t require external gas and can be transported more easily.

High deposition rate

The rate of deposition in flux-cored welding is the highest of any welding method, increasing productivity. Deposition rate refers to the amount of filler metal melted into the weld joint.

Versatility

Flux-cored welding can be performed in a variety of positions when the right filler material is used.

Cons

Fumes

FCAW needs to be performed in a well-ventilated area because it produces a large amount of fumes as a result of the high deposition rate.

Cleanup

Flux-cored welding is a process that produces slag, a layer of byproduct that takes time to be removed after a weld.

How Flux-Cored Arc Welding Works

Wondering how to weld flux core wire and the specific process? We have you covered.

Flux core welding process

In FCAW, an electric arc unites a continuous filler metal electrode with the base material. As the welding process happens, the shield gas provided by the flux protects the weld pool from oxidation and other atmospheric elements.

After the weld is completed, there is slag that must be removed. Welders need to account for the time to remove slag to make the weld look clean. The welder should remove the slag between each pass.

Flux core welding techniques

Flux-cored arc welding (FCAW) has a few different methods, and each one offers unique benefits. The two main types are self-shielded FCAW and gas-shielded FCAW.

• Self-shielded FCAW: This method doesn’t require any extra gas to shield the weld. It’s great for outdoor work, especially when the wind might blow away a gas shield. It’s commonly used in situations where you need to work quickly and efficiently in open spaces.
• Gas-shielded FCAW: This method uses external gas to protect the weld from contamination. It allows for deeper penetration and is better for welding in hard-to-reach positions. Gas-shielded FCAW is sometimes called “dual shield” because it combines the flux from the core of the electrode with the gas for extra protection.

Each type of flux-cored welding has its own advantages, depending on the environment and the project at hand.

Flux core welding patterns

There are a variety of welding patterns that can be achieved with flux-cored welds. High and narrow welds, for example, can be achieved by using a backhand flux core welding motion.

There is a stringer bead method that deposits weld beads in a straight line, as well as a weave bead technique that forms a zigzag pattern.

Flux core welding wire types

Wires for flux-cored arc welding differ depending on whether the process is self-shielded or gas-shielded. Self-shielded wires, or FCAW-S, don’t need an external gas cylinder. They are often used for portable jobs but do tend to produce more smoke and spatter.

Gas-shielded wires, or FCAW-G, require an external shielding gas. They are easier to control and produce aesthetically pleasing welds. They're typically used in shop settings because the gas could easily blow away when working outdoors.

FCAW-G wires are generally more affordable than FCAW-S wires and are available in diameters ranging from .035 to 7/64 of an inch. FCAW-G wires, used with a shielding gas, are ideal for precise welds in controlled environments like structural steelwork. FCAW-S wires, which don’t require external gas, are well-suited for outdoor welding or jobs requiring portability, such as construction or heavy equipment repair.

Flux core welding polarity

The polarity for flux-cored arc welding processes depends on whether they are self-shielded or gas-shielded. Most gas-shielded welds work best with a direct-current electrode positive (DCEP) polarity. When using a self-shielded process, direct-current electrode negative (DCEN) polarity is used.

Flux core welding equipment

To achieve a flux core weld, you will need:

• A power source (welding machine)
• A welding gun
• Welding wire
• A wire feeder
• Welding cables
• A ground clamp
• A chipping hammer

In addition to these tools, the welder should wear appropriate PPE (Personal Protective Equipment), including an auto-darkening helmet, gloves and protective clothing.

Flux Core Welding vs. Other Types of Welding

Flux core welding is often compared to stick and MIG welding, and while it can be similar to these methods, it’s also unique in a number of ways. Let’s discuss how.

Flux core welding vs. stick welding

The primary difference between stick welding, also known as shielded metal arc welding (SMAW), and flux core welding is the physical structure of their electrodes.

Stick electrodes are metal rods coated in flux. As you weld, the metal center melds with your metal base while the flux casing melts and releases gas to protect the molten metal from contamination.

Flux core electrodes use continuously fed wire containing flux on the inside. Additionally, FCAW electrodes come in a spool and are fed through a semiautomatic welding gun managed by the welder. On the contrary, stick electrodes are long rods attached to an electrode holder managed by the welder’s hand.

Both welding types are self-shielded, removing the need for a gas agent like carbon dioxide. Because stick welding does not require a gas shield, it is also portable and fit for outdoor use.

SMAW also leaves behind slag that requires cleaning between each pass. However, it has a lower deposition rate than FCAW, making for a slower process. Stick welding is common in construction, pipelines, shipbuilding and underwater welding.

Flux core welding vs. MIG welding

MIG welding, also called gas metal arc welding, uses a welding gun that is fed a solid wire from a spool. FCAW also receives a wire from a spool, except that the wire is tubular instead of solid.

The shielding process is another difference between these welding types. As indicated by its name, GMAW requires a gas shield to protect the weld pool. The welding gun contains a nozzle that sends gas through it along with the welding wire to ensure a clean process.

Because MIG welding requires a gas shield, little splatter occurs, minimizing slag and making for an overall cleaner weld. However, it’s not fit for outdoor use as a draft can easily blow away the gas shield. It is also less portable because it requires transporting both the MIG machine and the shielding gas.

MIG welding is more expensive than FCAW and less compatible with various welding positions due to a high heat input. However, the MIG machine eases use, making it simple to learn.

MIG welding is also more versatile, as it can be used on multiple metals and alloys. Industries like manufacturing, automotive maintenance and production, pipe welding, construction, and shipbuilding use this type of welding.

Flux Core Welding Frequently Asked Questions

Is flux core welding as good as MIG welding?

Because flux core wire is tubular and MIG wire is solid, many are inclined to believe MIG wire is the stronger of the two. However, both flux core and MIG welding wires meet the American Welding Society tensile strength standard of 70 KSI. Measuring which weld is stronger would come down to analyzing the welder’s skill.

Is flux core as strong as stick welding?

The stronger weld would depend on the wire used to perform the process. Both flux core and MIG wires come in various tensile strengths. However, the wire you select should correlate with the tensile strength of the metal you’re welding.

Aside from this, determining which type of weld is stronger would depend on the welder’s experience and technique. Both welding techniques can penetrate thick metals. Therefore, the kind you choose boils down to efficiency and comfort.

Is it better to push or pull flux core welding?

The flux core welding motion naturally produces slag. Therefore, it’s best to pull away from what you've welded. Pushing the wire will cause the flux to become trapped in the melted metal.

Is flux core welding hard to learn?

Flux core welding can be easier to learn for beginners compared to some other welding methods, like TIG welding, because it doesn’t require precise control of a filler rod. However, it still takes practice to master the technique and produce clean, strong welds. The key to learning flux core welding is understanding the right settings, how to manage heat and how to handle the welding gun. With hands-on practice and guidance, most welders can pick it up quickly.

Does flux core need gas?

No, flux core welding doesn’t always require an external shielding gas. The flux inside the wire core acts as a protective barrier, making it ideal for outdoor work or situations where using gas might be impractical. However, there is a variation called "gas-shielded flux core" (FCAW-G) that does use gas in addition to the flux for better results, but standard flux core welding (FCAW-S) operates without it.

What is flux core welding good for?

Flux core welding is particularly useful for outdoor projects or in windy conditions where traditional gas shielding would be blown away. It’s great for thicker materials, as it offers deeper penetration and faster welding speeds. Industries like construction, shipbuilding and heavy equipment repair often use flux core welding for tasks requiring strong, durable welds, especially on steel and other ferrous metals.

Discover Flux Core Welding Courses at UTI

Flux-cored arc welding is one of the main components of the Welding Technology program at Universal Technical Institute (UTI).1 In the program, students are introduced to welding tools including hand grinders, pedestal grinders, plasma cutters and more. State-of-the-industry equipment is provided by Lincoln Electric, a leading brand of welding equipment.

Students learn subjects like general safety and safe operation, math that’s practical to welding industry fabrication, welding theory, metallurgy, advanced welding machine functions, the science behind welding, and hands-on welding applications. Students take a specific FCAW course, which builds upon stick-welding skills so they learn how to perform overhead, vertical and horizontal welding operations.

Students then apply those skills in Welding Applications I, where they use blueprinting and planning skills to fabricate specific projects using FCAW welding. “Students choose this program because they like to work with their hands,” says Edward Lopez, Welding Technical Team Leader at UTI Rancho Cucamonga.