What is Flux-Core Welding? | A Detailed Guide to FCAW

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What is flux-core welding? Let’s dive into this welding technique and see how it can be useful for your welding career.

Introduced in the 1950s, flux-core arc welding, or FCAW, is an automatic or semiautomatic welding process. It uses a continuously fed consumable tubular electrode that has both a flux and a consistent voltage in most cases, although it can also use a constant-current welding power supply. A shielding gas supplied from an external source is sometimes used, but the flux is the primary defense against the surrounding atmosphere, as it produces both liquid flag and a gaseous shield.

Flux-core arc welding is used primarily in construction because it’s extremely fast and portable compared to other welding solutions.

How Flux-core Arc Welding Works

In a nutshell, flux welding works when an electric arc is produced and used to unite a base material with a filler metal electrode. This is opposed to a MIG welding technique, which uses a solid metal electrode. Flux-core arc welding processes use a hollow tubular electrode filled with a flux.

flux core welding system

The flux filled metal wire electrode is automatically fed to the center of the welding gun using the same type of equipment in MIG welding processes. A gas shield may be supplied by the welding gun to protect the pool from oxidation as the welding process occurs.

The flux material inside the hollow electrode tube then forms a slag, or smelting refuse, that covers and protects the current welding from the atmosphere. FCAW is useful for construction because the shield provided by the flux material allows the welding process to be completed outdoors and in windy conditions.

Flux-core Welding Process

The flux-core welding process requires the same safety measures to be taken as you would for MIG welding. This includes wearing safety apparel and preparing all your tools beforehand.

Next, the surface of the base metals to be used in the process should be cleaned thoroughly if possible, even though FCAW is much more tolerant of contamination than MIG welding. This ensures that rusty or scaly surfaces don’t contaminate the resulting weld. 

Once the equipment and base metals are prepared, all welding equipment must be plugged in and the welder will select an electrode polarity. Flux-core welding always requires a DC electrode negative, otherwise known as straight polarity. Most will use an E71T-11 wire for the majority of projects, as it’s a good all-around choice for beginners and works for a variety of metals and thicknesses.

Next, the flux welder will select the right voltage, amperage, and wire feed speed for the project. Most FCAW welders will use a pull or drag technique when flux-core welding, which means that they will be moving away from the completed weld.

The welding gun should be pointed toward the weld puddle as you drag it away from the metal base. This improves visibility and allows for deeper weld penetration. The best flux-core welders, naturally, will provide better performance.

Any flux-core welder will need to be careful to avoid burnback, which happens when the wire melts into a ball at the end of the gun tip.

The Suitability of Flux-core Arc Welding

FCAW is an extremely flexible welding method. This makes it suitable for a variety of tasks and needs. FCAW jobs have high productivity because they deposit lots of material quickly. It’s great for welding thicker sections together and can even produce a fully penetrated weld on both sides of a plate half an inch thick in one pass.

FCAW is best used with stainless steel, carbon steel, and other low alloy steels. It has a high welding speed and can be performed outdoors, so flux-core arc welding is a great choice for construction jobs or the industry at large. It’s also a good choice if you need to weld in a garage with open doors and a lot of wind or surrounding disturbances.

FCAW can’t be used with most non-ferrous metals like aluminum. This makes it a poor choice for jobs using these materials, and many MIG tasks.

What is the Difference Between FCAW and MIG Welding?

The primary difference between FCAW and MIG welding lies in their shielding techniques. Flux-core arc welding has a hollow wire with flux material in the center – this is the titular flux-core.

This flux material provides the shielding necessary to ensure a proper weld, even in outdoor or windy conditions. That’s because the flux material itself produces the gas necessary to shield the weld.

the wire coil

On the flipside, MIG welding relies on an external source of gas, usually in a bottle. This produces several side effects when welding in windy conditions or when outdoors. MIG welding techniques are also slower and bulkier because of this extra equipment. As a result, FCAW is usually faster and more agile.

Flux-core Wire Electrodes

Flux-core wire electrodes are the main piece of equipment from which the entire process derives its name. There are two types of these electrodes: self-shielded and gas-shielded. Gas shielded ones require an external shielding gas just like MIG welding techniques. Self-shielded do not.

flux core wire electrodes

For gas-shielded flux-core wires, the flux coating solidifies a little faster than the molten weld material. This makes a shelf or shield that holds the molten weld pool if you weld from overhead or vertically. 

Gas shielded flux electrodes, therefore, work quite well if working with thicker metals. Removing excess slag is easy with these electrode types.

Self-shielding flux-core wires don’t need external gas. Instead, shielding gases are generated from within the flux electrode; this protects the weld pool. Such an electrode is very easy to carry around with a welding gun, allowing welders to reach difficult positions or move quickly from weld to weld.

Advantages of Flux-core Wire Electrodes

The big advantages of flux-core wired electrodes are that they allow for a very high material deposition rate, among other benefits. Basically, this means that flux-core wire electrodes allow you to weld more material and often with greater penetration to the other side of a plate at the same time.

In addition, these electrodes allow you to work in outdoor or windy conditions because of the aforementioned shielding effect as a result of their flux material. Depending on the filler material used, these electrodes can make FCAW appropriate for all welding positions.

Finally, flux-core electrodes produce clean and strong welds more often than not. So they’re prized by beginner or expert welders alike for their consistency and excellent results.

flux core welds

Disadvantages of Flux-core Wire Electrodes

These wire electrodes are always used with the possibility that there might be an incomplete fusion between both base metals. This may result in cracks in the final weld or the inclusion of slide in the weld as it solidifies. This can negatively affect the operation and integrity of the finished job, of course.

In addition, flux-core wire electrodes might produce a melted contact tip. This can happen occasionally if the electrode directly contacts the base metal and produces a fuse between the two rather than welding properly.

Another possible disadvantage is that these welds might develop holes or become porous if certain gases don’t escape the welded area before the weld solidifies and the metal hardens. This, again, can affect the structural integrity and the quality of the finished welding job. 

How Fast is Flux-core Arc Welding?

FCAW is incredibly fast and is among the most productive manual welding processes available. MIG welders can usually produce between 5 or 8 pounds of weld in an hour, depending on plate thickness and other variables. FCAW welders can easily produce 25 pounds or more in the same hour if they have the expertise needed for fast welding.

In addition, FCAW welding is useful for the aforementioned ability to weld a half an inch-thick plate in a single pass with full penetration on either side of the material. This gives a great utility and speed and makes it appropriate for bigger jobs where lots of identical welds will be needed to make large objects or buildings. Ships are a good example of construction jobs that benefit from flux-core arc welding.

What Can FCAW Weld?

Because of its ability to do consistent work in outdoor or windy conditions, flux-core arc welding is particularly ideal for shipbuilding or general construction needs for buildings or larger vehicles. As a result, it’s typically seen in manufacturing for welding different car parts or plates for structures.

It can also be used for general repairs and maintenance work, especially since it's so maneuverable if you use self-shielding flux-core wire electrodes.

Generally, FCAW is primarily used with alloys like stainless steel, or mid or low alloy steels, along with some high nickel alloys. Because it has a higher weld metal deposition rate compared to MIG welding, it’s often used for dense metal sections that are more than an inch thick.

How Long Does it Take to Learn Flux-core Arc Welding?

This depends on whether you already know how to MIG or stick weld. The basics are the same as any other welding process, so it takes about the same amount of time if you’re starting from scratch. Beginners will likely need to spend several weeks practicing welding under the supervision of an expert or trainer before they can receive welding certification.

Flux-core arc welding specifically doesn’t take any longer than other processes. Those with welding experience can probably practice for a few hours and get the hang of things. They can then take certification tests and be allowed to flux-core arc weld at their job.

Manufacturing and Industrial Use

FCAW is typically used for shipbuilding and construction because of its high deposition rate, maneuverability, and excellent results when welding with half an inch-thick plates or plates thicker than 1 inch. For the former, flux-core arc welding produces fast and consistent results. For the latter, the high deposition rate allows flux-core arc welding to achieve strong and consistent final welds that will hold up under stress.

Furthermore, flux-core arc welding is used in many manufacturing and industrial environments because that work often takes place in the outdoors. Wind or other surface contamination doesn’t affect the quality of the weld by much, and self-shielding FCAW materials generate their own shields to protect weld integrity.

working outdoors

Welding for the Hobbyist

FCAW can be helpful for hobbyists because it doesn’t need to be used with a clean joint, and it works with contaminated welding surfaces much more reliably than MIG welding. You do need to remove excess moisture or oil from the welding site.

Flux-core arc welding can easily burn through mill scale or rust. This welding technique is further excellent for hobbyist welders because you don't need to use as much equipment if you pick a self-shielding electrode type.

You won't need an external gas source and will be able to carry your welding equipment around more easily. This will allow you to do more work in a cramped garage environment or outdoors.

Taking your welding outdoors is also a given, which is especially helpful if hobbyist welders don’t have space in their main shop for the process. Ultimately, FCAW is a great process for hobbyists for several reasons.

Flux-core Welding Equipment

You’ll use many of the same pieces of equipment for flux-core arc welding as you would for other welding techniques.

This includes basic welding safety gear like leather shoes or boots, fire-resistant jackets, leather gloves, a welding helmet, and safety glasses or a skullcap to protect your head.

leather gloves

All FCAW welders will use a flux-core welding electrode, which is hollow as opposed to solid. You’ll also need a good welding gun or torch, and you can use many of the same tools as you would with other welding processes. This torch will be air or water-cooled. 

You’ll need a CV power supply and a wire feeding system as well. Some FCAW welds generate a lot of material and can produce lots of smoke; this may require you to use fume extraction equipment if you weld in a confined indoor space.

Depending on the flux-core arc welding technique you’re using, you may also include a shielding gas.

About the Author Gregory

Hi, my name is Gregory! I have been welding practically all of my life and love it. As I have gotten older I have started to weld less and less, so in order to continue my love for welding I created this website. I like to write about my experiences and help you all become welders. I hope that you enjoy the site!

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