What is Flux Core Welding?


There is a lot to choose from on the menu of welding methods and some may ask, what is Flux Core (FCAW) welding? It’s a welding process powered by Direct Current (DC) that uses a continuous feed, consumable tubular wire to generate an arc that fuses the wire and material into the weld joint. The entire arc area is covered by a shielding gas, which is produced during the process, along with liquid slag that protects the weld pool from the atmosphere. Depending on the filter, FCA can be used with or without an additional shielding gas.

Flux Core Welding is very similar to the industry workhorse, Gas Metal Arc Welding (GMAW) or Metal Inert Gas (MIG) welding, with the exception of the wire and the need for constant voltage. FCAW is often used for welding structural steel, heavy equipment repair, and bridge construction, among other applications.

When explaining what goes into this main course in the fabrication industry, it’s important to note that the process is:

  • Fast – up to 25 deposits per hour
  • Flexible/mobile – flat, overhead, horizontal, vertical, forehand and backhand welding positions and techniques can be used.
  • Hearty – welds dirty and rusty metals.
  • Low-skill level – relies heavily on precise machine set-up, but otherwise referred to as a “point and shoot” method.
  • Wind-resistant – the welding process produces its own shielding gas, known as self-shielding. When used with additional gas, it’s known as dual-shielding – usually a mixture of 75% Aragon Gas and 25% Carbon Dioxide Gas.

The Golden Arc

The Flux Core Welding process – developed during the 1950s – is virtually interchangeable with MIG welding, including the machine. There are, however, a few differences between the welding methods. Unlike the solid MIG wire, the consumable filler wire used during the FCAW process is like a mini-rod, covered with metal and filled with flux material and metal powder. The constant DC power helps stabilize the arc, even during windy conditions.

The flux melts, along with the material inside the wire. That generates slag cover, nitride forms and helps de-oxidize the weld pool to prevent contamination. The ability to weld without using a shielding gas is what makes the Flux Core welding method so popular. It allows fast welding, which leads to high production.

In a Fog

There are drawbacks to Flux Core Welding. The melting flux and slag kick up such a fog of smoke and gasses that it is difficult to actually see what you’re welding. The slag can easily be removed with a wire brush or chipping.

Holding the Line

Flux Core Welding is less efficient than some other welding methods. It depends on what type of wire you’re using, and whether the wire feed is properly set up. A slow wire feed can lead to “burn-back,” when the wire melts into a ball at the end of the contact tip or “bird-nesting,” when the wire gets tangled.

A welder must be skilled enough to keep the tip from touching the base metal, so as not to fuse the hole in the wire. Managing the slag cloud can also be difficult. The gasses must be allowed to escape the weld area before the metal hardens — otherwise it causes porosity and holes in the weld.

A sure, steady hand, and proper machine set-up are needed for Flux Core Welding, but it’s a sure-fire way to get a lot of solid welding done quickly.

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For more than 70 years, LeJeune Steel has been an industry leader in steel fabrication. Since 1944, we have grown to become one of the largest structural steel fabricators in the Midwest, with more than 40,000 tons of steel fabricated annually by our shops in Minnesota and Wisconsin.