How to flux core weld?

Flux core welding, often referred to as FCAW (Flux-Cored Arc Welding), is a versatile and widely used welding technique that has many advantages. This method uses a flux-cored wire electrode. This article will provide you with a comprehensive step-by-step process of flux core welding and also give you some tips to flux core weld efficiently.

See also: What are the different types of welding defects?

 

Why is flux core welding done?

It protects the weld

The most important job of the flux is protecting the weld. When burned, it produces a shielding gas that protects the weld area from atmospheric contamination. Some wires need an external shielding gas to give enough gas coverage for this protection.

Adds alloys

The flux also adds alloys into the weld metal to improve certain aspects of the finished weld. Along with these alloys, flux has deoxidisers added to prevent the weld puddle from oxidising.

Slag protection

Another important job of the flux is the creation of a thin layer of slag over the weld. The slag protects the weld metal from the atmosphere as it cools it slowly and helps shape the weld.

Stabilise the arc

The flux can stabilise and control the welding arc. A side effect of smoothing and stabilising the welding arc is reducing the spatter.

 

Key components of flux core welding

• Power supply: Flux-core welding requires a constant voltage power supply to operate the welding gun.
• Wire feeder: A wire feeder is used to feed the flux-core welding wire through the welding cable to the welding gun.
• Welding gun: The welding gun transfers electricity through a copper contact tip to the flux-core wire.
• Work lead clamp: This clamp, also known as the ground clamp, provides the electrical connection to the workpiece.
• Flux core welding wire: The flux-core wire acts as both the electrode and filler metal in the welding process. It is a unique wire filled with flux.
• Shielding gas: In some cases, an external shielding gas is used to provide additional protection to the weld area. This is common in gas-shielded flux-core welding.

 

How does flux core welding work?

Arc formation

When the flux-core wire contacts the base metal, an electric arc forms. This arc melts the base metals and the wire, creating a weld puddle.

Flux combustion

As the wire melts, the flux inside it burns, generating a shielding gas that protects the weld from atmospheric contamination.

 

Science behind flux core welding

• Unique wire: Flux-core welding employs a special tubular wire filled with flux, setting it apart from other wire-feed welding processes such as GMAW and SAW.
• Flux core wire: The wire used in flux-core welding acts as both the electrode and filler metal, but it has a hollow centre filled with flux.

 

FCAW vs GMAW

• Unlike GMAW (Gas Metal Arc Welding), which relies on external shielding gas, flux-core wire (FCAW) contains flux that provides both protection and alloy elements for the weld metal.
• Flux-core wires come in compositions suitable for welding various base metals, including carbon steel, stainless steel and alloy steel.
• Flux-core wire is produced by forming a thin metal strip into a ‘U’ shape, filling the centre with flux, and then shaping it into a tubular wire of the required diameter.
• The outer shell of the flux-core wire, also known as the ‘sheath,’ serves multiple functions: conducting electricity, supplying filler metal, and safeguarding the flux from moisture or contamination.

How to flux core weld?

Gather supplies and equipment

Source: Pinterest (The Home Depot)

 

• Before starting flux core welding, ensure you have the necessary equipment and supplies.
• You will need a flux core welding machine, suitable safety gear (such as a welding helmet, gloves and a welding jacket), welding wire, wire brush, pliers and a chipping hammer.

Prepare the workspace

• Having a safe and organised workspace is essential for successful flux core welding.
• Ensure good ventilation to disperse welding fumes.
• Clear the area of any flammable materials and have a fire extinguisher on hand.
• Set up your welding machine according to the manufacturer’s instructions.

Metal and wire selection

Source: Pinterest (Instructables)

 

• Choose the metal you want to weld and choose the corresponding flux-cored welding wire.
• Check the wire manufacturer’s recommendations for the specific type and thickness of the metal.
• Ensure that your welding wire matches the metal you are working on and has strong and durable welds.

Set the voltage and amperage

• Adjust the voltage and amperage settings on your welding machine based on the metal thickness and wire diameter.
• Proper settings according to the manufacturer’s instructions are necessary for getting high-quality welds.

Use the pull technique

• Use the ‘pull’ technique, which involves moving the welding gun away from the direction of welding. This technique ensures proper shielding of the weld pool and reduces the risk of defects in the weld.

 

Flux core welding: Tips

1. Maintain proper drag angle: Depending on your welding position, the drag angle should be between 15 to 45 degrees for flat, overhead and horizontal positions and five to 15 degrees for vertical positions.
2. Avoid burnback: Prevent the wire from melting into a ball at the end of the contact tip (burnback) by adjusting the wire feed speed and keeping a distance between the welding gun and the metal you are working on.
3. Prevent bird nesting: Bird nesting happens when the wire becomes tangled and cannot feed properly. To avoid this, use U-groove or knurled-V wire instead of GMAW wire.
4. Keep marks at the top of your weld: Worm tracking or marks at the top of your weld can be avoided by using the correct settings recommended by the filler metal manufacturer. If it still happens, gradually reduce the voltage.

 

Flux core welding: Precautions

• Ensure proper ventilation and wear the appropriate safety gear, including a welding helmet and gloves.
• Keeping flammable materials away from the welding area.
• Know the location of fire extinguishers and how to use them in case of an emergency.

 

FAQs

What is the process for flux core welding?

To flux core weld, select the appropriate machine settings, prepare the metal surfaces, position the electrode wire and create a consistent weld bead while maintaining a proper travel speed.

Is flux core welding good for beginners?

Flux core welding can be suitable for beginners due to its ease of use, especially in outdoor or windy conditions but it requires practice to get quality welds.

Can you weld flux core without gas?

Yes, flux core welding can be done without external shielding gas, as the flux in the wire provides its own shielding.

What is the pull technique in flux core welding?

The pull technique is moving the welding gun away from the direction of welding to ensure proper shielding of the weld pool.

Is flux core welding AC or DC?

Flux core welding is typically done with DC (direct current) power sources.

What is the angle for flux core welding?

For flux core welding, a common angle is a 15-45 degree drag angle, where the gun is tilted back slightly from perpendicular to the workpiece, but this can vary based on the specific welding situation and joint configuration.

What size is flux core wire?

Flux core welding wires come in various sizes, with common diameters being 0.030 inches (0.8 mm) and 0.035 inches (0.9 mm) but other sizes are available depending on the welding application.

Is flux core a MIG?

Flux core welding is similar to MIG welding in that both processes use a continuous wire feed, but the key difference is the type of wire and shielding method. MIG welding uses a solid wire with external shielding gas, while flux core welding uses a tubular wire with flux inside, providing its own shielding. So, while they are related, they are not the same.

Got any questions or point of view on our article? We would love to hear from you. Write to our Editor-in-Chief Jhumur Ghosh at jhumur.ghosh1@housing.com