Flux core welding or FCAW is one of the most widely used welding methods, especially for beginners. It’s a viable welding method for a wide range of uses, including heavy equipment fabrication, repair, structural building, etc. One of the best things about flux core welding is it doesn’t require an extra gas supply like regular MIG welding.
Although it’s fairly easy for beginners to start flux core welding, there’s a lot to know to lay down a successful weld. Using a flux core welder can be a piece of cake once you understand how it works and you get the basic technique down.
In this article we provide some key flux core welding tips to help you level up your skills quickly and get the job done better.
#1 Safety First!
No matter what you’re welding or how you’re doing it, taking safety precautions with the right personal protective equipment (PPE) comes first. You must use a welding helmet with a full-face auto-darkening shield because flux core welders throw off a lot of spatter and UV light. The cheapo handheld shield that comes with many flux-cored MIG welders is useless and doesn’t offer the protection needed for your skin or eyes.
Your PPE for flux core welding should also include a full-sleeve leather jacket, a pair of welding gloves and steel-toed rugged boots. Don’t skimp on your protective clothing — especially your gloves — or you may suffer some pretty bad burns.
#2 Metal and Workplace Preparation
First, clean the metal of any dust, dirt and grime. Grind away any paint or rust until you see bare metal. Use an angle grinder with a flap sander wheel, wire brush or paint and rust stripping disk. Preparing the metal is essential if you want a strong joint between the pieces!
Next, prepare the workplace around your welding area. Clear your welding table and the ground around where you’re welding of any dust, metal scrap and shavings. Remove anything flammable from the area. That includes rags, fuel, oil, wood…even your lunch bag! (IMPORTANT: It’s always critical to have an ABC class fire extinguisher within reach when welding. Things light on fire quickly from red hot metal!)
Finally, securely attach the ground clamp to your welding table (if it’s metal), or the larger piece of base metal you’re welding to. Make sure the ground clamp has an excellent connection to bare metal or you won’t get a good arc. That means grinding or sanding away any surface gunk, rust and paint just like the weld area.
#3 Equipment Preparation
When it comes to preparing your welding machine and welding gun, there are a few things to consider depending on what type of metal you’re working on.
The first thing you want to consider is the type of flux cored filler wire (electrode), including the wire diameter and spool size. For most beginning to intermediate welding projects you want to use a self-shielded flux core wire (FCAW-S wire). This completely eliminates the need for a gas cylinder. As a starting point you want to use 70 KSI tensile strength wire for mild steel, and anywhere between 80-120 KSI tensile strength wire for alloy steel like chromoly. 0.30 inch wire is good for thin pieces in the 1/8 inch to 3/16 thickness range. For 1/4 inch plate and up you want 0.45 inch wire if your MIG welder can handle it.
Next, check the tip of the welding gun and make sure it’s intact and isn’t malformed, full of slag or heavily burned. You can usually file off the surface burn. But if the contact tip is oval or has dents and welded bits attached to it, throw it out and screw a new one in. They’re cheap so don’t skimp on this because it will affect your welds a lot.
#4 Proper Wire Feeding
For your welder to work right and deliver a consistent strong weld, your machine must feed the flux-cored wire smoothly. Open the side door of your machine and inspect the wire drive roll. The wire should be wound in an even pattern, with no crosses or kinks evident at the roll itself.
Then take a look at the wire feeding mechanism. This has 2 wheels with a spring tensioner that pulls the wire from the wire roll and pushes it down the wire feed line to the gun. A knurled drive feed wheel instead of a plain one can help the wire feed smoothly without slipping. Be careful not to over-tighten the tensioner — if you do it will ovalize the wire and cause it to hang up in the wire feed line.
If any pieces are worn out, broken or misaligned, be sure to replace or fix them before you start welding. The wire feed mechanism is one of the few moving parts on a MIG welder and these things do wear out after awhile.
#5 Welding Current Settings
Not every metal requires the same current settings and the same amount of heat. You must use the right current setting in voltage or amperage for the metal thickness, welding speed and angle between the parts.
The same goes for the wire feed speed; it entirely depends on the voltage / amperage and the thickness of the metal you’re welding. If the current is high, the flux-cored wire speed may also need to be set higher.
The best piece of advice is to start with the manufacturer’s suggested base settings for the metal you’re welding and flux-cored wire diameter in your welder. There should be an easy-to-read table inside your welder’s access door or manual that tells you exactly what settings to use.
Most modern flux-cored MIG welders do an excellent job of modulating the current to ensure you get a good arc and penetration with the standard settings, as long as they match the metal type, thickness and wire you’re using. Older welders may require you to play around with the settings more. A few test runs on some equivalent scrap metal before you start welding the workpieces will help you dial in your machine.
If you’re using self-shielded flux core wire (FCAW-S) it’s very important to set your machine to straight polarity (direct-current electrode negative, or DCEN). This type of wire is specifically designed for DCEN polarity and will result in the most stable arc and best quality weld.
#6 Weld Angle and Drag
Different welding angles require a different technique with flux core welders. Most of the time, with a flux core welder, you drag the gun backward instead of pushing it forward.
With a typical flat weld, you should hold the gun at 90° to the workpiece and about 10° tilted to the back.
For lap joints, it will be about 60° to 90° angled to the workpiece.
For vertical joints, you should flux-core weld at about a 10° to 15° angle with 10% lower power setting.
#7 Cleaning the Slag
After a weld is complete, you have to chip off the slag left behind. Use a chipping hammer to do the job then use a wire brush to clean the bead properly before you weld any further.
Failing to clean off the slag properly may cause subsequent welds to attract the slag and get pits and inclusions in the weld. This dramatically reduces the weld strength because slag is brittle and oxidized — essentially useless in a high-tensile strength situation.
Get Your Weld On!
A good quality flux-core welding machine comes with a lot of conveniences including great portability, a value price and usability over a wide range of situations. Flux-cored wire fed automatically from a MIG gun is simple to use and can produce excellent welds with a bit of practice. We hope you get some excellent value from these flux-core welding tips.
Nick Klamecki is a certified Fire and Workplace Safety expert with 15 years experience in product research and testing. He has a degree in Economics from U.C. Davis, is an active outdoorsman and spent years ensuring the safety of special needs children. Nick researches and tests workplace, industrial and safety products and provides advice on their safe use.