Flux Core VS Hard Wire MIG Welding | Everything You Need To Know

by Steve Darnell

Flux core and hard wire MIG welding has it’s benefits and differences. Every welder has their preferences, but I like to use both depending on the circumstances I am in. I’ll go over everything you need to know between the two. I’ll be using the same 110V welder for both so you can directly see how they perform and weld differently.

If you’re just getting into welding and are looking for a machine to get you started I recommend finding a welder with the option to run 110V or 220V. This will up the duty cycle of your machine. If you’re not sure what duty cycle means I’ll explain. This 110V welder I have here has a duty cycle of 12 minutes within the hour meaning you can weld continuously for 12 minutes before the machine shuts off. It will usually trip a breaker and the time can vary depending on how high you turn up the machine. For example, if I turn this welder all the way up and start welding, it will probably go for one minute before tripping a breaker. Duty cycle is important if you plan on doing a lot of welding. 110V are great for repair work and wrought iron welding. If you plan on buying a 110 welder be sure to check that it has a provision for gas because the option will be there if you ever need it when you want to run hard wire through your machine.

Flux Core

Flux core wire
Flux Core Wire

Its called flux core because there is flux in the core of the wire. I know, shocking. There’s no need to use gas when you weld because of the flux inside. Welding with this wire can be tough to make your welds consistently look good because it gets smoky, slag bounces everywhere, isn’t a clean weld and requires more clean up after. Welding with flux does have its benefits though. You can weld wherever you want and you can weld with wind. If you were to try and weld with hardwire when its windy your gas will be thrown all over the place with impurities on your weld and nothing but porosity which can be a train wreck.

On your flux core there is another wire I call dual shield. What this is is a flux core that runs consumable shielded gas where you can weld some big projects with. The penetration here is unbelievable and when finished, it leaves a flux slag on top of the weld. I’ll plan to show you how dual shielding works in the future.

Now we’re going to weld with flux core so you can see what it looks like. For those of you that haven’t taken the Welder 101 course, included in the course are metal tabs I send to you ready for you to practice welding different types of joints. Here we’re going to be welding T joints. Remember when you’re getting ready to weld to wear a long sleeve shirt because this flux core is extremely bright and will flash burn you quickly.

Flux core weld pre wire brush
Flux Core Weld Pre Wire Brush

Normally when I weld with flux I will take the tip off because you don’t need shielded gas and the tip is for your shielded gas. Make sure you have a good ground and if you can, ground it to your work piece because this will make it better. After putting a tac on each end you can already start to see it leaves a lot of dust, but that’s just part of the flux burning in there. A friendly reminder that anything with slag you will typically drag and not push because that slag will end up coming off and get on top. The slag is part of the welding process.

After this flux core weld you can see that it looks dirty and sloppy. This is what your average weld will come out to. You can be an excellent welder and still not be able to prevent slag being thrown everywhere. All of the flux is burning and that’s exactly what you see here with the final weld.

flux core weld post wire brush
Flux Core Weld Post Wire Brush

I’m going to take a wire brush and go down through the middle so you can actually see the weld that is under the flux. Don’t underestimate the flux core welding because it is very hot and penetrates well. You can see the heat line when I flip it over on the bottom. This is where it actually penetrates into the plate and this tells me that the weld is hot and that there’s not a ton of undercut in there where it’s going to break off. This ends up being a decent weld.

Plate Penetration

Switching the Machine

I’m going to show you the process of switching the machine so you can see what your 110 welder will do if you want to run the flux or shielded gas. Here are the steps described when switching over:

1. Unplug your machine

2. Change your wire and reverse polarity

Whenever you’re welding with flux core you need to remember that right now your positive lead is running negative and your ground becomes your positive. When you reverse polarity with hardwire it switches it. Ground goes back to ground and positive back to positive.

How polarity works is when you switch to hard wire and start welding, your ground works as a magnet to the hard wire that comes out of the machine so when you weld it penetrates and pulls it in. If you’ve ever welded with the polarity the wrong way it looks really crusty, dry and hard and the weld kind of sits up on top of the material. It doesn’t impregnate itself into the material so make sure your polarity is set right.

Now switch your leads like shown in the image.

3. Replace roll wire

Release the tension on your wire and I’ll show you the difference between the drive rollers on hard wire and on flux core. Open it up and take the wire out, but be cautious because normally these wires will spring everywhere and you can waste all your wire so make sure to tie it up.

Drive motor and drive roller
Drive Motor and Drive Roller

Now inside the machine you have your drive motor and drive roller wheel. You can see it bites into the wire and it pushes through the liner. With hard wire it’s more smooth.. Typically you will have to change your driver roller to the hardwire one, but for the purpose of the video tutorial I wont be doing that here. You can notice I don’t have a lot of tension on the drive motor because the problem especially with flux core is it will wear out the motor and crush your wire.

After you feed your hard wire into the machine and everything is lined up you will need to run the wire through the gun. Put the tip back on and make sure to run the nozzle. Tune into the video to see the entire process.

4. Apply gas and check your gauges

I like to run argon cO2 mix because it cleans up the metal when you weld and makes for a cleaner weld. You’ll need this gas for shielding to keep the atmosphere of the humidity. Make sure to check your gauges. I like to run my pressure anywhere from 25-30.

Hard Wire

When I weld with the hard wire I’m going to push. You can see with my first weld that my voltage was getting weak at the end. Nonetheless, you can still see a major difference between flux and hard wire. My second weld is solid as I’m moving along trying to really roll with it. I quickly weld the next one because I want to show you what it looks like with heat in the metal and we’ll see the difference in penetration. You can see I’m moving along faster and it’s absorbing easier because there’s so much heat in the material.


Keep in mind if you have a 110 welder to think about your voltage because you don’t have a lot like a 220. You can see the difference between preheating your metal versus running it cold. This is why I recommend investing in a 110 and 220 welder. Preheating becomes very important depending on the scope of certain projects.

If you enjoyed this video there is more where this came from inside my welder101 course. Feel free to check out my free training video here!

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