Flux Core welding is a type of Mig Welding that uses a hollow core electrode that is filled with a flux that will burn and melt over the weld to protect it from Oxidation while you weld. Welding with a standard solid core wire and Shielding Gas like Argon or CO2 is where the gas will flow over the weld to provide a shield from oxygen in the air while you weld.
Because Flux Core is often used by home and amateur welders only due to the additional cost of and difficulty getting shielding gas the methods that they might learn for shielded gas mig welding are a little different.
Flux Core welding is also very popular in the field because it does not require you to carry shielding gas to the worksite and if there is a breeze when you are welding with shielded gas Mig you will often find that the shielding gas is blown away. Flux Core is much more forgiving because it is a flux that melts over the weld.
Because of all of these factors whether you are welding outside or in a shop or if you are a weekend warrior that just has the cheapest setup vs a professional in a welding shop or body shop that has access to everything necessary at all times. These differences can cause confusion when you learn to weld one way for shielded gas and then try to weld with flux core. The same is true when you go the other way from flux core to shielded gas mig welding there will be differences in your technique that you need to change or you are likely to say that one or the other type of welding is not as good as the other.
Now honestly Shielded Gas Mig is always going to produce a better product because there is much more control and variation in the equipment. Normally with shielded Mig you can weld many different types of metal and different thicknesses. Everything from very thin sheet metal without blowing holes in it right on up to very thick steel bar or stainless steel or aluminum. However Flux Core can provide you flexibility in other ways.
Stacking Dimes and Pushing The Puddle
Welds that are of a good quality also look very nice. You might see exposed welds on different products that you buy or equipment where you think a robot must have made that weld. Often it is a robot but just as likely it is a highly skilled craftsman that has learned to control their welding equipment. Many people will tell you ugly welds hold just as good as pretty ones but Ugly Weld are really an indication of bad welding.
Normally when you weld you will clamp or secure your pieces to be welded and then you might also place some small tack welds to make sure thin material won’t warp or that your pieces will be held where you want.
When you begin welding you will start at one end of the weld and work your way directly through to the other or finish end of the weld without stopping if possible. Anytime you stop you are causing yourself problems with difference in the temperature of the metal when you restart your weld. Unfortunately a lot of people have been taught incorrectly that you make a 1 inch weld then jump to another part and make a 1 inch weld and eventually they will all make a completed weld. This is bad practice and can effect the strength of the weld along with other aspects. When someone is doing this it is normally because they lack training in how to set their heat and wire feed controls properly to match the metal they are welding or because they are using a welder that does not have good controls.
When you start your weld you will allow the electrode wire to contact your work piece and it will form a small pool of molten metal called the bead. From this point on you should hold your electrode so the tip just barely comes into contact with that bead of hot metal. If you pull away your arc will go out. If you penetrate the bead you will have splatter. You will be moving the electrode in a very small circular pattern that looks like you are writing cursive oooooooos and this will allow the electrode to progress down the weld while looping back into the hot pool of the bead to form a continuous weld.
This is where the difference between shielded and flux core Mig Welding techniques differ.
When you are using shielding gas you want to push the bead. Meaning you have your welding tip pointed at an angle so that the cone of the tip is pointed towards fresh unwelded material and you are pushing the bead down the surfaces using your circular ooooo pattern.
When you are using Flux Core electrode then you should reverse the angle of the welding torch so that the cone of the torch is pointing back at the weld you just completed and this is called pulling the bead.
The reason that you should reverse your torch tip is that you are not using shielding gas you are relying on the flux core of the electrode to protect the weld from oxidation.
When you use shielding gas the tip of the torch actually forces gas out onto the material that you are welding so you want the gas to be forced out along fresh new metal as you weld.
In practice you might find that you still need to change the position of your torch head to allow you to weld with more control however this is the premise behind Flux Core welding.
If you are using Flux Core and have your torch pointed at fresh metal that has not been welded yet then the flux is protecting a much smaller area while you weld. If you point it back towards the weld you just laid down then when you loop back into the bead and go out onto fresh unwelded area you have more protection from the flux core because you are always welding into the bead instead of welding away from the bead.
Final Note
Like said above there are situations where you must weld the way you must weld and in vertical or overhead positions it may not be the best way to weld by pulling the bead but if possible you should always weld by pulling the bead and into it to allow the flux to protect your weld from oxidation.
Welding takes a lot of practice before you can gain the skills to produce welds that are dependable.
If you are new to welding then you should pick up a few spools of wire and spend a few hundred hours pushing and pulling beads, checking your welds for full penetration and welding different types of materials.
Something as easy as you might think welding dissimilar thickness of metal can be very hard to master. Such as welding 1/8th inch brackets on 1 inch thick steel plate. You have to understand that the thicker material will not heat up at the same rate as the thinner material and it might require that you preheat the thicker part so that good penetration will happen.
In the field of professional welding there are inspections of welds where xrays and microscopes are used to inspect welds that are critical. If you are a weekend warrior welding your F150’s frame with a patch you won’t have someone to inspect your work so its important that you understand what is and what isn’t a good weld. This takes a lot of practice and honestly it does take someone teaching you vs learning on your own. With practice it is very doable for most people to create welds that are safe and dependable but without proper technique, cleaning your parts, using the right electrodes, checking for penetration then you won’t be able to trust your work. If you have very few hours welding and your work looks ugly there is probably a reason for it. Be Safe and get help when you need it.