Both MIG and MAG welding fall under the common name "gas metal arc welding" or GMAW.
However, MIG (metal inert gas welding) and MAG (metal active gas welding) have one significant difference — the type of used shielding gas.
In this article, we'll examine the difference between the MIG and MAG welding processes and explain what each is meant for.
Photo by @cirizawelding
How GMAW Works in Short
Gas metal arc welding (both MIG and MAG) joins metal by using a consumable electrode (solid wire) under the protection of a shielding gas.
The solid metal wire is pushed via an automated wire feeder through the MIG gun and energized via a power source. Small, portable, inverter-based MIG welders usually combine a wire feeder and a power source into one unit — the MIG welding machine.
For example, our YesWelder YWM-200 supports the MIG welding process because it has a wire feeder inside the unit, and an inverter-based power source that provides the necessary voltage and welding power in the wire.
GMAW works by short-circuiting electricity released from the welding machine. The ground clamp is attached to the positive terminal, while the MIG gun is negative. So, once you grip the welded material with the ground clamp and the positive wire (coming from the MIG gun) touches the metal, the electrical short occurs, melting the wire and a piece of the welding joint. Metal melts due to internal resistance to the flow of electrons in the circuit.
Source from: https://sparcwelders.com/blogs/news/why-welders-use-argon
As the wire melts away, it deposits a metal droplet into the joint. Then, the wire feeder pushes more wire to short with the metal, and this process keeps repeating many times per second. This gives GMAW its characteristic sizzling sound and causes the spatter. Every time the wire shorts with the grounded metal, the sparks and spatter fly around because shorting works like a small explosion.
Photo by @welderman_alex
This is why the most common GMAW metal transfer method is called "short circuit metal transfer." There are also other GMAW transfer methods like spray, globular, and pulse transfer. But, these are more advanced and out of this article scope. You can read about Pulsed MIG welding here if you want to learn more.
MIG - Metal Inert Gas Welding Process
MIG welding uses inert welding gas to shield the weld puddle from atmospheric contamination. Inert gasses like argon and helium don't chemically interact with the molten metal, so they don't influence the weld to a large extent.
You need to use 100% argon to weld non ferrous materials like aluminum, magnesium, copper, and nickel or its alloys. But, you cannot use 100% argon gas to weld ferrous metals like steel. We'll talk about this soon when we get to the MAG welding.
Source from: https://www.quora.com/Can-you-make-a-weld-with-100-argon
Argon gas produces a favorable atmosphere in the weld puddle that's very easy to ionize, so keeping a long arc with lower voltage is relatively easy.
Helium can be added to argon to increase arc heat, puddle fluidity, and weld penetration. You can also use 100% helium if welding very thick sections of aluminum or magnesium, but this will reduce arc stability.
MAG - Metal Active Gas Welding Process
MAG welding uses active gas or a combination of active and inert gasses. Active or reactive gasses directly influence the weld penetration, puddle fluidity, arc stability, weld spatter, and the resulting bead.
The two most commonly used reactive shielding gasses for MAG welding are oxygen ("O2") and carbon dioxide ("CO2"). Oxygen is only used as an addition to argon, while it's possible to weld with 100% CO2.
Source from: https://www.mig-welding.co.uk/forum/threads/custom-gas-mix.1944/
You cannot efficiently weld steel with 100% argon because the uneven iron oxides on the steel surface emit electrons that attract the arc in unpredictable directions. As a result, the weld deposits are irregular, and it becomes challenging to create a uniform weld.
Mixing oxygen with argon creates a reaction on the steel surface that results in a uniform iron oxide surface. This provides a stable path for the arc to follow and allows you to lay beautiful welds.
However, it's rare for regular folks to use oxygen and argon bland. Carbon dioxide provides an excellent substitute for oxygen.
You've probably heard about an argon and carbon dioxide blend numerous times because 75% argon and 25% CO2 is the most common shielding gas employed in GMAW.
Source form: https://weldguru.com/mig-welding-with-100-argon/
Adding carbon dioxide to argon creates a more favorable weld bead and a deeper penetration. Plus, the arc is more stable if using argon/CO2 than argon/O2.
However, you should use a MIG welding wire that contains deoxidizers to prevent reactive gasses like oxygen and carbon dioxide from causing porosity. For example, the YesWelder Carbon Steel MIG ER70S-6 solid wires contain enough manganese and silicon deoxidizers so that they can even be used with a 100% CO2 shielding gas.
Speaking of which, MAG welding with a pure CO2 gas produces very deep weld penetration, but it does cause more spatter and produces slightly less appealing welds compared to the 75/25 mixture discussed earlier. If you have enough skills to weld with a very short arc, you can mitigate the increased spatter. Just make sure you use a wire designed for welding with 100% CO2.
While most people use MAG welding more often than MIG welding, almost everyone calls both processes MIG welding. While this is technically incorrect, it has become somewhat of a norm in the industry to refer to all GMAW processes as MIG welding.
This causes little to no harm in everyday welding work. So, most people just stick to MIG welding as their go-to name for the process. Since there isn't a significant apparent difference, and most professionals know exactly which shielding gas to use with every metal, using the MIG welding term for both MIG and MAG is deemed acceptable.
It's not like a certified welder would use straight argon to weld steel if someone would ask them to MIG weld it. Instead, they'd know to use either straight carbon dioxide or a mixture with argon, which is technically MAG welding.