What is GMAW Welding?
GMAW, also known as MIG (Metal Inert Gas) or MAG (Metal Active Gas) welding, is one of the more commonly used welding processes among welders today. So what exactly is it?
GMAW (Gas Metal Arc Welding) is a welding process where a wire electrode is continuously fed through a welding gun to the weld site by the welder. All the while, a shielding gas is also supplied through to the welding site. This gas provides a shield around the weld site preventing external influences from weakening the weld.
The two biggest reasons why GMAW has become one of the most popular welding processes is thanks to its versatility and speed. The whole process can also be automated or semi-automated, making it ideal for both big and small businesses.
Some other advantages with GMAW include:
- A better weld bead appearance
- Lower heat input
- Less weld splatter and slag
- Minimal clean-up
- Compared to SMAW and FCAW, it produces a lot less harmful welding fumes.
- Lower cost electrodes
- Equipment is usually very affordable and easily accessible
- It provides good welds on a wide variety of base materials and thicknesses.
What are the different GMAW Metal Transfer Modes?
For GMAW, there are three main Metal Transfer Modes, along with a few variations. These modes include the following:
GMAW-S (Short-Circuiting Metal Transfer Mode)
GMAW-S is a metal transfer mode where a continuously fed wire electrode is deposited during repeating electrical short circuits.
- Can be used in all positions: Flat, Horizontal, Vertical-up, Vertical-Down, and Overhead
- Low heat input
- Electrode efficiency is very high
Globular Metal Transfer Mode
This next mode has a continuously fed wire electrode that is deposited with a combination of large irregularly shaped droplets and short-circuits.
- Uses inexpensive CO2 shielding gas
- Uses inexpensive Electrodes and equipment
- Can produce better welds at higher speeds
One thing to note with this transfer mode is that you will have more splatter.
Axial Spray Transfer Mode
In this mode, the wire electrode that is being fed continuously is getting deposited at higher energy levels. The higher energy level results in a stream of droplets that are sprayed across the arc. Advantages for the Axial Spray Mode include:
- Electrode efficiency is high
- A more extensive range of filler types
- Better weld fusions
- Less splatter
- Easier to cleanup
This mode also has some disadvantages that you should be aware of as well. It produces more welding fumes than the other metal transfer modes. Those welding fumes get nasty if you don't have the proper ventilation and could cause severe conditions like welder's lung. Also, you can only use this mode with two different welding positions, flat and horizontal.
GMAW-P (Pulsed Spray Metal Transfer Mode)
Pulsed Spray Metal Transfer Mode or, as it's also known, GMAW-P, is a variant of the Axial Spray Mode. GMAW-P cycles between high and low levels with the metal transfer occurring during the high energy levels with a single droplet instead of a stream.
- Little to no splatter
- Fast and easy cleanup
- Welds are less likely to get defects than the other metal transfer modes.
One thing to note with GMAW-P is that that equipment might be more expensive than the other methods.
Here are some frequently asked questions from our readers:
Q: What Equipment is Needed for GMAW
A: The equipment you'll need for GMAW is going to vary depending on what exactly you're doing. But here is a list of some of the essential stuff you'd most likely need:
- Welding Gun
- Wire Feed Unit
- Welding Power Supply
- Electrode Wire
- Shielding Gas Supply
Q: GMAW vs. SMAW
A: As most of you know, GMAW is a pretty fantastic welding process and can pretty much do anything that SMAW can. In most of the shops I've been to, GMAW was always the primary process that was used. However, I have found some circumstances where SMAW comes in handy.
For example, SMAW would be better in narrower spaces since you'll have trouble maneuvering the GMAW gun. Also, if you're outside and it's windy, SMAW is a better option. In my opinion, though, GMAW will always be a better welding process, especially since it is a lot more versatile and just a faster process overall.
Q: GMAW vs. FCAW
A: Like with SMAW, FCAW and GMAW will have certain situations where each one would do better than the other. Unlike with GMAW, welding with FCAW will produce slag over them due to the flux core. Using the flux core lets you be able to weld outside since you're not using a shielding gas to protect your welds.
The FCAW process can be useful as you can tell, but when it comes to something like welding on thin metal, it's nowhere near as good as GMAW. So again, this question mostly depends on what you would be welding.
More GMAW Resources
If you still have more questions, we’ve included a list of some great resources that should have the answers you need.
- PDF from Lincoln Electric that explains pretty much everything you need to know about GMAW welding
- Excellent beginner's video guide to MIG welding
- Troubleshooting and common problems with MIG welding
- Testing MIG welding techniques