Gas Metal Arc Welding (GMAW) is also known as Metal Inert Gas Welding (MIG welding). In this process, consumable electrode is used in the form of wire and a shielding gas such as Argon, Helium, Carbon dioxide or a mixture of these gases are used. These gases shield the molten weld pool from atmospheric contamination. The shielding gas is allowed to flow through the weld gun. Electrode of MIG welding (which comes in wire form) is fed continuously, at a fixed rate, by a feeding mechanism. The wire is consumed during the process and thereby provides filler metal. This process is illustrated in the below Figure.
Whenever Carbon dioxide is used as shielding gas in Gas Metal Arc Welding (GMAW). The term MAG (Metal Actve Gas) welding is used, because Carbon dioxide is an active gas. Whereas, other shielding gases such as Argon and Helium are inert in nature. Hence, whenever theses gases are used as shielding gas, the term MIG (Metal Inert Gas) welding is used
Selection of shielding gas should be done with lots of care. A mixture of CO2 and Argon is considered as a good combination. 75% Argon + 25% CO2 (very popularly known as “75/25” or “C25”) works as the best “all purpose” shielding gas for carbon steel. It results in least amount of spatter and proper weld bead.
100% carbon dioxide yields deeper penetration, but extra caution needed since it may increase the amount of spatters.
The equipment needed for GMAW set up are (Figure 1):
- Power Source
- Filler metal feeding Mechanism
- Welding Gun
- Shielding Gas
- Welding cables / leads and gas hoses
Figure – 1
In MIG welding, Voltage, Current and wire feed speed must be controlled for producing sound welding.
Voltage controls the weld profile. Whereas, Current controls the heat input, size of weld and the depth of penetration.
The following table (Table – 1) gives the relationship between current range and the filler wire feed speed, based on the filler wire diameter. This table is just a guide and the ranges may vary depending upon the shielding gas and parent metal.
Table – 1
Current Range (A)
|Wire feed speed (m/min)|
40 – 100
2 – 5
40 – 150
3 – 6
|3||1.0||100 – 280|
3 – 12
|4||1.2||120 – 350|
4 – 18
The following figure (figure – 2) shows a GMAW welding gun:
Figure – 2
Advantages of GMAW (MIG Welding)
- GMAW can be used to weld all commercial metals and alloys
- No restriction of limited electrode length as we face in shielded metal arc welding (SMAW).
- Due to the gas shielding, no additional flux is required for the protection of molten pool
- It can be used to weld in all positons.
- Higher deposition rates than shielded metal arc welding (SMAW)
- Due to the continuous electrode feeding mechanism, we can achieve higher welding speeds and higher filler metal deposition rates than shielded metal arc welding (SMAW)
- Due to the continuous electrode (wire feed) feed, longer welds can be deposited without intermediate stops and starts;
- Very less postweld cleaning is required due to the absence of any heavy slag;
- Comparatively easy to learn and less skilled welders can also do the MIG welding.
- This process can be easily automated
Limitations of GMAW (MIG Welding)
- The GMAW equipment is more complex, costlier, and less portable than that for shielded metal arc welding (SMAW)
- Due to the absence of flux covering, chances of faster cooling rates exists which may affect badly
- Shielding of molten weld pool is quite difficult during windy and drafty environments. High chances of porosity in the weld metal during windy environments.
- MIG welding requires moderate cleaning of joints prior to welding