MIG Welding

Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding.  MIG welding is a commonly used high deposition rate welding process.  Wire is continuously fed from a spool.  MIG welding is therefore referred to as a semiautomatic welding process. 

MIG Welding Benefits

•  All position capability
•  Higher deposition rates than SMAW
•  Less operator skill required
•  Long welds can be made without starts and stops
•  Minimal post weld cleaning is required

MIG Welding Shielding Gas

The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool.  There are three primary metal transfer modes:

•  Spray transfer (MP3 Audio)
•  Globular transfer (MP3 Audio)
•  Short circuiting transfer (MP3 Audio)

The primary shielding gasses used are:

•  Argon
•  Argon - 1 to 5% Oxygen
•  Argon - 3 to 25% CO₂
•  Argon/Helium

CO₂ is also used in its pure form in some MIG welding processes.  However, in some applications the presence of CO₂ in the shielding gas may adversely affect the mechanical properties of the weld. 

Weld Discontinuities

•  Undercutting
•  Excessive melt-through
•  Incomplete fusion
•  Incomplete joint penetration
•  Porosity
•  Weld metal cracks
•  Heat affected zone cracks