Instructions / Assembly

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GMAW
The gas metal arc process is dominant today as a
joining process among the world’s welding fabrica-
tors. Despite its sixty years of history, research and
development continue to provide improvements to
this process, and the effort has been rewarded with
high quality results.
This publication’s purpose is to provide the reader
with the basic concepts of the gas metal arc welding
(GMAW) process, and then provide an examination of
more recent process developments. Additionally, the
reader will find technical data and direction, providing
the opportunity to optimize the operation of the
GMAW process and all of its variants.
Process Definition
Gas Metal Arc Welding (GMAW), by definition, is an
arc welding process which produces the coalescence
of metals by heating them with an arc between a con-
tinuously fed filler metal electrode and the work. The
process uses shielding from an externally supplied
gas to protect the molten weld pool. The application
of GMAW generally requires DC+ (reverse) polarity to
the electrode.
In non-standard terminology, GMAW is commonly
known as MIG (Metal Inert Gas) welding and it is less
commonly known as MAG (Metal Active Gas) welding.
In either case, the GMAW process lends itself to weld
a wide range of both solid carbon steel and tubular
metal-cored electrodes. The alloy material range for
GMAW includes: carbon steel, stainless steel,
aluminum, magnesium, copper, nickel, silicon
bronze and tubular metal-cored surfacing alloys.
The GMAW process lends itself to semiautomatic,
robotic automation and hard automation welding
applications.
Advantages of GMAW
The GMAW process enjoys widespread use because
of its ability to provide high quality welds, for a wide
range of ferrous
and non-ferrous alloys, at a low price.
GMAW also has the following advantages:
•
The ability to join a wide range of material types and
thicknesses.
• Simple equipment components are readily available
and affordable.
•
GMAW has higher electrode efficiencies, usually between
93% and 98%, when compared to other welding processes.
• Higher welder efficiencies and operator factor, when compared
to other open arc welding processes.
• GMAW is easily adapted for high-speed robotic, hard
automation and semiautomatic welding applications.
• All-position welding capability.
•
Excellent weld bead appearance.
• Lower hydrogen weld deposit — generally less than
5 mL/100 g of weld metal.
• Lower heat input when compared to other welding processes.
• A minimum of weld spatter and slag makes weld clean up fast
and easy.
• Less welding fumes when compared to SMAW (Shielded
Metal Arc Welding) and FCAW (Flux-Cored Arc Welding)
processes.
Benefits of GMAW
• Generally, lower cost per length of weld metal deposited when
compared to other open arc welding processes.
• Lower cost electrode.
•
Less distortion with GMAW-P (Pulsed Spray Transfer Mode),
GMAW-S (Short-Circuit Transfer Mode) and STT™ (Surface
Tension Transfer™).
•
Handles poor fit-up with GMAW-S and STT modes.
• Reduced welding fume generation.
• Minimal post-weld cleanup.
Limitations of GMAW
• The lower heat input characteristic of the short-circuiting
mode of metal transfer restricts its use to thin materials.
• The higher heat input axial spray transfer generally restricts its
use to thicker base materials.
•
The higher heat input mode of axial spray is restricted to flat
or horizontal welding positions.
• The use of argon based shielding gas for axial spray and
pulsed spray transfer modes is more expensive than 100%
carbon dioxide (CO
2
).
Gas Metal Arc Welding