Gas Metal Arc welding is an arc welding process that uses an arc between a continuously-fed filler metal electrode and the weld pool. Shielding from an externally supplied gas and without the application of a pressure. It is also known as MIG welding (Metal Inert Gas) refers to the use of an inert gas while MAG (Metal Active Gas) welding involves the use of an active gas (i.e. carbon dioxide and oxygen).

1. GMAW Or MIGGMAW Or MIG
By: SURESH KUMAR MEENA

2. Introduction
Gas Metal Arc welding is an arc welding process
that uses an arc between a continuously-fed
filler metal electrode and the weld pool.
 Shielding from an externally supplied gas and
without the application of a pressure.
It is also known as MIG welding (Metal Inert
Gas) refers to the use of an inert gas while MAG
(Metal Active Gas) welding involves the use of
an active gas (i.e. carbon dioxide and oxygen).

3. Principles of GMAW
• Usually operates on direct current electrode positiveUsually operates on direct current electrode positive
(DCEP) or direct current reverse polarity (DCRP).(DCEP) or direct current reverse polarity (DCRP).
• A wire is used as an electrode and a welding arc is struckA wire is used as an electrode and a welding arc is struck
between the electrode and the base metal.between the electrode and the base metal.
• The molten puddle is shielded by an external shielding gasThe molten puddle is shielded by an external shielding gas
which may be inert gas or active gas .which may be inert gas or active gas .
• An operator may ‘push’ or ‘pull’ the welding gun dependingAn operator may ‘push’ or ‘pull’ the welding gun depending
on the mode of metal transfer and whether the desiredon the mode of metal transfer and whether the desired
result is increased penetration or a smoother appearance .result is increased penetration or a smoother appearance .
• The process is controlled by a constant voltage, which isThe process is controlled by a constant voltage, which is
set by the welder.set by the welder.

4. Typical Set-up of GMAW

5. Equipment
To perform gas metal arc welding, the basic
necessary equipment is are
• Welding gun
• Wire feed unit
• Welding power supply
• Electrode wire
• Shielding gas supply

6. GMAW Gun

8. POSITIVE
TERMINAL
NEGATIVE
TERMINAL

9. Power Source
 GMAW, the output characteristics fall into two main
categories:
(a) Constant current
(b) Constant voltage
 Alternating current is rarely used with GMAW; instead, direct
current is employed .
 Almost all GMAW is done with reverse polarity also known as
DCEP.
 Positive (+) lead is connected to the torch.
 Negative (-) lead is connected to the work piece.
 Provides a relatively consistent voltage to the arc.
 Arc Voltage is the voltage between the end of the wire and the
work piece.

10. Electrode

11. Shielding Gas
Purpose of shielding gas is the protect the weld area
from the contaminants in the atmosphere .
Gas can be Inert(Argon, Helium), Reactive( Oxygen,
hydrogen, nitrogen, and carbon dioxide (CO2), or
Mixtures of both(argon + helium, argon + CO2, or
argon + oxygen.)
Gas flow rate is between 25-35 CFH

12. FLOW METER
CYLCINDER
PRESSURE
GAUGE
CFH PRESSURE
ADJUSTMENT
KNOB

13. Types of Metal Transfer
The basic GMAW process includes three distinctive
process techniques:
1. Short Circuit (Short Arc)transfer
2. Modified short circuit transfer
3. Globular Transfer
4. Spray Arc Transfer
5. Pulse spray Transfer

14. Short circuiting transferShort circuiting transfer
•Also known as “short arc.”Also known as “short arc.”
•Uses a low electrical current, lowUses a low electrical current, low
voltage, and a small-diametervoltage, and a small-diameter
electrode.electrode.
•Metal is transferred when theMetal is transferred when the
electrode touches the base metalelectrode touches the base metal
and the molten metal from theand the molten metal from the
heated electrode enters into theheated electrode enters into the
weld pool.weld pool.
•Used to join thin sheet metal andUsed to join thin sheet metal and
parts that have large gaps.parts that have large gaps.

15. Globular transferGlobular transfer
•Uses a higher electrical currentUses a higher electrical current
and high voltage than used forand high voltage than used for
short circuiting transfer.short circuiting transfer.
•How it works:How it works:
An arc is created that meltsAn arc is created that melts
the end of the electrode andthe end of the electrode and
the base metal.the base metal.
The globule increases inThe globule increases in
size until it falls off the end ofsize until it falls off the end of
the electrode.the electrode.

16. Spray transferSpray transfer
•Uses a higher electrical currentUses a higher electrical current
and higher voltage than used forand higher voltage than used for
globular transfer.globular transfer.
•Produces good penetration andProduces good penetration and
very little splatter.very little splatter.
•Commonly used in the flatCommonly used in the flat
position or for horizontal filletposition or for horizontal fillet
welding.welding.
•Requires a shielding mixture of atRequires a shielding mixture of at
least 90% argon.least 90% argon.

18. Advantages of GMAW
 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.
 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.

19. 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 (CO2).
Welding equipment is more complex, more costly and
less portable.

20. Applications
(1) The process can be used for
the welding of carbon, silicon
and low alloy steels, stainless
steels, aluminum, magnesium,
copper, nickel, and their alloys,
titanium, etc.
(2)For welding tool steels and.
Dies.

21. (3) For the manufacture of refrigerator parts.
(4) MIG welding has been used successfully in industries
like aircraft, automobile, pressure vessel, and ship
building.

22. GMAW Safety Precautions
Electrical SafetyElectrical Safety
•Never dip a GMAW gun inNever dip a GMAW gun in
water.water.
•Never touch hot parts of theNever touch hot parts of the
electrode holders.electrode holders.
•Disconnect and lock out allDisconnect and lock out all
electrical power sources beforeelectrical power sources before
doing any work on electricaldoing any work on electrical
equipment.equipment.
•Always wear safety glassesAlways wear safety glasses
when working with electrodes.when working with electrodes.
•Make sure that you have theMake sure that you have the
correct spool or coil beforecorrect spool or coil before
leading and cutting tie wires.leading and cutting tie wires.
•Position the coils close to thePosition the coils close to the
reel before lifting and then liftreel before lifting and then lift
with your legs, not your back.with your legs, not your back.
Working with electrodesWorking with electrodes

23. References
http://www.millerwelds.com/pdf/mig_handbook.p
df
http://www.weldguru.com/Mig.html
http://www.praxair.com/praxair.nsf/0/c56dbfa8e
80d0dbd85256ab300140b28/$FILE/P-8126.pdf
http://en.wikipedia.org/wiki/Gas_metal_arc_wel
ding