1. GMAW Fundamentals
Gas Metal Arc Welding
Metal Inert Gas

2. Safety
 Electrocution hazard
� Skin burns from flying metal
� Skin burns from direct light from arc
� Skin burns from indirect light from arc
� Cotton clothing and leather gloves
� Helmet to protect eyes from light
� Safety glasses when chipping slag
�
� Ventilation to remove dangerous fumes
� Do not weld near water
� Do not weld near combustible materials
� Keep welding cables and jobs free grease
� Protect bystanders from arc rays

3. Introduction
 GMAW is defined as arc welding using a
continuously fed consumable electrode and
a shielding gas.
 GMAW is also known as MIG (Metal Inert
Gas).
 Produces high-quality welds
 Yields high productivity

4. Advantages
 Large gaps filled or bridged easily
 Welding can be done in all positions
 No slag removal required
 High welding speeds
 High weld quality
 Less distortion of work piece

5. Disadvantages
 Hard to reach locations are less easily welded
because of bulky torch and cables
 Wind or air drafts may compromise gas shielding
 Reactive metals (i.e. titanium) may need special
shielding provisions
 High heat may be uncomfortable to welders
 Correct parameter selection learning needs
dedicated training
 Equipment is more complex and expensive than
that of alternative processes

6. Several tips must be consider in
selecting mode of transfer
 Type, intensity and polarity of welding
current
 Electrode size
 Electrode composition
 Electrode extension
 Shielding gas mix composition

7. Types of Metal Transfer
The basic GMAW process includes three
distinctive process techniques:
1. Short Circuit (Short Arc)
2. Globular Transfer
3. Spray Arc Transfer

8. Modes of GMAW Transfer

9. Short Circuit (Short Arc)
 Operates at low voltages and welding current
 Small fast-freezing weld puddle obtained
 Useful in joining thin materials in any position, as
well as thick materials in vertical and overhead
positions
 Metal transfer occurs when an electrical short
circuit is established
 this cycle can repeat itself between 20 and as
much as 250 times per second.

10. Short Circuit
A - Electrode is short circuited to base metal. No
arc, and current is flowing through electrode
wire and base metal.
B - Resistance increases in electrode wire causing
it to heat, melt and “neck down”.
C - Electrode wire separates from weld puddle,
creating an arc. Small portion of electrode wire
is deposited which forms a weld puddle.
D - Arc length and load voltage are at maximum.
Heat of arc is flattening the puddle and increasing
the diameter tip of electrode.
E - Wire feed speed overcomes heat of arc and
wire approaches base metal again.
F - Arc is off and the short circuit cycle starts
again.

12. Advantages
 All-position capability, including flat, horizontal,
vertical-up, vertical-down and overhead.
 Handles poor fit-up extremely well, and is capable
of root pass work on pipe applications.
 Lower heat input reduces weldment distortion.
 Higher operator appeal and ease of use.
 Higher electrode efficiencies, 93% or more.

13. Limitations
 Restricted to sheet metal thickness range and open
roots of groove joints on heavier sections of base
material.
 Poor welding procedure control can result in
incomplete fusion. Cold lap and cold shut are
additional terms that serve to describe incomplete
fusion defects.
 Poor procedure control can result in excessive
spatter, and will increase weldment cleanup cost.
 To prevent the loss of shielding gas to the wind,
welding outdoors may require the use of a
windscreen(s).

14. Globular Transfer
 Welding current and wire speed are
increased above maximum for short arc
 Droplets of metal have a greater diameter
than the wire being used
 Spatter present
 Welding is most effectively done in the flat
position when using globular transfer

15. Globular transfer is often a
high voltage, high
amperage, high wire feed
speed transfer, and is the
result of using CO2
shielding gas (or 75% AR-
25% CO2) with parameters
higher than the short-
circuiting range

16. Advantages
 Uses inexpensive CO2 shielding gas, but is
frequently used with argon/CO2 blends.
 Is capable of making welds at very high
travel speeds.
 Inexpensive solid or metal-cored electrodes.
 Welding equipment is inexpensive.

17. Limitations
 Higher spatter levels result in costly cleanup.
 Prone to cold lap or cold shut incomplete fusion defects,
which results in costly repairs.
 Weld bead shape is convex, and welds exhibit poor
wetting at the toes.
 High spatter level reduces electrode efficiency to a range
of 87 – 93%.
 Less desirable weld appearance than spray arc transfer
 Welding is limited to flat positions and horizontally fillet
welds
 Welding is limited to metal 1/8 inch (3 mm) or thicker

18. Spray Arc Transfer
 Occurs when the current and voltage settings are
increased higher than that used for Globular
Transfer
 Used on thick sections of base material, best
suited for flat position due to large weld puddle
 Spatter is minimal to none
 Uses 5% to 10% co2 mix with argon or oxygen.
>Forms very small droplets of metal
>Very good stability
>Very little spatter

19. Spray arc transfer “sprays” a stream
of tiny molten droplets across the
arc, from the electrode wire to the
base metal.
Spray arc transfer uses relatively
high voltage, wire feed speed and
amperage values, compared to short
circuit transfer.

20. Advantages
 High deposition rates.
 High electrode efficiency of 98% or more.
 Employs a wide range of filler metal types in an
equally wide range of electrode diameters.
 Excellent weld bead appearance.
 High operator appeal and ease of use.
 Requires little post weld cleanup.
 Absence of weld spatter.
 Excellent weld fusion.
 Lends itself to semiautomatic, robotic, and hard
automation applications.

21. Limitations
 Restricted to the flat and horizontal welding
positions.
 Welding fume generation is higher.
 The higher-radiated heat and the generation of a
very bright arc require extra welder and bystander
protection.
 The use of axial spray transfer outdoors requires
the use of a windscreen(s).
 The shielding used to support axial spray transfer
costs more than 100% CO2.

22. Pulse Spray Transfer
 GMAW-P was developed for two demanding reasons:
control of weld spatter and the elimination of incomplete
fusion defects common to globular and short-circuiting
transfer.
 The welding current alternates between a peak current and
a lower background current.
 This faster-freezing weld puddle is what allows the pulsed-
spray transfer to be used fort thinner metals,
 better control on out-of-position work.
 allows for larger wire sizes to be used on varied metal
thicknesses.

23. In pulse spray transfer (GMAW-P) the
welding power source’s pulse control
pulses the welding output with
high peak currents (amperage) which are
set at levels which will cause the transfer
to go into a spray. The background
current (amperage) is set at a level that
will maintain the arc,
but is too low for any metal transfer to
occur.

25. Pulsed arc transfer

26. Advantages
 Absent or very low levels of spatter.
 More resistant to lack of fusion defects than other modes
of GMAW metal transfer.
 Excellent weld bead appearance and offers an engineered
solution for the control of weld fume generation.
 Reduced levels of heat induced distortion and tendency for
arc blow
 Ability to weld out-of-position and handles poor fit-up.
 When compared to FCAW, SMAW, and GMAW-S,
pulsed spray transfer provides a low cost high-electrode
efficiency of 98%.
 Lends itself to robotic and hard automation applications.
 Is combined for use with Tandem GMAW or other
multiple arc scenarios.
 Capable of arc travel speeds greater than 50 inches per
minute (1.2 M/min.).

27. Limitations
 Equipment to support the process is more
expensive than traditional systems.
 Blends of argon based shielding gas are
more expensive than carbon dioxide.
 Higher arc energy requires the use of
additional safety protection for welders and
bystanders.
 Adds complexity to welding.
 Requires the use of windscreens outdoors.

28. Manual GMAW Equipment
 Threemajor elements are :
1.) Welding torch and accessories
2.) Welding control & Wire feed motor
3.) Power Source
 GMAW equipment can be used either
manually or automatically

29. GMAW Schematic Diagram

31. WIRE CONTROL
&
WIRE FEED MOTOR
POWER SOURCE

32. Welding Torch & Accessories
 The welding torch guides the wire and
shielding gas to the weld zone.
 Brings welding power to the wire also
 Major components/parts of the torch are the
contact tip, shielding gas nozzle, gas
diffuser, and the wire conduit

34. Others types of torch

35. GAS DIFFUSER
NOZZLE
TRIGGER
CONTACT TIP
INSTALLED
COMPONENTS

36. Welding Control & Wire
Feed Motor
 Welding control & Wire feed motor are
combined into one unit
 Main function is to pull the wire from the
spool and feed it to the arc
 Controls wire feed speed and regulates the
starting and stopping of wire feed
 Wire feed speed controls Amperage

37. Types of Wire Feed Motor

38. Types of WFM Roller

39. Types of Wire Feeder

40. WIRE FEEDER

42. Power Source
 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

44. Contact Tip To Work Distance
In constant current, the CTWD (contact tip to
work distance) determines the arc length.
As the CTWD increases the arc length increases, and
as the
CTWD decreases the arc length decreases. This
presented a
problem for semiautomatic welding because it is
difficult to
maintain the same CTWD. To compensate for this
problem an arc voltage controlled wire

45. Constant voltage power source designs provide a specific
arc voltage for a given pre-selected wire feed speed The
volt-amp curve, or slope, is comparatively flat. As the
CTWD increases with these types of power sources, there
is a decrease in the welding current. As the CTWD
decreases there is an increase in the welding current. The
arc in this case becomes a series circuit, and the CTWD
provides resistance to current. In either scenario, the
voltage remains the same and the arc length remains the
same

46. POSITIVE NEGATIVE
TERMINAL TERMINAL

47. Shielding Gases
 Purpose of shielding gas is the protect the
weld area from the contaminants in the
atmosphere
 Gas can be Inert, Reactive, or Mixtures of
both
 Gas flow rate is between 25-35 CFH
 Argon, Helium, and Carbon Dioxide are the
main three gases used in GMAW

48. Properties of Gases
 Affect the performance of the welding process
include:
 1) Thermal properties at elevated temperatures.
 2) Chemical reaction of the gas with the various
elements in the base plate and welding wire.
 3) Effect of each gas on the mode of metal
transfer.

49. Types of shielding gases
 InertGas
1. Argon
2. Helium
3. Ar + He
 Active Gas
1. Carbon Dioxide
2. Inert gas + any type of active gas

50. Argon is an inert gas which is used both
singularly and in combination with other
gases to achieve desired arc characteristics
for the welding of both ferrous and non-
ferrous metals.
Carbon Dioxide Pure carbon dioxide is not an
inert gas, because the heat of the arc breaks down
the CO2 into carbon monoxide and free oxygen.
This oxygen will combine with elements
transferring across the arc to form oxides which are
released from the weld puddle in the form of slag
and scale.

51. Helium is an inert gas which is used on
weld applications requiring higher heat
input for improved bead wetting, deeper
penetration and higher travel speed. In
GMAW it does not produce as stable an arc
as argon. Compared to argon, helium has a
higher thermal conductivity and voltage
gradient

53. FLOW METER
CFH PRESSURE
ADJUSTMENT
KNOB
CYLCINDER
PRESSURE
GAUGE

54. Filler Wire

55. Wire Chemistries

56. GMAW Operation techniques
To setting WFS (Wire Feed Speed)

59. Voltage-bead Change

60. Electrode Stick-out

61. ESO Setting

62. EOS

64. Gun angles and techniques

67. Direction of Travel

68. THANK YOU