Download Introduction to(GMAW) Gas Metal Arc Welding

GMAW Unit 1 Lesson 1
Objective: Demonstrate proper setup and
maintenance of GMAW equipment.
Gas Metal Arc Welding (GMAW)
uses an electric arc to melt
a consumable wire electrode
and fuse it with the base
metal. The arc generates an
intense heat of 6,000 to
10,000 degrees Fahrenheit.
The process normally operates
with direct current electrode
positive (DCEP).
The wire electrode is fed by the
wire feeder through the gun cable
to the welding gun.
The electric current is transferred
from the power source through the
gun cable and to the contact tip.
The contact tip conducts the
electric current to the wire
electrode.
The gun cable also transports the
shielding gas to through the gas
diffuser and out the nozzle.
The welding arc is stabilized and
the molten filler and base metal are
protected from oxidation by the
shielding gas.
A.) Gas Machine Arc Welding
B.) Gas Metal Arc Welding
C.) Gas Material Arc Welding
D.) Gas Method Arc Welding
A.) Through the gun cable and liner
B.) Through the contact tube
C.) Through the wire feed rolls
D.) Through the gas diffuser
GMAW machines can come in 2 types.
The most common being the power source and
wire feeder in one unit.
The second type is when the power source and
wire feeder are separate machines
connected to each other.
Regardless of the machine type. The GMAW
process has two main controls.
 Wire speed- controls the amperage or heat
 Voltage- controls the arc gap
The basic power supply used for GMAW is
designed for the process. It is called a
Constant Potential (CP) or more commonly
Constant Voltage (CV).
The Arc gap is controlled by the machine
voltage. CV machines maintain a constant
voltage by varying the amperage to maintain
a consistent arc gap.
Spool Gun
Standard Gun
Push Pull Gun
A.) Constant Current
B.) Alternating Current
C.) Variable Voltage
D.) Constant Voltage
There are 3 basic types
of metal transfer
associated with
GMAW.
 Short Circuit Transfer
 Globular Transfer
 Spray Transfer
Commonly referred to as short arc, this is probably the most widely
used method of metal transfer. As the wire electrode touches the base
metal a short circuit is created causing the electrode to melt through
and deposit molten metal into the weld joint.
There are advantages and disadvantages to the short arc transfer
mode.
Advantages:
•Low heat input
•Welds in all positions
•Welds thin gauge materials
•Can be used to bridge gaps in
some weld joints
Disadvantages:
•Small diameter wire, expensive.
•Spatter
•Cold starts, can cause cold lap on
restarts.
•Limited to materials 1/8” thick
or less.
A.) Small diameter wire, expensive.
B.) Spatter
C.) Cold starts, can cause cold lap on restarts.
D.) Welds in all positions
The globular mode of metal transfer happens when
the electrode melts and burns off before
touching the base metal. Forming a molten
droplet falls and then melts to the base metal.
Advantages:
•High deposition rate
•High quality welds are
possible
•Good penetration at high
speeds
Disadvantages:
•Considerable amount of smoke
and spatter
•Rough weld appearance
•Can only be used in the flat
position
A.) High deposition rate
B.) Can only be used in the flat position
C.) High quality welds are possible
D.) Good penetration at high speeds
Spray-Arc often called Spray Transfer is a
metal transfer mode where the electrode is
fed into the weld zone and melted off above
the base metal. Electromotive force propels
the molten electrode to the base metal.
Advantages:
•Very little or no spatter
•High quality welds
•High metal deposition
•Faster welding speeds
•Deep penetration
Disadvantages:
•Very large weld pool
•Very fluid weld pool
•Can only be used in the flat position
when making groove welds
•Can only be used in the flat and
horizontal position when making fillet
welds
 Transitions
from Short Circuit - Globular
arc - Spray arc
A.) High quality welds
B.) High metal deposition
C.) Faster welding speeds
D.) Can only be used in the flat and horizontal position when
making fillet welds
A variation to the spray transfer process,
pulsed spray is a method of pulsing the
current forcing a drop of filler material from
the end of the electrode at controlled time
in the welding cycle.
Advantages:
Disadvantages:
•Greater metal deposition at
•Need for special power supplies
lower amperage levels.
•Requires special gas mixtures
•Decreased warpage is possible
•Decreased need for jigs or
weld tooling
•All positions