Transcript GMAW - Oklahoma State University–Stillwater

Gas Metal Arc Welding (GMAW)
1
Definition
GMAW: A semi-automatic or automatic arc welding process in
which a continuous and consumable wire electrode and a
shielding gas are delivered to the weld through a welding
gun.
2
GMAW Hazards
1
Electrical shock
2
Hot metal
3
Harmful rays
4
Hot spatter
5
Fumes
6
Shielding gas
7
Pinch points
How is the risk of these
hazards managed?
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Introduction
GMAW has the same three requirements of all arc welding.
How does GMAW meet these requirements?
Shielding
Heat
Filler Material
GMAW
4
GMAW Processes
The GMAW process provides four different metal transfer methods.
Short circuiting
Spray
Globular
Pulse spray
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Short Circuiting Transfer
When the gun trigger is activated, the wire starts to move toward the metal.
5. The wire
touches the
metal and
the process
continues
4. As the wire
continues to
move, the arc
restarts.
3. The current
pinches off the
droplet and the arc
stops.
2. The high
current flow
melts the end
of the wire
and a droplet
is formed.
1. When
the wire
touches
the metal it
shorts out.
 Process is recognizable by its sharp buzzing or crackling sound
 Most common method
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Spray Transfer
Requires high current density.
What is current density?
The current density of the spray process
causes the wire to melt into small
droplets (less than the diameter of the
wire).
The arc forces propels the droplets to
the metal.
What are the characteristics of the spray transfer method?
Would the process work better for thin metal or thick metal?
Why?
Is the spray transfer method recommended for all welding positions?
Why, Why not?
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Globular Transfer
• Low current density results erratic arc and
globules of metal larger than the diameter
of the wire.
• Minimum penetration.
• Excessive spatter
• Use is limited to submerged arc welding.
8
Pulse Spray Transfer
In the pulse spray transfer the current alternates from the desired
welding current to a background current.
The background current just maintains the arc.
The peak current, time of peak current, background current and
time of background current are all adjustable.
A = Peak Current
B = Background Current
C = Peak Time
D = Pulses per Second
What are the advantages of the metal transfer method?
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Stickout
• An important function
of all GMAW
processes is the
stickout.
• Stickout is the distance
from the end of the
contact tube to the
weld surface.
What is a potential problem of
insufficient stickout?
What is a potential problem of Excessive stickout?
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GMAW Equipment
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Equipment Requirements
1
2
3
4
Store and deliver gas to the weld at the correct rate.
Store and deliver welding wire to the weld at the correct
rate.
Provide correct current.
Automatically or semi automatically control all of the
features.
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G
M
A
W
C
o
m
p
o
n
e
n
t What is the function
s of each part?
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GMAW Equipment
•
•
•
•
•
Power source
Wire feeder and controls
Welding gun and components
Shielding gas delivery system
Weld cleaning and finishing tools
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GMAW System Parts
A.
B.
C.
D.
E.
Hand wheel
Flow meter
Wire spool
Wire
Feed roll tension
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P.
Q.
R.
Voltage meter
Wire speed meter
Wire speed adjustment
Voltage adjustment
Power switch
Gun cable
Gun
Ground clamp
Ground cable
Feed rolls
Wire guide
Wire overrun
Safety nut
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GMAW Gun
H
F
D
B
C
G
E
A
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Flow meter
What is the purpose of the flow meter?
Two types of flow meters are available.
One piece: the gas flow rate is regulated by
using a fixed orifice and changing the
pressure to change the flow rate.
Two piece: the gas flow rate is adjusted by
using a constant pressure regulator and
changing the flow rate with an adjustable
orifice (needle valve).
Which type will provide better control of the gas
flow?
Why?
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Welding Gun
• Function is to deliver the shielding
gas, wire and welding current to the
weld pool.
• MIG guns are rated on amperage
capacity.
 The reason is heat.
 >400 amps are water cooled.
• Welding wire is delivered to the gun by
the liner.
 Liner must sized to the welding wire.
 Small liner = excessive friction which
may cause the wire to seize.
 Large liner = wire can buckle and
spring forward causes erratic wire
feed.
 Liner must be correct length.
Gun end cutaway
1.
Cable
2.
Insulation ring
3.
Gas diffuser
4.
Contact tube
5.
Wire
6.
Nozzle
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Welding Gun--cont.
Contact tube
Sliding electrical connection.
Must match the diameter of the wire
Must be replaced frequently
The nozzle directs the shielding gas
towards the weld pool.
Nozzle
Contact tube
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Power Supply
• GMAW and FCAW both use a constant voltage power
supply.




Many different types are available.
Industrial rate are usually 100% duty cycle.
Non industrial power supplies have sloping duty cycle.
May have a built in heat sensitive overload switch.
• Install power supply so that the cooling air through the
machine is not restricted.
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Selecting Power Supply
Seven factors to consider when selecting a GMAW or
FCAW power supply.
1
2
3
4
5
6
7
Type of metal
Metal thickness range
Type of metal transfer
Wire diameter range
Primary power available
Capacity of power source
Control and adjustments
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Wire Feeding systems
Function is to deliver the welding
wire at a constant rate to the gun.
Three systems
Push
Pull
Push--pull
Two types
Constant speed
Voltage sensing
Two types of construction
Internal
External
22
Wire Drive Systems
The drive system is responsible for pulling the wire from the spool
and then pushing the wire down the cable.
• The wire drive systems
consisted of one or more
pair of feed rolls and wire
guides.
• The guides must be the
proper size and adjusted
close to the feed rolls and
aligned with gap between
the rolls.
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Feed Rolls
For a GMAW system to work correctly, the feed rolls must be the
correct type and size.
The feed roll tension must also be set correctly.
U Groove
V Groove
Knurled V groove
Cogged U groove
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Consumables—Shielding Gases
Carbon dioxide
 Requires special valve
 Must use washer between valve
and flow meter.
Argon
 Same valve as helium
Mixture
 Same valve as argon
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Consumables—Welding wire
Solid (Copper clad)
Flux core
Stainless steel
Hard surfacing
Aluminum
What three wire diameters
are most popular?
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FCAW
27
Introduction
FCAW (Flux Core Arc Welding) uses a
hollow wire that is filled with flux.
Same transfer methods as GMAW.
Two types
Externally shielded
Intershielded
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Self Shielded
•
•
•
•
Shielding is provided by flux in the
core of the wire.
Produces a larger volume of fumes.
Resistant to contamination caused
by sidedrafts.
Will have slag to remove.
Does this fume removal
system meet safety codes?
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Self Shielded--gun
Does not require the use of a nozzle.
GMAW gun
FCAW gun
No nozzle?
What is this?
What are the advantages of not using a nozzle?
What are the disadvantages of not using a nozzle?
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Questions
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