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When was GMAW first introduced?
1920s, commercially available 1948. Developed to eliminate use of fluxes when welding aluminum and magnesium alloys.
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What polarity does GMAW generally use?
DCEP (reverse polarity)
direct current, electrode positive
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How are electrode holders rated?
by their current carrying capacity
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Describe the regulator.
responsible for reducing the gas source pressure to a constant working pressure
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Desrcibe flow meter.
control the rate of flow of a sheilding gas to the nozzle.Calibrated in L/min or CFH.
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What are the three basic modes of metal transfer?
- - short-circuiting transfer
- - globular transfer
- - spray transfer
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Desrcribe Short Circuiting Metal Transfer
lower current settings and specific voltage range (19-20V)
only occurs when filler wire is in direct contact with the base metal
Can be used in all positions
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Describe Spray Transfer.
- - shielding gas >85%
- - weld current above critical value (transition current). 26-35 V
- - generally used for flat and horizontal positions
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Name the welding positions.
- 1- flat
- 2- horizontal
- 3- vertical
- 4- overhead
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What are the amperes range for machines?
100 to 500
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Does the DC Constant Current (CC) machine work well for GMAW?
NO. Good for SMAW and GTAW.
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What controls the amperage?
wire speed
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What are the preffered wire drive rollers for solid wires?
V-groove and U-groove
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What is voltage? In relation to GMAW?
- - force that overcome resistance to allow amperage flow
- - high voltage = wider, flatter weld bead w/ shallower penetration
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What is amperage? In relation to GMAW?
amount of current flow. Controls penetration and burn-off rate of electrode.
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What is DCEN known as?
straight polarity
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What is the distribution of arc energy when welding with DC current?
2/3= arc energy associated with the negative side of the welding circuit.
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What is stickout?
distance between electrode contact tip and the end of the unmelted electrode.
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List the basic components of a GMAW set-up.
- 1. power source
- 2. wire feeder
- 3. gun and cable assembly
- 4. spooled filler wire
- 5. shielding gas and gas control equipment
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What is a major advantage of pulsed spray transfer?
all-position welding on thinner materials
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Constant Arc Voltage machines produce:
a relatively flat volt-amp curve
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What type of volt-amp curve does a constant current machine produce?
drooping
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What is the recommended stickout for short circuiting metal transfer?
3/8"
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What may occur when too much slope is set on a CP machine?
bending and stubbing of the wire
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Slope and inductance are use to ...
reduce spatter and improve arc stability
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the power sources used for pulsed spray transfer are:
DC synergic, micro-processor controlled
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A pull type welding gun is designed to be used with...
soft wires.
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What type of wire-drive system allows greater machine-to-work distances?
push-pull system
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What is the purpose of the curved neck on a gmaw welding gun?
to ensure proper electrical transfer to the wire electrode.
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What is the max distance for a push wire system?
15 feet
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What is the main purpose of the contact tube?
to transfer the welding current to the filler wire
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Is carbon dioxide an inert gas?
no
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Which shielding gases are recommended for Al?
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When short-circuiting, number of short circuits varies from...
20-200 tiimes/second
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Welding power sources are construced to ______ standards.
NEMA
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OCV is defined as.
Open Circuit Voltage
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Another name for wire-hangups is.
bird nesting
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What is slope?
What is it's main purpose?
reduction in output voltage with increasing amperage
reduce spatter,
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Define Helix.
cork screw effect exhibited by a ring of electrode filler wire. If very large can cause wire to wander and produce poor welds
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Define Cast.
the permanent set wire takes when wound on a spool
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Classification of GMAW Wire
ER49S-X
E- electrode
R- Rod
49 - min. tensile strength
S - solid wire
X- chemical analysis of wire
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list some basic properties of shielding gases.
- - specific gravity
- - ionization potential
- - thermal conductivity
- - oxidation potential
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Describe some characteristics of Helium as a shielding gas.
- - flow rate is 2-3 times that of argon
- - high thermal conductivity
- - produces arc-plasma for uniformly distrubuted energy
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What is the benefit of O as a shielding gas?
up to 10% concentration increases puddle fluidity thus reducing undercut
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What is C25 characterize by?
- - stable arc
- - good puddle control
- - little spatter
- - can be used on lower voltage and current settings
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What polarity is generally used for GMAW?
Direct Current Eletrode Positive
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How is the work positioned for a 1F Tee joint?
90' and 0' to the horizontal plane
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What would be the normal electrode angle when doing single-pass 1F welds?
45' to the joint angle
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In what positions can you do surface welding with GMAW using short-circuit metal transfer?
all positions
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What is the most likely weld progression for the first pass on 3F weld on 3/8" material?
downhill
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What type of bead is usually used for the cover pass on a 3F weld on 3/8" material?
weave bead
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What is the recommended gun angle for the first pass of a 2F weld on 3/8" material with three stringer bead passes?
45' to the horizontal and vertical planes
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What amount of argon is needed to achieve spray transfer?
85%
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What GMAW mode of metal transfer is best suited for all-position welding?
pulsed spray arc transfer
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The power source best suited for short-circuit mode of metal transfer is:
constant voltage power source
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When using teh short circuiting mode of metal transfer, inductance controls the:
rate of rise and fall of amperage
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The purpose of a flowmeter is to:
maintain a constant flow of gas
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What would be a cause of excessive root pentration?
to slow of a travel speed
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Welds having longitudinal cracks are the result of:
the travel speed being too fast
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How will penetration be affected when stickout is increased?
will decrease pentration
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What can excessive spatter on the gun nozzle cause?
inadequate gas coverage
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When arc hunting occurs, the problem is likely in the:
contact tip or the conduit liner
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Stubbing is caused by:
excessive wire feed speed.
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What is the major cause of cold lap when using GMAW short-circuit metal transfer?
slow travel with a large bead
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