Year2, Mod3, Welding
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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.
What polarity does GMAW generally use?
DCEP (reverse polarity)
direct current, electrode positive
How are electrode holders rated?
by their current carrying capacity
Describe the regulator.
responsible for reducing the gas source pressure to a constant working pressure
Desrcibe flow meter.
control the rate of flow of a sheilding gas to the nozzle.Calibrated in L/min or CFH.
What are the three basic modes of metal transfer?
- - short-circuiting transfer
- - globular transfer
- - spray transfer
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
Describe Spray Transfer.
- - shielding gas >85%
- - weld current above critical value (transition current). 26-35 V
- - generally used for flat and horizontal positions
Name the welding positions.
- 1- flat
- 2- horizontal
- 3- vertical
- 4- overhead
What are the amperes range for machines?
100 to 500
Does the DC Constant Current (CC) machine work well for GMAW?
NO. Good for SMAW and GTAW.
What controls the amperage?
What are the preffered wire drive rollers for solid wires?
V-groove and U-groove
What is voltage? In relation to GMAW?
- - force that overcome resistance to allow amperage flow
- - high voltage = wider, flatter weld bead w/ shallower penetration
What is amperage? In relation to GMAW?
amount of current flow. Controls penetration and burn-off rate of electrode.
What is DCEN known as?
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.
What is stickout?
distance between electrode contact tip and the end of the unmelted electrode.
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
What is a major advantage of pulsed spray transfer?
all-position welding on thinner materials
Constant Arc Voltage machines produce:
a relatively flat volt-amp curve
What type of volt-amp curve does a constant current machine produce?
What is the recommended stickout for short circuiting metal transfer?
What may occur when too much slope is set on a CP machine?
bending and stubbing of the wire
Slope and inductance are use to ...
reduce spatter and improve arc stability
the power sources used for pulsed spray transfer are:
DC synergic, micro-processor controlled
A pull type welding gun is designed to be used with...
What type of wire-drive system allows greater machine-to-work distances?
What is the purpose of the curved neck on a gmaw welding gun?
to ensure proper electrical transfer to the wire electrode.
What is the max distance for a push wire system?
What is the main purpose of the contact tube?
to transfer the welding current to the filler wire
Is carbon dioxide an inert gas?
Which shielding gases are recommended for Al?
When short-circuiting, number of short circuits varies from...
Welding power sources are construced to ______ standards.
OCV is defined as.
Open Circuit Voltage
Another name for wire-hangups is.
What is slope?
What is it's main purpose?
reduction in output voltage with increasing amperage
cork screw effect exhibited by a ring of electrode filler wire. If very large can cause wire to wander and produce poor welds
the permanent set wire takes when wound on a spool
Classification of GMAW Wire
49 - min. tensile strength
S - solid wire
X- chemical analysis of wire
list some basic properties of shielding gases.
- - specific gravity
- - ionization potential
- - thermal conductivity
- - oxidation potential
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
What is the benefit of O as a shielding gas?
up to 10% concentration increases puddle fluidity thus reducing undercut
What is C25 characterize by?
- - stable arc
- - good puddle control
- - little spatter
- - can be used on lower voltage and current settings
What polarity is generally used for GMAW?
Direct Current Eletrode Positive
How is the work positioned for a 1F Tee joint?
90' and 0' to the horizontal plane
What would be the normal electrode angle when doing single-pass 1F welds?
45' to the joint angle
In what positions can you do surface welding with GMAW using short-circuit metal transfer?
What is the most likely weld progression for the first pass on 3F weld on 3/8" material?
What type of bead is usually used for the cover pass on a 3F weld on 3/8" material?
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
What amount of argon is needed to achieve spray transfer?
What GMAW mode of metal transfer is best suited for all-position welding?
pulsed spray arc transfer
The power source best suited for short-circuit mode of metal transfer is:
constant voltage power source
When using teh short circuiting mode of metal transfer, inductance controls the:
rate of rise and fall of amperage
The purpose of a flowmeter is to:
maintain a constant flow of gas
What would be a cause of excessive root pentration?
to slow of a travel speed
Welds having longitudinal cracks are the result of:
the travel speed being too fast
How will penetration be affected when stickout is increased?
will decrease pentration
What can excessive spatter on the gun nozzle cause?
inadequate gas coverage
When arc hunting occurs, the problem is likely in the:
contact tip or the conduit liner
Stubbing is caused by:
excessive wire feed speed.
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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