GMAW And FCAW Flashcards
A metal transfer mode in which molten metal from consumable welding wire is deposited during repeated short circuits. The number of these short circuits can occur up to 200 times per second.
Short circuit transfer (GMAW-S)
Occurs when the wire feed speed and voltage are increased above the upper range for GMAW-S. The transfer of the molten metal in large droplets from the welding wire across an arc to the workpiece. Occurs at the rate of a few droplets per second.
Globular Transfer.
Metal transfer mode in which welding wire is propelled axially across the arc. The arc is a steady, quiet column with a well-defined, narrow, cone-shaped core in which metal transfer takes place.
Spray transfer
Type of GMAW metal transfer that is limited to welding thicker materials in the 1G, 1F and 2F positions.
SPRAY TRANSFER
The modes of metal transfer for GMAW are:
Short-circuiting transfer
Globular transfer
Spray transfer
GMAW modes of transfer are determined by a number of factors:
Electrode diameter
Electrode extension
Shielding gas composition
Mode of GMAW metal transfer suited for the joining of thin sections, out of position welding and bridging root openings.
Short-circuit transfer
In short-circuit mode, the shielding gas that produces the highest spatter.
Pure CO2
Advantages of spray transfer compared to other modes of transfer:
Increased rates of deposition and minimum post weld clean-up
Although first introduced in the 1920s, GMAW did not become commercially available until 1948
T/F
TRUE
GMAW was primarily first used for welding:
Aluminum
GMAW is used to weld:
Pipe
Pressure vessels
Structural steel
Metals that can be welded with GMAW include:
Carbon steel
High-strength low-alloy steel
Stainless steel
Aluminum and Copper
Important advantages associated with GMAW are:
An efficient consumable-electrode process that can be used to weld all commercial and can also be performed in all positions.
Limitations associated with GMAW include:
Complex, costly equipment to operate the process and can be performed in windy conditions.
GMAW was 1st called MIG as a result of:
Metal inert gas, using an inert gas for arc shielding
Because of it versatility, GMAW has become more widely used and has replaced ________ for many applications.
SMAW
The manufacturer describes their aluminum electrode process of:
Continuous casting
Drawing and testing the wire
Controlling alloys
According to the article, most aluminum MIG welding problems are caused by:
Poor feeding
Aluminum did not become available in commercial quantities until the discovery of the _________ __________ for obtaining pure aluminum from aluminum oxide in 1886.
Electrolytic processes
The characteristics of aluminum alloys which make them attractive as structural materials are their:
Light weight
Relatively high strength
Aluminum can be alloyed with a number of different elements, both primary and secondary, to provide:
General weldability
Improved strength
Corrosion resistance
Some primary elements that alloy with aluminum are:
Copper and Zinc
A piece of 6061:
Contains magnesium and silicon
Is wrought alloy (4 digits)
Is heat treatable
The 6XXX series is prone to hot cracking, but this problem can be overcome by the. Correct choice of:
Joint and filler metal
In heat-treatable aluminum alloys:
The weld will generally be weaker than the parent material.
Most common aluminum filler alloys fall into the:
4XXX and 5XXX families
ER4043 filler wire has a silicone percentage of:
4.5-6.0
Oxides on aluminum plate can be removed by:
Power wire brushing
Sanding
Grinding or chemical etching
All of these
Common weld preparation techniques for aluminum include:
Sawing and shearing
Grinding and sanding
Machining
The recommended shielding gas for welding aluminum up to approximately 1/2” (12.7 mm) in thickness is:
100% Argon
Small changes in wire diameter, wire feed speed, and current produce ____________ changes in weld bead profile, arc length and can even cause equipment ____________ due to wire burn back and fusing tip.
Heat-Treatable
Non Heat treatable
With the no heat-treatable alloys it is possible to increase strength only through ___________ ____________ or ______________ _____________.
Cold working
Strain hardened
__________ __________ and _____________ ____________ are the two recommended GMAW modes of metal transfer for aluminum.
Axial spray
Pulsed spray
The formation of black soot on the surface, or the adjacent areas of a weld, is referred to as smut. It is made up of finely divided oxides of aluminum and magnesium. They usually indicate that _____________ in _____________ are necessary.
Adjustments
Technique
GMAW electrode specs
E R 7 0 S - 6
What does the following mean?
E... R... 70... S... 6...
Electrode Rod (may be omitted) Tensile strength Solid wire Indicates the filler metal composition
Definition of Electrode Extension…
Is the distance from the contact tip to the end of the welding wire.
modes of metal transfer…
Short circuiting transfer
Globular transfer
Spray transfer
- as well as a variation of spray transfer called pulsed spray transfer
Definition of metal transfer…
Is the manner in which molten metal transfers from the end of the electrode across the welding arc to the weld pool
Define GMAW…
Gas metal arc welding Is an arc welding process that uses an arc between a continuous ire electrode and the weld pool.
GMAW welds can be applied by the…
Semiautomatic - wfs, voltage setting and gas flow rate are preset but welding gun is manually operated.
Mechanized - operator sets welding parameters and monitors welding operation while a mechanical device controls the welding gun
Automatic - welding parameters and welding gun movements are programmed into a computer and all aspects of the process are controlled by equipment
GMAW produces…
On what metals?
Cost effective?
High quality welds on a variety of ferrous and nonferrous metals at low cost
GMAW welds are _________-___________. Therefore there is very minimal, if any, post weld clean up
Slag free
GMAW process allows…
Higher deposition rates
Faster travel speeds
Less electrode waste
Easier than manual welding processes like
- SMAW, OAW, GTAWGMAW disadvantages…
- won’t function in windy environment (outside)
- Required careful setting of electrical components
- not very portable
- cost is high due to many parts
- need clean base metal
- potential for cold lap and undercut
- skill
- high radiated heat
The most common current selected for GMAW Is…
Direct current electrode positive (DCEP)
DCEP is the most efficient current because…
It produces deeper penetration
Greater surface cleaning
In GMAW, current is a function of…
Wire feed speed
What current should NOT be used for GMAW? Why?
DCEN And AC
Because weld penetration is shallow and wide, there’s excessive spatter and no surface cleaning occurs.
GMAW uses __________ ____________ welding power source capable of producing ___________ ___________
Direct current
Constant voltage (CV)
CV welding power sources are also known as…
Constant potential (CP) machines
Generally, electrode classifications for GMAW are interchangeable with electrode number classifications for GTAW
T/F
False
In the electrode number ER70S-4, the 4 indicate the filler metal composition and welds mechanical properties.
T/f
True
In the GMAW electrode classification system, the R stands for “rod out to length” and may be omitted.
T/f
True
ER90S-2
The electrode tensile strength is
90k
EER75S-6
The ‘S’ in the electrode classification indicates
Solid wire
Choose an electrode for preforming a weld with a tensile strength of 95,000 PSI on fully prepared base metal with maximum alloying elements of manganese and silica.
ER75S-6
ER85S-6
ER95S-6
ER95S-2
ER95S-6
GMAW wire packaging and delivery systems consist of….
Spools
Coils w/ support
Coils w/o support
Drums
Explain the welding process of GMAW:
a consumable wire electrode is feed at a controlled rate into a weld joint while a continuous blanket of shielding gas is feed to shield the weld zone from contaminants
What does MIG stand for?
Metal inert gas
What’s ESO and what should it be?
electrode stickout: the distance from the contact tip of the gun to the end of the electrode. should be 3/8”
Short circuit transfer
where low currents, low voltages, and smaller diameter wires are used to weld in all positions on thing to heavy metals
Spray arc transfer
where high currents, high voltages, and larger diameter wires are used to weld thicker metal mostly in flat and horizontal positions
Inductance
the rate of rise of current as opposed to the final amount of current available; used to increase or decrease the number of short circuit metal transfer per second
What is travel speed measured in?
Inches per minute
GMAW Advantages
- beginners can be quickly trained
- better control of heat which reduces distortion in base metals
- better welds because arc is always visible
- high deposition efficiency, 98% of wire deposited in the joint
- adaptable to both ferrous and non-ferrous metals in all thicknesses
- adaptable to either auto or semiautomatic operation
- usually requires no clean up and reduces cost
- little to no slay when using fluxcore wire
GMAW equipment needed…
- welding machine
- wire feeder
- weld gun
- electrode wire
- shielding gas supply and controls
Air cooled weld gun
used in short circuit transfer when short distances or weld times are required
Water cooled weld gun
used in spray arc transfer when long distances or weld times are required especially with larger diameter electrodes
Spool gun
a gun with housing capable of holding a small spool of wire, usually used when weld aluminum where the wire is to soft to be pushed/pulled long distances
Gas diffuser
copper device that spreads shielding gas
Nozzle
directs and holds shielding gas around the weld zone
Why are drive rolls sometimes knurled?
to keep it from smashing the wire, mostly for FCAW
Most commonly used gas in shot circuit transfer…
75% Argon
25% CO2
what’s the first letter in the aws classification of wire and what’s it stand for
E for electrode
in the aws classification of wire, what’s it mean if the E is followed by a R
Indicates that filler metal may be used as an electrode
in the aws classification of wire, what might be after the interior numbers and what do they stand for?
Wire Type
S- solid bare electrode
T- flux core wire
C- metal core wire
In the AWS classification of wire, what does the last letter/number stand for?
Indicates chemistry of the wire
What is FCAW?
flux core arc welding: electrode wire contains shielding gas/flux inside of it
FCAW self shielded
when the weld zone is protected by fluxing elements released from within inner core of the electrode wire as the arc is made
What is FCAW dual shielded
used in the presence of a shielding gas to provide double protection for the weld
FCAW-SS advantages
- outdoor usability
- minimize restarts
- no shield gas costs
- high deposition rates
- bead
FCAW-DS advantages
- appearance
- little to no spatter
- high deposition rates
- mechanical properties
FCAW-DS Disadvantages
- smoke/fumes
- portability
- outdoor weldability
- potential for gas marks
- high radiated heat
Short circuit transfer
short circuit between the base metal and electrode every 20-200 times per second causing metal from electrode to enter weld
Globular transfer
arc melts the end of the electrode and base metal causing drops of metal to fall into weld. flat/horizontal only
Spray transfer
hundreds of small droplets are formed every second, spraying into the weld at high rates of speed. requires a shielding gas mixture with at least 80% argon or helium
Pulsed spray transfer
spray approximately 60 to several hundred times per second
What does carbon do as a shielding gas?
Increase strength
What doe. Manganese do as a shielding gas?
- Deoxidize
- Increase strength
Contact tip
Transfer electricity
Nozzle
Protects contact tip
Wire liner
Protects rubber and prevents tangles
Drive roller
Pulls wire off spool and guides through the liner
Spool nut
Holds spool in place
Flow meter
Measures how much gas is coming out in cubic feet per hour
Gas tank regulator
Gauges the pressure inside tank
Silica
Protects weld from outside contaminates, deoxydizer
Pulsed gas
85/15
88/12
90/10
95/5
What’re the 3 types of wire feeding?
Spray transfer
Globular
Spray
MiG polarity
DCEP
CV (constant voltage)
What is Shielding gas
The protective inert gas seed in the welding process
WFS
A.K.A
Wire Feed Speed
Adjusts the speed at which the wire exits the welding gun.
Forehand welding
The tip of the electrode points in the direction of travel
Backhand welding
The electrode tip points away from the direction of travel
Arc blow
The deflection of a welding arc from its normal path because of magnetic forces.
Porosity
Created by contamination of trapped gasses in weld
Cracked welds
Can be caused by improper cooling or cooling too fast
Incomplete Fusion
When a weld does not adhere both pieces of base metal together.
Incomplete penetration
A weld that does not penetrate deep enough into the base metal.
What is flux and what does it do?
A protective coating around the wire that burns away when welding to protect the weld pool.
Welding splatter
Small unwanted droplets of metal that develop around the weld.
Flow meter is measured in what?
Cubic feet per hour (CFH)
Common GMAW wire sizes…
.023,
.030,
.035,
.045
Definition of MIG welding
A method of welding in which the filler metal wire is consistently fed into an electric arc, this creates a welding puddle which is shielded from the access of air by an inert gas, usually argon and Co2.
In order to weld there must be a _______________________ circuit between the positive and negative side of the welding machine
Complete
Pulse spray transfer mode
the power supply cycles between a high spray transfer current and a low background current. sounds like hair clippers
What almost all GMAW is done in…
Reverse polarity/DCEP
Wire speed is the same as __________?
Amperage
Insulator
Doesn’t allow electricity to escape the gun
Name an inert gas
Argon
Steel from 1/4” to 1/2” thick may be butt welded with no edge preparation.
T/f
False
The backhand technique is generally used for welding stainless steel.
True or false
False
Using short circuiting transfer on aluminum produces a colder arc than is produced with spray transfer.
True or false
True
When using GMAW on aluminum, a lower current than that used for other metals is required.
T/f
True
A 95% Ar/5% O2 shielding gas mixture provides higher heat input when welding aluminum between 1” and 2” thick.
T/f
False
When welding stainless steel more than 1/4” thick using GMAW, a slight side-to-side movement should be used.
T/f
True
Spray transfer is commonly used for thin stainless steel in overhead position.
T/f
False
Using GMAW on copper is usually restricted to the deoxidized types of copper.
T/f
True
The preferred shielding gas for welding thin copper is argon.
T/f
True
An argon back-up gas may be used when welding stainless steel to prevent air from contacting the underside of the weld, causing embrittlement.
T/f
True
For short circuiting transfer on carbon steels and low-alloy steels, the preferred shielding gas is ___.
a mixture of 75% argon and 25% CO2
A 50 to ___ groove angle is required on carbon steel up to 1” thick.
60
For carbon steel welded without edge preparation, a ___” root opening is recommended.
1/16th
___ is the shielding gas most commonly used for aluminum up to 1” thick
Argon
Neither oxygen, hydrogen, nor CO2 should ever be used for welding ___ with GMAW, not even in trace amounts.
Aluminum
Spray mode of metal transfer
Higher heat input than short circuit mode of transfer, little or no spatter; metal is 1/4” and greater in thickness; flat and horizontal positions only.
Pulsed spray mode of metal transfer
Lower heat input than spray transfer, little or no spatter;l out of position welding; material thickness is 1/16” and greater; more sensitive to Contamination than short circuit; more sensitive to fit up than short circuit; slower travel speeds.
