Transcript Course Name

Manufacturing Processes Lab I, MET 1321
Gas Tungsten Arc Welding (TIG)
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding Processes
ARC Welding
(AW)
Oxyfuel Welding
OFW
Resistance Welding
RW
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
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Shielded Metal Arc Welding (Stick welding)
Gas Metal Arc Welding (MIG)
Gas Tungsten Arc Welding (TIG)
Flux Cored Arc Welding
Submerged Arc Welding
Plasma Arc Welding
Oxyacetylene Welding (OAW)
Gas Tungsten Arc Welding (GTAW)
Tungsten Inert Gas (TIG)
GTAW or TIG is an arc welding process in which a shielding gas protects
the arc between a non consumable tungsten electrod and the weld area.
Gas is fed through the torch to shield the electrode and molten weld
pool. If filler wire is used, it is added to the weld pool separately.
Usage:
Joining thin-wall tubing and depositing
the root pass in pipe joints.
GTAW Produces high quality weldment.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
TIG equipment
Equipment consists of the welding torch plus additional apparatus to
supply electrical power, shielding gas, and a water inlet and outlet.
Personal protective equipment should be worn to protect the
operator from the arc rays during welding operations.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
TIG equipment
Argon regulator with
flowmeter
TIG welding torch
(1) Cap. Prevents the escape of gas from the top of the torch and locks the electrode in
place.
(2) Collet. Made of copper; the electrode fits inside and when the cap is tightened, it
squeezes against the electrode and leeks it in place.
(3) Gas orifice nut. Allows the gas to escape.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Shielding Gas
In general, the shielding gas is Argon or its mixture
with other gases. The gas is regulated by a
flowmeter.
Summary of all gases used:
Argon
Argon + Hydrogen
Argon + Helium
Helium is generally added to increase heat input (increase
welding speed or weld penetration).
Hydrogen will result in cleaner looking welds and also increase
heat input, however, Hydrogen may promote porosity or
hydrogen cracking.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Advantages
TIG welding benefits:
It can weld more types of metal and metal alloys than
any other welding process.
Superior quality welds
Welds can be made with or without filler metal
Precise control of welding variables (heat)
Free of slag and spatter
Low distortion
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Current
The welding machine used for TIG can provide either AC or DC
current.
The choice of using AC or DC current depends on the metal to be
welded.
Aluminum, Magnesium, Thin
stainless steel
MOST FERRUS METALS (Steel,
Thick Stainless Steel, Cast Iron),
Silver, Brass, Copper
AC
DC (DCEN)
TIG requires precise current control, especially in the low range
(to maintain a stable arc), particularly for welding light-gauge
metals.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Derating
A welding machine originally designed for use with SMAW (stick
welding) must be de-rated to protect it from the effect of
internal heating that occurs during GTAW.
Derating is a lowering of the current output level (or
the duty cycle or both) of an AC welding machine.
Duty cycle is a welding equipment specification which defines the
number of minutes, within a 10 minute period, during which a given
welder can safely produce a particular welding current.
For example, a 150 amp. welder with a 30% duty cycle must be
"rested" for at least 7 minutes after 3 minutes of continuous
welding.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
Before starting to weld, ensure
that the Tungsten electrode
has the proper stickout beyond
the end of the gas nozzle.
The diameter of the
electrode selected for a
welding operation is
determined by the
required welding current.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Joint
Stickout
T-joint
1/4” to 3/8”
Butt-joint
1/8” to 3/16”
Corner joint
1/8”
How to weld
The type and amount of shielding gas used is
determined by current, type of weld, base metal and
welding conditions.
Gas nozzles that are too small for the welding task may
overheat, crack, or deteriorate rapidly.
A water-cooled torch is recommended when using
currents over 200A. Ensure cooling water is flowing
before welding.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
When welding light-gauging metals, a copper backing bar
is usually required.
Ensure that there is good ventilation when
welding copper or copper alloys. Fumes of these
metals are highly toxic.
Filler metal containing deoxidizers should be used when
welding with GTAW to prevent porosity in the weld.
Medium and high-carbon steels require preheat and
postheating to avoid loss of toughness and ductility.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Striking an arc
Set the welding current and hold the torch in a horizontal position
about 2” above the workpiece.
When using DC current, lower the torch until the electrode
touches the workpiece. Once the arc is started, withdraw
the electrode so it is about 1/8” above the workpiece.
When using AC (ACHF or Alternating current high frequency),
the electrode should not touch the workpiece to start the
arc. Keep it 1/8” above the workpiece. Use this method for
the DC welding machine with a high-frequency start up.
To stop the arc during welding, swing the electrode back to the
horizontal position without touching the welding area.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
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Clean
Striking an arc
Establish an arc.
Create a weld puddle.
Add filler metal "dip" into the puddle while pushing the weld
puddle along the weld joint.
End the arc and leave the torch over the weld puddle to
protect it until the puddle cools.
Cleaning both the weld joint area and the filler metal is an important
preparation. Remove all oil, grease, dirt, paint, etc. The presence of
these contaminants may result in arc instability or contaminated
welds.
Clamp
Clamping may be required if the work piece cannot be supported
during welding.
Tack weld
Make short 1/4 in. tack welds along the work pieces to hold them
together.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How do I position my TIG torch for
different types of joints?
Butt welds: When welding a butt joint,
center the weld pool on the adjoining
edges. When finishing, decrease the
heat (amperage) to aid in filling the
crater.
Work angle
Lap joint: For a lap weld, form the
weld pool so that the edge of the
overlapping piece and the flat surface
of the second piece flow together.
Since the edge will melt faster, dip the
filler rod next to the edge and make
sure you are using enough filler metal
to complete the joint.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Push angle
How do I position my TIG torch for
different types of joints?
T-joint: When welding a Tjoint, the edge and the flat
surface are to be joined
together, and the edge will melt
faster. Angle the torch to
direct more heat to the flat
surface and extend the
electrode beyond the cup to
hold a shorter arc. Deposit the
filler rod where the edge is
melting.
Corner joint: For a corner joint,
both edges of the adjoining
pieces should be melted and the
weld pool should be kept on the
joint centerline. A convex bead
is necessary for this joint, so a
sufficient amount of filler metal
is needed.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Work angle
Push angle
Test yourself!
GTAW or TIG is an arc welding process in which a shielding gas
protects the arc between a consumable tungsten electrod and
the weld area.
non-consumable
True
False
In TIG welding, the main shielding gas is Argon.
True
False
The TIG current used for welding the most ferrous metals (Steel,
Thick Stainless Steel, Cast Iron), is AC.
True
DC (DCEN)
False
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Test yourself
Derating (lowering of the current output level or the
duty cycle of an AC welding machine) is done
– to increase the minutes during which a given
welder can safely produce a particular welding
current.
– to protect the machine from the effect of internal
heating that occurs during GTAW.
– to have a high-frequency start up in welding.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Test yourself
Filler metal containing deoxidizers should be used when
welding with GTAW to prevent …… in the weld.
– contaminations
– porosity
– instability
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri