6_GTAW

Report
GTAW
(TIG)
Definition
Gas Tungsten Arc Welding (GTAW) is an arc welding process that
uses a non consumable tungsten electrode to establish the arc and
gas from a cylinder to provide shielding. The filler metal is supplied
by a manual rod.
Also called Tungsten Inert Gas (TIG) welding.
2
Machine Functions
1
2
3
4
5
Store and provide shielding gas at the correct
rate
Provide desired welding current
Variable current control
Store and circulate water through the torch
(watered cooled)
Semiautomatic control
Machine Nomenclature
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P.
Q.
R.
Torch
Power switch
AC balance control
Mode switch
Digital Amp meter
Output (Amp) control
Cylinder
Flow meter
Roto meter
Flow control valve
Regulator
Post flow timer
Pulse frequency control
Polarity switch
Output connector
Remote pedal
Ground clamp
Remote receptacle
Explain the function(s) of each one of these
controls/parts.
Torch Nomenclature
A.
B.
C.
D.
E.
F.
G.
Cap
Collet
Torch body
Collet body
Gas orifice
Cup
Electrode
What is the function of each part?
How are GTAW torches cooled?
Introduction
How does the GTAW process meet the three
requirements of arc welding?
Heat
GTAW
Shielding
Filler metal
Hazards Associated with GTAW
Hot metal
Harmful rays
Fumes
High frequency RF
Flying objects
Loud Noise
What is the best management practices for these hazards?
Heat
The heat produced by an electric arc between the
nonconsumable tungsten and the metal is sufficient to melt
the base metal and the filler rod.
What determines the amount of heat produced by the
electric arc?
For the TIG welding process, is the current adjusted by
changing the amperage or the voltage?
Heat – Currents
Three common currents:
DCDC+
AC--HF
Note: many power supplies have the option of pulsed
current for better puddle control.
Why is HF (high frequency) used with AC?
Heat – Current - Polarity
For the best welds, and
ease of welding, the
correct current must be
used for the metal being
welded.
Heat - Tungsten
The tungsten electrode is nonconsumable and is used to form the arc
between the torch and the metal.
Different alloys of tungsten are available.
ID
% Alloy
Color
Characteristic
EWP
100 % Tungsten
Green
Good arc stability with AC
EWTh-2
2 % Thorium
Red
Better Arc with DC
EWZr-1
1 % Zirconium
Brown
AC when high weld quality is required
EWCe-2
2 % Cerium
Orange Better starting, higher current
EWLa-2
2 % Lanthanum
Black
50% greater current capacity with AC
Which alloy/color should be used when welding thicker aluminum with AC?
Heat – Tungsten - Preparation
The shape of the tungsten electrode end must be
appropriate for the current being used.
AC
Hemispheric or balled end no more than 1.5 times the electrode
diameter. Grinder lines parallel with electrode.
DC-
Needle point for very thin metal, blunt point for thicker metal.
Taper = 2 to 2-1/2 times the diameter.
What does it mean if the end of the electrode appears dull?
What does it mean if the end of the electrode is blue or blackened?
How long should the the shielding gas flow after the welding has stopped?
Heat – Tungsten - Size
Diameter
(in)
Gas Cup
Inside Dia.
DC(Ce, Th % La)
AC
(Pure)
AC
(Ce, Th % La)
0.040
#5 (3/8 in)
15 – 80
20 – 60
15 - 80
0.060 (1/16 in)
#5 (3/8 in)
70 - 150
50 – 100
70 – 150
0.093 (3/16 in)
#8 (1/2 in)
150 – 250
100 - 160
140 – 235
0.125 (1/8 in)
#8 (1/2 in)
250 – 400
150 – 200
225 - 325
Shielding
In the GTAW process shielding is supplied from a cylinder.
How is the flow of the shielding gas controlled?
For best results the
shielding gas must be
appropriate for the type
and thickness of metal.
How much gas (ft3) will
each gallon of liquid
argon produce?
Filler Metal
A welding rod is used to fill in the joint.
Most common type is 36 inch rods that are fed into the
weld pool by hand.
What are three important characteristics of GTAW rods?
AWS GTAW Aluminum Filler Rods
Aluminum
Alloy
Filler Rod
1100
2014-T6
2219-T81
3003
5005
ER1100
ER4043
ER2319
ER1100
ER5356
Process
Preparation for Welding
Three (3) steps in preparing to weld:
1 Safety check
2 Metal preparation
3 Set up machine
Preparation - Safety
1
2
3
Check the machine, cables, torch and ground clamp.
Insure the helmet is in good condition and the correct
shade of lens.
Cover all exposed skin.
Preparation – Metal – Aluminum
• Contamination is the biggest problem when welding
aluminum with the GTAW process.
• The metal must be cleaned with a stainless steel wire
brush.


The brush can only be used to clean aluminum.
Must clean the adjoining faces and the back edge
• Insure the filler rod is clean also.
Preparation - Machine
•
•
•
•
Attach the GTAW torch to the output connector.
Attach the remote control pedal to the remote
receptacle.
Position the polarity switch on AC.
Turn on the machine.
 Insure the torch is not grounded
•
•
Set the mode switch to TIG
Set the amperage.
 150 amp maximum for air cooled torch.
•
•
•
Set the AC balance control.
Set the pulse control.
Set the postflow timer.
Preparation – Machine - Torch
•
•
•
•
If the torch has been used to weld carbon steel or
stainless steel then the cup and electrode must
be replaced.
The tungsten electrode must be clean and the
correct shape.
The torch cup must be clean
The electrode must be set with the correct
stickout.
Welding aluminum
Setting Amperage
Aluminum is a good conductor of heat.
Aluminum melts at a lower temperature that steel.
Aluminum Amperage ACHF
Tungsten
electrode
diameter
Filler rod
diameter
Amperage
Butt
3/32 – 1/8 in
3/32 in
Lap
3/32 – 1/8 in
Corner
Type
CFH
125 - 150
Argon
20
3/32 in
130 - 160
Argon
20
3/32 – 1/8 in
3/32 in
120 - 140
Argon
20
Fillet
3/32 – 1/8 in
3/32 in
130 - 160
Argon
20
Butt
1/8 – 5/32 in
1/8 in
180 - 225
Argon
20
Lap
1/8 – 5/32 in
1/8 in
190 - 240
Argon
20
Corner
1/8 – 5/32 in
1/8 in
180 - 225
Argon
20
Fillet
1/8 – 5/32 in
1/8 in
190 – 240
Argon
20
Butt
5/32 – 3/16
in
3/16 in
240 - 280
Argon
25
Lap
5/32 – 3/16
in
3/16 in
250 – 320
Argon
25
Corner
5/32 – 3/16
in
3/16 in
240 - 280
Argon
25
Thickness
1/8 in
3/16 in
Gas
Joint
1/4 in
Troubleshooting GTAW
•
•
•
Troubleshooting is the process of determining the
cause of a problem.
Assumes the welder is in proper working order.
Requires gathering information and a logical
thought process.
Troubleshooting - 1
Problem
Cause
Excessive electrode consumption
Inadequate gas flow
DCEP electrode
Excessive current density
Tungsten oxidation during cooling
What would you do to remedy these causes?
Troubleshooting - 2
Problem
Cause
Aluminum contamination of electrode
Electrode contacting filler rod
Electrode contacting metal
What would you do to remedy these causes?
Troubleshooting - 3
Problem
Weld porosity and dark color
Cause
Condensation in system
Atmospheric contamination
Contaminated filler metal
What should be done to remedy
these causes?
Contaminated base metal
Troubleshooting - 4
Problem
Yellow powder or smoke on cup
Cause
Insufficient gas flow
Atmospheric contamination
Inadequate post flow
What should be done to remedy
these causes?
Incorrect shielding gas
Incorrect tungsten size or cup size
References
http://www.millerwelds.com/resources/TIGhandbook/

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