Welding GTAW-Advanced-Feilbach
Gas Tungsten Arc Welding
GTAW, TIG
GTAW
Gas Tungsten Arc Welding, sometimes referred to as TIG or Heliarc.
EWP
Green, Pure Tungsten Electrode - has the poorest heat resistance and electron emission characteristics of all the tungsten electrodes. It can be used with AC for welding metals
Ways of removing tungsten contamination
Grinding, chemical cleaning, breaking, chemical cleaning and pointing, pointing and remelting
EWCeO2
Orange, Cerium Tungsten Electrode - Improves current carrying capacity. Not made of radioactive material. Improved arc starting and arc stability. Slightly higher voltage.
Hydrogen in GTAW
Not a primary shielding gas, can be added when deep penetration and high welding speeds are needed. Improves the weld surface cleanliness
In general, the current-carrying capacity at direct-current electrode negative (DCEN) is __________
ten times greater than at DCEP
Nozzles may be made from
a ceramic such as alumina or silicon nitride (opaque) of from fused quartz - clear. The nozzle may also have a gas lens to improve the gas flow pattern
Argon when used with DCEP
acts as a cleaning agent. The electrons from the cathode surface lift the oxides that interfere with their movement.
Torches are available in two kinds, _____ cooled and ______ cooled
air, water
Hot Start
allows a controlled surge of welding current as the arc is started to establish a molten weld pool quickly
Avoid touching the metal table with unprotected skin as you may experience ______________
an uncomfortable shock due to high frequency start
Lanthanum Tungsten, EWLa-1
are not radioactive, Similar current carrying capacity to thorium tungstens, but have a slightly higher arc voltage.
_____________ is relatively easy to ionize
argon
Noble inert gases
argon and helium - they will not combine chemically with any other material.
Argon
argon is denser than air - it effectively shields welds in deep grooves. Can be a hindrance when welding overhead.
The shielding gasses used for GTAW are
argon, heium, hydrogen, and nitrogen - or a mixture of two or more of these gasses.
___________ has been combined with __________ to gain the benefits of cathode cleaning and deeper penetration
argon, helium
Remote Controls (in GTAW)
can be used to start the weld, increase of decrease the current, and stop the weld - either foot-operated or hand-operated
GTA welding is the ____ of all the manual welding processes.
cleanest.
_____________ is next to godliness in GTAW
cleanliness
The _______ is the cone-shaped sleeve that holds the electrode to the torch
collet
The rate of flow is measured in CHF
cubic feet per hour or liters per minute
DCEN heat distribution
deep penetration - narrow - conical end
GTA welding torches are available in a wide variety of ________ and ________
designs and amperage ranges
The nozzle size is determined by the
diameter of the opening and its length
The __________ at which the current cycles is the rate at which it makes a full change in direction
frequency
One full cycle
from peak to peak of sine wave
Ways to eliminate tungsten degradation
good mechanical contact, good electrical contact, low a current as possible, water-cooled torch, using DCEN, large a size of tungsten as possible
Tungsten is ________, but ________
hard, brittle
_____________ gas offers the benefit of _____________ penetration
helium, deeper (better)
GTA can be used to make extremely ___ quality welds.
high
Thoriated Tungsten EWTH-1 EWTH-2
improves it's current carrying capacity - The addition of 1% to 2% of thorium oxide does not further improve current-carrying capacity. It does, however, help with electron emission.
Thorium - longevity
increases the serviceable life of the tungsten
GTAW History
late 1930's, originally used Helium and DCEP
Grind the tungsten so the grinding marks run ___________
lengthwise
The amperage listed on a torch is the __________ rating and cannot be exceeded without possible damage to the torch.
maximum
Flowmeter
may be merely a flow regulator on a manifold system or it may be a ball float mete.
Too steep of an angle may....
may draw in air
The electrode in GTAW is:
non consumable.
The ___________ or _______ is used to direct the shielding gas directly on the welding zone.
nozzle, cup
The nozzle size - both length and diameter - are often based on the welder's _________________
personal preference
With DCEN a ________ tip concentrates the arc as much as possible
pointed
Three tungsten tip shapes
pointed, rounded, balled end
__________is the time during which the gas continues flowing after the welding current has stopped
postflow
__________ is the time during which the gas flows to clear out any air in the nozzle
preflow
Melting the tungsten end shape
properly install the tungsten, set the argon gas flow, switch the current to DCEP, and turn on the machine. strike arc, slowly increase amperage, stop when desired shape has been reached.
Nitrogen in GTAW
useful as an austentite stabilizer in the alloy.
24. What is the heat distribution with AC welding current?
• Electrode absorbs ½ of the heat. • Work absorbs ½ of the heat.
Why should the grinding marks run lengthwise on the tungsten electrode?
• Lengthwise grinding reduces the amount of small particles of tungsten contaminating the weld.
EWTH
1 and EWTH-2 Yellow and Red, Thoriated Tungsten - Thorium oxide (ThO2), when added in percentages of up to 0.6% to tungsten, improves its current carrying capacity. The addition of 1% to 2% of thorium oxides improves electron emission. Thorium increases the serviceable life of the electrode. Easier arc starting. Work well with DCEN. Good for steel, steel alloys, nickel alloys, and most other metals other than aluminum or magnesium. Not suitable for AC.
EWLa
1- Black, Lonathium Tungsten Electrode - Not radioactive. Improved current carrying capacity. Slightly higher arc voltage than cerium and thorium.
AC
1/2 heat - 1/2 heat - equal cleaning - penetration
DCEP concentrates about.......
1/3 on the work and the remaining 2/3 on the electrode
33. Using Table 15
4, determine the minimum gas flow rate for a 1/2'" (13mm) nozzle. - • 17-20 cfh, or 8-9.4 L/min
In the United States, the electric current cycles at the rate of ______________ per second
60 times
Because ________ does not put much heat on the tip, it is relatively cool, the point is stable, and it can survive extensive use without damage to the tungsten
DCEN
cleaning action
DCEP has a cleaning action -
Alloy Not Specified
EWG
GTAW Electrodes
EWP = Pure Tungsten EWTh-1 = 1% Thorium Tungsten EWTh-1 = 2% Thorium Tungsten EWZr = 1/4% to 1/2% zirconium tungsten. EWCe-2 =2% cerium tungsten EWLa-1 = 1% lanthanum tungsten EWG = Alloy not specific
What is the ideal heat distribution with DCEP Welding Current?
Electrode absorbs 2/3 of the heat. Work absorbs 1/3 of the heat.
1. What materials were weldable only by the GTAW process before GMAW was developed?
Reactive Materials (prone to contamination at welding temps). • Aluminum • Magnesium • Titanium • Some grades of Stainless Steel
Argon is also good for welding in deep grooves because it is denser than air.
TRUE
Tungsten is easily broken so the welder must be careful when breaking it.
TRUE
Reading the ball
The ball may be read on a flowmeter from the bottom, center, or top of the ball
Why must AC welding power use high frequencies in order to work?
• The high frequency ensures that a voltage peak will occur reasonably close to the current reversal in the welding arc, creating a low resistance ionized path for the welding current to follow.
TIG
Tungsten Inert Gas Welding
Ways to prevent tungsten electrode erosion:
1. Having good mechanical and electrical contact. 2. Using as low a current as possible. 3. Using a water-cooled torch. 4. Using as large a size of tungsten electrode as possible. 5. using DCEN current. 6. Using as short an electrode extension from the collet as possible. 7. Using the proper electrode end shape. 8. Using an alloyed tungsten electrode.
DCEN concentrates about.......
2/3 on the work and the remaining 1/3 on the electrode
Thoriated tungsten does not work well with ______
AC
GTAW Process
An arc is established between a nonconsumable tungsten electrode and the base metal which is called the work. The electrode doesn't melt, but the work does at the spot where the arc impacts its surface and produces a molten weld pool where it melts. Since hot tungsten is sensitive to oxygen contamination, a goodinert shielding gas is required to keep the air away from the hot tungsten and molten weld metal.
inert gas
An inert gas is any gas that is not reactive with elements. Argon is an inert gas used in GTAW
_________ gas is much cheaper than __________ gas - and therefore more widely used.
Argon, helium
28. What makes helium difficult to use for manual welding?
Because penetration and bead profile are sensitive to the arc length and the long arcs needed for feeding filler wires are more difficult to control.
EWZr
Brown, Zirconium Tungsten Electrode - Helps emit electrons freely. Same effect as thorium, but to a lesser degree. Are more easily melted than thorium tungsten so can be used with both AC and DC currents. They can be used with the balled end and are good for AC welding of aluminum and magnesium. Good resistance to weld pool contamination.
Properties of Tungsten
High Tensile Strength Hardness, Rockwell C45 High Melting Temperature: 6170 F High Boiling Temperature: 10700 F Good electrical conductivity
Function of Inert Gas in GTAW welding:
Inert gas provides the needed arc characteristics and protects the molten weld pool. Because flexes are not used, the welds produced are sound, free of slags, and as corrosion resistant as the parent metal.
EWG
No color specified, Alloy not specified Electrode - Manufacturer specific alloys.
Types of Tungsten Electrodes
Pure Tungsten = Green 1% thorium added = Yellow 2% thorium added = Red 1/4% to 1/2 zirconium added = Brown 2% Cerium added = Orange 1% lanthanium added = Black
Grinding Stone for GTAW
Should be used only for tungsten, to avoid contamination - should have a fine, hard stone
"How might air be drawn into the shielding gas between the nozzle and the weld?"
The air can be drawn in under the nozzle if the torch is held at too sharp an angle to the metal.
Cerium Tungsten, EWCe-2
These electrodes were developed because they are not made of a radioactive material, like thoriated tungstens. Have a similar current carrying capacity to pure tungsten, but have an improved arc starting and stability
Non-consumable
Tungsten is non-consumable, however it slowly degrades
What does adding thorium oxide do for the tungsten electrode?
What does adding thorium oxide do for the tungsten electrode? • When added in percentages of up to .6% to tungsten, current carrying capacity is improved. • Further addition of thorium oxide to 1-2% helps with electron emission allowing it to carry approximately 20% more current. This results in a reduction of the electrode tip temperature, resulting in less tungsten erosion and subsequent weld contamination. • Also provide a much easier arc starting characteristic than pure or zirconiated tungsten. • They work well with DCEN and maintain a sharpened point well. Do not use with AC. • Very suitable for welding on steel, steel alloys, nickel alloys, and most metals other than aluminum and magnesium.
_______________________ tungstens are more resistant to weld pool contaminations than pure tungsten
Zirconiated
A high-voltage, but low-current _______________ commonly provides the assist a relatively low cost
spark-gap oscillator
Because there is no ____ used to clean the weld in GTA welding, all surface contamination such as oxides, oil, dirt, and so on, must be cleaned from the part being welded and the filler metal so they do not contaminate the weld.
flux
Rate of Flow - GTAW
should be as low as possible while still giving adequate coverage.
Gas Tungsten Arc Welding (GTAW)
uses a noncomsumable electrode made of tungsten. In GTA welding the arc between the electrode and the base metal melts the base metal and the end of the filler metal as it is manually dipped into the molten weld pool. A shielding gas flowing from the gun nozel protects the molten weld metal from atmospheric contamination. A foot or thumb remote control switch may be added to the basic GTA welding setup to allow the welder better controls.
DCEP heat distribution
wide - shallow penetration - strong cleaning action - rounded end
When holding one end of the tungsten against the grinding wheel, the other end of the tungsten must not be pointed towards _________
your palm / hand
12. Why should a grinding stone that is used for sharpening tungsten not be used for other metals?
• Because of the hardness of tungsten and its brittleness, the grinding stone chips off small particles of the electrode. A course grinding stone will result in more tungsten breakage and a poorer finish. If the grinder is used for metals other than tungsten, particles (of other metals) may become trapped on the tungsten as it is ground. The metal particles will quickly break free when the arc is started resulting in contamination.
What materials can be used to make nozzles?
• Ceramic such as Alumina or Silicon Nitride (opaque) • Fused Quartz (clear)
What is the heat distribution with DCEN welding current?
• Electrode absorbs 1/3 of the heat. • Work absorbs 2/3 of the heat.
How can the end of a tungsten electrode be shaped?
• Grinding • Breaking • Remelting the end • Chemical Compounds
1. What early advancements made the GTA welding process more effective and reduced its cost?
• Improvement in gas composition (switching from helium to tungsten) and a better understanding of the importance of polarity (all three polarities are used, but differ for different applications) improved the effectiveness of the process and reduced its cost
27. Why is argon's ease of ionization a benefit?
• It makes it suitable for alternating current applications and easier starts. It also permits fairly long arcs at lower voltages, making it virtually insensitive to changes in arc length..
2. Which two of tungsten's properties make it the best choice for GTA welding?
• The high melting temperature and good electrical conductivity. Hardness Tensile Strength
What holds the molten ball of tungsten in place at the tip of the electrode during DCEP welding?
• The liquid tungsten surface tension with the larger mass above the molten ball holds it in place like a drop of water on your fingertip.
7. What problem can an excessively large tungsten cause?
• They may result in too low a temperature for a stable arc.
