-arc is established between the tip of a tungsten...
Transcript of -arc is established between the tip of a tungsten...
GTAW – Gas Tungsten Arc Welding
-arc is established between the tip of a tungsten electrode and the workpiece to
melt the base material (possibly also filler)
-tungsten electrode is considered to be non-consumable
-inert shielding gas protects the molten weld pool
FSW – Friction stir welding
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GTAW welding
GTAW is defined as arc welding using
a non consumable tungsten electrode
and a shielding gas protecting the weld.
Method no. acc. ČSN EN ISO 4063
14 – Gas shielded arc with non consumable
tungsten electrode141
142
143
145
146
147
used names
GTAW –USA
TIG – Tungsten inert gas
WIG - Wolfram inert gas
FSW – Friction stir welding
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Basic parameters
Positions : all
Base material : all
steels, alloyed steels, Al, Cu, Ni alloys
Welded thickness : 0,5 - 10 mm
Current, voltage short circuit : I = 10 -500 A
U = 16 - 21 V
Tungsten electrod diameter : 2 – 4 mm
Welding source : steep, AC, DC +/-
GTAW - advantages
very regular and well controlled welding proces results in good
mechanical, chemical properties
High quality and precision
Pin point control
Aesthetic weld beads
No sparks or spatter
No flux or slag
No smoke or fumes, no spatter,
molten pool is well visible and so controlable
welding in all positions
No need for further machining
Easy automation
GTAW - disadvantages
Lower filler metal deposition rates
Good hand-eye coordination a required skill
Brighter UV rays than other processes
Slower travel speeds than other processes
Low productivity
Difficult, expensive
GTAW - use
Welds more metals and metal alloys than any other process
sealing joints
precision welding
atomic energy, aircraft – turbine blades
repair of dies, forming tools
Root welds
for thin sheets
especially for highly alloyed materials - SS, HSS, AHSS
especially for light alloys - Al, Mg
heat exchangers, exhausts, pressure wessels
FSW – Friction stir welding
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Tungsten electrodes
normalized ČSN EN ISO 6848 –size, composition, color
Diameter 0,5 - 10 mm, standard 2-4 mm, lengths – 50-200 mm
Color + name = composition
Wolfram + alloying
- WP - pure W Tt = 3 420 °C
- WT – W+ThO2 - Tt = 3 300 °C
- WZ – W+ ZrO2 - Tt = 2 700 °C
- WL – W+ La2O3 - Tt = 2 300 °C
- WC – W+ CeO2 - Tt = 2 600 °C
- Electron emisivity –
- Longevity
- Stability
- Temperature decrase 1 000 °C
FSW – Friction stir welding
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Electrode shape
Direct current Alternative current
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Sharpening
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Grinders
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Filler wire – solid, cored wire
Shielding gases
Most often inert gases used - Ar, He
• Ar + He mixtures
• Ar + H2
Hydrogen is reduction gas – reduces oxygen, High heat transfer, improved
penetration, stability, for austenitic steels,
• Ar + N2
for austenitic steels and duplex steels – nitrogen stabilizes austenite
Argon► Good arc starting
► Good cleaning action
► Good arc stability
► Focused arc cone
► Lower arc voltages
Helium► Faster travel speeds
► Increased penetration
► Difficult arc starting
► Less cleaning action
► Less low amp stability
► Flared arc cone
► Higher arc voltages
► Higher flow rates (2x)
► Higher cost than argon
FSW – Friction stir welding
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Effect of shielding on the arc
Argon Ar + He Helium
I=240 A, material 1.4301
FSW – Friction stir welding
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Ar-He mixtures
Argon
280 A / 25 V
75% Argon / 25% Helium
282 A / 27 V
50% Argon / 50% Helium
285 A / 30 V
25% Argon / 75% Helium
285 A / 34 V
FSW – Friction stir welding
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Shielding quality – root shielding
Demands
Corrosion
Outlook
Shape
Proper shielding
Shielding when cooling
High purity gas
No oxygen presence - tubes
FSW – Friction stir welding
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Shielding
FSW – Friction stir welding
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Arc start
1) Electrode touch
2) Lift arc
3) High frequency start - standard
Non contact start is a must for non contamination
of electrode and WM.
Technique
Arc Length
Arc length normally one electrode diameter, when AC welding with a balled end electrode
When DC welding with a pointed electrode, arc length may be much less than electrode
diameter
Gas Cup SizeInside diameter of gas cup should be at least three times the tungsten diameter to provide adequate shielding gas coverage
Picture on right shows example of gas cup size and torch position
Electrode Extension
Refers to distance the tungsten extends out beyond the gas cup
May vary from flush with the gas cup to no more than the inside diameter of the gas cup
Longer the extension, the more likely it may contact something by accident
General rule would be to start with an extension of one electrode diameter
Gas cup size
El. Extension
Arc length
GTAW – change of polarity
non consumable electrode and invertor welder makes
possible change of polarity, square pulse, arc pulse, pulse
frequency atc.
FSW – Friction stir welding
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Polarity and heat input
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Arc cleaning effect during Al welding
+ +
--
Kinetic energy, momentum Electron emission energy
IontyAl2O3
Elektronybez
Al2O3
AlAl
1,77 eV 3,95 eV
FSW – Friction stir welding
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AC pulse
FSW – Friction stir welding
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AC
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Pulsing DC current
Average current is low, so heat input as well. Small HAZ, deformations etc.
FSW – Friction stir welding
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DC pulse - U, I time curves
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Arc Spot welding
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Automation
TIG welding has low effectivity
Solution by:
Filler wire feed
Wire preheating
Torch movement
Narrow gap
Orbital welding
Robotic welding
FSW – Friction stir welding
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Filler wire feed
FSW – Friction stir welding
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Narrow gap welding
FSW – Friction stir welding
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Orbital welding of tubes
Over 200 mm
FSW – Friction stir welding
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Orbital welding of tubes
Diameter 10 - 220 mm
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování