GTAW Gas Tungsten Arc Welding

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Jakub Slavík
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1 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

2 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 Gas shielded arc with non consumable tungsten electrode used names GTAW USA TIG Tungsten inert gas WIG - Wolfram inert gas ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

Ni alloys : 0,5-10 mm short circuit : I = 10-500 A U = 16-21 V

3 Basic parameters Positions Base material Welded thickness Current, voltage : all : all steels, alloyed steels, Al, Cu, Ni alloys : 0,5-10 mm short circuit : I = A U = V Tungsten electrod diameter : 2 4 mm Welding source : steep, AC, DC +/-

4 Equipment

5 Welding torch

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

6 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

7 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

tools Root welds for thin sheets especially for highly alloyed materials - SS, HSS,

8 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

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

9 Tungsten electrodes normalized ČSN EN ISO 6848 size, composition, color Diameter 0,5-10 mm, standard 2-4 mm, lengths mm Color + name = composition Wolfram + alloying - WP - pure W Tt = C - WT W+ThO 2 - Tt = C - WZ W+ ZrO 2 - Tt = C - WL W+ La 2 O 3 - Tt = C - WC W+ CeO 2 - Tt = C - Electron emisivity - Longevity - Stability - Temperature decrase C

10 Electrode shape Direct current Alternative current

11 Sharpening

12 Grinders

13 Filler wire solid, cored wire

14 Basic weld joints Butt Weld and Stringer Bead Lap Joint T-Joint Corner Joint

15 Shielding gases Most often inert gases used - Ar, He Argon Good arc starting Good cleaning action Good arc stability Focused arc cone Lower arc voltages Ar + He mixtures 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 Ar + H 2 Hydrogen is reduction gas reduces oxygen, High heat transfer, improved penetration, stability, for austenitic steels, Ar + N 2 for austenitic steels and duplex steels nitrogen stabilizes austenite

16 Effect of shielding on the arc I=240 A, material Argon Ar + He Helium

17 Ar-He mixtures Argon 75% Argon / 25% Helium 280 A / 25 V 50% Argon / 50% Helium 282 A / 27 V 25% Argon / 75% Helium 285 A / 30 V 285 A / 34 V

18 Shielding quality root shielding Demands Corrosion Outlook Shape Proper shielding Shielding when cooling High purity gas No oxygen presence - tubes

19 Shielding

20 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

21 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 Size Inside 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

22 GTAW change of polarity non consumable electrode and invertor welder makes possible change of polarity, square pulse, arc pulse, pulse frequency atc.

23 GTAW change of polarity

24 Polarity and heat input

25 Arc cleaning effect during Al welding Kinetic energy, momentum Electron emission energy + + Ionty Elektrony bez Al 2 O 3 Al 2 O 3 1,77 ev 3,95 ev Al - Al - ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

26 AC pulse

27 AC

28 Pulsing DC current Average current is low, so heat input as well. Small HAZ, deformations etc.

29 DC pulse - U, I time curves

30 Arc Spot welding

31 Automation TIG welding has low effectivity Solution by: Filler wire feed Wire preheating Torch movement Narrow gap Orbital welding Robotic welding

32 Filler wire feed

33 Narrow gap welding

34 Orbital welding of tubes Over 200 mm

35 Orbital welding of tubes Diameter mm

36 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

37 Orbital welding heat exchangers

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