TIG Process (141): Fundamentals and Applications
Introduction
The TIG (Tungsten Inert Gas) process, designated 141 in EN ISO 4063, is an arc welding process using a non-consumable tungsten electrode and inert gas shielding. It produces high-quality welds and is widely used on demanding materials: stainless steel, aluminium, titanium and nickel alloys.
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Operating Principle
The arc is established between the tungsten electrode (which does not melt) and the base metal. Filler metal, when required, is fed manually into the weld pool. The inert gas (Ar or He) protects the arc, electrode and weld pool from atmospheric contamination.
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Welding Current
| Current type | Polarity | Application | Penetration | Cathodic cleaning |
|---|---|---|---|---|
| DC— (DCEN) | Electrode negative | Steels, stainless, titanium | Deep | No |
| DC+ (DCEP) | Electrode positive | Rare | Shallow | Yes |
| AC | Alternating | Aluminium and magnesium | Medium | Yes (+ half-cycle) |
Note: Aluminium requires AC because cathodic cleaning (positive half-cycle) removes the refractory Al₂O₃ oxide layer that would prevent fusion.
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Tungsten Electrodes (EN ISO 6848)
| Designation | Colour | Composition | Application |
|---|---|---|---|
| W (WP) | Green | Pure tungsten | AC — aluminium |
| WCe 20 | Grey | W + 2% CeO₂ | DC — steel, stainless |
| WLa 10 | Black | W + 1% La₂O₃ | DC and AC — versatile |
| WTh 20 | Red | W + 2% ThO₂ | DC — (radioactive, declining use) |
| WZ 8 | White | W + 0.8% ZrO₂ | AC — aluminium |
Electrode preparation:
- DC: ground to a point (20–30° cone) → stable, concentrated arc
- AC: balled tip (forms naturally) → use WP or WZ electrodes
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Shielding Gases
| Gas | Application | Advantage |
|---|---|---|
| Argon (Ar) | Universal | Good arc stability, cost-effective |
| Helium (He) | Thick sections | Higher energy → deeper penetration |
| Ar + He (30–70%) | Stainless, aluminium | Penetration/stability compromise |
| Ar + H₂ (2–5%) | Austenitic stainless | Higher welding speed |
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Typical Parameters
| Thickness (mm) | Electrode diam. (mm) | Filler diam. (mm) | Current (A) | Gas flow (l/min) |
|---|---|---|---|---|
| 1.0 | 1.6 | 1.6 | 40–70 | 6–8 |
| 2.0 | 2.4 | 2.4 | 80–120 | 8–10 |
| 3.0 | 2.4–3.2 | 3.2 | 120–180 | 10–12 |
| 5.0 | 3.2 | 3.2–4.0 | 180–250 | 12–15 |
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Advantages and Limitations
Advantages: superior weld quality, no spatter, precise heat input control, applicable from 0.5 mm thickness.
Limitations: low deposition rate, gas cost (He very expensive), requires high-quality joint preparation, wind-sensitive.
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Reference Standards
- EN ISO 4063:2010 — Welding and allied processes. Nomenclature of processes and reference numbers
- EN ISO 6848:2015 — Welding and allied processes. Non-consumable tungsten electrodes
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