TIG welding — formally known as Gas Tungsten Arc Welding (GTAW) — is the most precise and highest-quality arc welding process available. It is used for root passes on pressure vessels and pipelines, critical aerospace structures, exotic alloys like titanium and Inconel, and anywhere that weld appearance and integrity cannot be compromised.
Unlike MIG welding where the machine self-regulates, TIG is entirely operator-controlled. The welder manages torch angle, arc length, travel speed, and filler rod addition simultaneously — which is why TIG takes years to master. But getting the settings right is the foundation: no amount of skill can compensate for a machine set incorrectly.
This guide covers every TIG parameter — amperage, tungsten selection, polarity, shielding gas, cup size, filler rod — with the formulas behind them, a fully working calculator, and complete reference tables for all common materials.
How TIG Welding Works — Process Overview
Understanding the process is essential before setting parameters. TIG welding generates heat from an arc between a non-consumable tungsten electrode and the workpiece. The electrode does not melt — it only carries current and sustains the arc.
Figure 1 — GTAW/TIG process schematic: non-consumable tungsten electrode, separate filler rod, and inert gas shielding.
Key facts about the TIG process:
- The tungsten electrode creates the arc but does not melt or deposit into the weld
- Filler metal is fed separately by hand as a rod (or can be autogenous — no filler)
- Constant Current (CC) power source is required — NOT constant voltage like MIG
- Amperage is set on the machine; the welder controls it further with a foot pedal or torch-mounted amperage control
- Travel speed is entirely welder-controlled — there is no wire feed mechanism
TIG Welding Parameters — What You Set and Why
| Parameter | Controls | Set By | Key Rule |
|---|---|---|---|
| Amperage | Arc heat, penetration, fusion | Machine dial + foot pedal | ~1A per 0.025mm (1A per 0.001″) of thickness |
| Polarity (DC−/AC) | Penetration pattern, cleaning action | Machine switch | DC− for steel/SS/Ti/Cu; AC for aluminium |
| Tungsten Diameter | Current-carrying capacity, arc stability | Welder selects | Larger diameter = higher current capacity |
| Tungsten Type | Arc stability, contamination resistance | Welder selects | 2% Thoriated (red) for DC; Pure/Zirconiated for AC |
| Shielding Gas | Weld protection, heat input, travel speed | Machine/regulator | 100% Argon for most; Ar/He mix for thick sections |
| Gas Flow Rate | Coverage area, turbulence | Flowmeter regulator | Cup ID (mm) × 0.4–0.5 = LPM approx. |
| Cup/Nozzle Size | Gas coverage width | Welder selects | #4–#6 for thin; #7–#10 for thick/critical |
| Arc Length | Voltage (indirect), penetration, stability | Welder controls | = tungsten electrode diameter (rule of thumb) |
| Filler Rod Diameter | Bead profile, deposition | Welder selects | Typically = plate thickness / 2, min 1.6mm |
The Formulas Behind TIG Welding Parameter Selection
Formula 1: Amperage from Thickness
The fundamental rule for TIG amperage is the “1-amp-per-thou” rule from traditional imperial practice:
i.e. 1 amp per 0.001 inch of base metal thickness
In metric, this translates to approximately:
I (Amps) ≈ Thickness (mm) × 35 [for AC, aluminium — 10–15% less]
Worked Example (DC−, Stainless Steel, 3mm):
I = 3 × 40 = 120 A starting point. With a foot pedal, you would dial 140A on the machine and feather down to 100–120A during the weld.
Formula 2: Amperage Correction for Position and Material
Position Factors:
Flat (1G): × 1.00
Horizontal (2G): × 0.95
Vertical (3G): × 0.85
Overhead (4G): × 0.80
Material Factors:
Mild Steel: × 1.00
Stainless: × 0.90 (lower conductivity, retains heat)
Aluminium (AC):× 1.25 (high thermal conductivity, needs more heat)
Titanium: × 0.85 (very sensitive — reduce heat)
Copper: × 1.40 (extremely high conductivity, needs much more heat)
Formula 3: Gas Flow Rate from Cup Size
Flow Rate (LPM) ≈ Cup # × 5 × 0.472
Example: #7 cup → 7 × 5 = 35 CFH → 16.5 LPM
Note: For Helium shielding gas, double the flow rate shown for Argon (Helium is much lighter and disperses faster).
Formula 4: Heat Input
GTAW thermal efficiency η = 0.60 per EN ISO 1011-1
HI_net = HI × 0.60
DC− vs DC+ vs AC — Polarity Explained
Polarity is one of the most critical settings in TIG welding. Using the wrong polarity will either destroy your tungsten, contaminate the weld, or fail to achieve fusion.
Figure 2 — TIG welding polarity comparison: penetration profiles and material applications for DC−, DC+, and AC.
Tungsten Electrode Selection — Types, Colours & Current Ranges
Selecting the wrong tungsten type is one of the most common TIG setup errors. Each tungsten alloy has different arc stability, current-carrying capacity, and behaviour on AC vs DC.
Figure 3 — TIG tungsten electrode types, colour codes, and amperage ranges (AWS A5.12).
Tungsten Tip Preparation
How you prepare the tungsten tip dramatically affects arc stability and weld quality:
| Current Type | Tip Shape | How to Prepare | Included Angle |
|---|---|---|---|
| DC− (all DC steels, SS, Ti) | Ground to a point (tapered) | Grind longitudinally on dedicated aluminium oxide wheel | 30°–60° cone angle |
| AC (aluminium) | Balled end | Strike arc on copper block — tungsten balls naturally with AC current | N/A — hemispherical ball |
| DC− automated/robotic | Truncated cone (blunt tip) | Grind to point, then flat 0.5–1mm dia at tip | 30°–45° + 0.5–1mm flat |
TIG Welding Settings by Material
Mild Steel (DCEN)
| Thickness (mm) | Amps | Tungsten Ø | Filler Ø | Gas (LPM) | Cup # |
|---|---|---|---|---|---|
| 0.8 | 25–40 | 1.0 mm | 1.0 mm | 6–8 | #4 |
| 1.5 | 50–70 | 1.6 mm | 1.6 mm | 7–9 | #5 |
| 2.0 | 70–90 | 1.6 mm | 1.6 mm | 8–10 | #5 |
| 3.0 | 100–130 | 2.4 mm | 2.4 mm | 9–12 | #6 |
| 5.0 | 150–180 | 3.2 mm | 2.4 mm | 10–14 | #7 |
| 8.0 | 190–240 | 3.2 mm | 3.2 mm | 12–16 | #8 |
| 10 | 220–280 | 4.0 mm | 3.2 mm | 14–18 | #8–#10 |
Stainless Steel (DCEN)
Stainless retains heat far more than mild steel — reduce amperage 10–15% and increase travel speed to avoid overheating the HAZ (which causes sensitisation — carbide precipitation — in unstabilised grades like 304).
| Thickness (mm) | Amps | Tungsten Ø | Filler | Gas | Interpass Limit |
|---|---|---|---|---|---|
| 1.0 | 30–50 | 1.6 mm | ER308L/ER316L 1.6mm | 100% Ar 8–10 LPM | 150°C max |
| 2.0 | 60–80 | 1.6 mm | ER308L/ER316L 1.6mm | 100% Ar 9–11 LPM | 150°C max |
| 3.0 | 85–110 | 2.4 mm | ER308L/ER316L 2.4mm | 100% Ar 10–13 LPM | 150°C max |
| 5.0 | 130–160 | 3.2 mm | ER308L/ER316L 2.4mm | 100% Ar 12–15 LPM | 150°C max |
| 8.0 | 170–210 | 3.2 mm | ER308L/ER316L 3.2mm | 100% Ar 14–17 LPM | 150°C max |
Aluminium (AC)
Aluminium requires AC current for the oxide-cleaning action. The AC positive half-cycle blasts away the refractory aluminium oxide (Al₂O₃, melting point 2,072°C) while the negative half-cycle provides penetration heat.
| Thickness (mm) | Amps (AC) | Tungsten Ø | Filler | Gas (LPM) | Cup # |
|---|---|---|---|---|---|
| 1.5 | 50–70 | 1.6 mm (Pure/Zr) | ER4043/ER5356 2.4mm | 10–12 | #6 |
| 2.0 | 70–90 | 2.4 mm (Pure/Zr) | ER4043/ER5356 2.4mm | 11–13 | #6–#7 |
| 3.0 | 100–130 | 2.4 mm (Pure/Zr) | ER4043/ER5356 3.2mm | 13–16 | #7 |
| 5.0 | 160–200 | 3.2 mm (Pure/Zr) | ER5356 3.2mm | 15–18 | #8 |
| 8.0 | 200–260 | 4.0 mm (Pure/Zr) | ER5356 4.0mm | 17–20 | #8–#10 |
| 10 | 250–320 | 4.8 mm (Pure/Zr) | ER5356 4.0mm | 18–22 | #10 |
TIG Welding Settings Calculator
Enter your material details below. The calculator outputs amperage range, tungsten diameter and type, filler rod size, shielding gas, cup size, gas flow rate, and heat input — with full formula workings shown.
TIG / GTAW Settings Calculator
Amperage · Tungsten · Filler Rod · Gas Flow · Cup Size · Heat Input
① Base Metal
② Process Setup
③ Optional — Travel Speed for Heat Input
📊 Recommended TIG Parameters
Step-by-Step: How to Set Up Your TIG Welder
- Select and prepare the tungsten electrode — correct type, diameter, and tip geometry for your material and polarity. Install with correct stick-out (5–8mm typical).
- Set polarity — DC− for all ferrous and titanium; AC for aluminium and magnesium.
- Set amperage — use the calculator above. If you have a foot pedal, set 15–20% higher than calculated and use the pedal to control the puddle.
- Set gas flow rate — connect Argon (or appropriate gas), set flowmeter to recommended LPM. Let gas flow for 5–10 seconds before striking arc (pre-flow).
- Set pre-flow and post-flow times — pre-flow: 0.5–1 second; post-flow: 5–15 seconds depending on material (titanium needs 30+ seconds post-flow to prevent oxidation).
- Select and cut filler rod — correct classification for base metal. Clean with acetone. Do NOT touch the filler rod tip with bare hands.
- Prepare base metal — clean with dedicated stainless brush or acetone/IPA. For aluminium, use dedicated stainless brush and weld within 2–4 hours of cleaning.
- Strike the arc — use HF (high frequency) start or lift-arc. Never scratch-start on the base metal (causes tungsten contamination).
- Establish puddle, then feed filler — get a molten pool first, then introduce filler at the leading edge of the pool at 15–20°.
- Maintain consistent arc length — equal to electrode diameter. Too long = arc wanders; too short = risk of dipping tungsten into pool.
- End the weld properly — use down-slope (foot pedal or machine down-slope setting) to slowly reduce current and fill the crater. Do NOT abruptly stop the arc.
- Post-flow shielding — keep torch over weld until gas post-flow is complete. For titanium, use trailing shield or keep in argon purge environment until below 400°C.
TIG Welding Troubleshooting — Defects & Parameter Fixes
| Symptom | Likely Cause | Fix |
|---|---|---|
| Tungsten contamination (black tip) | Dipped tungsten in weld pool; wrong polarity | Regrind/re-prep tungsten; check polarity setting; maintain correct arc length |
| Porosity | Gas contamination or low flow; base metal not clean; moisture | Increase flow rate; check for gas leaks; clean base metal; check pre/post flow times |
| Arc wander (arc moves around) | Magnetic arc blow; tungsten not pointed correctly; long arc length | Reposition earth clamp; regrind tungsten; shorten arc length |
| Burn-through on thin material | Amperage too high; travel speed too slow; poor fitup (gap too wide) | Reduce amperage; increase travel speed; use foot pedal; use backing bar/copper chill |
| Lack of fusion | Amperage too low; travel speed too fast; arc length too long | Increase amperage; slow travel speed; maintain shorter arc; clean joint surfaces |
| Grey/black weld colour (SS) | Gas contamination; overheating/sensitisation | Check gas purity and flow; reduce interpass temperature; check post-flow time |
| Coloured oxidation on titanium | Insufficient shielding or purge; gas contamination | Silver only = acceptable; straw yellow = borderline; blue/purple/grey = REJECT and grind out |
| Aluminium weld turning grey/black (AC) | Incorrect gas (not pure Ar); contaminated base metal; too low frequency (old transformer) | Use only 100% pure Argon; re-clean with dedicated brush; check AC frequency setting |
| Crater crack at weld end | Abrupt arc stop without down-slope; crater not filled | Use down-slope function; feather the pedal at end; fill crater with filler rod before stopping |
Worked Example — Fully Solved
Problem: TIG weld a 316L stainless steel butt joint, 4mm thick, in the flat position (1G). Open root, no backing. Calculate all settings.
Step 1 — Polarity: Stainless steel → DC− (DCEN)
Step 2 — Amperage:
A_base = 4mm × 40 × 0.90 (SS factor) × 1.0 (flat) = 144 A
With foot pedal: machine set = 144 × 1.18 = 170 A on machine dial
Working range: 120–158 A
Step 3 — Tungsten:
170A, DC−: 2.4mm Ceriated (grey) or 2% Thoriated (red)
Tip: ground to 30–45° taper point, longitudinally
Step 4 — Filler Rod:
4mm SS316L → 2.4mm ER316L (AWS A5.9)
Step 5 — Cup and Gas:
~144A → #6 Gas Lens nozzle
Gas: 100% Argon, 12–14 LPM shielding + 100% Argon back-purge
Step 6 — Heat Input (at estimated 130 mm/min travel speed):
V ≈ (0.04 × 144) + 10 = 15.8V
HI = (15.8 × 144 × 60) / (130 × 1000) = 136,512 / 130,000 = 1.050 kJ/mm
HI_net = 1.050 × 0.60 = 0.630 kJ/mm (net, EN method)
Summary: 170A (pedal to 130–155A), DC−, 2.4mm ceriated tungsten (pointed), 2.4mm ER316L filler, #6 gas lens, 100% Ar at 13 LPM shielding + purge, interpass max 150°C. ✅
Frequently Asked Questions
Q: Why does TIG use constant current (CC) instead of constant voltage (CV)?
In TIG welding, the arc length is controlled manually by the welder. With a Constant Voltage source, any change in arc length would cause a large change in current — making the process uncontrollable. A Constant Current source maintains a relatively stable amperage despite small arc length changes, giving the welder precise thermal control. This is why TIG machines have steep (drooping) volt-amp curves.
Q: When do I use AC vs DC for TIG welding?
Use AC for aluminium and magnesium — the cleaning action of the AC positive half-cycle removes the refractory oxide layer, enabling fusion. For all other metals (steel, stainless, titanium, copper, nickel alloys), use DC− (DCEN) which concentrates ~70% of arc heat into the workpiece for efficient fusion and deep penetration while keeping the tungsten cooler.
Q: What does a foot pedal actually do in TIG welding?
The foot pedal is a remote amperage control. It varies current from near-zero up to the machine’s maximum set amperage. This lets you increase heat to establish the puddle, then reduce heat as the joint heats up (preventing burn-through or distortion). It also allows precise crater filling at the end of a weld. It is strongly recommended for all manual TIG welding — fixed amperage without a pedal is only suitable for automated/mechanised TIG.
Q: What colour should my TIG weld on stainless steel be?
A properly shielded stainless steel TIG weld should be silver/bright metallic to light gold. Darker straw-gold is borderline. Brown, blue, purple, or grey/black indicates oxidation (sensitisation or sugar) caused by insufficient gas shielding or back-purge. For hygienic or corrosion-critical applications, only silver welds are acceptable — re-weld or use electrolytic polishing to restore corrosion resistance.
Q: How long should post-flow shielding gas run after the arc stops?
As a guide: post-flow time (seconds) ≈ amperage / 10. So at 150A, post-flow should run for ~15 seconds. For titanium, the rule is more strict — maintain shielding until the weld is below 400°C (~40–60 seconds or more). Most TIG machines have an adjustable post-flow timer — set it correctly before welding.
Related Calculators on WeldFabWorld
- Welding Heat Input Calculator — kJ/mm from your TIG settings
- Preheat Temperature Calculator — Required preheat from steel chemistry
- Carbon Equivalent Calculator — Weldability assessment
- Ferrite Number Calculator — FN prediction for stainless TIG welds
- Schaeffler Diagram Calculator — Microstructure prediction for stainless welds
- MIG Welding Settings Calculator — Compare GMAW parameters
References & Standards
- AWS A5.12 / ISO 6848 — Specification for tungsten and tungsten-alloy electrodes for arc welding and cutting
- AWS A5.18 — Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding (ER70S series)
- AWS A5.9 — Stainless Steel Electrodes and Rods for Arc Welding (ER308L, ER316L, ER2209)
- AWS A5.10 — Aluminium and Aluminium Alloy Electrodes and Rods (ER4043, ER5356)
- AWS A5.16 — Titanium and Titanium Alloy Filler Metals (ERTi-2, ERTi-5)
- EN ISO 1011-1 — Welding. Recommendations for welding of metallic materials. Part 1: General guidance for arc welding
- Miller Electric — Guidelines for Gas Tungsten Arc Welding (GTAW), Publication 804846
- CK Worldwide — Technical Specifications for TIG Welding, Form 116
- Haynes International — GTAW/TIG Welding of Nickel Alloys — Technical Guide