TIG Welding
Also: GTAW, gas tungsten arc welding, heliarc, tungsten inert gas welding, argon welding, orbital welding, micro TIG, precision welding
TIG welding (GTAW) uses a tungsten arc under argon with hand-fed filler: the cleanest, most controlled welds on aluminum, stainless, titanium and thin parts.
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TIG strikes an arc between a non-consumable tungsten electrode and the work under argon shielding; the welder controls the current with a foot pedal and adds filler rod by hand, or none at all on thin edge joints. Steel, stainless, titanium and nickel alloys weld on direct current with the electrode negative; aluminum welds on alternating current, whose positive half-cycle strips the oxide off the puddle. Pulsed TIG narrows the heat-affected zone on thin sheet, and orbital TIG heads clamp on tube and weld a full circle automatically for sanitary and semiconductor piping.
The reward for the slow pace is control: a small puddle, no spatter, a smooth evenly rippled bead, and a weld that meets aerospace (AWS D17.1) and pressure (ASME IX) radiographic standards. Stainless and titanium need the back side of the joint purged with argon too, or the root oxidizes (sugaring); titanium needs trailing shields or a purge chamber until it cools below about 425 °C (800 °F), and a straw or silver color on the finished weld is the proof it was done right.
TIG runs at a third to a fifth the speed of MIG and deposits little metal, so it is priced per inch three to five times higher and is not the choice for thick plate or long structural welds. It is the choice for sheet under 3 mm (0.120"), for tube, for aluminum that will be anodized, for anything titanium or nickel, and for any weld that will be seen without grinding.
At a glance
| Typical tolerances | Fixtured assemblies ±0.8 mm (±1/32") standard, ±0.4 mm (±0.015") with care on small precision weldments; angles ±0.5° fixtured. Bead width consistent to ±0.5 mm. Distortion on thin sheet is lower than MIG because the heat input per pass is controlled. Anything tighter than ±0.4 mm is machined after welding. Orbital tube welds hold full penetration with helium leak-tight roots. |
|---|---|
| Size limits | Thickness from 0.25 mm (0.010") foil with micro TIG to about 6-10 mm (1/4-3/8") economically; thicker joints get a TIG root and a MIG or flux-cored fill. Tube from 3 mm (1/8") OD up to 300 mm (12") with orbital heads. Part size is limited by handling and by the purge chamber for titanium, typically under 1 m (40"). |
| Surface finish | A smooth, uniform bead with even ripples and no spatter, usable as welded on cosmetic parts. Stainless shows a straw or light-blue tint that passivation or pickling removes; titanium must be silver to straw, and blue or gray is rejected. Sanitary and pharmaceutical welds are ground and polished to 0.4-0.8 µm Ra (16-32 µin) and electropolished. |
| Lead time | Prototypes in 3-10 business days; aerospace-certified work in 2-4 weeks when fixtures and purge setups are needed; production runs in 2-6 weeks. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Stainless 304, 316 and 17-4 PH (welded in Condition A and aged afterwards), aluminum 5052, 5083 and 6061, titanium Grade 2 and Ti-6Al-4V, Inconel 625 and 718, Hastelloy C-276 and copper (with helium in the mix and preheat) are the TIG materials. Carbon steel and 4130 weld well; 4130 aircraft tube frames are TIG welded without preheat below 3 mm (0.120") wall. Free-machining 303, 416 and 12L14 crack; 7075 and 2024 are not welded for structure; brass loses zinc in the arc. Magnesium welds like aluminum on AC.
What drives the cost
- Weld length: TIG is priced per inch at three to five times MIG
- Material: titanium and nickel alloys need purging, chambers and certified welders
- Thickness and number of passes
- Cosmetic requirements: an as-welded bead with no grinding takes a skilled hand
- Certification and inspection: D17.1 or ASME IX, radiography, penetrant testing
- Fixturing, purging and pre-weld cleaning of aluminum and titanium
When to use it
- Sheet and tube under 3 mm (0.120") in stainless, aluminum, titanium and nickel alloys
- Cosmetic welds on enclosures, furniture, exhausts, handrails and anodized aluminum
- Aerospace, medical, food and semiconductor work under D17.1, ASME IX or sanitary standards
- Leak-tight tube and vessel joints, by hand or orbital
- Repairs and build-ups on precision parts where heat must be minimal
When not to
- Thick plate and long structural welds: MIG or flux-cored
- High-volume production without automation
- Free-machining grades, 7075 and 2024 aluminum, hardened steel
- Joints with poor access for a torch and a filler rod
- Budget-driven mild steel work where a ground MIG weld would do
Design tips
- Design edge, flange and corner joints on thin sheet so they can be welded without filler.
- Hold joint gaps to 10% of the thickness or less for autogenous welds, and keep thickness ratios at the joint under 3:1.
- Give the shop access to the back of stainless and titanium joints for purging, or note that purge fittings are required.
- Say whether the bead may be ground or must stay as welded, and give the weld class (D17.1 Class A, B or C) when it applies.
- For 6061-T6, expect about 165-185 MPa (24-27 ksi) tensile in the heat-affected zone and either design for it or specify re-heat-treatment to T6.
- Choose 5356 filler for aluminum that will be anodized (4043 turns darker), and 4043 for crack-sensitive 6xxx joints that will not be.
- Leave stock on machined faces near the weld and machine after welding.
- Send parts clean: no oil, anodize or plating in the weld zone, and say so on the drawing.
Frequently asked questions
- What is TIG welding used for?
- Thin, precise and cosmetic welds in stainless, aluminum, titanium and nickel alloys: aerospace and medical hardware, sanitary tube, exhausts, race-car frames, enclosures, furniture, and any repair where the heat must be small and controlled.
- Is TIG welding stronger than MIG?
- Both give full-strength welds when done correctly. TIG has fewer defects on thin and exotic material because the welder controls the heat and the filler separately, and TIG welds pass radiographic inspection more reliably; on thick steel, a MIG weld is just as strong and far cheaper.
- Can titanium be TIG welded?
- Yes, and TIG is the standard process for it. The weld and the heat-affected zone must be shielded with argon on both sides until they cool below about 425 °C (800 °F), using trailing shields, back purges or a glove box; the finished weld should be silver to straw. Blue, gray or white welds are contaminated and are rejected.
- Why is TIG welding more expensive?
- It is slow: a third to a fifth the travel speed of MIG, with little filler deposited per pass, and it needs a more skilled welder, more cleaning and often purging. The result is priced per inch at three to five times MIG, which is worth it on thin, cosmetic and exotic work and not on plate.
- What does a good TIG weld look like?
- A uniform bead of even width with regular, fine ripples, no undercut at the edges, no spatter, full penetration at the root, and, on stainless and titanium, a silver to light-straw color rather than blue or gray. On aluminum, a bright bead with a clean etched band on each side.
