TIG Welding Setup Guide: Tungsten, Gas, and Technique

AC vs DC for TIG Welding

Polarity is the first setup decision in TIG welding and it determines what metals you can weld and how the arc behaves.

DC Electrode Negative (DCEN) — the standard polarity for steel, stainless steel, titanium, copper, and most non-aluminum metals. With DCEN the electrons flow from the tungsten into the base metal, concentrating heat in the weld pool and producing deep, narrow penetration. The tungsten runs cooler, lasts longer, and holds a sharp point.

AC (Alternating Current) — required for aluminum and magnesium. The AC cycle alternates between electrode negative (penetration) and electrode positive (oxide cleaning). The electrode-positive half-cycle blasts away the aluminum oxide layer that would otherwise contaminate the weld. Without this cleaning action, aluminum welds will be porous and weak.

Modern inverter TIG machines let you adjust AC frequency. Higher frequency (e.g., 120–200 Hz) produces a narrower, more focused arc — ideal for thin aluminum and tight joints. Lower frequency (60 Hz, the transformer machine default) produces a wider, softer arc suited to thicker material. Older transformer-based machines run fixed 60 Hz AC.

Tungsten Electrode Selection

Tungsten electrodes are color-coded by alloy type. Choosing the wrong tungsten causes poor arc starts, contamination, and shortened electrode life.

Size guide:1/16" for up to ~80A, 3/32" for 80–180A, 1/8" for 150–250A and above.

Shielding Gas for TIG Welding

TIG welding is far less forgiving of gas choice than MIG. The wrong gas will contaminate the tungsten, cause porosity, and ruin the weld appearance.

• Pure Argon (99.997% welding grade) — the standard shielding gas for virtually all TIG applications including steel, stainless, aluminum, titanium, and copper. Produces a stable, smooth arc and excellent bead appearance.
• Argon/Helium Blends (25–75% He)— used on thick aluminum sections where extra heat input is needed. Helium increases arc voltage and heat input without changing the current, useful when the standard argon arc cannot achieve adequate fusion on material over 3/8".
• Never use CO₂ or mixed MIG gases for TIG. CO₂ and Ar/CO₂ mixtures oxidize the tungsten immediately, causing arc instability, tungsten inclusions, and porosity. They are for GMAW (MIG) only.

Flow rate: 15–20 CFH for standard cup setups. 20–30 CFH when using a gas lens or large cup (size 7–8). Do not over-flow — excessive flow creates turbulence that pulls in atmospheric contamination.

Gas Lens Setup

A gas lens replaces the standard collet body with one that contains a stainless mesh diffuser screen. This screen converts the turbulent gas flow from the cylinder into a smooth, laminar envelope around the tungsten.

The benefits are significant: you can extend the tungsten stick-out 1/2" or more, giving better visibility and access to tight joints. Coverage is more consistent across the weld zone, reducing the risk of oxidation on stainless or titanium. Gas consumption is typically lower for equivalent coverage compared to a standard setup.

Gas lenses are paired with larger ceramic cups (size 6, 7, or 8 — the number indicates the inside diameter in 1/8" increments). Pyrex/clear glass cups are popular because they let you see the weld pool and tungsten position clearly. Gas lens setups are considered essential for stainless steel pipe welding, titanium, and aerospace work.

Back Purging Stainless Steel and Titanium

When TIG welding stainless steel pipe or tubing, the inside surface of the weld (the back side) is exposed to oxygen while the metal is still hot enough to oxidize. This creates a phenomenon called "sugaring" — a rough, granular oxidized surface that looks like brown or black sugar crystals. Sugaring significantly reduces corrosion resistance in the heat-affected zone.

Back purging involves flowing inert gas (argon or nitrogen) through the interior of the pipe to displace oxygen before and during welding. Use backing dams made from water-soluble tape or foam to contain the purge gas near the weld zone. Flow at 5–10 CFH and purge for at least 30–60 seconds before welding to achieve sufficient oxygen displacement. Many shops use an oxygen meter (O₂ analyzer) to verify the purge is below 50 ppm before welding.

Titanium requires even more care. The entire heat-affected zone must remain below 400°F (204°C) while in contact with oxygen — not just the weld pool, but the solidified bead and adjacent metal. Titanium welding requires a purge box or trailing shield on the torch to maintain inert coverage as the metal cools. Full enclosure purge chambers are used for complex titanium assemblies.

Filler Metal Selection for TIG

TIG filler rods are selected to match or overmatch the base metal. Using the wrong filler causes cracking, porosity, or poor corrosion resistance.

Tungsten Preparation

How you prepare the tungsten tip directly affects arc stability, weld bead geometry, and contamination risk.

For DCEN (steel, stainless, titanium): Grind the tungsten to a sharp point using a dedicated grinding wheel (do not use a wheel that has ground other metals). Grind parallel to the tungsten axis — not in a circular motion — so the grind marks run lengthwise. Circular grinding marks cause the arc to wander. The included angle of the point affects penetration: a 30° included angle produces a narrow, deep penetrating arc; a 60° angle produces a wider, more stable arc better for general use.

For AC (aluminum): Use pure or zirconiated tungsten and do not grind it to a point. Insert the blunt-cut tungsten, start the AC arc on a scrap piece, and allow the electrode tip to naturally form a smooth hemisphere ("ball up"). The balled tip is normal and desirable for AC stability. If the ball becomes irregular or spits, the tungsten is too small for the amperage — move to a larger diameter.

Always break off a contaminated section rather than grinding it back if the contamination is deep. Tungsten inclusions in the weld are a rejectable defect in code work.

Foot Pedal and Heat Control

The foot pedal is one of TIG welding's most powerful features. It allows the welder to continuously modulate amperage throughout the weld — ramping up to establish the pool, holding steady through the joint, and tapering down at the end to prevent crater cracks.

On thin material (16 gauge stainless, for example), heat builds as the weld progresses. Without amperage control, the pool grows wider and the travel speed must constantly increase to compensate. With a foot pedal, the welder simply reduces amperage as the material heats up, maintaining consistent bead width and penetration.

Pulse TIG is available on most modern inverter machines and provides electronic amperage modulation without foot pedal dexterity. The machine alternates between a high peak current (fusion) and a low background current (cooling). This reduces average heat input, minimizes distortion on thin stainless and titanium, and can slow the effective travel speed needed for consistent feeding. Pulse settings to start with: 50% peak time, 1 pulse per second (PPS), background current at 25–30% of peak.