TIG Welders (GTAW): How They Work and How to Choose One

In TIG welding, an arc forms between a tungsten electrode and the workpiece. The tungsten does not melt into the weld — it only carries the arc. Filler metal, when needed, is fed in separately by hand as a rod. An inert shielding gas, almost always pure argon, flows from the torch to protect the molten weld pool and the hot tungsten from the atmosphere.

Because the heat and the filler are controlled independently, the welder dictates exactly how much energy goes into the joint and exactly how much metal is added. That separation is why TIG produces such clean, accurate, low-spatter welds — and why it is the process of choice for stainless steel, aluminium, thin sheet and visible welds.

This is the single biggest choice when buying a TIG welder.

• DC TIG welds steel, stainless steel, copper, titanium and most common metals. The current flows in one direction, concentrating heat in the workpiece for deep, efficient penetration.
• AC TIG is required for aluminium and magnesium. These metals form a tough, refractory oxide layer that melts at a far higher temperature than the metal beneath it. Alternating current reverses polarity many times a second; the reverse-polarity (electrode-positive) half of each cycle blasts that oxide off the surface — the “cleaning action” — while the electrode-negative half puts heat into the joint. Without AC, the oxide layer prevents a sound aluminium weld.

A DC-only machine is cheaper and perfect if you never weld aluminium. An AC/DC machine does everything a DC machine does and adds aluminium capability, so it is the more versatile (and more expensive) choice. If aluminium fabrication is on your horizon at all, buy AC/DC.

How the arc is initiated affects both ease of use and weld cleanliness:

• High-frequency (HF) start is the premium method. The machine fires a high-frequency, high-voltage spark across the gap so the arc strikes without the tungsten ever touching the work. There is no contamination of the tungsten or workpiece — ideal for clean stainless and aluminium work. HF is also what sustains the AC arc on AC/DC machines.
• Lift-arc (lift TIG) touches the tungsten lightly to the work and lifts it; electronics sense the lift and ramp up the current cleanly, with little risk of contamination or tungsten inclusion. A good HF-free option, common on more affordable machines and useful where HF interference with nearby electronics is a concern.
• Scratch start is the most basic: you scratch the tungsten on the work like a match. It is cheap and rugged but contaminates the tungsten and the weld, so it is typically only found on TIG-capable MMA machines rather than dedicated TIG units.

For precision and aluminium work, insist on HF start. For occasional DC TIG on a budget or multi-process machine, lift-arc is a sensible compromise.

Pulse TIG switches the current rapidly between a high “peak” amperage and a low “background” amperage. The peak gives penetration; the background lets the weld pool cool slightly before the next peak. The result is lower overall heat input, which means less distortion on thin material, better control of the weld pool out of position, and a neat “stacked dime” bead appearance. Pulsing is especially valuable on thin stainless and aluminium, where too much heat warps the part. Better machines offer adjustable pulse frequency, peak/background amperage and the time split between them.

On AC/DC machines, two controls fine-tune aluminium welding:

• AC balance sets the ratio between the cleaning (electrode-positive) and penetrating (electrode-negative) halves of the AC cycle. More cleaning helps with dirty or heavily oxidised aluminium; more penetration gives a narrower, deeper, faster weld on clean material and keeps the tungsten cooler.
• AC frequency adjusts how many times per second the current alternates. A higher AC frequency tightens and stiffens the arc, narrowing the weld bead and giving more precise control on intricate work; a lower frequency gives a broader, softer arc that fills wider joints.

These two controls are why a quality AC/DC machine produces noticeably better aluminium welds than a basic one.

TIG’s hallmark is real-time heat control. A foot pedal lets the welder vary the current on the fly — easing off as the joint heats up, feathering the amperage to fill a crater at the end of a weld. It is the preferred method for bench and precision work. A torch-mounted amperage control (thumbwheel or finger control, sometimes called an Amptrol) does the same job by hand and suits work where a foot pedal is impractical, such as positional or site welding. Whichever you prefer, current control while welding is what separates TIG from less precise processes.

• Amperage range vs thickness. The output range must cover your work. As a rough guide, thin sheet needs low, finely controllable amperage at the bottom of the range, while thicker material needs higher peak current. Aluminium generally needs more amperage than steel of the same thickness because it conducts heat away so quickly.
• Duty cycle. Check the duty cycle at the amperage you’ll actually use, not the headline maximum — see duty cycle on the machines hub. Production work needs a high duty cycle; intermittent fabrication is less demanding.
• Single vs three phase. Lighter machines run on single-phase 230V; higher-output industrial units need three-phase 400V. Confirm your supply before you commit.
• Gas valve vs solenoid. A basic torch has a manual gas valve you open and close by hand — cheap, but no automatic pre-flow or post-flow. A machine with a gas solenoid controls gas flow electronically, giving programmable pre-flow and post-flow that shields the tungsten and weld as it cools. A solenoid is well worth having for clean stainless and aluminium results.
• Combined TIG/MMA. Most DC TIG inverters also run MMA (stick) electrodes, adding rugged, portable capability for thicker or dirtier steel at little extra cost — a practical bonus for a general workshop.

• Precision and thin sheet → a machine with fine low-end amperage control, HF start, pulse and a foot pedal.
• Stainless steel fabrication → DC TIG with HF start, pulse and good gas control (solenoid with post-flow) for clean, oxide-free welds.
• Aluminium fabrication → AC/DC with adjustable AC balance and AC frequency, HF start and pulse.
• Mixed workshop / site work → a combined TIG/MMA inverter; AC/DC if aluminium ever features.

A TIG welder is only as good as what runs through it. You’ll need the right tungsten electrodes (type and diameter to suit the metal and current), matched filler rods, the correct collets, collet bodies and gas cups for your torch, and a steady supply of pure argon. Browse our TIG consumables and read up on shielding gas to get the most from your machine. And because every arc process generates hazardous fume — including from stainless and aluminium — protect your welders with proper fume extraction.