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Pulse frequency is one of the most useful TIG controls for thin stainless steel, but it is not a substitute for correct amperage, fit-up, shielding, or torch control. Used properly, pulsing limits heat input, makes the weld puddle easier to read, and can reduce distortion and burn-through. Used incorrectly, it produces a narrow, irregular bead with poor fusion.
What Pulse Frequency Does
A pulsed TIG weld alternates between a higher peak current and a lower background current. Pulse frequency is the number of these cycles per second, measured in hertz (Hz). For example, 1 Hz produces one peak-and-background cycle each second, while 100 Hz produces 100 cycles each second.
Frequency mainly changes how quickly the puddle is heated and allowed to cool. It does not directly set total weld heat. Peak amperage, background amperage, peak-time percentage, travel speed, and arc length all affect heat input as well.
For thin stainless sheet, a useful starting range is usually 0.5 to 2 Hz. This slow pulse is easy to see and lets you coordinate filler additions with the peak portion of the cycle. Faster settings, such as 10 to 30 Hz, can tighten the arc and smooth the bead, but the effect is less visible and easier to misuse.
Starting Settings for Thin Stainless
Begin with clean material and a sharp tungsten. The following settings are practical starting points, not fixed rules. Stainless thickness, joint type, fit-up, and the welder’s actual output all matter.
| Stainless thickness | Peak current | Background current | Frequency | Peak time |
|---|---|---|---|---|
| 0.5–0.8 mm (24–20 gauge) | 25–45 A | 20–35% | 1–2 Hz | 25–35% |
| 0.9–1.2 mm (20–18 gauge) | 40–70 A | 25–40% | 1–3 Hz | 30–40% |
| 1.5 mm (16 gauge) | 60–90 A | 30–50% | 1–5 Hz | 35–50% |
The current figures assume DC TIG with argon and a tight butt or fillet joint. Use less current for a lap joint or a small corner, and more for a wide gap or a heat-sinking fixture. If your machine displays background amperage rather than a percentage, start around 10–25 A for very thin sheet and increase it only enough to keep the puddle from freezing between pulses.
How to Tune the Frequency
Set the machine to about 1 Hz first. At this rate, the puddle should visibly grow during peak current and shrink during background current. Add filler during the peak portion, then move slightly during the background portion. This gives a steady “dab, move, dab, move” rhythm without requiring exaggerated torch movement.
If the puddle remains too large or the sheet starts discoloring quickly, lower the background current or reduce the peak-time percentage. You can also raise travel speed. If the puddle freezes completely between pulses, increase the background current, raise the frequency slightly, or shorten the time between filler additions.
Increase frequency when you want a tighter, more controlled arc rather than a clearly visible pulse. A setting around 5–10 Hz can help on narrow seams where a slow pulse makes the bead look lumpy. Above roughly 20–30 Hz, many operators can no longer time filler additions to each pulse. At that point, frequency is being used for arc behavior and bead appearance, not for hand timing.
Some TIG welders offer very high pulse frequencies, such as 100–500 Hz. These settings can narrow the arc and concentrate the weld, but they are rarely the best first choice for thin stainless sheet. They also make it harder to diagnose whether a problem comes from current, travel speed, shielding, or pulse settings.
Avoiding Burn-Through and Distortion
Pulse helps, but joint preparation has a larger effect than frequency alone. Keep the gap close to zero on thin butt joints. A gap makes the arc bridge more material and encourages burn-through. Tack frequently—often every 25–50 mm—and alternate between tacks to spread heat.
Use copper or aluminum backing where the joint allows it. Backing draws heat away and supports the molten metal. For stainless exhaust parts, tanks, or tubing, purge the inside with argon when the rear surface will see corrosion, pressure, or flow. A shiny front bead with dark, sugary oxidation on the back is not an acceptable stainless weld.
Keep the torch angle close to 10–15 degrees from vertical and maintain a short arc, commonly 1.5–2.5 mm. A long arc spreads heat and weakens shielding. Start with approximately 10–15 cubic feet per hour of argon, adjusted for cup size and shop drafts. Excessive gas flow can create turbulence and pull air into the arc.
Equipment and Consumables
A machine with adjustable peak current, background current, pulse frequency, and peak time gives you useful control. For occasional repair work, a basic DC TIG welder with a stable low-amp output and simple pulse function is often enough. You do not need an expensive AC/DC unit for stainless steel; AC is primarily useful for aluminum.
When comparing machines, look for a reliable low-current arc, a foot pedal or torch amperage control, adjustable post-flow, and a torch that accepts common consumables. A DC TIG welder with adjustable pulse is the sensible category for this work.
Use 1.0 or 1.6 mm, 2% lanthanated tungsten and grind it lengthwise to a sharp point. A 1.0 mm tungsten suits very thin sheet and low current; 1.6 mm is more durable and covers a wider current range. Use filler close to the base thickness, such as 0.8 or 1.0 mm stainless TIG wire. Buy matching stainless TIG filler rod rather than relying on unknown general-purpose wire.
Common Pulse Mistakes
Burn-through despite pulsing: peak current or travel speed is wrong, the gap is too large, or the torch is dwelling. Lower peak current and keep moving before changing frequency.
Cold, rope-like bead: background current is too low, frequency is too fast for the travel speed, or the surface is contaminated. Increase background slightly and clean with a dedicated stainless brush and solvent.
Wide blue or gray discoloration: shielding is poor, the arc is too long, or the work is overheating. Check gas leaks, drafts, cup coverage, post-flow, and torch position. Stainless should normally retain a clean silver to light-gold appearance, depending on alloy and heat.
Uneven ripples: the pulse frequency is too slow for your hand rhythm, or filler is being added at inconsistent times. Raise frequency to 2–5 Hz or turn pulse off and concentrate on steady travel. A stable non-pulsed weld is better than a poorly timed pulsed weld.