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When TIG makes sense for a thin stainless fillet
TIG gives you control over a small weld pool, which helps when joining thin stainless without burning through or leaving a bulky bead. It is slower than MIG, and it takes steady torch and filler-hand coordination. For a short, visible fillet on 20- to 16-gauge stainless (about 0.9 to 1.5 mm), that control is often worth the extra time. For long production seams, MIG may be faster if you can manage heat and distortion.
This method assumes clean, uncoated stainless and a sound fit-up. It is not a substitute for a qualified welding procedure on pressure vessels, structural work, or anything safety-critical. Stainless fumes and intense arc light are hazards: use local fume extraction, a suitable welding helmet, gloves, and protective clothing. Avoid welding chlorinated solvents or unknown coatings.
Equipment and consumables
Use a DC TIG machine with high-frequency start if available, a foot pedal or torch amperage control, and pure argon. A small air-cooled torch is adequate for brief thin-sheet work; a water-cooled torch is more comfortable for long runs but costs more and adds equipment. A TIG torch consumables kit is useful if you need a selection of cups, collets, and tungstens, but check that it fits your torch before ordering.
For common austenitic stainless such as 304, ER308L filler is a usual choice; for 316 base metal, use ER316L. Match filler to the actual alloy when known. A 1.0 mm or 1.6 mm rod is easier to control on thin sheet than a thick rod. Use a sharp 1.0 or 1.6 mm 2% lanthanated tungsten with a pointed grind. A dedicated stainless wire brush and clean abrasives help prevent contamination from carbon steel.
Starting settings by thickness
These are starting ranges, not guaranteed settings. Joint design, gap, position, torch angle, and machine controls all change the heat needed. Set the machine to DC electrode negative (DCEN), use argon at roughly 6–9 L/min (13–19 cubic feet per hour) indoors without drafts, and test on offcuts of the same thickness. Too much gas can cause turbulence and pull air into the arc.
| Base thickness | Starting peak current | Filler diameter | Practical note |
|---|---|---|---|
| 0.8–1.0 mm (22–20 gauge) | 25–45 A | 0.8–1.0 mm | Very tight fit-up and short pulses reduce burn-through risk. |
| 1.2–1.5 mm (18–16 gauge) | 40–65 A | 1.0–1.6 mm | A small, steady pool is easier than a long, slow dwell. |
| 1.6–2.0 mm (16–14 gauge) | 55–85 A | 1.6 mm | More tolerance for a continuous bead, but heat still accumulates. |
If your machine has pulse, start around 1–2 pulses per second with a modest background current, roughly 30–50% of peak, and adjust by testing. Pulse is not magic: poor fit-up or a slow travel speed can still overheat the joint. A basic DC TIG welder without pulse can do the job; it just asks more of your timing.
Prepare and tack the joint
Degrease both faces, then remove oxide and dirt from the weld area with a stainless-only brush or clean abrasive. Keep fingerprints, marker residue, oil, and carbon-steel dust away from the joint. Fit the parts so the fillet root closes consistently; a gap approaching the sheet thickness makes burn-through much more likely. Use clamps or a fixture to hold a square corner without forcing a warped part flat.
Tack the joint at intervals of about 25–50 mm (1–2 inches), alternating positions to spread heat. On a small part, use more tacks rather than one long tack. Recheck alignment before welding. If the work is thin, copper backing can absorb heat and support the root, but it must fit closely and stay clean.
Weld the fillet
Clamp the work to a clean return lead connection. Hold the torch near 70–80 degrees to the work surface, aiming the arc into the joint so both pieces melt evenly. Keep the tungsten close—about 1–2 mm from the work—without touching it. If tungsten contacts the puddle or filler, stop and regrind it; a contaminated electrode makes an unstable arc.
Start the arc on a tack or at the edge of the joint. Form a small pool that wets both sides, then add just enough filler to maintain a neat, slightly convex fillet. Move steadily and keep the filler tip inside the shielding-gas envelope. For very thin sheet, short controlled bursts can limit heat, but pause only long enough to let the pool solidify; repeated stop-starts can leave craters and uneven fusion. Use downslope or a brief filler addition at the end if available, and fill the crater before breaking the arc.
Watch the puddle, not the tungsten. If the edges begin to sag, the pool grows wider, or the sheet turns bright orange, stop and let it cool. A small fan across the part is not a substitute for controlling heat, and it can disturb shielding gas. Weld short sections in a skip pattern, moving to a cooler area between sections.
Inspect and fix common problems
A sound fillet should have a consistent profile and visible tie-in on both members. On stainless, straw or light-gold heat tint is common; dark blue, gray, or crusty oxide points to excess heat or poor shielding. Remove discoloration with a stainless-appropriate cleaning method when corrosion resistance matters. Do not use a carbon-steel brush. Pickling products can be hazardous and require the label’s protective equipment and handling instructions.
Burn-through usually means excessive current, a gap, or too much dwell: improve fit-up, shorten the arc time, or reduce current. A bead sitting on one side without blending into the other suggests poor torch aim or travel too fast; direct the arc into the joint and pause briefly on each leg. Porosity often comes from drafts, leaks, dirty material, or inadequate gas coverage. Check the hose and connections, clean the metal again, and avoid excessive stick-out. If the joint pulls out of square, use more tacks, shorter weld segments, and a more balanced sequence rather than trying to straighten it by adding more heat.