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Burn-through happens when the weld pool melts through the sheet before you can move on. On thin steel, the fix is usually a combination of lower heat input, shorter welds, a tight joint and steady travel—not simply turning the wire speed down. The settings below are starting points; the right ones depend on your welder, wire, shielding gas, joint and material.

Prepare the joint before adjusting the welder

Clean paint, rust, oil and heavy mill scale away from the weld area. Contamination makes the arc less predictable and can leave you chasing poor fusion with extra heat. Use a grinder or abrasive pad without thinning the sheet around the joint.

Fit-up matters just as much. A gap between thin panels gives the pool somewhere to fall through. Clamp the parts flush and keep the gap as small and even as possible. If the edges are irregular, trim or reshape them rather than trying to fill a wide gap with repeated passes. On a butt joint, a backing bar can support the pool and draw heat away; copper is useful because weld metal is less likely to fuse to it than to a steel backing bar.

For sheet that may be galvanized, remove the coating well back from the weld and work with effective ventilation. Zinc fumes are hazardous. Do not rely on a respirator as a substitute for controlling the fumes at the source.

Choose wire and shielding gas for thin steel

For mild steel, .023-inch (0.6 mm) solid wire is a useful choice on thin sheet because it can run at lower current than thicker wire. .030-inch (0.8 mm) wire is more versatile if the same machine must also handle heavier work, but it may be harder to control at the low end. Check that your welder’s drive rolls, liner and contact tip suit the wire diameter.

Use the shielding gas specified for your wire and machine. A common mix for short-circuit MIG on mild steel is 75% argon and 25% carbon dioxide. It generally gives a smoother arc and less spatter than straight carbon dioxide, though the cylinder and gas setup add cost. Flux-cored wire avoids a gas cylinder, but many small machines run it hotter or with more spatter, so it is not automatically the easier choice for very thin sheet.

If you need the wire, gas, regulator or other consumables, compare options in .023-inch MIG wire and make sure the wire type matches your process.

Set voltage and wire speed together

Use the machine’s chart as a starting point for the material thickness, wire and gas you have. On a voltage-controlled welder, voltage largely sets arc length and heat, while wire speed affects how much wire enters the arc and the resulting current. The controls interact: excessive wire speed can make the wire stub into the work, while too little can produce a harsh, unstable arc. Do not treat wire speed as a simple “less heat” knob.

Test on a scrap piece of the same thickness and joint type. Make short beads, then check the back of the sheet. A sound weld should show fusion without a hole or a tall, cold-looking bead sitting on top. If the arc is harsh and the sheet quickly warps or burns through, reduce voltage or wire speed in small steps and retest. If the wire stubs, increase voltage slightly or reduce wire speed. Change one setting at a time so you know what helped.

Control heat with short welds

Do not try to run one continuous bead along a long, thin seam. Place short tacks spaced along the joint, then connect them with brief welds, moving between areas so one spot can cool. Keep the gun moving steadily; pausing in one place increases the chance of a hole. A slight weave is rarely useful on thin sheet because it spreads heat. A straight, narrow bead is easier to control.

For a patch or butt joint, tack one end, then the other, and add tacks between them. Continue filling the gaps in a staggered sequence instead of welding adjacent sections back to back. If the panel starts to discolor heavily, distort or soften, stop and let it cool. Compressed air can speed cooling, but avoid quenching a hot, restrained panel in a way that creates additional distortion.

Keep the arc and gun position consistent

Keep a short, steady stickout—roughly 3/8 inch (10 mm) is a practical starting point for many short-circuit setups—and hold the gun at a consistent angle. Follow the machine and wire manufacturer’s guidance if it differs. An excessively long stickout can make the arc unstable; an inconsistent angle or distance makes it harder to judge heat and bead placement.

If a hole opens, stop rather than trying to bridge it with a long, hot pass. Let the area cool, clean the edges and use short tacks around the opening to rebuild the joint. On badly gapped or paper-thin sheet, fitting a patch or adding a backing strip can be more reliable than repeatedly filling the gap. A dedicated MIG welder with low-range voltage control can help if your current machine’s lowest stable setting is still too hot, but a new welder will not fix poor fit-up or an unsuitable wire-and-gas combination.

Practice and protect yourself

Use offcuts of the same thickness to settle the settings before welding the actual panel. A cheaper machine is fine for occasional repairs if it has a stable low-heat range, feeds wire consistently and accepts the wire and gas you plan to use. If it cannot maintain a controlled arc at the required setting, more practice may not solve the limitation.

Wear a properly rated welding helmet, gloves and flame-resistant clothing, and keep sparks away from fuel, paint and other combustibles. Thin sheet can still produce hot spatter and sharp edges. Clamp the work securely, maintain ventilation and inspect the finished joint for holes, lack of fusion and excessive distortion before relying on it.