Troubleshooting guide › Weld defects › Burn-through
Burn-through (melt-through) is when the arc melts a hole right through the plate, or the root sags through the back of the joint. It happens on thin sheet, at wide root gaps and wherever the heat input is too high for the metal under the arc. Thin-sheet work in MIG and TIG is where it costs the most time.
Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.
A hole through the sheet, or a bead that has dropped through and hangs on the back side. On a root pass, excessive penetration that forms a lump inside the pipe or behind the plate.
Illustration, not a photo. Orange marks the defect.
More heat than the sheet can carry away.
Heat builds up in one spot.
Nothing under the arc to hold the pool.
A steep angle drives the arc down into the sheet.
Small parts heat up fast.
Machine set for 6 mm, operator welding 1.5 mm.
| Process | Typical reason on this process | What to do |
|---|---|---|
| MIG / MAG on thin sheet | Current and voltage too high, travel too slow, root gap too wide, wire too large. | Use 0.8 mm wire below 3 mm sheet, pull the torch, speed up, close the gap, use a copper backing. |
| ARC / MMA | Electrode too large, current too high, arc held too long in one spot, excessive gap. | 2.5 mm electrode on 3 mm sheet at 70-90 A, keep moving, vertical-down for thin sheet. |
| TIG | Current too high, dwelling too long, no filler added to cool the pool, gap too wide. | Pulse mode, foot pedal to back off, add filler as the pool sags. |
| Submerged arc | Current too high, travel too slow, root gap too wide, backing bar not tight. | Reduce current, speed up, tighten the backing. |
| Spot welding (expulsion / holes) | Current too high, force too low, tip too small, sheets not in contact. | Drop a tap step, tighten the spring, use the correct tip diameter. |
MIG / MAG, 0.8 mm solid wire on 1.5 mm mild steel sheet. A starting point only; confirm on a test piece of the same plate.
| Gas | Ar/CO2 mix, 10-12 L/min |
| Current / voltage | about 60-90 A / 16-18 V |
| Travel | fast; short stitches on long seams |
| Torch angle | 20-30 degrees, pulling |
| Backing | copper or steel backing bar on butt joints |
Typical values for mild steel. Your wire, plate condition and machine will move them. Our technical team can set them with your operator on a video call.
Burn-through is visible: a hole, or a sagging bead on the back of the joint. Repair by letting the plate cool, grinding the edges of the hole bright, and filling from the edges inwards with short welds at reduced current, or by welding a patch where the hole is large.
With 0.8 mm wire and a steady hand, about 1 mm. Below that TIG or spot welding is the right process. The product finder points you to the machine for the thickness you weld most.
Short-arc (dip transfer) at low voltage is the normal thin-sheet mode on MIG. Pulse helps on stainless and aluminium sheet where short-arc gives lack of fusion.
Up to about the wire diameter without a backing. Beyond that use a copper or ceramic backing, or close the gap by re-fitting the parts.
A machine that starts smoothly at low current matters more than peak current for sheet work. For regular thin-sheet production, TIG or a low-current MIG setting gives the most control; spot welding avoids burn-through altogether on lap joints.
Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.
45+ years of welding expertise · GeM Registered OEM Manufacturer · Supported Worldwide
