How Thick Can a Fiber Laser Cut? A Guide by Power Level
The honest answer to "how thick can this machine cut" is two numbers, and most suppliers only quote the larger one.
The first is the separation limit: the thickness at which the beam will go through the plate and the part drops free. The second is the production limit: the thickness you can cut all day, at acceptable speed, with a clean edge and a nozzle that survives a full shift. In practice they differ by a wide margin.
Separation limits by power
The table below reflects typical single-mode and multi-mode fiber sources cutting with correct gas and focus. Treat these as the upper edge of what is possible, not as daily production capability.
| Laser power | Carbon steel (O₂) | Stainless steel (N₂) | Aluminium (N₂) |
|---|---|---|---|
| 1.5 kW | 12–16 mm | 4–6 mm | 3–5 mm |
| 3 kW | 18–22 mm | 8–10 mm | 6–8 mm |
| 6 kW | 22–25 mm | 12–16 mm | 10–14 mm |
| 12 kW | 30–40 mm | 20–30 mm | 18–25 mm |
Three caveats sit behind that table.
Carbon steel thickness depends on oxygen-assisted cutting, so the edge is oxidised and the cut face is not suitable for welding without cleaning. Stainless and aluminium are cut with nitrogen, which is why they thin out faster as thickness climbs: nitrogen cutting consumes far more energy per millimetre.
Beyond roughly 20mm on carbon steel, plasma or waterjet often beats laser on cost per metre. Laser wins on edge quality and on thin-to-medium plate, and that advantage shrinks as thickness rises.
Air cutting changes the numbers again. Air is cheaper than nitrogen and works on thin material, but the edge oxidises, so it is not a substitute for nitrogen on visible stainless parts.
Why the production limit is lower
Running a machine at its separation limit means running at minimum speed with maximum power. Three things follow.
Consumables wear fast. Laser nozzles, protective lenses and ceramics degrade faster at high power density, and the cost per part can double even though the machine technically made the cut.
Quality drops. The kerf widens, dross appears on the underside, and the edge angle gets steeper. On stainless above about 10mm, the edge often needs a secondary operation anyway, which is where a CNC press brake enters the process rather than the laser.
Repeatability suffers. A process running at 95 percent of its capability has little tolerance for a change in plate chemistry or a slightly worn nozzle, and the failure mode is a failed cut mid-nest rather than a slightly worse part.
For daily production, a working rule is to stay 20 to 30 percent below the separation limit. A 6kW machine cutting 25mm carbon steel occasionally is realistic. The same machine cutting 25mm all day is not.
The variables that decide the real number
Nozzle diameter and condition come first. A worn nozzle changes the gas flow pattern, and the effect on cutting capacity is larger than most operators expect. Inspecting nozzles at the start of each shift catches most of this.
Focus position comes second. Thick plate wants a focus position below the surface for carbon steel and near the surface for nitrogen cutting. A focus set for thin material will not cut thick plate properly no matter how much power is available.
Gas pressure and purity come third. Contaminated nitrogen, or pressure dropped at the end of a long run, shows up as dross and incomplete separation.
Edge quality requirements come last but matter most commercially. A part that only needs separation can be cut faster than a part that needs a weldable edge.
Questions that come up often
Can a 3kW machine cut 20mm stainless steel? Not usefully. It may separate the material at very low speed, but the edge quality and consumable cost make it impractical for production.
Is a higher power source always better? No. A 12kW source on 3mm stainless is running far below its efficient band. Matching power to the thickness range you actually process matters more than headline power.
Does the machine or the source set the thickness limit? Both. The source provides the energy, but the cutting head, nozzle, motion system and gas supply decide whether that energy arrives at the plate correctly. A high-power source on a light gantry will not deliver its rating.
How do nozzles change the numbers? A larger, correctly matched nozzle handles thick plate better. An oversized nozzle on thin plate wastes gas; an undersized one on thick plate loses the cut. Keep a range of diameters on hand rather than one general-purpose size — the difference between a single layer nozzle and a double layer high-speed nozzle is exactly this choice.
Choosing by thickness, not by power
If your work is mostly 1 to 6mm stainless, a 3kW machine with a good cutting head will outperform a 6kW machine with a poor one. If you process 16 to 25mm carbon steel regularly, the power matters, but so does the table, the chiller and the gas supply.
Two configurations cover most of that range: the 3015 series single-drive fiber laser cutting machine for general sheet work, and the closed dual-drive machine with an exchange worktable where the cutting head should not idle between sheets. If the work includes tube as well as plate, the sheet and tube configuration removes the second machine from the plan.
Send us your thickness mix and material split, and we can work out which configuration actually fits your production rather than which one has the biggest number on the label. The full range is listed under all products.
