What actually happens when a laser beam meets a steel plate? How do kilowatts, cutting speed and assist gas affect the result? This article walks through the technical side of laser cutting in practical terms, and ends with what you can order through LeikePaja.
Most modern industrial laser cutting machines are fibre lasers. In a fibre laser the light is generated in, and carried through, an optical fibre to the cutting head. In older CO₂ lasers the beam is generated in a gas and guided to the head with mirrors.
A fibre laser's wavelength is about 1 µm (typically 1,070–1,080 nm), while a CO₂ laser's is about 10.6 µm. Metals absorb the shorter wavelength better, so thin and medium plate cuts faster and uses less electricity.
* Wall-plug efficiency: how much of the electrical power ends up as laser light. Figures vary by machine; see the sources at the end of the page.
Laser power is given in kilowatts (kW). More power means thicker plate can be cut, and thin plate goes through faster.
Manufacturers usually quote two numbers: the maximum thickness that can be cut at all, and the range where edge quality and speed are good in production. In practice the second one matters more.
| Power | Good quality up to | Maximum thickness |
|---|---|---|
| 3 kW | about 12 mm | about 20–25 mm |
| 6 kW | about 16 mm | about 25 mm |
| 12 kW | about 25 mm | about 35–40 mm |
Structural steel, oxygen cutting. Indicative figures from manufacturers' charts; actual values vary by machine.
NitroCut's 12 kW fibre laser cuts S355 steel up to 25 mm. A 12 kW laser can in theory go thicker, but it is no longer practical: speed drops and edge quality suffers. That is why 30 and 40 mm plate is flame-cut.
Cutting speed falls steeply as thickness increases. Below are indicative speeds for a 12 kW fibre laser on structural steel. The real speed depends on the gas, nozzle, plate quality and the edge finish required, and manufacturers' charts vary a lot.
| Thickness | Speed (m/min) | Typical gas |
|---|---|---|
| 1 mm | 30–50 | nitrogen, air |
| 3 mm | 5–20 | nitrogen, air, oxygen |
| 6 mm | 3–8 | oxygen, air |
| 10 mm | 2–4 | oxygen |
| 15 mm | 1–2 | oxygen |
| 20 mm | 0.5–1 | oxygen |
| 25 mm | 0.3–0.7 | oxygen |
Speed shows up directly in the price: on thick plate the same cutting path takes many times more machine time. That is why the LeikePaja price is based not only on material and thickness but also on cutting path length and the number of pierces, and you see it instantly while drawing.
Kerf is the width of the slot the laser beam cuts, typically about 0.1–0.3 mm on thin sheet and wider on thick plate.
You don't need to allow for kerf in your drawing. The cutting software offsets the path by half the kerf width: holes are cut on the inside and the outer contour on the outside, so the finished part matches the drawing.
The assist gas blows molten metal out of the kerf, and it has a big effect on the cut edge.
Oxygen reacts with the hot steel and adds energy to the cut, which makes thick steel easier to cut. The downside is an oxidised, dark cut edge that is often cleaned or ground before painting or welding.
Nitrogen is inert and does not react with the material. The result is a clean, oxide-free edge, and nitrogen is widely used for stainless steel and aluminium. The downside is high gas consumption.
The most affordable option, typically for thin and medium plate. Air contains oxygen, so the edge oxidises slightly, but the quality is good enough for many uses.
Many steel and aluminium grades can be laser-cut in general. LeikePaja currently offers four materials, and only these can be ordered:
| Material | Thicknesses |
|---|---|
| Steel S355 | 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20 and 25 mm by laser; 30 and 40 mm flame-cut |
| Wear plate Hardox 400 | 6, 8, 10, 15 and 20 mm |
| Stainless 1.4307 (304L) | 1, 2, 3, 4, 5, 6, 8 and 10 mm |
| Aluminium 5754 | 1, 2, 3, 4, 5, 6, 8 and 10 mm |
Other steel or aluminium grades are not available. More details: materials and thicknesses.
A LeikePaja order covers cutting the plate parts. Parts often go on to bending or welding, though, so here are a few things that affect design.
In bending, a press brake forms the plate: the upper tool (punch) presses it into the lower tool (die). A key design factor is the bend radius. Too small a radius can crack the outer surface. For structural steel the rule of thumb for the inside radius is typically at least about the plate thickness, and higher-strength steels and aluminium often need a larger radius.
If the part will be bent later, allow for bend allowance in the blank dimensions. The outer surface stretches and the inner surface compresses, so the flat blank is shorter than the sum of the finished part's outside dimensions.
Laser-cut parts are dimensionally accurate with straight edges, which makes fitting and welding easier.
The most common method for structural steel. MAG uses an active shielding gas such as carbon dioxide or a mixed gas; MIG uses an inert gas such as argon and is used for example on aluminium. It is fast and affordable, but the weld is not as neat as TIG.
A more precise and slower method where the welder feeds filler by hand. The result is a neat weld with little spatter. TIG is widely used on stainless steel and aluminium, and a straight laser-cut edge makes an even joint easier.
The sheets are clamped between electrodes and a large current is passed through them, joining them without filler. It is fast and common in thin-sheet structures.
A laser can also weld. The melt zone is narrow and heat input low, so distortion stays small. It suits thin parts and work where appearance matters.
Oxygen-cut steel has an oxide layer on the edge. It is worth grinding it off before welding to avoid weld defects. A nitrogen-cut edge can usually be welded without preparation.
| Topic | What it means in practice |
|---|---|
| Fibre laser | Fast and energy-efficient for cutting metals |
| Power (kW) | More power = thicker plate or faster cutting |
| Kerf | About 0.1–0.3 mm on thin sheet, compensated by the software |
| Oxygen | Thick steel, oxidised edge |
| Nitrogen | Clean edge, higher gas consumption |
| Tolerance at LeikePaja | ±2 mm laser, ±5 mm flame cutting |
| Bending | Allow for bend radius and bend allowance |
Draw a part in your browser or import a DXF, choose material and thickness, and the price updates instantly. You only pay once the workshop has checked your drawing.
General technical figures (wavelength, efficiency, thickness by power class and cutting speeds) were checked in September 2026 against manufacturers' publications. They are indicative and vary by machine. Information about LeikePaja (materials, thicknesses, tolerances) is the service's own. Sources: