Fiber laser cutting is a thermal cutting process: a laser beam of very high power density melts the material in a narrow zone and a jet of assist gas blows the melt out of the kerf. Over the past years it has largely replaced CO₂ lasers in sheet processing, becoming the standard method for speed on thin and medium gauges and, as power levels have risen, for capacity on thick plate.
This article explains the physics of the fiber laser, how assist gas affects edge quality, how laser compares with other thermal cutting methods, how cut quality is specified under EN ISO 9013, and the design rules for parts that will be laser cut.
How it works
In a fiber laser the beam is generated in optical fibres doped with a rare-earth element (usually ytterbium) and pumped by diode lasers. The beam travels through a flexible fibre cable to the cutting head, where optics focus it to a very small spot. The power density at the focus melts the metal instantly, and a gas jet from the coaxial nozzle ejects the melt through the bottom of the kerf. The head follows the part contour under CNC control, and a capacitive sensor holds the stand-off distance constant.
The fiber laser wavelength is around 1 µm, against roughly 10.6 µm for a CO₂ laser. Metals absorb the shorter wavelength better, so a fiber laser cuts more efficiently at the same power and can also process reflective metals such as aluminium, brass and copper. Delivering the beam through a fibre rather than mirrors removes the need for beam-path alignment and reduces maintenance.
The main process parameters are laser power, cutting speed, focus position, nozzle diameter, stand-off distance and gas pressure. They are set in cutting tables by material and thickness, and need fine-tuning on thick plate to achieve good edge quality. Every contour begins with a pierce; on thick plate piercing can take a significant share of total cutting time, and the pierce point is placed outside the part contour, in the scrap.
Assist gas: oxygen, nitrogen and compressed air
The assist gas defines the physics of the cut and the properties of the edge. With oxygen, the gas reacts exothermically with the iron and adds energy to the cut, so thick carbon steel can be cut with relatively modest power, at the cost of a thin oxide layer on the edge. With nitrogen, the gas is inert and simply blows the melt out at high pressure; the edge is bright and oxide-free, but more laser power and gas are needed. Compressed air is an economical middle option on thin and medium gauges.
Nitrogen-based cutting of carbon steel needs far more laser power than oxygen cutting, which is why many plants limit it to thin and medium gauges and cut thicker plate with oxygen. On our 20 kW fiber laser we cut carbon steel up to 20 mm with nitrogen-based mixed-gas technology: a nitrogen-rich mix with a small share of oxygen. Oxidation of the cut edge is kept to a minimum, so cut faces are cleaner and corners, small holes and fine details come out sharper and truer to size. Because no heavy oxide layer forms on the edge, priming, painting, powder coating, coating and hot-dip galvanizing give far more consistent results on the cut edges. Thicker plate is cut with oxygen.
| Gas | Mechanism | Edge | Typical use |
|---|---|---|---|
| Oxygen (O₂) | Reactive cutting; exothermic reaction adds energy | Thin oxide layer; may need cleaning before painting or some welding | Medium and thick carbon steel |
| Nitrogen (N₂) | Fusion cutting; gas only ejects the melt | Oxide-free and bright; ready for paint, coating, galvanizing or welding | Stainless, aluminium, visible or painted parts |
| Nitrogen mixed gas (N₂ + some O₂) | Mainly fusion; the small oxygen share speeds the cut | Minimal oxidation; suited to paint, coating and galvanizing | In our plant, carbon steel up to 20 mm |
| Compressed air | Mainly fusion with slight oxidation | Lightly oxidised; adequate for most general work | General fabrication in thin and medium gauges |
Laser power and thickness capacity
Laser power determines two things: the maximum thickness that can be cut and the cutting speed at a given thickness. More power means higher speed on thin sheet and better process stability and edge quality on thick plate, and it raises the thickness that can be cut with nitrogen. As thickness increases, cutting speed drops non-linearly and pierce time grows, so on thick material machine power feeds directly into cost per part.
Our 20 kW fiber laser cuts carbon steel up to 30 mm at laser quality. Above that, and for some heavy fabrication parts, plasma and oxy-fuel cutting is the more economical choice. The right process is decided part by part on thickness, tolerance and edge requirements.
Laser, plasma and oxy-fuel compared
All three are thermal cutting processes, but they differ in energy source and kerf width. The table compares their general character; exact limits depend on equipment and material.
| Property | Fiber laser | Plasma | Oxy-fuel |
|---|---|---|---|
| Kerf width | Very narrow | Medium | Wide |
| Dimensional accuracy | High | Medium | Low to medium |
| Heat-affected zone | Narrow | Medium | Wide |
| Small holes and fine detail | Very good | Limited | Not suitable |
| Edge squareness | Good | Tendency to slight bevel | Good on thick plate |
| Materials | Carbon steel, stainless, aluminium, coated sheet | Electrically conductive metals | Carbon and low-alloy steel only |
| Economic range | Thin to medium; thick plate at high power | Medium and thick plate | Very thick plate |
Cut quality: EN ISO 9013 and dimensional accuracy
The quality of thermal cuts is specified in EN ISO 9013. The standard classifies the cut face by two main parameters: perpendicularity or angularity tolerance (u) and mean height of the profile (Rz5), which describes the depth of the drag lines on the cut face. It also defines tolerance classes for part dimensions. Referencing the standard on the drawing gives buyer and supplier a shared, measurable basis.
Other aspects of cut quality are drag lines that become more pronounced towards the bottom of the cut on thick plate, dross that may remain on the lower edge, a tendency for the kerf to taper, and a narrow heat-affected zone. We work to ±0.1 mm on laser-cut parts. Stating the required quality for thick material and critical edges at the quoting stage ensures the right parameters and gas are chosen.
Material-specific considerations
Carbon steel (hot-rolled, cold-rolled, pickled): the most common laser-cut material. In our plant it is cut with nitrogen-based mixed gas up to 20 mm and with oxygen above that. Mill scale and surface rust can impair cut quality. Stainless steel (304/316): cut with nitrogen to preserve corrosion resistance and obtain an oxide-free edge. Aluminium: high thermal conductivity and reflectivity make it a material where the fiber laser has a clear advantage; cut with nitrogen.
Galvanized and Zn-Al-Mg coated sheet: the coating vaporises locally at the cut edge; parameters are set so as not to damage the coating elsewhere. Wear plate (Hardox): thermal cutting can locally affect hardness at the cut edge, and the narrow heat-affected zone of the laser is an advantage here. The full list of materials we cut is on the laser cutting page.
Designing parts for laser cutting
Hole diameter versus thickness. On thin sheet, holes smaller than the material thickness can be cut; on thick carbon steel, hole geometry and edge quality become difficult as the diameter approaches or falls below the thickness. Drilling or machining such holes afterwards is worth considering.
Spacing between features. Cuts very close to an edge or to each other cause heat build-up and distortion. Narrow webs, thin slivers and closely spaced holes reduce cut quality, especially on thick plate.
Designing for bending. On parts that will be bent, relief cuts at the ends of bend lines prevent tearing, and holes too close to a bend line will distort after bending. Laser-cut tab-and-slot features reduce the need for welding fixtures and locate parts accurately.
The drawing file. DXF or DWG files should be at 1:1 scale in millimetres, with closed contours and no duplicate lines or stray layers. Keeping dimensions, text and non-cut geometry on separate layers lets the file go straight into the cutting program. If part marking (etching) is required, put it on its own layer.
Nesting and micro-joints. Parts are arranged on the sheet according to a nesting plan. Micro-joints may be left to stop small parts tipping up and colliding with the head during cutting; they leave a small witness mark on the edge. If marks are not acceptable on visible edges, say so on the drawing or in the quote request. On straight-edged parts, common-line cutting reduces both time and scrap.
Tube and profile laser cutting
A tube laser rotates the tube or box section and produces holes, slots, notches, mitres and end profiles in a single set-up. Conventionally, sawing, drilling and marking are separate operations; doing it in one clamping saves time and removes dimensional error between operations.
Laser-cut interlocking and locating features let welded frames fit together at the correct angles and reduce the need for assembly fixtures. Besides the sheet laser we run a dedicated tube laser unit. Cut parts can be bent in the same plant on the 1,000-tonne press brake up to 8 m long, and delivered ready for welding and assembly.
What to send for a quote
For a fast, accurate quote send: drawing (DXF/DWG preferred; a PDF drawing or dimensioned sketch also works); material and thickness (for example S235JR 10 mm, AISI 304 2 mm); quantity and any recurring requirement; edge requirement (painted, welded, visible, or an EN ISO 9013 quality class where needed); secondary operations (bending, welding, assembly); delivery address.
The cost drivers are covered in detail in how laser cutting is priced. For our subcontract capacity see laser cutting services, and send your files through the quote form.