Steel sheet cutting methods -
matching the technology to the material and part
Choosing a cutting method is rarely a choice between a better and a worse technology. A 6 kW fibre laser cuts structural steel up to 25 mm, high-end plasma delivers dross-free cutting up to 38 mm and severance up to 80 mm, and oxy-fuel cutting works on thicknesses of up to 500 mm. Each method gives a different edge quality, a different accuracy and a different unit cost. The result is determined by the combination of thickness, grade, required tolerance and number of parts, not by the name of the technology.
Laser cutting
The fibre laser has come to dominate cutting of thin and medium sheet, mainly thanks to its accuracy and edge quality. Thickness ranges depend directly on the resonator power. For the basic version of a machine from one of the leading European manufacturers they are as follows.
| Resonator power | Structural steel | Stainless steel | Aluminium |
|---|---|---|---|
| 3 kW | up to 20 mm | up to 16 mm | up to 16 mm |
| 6 kW | up to 25 mm | up to 25 mm | up to 25 mm |
Higher power does not translate linearly into greater cutting thickness. Above a certain threshold, it is mainly the cutting speed in the medium thickness range that increases, not the maximum thickness. This matters when assessing service offers: a higher-power machine usually means a shorter lead time, not necessarily a wider material range.
The cutting gas and process technology also matter. Machine manufacturers are developing solutions that reduce gas consumption, declaring reductions of up to 70%, which in large series has a real impact on the unit cost of a part.
In terms of edge quality, laser cutting typically falls within ranges 2-4 to EN ISO 9013, i.e. in the upper part of the scale available for thermal methods.
Plasma cutting
Plasma has the widest range of applications among thermal technologies. High-end industrial systems achieve dross-free cutting up to 38 mm, production piercing and severance up to 50 mm and maximum severance up to 80 mm on carbon steel. For stainless steel the figures are 75 mm for production severance and 160 mm for maximum severance. Precision systems from other manufacturers declare a range from 0.45 mm to 152 mm on carbon steel.
Accuracy depends mainly on the class of machine equipment, not on the plasma source itself.
| System type | Typical accuracy |
|---|---|
| manual cutting | about ±1.6 mm |
| basic CNC system without torch height control | about ±0.77 mm |
| CNC system with automatic torch height control | ±0.38-0.64 mm |
| high-end industrial system | ±0.25-0.51 mm on steel up to 50 mm |
The heat-affected zone in plasma cutting is narrow, typically below 0.25 mm. The edge angle deviation is 2-3 degrees for material below 10 mm and falls below 1 degree at a thickness of 50 mm, which often surprises designers used to the opposite relationship.
Standard plasma cutting usually falls within range 5 to EN ISO 9013, while precision systems achieve ranges 2-4 with an angle deviation of around 2 degrees, a level comparable to laser cutting. Underwater cutting variants, which reduce noise and emissions, and bevel cutting, which prepares the edge for welding in a single operation, are also available.
Oxy-fuel cutting
Oxy-fuel cutting remains the method of first choice for the thickest materials. Machine-mounted heavy-duty torches work on thicknesses of up to 500 mm and up to 600 mm depending on the version, using propane or natural gas mixed with oxygen.
The limitation of the method lies in the process mechanism itself, based on exothermic combustion of iron in an oxygen stream. It works in non-alloy and low-alloy steel. Machine manufacturers explicitly specify these units for non-alloy material. In high-alloy steels and aluminium the process does not run properly, so these materials are cut with plasma, laser or waterjet.
Waterjet cutting
Abrasive waterjet cutting covers practically all materials and thicknesses up to about 200 mm. Its distinguishing feature is the absence of thermal input, which eliminates the heat-affected zone and structural changes at the edge.
The comparison with laser given by a manufacturer of both machine types is instructive. For carbon and stainless steel up to a thickness of about 2 mm, the laser gives better edge quality. Above that thickness, waterjet has the quality advantage. The laser, however, remains far faster: five to ten times at 3 mm sheet and three to five times at 10 mm. The approximate operating cost of both technologies is similar, in the range of several tens of zlotys per machine hour.
The practical conclusion: waterjet is chosen when it is critical to avoid thermal changes in the material or when the material rules out thermal methods, not when throughput matters.
Mechanical cutting and material preparation
A separate group consists of methods that do not cut a shape but prepare the material for further processing.
Guillotine shears provide fast and inexpensive straight cutting. The edge has a characteristic fracture with a burr, and the material in the cutting zone is locally deformed, which matters for parts requiring a straight edge for welding or painting.
Punching on turret presses works well for repeatable parts with many holes, where the advantage comes from the number of operations performed in one pass.
Longitudinal slitting of coil and transverse cutting on a cut-to-length line are service centre operations, not processing plant operations. In Poland, slitting lines typically handle material from 0.2 to 3.0 mm thick and up to about 1500 mm wide, with a minimum strip width of around a dozen or so millimetres and coil inner diameters of 508 or 610 mm. Width tolerances after cutting are defined by EN 10051: for a trimmed edge they are 0 to +3 mm for widths below 1200 mm, 0 to +5 mm for 1200-1500 mm and 0 to +6 mm above 1500 mm. Thickness tolerances are described in a separate article on steel sheet thickness tolerances.
The choice of delivery form, i.e. coil, slit strip or sheet, is made at this stage and affects the yield per tonne more than the later method of cutting the part.
Edge quality in the order
Thermal cutting has its own quality standard. EN ISO 9013 describes the cut surface with two parameters: perpendicularity or angularity tolerance, designated u, and mean height of the profile, designated Rz5. On this basis it defines quality ranges that can be referenced in an order instead of descriptive wording about a clean edge.
This standard should not be confused with ISO 17916, which covers the safety of thermal cutting machines, not cutting quality. This mistake appears in industry materials.
In structures covered by EN 1090-2 the requirements are stated directly. The standard relates the results of roughness and perpendicularity tests of thermally cut edges to execution classes. For the most commonly required classes EXC3 and EXC4, range 4 applies to both roughness and perpendicularity. The standard also provides for hardness testing in the cut zone for steels susceptible to hardening, with a limit of 450 HV10 for S460 steel, and for visual inspection of the edge.
Cutting coated sheet
Every thermal method removes the coating in the cutting zone. The edge is left unprotected, and in a narrow strip adjacent to it the coating is damaged by heat. For galvanised sheet this is of limited practical significance, because zinc protects the edge cathodically and the reach of this protection depends on sheet thickness. In thin material the edge may remain rust-free throughout the life of the product; in thicker material it requires protection.
Plasma cutting of galvanised sheet is technically possible but requires ventilation because of zinc fumes released in the cutting zone. It is the same mechanism that produces zinc oxide fumes in welding.
Selection criteria
In plant practice the decision follows a few questions asked in a set order.
What material and what thickness. High-alloy steel and aluminium rule out oxy-fuel cutting. Thicknesses above 25-30 mm in practice rule out laser. Thicknesses above 80 mm point towards oxy-fuel cutting.
What part tolerance. Accuracy in tenths of a millimetre is achieved by laser and by precision plasma with automatic torch height control. Manual cutting and basic CNC systems work to tolerances an order of magnitude wider.
What happens to the edge next. An edge for welding in a structure covered by EN 1090-2 must meet the quality range assigned to the execution class. An edge for painting requires deburring. An edge that remains visible adds visual requirements.
How many parts and how repeatable. For large series of repeatable parts, cycle time and gas cost matter. For single large parts, availability and versatility of the method prevail.
Is thermal input acceptable. If not, waterjet or mechanical methods remain.
It is worth bearing in mind that before a part reaches the cutting table, most of the material cost has already been decided. Matching sheet format, strip width and thickness to a specific nesting affects yield more than optimising the cutting process itself.
Available steel grades, coating types and formats of coils, slit strip and sheets are presented in the HEN-STOL steel sheet offer, with separate pages for galvanized steel sheet, cold-rolled steel sheet and hot-rolled steel sheet.
See how we can help
HEN-STOL matches the delivery form and material dimensions to the planned nesting to reduce scrap already at the ordering stage. Send us the specification and the planned nesting, and we will check availability and propose the most favourable option.
Frequently asked questions
Up to what thickness does a fibre laser cut?
It depends on resonator power. A 3 kW machine cuts structural steel up to 20 mm and a 6 kW machine up to 25 mm. Increasing power beyond this level mainly increases cutting speed in the medium thickness range.
How does standard plasma differ from precision plasma?
In edge quality. Standard plasma cutting usually falls within range 5 to EN ISO 9013, while precision systems achieve ranges 2-4 with an angle deviation of around 2 degrees, close to laser cutting.
Why is oxy-fuel cutting unsuitable for stainless steel?
The process is based on combustion of iron in an oxygen stream and works in non-alloy and low-alloy steels. Machine manufacturers specify heavy-duty torches explicitly for non-alloy material, and high-alloy steels are cut with plasma, laser or waterjet.
When is waterjet cutting worth choosing?
When avoiding thermal input into the material is critical, at thicknesses above a few millimetres where edge quality exceeds laser cutting, and for materials that rule out thermal methods. The cost is clearly lower throughput.
How should the required edge quality be stated in an order?
By referencing EN ISO 9013 and specifying the quality range for perpendicularity tolerance and roughness. In structures covered by EN 1090-2, range 4 is required for both parameters for execution classes EXC3 and EXC4.
Can galvanised sheet be cut thermally?
Yes, provided there is ventilation because of zinc fumes released in the cutting zone. The coating is removed at the cut, and in thinner sheet the edge remains cathodically protected by the surrounding zinc.
Sources
- EN ISO 9013, Thermal cutting - classification of thermal cuts, geometrical product specification and quality tolerances
- EN 1090-2, Execution of steel structures and aluminium structures - technical requirements for steel structures
- EN 10051, Continuously hot-rolled strip and plate/sheet cut from wide strip - tolerances on dimensions and shape
- TRUMPF, technical data for TruLaser 1000 series machines
- Hypertherm, HyPerformance system documentation and plasma cutting accuracy materials
- Kjellberg, HiFocus neo system documentation and cut quality parameters
- Messer Cutting Systems, machine-mounted heavy-duty oxy-fuel cutting torches