Laser Cutting Materials & Thickness Guide

Fiber laser cutting range and accuracy depend on the material and its thickness. This guide summarizes the practical thickness limits and the tolerance you can expect for common sheet metals, and it pairs each material with the assist gas and the cut quality that suit it. The reference table above gives the tolerance by material and thickness range, and the notes below explain the behavior behind those numbers. As a guide within laser cutting, this is the page to check when sizing a part to what the process can actually hold.

The pattern across all materials is the same: thin sheet cuts precisely and quickly, and tolerance widens as thickness grows, because the heat of the cut disperses into more material and becomes harder to control. Mild steel, stainless, and aluminum all follow this curve, each with its own assist gas and its own limits, and understanding the curve is the key to specifying a tolerance that the process can meet.

How material and thickness drive the cut

The beam delivers a fixed amount of energy per unit of time, and the cut forms where that energy melts the material faster than the assist gas can clear it.

Energy, melt, and the thickness curve

On thin sheet, the beam punches through quickly and the cut is precise, because the small volume of material melts and clears with little heat spreading into the surrounding metal. As thickness grows, more material must be melted and cleared per unit of path length, so the cut slows, the heat disperses further into the sheet, and the tolerance widens. Above the practical range, the process cannot hold a workable cut at all, and the part moves to CO2, plasma, or waterjet.

How assist gas shapes the cut

The assist gas manages the molten material and shapes the edge chemistry, and the right gas differs by material. Mild steel cuts readily with oxygen, whose exothermic reaction with iron adds heat and speed. Stainless and aluminum use nitrogen, an inert gas that leaves an oxide-free edge ready for welding or coating. The gas choice, the pressure, and the nozzle geometry are tuned to the material and thickness, and getting them right is a large part of holding tolerance and edge quality across the range.

Mild steel

Mild steel is the most common fiber-laser material, and it cuts cleanly across the full practical range.

Tolerance and edge quality

Thin sheet (0.5 to 3mm) holds about ±0.10mm (±0.004in), widening to ±0.15mm at 3 to 6mm, ±0.25mm at 6 to 12mm, and about ±0.50mm at 12 to 25mm. The kerf is narrow (0.15 to 0.30mm) and the heat-affected zone small (0.13 to 0.25mm), which is why mild steel brackets, enclosures, and panels cut so well on fiber. Above about 25mm, fiber laser is not recommended, and the part moves to plasma, CO2, or waterjet.

Oxygen versus nitrogen assist

Oxygen assist is common, driving the exothermic reaction that speeds the cut and extends the thickness range, at the cost of an oxidized edge. Nitrogen is used when a clean, bright, oxide-free edge is wanted, such as on parts that will be powder-coated or welded without grinding, since it leaves the edge ready for the next step.

Stainless steel

Stainless steel cuts cleanly to about 20mm on fiber, usually with nitrogen assist to leave a bright, oxide-free edge that is ready for welding or coating. Thin sheet (0.5 to 3mm) holds about ±0.10mm, widening to about ±0.20mm at 3 to 10mm as thermal dispersion grows. The kerf on stainless with nitrogen is tight, and the heat-affected zone is small, which suits the food, medical, and architectural applications where stainless is common. Stainless’s lower thermal conductivity than mild steel changes the cut parameters slightly, favoring nitrogen and careful tuning, but the practical range and tolerance are similar.

Aluminum

Aluminum cuts to about 15mm practically on fiber, with nitrogen assist for a clean edge.

Conductivity and reflectivity limits

Its high thermal conductivity carries heat away from the cut quickly, which is good for the surrounding metal but demands more beam power per unit of thickness, and its reflectivity at 1064nm limits the upper thickness range. These two traits together cap the practical thickness lower than steel, which is why thick aluminum often moves to waterjet.

Tolerance and edge

Thin sheet (0.5 to 3mm) holds about ±0.13mm (±0.005in), widening to about ±0.40mm at 6 to 12mm. The kerf is slightly wider than on steel due to aluminum’s thermal conductivity, and the edge is clean when cut with nitrogen. Thicker aluminum is increasingly difficult and is often routed to waterjet or mechanical cutting.

Galvanized steel

Galvanized steel, carbon steel with a zinc coating for corrosion protection, is cuttable on fiber, but the zinc coating needs attention. Cutting with nitrogen avoids the zinc-oxide residue that oxygen would leave, which can hurt later powder-coat adhesion, so nitrogen is the preferred assist gas for galvanized. Alternatively, the part can be cut from uncoated steel and galvanized after, if the geometry allows hot-dip galvanizing without distortion. The zinc coating also vaporizes into fumes during cutting, so fume extraction is important for operator safety. Within these notes, galvanized cuts at tolerances similar to mild steel of the same base thickness.

Tolerances by thickness

The tolerance a fiber laser holds tracks the thickness closely, because thermal dispersion grows with material mass.

The tolerance curve

The reference table gives the per-material, per-range values, and the curve is consistent: about ±0.10mm on thin sheet (0.5 to 3mm), widening through ±0.15mm at 3 to 6mm, ±0.25mm at 6 to 12mm, to about ±0.50mm at 12 to 25mm in mild steel. Stainless follows a similar curve; aluminum runs slightly looser due to its thermal conductivity.

Where the process stops

Above about 25mm in steel, the tolerance and edge quality fall off enough that the part is better routed to plasma, CO2, or waterjet, and fiber laser is not recommended. Pushing fiber beyond its practical range raises cost and lowers quality, since the cut slows and the heat becomes hard to control.

Checklist

• Confirm the material and the exact thickness before specifying a tolerance or requesting a quote, since the range and accuracy depend on both.
• Pick the assist gas for the material and edge: nitrogen for clean, oxide-free edges on stainless, aluminum, and galvanized; oxygen for speed on carbon steel where an oxidized edge is acceptable.
• Scale minimum hole, slot, and tab sizes to the thickness, with holes and slots at least 1x thickness and tabs at least 2x thickness.
• Account for kerf compensation, about half the kerf per edge, on fit-critical dimensions.
• Above about 25mm in steel, switch to plasma, CO2, or waterjet rather than pushing fiber laser beyond its practical range.

Cut quality and surface finish by thickness

Cut quality follows the same thickness curve as tolerance, because both depend on how well the heat of the cut is controlled.

Cut face and ISO 9013-1 level

On thin sheet, the beam punches through quickly and the cut face is smooth, with low dross and a clean edge, achieving ISO 9013-1 Level 2 to 3 readily on fiber. As thickness grows, the cut face becomes rougher, dross can build on the bottom edge, and the edge bevel increases, because the heat disperses further and the molten material is harder to clear cleanly. By the upper end of the practical range, around 20mm in steel, the cut quality is acceptable for structural parts but no longer suited to fine work, and the part may need a secondary cleanup pass for appearance or fit.

Surface finish (Ra) and edge chemistry

Surface finish, measured as Ra on the cut face, is generally good on fiber laser, smoother than plasma and comparable to a clean machined edge on thin sheet. Stainless cut with nitrogen leaves a bright, oxide-free finish; carbon steel cut with oxygen leaves a darker, oxidized edge; aluminum cut with nitrogen is bright and clean. The finish matters where the edge is visible, where it must mate with another part, or where it affects a downstream process like welding or coating. Specifying the finish and the ISO 9013-1 level the part needs, rather than assuming the best available, keeps cost down while delivering the function the edge must perform.

Assist gas and edge chemistry

The assist gas shapes the edge chemistry, and the right gas differs by material and by what the edge must do next. Nitrogen, inert and used at high pressure, leaves an oxide-free edge on stainless, aluminum, and galvanized steel, which is ready for welding, coating, or painting without cleanup. Oxygen drives an exothermic reaction with iron that speeds the cutting of carbon steel and extends its thickness range, at the cost of an oxidized edge that may need grinding before welding or coating. The gas choice is a trade between edge quality and cutting speed or thickness range, and it is set for the material and the application. For a part that will be welded, nitrogen is usually specified for its clean edge; for a part where speed and thickness matter more than a bright edge, oxygen may be the better choice.

Gas pressure and nozzle geometry also enter the cut parameters, tuned to the material and thickness to manage the molten material and the edge quality. High-pressure nitrogen, in particular, is a significant running cost on high-throughput work, so specifying it where the part needs a clean edge, and accepting oxygen where an oxidized edge is tolerable, balances edge quality against gas cost and is part of specifying a laser-cut part economically.

Design rules

• Scale minimum features with thickness, since a feature that is practical at 2mm may be impossible at 12mm.
• Batch parts of the same material and thickness on one sheet to share parameters and setup.
• Specify the assist gas and the ISO 9013-1 edge-quality level the part needs, since both affect cost.
• For galvanized parts, plan for nitrogen cutting or post-cut galvanizing to protect downstream coating adhesion.
• Route thick or reflective parts to the right process rather than forcing fiber laser beyond its range.