Laser Steel Cutting Guide

• 1
  How laser steel cutting removes material
• 2
  Which steels cut well, and which fight back
• 3
  Thickness, hole size and taper limits
• 4
  What the heat-affected zone means for the part
• 5
  Design choices that keep laser steel cutting cheap
• 6
  Laser cut edges versus machined edges
• 7
  When laser steel cutting is the right call

A fiber laser sends a beam through a focusing lens or collimator, and the spot that lands on the sheet is small. On a typical 3–6 kW machine the focused spot is around 0.1–0.3 mm across. That spot carries enough power density to take steel past its melting point in microseconds, and the assist gas pushes the molten pool out of the bottom of the kerf.

The beam does not touch the steel. There is no tool wear, no clamp load on a cutter, and no deflection from cutting force. The cut is a thermal event, not a mechanical one. That single fact explains most of the process behavior: what it does well, what it cannot do, and why the heat-affected zone matters more than the cut face looks.

Assist gas does half the work. Oxygen reacts with iron and adds exothermic heat, so it cuts carbon steel faster and thicker. Nitrogen is inert and keeps the cut edge clean on stainless and on steel that will be welded or plated. Compressed air sits in between and is often good enough for brackets and covers.

The kerf is the width of material the beam and gas remove. On 1 mm cold-rolled steel it can be 0.2–0.3 mm. On 12 mm plate it grows to roughly 0.8–1.2 mm, and the cut face tapers slightly from top to bottom. Design the flat pattern around the kerf, not around a nominal line.

• 1
  No contact forceThin walls and long slender parts do not spring or chatter during the cut.
• 2
  Gas choice drives edge chemistryOxygen leaves an oxide layer; nitrogen keeps the edge bright and weldable.
• 3
  Kerf is not zeroAllow 0.2–1.2 mm depending on thickness and lens setup.

Mild and carbon steels are the easy case. Grades such as 1018, 1045, A36 and 4130 cut cleanly from 1 mm to 20 mm on a modern fiber machine. Thin sheet runs fast, and the oxide edge is acceptable for most brackets, plates and weldments. If the part will be powder coated, the oxide is usually blasted off first anyway.

Stainless grades behave differently. 304 and 316 cut well with nitrogen, but they need more power for the same thickness because the material reflects less and conducts heat away faster than carbon steel. 316L is common in food and medical work; the cut edge is bright but still has a narrow heat-affected zone that can affect corrosion resistance on a machined sealing face.

High-carbon and tool steels bring risk. 440C, 420 and hardened tool steel above roughly 40 HRC tend to crack along the cut because the thermal cycle creates a hard, brittle zone. Preheating helps on thick sections, but many shops simply will not laser-cut a hardened die insert. That part goes to wire EDM or to a grinder.

Coated and clad material is the other trap. Galvanized sheet releases zinc fume that needs extraction and can contaminate the lens if the nozzle is set wrong. The cut edge loses its zinc coating for a band of a few tenths of a millimeter, so a galvanized part that will see weather needs that edge protected after cutting.

• 1
  Best candidates1018, 1045, A36, 4130, 304, 316L in sheet and plate up to 20 mm.
• 2
  Use caution4140 and 4340 above 6 mm, hardened tool steel, thick galvanized sheet.
• 3
  Usually the wrong processHardened die inserts, high-reflection copper alloys, thick cast iron.

Thickness sets the practical ceiling on everything else. As the sheet gets thicker, the cut slows, the kerf widens, and the hole you can produce gets larger. A useful rule for holes in carbon steel is that the minimum hole diameter should be at least equal to the material thickness, and 1.2× to 1.5× is safer on stainless or on anything above 6 mm.

Below that ratio the beam cannot clear the molten material from a small circle. You get a hole that is tapered, out of round, or blocked by dross. For a 10 mm plate, a 6 mm hole is asking for trouble; a 12 mm hole is routine. If the design needs a small hole in thick plate, drill it after cutting instead of fighting the laser.

Taper is real and predictable. On a 12 mm carbon steel cut, the top of the kerf may be 0.9 mm wide and the bottom 0.7 mm, so a nominally straight wall leans by roughly 0.01–0.02 mm per mm of thickness. That is fine for a bracket and unacceptable for a bearing bore. Bores get reamed or milled after cutting.

Corner radii also follow thickness. A sharp internal corner in 12 mm plate will show a small radius no matter what the CAD file says, because the machine has to decelerate and the beam keeps burning. Design a 0.5–1.0 mm minimum internal radius on thin sheet, and scale that up with thickness. It costs nothing in CAD and saves a deburring argument later.

Every laser cut leaves a heat-affected zone, or HAZ. It is a band along the cut face where the steel was hot enough to change microstructure but not hot enough to be removed. On thin carbon steel it is often 0.05–0.1 mm. On 12 mm plate with oxygen assist it can reach 0.3 mm. The rest of the sheet stays at room temperature.

In mild steel the HAZ is mostly harmless. In high-carbon and alloy steel it can harden. A 4140 plate cut at 10 mm may show a file-hard skin of a few hundredths of a millimeter along the edge. If that edge will be machined later, the tool simply cuts through it. If that edge is a finished surface, it can chip or crack in service.

For parts that will be welded, the HAZ matters less than the edge chemistry. An oxygen-cut edge carries iron oxide that can cause porosity in a weld. Grinding or a nitrogen cut removes most of that risk. For structural weldments we usually specify nitrogen on anything 6 mm and up that will take a full-penetration weld.

For parts that will be plated, anodized or painted, the cut edge is the weak point. Oxide, dross and a rough profile all hurt coating adhesion. Bead blasting before finishing is standard practice, and a light tumble will knock off the dross on small parts. The cut face itself should not be a sealing or bearing surface.

• 1
  HAZ widthRoughly 0.05 mm thin sheet, up to 0.3 mm on 12 mm plate.
• 2
  Weld prepNitrogen assist and a light grind on oxygen-cut edges.
• 3
  Coating prepBead blast or tumble before plating or powder coat.

Cut length is the main cost driver, not part count. Two parts nested side by side share a common cut line and cost less than two parts cut apart. If a design can be split into identical halves that mate, or if a bracket can share an edge with its neighbor, the nesting software will find the saving. Send a full sheet layout when the quantity is high.

Avoid unnecessary holes and slots. Each internal feature adds pierce time and a risk of dross. A slot narrower than the material thickness will cut poorly and may need a secondary operation. If the slot is for a cable tie or a locating tab, widen it to 1.5× the thickness and the laser will do it in one pass.

Do not put a tight tolerance on a laser-cut profile if a milled feature sits on the same part. The two processes have different capability. We hold ±0.005 mm on machined features and ±0.1–0.3 mm on the laser profile, and the drawing should say which is which. Mixing them into one blanket tolerance is the most common cause of a rejected first article.

Think about the second operation before the first one. If a laser-cut blank will go onto a 5-axis machine for finishing, the blank only needs enough accuracy to locate in the fixture. Leaving 0.3–0.5 mm of stock on the machined faces is cheaper than trying to cut them to size on the laser. This is how we combine the two processes on the same part.