In the flash, the laser moves like a brush

• 1
  What the laser moves like a brush means at 1,064 nm
• 2
  Kerf width, taper and the heat-affected zone
• 3
  Where laser cutting stops and milling takes over
• 4
  Nesting, setup time and the real cost driver
• 5
  Design rules that keep laser parts cheap
• 6
  Laser cutting vs CNC milling for flat parts

A fiber laser emits light at about 1,064 nm. That beam is focused by a lens to a spot 0.1 to 0.3 mm wide. Power density at the spot reaches 10^6 W/cm² or more, so the metal does not melt gradually. It vaporizes in microseconds, and the cut edge stays narrow.

The head then moves. On a gantry machine, linear motors drive the cutting head along X and Y while the sheet stays clamped. A 1.5 kW source can travel 30 to 80 m/min on 1 mm mild steel. The path looks smooth because acceleration is high and the controller keeps the beam on the programmed contour.

That is the brush analogy. A paint brush lays a line as the hand moves; the laser lays a kerf as the head moves. The metal is not pushed aside. It leaves as molten droplets and vapor, blown out of the kerf by assist gas at 10 to 20 bar.

The comparison breaks down in one place. A brush can lift off and start again anywhere. A laser cannot cut a closed path without a lead-in, because the beam has to enter the material somewhere. That lead-in is the only mark the flash leaves behind.

The kerf is the slot the beam removes. On 1 mm stainless with a 1.5 kW source and nitrogen assist gas, kerf runs about 0.1 to 0.2 mm. On 6 mm mild steel with oxygen assist gas, it widens to 0.4 to 0.6 mm. The kerf sets the smallest inside radius you can cut, roughly half the kerf width.

Taper is the difference between kerf width at the top and bottom of the cut. Good parameters hold taper under 0.05 mm on thin sheet. Push feed rate too high and the bottom of the kerf narrows into a V shape. Push it too low and the edge drosses, because the molten metal is not ejected cleanly.

The heat-affected zone (HAZ) is the band next to the cut where the microstructure changed. On 1 mm cold-rolled steel, HAZ is often under 0.1 mm. On 6 mm plate it can reach 0.3 mm. For most brackets and covers this does not matter. For a part that will be fatigue-loaded or welded, it does.

Edge finish depends on the gas. Nitrogen gives a bright, oxide-free edge, usually Ra 0.8 to 1.6 μm. Oxygen gives a faster cut but leaves a dark oxide layer and rougher edge, often Ra 1.6 to 3.2 μm. If the part gets powder coated or welded, the oxide is usually acceptable. If it gets anodized, it is not.

Laser cutting is a 2D process. It goes through the sheet, not into it. The moment a part needs a pocket, a counterbore, a thread or a chamfer with a defined angle, the laser cannot produce it. Those features need a rotating cutter, which means CNC milling or a mill-turn center.

Thickness is the next boundary. A 1.5 kW fiber source cuts 1 mm mild steel at 30 to 80 m/min, but the same source on 12 mm plate slows to roughly 1 m/min and the edge quality drops. Above about 20 mm, plasma or waterjet is normally the better choice for carbon steel.

Feature size matters too. A laser can cut a 1 mm hole in 1 mm sheet, but the hole will taper and the diameter tolerance is loose, often ±0.1 mm. If a hole has to hold ±0.005 mm for a dowel pin, drill it or mill it after laser cutting. Laser first, machine second is a common sequence.

Material reflectivity is the last limit. Copper, brass and aluminium reflect a large share of 1,064 nm light. Modern fiber sources handle these metals with the right settings, but thin reflective sheet can still be slow or unstable. For 0.5 mm copper, a dedicated source or a different process is often faster.

Laser cutting has almost no tooling cost. There is no fixture to build, so a one-off bracket and a 500-piece run use the same program. That is why it fits prototyping and low-volume production. The setup is the nesting and the cut program, not a physical die.

Nesting is where the cost lives. Parts are arranged on a standard sheet, usually 1,250 × 2,500 mm or 1,500 × 3,000 mm. A good nest uses 70 to 85 percent of the sheet. A poor nest wastes material, and material is often the largest line item on a laser-cut quote.

Cut length also drives cycle time. A part with a long perimeter and many internal cutouts takes longer than a simple rectangle. On thin sheet the difference is small. On 6 mm plate, a 3 m cut path can add several minutes per part.

For runs above roughly 10,000 pieces of the same flat part, stamping or die cutting can beat laser on unit cost, because the die cost is spread across the volume. Below that, laser is usually cheaper once you count the die and the lead time to build it.

Keep hole diameter at least equal to sheet thickness. A 1 mm hole in 1 mm sheet is cuttable but taper is hard to control. A 2 mm hole in 1 mm sheet cuts clean and holds tolerance better. If the hole is critical, note it on the drawing so it can be drilled after cutting.

Keep inside corners radiused. A sharp inside corner forces the beam to slow down and reverse, which leaves a small dwell mark and can overheat the corner. A radius of at least half the sheet thickness avoids this. Add the radius in the CAD model, not in a note.

Leave at least 2 mm between parts in the nest and 3 mm from the sheet edge. Closer spacing risks the parts shifting as the skeleton weakens, and a shifted part ruins the whole sheet. The skeleton is the leftover web that holds parts in place until the end of the cut.

Add a lead-in and lead-out on closed contours. The lead-in is where the beam pierces and enters the path. Put it on a scrap area or a non-critical edge. On a visible edge, a lead-in mark will show after anodizing, and it cannot be polished out.