How thick can a laser cut? Steel, stainless, aluminium and copper

On the shop’s 6 kW fiber laser we cut steel, stainless and aluminium up to 25 mm thick and copper and brass up to 10 mm, on a 3,000 × 1,500 mm bed. Tube goes on a separate tube laser, from Ø15 to Ø114 mm and up to 6 m long. The table shows the gas each material is cut with and the edge it leaves.

Limits are for the 6 kW machine. Thickness also sets the smallest hole, slot or web a part can have; see below.

Two things decide how thick a fiber laser can cut: power and assist gas. The beam has to melt through the full thickness fast enough to keep the cut moving, and the gas has to blow the molten metal out of the bottom of the cut. On mild steel, oxygen burns with the iron and adds heat, which is why thick mild steel cuts readily with O₂, at the cost of an oxide skin on the edge. Stainless and aluminium are cut with high-pressure nitrogen for a clean, bright edge; nitrogen adds no heat, so the laser does all the work. Copper and brass reflect much of the beam, which is why their limit is lower.

A cut in 20 mm plate is not a scaled-up cut in 2 mm sheet. The cut gets wider, from about 0.1 mm on 1 mm sheet to about 0.5 mm on 20 mm. The edge picks up a slight taper, and the tolerance opens from about ±0.1 mm on thin sheet to ±0.3 mm or more above 15 mm, because heat moves the plate as it cuts. The cut also runs slower, so cutting time becomes a larger share of the price.

Working figures from our kerf and tolerance note, not a guarantee.

The thicker the plate, the larger the smallest hole that comes out round and clean. Start from one millimetre of hole per millimetre of plate: mild steel cut with oxygen can go to about 0.8 × t, while stainless cut with nitrogen needs about 1.2 × t. A Ø6 hole in 20 mm plate will not come out clean; that hole is a job for a drill after the laser.

We don’t laser-cut plate above 25 mm. Plate that heavy is usually cut by plasma or oxy-fuel and then machined where it has to be accurate. If one part of an assembly is heavier than our limit, send the whole drawing anyway: we’ll tell you which parts we can cut, bend and weld, and which need another process.