Manufacturing processesReading time 12 min

What a laser will cut, and what it will not

A laser is not a universal tool. Whether it can process a material is decided first not by power, but by whether that material absorbs that wavelength.

01Three mainstream lasers

Type	Wavelength	Good at	Poor at
Fibre	About 1.06 μm	Metals: carbon steel, stainless, aluminium, copper, brass	Most plastics, wood, glass
CO₂	10.6 μm	Non-metals: acrylic, wood, leather, fabric, paper	Highly reflective metals
UV	355 nm	Cold processing: films, glass, ceramics, fine plastics	Cutting thick sections

Wavelength decides whether the material absorbs. That is the first question in choosing a laser, not power.

Metals absorb far more at around 1 μm than at 10.6 μm, which is why metal is cut with fibre lasers while acrylic and wood are the other way round. Copper and brass remain highly reflective even to fibre; early fibre machines risked reflected light returning into the resonator, and most models now include an isolator before anyone will cut copper.

02How to judge cut quality

Kerf width. Affects nesting spacing and finished size; the program has to compensate.
Taper. On thick plate the kerf differs top to bottom, and the tolerance has to allow for it.
Dross. Molten residue on the lower edge, needing secondary work.
Striation. The ripple pattern on the cut face, showing whether speed and gas pressure are matched.
Heat-affected zone. The region where the microstructure changed, affecting later bending and welding.

Assist gas	What it does	Typical use	Cut face
Oxygen	Exothermic oxidation, supports burning	Medium-thickness carbon steel	Oxide layer present, must be cleaned before welding
Nitrogen	Blows the melt away and excludes oxygen	Stainless, aluminium	Oxide-free, weldable as cut
Air	Cheapest	Thin sheet, non-critical parts	Slight oxidation

The gas decides directly whether the cut face can go straight into the next operation.

03Laser marking: readability is the specification

The aim of marking is not that the mark goes on, but that it can be read afterwards, especially where DataMatrix or QR traceability is required. ISO/IEC 29158, the DPM quality guideline, scores it on a set of indicators.

Metric	What it looks at
Cell Contrast	Contrast between cell and background
Cell Modulation	How consistent the cell brightness is
Fixed Pattern Damage	Whether the finder pattern is intact
Axial Non-uniformity	Whether the code's aspect ratio is distorted
Grid Non-uniformity	Whether the grid positions have drifted

DPM grades run A to F. Marking deeper is not marking better, too deep and contrast suffers.

Marking mechanisms by material

Annealing. Heat discolours the surface by oxidation without removing material. Suits stainless and titanium, keeps the surface flat and corrosion resistant, common on medical devices.
Engraving. Melts and vaporises material to form a groove. High contrast, but the surface is damaged.
Foaming. Heat produces bubbles in plastic, giving a lighter mark.
Carbonising. Organic materials char and darken under heat; suits wood and leather.

04Laser-related callouts on the drawing

A few things on the drawing of a laser-cut part are easy to overlook and directly affect the process.

Thickness and material decide the machine, the power and the gas.
Minimum internal radius. Laser cutting has a minimum internal corner radius, roughly the kerf width. A sharp corner on the drawing cannot actually be made.
Hole diameter against thickness. The usual rule is that hole diameter should not be less than the thickness, or the cut is not clean.
Cut face roughness or dross requirements. If the drawing gives an Ra value, secondary work may be needed.
Marking content, character height and position, including serial number rules and whether a barcode is required.