Laser Cutting Wood

Insofar as laser cutting is concerned, wood can be separated into two distinct groups:

1. Natural timber from various species of tree. For example, maple or cherry wood.
2. Man-made wood manufactured by bonding wood pulp, fibers or shavings. For example, MDF or plywood

All natural timbers can be cut by a CO2 laser at the 10.6µm wavelength. Limitations only apply with regard to thickness and the degree of charring that is acceptable to the customer.

Special versions of laser cutting machine are made for specific wood cutting applications such as, for example, laser cutting plywood for label dies. However, for the purpose of this article we are referring to a typical benchtop format laser cutter <100w.

For most industries laser cutting anything beyond 12mm natural timber and 9mm plywood produces an undesirable result because the feed rate (speed of cut) combined with optical limitations causes the wood to adversely burn.

When laser cutting wood the rate of laser fume extraction, particularly underside extraction and air assist delivered through the nosecone, can never be too much. When vaporised, wood produces a very dense fume that if not immediately evacuated from the cutting line will rise into the path of the beam and absorb laser power, significantly dropping the feed rate of the cut and in turn accelerating the degree of charring at the edge of the cut.

High amounts of debris from laser cutting wood can also contaminate laser optics causing them to fail prematurely and also cause HAZ (Heat Affected Zone), which is an undesirable staining to the edge and surfaces of the material.

In machines where the design of extraction is poor, surface HAZ can be minimised by first applying a low-tack, paper based tape to both surfaces of the wood. The tape acts as a masking barrier, attracting the contamination. After laser cutting the paper is removed and the wood surface underneath is clean.

Natural timber has a tendency to warp, which is challenging for laser cutting as this causes the beam to defocus, producing undesirable results. Therefore, if the application calls for laser cutting of natural timber it is best to process the material as soon as possible after receiving it from the mill.

Man-made or engineered woods can contain resins that are actually designed to be fire retardant. This is unhelpful when trying to burn through the wood with a laser cutter! Therefore, if the application calls for using a form of engineered wood it’s wise to be very selective about the exact type of material you use. For example, plywood is most commonly available in a WBP or exterior grade. The resins used to bond this type of plywood are among the least laser friendly and will resist thelaser cutting process, accelerating HAZ.

Interior grade plywood, sometimes called white glue plywood, is among the most laser friendly plywood’s. Not as commonly available as exterior grade, interior grade should be used as a preference for laser cutting if the job specification allows it as the resins in the material will vaporise much cleaner.

An often overlooked aspect is that of the surface finish of wood prior to laser cutting. If the part to be laser cut is the finished item then the surface should always be sealed/finished before it is laser cut. This reduces HAZ and any HAZ present can be wiped off with a slightly damp cloth. If however the material is to be post processed, such as sanding for example, then pre-sealing the wood is not absolutely necessary as the HAZ will be removed during post processing.

At Lotus Laser Systems we manufacture a wide range laser, marking and engraving solutions ideally configured for laser cutting and laser engraving wood. Our experts would be happy to recommend which configuration best suits your application.