Many people falsely believe
that a laser cuts like a "torch" simply burning through
everything it touches.
This is not the case, for non-metallic materials, the laser beam
actually vaporizes or ablates the material it contacts. If
oxygen is not available, the process does not cause oxidation or
burning. For cutting thin non-metallic materials, inert gasses
such as nitrogen or argon are used with the gas-assist nozzle.
This can virtually eliminate oxidation and produces edges that
are free from charring.
Acrylic is an example of a material that vaporizes easily
and does not tend to oxidize. With acrylic, the laser produces
extremely smooth "flame polished" edges. Polycarbonate (Lexan)
on the other hand, tends to oxidize, rather than vaporize and
requires inert assist-gas for clean cutting. For this reason,
Ryan recommends acrylic when the project does not specify a
different plastic.
For thicker non-metallic materials, such as wood, the
heat of laser cutting can produce secondary oxidation and
charred edges are more difficult to eliminate. Laser cutting
produces a "heat affected zone" (HAZ). For thicker materials the
HAZ is larger and it is more difficult to remove all of the
oxygen. Wood also can contain moisture and oxygen which will
increase the burning. The result with thicker wood (around ˝"
and above) is that the gas assist will reduce the heat and HAZ,
eliminate much of the oxygen and significantly reduce charring.
Metal cutting with a laser is a very different process.
To cut metal, oxygen assist is sometimes used to increase the
burning and help remove material. This operates somewhat like a
small-scale acetylene torch.
Thermoplastics
with relatively low melting temperatures typically display clean
cuts with flame-polished edges as a result of resolidified
melting. Process control can be exercised to minimize or
eliminate bubbling or the presence of small burrs on the
backside of the cut.
Laser cutting Wood
The laser offers a number of attractive advantages for the
cutting of timber, plywood, and particleboard. In particular, it
provides narrow kerfs, the absence of sawdust, the ability to
contour cut in any direction and no tool wear and noise. While
the use of a laser likewise eliminates rough, torn-out, and
fuzzy edges as evident with conventional sawing techniques, it
is characterized on many woods by darkened edges produced by the
laser's heat. Appears as a burnt edged.
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