Engraving and Cutting Acrylic material / Daniel
Acrylic is produced in
two basic versions, , cast (GS) and extruded (XT). The different production methods used to create these
materials leave the finished product with different material properties.
. Cast acrylic is
produced by mixing the acrylic liquid ingredients in molds. For acrylic plates
between two glass plates. A chemical process in the mold create a homogeneous
material with equivalent properties in all directions. In contrast, extruded
acrylic is produced by continuously pushing acrylic mass through a form, while
the chemical process takes place. Extruded acrylic is therefore heterogeneous,
with properties which vary depending on the direction. We call it the extrusion
direction for acrylic sheets. Cast acrylic is usually regarded as a better
quality than extruded acrylic even though it is in fact two different materials
with the advantages and disadvantages.
Cast acrylic (GS)
Cast acrylic is
produced by mixing the acrylic liquid ingredients in molds , Cast
acrylic is poured as a liquid mass between two glass plates, resulting in
a homogeneous, tension-free material with equal mechanic
properties in directions x and y.
Benefits of
cast acrylic
Laser cutting cast
acrylic creates burr-free cuts on both sides, Laser engraving also yields
better results than with extruded acrylic, with a perfectly white engraved image being created.
The manufacturing
process for cast laser acrylic is more expensive
You can achieve optimum cut edges
without burrs.
GS acrylic allows for excellent
engravings with colour changes to the engraved areas. Unlike with acrylic
XT, the laser engravings are more contrasting and thus achieve clearer
results and a better effect.
Chemical
Resistance
Cast acrylic is more resistant to the same solvents.
Laser
cutting
When laser cutting extruded acrylic , there will come a burr on one side
of the part. On the cast acrylic there is almost no burrs. The edges on
extruded acrylic parts can look a bit different depending on the direction
of the acrylic extrusion.
Laser
engraving
The Laser engraving will on extruded acrylic look matt gray. On the cast acrylic will look matt white.
Heat
bending and thermoforming
A sheet of extruded acrylic can, because of the acrylic extrusion
direction, behave differently depending on the bending direction
relatively to the extrusion. With cast acrylic, it makes no difference.
When cast colored acrylic is heated for thermoforming or heat bending the
color can change. Matt-colored surfaces can become clear and clear
surfaces can become matt. In addition, the shade of color can change. Cast
acrylic is harder to bend / shape.
Thickness
tolerance
Sheets of cast acrylic vary more in thickness. A cast 3 mm acrylic sheet
vary +/- 15%. While an extruded sheet only vary +/- 5%. The dispersion
within the tolerance also seems to be less on extruded sheets.
The high tolerance on cast acrylic sheets often comes as a surprise to
designers, with many construction errors to follow.
Scratch-resistant
Cast acrylic it more scrats resistant than extruded acrylic.
Flame
polishing
Cast acrylic is harder to flame polish.
Colors
Cast acrylic is produced in a many different color and thicknesses. The
color selection is more more limited for extruded acrylic. If one order a
special color from a supplier, it will in most cases be cast acrylic.
Tension
There is more tension in extruded acrylic.
Extruded acrylic (XT)
For the manufacture of extruded acrylic (XT), granules are
melted in an extruder using rotating screws. The resulting acrylic melt is
shaped into the desired form at the end of the extruder by nozzles with the desired thickness.
Benefits of
extruded acrylic:
Extruded acrylic demonstrates
significantly lower thickness tolerances in contrast to cast acrylic. This
property can have a positive effect on the dimensional stability of your
production.
Acrylic XT is cheaper, meaning it can be
more economical for use in series product.
§
Extruded acrylic is
generally less expensive, because of its production method and, as a series production is cheaper.
§
extruded acrylic requires less laser power than for cast acrylic in the same sheet thickness
§
Laser engraving on extruded acrylic is not recommended as unlike the
white image produced on cast acrylic, extruded acrylic produces a matt grey
result when laser engraved.
Setting the Air Assist
When laser cutting
acrylic, the nozzle with the large diameter should be used and – if controllable – lessen the Air Assist to a max. of 0.2 bar. (3PSI) This will give the material enough time to cool off
thus giving a glass-clear result on the edges.
In contrast, if a
nozzle with the small diameter is used or the air pressure is too high, a dull,
milky laser cutting edge is created as the material cools off too quickly.
Cutting acrylic
As a material, acrylic
requires a higher frequency when laser cutting compared to other common materials
such as wood.
The higher
frequency distributes the energy evenly into the material. This causes an
even melting of the laser cut acrylic edges creating a glass-clear,
flame-polished edge.
For GS
materials, we recommend a frequency of 5,000-20,000 Hz
For cutting XT
materials, a frequency of a max. of 5,000 Hz.
If the frequency is too
low, fine ridges, also known as chatter marks, become visible on the laser cut
edges. To counteract these, increase or lower the frequency of the laser
cutting speed. However, if the cutting speed is too slow, this can lead to a
cutting kerf below which increases the risk of fire.
The number of
nodes in the cutting contour needs to be reduced to a minimum. This allows the
laser to process homogeneously without unnecessary stops.
Engraving
acrylic
The best results are
achieved when only the surface of the acrylic is scratched, as this creates a
white engraved image. Using a lot of laser power creates deep laser engraving
results, however they will no longer be white.