Graphics Reference
In-Depth Information
of LOM printers fuse cut sheets of aluminum foil with powerful ultrasound
vibrations that cause the sheet to rub against the previous layer and consolidate
into densely packed layers.
Printers that fuse, bind, or glue
The second major family of 3D printers is made up of printers that use a
selective binding process to fuse or bind raw material into layers. Many of
the earliest commercial printers used this approach. Two variations of this
method, in particular, are in widespread use: stereolithography (SL) and laser
sintering (LS).
Stereolithography (SL)
Stereolithography (SL) was one of the earliest commercial methods of 3D
printing. Imagine a small vat of liquid polymer sitting inside a printer the size
of an apartment-sized refrigerator. The printer sweeps a laser beam over the
surface of a special type of plastic, a UV-sensitive photopolymer that hardens
when exposed to UV light. Each sweep of the laser traces the outline and cross
section of the printed shape in consecutive layers.
After each sweep of the laser, a moveable table holding the printed part is
lowered a fraction of a millimeter. The part sinks a bit into the liquid, and
fresh photopolymer loods its top side. Some SL printers work in the opposite
direction by aiming the laser upwards into the photopolymer, then lifting
(rather than lowering) the printed object to lood its base (rather than its top)
with fresh liquid.
After an object is 3D printed in this method, there's still more work to be
done. Excess material needs to be rinsed off and the surfaces sometimes need
to be sanded by hand. Depending on what's printed, sometimes further curing
is done in an ultraviolet light “oven.”
The upside of SL printing is that the laser is fast and precise. Multiple lasers
can work in parallel to trace out shapes at a higher resolution than can today's
extrusion-style 3D print heads. Today's industrial-scale 3D printers can fab-
ricate precise models and parts in layers as thin as 10 micrometers—thinner
than a sheet of thin paper. As the quality and range of raw photopolymers
continues to expand, SL printers can fabricate a broader range of objects with
specialized material properties.
