The most commercially
used and still fastest growing solid free-form fabrication (SFF)
method is stereolithography, launched by 3-D Systems Inc. in 1987.
The first step is to translate a CAD file into surface model made
up of thousands of small triangles. The current industry standard
format for this data is called STL. The file is then sliced into
many layers like a stack of playing cards. This is known as an slice
file or SLI. These SLI files are loaded into the machine which drives
the motions of a laser.
The laser exposes the
photopolymers in the bath shown below, causing curing from liquid
to solid. Once the first layer is cured, the elevator type stage
lowers by 0.002 to 0.015 inches depending on the desired accuracy,
and further layers are cured and connected by self-fusing to the
previous ones. At the end of the process, the elevator rises and
the component is lifted out and cured in its entirety. Curing is
needed, probably overnight, before the prototype is ready for use.
Hand-sanding may be required to mitigate the stair-stepping effect
Note that the object above has overhanging areas about half-way
down its height dimension. During the actual process these will
need to be supported by slender sacrificial columns. Without these,
the horizontal part of the component will sag. Thus, additional
hand-finishing will be needed to snap-out these slender sacrificial
columns and hand-sand any small stubs away from the surface.
Taken from Paul Wright's
"Management of Technology"
Additionally post processing
can take the form of "baking" the model in a UV oven to
fully cure thick sections.