Using
the 3D systems SLA (Stereolithography Apparatus), CAD data of
the product design is first sliced into very thin cross sections.
This CAD data comes from 3D solid modeling software packages
such as SolidWorks, ProE, SDRC IDEAS, and many others. It is
a file 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 a slice file or SLI. These SLI files are loaded
into the machine, which drives the motions of the laser. A laser
beam of ultra violet light is then focused onto the surface
of a vat of liquid photopolymer (see below).
The
laser beam traces the cross section of a part, exposing the photopolymers
in the vat, turning a thin layer of the liquid plastic to solid.
Once the first layer is cured, the elevator type stage is lowered
(0.002 to 0.015 inches) and recoated with liquid photopolymer.
The laser then traces the next slice on top of the previous one
fusing together layer be layer until the part is complete. Completion
time depends on the size of the part in the vertical direction
(z-motion).
Note
that the object above has overhanging areas about halfway down
its height dimension. During the actual process these will need
to be supported by slender sacrificial columns or supports. These
supports are only used for fabrication, and can be generated by
the software program that creates the slices.
After the build process, uncured resin and all supports are removed
and the model is post-cured in a UV oven to fully cure the resin.
Because of the layered process, the model has a surface composed
of stair steps. Sanding can remove the stair steps for a cosmetic
finish. Model build orientation is important for stair stepping
and build time. In general, orienting the long axis of the model
vertically takes longer but has minimal stair steps. Orienting
the long axis horizontally shortens build time but magnifies the
stair steps.
For aesthetic purposes, the model can be primed and painted.
SLA
Uses:
- Very accurate form/ fit plastic prototypes for design verification
and testing
- Precision patterns for casting and molding
- Tools for pre-production tooling
- Parts for manufacturing aids, vendor solicitation,
and limited production runs.
- Many photopolymer materials are now available
providing options for the designer.
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