Stereolithography Variations
The different methods
shown here are alternatives to the more widespread traditional SLA
process.
Solid Laser Plotting
- Denken Engineering, Inc.
 This
variation inverts the part by attaching it to a platform that rises
up as each successive layer is drawn and attached to the bottom-most
face. The liquid resin layer is deposited on a specailly prepared
window that is transparent to the laser and to which cured polymer
adheres poorly. The platform and prior-built structure are lowered
into the resin, leaving a liquid film - with the thickness of the
next layer - between the part and the plate. The new layer is drawn
from beneath the plate. After the layer is drawn, the new structure
is raised, separating the layer form the plate, and the process
is repeated until all layers are fabricated. This eliminates the
trapped volume problem discussed in the design
guide.
Microlithography - Nagoya
University
 This
variation is intended for smaller, more accurate components than
produced by standard SLA - the laser spot size is five micro-meters.
In this system, a transparent plate is lowered into the vat to form
a thin layer of liquid film over the part being built up. The growing
part remains stationary in the vat, and the vat is moved relative
to a fixed laser beam that passes through the plate, drawing the
cross-section. The laser moves up with the plate to maintain precise
focusing on the film layer.
Solid Ground Curing
(SGC) - Solider Cubital, Inc.
 In
contrast to "drawing out" each cross-section with laser
photolithography, it is possible to image an entire cross-section
in a single operation using photomasks. In SGC, each cross-section
is imaged onto an erasable mask plate produced by charging the plate
via an ionographic process and then developing the image with an
electrostatic toner (e.g., like the Xerogrpahy process). The mask
is then positioned overa uniform layer of liquid photopolymer, and
an intense puble of UV light is passed through it to selectively
cure the material. Uncured photopolymer is removed from the layer
with a vacuum system, and replaced with a low melting point, water
soluable wax that serves as the sacrificial support. After the wax
has cooled, the layer is milled to produce a flat surface. The pattern
on the exposed mask is erased by wiping off the toner, and the entire
process is repeated. After the part has been completed, the mas
is removed by melting. The various process used to implement SGC
are performed at different stations.
A unique feature of the
photomasking approach the the capability to build multiple parts
in a timely fashion in a single batch. Since the building time to
form each layer is independent of the part geometry or size, multiple
parts can be fabricated in the same time to build a single part.
Furthermore, the SGC
system builds parts in a solid sacrificial wax that multiple parts
packed into the sacrificial wax. Trapped volumes and the difficulties
with support structures marring the overhang surfaces are also eliminated
by the use of the wax.
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