Transcript How Stereolithography Works

Stereolithography
Apparatus (SLA)
What is SLA?
Stereolithography Apparatus (SLA) is a
liquid-based process which builds parts
directly from CAD software.
 SLA uses a low-power laser to harden photosensitive resin and achieve polymerization.
 A hopper full of the resin lies under a laser
which uses its beam to harden the part in
layers a Min. of 0.001” and up to 150lbs.
Part weight.
 Parts can reach a Max. size of 20”x20”x23”.
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Click here to view a diagram of a RP
Stereolithography Apparatus (SLA).
SLA
Click here to view an SLA machine
along with an introduction.
Companies
3D Systems Corp. in
Valencia, CA.
Other vendors are in the
market but do not have
significant market share.
The Process

The process begins with a 3D CAD file. The file is
digitally sliced into a series of parallel horizontal
cross-sections which are then provided to a
StereoLithography Apparatus (SLA) one at a time. A
laser traces the cross-section onto a bath of
photopolymer resin which solidifies the cross-section.
The part is lowered a layer thickness into the bath
and additional resin is swept onto the surface. The
laser then solidifies the next cross-section. This
process is repeated until the part is complete. Most
parts are completed in a matter of hours, thereby
defined as a "Rapid Prototype".
The Process cont
The process is still in use however,
the software has changed
dramatically.
 The technology first appeared on
UNIX-Systems and MSDOS.
 Now, Windows NT, 3D Lightyear,
and Buildstation are compatible.

The Process cont

A platform is lowered into the resin (via an elevator
system), such that the surface of the platform is a
layer-thickness below the surface of the resin. The
laser beam then traces the boundaries and fills in a
two-dimensional cross section of the model,
solidifying the resin wherever it touches. Once a layer
is complete, the platform descends a layer thickness,
resin flows over the first layer, and the next layer is
built. This process continues until the model is
complete.
The Process cont

Once the model is complete, the
platform rises out of the vat and the
excess resin is drained. The model is
then removed from the platform,
washed of excess resin, and then
placed in a UV oven for a final curing.
The model is then finished by
smoothing the "stair-steps."
Advantages

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Probably the most accurate functional
prototyping on the market.
Smooth surface finish, high dimensional
tolerance, and finely detailed features (thinwalls, sharp corners, etc…)
Used in: Investment Casting, Wind Tunnels,
and Injection Molding as tooling
Resins can be custom engineered to meet
different needs: higher-temps, speed, finish…
Cost
Cost of materials: the resin costs as much as
$600-$800 per gallon. (For a 20”x20”x23”
cube that’s 39.8 gallons! …$27,860)
 Post processing Requirements:
 Careful practices are required to work with
the resins.
 Frameworks must be removed from the
finished part.
 Alcohol baths then Ultraviolet ovens are
used to clean and cure the parts.

Development

The Rapid Prototyping Stereolithography
(SLA) process was developed by 3D Systems
of Valencia, California, USA, founded in 1986.
A vat of photosensitive resin contains a
vertically moving platform. The part under
construction is supported by the platform that
moves downward by a layer thickness
(typically about 0.1 mm / 0.004 inches) for
each layer. A laser beam traces out the shape
of each layer and hardens the photosensitive
resin.
Development cont.

The SLA rapid prototyping process was
the first entry into the rapid prototyping
field during the 1980’s and continues to
be the most widely used technology.
Highlights
First Rapid Prototyping technique.
 Inexpensive compared to other techniques.
 Uses a light-sensitive liquid polymer.
 Requires post-curing.
 Long-term curing can lead to warping.
 Parts are quite brittle and have a tacky surface.
 No milling steps so “z” accuracy suffers.
 Support structures are typically required.
 Simple process: No milling or masking steps
 Uncured material is toxic.

Materials:
The laser can be either: HeCd or Solid
State and can range in power from 12 –
800mW
 The original resin was acrylate based,
then epoxy-based: ACES (Acrylic Clear
Epoxy System).
 The resin can be modified to improve
different characteristics; depending on
the users needs.

Materials cont :
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SLA Somos 7120 - A high speed general use resin that is heat
and humidty resistant. For more information on this material
please read the material technical data sheet. Somos 9120 - A
robust accurate resin for functional parts. For more information
on this material please read the material technical data sheet.
Somos 9920 - A durable resin whose properties mimic
polypropylene. Offers superior chemical resistance, fatigue
properties, and strong memory retention. For more information
on this material please read the material technical data sheet.
Somos 10120 WaterClear - A general purpose resin with mid
range mechanical properties. Transparent parts are possible if
finished properly. Note that finishing for transparent parts
must be special ordered. For more information on this
material please read the material technical data sheet.
Materials cont :
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Somos 11120 WaterShed - Produces strong, tough, waterresistant parts. Many of its mechanical properties mimic that of
ABS plastic. For more information on this material please read
the material technical data sheet.
Somos 14120 White - A low viscosity liquid photopolymer
that produces strong, tough, water-resistant parts. For more
information on this material please read the material technical
data sheet.
Somos ProtoTool - ProtoTool is a high density material that
transcends currently available stereolithography resins by
offering superior modulus and temperature resistance. For more
information on this material please read the material technical
data sheet.
Models
Click here to view product examples
from AcuCast.com.
Click on Photo 009 to view models from their
StereoLithography Apparatus (SLA).
REFERENCES
http://www.acucast.com/rapid_prototyping.htm
 http://www.milparts.net/sla.html
 http://rpdrc.ic.polyu.edu.hk/old_files/sla_introduction.
htm
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