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General Design Guidelines
Stereolithography
Stereolithography (SLA) is often considered the pioneer of
the Rapid Prototyping industry with the first commercial system introduced in
1988 by 3D Systems. The system consists of an Ultra-Violet Laser, a vat of
photo-curable liquid resin, and a controlling system.
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.
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."
Resolution
Standard SLA parts are manufactured using the standard layer resolution of
.005". High Resolution parts, parts with very small features and details, are
manufactured using a layer resolution of .002", and a high-res laser spot size
of .003".
Materials
The materials used by SLA equipment are epoxy-based resins that offer strong,
durable, and accurate models. It is ideal for form, fit, and function testing as
well as for visual aids and patterns for tooling. In many cases, SLA is capable
of reproducing snap fits. In general SLA materials have a low heat tolerance
with typical heat deflection temperatures are around 110-120ºF. Standard
tolerances are ± 0.005" for the first inch, and ± 0.002" in/in on most parts and
features. These characteristics make SLA an excellent all-round choice for
prototypes.
SLA Material Properties
|
Mechanical Properties |
Test
Method |
Units
|
Rigid
Resin
(Somos 10120) |
WaterClear Resin
(Somos 10120) |
Durable
(Somos 9100) |
Durable
(SL 7540) |
Semi
Flexible
(Somos 8100) |
|
Tensile Strength |
ASTM D638 |
psi |
6,237 |
6,237 |
4,700 |
5,500 |
3,800 |
|
Tensile Modulus |
ASTM D638 |
psi |
318,000 |
318,000 |
212,000 |
223,000 |
73,500 |
|
Tensile Elongation at
Break |
ASTM D638 |
psi |
18% |
18% |
25% |
11-22% |
22% |
|
Flexural Strength |
ASTM D790 |
psi |
11,000 |
11,000 |
6,700 |
7,000 |
3,700 |
|
Flexural Modulus |
ASTM D790 |
psi |
344,000 |
344,000 |
211,000 |
199,000 |
91,000 |
|
Hardness |
DIN 53505/2240
|
Shore D |
83 |
83 |
82 |
79 |
81 |
|
Izod Impact - Notched |
ASTM D256 |
(ft-lb)/in |
.57 |
.57 |
1.0 |
0.72 |
1.1 |
|
Heat Deflection Temp |
ASTM D648 |
degF |
136 |
136 |
142 |
135 |
130 |
|
|