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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. A 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."
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" on
most parts and features. These characteristics make SLA an
excellent all-round choice for prototypes.
SLA
Material Properties Available
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Mechanical
Properties
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Test Method
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Units
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Rigid
(SL5195)
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Durable
(SL 7540)
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Flexible
(Somos 8100)
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Tensile Strength
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ASTM D638
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psi
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6,740
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5,500
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3,800
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Tensile Modulus
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ASTM D638
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psi
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303,000
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223,000
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73,500
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Tensile Elongation
at Break
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ASTM D638
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11-22%
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22%
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17-24%
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Flexural Strength
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ASTM D790
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psi
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7,150
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7,000
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3,700
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Flexural Modulus
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ASTM D790
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psi
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236,000
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199,000
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91,000
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Hardness
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DIN 53505/2240
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Shore D
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83
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79
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81
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Izod Impact - Notched
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ASTM D256
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(ft-lb)/in
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1
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0.72
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1.1
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Heat Deflection Temp
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ASTM D648
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Deg F
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117
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135
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130
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