Stereolithography (SLA)

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

Mechanical Properties    Test Method Units Rigid(SL5195) Durable(SL 7540) Flexible(Somos 8100)    
Tensile Strength ASTM D638 psi 6,740 5,500 3,800  
Tensile Modulus ASTM D638 psi 303,000 223,000 73,500
Tensile Elongation at Break ASTM D638   11-22% 22% 17-24%
Flexural Strength ASTM D790 psi 7,150 7,000 3,700
Flexural Modulus ASTM D790 psi 236,000 199,000 91,000
Hardness DIN 53505/2240 Shore D 83 79 81
Izod Impact – Notched ASTM D256 (ft-lb)/in 1 0.72 1.1
Heat Deflection Temp ASTM D648 Deg F 117 135 130