Stereolithography Rapid Prototyping Review

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Stereolithography ( SLA or SL ; also known as optical fabrication , photo-solidification , solid free-form fabrication , solid imaging and Resin printing ) is an additive manufacturing or 3D printing technology used for producing models , prototypes , patterns , and production parts up one layer at a time by curing a photo-reactive resin with a UV laser or another similar power source.

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 resolution 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 110-120F. 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)
Water Clear 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 Modulus 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 deg F 136 136 142 135 130

Advantages

One of the advantages of stereolithography is its speed; functional parts can be manufactured within a day. The length of time it takes to produce one particular part depends on the size and complexity of the project and can last from a few hours to more than a day. Most stereolithography machines can produce parts with a maximum size of approximately 50??50??60 cm (20"??20"??24") and some, such as the Mammoth stereolithography machine (which has a build platform of 210??70??80 cm), are capable of producing single parts of more than 2 m in length. Prototypes made by stereolithography are strong enough to be machined and can be used as master patterns for injection molding , thermoforming , blow molding , and various metal casting processes.

Although stereolithography can produce a wide variety of shapes, it has often been expensive; the cost of photo-curable resin has long ranged from $80 to $210 per liter, and the cost of stereolithography machines has ranged from $100,000 to more than $500,000.

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