STEREOLITHOGRAPHY

Stereolithography is a common rapid manufacturing and rapid prototyping technology for producing parts with high accuracy and good surface finish. A device that performs stereolithography is called an SLA or Stereolithography Apparatus. Stereolithography is an additive fabrication process utilizing a vat of liquid UV-curable photopolymer "resin" and a UV laser to build parts a layer at a time. On each layer, the laser beam traces a part cross-section pattern on the surface of the liquid resin. Exposure to the UV laser light cures, or, solidifies the pattern traced on the resin and adheres it to the layer below.

After a pattern has been traced, the SLA's elevator platform descends by a single layer thickness, typically 0.05 mm to 0.15 mm (0.002" to 0.006"). Then, a resin-filled blade sweeps across the part cross section, re-coating it with fresh material. On this new liquid surface the subsequent layer pattern is traced, adhering to the previous layer. A complete 3-D part is formed by this process. After building, parts are cleaned of excess resin by immersion in a chemical bath and then cured in a UV oven.

Stereolithography requires the use of support structures to attach the part to the elevator platform and to prevent certain geometry from not only deflecting due to gravity, but to also accurately hold the 2-D cross sections in place such that they resist lateral pressure from the re-coater blade. Supports are generated automatically during the preparation of 3-D CAD models for use on the stereolithography machine, although they may be manipulated manually. Supports must be removed from the finished product manually; this is not true for all rapid prototyping technologies. Stereolithography has many common names such as: 3D printing, optical fabrication, photo-solidification, solid free-form fabrication, and solid imaging. One of the appealing aspects about SLA is that a functional part can be created within one day which becomes useful when working in a “ time is money” environment.

However the amount of time to produce any one part depends on the size and complexity of it and can take anywhere from a few hours to more than a day. Most SLA machines can produce parts with a maximum size of 20” x 20” x 24”. Prototypes made by SLA can be very beneficial as they are strong enough to be machined and can be used as master patterns for injection molding, thermoforming, blow molding, and also in various metal casting processes. Although there are almost no limitations when it comes to the shapes of the parts that can be created the process is not by any means inexpensive.