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.
The term “stereolithography” was coined in 1986 by Charles (Chuck) W. Hull. Stereolithography was defined as a method and apparatus for making solid objects by successively “printing” thin layers of the ultraviolet curable material one on top of the other. Hull described a concentrated beam of ultraviolet light focused onto the surface of a vat filled with liquid photopolymer. The light beam draws the object onto the surface of the liquid layer by layer, causing polymerization or crosslinking to give a solid. Because of the complexity of the process, it must be computer-controlled. The first company aiming to generalize and commercialize the procedure was founded immediately alongside the invention.
Laser Prototypes (Europe) Ltd and Formation Ltd were the first two companies to start rapid prototyping in the UK. Laser Prototypes was also the first company to purchase a EOS stereolithography machine (SLS machine) in the UK although this was quickly followed by Rover (Coventry) and Daewoo (Worthing). Unfortunately after a period of rapid expansion Formation ceased trading in 1996 but Tim Plunkett its founder has continued his interest in the industry by working for various companies in the rapid prototyping field. Laser Prototypes are now the longest established rapid prototyping bureau in the UK and Ireland and recently completed another first by installing the latest EOS P390 selective laser sintering machine from EOS of Germany.