Rapid+Prototyping

=Rapid Prototyping = Stereolithography is an additive manufacturing process using 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, 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. Watch the video: media type="custom" key="8000750"

**The first Rapid Prototyping technique and still the most widely used. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Inexpensive compared to other techniques. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Uses a light-sensitive liquid polymer. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Requires post-curing since laser is not of high enough power to completely cure. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Long-term curing can lead to warping. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Parts are quite brittle and have a tacky surface **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">No milling step so accuracy in z can suffer. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Support structures are typically required. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Process is simple: There are no milling or masking steps required. **
 * **<span style="border-collapse: collapse; font-family: arial,helvetica,sans-serif; font-weight: normal; line-height: normal;">Uncured material can be toxic. Ventilation is a must **

The sequence of steps for producing an Stereolithography (SLA) layer is shown in the following figures:
 * Sequence of Stereolithography**









Uncured resin is removed and the model is post-cured to fully cure the resin. Because of the layered process, the model has a surface composed of stair steps. Sanding can remove the stair steps for a cosmetic finish. Model build orientation is important for stair stepping and build time. In general, orienting the long axis of the model vertically takes longer but has minimal stair steps. Orienting the long axis horizontally shortens build time but magnifies the stair steps. For aesthetic purposes, the model can be primed and painted. During fabrication, if extremities of the part become too weak, it may be necessary to use supports to prop up the model. The supports can be generated by the program that creates the slices, and the supports are only used for fabrication. The following three figures show why supports are necessary:






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