Stereolithography

Stereolithography, or STL, is an additive technology which uses a UV laser to create parts from a UV curable liquid within an SLA, or Stereolithography Apparatus, system.

For a part to be created using STL, a 3D model of the desired part must first be created, after which the 3D data is seperated into a group of 2d layers of the entire part. These layers typically range from 0.10mm to 0.050mm in thickness (although a resolution of 0.050mm in thickness is usually used) and this group layers is called called "slice data." The slice data is then fed into the SLA system and the actual fabrication process begins. The platform is first lowered into the vat of clear, liquid plastic photopolymer. The polymer used is sensitive to ultraviolet light, allowing the polymer to solidify when it is exposed to the light provided by the UV laser and the materials used in this process range from soft durable plastic to hard plastics. The ultraviolet laser traces and selectively solidifies the first layer within the resin onto the platform, which is currently submerged one layer under the resin.

After the first layer has been created, the following layers are added to the first layer while adhering to the previous layer. A resin-filled "re-coater" blade is swept across the top the previous layer removing the uncured polymer while re-coating it with fresh material. The platform is then lowered gradually submerging the platform along with the base of the part (and the part itself, or rather the section of the part, which has been already created layer by layer) deeper under the resin. This process repeats itself until the last layer has been created and the part is completed. This is a relatively quick process. Up to about two minutes is needed for each layer to be created whereas an entire run might take six to 12 hours.

Because this process occurs while immersed in a tank of liquid, support structures are automatically constructed in order to hold the part in place and anchor unsupported sections of the part within the resin. The amount of supports needed depend on geometry as well as the orientation of the part.

When the part is completed the platform rises above the liquid, allowing excess resin to drain away from the part. The platform is then removed and a series of post processes must take place such as cleaning the part. (often in a chemical bath) Then it is sprayed thoroughly with alcohol and then placed in a UV oven to finish curing the polymer. Once the final curing process has finished, the support structures are removed. Then the surface of the part that was attached to the platform or supports is sanded. Later the part can be polished and processed furthered, if necessary.

Stereolithography is the first Rapid Prototyping (or RP) process and is still used 90% of the time. And although this fabrication process is used in Rapid Prototyping, a more current term, Rapid Manufacturing (or RM) is used because quite often the parts created can be used as end use parts. It allows for parts with complex geometries and intricate details to be built with the highest of accuracy.