SLA - Stereolithography
Stereolithography (SLA) is an additive manufacturing method in which an ultraviolet laser is used to solidify a liquid polymer layer by layer.
Objects are built in a tank filled with liquid photopolymer , which is a plastic which reacts to light. An adjustable building platform is initially placed in its highest position, only covered by a thin layer of photopolymer. A movable mirror controls the ultraviolet laser beam, and draw out the cross section of a CAD model on the platform, which solidifies the plastic. The platform is lowered so that the previous layer is now covered by a new, thin layer of liquid. The laser beam solidifies a new layer which is then joined with the previous layer.
Support structures can be created if needed, if the liquid cannot support the weight of the overhanging parts of the component. The process is repeated until the object is completed and the finished part is usually cleaned by ultrasound and alcohol. Support structures are removed and the object is cured in a UV oven. Non solidified liquid can be recycled to produce new items.
A common variation to the method is that the detail is built from below hanging from the building platform and the laser beam instead cures the polymer through the tank's translucent bottom.