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The most commercially used and still fastest growing solid free-form fabrication (SFF) method is stereolithography, launched by 3-D Systems Inc. in 1987. The first step is to translate a CAD file into surface model made up of thousands of small triangles. The current industry standard format for this data is called STL. The file is then sliced into many layers like a stack of playing cards. This is known as an slice file or SLI. These SLI files are loaded into the machine which drives the motions of a laser.

The laser exposes the photopolymers in the bath shown below, causing curing from liquid to solid. Once the first layer is cured, the elevator type stage lowers by 0.002 to 0.015 inches depending on the desired accuracy, and further layers are cured and connected by self-fusing to the previous ones. At the end of the process, the elevator rises and the component is lifted out and cured in its entirety. Curing is needed, probably overnight, before the prototype is ready for use. Hand-sanding may be required to mitigate the stair-stepping effect described later.

Note that the object above has overhanging areas about half-way down its height dimension. During the actual process these will need to be supported by slender sacrificial columns. Without these, the horizontal part of the component will sag. Thus, additional hand-finishing will be needed to snap-out these slender sacrificial columns and hand-sand any small stubs away from the surface.

Taken from Paul Wright's "Management of Technology"

Additionally post processing can take the form of "baking" the model in a UV oven to fully cure thick sections.