Stereolithography (SLA) is a type of additive manufacturing process used for creating tangible 3-dimensional objects from CAD designs or 3D scanned digital files.

The process, invented and named by Chuck Hull in 1986, uses photo-reactive (usually acrylic-based) polymers that instantly harden when exposed to an ultraviolet beam.

The first step in the process involves an stereolithography (SLA) machine being uploaded with a file containing a digital object that has been “sliced” into hundreds or even thousands of individual layers. The machine creates the first physical layer of the object by submerging a perforated metal platform into a vat of the photopolymer to a depth equivalent to the corresponding digital layer in the computer file. This layer is then hardened by a small ultraviolet laser beam tracing the predetermined pattern. Once this first layer is completed, the platform descends to the depth of the next layer hence leaving a thin coating of uncured polymer on the top of the hardened layer. The laser repeats the process and seamlessly affixes the two layers together. The SLA machine continues by sequentially adding each individual layer until the object is finished.

Although stereolithography is the oldest form of 3D printing, and many other types of additive manufacturing now exist, this original technology is still used today. Advances in viable materials, computers, and hardware have helped stereolithography remain an important part of the booming 3D printing industry.