Stereolithography

Stereolithography (SLA or SL; also known as vat photopolymerisation,[1] optical fabrication, photo-solidification, or resin printing) is a form of 3D printing technology used for creating models, prototypes, patterns, and production parts in a layer by layer fashion using photochemical processes by which light causes chemical monomers and oligomers to cross-link together to form polymers.

Research in the area had been conducted during the 1970s, but the term was coined by Chuck Hull in 1984 when he applied for a patent on the process, which was granted in 1986.

In the early 1980s, Japanese researcher Hideo Kodama first invented the modern layered approach to stereolithography by using ultraviolet light to cure photosensitive polymers.

[7][8] The term “stereolithography” (Greek: stereo-solid and lithography) was coined in 1984 by Chuck Hull when he filed his patent for the process.

Hull's patent described a concentrated beam of ultraviolet light focused onto the surface of a vat filled with a liquid photopolymer.

The beam is focused onto the surface of the liquid photopolymer, creating each layer of the desired 3D object by means of crosslinking (generation of intermolecular bonds in polymers).

[13] Stereolithography is an additive manufacturing process that, in its most common form, works by focusing an ultraviolet (UV) laser on to a vat of photopolymer resin.

Photopolymers are sensitive to ultraviolet light, so the resin is photochemically solidified and forms a single layer of the desired 3D object.

[17] An inverted stereolithography machine starts a print by lowering the build platform to touch the bottom of the resin-filled vat, then moving upward the height of one layer.

[5] Stereolithography requires the use of supporting structures which attach to the elevator platform to prevent deflection due to gravity, resist lateral pressure from the resin-filled blade, or retain newly created sections during the "vat rocking" of bottom up printing.

There are potential errors possible when making medical models using stereolithography but these can be avoided with practice and well trained operators.

[30][31] In 2019, scientists at Rice University published an article in the journal Science, presenting soft hydrogel materials for stereolithography used in biological research applications.

[10] SLA printed parts, unlike those obtained from FFF/FDM, do not exhibit significant anisotropy (structural non-uniformity) and there's no visible layering pattern.

Prototypes and designs made with stereolithography are strong enough to be machined[34][35] and can also be used to make master patterns for injection molding or various metal casting processes.