Stereolithography by photopolymerization

Created in the 1980s-1990s, additive manufacturing today has seven basic technologies. While all are based on the principle of adding elementary volumes called voxels, the first (in 1984) is linked to spatially resolved photopolymerization of a resin induced by light from UV or IR lasers. It's called stereophoto lithography or, more simply, Stereo Lithography (SL).

The process consists of polymerizing a layer of liquid monomer with light according to a computerized pattern, then depositing a second layer polymerized according to the same principle, and so on. The part is thus built up step by step. Since then, the "one-photon" process has improved both in terms of process and monomer resins, as the choice of light sources has diversified. Moreover, what was difficult to envisage at the time has now been demonstrated: a so-called "two-photon" polymerization induced by pulsed lasers avoids, as the article shows, the need for a complex resin lay-up stage. The principles are defined, with the emergence of optical, chemical, physical and computer constraints, and with proposals for acceptable compromises that today keep stereolithography at the top of the seven basic additive manufacturing technologies.

The article concludes with a (non-exhaustive) list of stereolithography machine manufacturers.

A glossary and table of symbols are provided at the end of the article.