Hull first came up with the idea in 1983 when he was using UV light to harden tabletop coatings. But on July 16, 1984 Alain Le Méhauté, Olivier de Witte and Jean Claude André filed their patent for the stereolithography process. It was three weeks before Chuck Hull filed his own patent for stereolithography. The application of French inventors were abandoned by the French General Electric Company (now Alcatel-Alsthom) and CILAS (The Laser Consortium). The claimed reason was “for lack of business perspective”. Hull coined the term “stereolithography” in his U.S. Patent 4,575,330 entitled “Apparatus for Production of Three-Dimensional Objects by Stereolithography” issued on March 11, 1986. He defined stereolithography as a method and apparatus for making solid objects by successively “printing” thin layers of the ultraviolet curable material one on top of the other. In Hull's patent, a concentrated beam of ultraviolet light is focused onto the surface of a vat filled with liquid photopolymer. The light beam, moving under computer control, draws each layer of the object onto the surface of the liquid. Wherever the beam strikes the surface, the photopolymer polymerizes/crosslinks and changes to a solid. An advanced CAD/CAM/CAE software mathematically slices the computer model of the object into a large number of thin layers. The process then builds the object layer by layer starting with the bottom layer, on an elevator that is lowered slightly after solidification of each layer.
