STEREOLITHOGRAPHY

The term "stereolithography" was coined by the inventor, Charles W. Hull, in his US Patent 4,575,330, entitled "Apparatus for Production of Three-Dimensional Objects by Stereolithography" issued in 1986. Stereolithography was defined as a method and apparatus for making solid objects by successively "printing" thin layers of the curable material, e.g., a UV-curable material, one on top of the other.

It is an imaging process in three dimensions. It is one of the leading processes of the rapid prototyping industry which includes jetting of photopolymers in an inkjet type of equipment. Some of synonyms used for stereolithography include 3D printing, optical fabrication, photosolidification, solid freeform fabrication, solid imaging, optical shaping, steric polymerization, desk-top manufacturing, automatic modeling etc.

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.

Non-photopolymer-based rapid prototyping processes include fusion deposition modeling (FDM® ), laser sintering and an inkjet system. The FDM process developed by Stratasys extrudes a thin thermoplastic filament layer by layer. Laser sintering process uses data from a CAD/CAM/CAE system and laser technology to transform a variety of powdered materials into three-dimensional prototypes. An inkjet equipment marketed by Z Corp. builds models by depositing a binder solution through an inkjet print head onto layers of a plaster-based powder.

A variety of liquid photopolymers are available for stereolithography. Epoxy-based systems and hybrids are now preferred to older acrylates because of former's higher green strength, higher temperature resistance, lower moisture absorption and lower shrinkage. Radiation-cured acrylates also suffer from oxygen inhibition. The hybrids cure under light by cationic as well as free radical polymerization. Photopolymer resins with mechanical properties similar to engineering plastics such as ABS, nylon and polycarbonate are now available.

Stereolithography is now making transition from rapid prototyping to rapid manufacturing. Both photopolymer-based as well as non-photopolymer-based processes are now used for short run manufacturing. The US army is studying using such systems in war zones to create replacements for broken parts of planes and tanks. Soon desktop 3D printers will be available to consumers to make small appliance parts or toys at home!

Manufacturers of Equipment:

3D Systems
Light Sculpting
Sony Precision Technology America

Teijin Seiki/CMET, Japan
D-MEC, Japan
Denken Engineering, Japan

Laser Solutions, Japan
Unirapid, Japan

Meiko, Japan

Autostrade Limited, Japan

Objet Geometries, Israel

Envision Technologies GmbH, Germany

microTEC, Germany

F&S Stereolithographietechnik GmbH, Germany

Suppliers of Photopolymers:

Huntsman Advanced Materials

DSM Somos

3D Systems

JSR, Japan

American Dye Source/Tuxedo Resin, Canada

Objet Geometries, Israel

Asahi Denka, Japan

Teijin Seiki, Japan