http://www.additive3d.com/techn.htmRapid prototyping is the name given to a host of related technologies that are used tofabricate physical objects directly from CAD data sources. These methods are generally similarto each other in that they add and bond materials in layerwise-fashion to form objects. This isdirectly the opposite of what classical methods such as milling or turning do. Objects areformed in those processes by mechanically removing material. Rapid prototyping is also knownby the names of freeform fabrication (FFF), layered manufacturing, automated fabrication andother variants. Sometimes the names of the specific processes themselves are also usedsynonymously to denote the field as a whole.While additive fabrication seems like a new idea, it isnt. The underpinnings of the technologydate back to at least the eighteenth century. Dr. Joseph Beaman has written a fascinatingaccount of RPs early history. His paper includes information about early patents which shouldbe of continuing interest to system developers today. The thrust for much of this seminal workwas to develop an automated form of representational sculpture, a subject still much underdiscussion, but as yet economically unfulfilled.Rapid prototyping isnt necessarily very rapid and doesnt necessarily have to do withprototypes, either. Speed is relative: The processes can shave weeks to months off a design cycle,but still may require many hours to fabricate a single object. Prototypes for design evaluation areoften made using these processes, but the technology also is beginning to address the directproduction of final useful parts and assemblies, and injection molding and other types of tools.Additive fabrication technologies have been based on just about every form of matter known toman. Liquids that change into solids with application of light (photopolymers) formed the firstgeneration of practical machines (stereolithography). Quick to follow were methods based onbonding powders (selective laser sintering), extrusion of thermoplastics (fused depositionmodeling), stacking of web materials (laminated object manufacturing) and many others. Evengases have been used as a starting point to form small objects.Some idea of the wide variety of approaches that have been utilized can be found on HenriKoukkas Whole RP Family Tree web page. An additional exhaustive resource describingvirtually every early approach taken is provided in a family tree diagram authored by ErkutNegis in 1995. Classification is made according to the materials utilized and their phases. It canbe downloaded here.