<br> [MAS.865](http://fab.cba.mit.edu/classes/MAS.865/index.html) > [Additive](index.html) # Additive Processes Additive fabrication refers to a class of manufacturing processes, in which a part is built by adding layers of material upon one another. These processes are inherently different from subtractive processes or consolidation processes. The 3D file source is usually sliced into several layers, each layer generating a set of computer controlled instructions. Additive manufacturing invention can be traced back to the 1980’s by Japanese, French and American researchers. The very first [patent](https://patentimages.storage.googleapis.com/5c/a0/27/e49642dab99cf6/US4575330.pdf) of 3D printing was coined in 1984 by Chuck Hull of 3D Systems Corporation. Hull defined the 3D printing process as a system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed. His invention consists of a stereolithography fabrication system, in which layers are added by curing photopolymers with ultraviolet light lasers. Stereolithography is still one very popular 3D printing manufacturing technique, also known as SLA Yet, the technology used by most 3D printers in the 2010’s, especially by hobbyist and consumer-oriented products, is Fused Filament Fabrication (FFF), also known as material extrusion or the proprietary Stratasys denomination’s Fused Deposition Modeling (FDM). FDM was [patented](https://patentimages.storage.googleapis.com/21/01/d3/69165ba25d15e0/US5121329.pdf) in 1989 by S. Scott Crump just before he launched the Stratasys company with his wife, Lisa Crump. - ###[Material Extrusions](MaterialExtrusions.html) <ul> <li> FDM </li> <li> Planar vs Non-Planar Printing </li> <li> Free Form Extrusions </li> <li> Rapid Liquid Printing </li> <li> Multi-Material Printing </li> </ul> - ###[Photoresin Processes](prprocesses.html) <ul> <li> StereoLithogrAphy (SLA) </li> <li> Digital Light Processing (DLP) </li> <li> Continuous Liquid Interface Production (CLIP) </li> <li> High Area Rapid Printing (HARP)</li> <li> Computed Axial Lithography (CAL) </li> <li> Stereolithography Apparatus for Tissue Engineering (SLATE) </li> </ul> - ###[Binder Jetting](Binder.html) - ###[4D Printing](4d.html) # Folding Processes - ###[Folding](folding.html)