David L. Bourell and Joseph J. Beaman, Jr.
Additive manufacturing is a collection of computer-controlled processes that create parts in a layerwise fashion without part-specific tooling. Applications share the common characteristics of part production with complex geometry in relatively small production runs. Historically, applications were limited to production of prototypes and casting inserts, since part mechanical properties and surface finish were inadequate for actual structural applications. More recently, coupled with post processing, additive manufacturing has been used to produce a variety of production tooling, short-run structural parts, customized bio-engineered parts, mass-customized parts, architectural designs, parts for automotive and aerospace applications, archaeological replicas and artwork . The demand for products and services from additive-manufacturing technology has been strong over its 23-year history (1988-2010). The compound annual growth rate of revenues produced by all products and services over this period is an impressive 25.1% . This article describes an historical context of additive manufacturing technology based largely on US patent literature.
Additive Manufacturing Timeline
The figure displays an early chronological timeline of additive manufacturing. This chronology should not be considered complete; it indicates some but not all of the major time events in this field up to about 2002. Two early roots of additive manufacturing are topography and photosculpture. In the late 1960s, “proto-additive manufacturing” technologies
appeared which ushered in actual additive manufacturing process development in the mid-1980s, concurrent with the advent of low-cost, desktop computing.
As early as 1890, Blanther  suggested a layered method for making a mold for topographical relief maps. The method consisted of impressing topographical contour lines on a series of wax plates and cutting these wax plates on these lines. After stacking and smoothing these wax sections, both a positive and negative three-dimensional surface was generated that corresponded to the terrain indicated by the contour lines. After suitable backing of these surfaces, a paper map was then pressed between the positive and negative forms to create a raised relief map.
In 1974, DiMatteo  recognized that stacking techniques could be used to produce surfaces that were particularly difficult to fabricate by standard machining operations. In one embodiment, a milling cutter contoured metallic sheets, and these sheets were then joined in layered fashion by adhesion, bolts or tapered rods. In 1979, Professor Nakagawa of Tokyo University used lamination techniques to produce actual tools such as blanking tools , press forming tools  and injection molding tools . This is a precursor to all “cut-and-stack” additive manufacturing technologies, including laminated object manufacturing.
Photosculpture arose in the 19th century as an attempt to create exact three-dimensional replicas of any object, including human forms . One somewhat successful realization of this technology was developed by François Willème in Paris in 1860. A subject or object was placed in a circular room and simultaneously photographed by 24 cameras placed equally about the circumference of the room. An artisan then carved a 1/24th cylindrical portion of the figure using a silhouette of each photograph, and these were later assembled.
In 1951, Munz  proposed a system that has features of present day stereolithography techniques. He disclosed a system for selectively exposing a transparent photo emulsion in a layerwise fashion where each layer comes from a cross section of a scanned object. Lowering a piston in a cylinder and adding appropriate amounts of photo emulsion and fixing agent created these layers. After exposing and fixing, the resulting solid transparent cylinder contained an image of the object. Subsequently this object could be manually carved or photochemically etched out to create a three-dimensional object.
Early Chronology of Additive Manufacturing Processes based on US Patent Filings
In 1971, Ciraud proposed a powder process that has the features of modern powder-based direct deposition additive manufacturing techniques . This disclosure described a process for the manufacture of objects from a variety of materials that were at least partially able to melt. To produce an object, small particles were applied to a matrix, and a laser, electron beam or plasma beam then heated the particles locally. As a consequence of this heating, the particles adhered to each other to form a continuous layer. Brown, Breinan and Kear at United Technologies Corporation in 1982 patented a similar powder-based technique for building up material in a near net shape fashion to produce rotors for the aerospace industry .
Early Additive Manufacturing Laser-Based Powder Processes of Ciraud  and Housholder 
In 1979, Housholder  presented the earliest description of a powder laser sintering process in a patent. He discussed sequentially depositing planar layers and solidifying a portion of each layer selectively. The solidification can be achieved by using heat and a selected mask or by using a controlled heat scanning process.
Hideo Kodama of Nagoya Municipal Industrial Research Institute was the first to publish an account of a functional photopolymer rapid prototyping system in 1981 . In his method, a solid model was fabricated by building up a part in layers where exposed areas corresponded to a cross-section in the model. He studied three different methods for achieving this using both a mask and an x-y plotter with an optical fiber.
The roots of modern additive manufacturing trace back about 50 years, although preceding topographic and photosculpture methods share much in common with additive manufacturing and are over 100 years old. The prehistory of additive manufacturing provides a rich backdrop for current and future developments. One such articulation of the future was a research roadmap exercise for additive manufacturing organized by one of the authors . In addition to technical targets, educational needs and a national testbed center were highlighted.
 Proceedings of the Solid Freeform Fabrication Symposium, (Mechanical Engineering Department, The University of Texas, Austin, Texas 78712, 1990-2010). Available at http://utwired.engr.utexas.edu/lff/symposium/proceedingsArchive/toc.cfm.
 “Wohlers Report 2011:State of the Industry/Annual Worldwide Progress Report”, T.T. Wohlers, ed., Wohlers Associates, Inc., Fort Collins CO, 2011.
 J.E. Blanther, “Manufacture of Contour Relief Maps ”, US Patent #473,901, 1892.
 P.L. DiMatteo, “Method of Generating and Constructing Three-Dimensional Bodies”,US Patent #3,932,923, 1976.
 T. Nakagawa, et al, “Blanking Tool by Stacked Bainite Steel Plates ”, Press Technique, 1979, pp. 93-101.
 M. Kunieda, T. Nakagawa,“Development of Laminated Drawing Dies by Laser Cutting”, Bull of JSPE ,1984, pp.353-54.
 T. Nakagawa, et al, “Laser Cut Sheet Laminated Forming Dies by Diffusion Bonding”, Proc 25th MTDR Conf ,1985, pp.505-510.
 M. Bogart, “In Art the End Don’t Always Justify Means ”, Smithsonian, 1979, pp.104-110.
 O.J. Munz, “Photo-Glyph Recording”, US Patent #2,775,758, 1956.
 P.A. Ciraud, “Process and Device for the Manufacture of any Objects Desired from any Meltable Material”, FRG Disclosure Publication 2263777, 1972.
 Clyde O. Brown, Edward M. Breinan, Bernard H. Kear, “Method for Fabricating Articles by Sequential Layer Deposition”, US Patent #4,323,756, 1982.
 R.F. Housholder, “Molding Process”, US Patent #4,247,508, 1981.
 H. Kodama, “Automatic Method for Fabricating a Three-Dimensional Plastic Model with Photo Hardening Polymer”, Rev Sci Instrum, 1981, pp.1770-73.
 “Roadmap for Additive Manufacturing: Identifying the Future of Freeform Processing”, D.L. Bourell, M.C. Leu, D.W. Rosen, eds., Univ. of Texas, 2009, 92 pages. Available for free as on-line download at http://wohlersassociates.com/roadmap2009.pdf.