Additive manufacturing is a method of making 3D objects by building up material, layer upon layer, using a digital design. And, the number of technologies customized and created using additive manufacturing processes is growing each year. But did you know that many of the foundational techniques for additive manufacturing were discovered and patented in the 1980s? The National Science Foundation offers a brief history.

Stereolithography: was invented by Charles Hull, the founder of 3D Systems, Inc. This process, sometimes called vat photopolymerization, begins with a vat filled with a special resin. Following a digital design, a laser targets an area just above a platform within the vat, causing the liquid resin there to selectively harden. Then, the platform moves down slightly, and the laser activates the next layer of liquid resin, linking the molecules together in a process called polymerization to form a solid object.

Selective laser sintering: was invented by a University of Texas at Austin graduate student, Carl Deckard, and his advisor, Joseph Beaman. This technique uses a computer-controlled laser to selectively "sinter," or fuse, cross-sections of powder into a solid. The energy from the laser heats the powder just enough to join the pieces together. After one layer is sintered, the next layer of powder is applied and sintered according to the design.

Sheet lamination: also known as laminated object manufacturing, was invented by Michael Feygin, the founder of Helisys, Inc., formerly Hydronetics, Inc. In this process, a laser cuts a thin sheet of paper, plastic, or metal into the desired shape, and then another layer is bonded on top and also cut. By repeating these steps, objects with intricate, complicated shapes can be quickly formed at low cost.

Material extrusion, or fused deposition modeling: was invented by S. Scott Crump, founder of Stratasys Ltd. The process pushes liquid plastic or metal out through a nozzle, right along the path on the digital map. The molten material quickly cools and hardens, and a new layer can then be added on top.

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