How does a 3D printer build objects layer by layer?

Most 3D printers use a process called additive manufacturing, which builds parts by depositing material instead of cutting it away. In common fused deposition modeling, plastic filament is melted and extruded through a nozzle that moves in precise patterns. After one layer cools, the printer adds the next, gradually creating the finished shape. Other 3D printing methods use resin cured by light or powders fused by lasers. Since the 1980s, 3D printing has been used for prototypes, medical models, custom tools, and increasingly for production parts.