How 3D printers work [Cómo funciona una impresora 3D]

Vía The Economist / Arquitectura Viva.

AT FIRST, 3D printing was known as stereolithography, a process invented in 1986 by Chuck Hull of 3D Systems. Variations of this process are still used. It begins, like all 3D printing, with software that takes a series of digital slices through a computer model of an object. The shape of each slice is used selectively to harden a layer of light-sensitive liquid, usually with ultraviolet light, to form the required shape. After each layer has been made, the build tray lowers by a fraction, another layer of liquid is added and the process is repeated until the object is complete.

Many other approaches have since been developed. Laser-sintering involves zapping layers of powdered plastic or metal with a laser to harden the powder in some places, but not others. Other machines use an electron beam in a similar way. An alternative process melts a metallic powder as it is deposited. This can be used to repair worn parts, such as turbine blades. Some machines operate a bit like 2D inkjet printers, jetting light-sensitive liquid materials to form layers and then hardening them. Some machines can print a dozen different materials in a single pass of the print head.
Technology Quarterly

One of the most popular techniques is fused deposition modelling (FDM), which is akin to a computer-controlled glue gun (pictured below). A heated nozzle extrudes a filament of thermoplastic, which sets as it cools. Multiple heads can extrude different colours. FDM is the mechanism used in many of the small 3D printers used by hobbyists, some of which now cost less than $1,000. More capable 3D printers cost tens of thousands of dollars, and big industrial systems, like the laser-sintering machines capable of printing aerospace parts in titanium, cost as much as $1m.