The making of parts and products using a computer-driven, additive process, one layer at a time. 3D printing builds parts out of plastic, metal and other materials directly from CAD drawings that have been cross sectioned into thousands of layers. Sizes of printed objects run the gamut from approximately 16 to 4,000 cubic inches; however, Shanghai-based WinSun built huge machines to print house walls and trusses. See 3D printing materials.Used for making prototypes as well as final products, 3D printing evolved from the "rapid prototyping" industry, pioneered by Chuck Hull of 3D Systems in the mid-1980s. It provides a faster and less costly alternative to machining (cutting, turning, grinding and drilling solid materials).Concept, Prototype and Final ProductCapable of making a part from scratch in hours, or just minutes for small objects, 3D printing is used to create models to determine if a design meets customer expectations. 3D printing can more easily create prototypes of parts to test their form, fit and function with the rest of an assembly.Tooling molds and dies, as well as patterns for castings, are 3D printed. Either the actual mold or the model to make the mold can be produced more quickly and economically than with conventional methods.Laser sintering and electron beam melting technologies turned "rapid prototyping" into "rapid manufacturing," in which short runs of actual finished parts are made. These techniques have created breakthroughs in the medical industry, including products customized for humans such as hearing aids, dental crowns and medical implants. In 2019, Israeli scientists at Tel Aviv University 3D printed a heart with human tissue. Although only the size of a rabbit's heart, human hearts suitable for transplanting are hopeful in the years to come.One Layer at a TimeAll 3D printers are "additive fabrication" machines that build one layer after the other. The layers can be as thin as 1/1,000th of an inch or much thicker. The building material can be a liquid, powder or sheet material that is cured by heat, UV light, a chemical reaction or other method. The thickness exception is the cement mixture used by WinSun to print house walls in China. Following are the more common methods used to print 3D objects. See 3D printer, personal 3D printer, nanofactory and STL.