The term 3D printing originally referred to a process employing standard and custom inkjet print heads. The technology used by most so-called 3D printers to date—especially hobbyist and consumer-oriented models—is fused deposition modeling, a special application of plastic extrusion. The term stereolithography was defined by Charles W. Hull as a "system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed"—in a 1984 patent.
AM processes for metal sintering or melting (such as SLS, DMLS, SLM, and EBM) usually went by their own individual names in the 1980s and 1990s. Nearly all metalworking production at the time was by casting, metal fabrication, stamping, and machining; even though plenty of automation was applied to those technologies (such as by robot weldingand CNC), the paradigm of a tool or head moving through a 3D work envelope transforming a mass of raw material into a desired shape layer by layer was the sole domain of processes that removed metal (rather than adding it), such as CNC milling, CNC EDM, and many others. The umbrella term additive manufacturing gained wider currency in thedecade of the 2000s as the various additive processes matured and it became clear that they would soon be displacing metal removal as the sole occupant of the aforementioned paradigm. It was during this decade that the term subtractive manufacturing appeared as a retronym for the large family of machining processes with metal removal as their common theme. However, at the time, the term 3D printing still referred only to the polymer technologies in most minds, and the term AM was likelier to be used in metalworking contexts than among polymer/inkjet/stereolithography enthusiasts.
By the early 2010s, the terms 3D printing and additive manufacturing developed senses in which they were synonymous umbrella terms for all AM technologies. Although this was a departure from their earlier technically narrower senses, it reflects the simple fact that the technologies all share the common theme of sequential-layer material addition/joining throughout a 3D work envelope under automated control. The 2010s were the first decade in which metal parts such as engine brackets and large nuts would be grown (either before or instead of machining) in job production rather than obligately being machined from bar stock or plate. And the term subtractive has not replaced the termmachining, but merely sometimes complements it when people discussing manufacturing technologies at the most general levels of abstraction need a succinct shorthand.
