Every 3D printer you've used — desktop FDM machine, resin printer, or six-figure metal system — belongs to one of exactly seven process families. That's not marketing shorthand; it's an engineering standard. In 2009 the American Society for Testing and Materials formed Committee F42 to bring order to a field that had spawned dozens of trademarked process names for what were often the same underlying mechanisms. F42 partnered with ISO's own AM group, and the result — published as ISO/ASTM 52900 — sorts every AM process into seven categories, defined by how a machine actually builds a layer, not by brand name. Here's what each one is, how it works, and where you'd run into it.

Material Extrusion (FDM/FFF)

The category covering the printer on most makers' desks. A nozzle heats and selectively dispenses material — almost always thermoplastic filament — one layer at a time, per ISO/ASTM 52900's definition. Stratasys notes the process runs on PLA and ABS for hobbyists and climbs to PC, ULTEM, and PEKK for aerospace and automotive tooling. Strengths: cost, material familiarity, ease of use. Weaknesses: anisotropic strength (weaker along the Z-axis) and visible layer lines. FilamentFeed covers filament chemistry and technique in depth elsewhere — this is the 30,000-foot view.

Vat Photopolymerization (SLA/DLP/MSLA)

A vat of liquid photopolymer resin is selectively cured, layer by layer, by light. The common flavors differ only in how that light lands: SLA traces each layer with a laser, DLP flashes a whole layer at once with a projector, and MSLA (also called LCD) masks an LED array with an LCD panel, per Formlabs' comparison guide. Materials are photopolymer resins from general-purpose to flame-retardant, biocompatible, and castable formulations. Strengths: resolution and surface finish. Weaknesses: brittleness and mandatory post-processing (washing, curing). Budget LCD units run $200–$1,000; professional systems reach $25,000+ for dental, medical, and casting work. FilamentFeed's SLA vs. MSLA vs. DLP guide covers the granular differences.

Powder Bed Fusion (SLS, DMLS/SLM, EBM)

Thermal energy — a laser or electron beam — selectively fuses regions of a powder bed, one cross-section at a time. For polymers, that's Selective Laser Sintering (SLS), which needs no supports since surrounding powder does the job. For metals, it splits into laser-based (DMLS/SLM) and electron-beam (EBM) variants. Per Xometry's comparison, SLM works a broad range of alloys — aluminum, nickel, cobalt, copper — at finer resolution (20–50 micron layers), while EBM runs in a vacuum at higher temperature and is largely reserved for titanium alloys and superalloys like Inconel 718, making it a mainstay for aerospace turbine parts and orthopedic implants. Weaknesses across the category: metal-build supports, mandatory post-build heat treatment, and six-figure equipment costs.

Binder Jetting

A print head deposits a liquid binding agent onto a powder bed to glue particles together rather than melt them — a room-temperature process, per HP's process comparison. It works with polymers, metals, ceramics, sand, and glass, and needs no support structures since the powder bed supports the part. That speed and flexibility make it popular for sand-casting molds, full-color prototypes, and — after a secondary sintering step — metal parts. The tradeoff is mechanical performance: bonded-not-fused parts are weaker than powder-bed-fusion equivalents, which is why metal binder-jetted parts need the debinding and sintering process FilamentFeed has covered separately to reach full density.

Material Jetting

Distinct from binder jetting despite the similar name: droplets of the actual build material — typically photopolymers or waxes — are jetted from inkjet-style heads and cured with UV light as they land, rather than glued to powder. HP's guide notes it enables genuinely multi-material and multi-color parts in a single build, with high accuracy and minimal waste — a favorite for full-color anatomical models, dental work, and investment-casting patterns. Its weakness is mechanical: parts commonly need dissolvable supports and tend toward brittleness, so it suits prototyping and visual models far better than load-bearing, end-use parts.

Sheet Lamination

The oldest of the seven categories and the least visible to hobbyists. Thin sheets of material — paper, polymer film, or metal foil — are bonded layer by layer, then cut to the part's cross-section, per Xometry's process guide. Laminated Object Manufacturing (LOM) bonds paper or polymer sheets with heat and adhesive, then trims each layer with a laser; Ultrasonic Additive Manufacturing (UAM) instead welds metal foils together with ultrasonic vibration, without melting them, letting it embed wiring or sensors between layers and join dissimilar metals. Xometry pegs UAM metal builds at up to roughly 300 cm³/hr — several times faster than comparable FDM output — but layer interfaces run 10–40% weaker than in-plane strength, and cut edges need machining for tight tolerances.

Directed Energy Deposition (DED)

The category built for repair and hybrid manufacturing more than net-new parts. A focused energy source — usually a laser, sometimes an electron beam or arc — melts metal powder or wire as it's fed into the melt pool, fusing it onto an existing surface. DMG MORI's powder-nozzle systems describe build-up rates as high as roughly 1 kg per hour, with the coaxial nozzle depositing metal — steels, superalloys like Inconel, copper alloys — with pinpoint accuracy directly onto a workpiece. That makes DED the go-to process for restoring worn turbine blades and tool molds instead of scrapping them, and for cladding wear-resistant coatings onto cheaper base metals. Several machine builders now integrate DED heads into CNC mills for hybrid manufacturing — printing near-net shape, then machining to final tolerance in one workspace. The tradeoff is resolution: DED is a bulk-deposition process, so parts almost always need secondary machining.

Why the Map Matters

None of these seven categories is "better" in the abstract — each trades speed, resolution, material range, and cost differently, which is exactly why ASTM built a vocabulary around mechanism rather than marketing name. A "3D printer" claim means something different depending on which of these seven boxes it falls into, and knowing the category tells you immediately what materials, tolerances, and post-processing to expect before you ever read a spec sheet.

Sources