3D printing processes

A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing.
Techniques include jetting, extrusion, additive friction stir deposition, powder bed fusion, binder jetting, stereolithography, computed axial lithography, liquid alternative, lamination, directed energy deposition, selective powder deposition, and cryogenic manufacturing.

Types

3D printing processes, are grouped into seven categories by ASTM International in the ISO/ASTM52900-15:

Each process and piece of equipment has advantages and disadvantages associated with it. These usually involve aspects such as speed, costs, versatility with respect to feedstock, geometrical limitations and tolerances, as well as a mechanical and appearance properties of the products such as strength, texture, and color.
The variety of processes and equipment allows for numerous uses by amateurs and professionals alike. Some lend themselves better toward industry use whereas others make 3D printing accessible to the average consumer. Some printers are large enough to fabricate buildings whilst others tend to micro and nanoscale sized objects and in general many different technologies can be exploited to physically produce the designed objects.

History

Inkjet printing was pioneered by Teletype which introduced the electrostatic pull Inktronic teleprinter in 1966. The printer had 40 jets that offered a break-through speed of 120 characters per second.
Continuous inkjets were popular in the 1950–1960's before Drop-On-Demand inkjets were invented in 1972. Continuous three-dimensional inks were wax based and low temperature metal alloys. Printing with these hot-melt inks produced alpha-numeric characters that were solid and raised, but no one recognized them as 3D printing. In 1971, a young engineer, Johannes Gottwald patented a liquid metal recorder that printed large characters in metal for signage, but Teletype Corp ignored the discovery. Braille was printed with wax inks but never commercialized in the 1960s.
R.H. Research researched printing from 1982 -1983 and decided that single-nozzle inkjet was a possible fit. He recruited engineers Al Hock, Tom Peer, Dave Lutz, Jim and Kathy McMahon to join the company, which became Howtek, Inc. The company's Pixelmaster device used Tefzel nozzles, which allowed the inkjet to work at high temperature and support thermoplastic hot-melt inks. The device could handle a frequency range of 1–16,000 drops per second. It featured 32 inkjet single nozzles per printhead, printing 4 colors CMYK. The printhead rotated at 121 rpm and placed uniform drops precisely as subtractive printing. This technology of hot-melt inks printing layers of CMYK was a precursor to a 3D patent by Richard Helinski.
Chuck Hull patented stereolithography in 1986.
In 1993, Helinski's patent was licensed first by Sanders Prototype, Inc., manufacturer of the first desktop rapid prototype printer, the Modelmaker 6 Pro. It used Howtek style inkjets and thermoplastic inks. Models printed with thermoplastic were perfect for investment casting with no ash during burnout. Thermoplastic ink drop printing is accurate and precise enough for jewelers and detail sensitive CAD designers. The Howtek inkjets that were designed to print a page in 4 minutes were employed to print for as long as 4 days straight.

Processes

Several 3D printing processes have been invented since the late 1970s. The printers were originally large, expensive, and highly limited in what they could produce.
A large number of additive processes are now available. The main differences between processes are in the way layers are deposited to create parts and in the materials that are used. Some methods melt or soften the material to produce the layers, for example. selective laser melting or direct metal laser sintering, selective laser sintering, fused deposition modeling, or fused filament fabrication, while others cure liquid materials using different sophisticated technologies, such as stereolithography. With laminated object manufacturing, thin layers are cut to shape and joined. Particle deposition using inkjet technology prints layers of material in the form of individual drops. Each drop of solid ink from hot-melt material actually prints one particle or one object. Color hot-melt inks print individual drops of CMYK on top of each other to produce a single color object with 1–3 layers melted together. Complex 3D models are printed with many overlapping drops fused together into layers as defined by the sliced CAD file. Inkjet technology allows 3D models to be solid or open cell structures as defined by the 3D printer inkjet print configuration. Each method has its own advantages and drawbacks, which is why some companies offer a choice of powder and polymer for the material used to build the object. Others sometimes use standard, off-the-shelf business paper as the build material to produce a durable prototype. The main considerations in choosing a machine are generally speed, costs of the 3D printer, of the printed prototype, choice and cost of the materials, and color capabilities.
Printers that work directly with metals are generally expensive. However less expensive printers can be used to make a mold, which is then used to make metal parts.

Type	Technologies	Materials
Material jetting	Drop-on-demand or continuous particle deposition	Hot-melt materials, dispersed materials
Material extrusion	Fused deposition modeling or fused filament fabrication and fused pellet fabrication or fused particle fabrication	Thermoplastics, eutectic metals, edible materials, rubbers, modeling clay, plasticine
Material extrusion	Robocasting or MIG welding 3D printing or direct ink writing or extrusion based additive manufacturing of metals and ceramics	Metal-binder mixtures such as metal clay, ceramic-binder mixtures, cermet, metal matrix composite, ceramic matrix composite, metal
Material extrusion	Additive friction stir deposition	Metal alloys
Material extrusion	Composite filament fabrication	Nylon or nylon reinforced with carbon, Kevlar or glass fibers
Light polymerized	Stereolithography	Photopolymer
Light polymerized	Digital light processing	Photopolymer
Light polymerized	Continuous liquid interface production	Photopolymer + thermally activated chemistry
Light polymerized	Dynamic Interface Printing	Photopolymer
Powder bed	Powder bed and inkjet head 3D printing	Almost any metal alloy, powdered polymers, Plaster
Powder bed	Electron-beam melting	Almost any metal alloy including titanium alloys
Powder bed	Selective laser melting	Titanium alloys, cobalt-chrome alloys, stainless steel, aluminium
Powder bed	Selective heat sintering	Thermoplastic powder
Powder bed	Selective laser sintering	Thermoplastics, metal powders, ceramic powders
Powder bed	Direct metal laser sintering	Metal alloys
Laminated	Laminated object manufacturing	Paper, metal foil, plastic film
Powder fed	Laser metal deposition or Directed Energy Deposition	Metal alloys
Powder fed	Extreme high-speed laser cladding	Metal alloys
Wire	Electron beam freeform fabrication	Metal alloys
Wire	Wire-arc additive manufacturing	Metal alloys

Jetting

Material jetting

In material jetting a nozzle is drawn across an absorbent surface. The material is either wicked, electrostatically pulled from a larger jet, pressurized to expel material either continuously, or in short bursts as spray or drops.
Nozzles can be single nozzle with one fluid chamber or multi-nozzle with single or multi-fluid chambers, or combinations of these.
The material needs to have low enough viscosity to pass through the nozzle opening. Hot-melt materials can be melted to become liquid. The inks must be thick enough to accumulate vertically.
Continuous inkjet technology began by printing signs and documents on paper, later adapted to print metals. Wax and thermoplastics were the first 3D materials, printed by drop-on-demand inkjets.

Binder jetting

Binder jetting deposits binding adhesive onto layers of powdered material. Also known as inkjet 3D printing, the process spreads powder across a platform. A print head deposits binder in the cross-section of each layer. Modern printers cure the binder at each layer. The resulting part is further cured in an oven to remove most binder. Operators sinter it in a kiln following a material-specific time-temperature curve. Unbound powder supports overhangs during printing. The method enables full-color prototypes and elastomer parts. Strength improves by impregnating voids with wax, thermoset polymer, bronze, or other compatible materials.

Extrusion

Fused filament fabrication, trademarked as fused deposition modeling, extrudes thermoplastic material to build objects layer by layer. As of 2023, FDM was the dominant 3D printing method.
A filament of thermoplastic feeds into an extrusion nozzle. The nozzle head heats the material to its melting point and extrudes it onto a build platform. Stepper or servomotors move the head and control flow along three axes. Computer-aided manufacturing software generates G-code. A microcontroller drives the motors.
Common materials include acrylonitrile butadiene styrene, polycarbonate, polylactic acid, high-density polyethylene, PC/ABS, polyphenylsulfone, and high impact polystyrene. The filament forms from virgin resins.
Open-source projects recycle post-consumer plastic waste into filament using shredders and extruders like recyclebots. PTFE tubing transfers filament due to high-temperature resistance. Variants use pellets or particles instead of filament, known as fused pellet/particle/granular fabrication, aiding the use of recycled materials. Metal wire enables printing via wire arc additive manufacturing, reducing costs. Molten glass deposition creates artistic works. Use of FDM limits complex geometries such as overhangs or stalactite structures. Slicer software adds removable support structures for such features.
S. Scott Crump developed the process in the late 1980s. Stratasys commercialized it in 1990. It evolved from automated polymeric foil hot air welding, hot-melt gluing, and gasket deposition. After patent expiration, open-source RepRap projects fostered community development and DIY variants. Prices fell by two orders of magnitude.