Several 3D printing processes have been invented since the late 1970s. 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 (SLM) or
direct metal laser sintering (DMLS),
selective laser sintering (SLS),
fused deposition modeling (FDM), or fused filament fabrication (FFF), while others cure liquid materials using different sophisticated technologies, such as
stereolithography (SLA). With
laminated object manufacturing (LOM), thin layers are cut to shape and joined (e.g., paper, polymer, metal).
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.
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, Also known as inkjet 3D printing, the process spreads powder (ceramic, metal, or plastic-based, including plaster and resins) across a platform. A print head deposits binder in the cross-section of each layer. Modern printers cure (solidify) 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 (FFF), trademarked as fused deposition modeling (FDM), 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 (ABS),
polycarbonate (PC),
polylactic acid (PLA),
high-density polyethylene (HDPE), PC/ABS,
polyphenylsulfone (PPSU), and
high impact polystyrene (HIPS). The filament forms from virgin
resins. ) being printed using FDM on a RepRapPro Fisher printer. 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 (FPF/FGF), aiding the use of recycled materials. Metal wire enables printing via wire arc additive manufacturing (WAAM), 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. AFSD offers a number of advantages over other metal additive manufacturing processes, including high material utilization, low energy consumption, and the ability to print metal alloys incompatible with melt-based processes.
Powder bed fusion Powder bed fusion (PBF) selectively fuses material in a granular bed. The process fuses layer parts, raises the working area, adds granules, and repeats until completion. Unfused powder supports overhangs and thin walls, reducing auxiliary supports. PBF includes
direct metal laser sintering (DMLS),
selective laser sintering (SLS),
selective laser melting (SLM),
multi-jet fusion (MJF), and
electron beam melting (EBM). These methods handle diverse materials and enable complex geometries.
Selective laser sintering Selective laser sintering (SLS) uses polymers and metals (e.g., PA, PA-GF, PEEK,
alumide, carbonmide,
elastomers) and
direct metal laser sintering (DMLS).
Deckard and Joseph Beaman developed and patented it in the mid-1980s under
DARPA sponsorship. R. F. Housholder patented a similar, uncommercialized process in 1979.
Selective laser melting Selective laser melting (SLM) does not use sintering for the fusion of powder granules but melts the powder using a high-energy laser to create fully dense materials in a layer-wise method that has mechanical properties similar to those of conventional manufactured metals. File:FZU_3Dprinting_1.jpg|Selective laser melting in
TRUMPF TruPrint 1000 - view of the printing chamber with print in progress. File:FZU_3Dprinting_2.jpg|Print in progress File:FZU_3Dprinting_3.jpg|Print finished File:FZU_3Dprinting_4.jpg|Print finished (excess powder cleaned)
Electron beam melting Electron beam melting (EBM) melts metal powder (e.g., titanium alloys) layer by layer with an
electron beam in high
vacuum, producing void-free parts.
Multi-jet fusion Multi-jet fusion (MJF) combines fusing and detailing agents with an inkjet array that it heats to solidify layers without lasers. Binder jetting spreads powder (plaster or resins) and prints binder via inkjet. Selective heat sintering applies heat with a thermal printhead to thermoplastic powder, offering a cheaper, scalable alternative. Another 3D printing approach is the selective fusing of materials in a granular bed. The build platform moves incrementally. Excess liquid resin drains after completion. Objet PolyJet systems spray photopolymer in ultra-thin layers (16–30 μm). UV light cures each layer immediately, enabling instant handling without a later curing step. Gel-like supports are removed by hand or water jetting. The method suits elastomers and ophthalmic lenses.
Multiphoton polymerization uses focused lasers to cure gel only at focal points due to nonlinear photoexcitation. Excess gel washes away. This enables features under 100 nm and complex moving structures. Mask-image-projection stereolithography slices models into planes, converts slices to masks, and projects them onto resin to cure layers. Some systems support multiple materials.
Continuous liquid interface production (CLIP) uses an oxygen-permeable window below the resin pool to create a persistent liquid "dead zone." This enables continuous extraction of the object, reducing times from hours to minutes. Dynamic Interface Printing (DIP) submerges a hollow print head with a transparent window into prepolymer. Visible light cures at the air-liquid
meniscus. Air pressure and acoustic modulation control the interface for precision and material flow. Preceramic polymers enable ceramic printing (e.g.,
silicon carbide) via photopolymerization. Powder-fed directed-energy deposition melts supplied metal powder with a laser, a localized analog of selective laser sintering.
Computed axial lithography Computed axial lithography reverses the principle of
computed tomography (CT) to create prints in photo-curable resin. It was developed by a collaboration between the
University of California, Berkeley with
Lawrence Livermore National Laboratory. It creates objects using a series of 2D images projected onto a cylinder of resin. The process was created by
Adrian Bowyer and extended by German company RepRap. Programmable tooling involves creating a temporary mold, which is then filled via a conventional
injection molding process and then immediately dissolved.
Lamination In some printers, paper can be used as the build material, lowering costs. These printers that cut cross-sections out of special adhesive
coated paper using a
carbon dioxide laser and laminates them. Alternatively, ordinary sheets of office paper can be cut by a
tungsten carbide blade, followed by selective deposition of adhesive and pressure to bond layers. Other printers print laminated objects using plastic and metal sheets.
Ultrasonic consolidation (UC) or
ultrasonic additive manufacturing (UAM) is a low temperature additive technique for metals.
Directed energy deposition (DED) Powder-fed directed-energy deposition A high-power laser melts metal powder supplied to the focus of the laser beam. The laser beam typically travels through the center of the deposition head and is lens-focused to a small spot. The build occurs on an
X-Y table which is driven by a tool path created from a digital model. The deposition head is moved vertically as each layer is completed. Some systems make use of 5-axis or 6-axis systems (
i.e. articulated arms) capable of delivering material on the substrate (a printing bed, or a pre-existing part) with few to no spatial access restrictions. Metal powder is delivered and distributed around the head or can be split by an internal manifold and delivered through nozzles arranged around the deposition head. A hermetically sealed chamber filled with inert gas or a local inert shroud gas (sometimes combined) are often used to shield the melt pool from atmospheric oxygen, to limit
oxidation and better control material properties. The powder-fed directed-energy process is similar to
selective laser sintering, but the metal powder is projected only where material is to be added to the part at that moment. The laser heats and creates a "melt pool" on the substrate, in which the new powder is injected quasi-simultaneously. The process supports materials including titanium, stainless steel, aluminum, tungsten, and other specialty materials as well as composites and functionally graded material. The process can build new metal parts, but can also add material to existing parts, supporting coatings, repair, and hybrid manufacturing applications.
LENS (Laser Engineered Net Shaping), is one example.
Metal wire processes Laser-based wire-feed systems, such as
laser metal deposition-wire (LMD-w), feed wire through a nozzle that is melted by a laser using inert gas shielding in either an open environment (gas surrounding the laser), or in a sealed chamber.
Electron beam freeform fabrication uses an electron beam heat source inside a vacuum chamber. It is also possible to use conventional
gas metal arc welding attached to a 3D stage to 3-D print metals such as steel, bronze and aluminum. Low-cost open source
RepRap-style 3-D printers have been outfitted with
Arduino-based
sensors and demonstrated reasonable metallurgical properties from conventional welding wire as feedstock.
Selective powder deposition In selective powder deposition (SPD), build and support powders are selectively deposited into a crucible, such that the build powder takes the shape of the desired object and support powder fills the rest of the crucible. Then an infill material is applied, such that it comes in contact with the build powder. Then the crucible is fired in a kiln between the melting point of the infill and the powders. When the infill melts, it soaks the build powder. But it doesn't soak the support powder, because the support powder is chosen to not be wettable by the infill. If at the firing temperature, the atoms of the infill material and the build powder are mutually defusable, such as with copper powder and zinc infill, then the resulting material is a uniform mixture of those atoms, in this case, bronze. But if the atoms are not mutually defusable, such as tungsten and copper at 1100°C, then the resulting material is a composite. To prevent shape distortion, the firing temperature must be below the
solidus temperature of the resulting alloy.
Cryogenic Cryogenic 3D printing is a collection of techniques that forms solid structures by freezing liquid materials as they are deposited. As each liquid layer is applied, it is cooled by the low temperature of the previous layer and printing environment which solidifies it. Cryogenic techniques requires a controlled printing environment. The ambient temperature must be below the material's freezing point to ensure the structure remains solid during manufacturing and the humidity must remain low to prevent frost formation between layers. Materials typically include water and water-based solutions, such as
brine,
slurry, and
hydrogels. Cryogenic techniques include rapid freezing prototype (RFP), and freeze-form extrusion fabrication (FEF). ==Printers==