What is 3D printing?
3D printing is a fabrication technique used to build three-dimensional structures and objects. It falls under additive manufacturing (AM) techniques, as opposed to subtractive manufacturing methods such as CNC milling. With 3D printing, the final object is created by adding layers of material on top of each other, whereas subtractive technologies remove material to “sculpt” an object.
Broadly speaking, a 3D printer fabricates objects by depositing material onto a print bed (also called build platform) following instructions from a special 3D file, which is often in STL format. The material, typically melted thermoplastic for FFF and FDM 3D printers, is deposited layer by layer. Each layer is very thin and quickly solidifies, thus forming a three-dimensional object as layers are added. Most desktop 3D printers use plastic filament spools as consumables.
However, many other 3D printing technologies exist!
Main 3D printing technologies
There are many types of 3D printing technologies currently available commercially or at the early development stage. Each of these additive manufacturing techniques requires a specific type of 3D printing material, from plastic filament (PLA, ABS…) to photosensitive resin and powdered material (metal, plastic, etc).
Every 3D printing technology has its own advantages and limits and can be used for specific applications and use cases.
These are three main categories of 3D printing technologies:
- Extrusion (FFF, FDM, …): A plastic filament is melted and deposited on the build platform of the 3D printer to form the object layer by layer.
- Photopolymerization (SLA, DLP, MSLA, …): A laser or light projector cures liquid, photosensitive resin directly within the 3D printer’s tank.
- Powder (SLS, SLM, DMLS, …): A laser sinters or melts powdered material layer by layer.
Shedding many of the constraints that traditional fabrication techniques present, 3D printers are a great tool for rapid prototyping, one of the most common uses for 3D printing. Advanced, industrial-level 3D printing systems are also used for the direct manufacturing of end products.
The rise of 3D printing is already greatly impacting manufacturing and design processes across many industries.
Extrusion: FDM (Fused Deposition Modeling) and FFF (Fused Filament Fabrication)
FDM (Fused Deposition Modeling) and FFF (Fused Filament Fabrication)
Extrusion (also known as FDM for Fused Deposition Modeling or FFF for Fused Filament Fabrication) is the most common 3D printing technique. Filament– often a thermoplastic such as PLA or ABS– is heated and melted by the 3D printer’s print head and comes out of a thin nozzle. Either the print head moves horizontally in X and Y while the print bed moves vertically in Z, or the print head moves vertically while the print bed moves horizontally.
The 3D printer deposits the melted filament in layers, one after the other, to build the object. Deposited layers are fused together as the melted plastic quickly solidifies.
The precision and quality of the final object depend, among other factors, on the minimum layer thickness of the 3D printer; the thinner the layers, the higher the 3D print resolution.
Compatible materials include a wide range of plastic filaments (spools), mainly PLA filament or ABS filament. FFF 3D printers are also compatible with exotic plastic filaments containing a percentage of metal or wood for example. Most desktop 3D printers feature FFF 3D printing technology.
Extrusion is also possible with materials such as silicone, clay, high-temperature polymers, and more.
Directed Energy Deposition (DED)
Directed Energy Deposition (DED), also known as Direct Energy Deposition, is a quite advanced 3D printing technology used by only a handful of industrial 3D printer manufacturers. We chose to classify it as an “extrusion” technique because, in DED, the printing material is slowly pushed towards a powerful energy source (like a laser or an electron beam) to be directly melted and fused.
A typical DED 3D printer consists of a nozzle mounted on a multi-axis arm (up to 5 axes), which deposits melted material onto a surface, where it solidifies. The process is therefore quite similar to material extrusion, but the nozzle can move in multiple directions and is not fixed to a specific axis. As soon as it is deposited, the material is melted by a laser or electron beam.
Direct energy deposition 3D printing technology can be used with polymers or ceramics but is mostly used with metal powders or wire feedstock. This 3D printing process is commonly used to repair or add additional material to existing components or parts.
Photopolymerization and resin 3D printing: SLA and DLP
How do resin 3D printers work?
Resin 3D printers are based on the photopolymerization process: a laser or light source cures the resin that is stored in the printer’s tank (or vat).
3D printing resins are light-sensitive photopolymers (photo resins) that solidify when exposed to specific light beams. The build tray can either go from top to bottom (“top-down resin 3D printing“) or the other way around while the laser or light cures the resin layer after layer.
Laser stereolithography makes use of a laser to solidify the resin point by point, while light-projector-based printers (DLP, LCD, MSLA, …) are able to solidify entire layers at once.
Resin-based technologies are recommended for 3D printing objects with a high level of detail and requiring a smooth surface finish. Hence, resin 3D printers are often used to make molds for casting, typically in jewelry or dental applications. They generally offer smaller build volumes than FFF printers, but some large resin 3D printers do exist.
What is SLA and how does it work?
Stereolithography, commonly known as SLA, is an additive manufacturing process in which a UV (ultraviolet) light is projected via a laser beam to solidify liquid resin. The resin tank (also called vat) is filled with a photo-sensitive liquid resin (photopolymer resin). The UV laser beam traces the shape of the 3D design in the resin tank and solidifies the curable resin to form the final object, point by point (high accuracy), and layer by layer.
DLP 3D printers (Digital Light Processing)
Digital Light Processing (DLP) is a 3D printing technology in which a digital light projector is the UV light source. The projector’s resolution will determine the 3D printing resolution. DLP 3D printers offer a superior print speed because the light is projected onto an entire layer at once (versus point by point with a laser).
LCD 3D printers (or MSLA, Masked Stereolithography)
MSLA or LCD resin 3D printers use an LCD screen as a photomask– like a stencil– above another light source (LED, UV…). Similarly to DLP 3D printers, MSLA printers are able to solidify entire layers at a time.
SLA vs DLP: resin 3D printing technologies comparison
The main difference between SLA and DLP is that in DLP, the resin is cured layer by layer, as the UV light is emitted by a projector, whereas in SLA, the object is formed dot by dot by the laser.
SLA can be more accurate that DLP but is also a potentially slower 3D printing process. Lasers are also more costly and difficult to maintain versus projectors or LCD screens which can be easily found and at a relatively low price.
Powder bed fusion: SLS, SLM, and EBM
Powder 3D printers use powder materials as consumables (metal powders for example). The main types of powder 3D printing technologies are SLS (Selective Laser Sintering) and SLM (Selective Laser Melting). Powder-based 3D printers are typically used for metal 3D printing in various categories of industrial applications.
SLS 3D printers (Selective Laser Sintering)
With selective laser sintering 3D printing technology, a laser beam is used to sinter powdered material (plastic, ceramic, metal…). The energy of the laser bonds the tiny grains of powdered material together to form a solid structure.
SLS 3D printers have a print bed full of powder material (a bit like a small sandbox). A laser, monitored by the 3D printer software, then traces the pattern of the 3D design to form the final object layer by layer. After each layer is complete, the print bed lowers on the Z-axis, and another layer is built on top of the previous one.
SLM 3D printers (Selective Laser Melting)
Selective laser melting (SLM) is quite similar to SLS. The difference between SLS and SLM is that in SLM, the powdered material is melted and not sintered. The high-power laser used in SLM 3D printers fuses the particles of powder together to form the solid object.
This additive manufacturing process is mainly used for the direct manufacturing of end-use metal parts for industrial applications in the aerospace or medical industries, although office-friendly plastic SLS 3D printers do exist. Dental SLM 3D printers are also becoming more common for the production of metal dental appliances (e.g. crowns and other implants).
EBM additive manufacturing (Electron Beam Melting)
The Electron Beam Melting (EBM) 3D printing process is based on the same principle as the SLM additive manufacturing technology: a powdered material (usually metal or alloys) is solidified into a 3D object by energy, in this case the energy generated by an electron beam. Electron Beam Melting 3D printers build solid objects by melting the powdered material (unlike SLS where the material in sintered).
Other powder 3D printing technologies (DMLS, SLM, SHS, LM, …)
3D printers using powdered materials are designed for industrial applications, such as rapid prototyping or direct manufacturing of parts. In addition to the powder-based 3D printing technologies listed above, you can also find: Laser Sintering (LS), Laser Melting (LM), Selective Heat Sintering (SHS), Direct Metal Laser Sintering (DMLS), or Plaster-based 3D Printing (PP).
The main difference between these advanced manufacturing technologies is the way the powder material is melted. EBM, EBAM, and SLM entirely melt the material while SLS and LS rather fuse grains of powder together. Compatible 3D printing materials for SLS or SLM are Titanium alloys, thermoplastics, ceramic powders, and metals, thus making powder 3D printers a fixture in industries such as Aerospace, where high resistance parts in metal are often required.
Material jetting (MJM, BJ, PJ…)
Material Jetting (Multijet Modeling or MJM)
Material Jetting is a 3D printing technology where inkjet print heads jet melted material on the build platform of the 3D printer, which then cool and solidify to form a 3D object layer by layer. Material jetting is also known as MultiJet Modeling (MJM), Drop On Demand (DOD), or Thermojet/Inkjet printing. Material Jetting 3D printers produce high-quality prints and surface finishes.
Photopolymer Jetting (PolyJet or PJ)
In Photopolymer Jetting 3D printing, the print heads jet a liquid photopolymer material (sensitive to light) onto the print bed. This material is directly cured by a UV lamp attached to the print head to form the solid object. Stratasys namely uses this additive manufacturing technology with their proprietary PolyJet 3D print technology.
Binder Jetting (BJ)
A liquid bonding agent is deposited (jetted) onto a powdered material to bind powder particles together and form the final object. Both Photopolymer Jetting (PJ) and Binder Jetting (BJ) can be categorized in the Material jetting category.
The lamination 3D printing technique uses thin-layered sheets of material (paper or aluminum foil, for example) to produce highly detailed and full-color 3D objects. The sheets are cut following the 3D design of the desired object, often by lasers or a very sharp blade. Layers are then coated with an adhesive and glued together layer by layer, similar to other additive manufacturing techniques.
The precision of the result mainly depends on the sheet’s thickness. Paper is a popular base material as it is affordable and easy to work with.
3D bioprinting is the process of generating spatially-controlled cell patterns using 3D printing, where cell function and viability are preserved within the printed construct. The goal of bioprinting is to fabricate living tissues and functional human organs. With bioprinting, it is already possible to fabricate bones, cartilage, and (almost!) functional 3D printed muscles and organs. That said, today’s 3D bioprinters are not yet ready to 3D print ready-to-use replacement organs or limbs.
One of the world’s first 3D bioprinters was called “Regenovo” and was designed by researchers from Hangzhou Dianzi University in China. This 3D bioprinter has been used to successfully 3D print tissue samples, including functional livers and human ear cartilage.
Find out more about this technology in our guide to 3D bioprinting.