There are several ways to 3D print. All these technologies are additive, differing mainly in the way layers are build to create an object.
Some methods use melting or softening material to extrude layers. Others cure a photo-reactive resin with a UV laser (or another similar power source) layer by layer.
To be more precise: since 2010, the American Society for Testing and Materials (ASTM) group “ASTM F42 – Additive Manufacturing”, developed a set of standards that classify the Additive Manufacturing processes into 7 categories according to Standard Terminology for Additive Manufacturing Technologies. These seven processes are:
Below you’ll find a short explanation of all of seven processes for 3D printing:
A 3D printer based on the Vat Photopolymerisation method has a container filled with photopolymer resin which is then hardened with a UV light source.
Vat photopolymerisation schematics. Image source: lboro.ac.uk
The most commonly used technology in this processes is Stereolithography (SLA). This technology employs a vat of liquid ultraviolet curable photopolymer resin and an ultraviolet laser to build the object’s layers one at a time. For each layer, the laser beam traces a cross-section of the part pattern on the surface of the liquid resin. Exposure to the ultraviolet laser light cures and solidifies the pattern traced on the resin and joins it to the layer below.
After the pattern has been traced, the SLA’s elevator platform descends by a distance equal to the thickness of a single layer, typically 0.05 mm to 0.15 mm (0.002″ to 0.006″). Then, a resin-filled blade sweeps across the cross section of the part, re-coating it with fresh material. On this new liquid surface, the subsequent layer pattern is traced, joining the previous layer. The complete three dimensional object is formed by this project. Stereolithography requires the use of supporting structures which serve to attach the part to the elevator platform and to hold the object because it floats in the basin filled with liquid resin. These are removed manually after the object is finished.
This technique was invented in 1986 by Charles Hull, who also at the time founded the company, 3D Systems.
DLP or Digital Light Processing refers to a method of printing that makes use of light and photosensitive polymers. While it is very similar to stereolithography, the key difference is the light-source. DLP utilises traditional light-sources like arc lamps.
In most forms of DLP, each layer of the desired structure is projected onto a vat of liquid resin that is then solidified layer by layer as the buildplate moves up or down. As the process does each layer successively, it is quicker than most forms of 3D printing.
The Envision Tec Ultra, MiiCraft High Resolution 3D printer, and Lunavast XG2 are examples of DLP printers. Companies that specialise in DLP technology include ONO and Carbon (who invented a subtype of DLP called CLIP).
Other technologies using Vat Photopolymerisation are the new ultrafast Continuous Liquid Interface Productionor CLIP and marginally used older Film Transfer Imaging and Solid Ground Curing.
In this process, material is applied in droplets through a small diameter nozzle, similar to the way a common inkjet paper printer works, but it is applied layer-by-layer to a build platform making a 3D object and then hardened by UV light.
With binder jetting two materials are used: powder base material and a liquid binder. In the build chamber, powder is spread in equal layers and binder is applied through jet nozzles that “glue” the powder particles in the shape of a programmed 3D object. The finished object is “glued together” by binder remains in the container with the powder base material. After the print is finished, the remaining powder is cleaned off and used for 3D printing the next object. This technology was first developed at the Massachusetts Institute of Technology in 1993 and in 1995 Z Corporation obtained an exclusive license.
The following video shows a high-end binder jetting based 3D printer, the ExOne M-Flex. This 3D printer uses metal powder and curing after the binding material is applied.
The most commonly used technology in this process is Fused Deposition Modeling (FDM).
The FDM technology works using a plastic filament or metal wire which is unwound from a coil and supplying material to an extrusion nozzle which can turn the flow on and off. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a computer-aided manufacturing (CAM) software package. The object is produced by extruding melted material to form layers as the material hardens immediately after extrusion from the nozzle. This technology is most widely used with two plastic filament material types: ABS (Acrylonitrile Butadiene Styrene) and PLA (Polylactic acid). Though many other materials are available ranging in properties from wood fill to flexible and even conductive materials.
FDM was invented by Scott Crump in the late 80’s. After patenting this technology he started the company Stratasys in 1988. The term Fused Deposition Modeling and its abbreviation to FDM are trademarked by Stratasys Inc.
The exactly equivalent term, Fused Filament Fabrication (FFF), was coined by the members of the RepRap project to give a phrase that would be legally unconstrained in its use.
There are many different FFF 3D Printer configurations. The most popular arrangements are:
Looking for an overview of all FFF 3D printers? Use our tool and compare 3D Printers.
Pioneer of Contour Crafting, Dr. Behrokh Khoshnevis of USC, developed a method which leverages the power of additive manufacturing to build homes. Contour crafting essentially uses a robotic device to automate the construction of large structures such as homes. This device prints walls layer-by-layer by extruding concrete. The walls are smoothed as they are built, thanks to a robotic trowel.
The most commonly used technology in this processes is Selective Laser Sintering (SLS).
SLS uses a high power laser to fuse small particles of plastic, ceramic or glass powders into a mass that has the desired three dimensional shape. The laser selectively fuses the powdered material by scanning the cross-sections (or layers) generated by the 3D modeling program on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness. Then a new layer of material is applied on top and the process is repeated until the object is completed.
DMLS is basically the same as SLS, but uses metal instead of plastic, ceramic or glass.
All untouched powder remains as it is and becomes a support structure for the object. Therefore there is no need for any support structure which is an advantage over SLS and SLA. All unused powder can be used for the next print. SLS was developed and patented by Dr. Carl Deckard at the University of Texas in the mid-1980s, under sponsorship of DARPA.
Sheet lamination involves material in sheets which is bound together with external force. Sheets can be metal, paper or a form of polymer. Metal sheets are welded together by ultrasonic welding in layers and then CNC milled into a proper shape. Paper sheets can be used also, but they are glued by adhesive glue and cut in shape by precise blades. A leading company in this field is Mcor Technologies.
Here is a video with a metal sheet 3D printer by Fabrisonic that uses additive manufacturing paired with CNC milling:
… and here is an overview of Mcor 3D printers that use standard A4 paper sheets:
This process is mostly used in the high-tech metal industry and in rapid manufacturing applications. The 3D printing apparatus is usually attached to a multi-axis robotic arm and consists of a nozzle that deposits metal powder or wire on a surface and an energy source (laser, electron beam or plasma arc) that melts it, forming a solid object.
Sciaky is a major tech company in this area and here is their video presentation showing electron beam additive manufacturing:
Six types of materials can be used in additive manufacturing: polymers, metals, concrete, ceramics, paper and certain edibles (e.g. chocolate). Materials are often produced in wire feedstock (filament), powder form or liquid resin. All seven previously described 3D printing techniques, cover the use of these materials, although polymers are most commonly used and some additive techniques lend themselves towards the use of certain materials over others. Read more about which materials you can use for 3D printing on our materials page.