A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing. 3D printing is also known as additive manufacturing, because the numerous available 3D printing process tend to be additive in nature, with a few key differences in the technologies and the materials used in this process.
Some of the different types of physical transformations which are used in 3D printing include melt extrusion, light polymerization, continuous liquid interface production and sintering.
Types of 3D printing processes
There are many different 3D printing processes, that can be grouped into seven categories:
Vat photopolymerization
Material jetting
Binder jetting
Powder bed fusion
Material extrusion
Directed energy deposition
Sheet lamination
Each process and piece of equipment has pros and cons associated with it. These usually involve aspects such as speed, costs, versatility with respect to feedstock material, 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 (in this case the term Additive Manufacturing is preferred) 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.
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 (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.
Material jetting
A nozzle with liquid material can be drawn over an absorbent surface to wick out material, electrostatically pulled from a larger jet orifice, pressurized to stream material or fluid pressure surged to expel short burst of fluid in the form of spray or individual drops. A fountain pen with nib tip is an example of wicking material. A hose is an example of streaming fluid. A pump short burst is an example of drop or spray ejection.
Nozzles can be made of any material and can be single nozzle with one fluid chamber or multi-nozzle with single or multi-fluid chambers. Today's inkjet printer products can be any variation of these inkjet styles.
Ink material for inkjets only needs to be a low enough viscosity to allow the fluid to pass through the nozzle opening. Materials can be melted to be liquid. These are called Hot-melt inks. In all cases the inkjet inks must be three-dimensional on the printed surface to produce a Z height component for a 3D object.