The term 3D-printing only came into common use recently and is often used inaccurately. The accepted industry term is actually “additive manufacture” which distinguishes all the methods below from subtractive manufacture, such as milling and turning.
Stereolithography (SLA) is the oldest 3D printing system and developed by Chuck W. Hull (co-founder of 3D Systems) in 1986. SLA uses a vat of liquid photo-sensitive “resin” and exposure to the UV laser light which solidifies a profile in the ‘x,y, axes in the thin layer of resin flooding a platform which moves down in fine incremental units in the ‘z’ axis. Parts created this way are very accurate, require minimal post processing and are ideal for use as master patterns for vacuum casting.
PolyJet inkjet technology also works by using photo sensitive materials. These are deposited in the slice profile and immediately set and bonded to previous layers by exposure to UV light. It was developed by Objet Geometries (now Stratasys) in early 2000.
The ‘extrusion’ process (FDM – Fused Deposition Modelling) uses filaments of any extrudable material (such as wax, Polycarbonate, PLA, ABS, clay, chocolate) which is deposited as a softened stream through a nozzle onto a base. Either the base moves down or the nozzle moves upwards, while also building support structures for the overhanging parts of the model. The support material is either dissolvable or easy to break off. This system is used to create functional parts of any geometry and was developed by S. Scott Crump (Stratasys co-founder) in the late 1980s and commercialized in 1990. Most DIY 3D Printers use the FDM technology.
For the ‘binding’ process powdered grains are spread thinly by a roller over the movable base plate in the “build chamber” over which a mechanical arm rapidly moves to either fuse, glue or melt one layer of grains together in the x, y slice’s profile. Another thin layer is then rolled over the top of that (the ‘z’ axis) and so on and upwards to create the model. The excess un-bonded powder is vacuumed off and the model carefully removed for further cleaning and the addition of extra bonding material to stabilise the piece to make it more robust.
‘3D Printing’ uses an ‘inkjet printing’ process to deposit a liquid binder and is a reasonably accurate term to describe this system which was developed at the Massachusetts Institute of Technology (MIT) in the late 1980s and licensed by several companies. With this system full colour, multi-colour robust objects can be created.
Another ‘Wax Printing’ process is similar, with wax jetted into a profile in layers to build objects which can then be used for investment casting by coating the wax with investment plaster, burning out the wax and casting in metal.
The ‘deposition’ process is closer to an inkjet printer technique as a print head moves across the build chamber depositing the material in each of the model’s x,y profile slices. It is the base plate in the build chamber that lowers incrementally to create the subsequent z axis layers to build up the object.
The ‘profiling’ process uses sheets of paper, plastic inserted one at a time into the build chamber to be cut and bonded to the previous layer to build the object which is broken out of the unbonded or sliced waste material. As paper printers produce the least expensive models they are used to prototype large forms.
The ‘sintering’ process (SLS – selective Laser sintering) has the greater range of materials as many can be granulated and laser sintered together to also fuse to the previous layer. This process which uses high power lasers was developed and patented by Dr. Carl Deckard at the University of Texas in the mid-1980s. The most common and useful material used is nylon powder and apparently adding ground glass gives even greater strength for performance and durability. Other materials include ceramic, glass powder and metals (direct metal laser sintering) including steel, titanium, silver and gold, These developments are very exciting for designer makers but as yet hard to justify price-wise.
The process of ‘Electron Beam Melting’ (EBM) melts metal powder in a high vacuum and is distinguished from metal sintering techniques, by producing parts that are extremely strong because they are fully dense and free of any voids. It was developed by Arcam AB.