3D Printing: A Technology Overview
Today I wanted to give an overview of the types of 3D printers out there. 3D printing is a term used rather loosely, and it can be confusing to go from news stories on 3D printing masks to 3D printing buildings to 3D printing organs. They are all 3D printing (also known as additive manufacturing), in that the machines build up material to construct a final shape, as opposed to subtractive manufacturing, in which material is removed to reveal the desired form (think of carving a sculpture out of a big block of marble). However, how they work, what materials they print in, and what applications they’re used for can vary quite dramatically.
Though the summary I’ve put together here is certainly far from exhaustive, I’ve tried to cover the main types of 3D printing you’re most likely to hear about or come across. If there’s something crucial you think I missed, or that you’d like to learn more about, let me know at email@example.com!
FFF (or FDM) Printing
FFF stands for Fused Filament Fabrication, but the process is often referred to as FDM, or Fused Deposition Modeling. They both mean the same thing, but Fused Deposition Modeling is a term trademarked by the 3D print manufacturer Stratasys, while FFF is a general term.
In FFF, material is fed into the printer in the form of a long, thin filament. The filament is melted and then extruded through a nozzle, which draws the form out layer by layer.
Gravity is a limitation to keep in mind when designing for FFF. Supports are needed to create parts with steep overhangs, as the parts are usually built from the bottom up, and this impacts print time and quality.
Almost any material can be used with this process. Desktop printers, like the MakerBots and Ultimakers most associated with 3D printing, generally print plastics such as PLA and ABS, but more industrial machines can also print Nylon, PET, TPU, and polycarbonate. FFF machines can also be designed or modified to print materials such as concrete or chocolate. Desktop Metal even has a metal FFF printer that will print a metal “green” (meaning unsintered) part with ceramic supports.These can be sintered in a furnace afterwards to create solid metal final parts.
You’ve probably seen figurings and tchotchkes prited with FFF, but a large-scale example of the technology is the Icon 3D-printed house that was shown at SXSW. And, of course, Styklets are produced with FFF as well!
SLA and DLP
I’ve combined SLA (Stereolithography) and DLP (Digital Light Processing) together because although they are slightly different, at their core they both use some form of light to cure resin into parts. In SLA, one or more lasers move through a bath of liquid resin, tracing out each layer much like an FFF nozzle does and selectively solidifying the material. With DLP, a projector flashes and cures entire layers of the resin at once, allowing the process to move along much faster.
Parts can be printed either bottom up or upside down. Supports are needed to prevent cured areas from floating away in the resin bath, but these supports tend to be much smaller and more delicate than those you see in FFF.
A wide variety of thermoset resins can be used with SLA, including varieties of polyurethane, silicone, and cyanate ester. Thermoset resins undergo a chemical change when curing in the SLA and DLP processes, and so parts cannot be re-melted or recycled like the thermoplastics used in FFF, or SLS (covered next).
An example of DLP printing you can buy today are the Adidas 4D Run shoes, which have 3D printed lattice soles.
SLS and DMLS
SLS, or Selective Laser Sintering, starts with a bed of powdered plastic material, rather than the filament or resin baths of the previously discussed 3D print technologies. As the name implies, in SLS one or more lasers move along the bed of powder, selectively melting material along the way to create solid forms.
One great feature of SLS is that the powdered material works as support material for complex shapes, meaning you don’t have to worry about building additional structures that may damage your design. Your part simply needs to have the excess powder blown or scraped off.
Closely related to SLS is DMLS, or Direct Metal Laser Sintering. The lasers in DMLS machines melt metal powder, rather than plastic, and the parts are sintered on a metal build plate that uses some supports.
SLS can be used with a wide assortment of thermoplastics (plastics which don’t undergo a chemical change when melted and therefore can be re-melted and recycled, unlike the thermoset plastics used in SLA) that are available in powder form. Several varieties of nylon plastic can be printed, such as Nylon 11 and Nylon 12, as well as some TPUs and polypropylenes.
DMLS powders include various stainless steels, cobalt-chrome, titanium, and aluminum. Parts come out fully-dense, and don’t require a secondary sintering process.
One famous example of an SLS product is Nervous System’s Kinematics Dress, which has been shown in several museums, including MOMA. Chanel also has a mascara that features an SLS-printed brush. DMLS, meanwhile, is largely used in the aerospace industry.
Binder Jet and Multi Jet Fusion
Though Multi Jet Fusion (MJF, HP’s 3D print technology) and Binder Jet are fairly different, I’ve decided to discuss them together because in both, a print bar deposits a complete layer of a secondary material (in MJF it’s a fusing agent, while in binder jet it’s a binder or glue) in one sweeping pass. In binder jet, the printer then moves on to the next layer, while in MJF a fusing lamp subsequently applies energy to melt the entire layer at once before moving on to the next.
Binder jet parts are generally more fragile than SLS parts as the particles are glued together, while MJF parts are stronger as the plastic is melted all at once rather than bit by bit. Both methods don’t require additional supports for complex parts, because the powder acts as a support.
For MJF, the materials available are similar to SLS, with multiple Nylons and a TPU material available. For binder jet, common materials are gypsum, sand, and ceramics, and metal powders. In the case of metal prints, the green parts out of the printer will then be sintered in a furnace for the metal particles to fuse together.
SmileDirectClub’s aligners are a great example. Though the clear aligners that actually go in your mouth are not 3D printed, the molds on which those clear aligners are thermoformed are printed using MJF machines.
Bioprinters use cells as their material, rather than plastics or metals. The cells are supported and bound together with a scaffolding “glue.” Though there are several different types of bioprinters, the most common is syringe-based extrusion, which is similar to FFF but uses syringes to deposit organic material rather than nozzles depositing melted plastic.
The cells used in bioprinters can vary, from stem cells to cultivated cells. They print with hydrogel, collagen, or other substrates that can bind the cells together and provide a base to grow on.
In 2019 researchers from the University of Tel Aviv printed a miniature heart, complete with blood vessels.
Though this post definitely didn’t cover everything (and it feels like there are new innovations rolling out every day), I hope it was a useful overview of some of the major differences between types of 3D printing, and that it will provide some context for the next 3D printing headline you come across on the news. If there’s something you think I missed, or that you’d like to learn more about, let me know at firstname.lastname@example.org!
Until next time,