3D printing technology has been developing so fast that a new printer model is put on the market almost every week. Still, they fall into a handful of categories that describe how the printer builds up a part. If you’re looking into building or buying a 3D printer, you might want to start by deciding what type of printer you want. There are big differences in cost, speed, part detail, part strength, build volume, and other key criteria.
Fused filament fabrication is also known as fused deposition modelling (FDM), a term trademarked by Stratasys. In this process, a coil of plastic is unwound and fed into an extruder, which melts it like a hot glue gun and moves around the build plate laying down plastic to form a slice of the part. When it’s done one 2D layer, it moves up a small distance and builds another one on top.
At McMaster 3D Printing we currently only use FFF printers, because they are best suited for the engineering parts we usually print. Of course, they’re very useful for other printing applications, and that versatility is the reason FFF printers are the most popular within the maker/hobbyist community.
The parts are strong because the plastic from each layer bonds with the layer underneath it. This makes FFF printers useful for engineering prototypes and parts that move or are subject to loads.
FFF printers can be made in almost any size, which means your parts can be big. Construction companies have developed a 3D printer that can print an entire full size house using concrete instead of plastic, but even desktop 3D printers can make decent size parts.
FFF printers print faster than other technologies. This combined with the large part capability make this type of printer useful for iterating and prototyping, and even small production runs.
Finally, this is the most economical category to invest in. Not only are the printers themselves cheaper, but the plastic filament that feeds them is, too.
Because the part is made layer by layer, you can see the lines that separate them. The surface is not perfectly smooth, but it can be sanded down or painted in many cases. There are also products that coat the surface and help fill in these striations, such as XTC-3D.
Accuracy is average because the flowing plastic can be unpredictable. Small details or features won't come through or won’t be well defined depending on the size of the nozzle.
For a thorough look into FFF printers, read 3D Printing for Beginners' article on the subject.
These printers use a vat of photopolymer resin and a laser that hardens the resin in layers. Starting with a full tank, the print bed is immersed in the liquid. The laser then traces out a cross section of the part, hardening it and fusing it to the bed. The bed moves and the process is repeated over and over until a fully formed part rises from the remaining liquid.
Because the laser is focused on a small point, SLA printers have impressive resolution. Your small parts and fine details are no problem for a well calibrated machine. The industry standard resolution is around 0.1mm, which means you can design your parts to exacting tolerances.
The trade off for greater accuracy is slower speed. The small cross section of the laser doesn’t cover as much ground as FFF printers’ extruder nozzles, making it many times slower.
The parts can be strong but may weaken and become brittle with exposure to sunlight.
SLA printers are usually much smaller than other types of printers. They are better suited to producing small, detailed parts.
The printer itself will be costly, usually upwards of $2,000. The photopolymer resin is also more expensive than plastic filament, usually $100-$150 per litre.
SLS printers use metal or plastic powder and a laser that melts the powder to form successive layers. While similar to the SLA process, SLS printers are usually big industrial units that you wouldn't find on a desktop, since a larger more powerful laser is needed to melt and fuse metal particles together.
Pros include large part volumes, strong steel, stainless steel, and other metal alloy parts, and excellent accuracy. The biggest con is of course the price tag, into the hundreds of thousands of dollars.