Editor's Note: This is the third of a series of posts excerpted from Jason Griffey's Library Technology Report "3D Printers for Libraries."
The substrate for FDM printers are almost exclusively some form of thermoplastic that is delivered in an extruded wire-like form on a spool. It is usually called “filament” in the generic. The two common diameters for use in FDM printing are 1.75mm and 3mm, and a specific diameter is called for by the print head being used for the printer in question. A printer that uses 1.75mm diameter filament won’t be able to use 3mm without retrofitting the hardware for the difference, and vice versa. Slightly more common, the 1.75mm diameter is used by Makerbot Industries, the most popular manufacturer of FDM printers.
In later postss, when I write on the different printer types and manufacturers, I’ll note what type of filament they are capable of printing, because that turns out to be a major limitation and purchasing decision factor.
The original fused deposition printers almost exclusively used ABS (Acrylonitrile butadiene styrene) as their substrate for printing. ABS is nearly ideal from a material property point of view for rapid prototyping in plastic, as it’s strong, slightly flexible plastic, which extrudes cleanly at between 220° and 240° celsius. ABS is the type of plastic used in Lego bricks, and is one of the most commonly used industrial/commercial plastics.
For FDM printing, ABS requires a heated print bed to ease the thermal shock for printing. Heating the print build plate aids the plastic in both adhering to the plate for stability, and in preventing cooling too quickly, which leads to thermal deformation, or a sort of curling separation. ABS is sensitive enough in this arena that many people who print ABS learned early on that enclosing the printer was a way to increase the stability of prints because it regulated the temperature around the printer. I soon discovered in my printing experiments with an early Makerbot printer (Replicator 1) that even a strong breeze blowing in the wrong place (across the print bed) could wreak havoc. Higher end printers will have an enclosed print area, while less expensive ones don’t.One of the advantages of ABS is that it dissolves in acetone. Acetone dissolves ABS completely, but used sparingly it can act as a glue to fuse two ABS printed pieces together permanently. Acetone is also used to make a “glue” for print beds, to help in making the print bed sticky for the initial printed layers. Acetone vapor is heavier than air, and some people have used this to build acetone vapor baths that act to smooth the edges of layers of an FDM ABS print.ABS has caught some bad press recently, as the potential effects of off-gassing of the heated plastic and microparticulate effects are studied. As a petroleum based plastic, ABS does produce a distinctive stink when printing. Fumes have been reported to cause headaches, and studies link ABS fumes to olfactory loss; one study that found ABS printing released high volumes of ultrafine particles that could be dangerous when inhaled. These are preliminary studies. Most haven’t been repeated, and the science is still rough on the health effects here. But if you need to print with ABS, it may be a good idea to take venting into account.
PLA (Polylactic acid) is the second most popular printing substrate for FDM printers. A bioplastic, PLA is made from corn, beets, or potatoes. It is compostable in commercial compost facilities (the heat and bacterial action isn’t high enough in home composting to break it down). It melts at a much lower temperature than ABS (150-160°C), but is typically extruded at a higher temperature, anywhere from 180-220°C depending on the PLA itself. Because of it’s lower temperature, it’s not suitable for uses that involve high temperatures and direct sunlight. PLA is also very different than ABS in term of fragility. Far more crystaline, PLA shatters or cracks more readily than ABS, whih instead will deform under pressure.
However, Makerbot and other major manufacturers are now starting to go with PLA as their primary printing plastic. PLA doesn’t require a heated bed for adhesion or thermal curling reasons, which lowers the price of the printers that use it. As well, it’s far more thermally stable during printing than ABS, and much less likely to warp or curl due to errant breezes. It is possible to reliably print PLA without needing to enclose your printer, which can be a huge benefit in many circumstances.
The other significant advantage is that PLA is far more pleasant when printing than ABS. Because it is a bioplastic, when heated it smells like waffles or syrup, and not like an oil spill. It also hasn’t been linked to any types of medical issues from being heated, although the study of all these plastics is young when it comes to 3d printing specifically.
One of the other advantages of PLA is that it’s available in dozens and dozens of colors, including both opaque and partially transparent, as well as a couple of colors of glow-in-the-dark. It also is available in a flexible form, which can produce prints that are almost rubber-like in consistency.
If you are printing in a library setting, I would suggest focusing on PLA. Between the reliability and the ease of working with it, it’s a far better choice than ABS for printing in a public space.
Once you get beyond ABS and PLA, you’re in the realm of specialized plastics that are used for specific properties rather than for general 3D printing. More of these appear every day, practically, but generally they fall into a couple of categories: dissolvable support material, specific material qualities that are needed, or non-plastic powder suspended in a thermoplastic resin. I’ll describe the most common of these below.
High Impact Polystyrene or HIPS is a plastic filament used for dissolvable support structures in FDM printers. It extrudes at around 235°C and has a set of material properties that make it similar to ABS. The main difference is that HIPS is completely soluble in a liquid hydrocarbon called limonene. This means that if you have an FDM printer with more than one print head, you can extrude ABS from one and HIPS as a support material from the other, and sit the final printed model in a bath of Limonene. The HIPS will dissolve away, leaving only the ABS behind, thus allowing for nearly impossible geometries to be printed, including moving ball bearings and more.
There are at least 4 types of nylon currently available for use in FDM printers: Nylon 618, Nylon 645, Nylon 680 and Nylon 910. These vary in their color from medium transparency to fully opaque white, and all are extraordinarily strong as compared to other FDM substrates. They are also very resistant to solvents and such, although they are dyeable with acid-based dyes for coloring.
Nylon as an FDM printing material is more expensive than PLA or ABS. The major reason for using them would be for specific material properties (resistance to specific chemicals) or due to the need for FDA approved materials, as both Nylon 680 and 910 are undergoing FDA approval for use, something rare in the 3D printer world.
T-Glase is a brand name for a filament composed of Polyethylene terephthalate. Of all 3D printer filaments, it is the most glass-like. Nearly transparent, especially at small sizes, it could easily be mistaken for glass. At larger sizes it is still very light-transmissive, if not fully transparent. T-Glase prints at around 221°C, on a heated bed, but is very stable and resistant to curling.
LayBrick & LayWood
Another type of printing material for FDM printers, these fall squarely in the experimental realm. They are made by a single manufacturer, and are both a sort of hybrid filament, with a powdered material being supported inside a resin. In the case of LayWood, fine wood particles are suspended in a thermoplastic resin, and in the case of LayBrick, it would be very finely crushed chalk and other minerals suspended in the resin.
Both LayBrick and LayWood have the interesting property of variability in appearance depending on the temperature at which they are printed. LayBrick can range from a very smooth, almost ceramic feel, to very rough sandstone, just by increasing the heat of extrusion. For very smooth, you print at a low temperature (165°C to 190°C) and then going up from their to around 210°C will render the printed part more and more rough. For LayWood, the difference is in the appearance of the final product. By increasing the temperature, you get darker and darker wood grain from the output, so you can actually vary the look from light to dark wood (or, if you have a printer that supports variable temperatures during a single print, you can get different colors in a single print by varying the temperature).
One of the risks, however, with both of these is that the filament isn’t uniform in construction, which means that it’s possible to clog your extruder if the nozzle opening is smaller than the particulate in the filament itself. FDM printers nozzle openings range from .35 to .5mm, and on the lower end of that, especially with the LayWood (organic particles are harder to ensure regular sizes than inorganic particulate) you risk clogging a nozzle. I know 3D printers that have clogged even at .4mm nozzle using LayWood. For printing these sorts of filaments, the larger the nozzle the better.
Still very experimental, polypropylene (PP) offers the possibility of food-grade 3D prints. Polypropylene should work with any FDM printer, at an extrusion temperature of 201°C and a heated print bed set to 90°C. It looks like PP is only really available in black.
Challenges with Fused Deposition Modeling
Most of the issues with FDM printing are related to the fact that it’s a very mechanical process, and tuning the printer is key. The most sensitive aspect of the process is the relationship between the extruder and the build plate. Because the printhead has to extrude an even layer of plastic onto the build plate, it’s necessary that the build plate be perfectly flat relative to the nozzle. If there is any warp or uneven-ness, you’ll get uneven attachment to the plate or other forms of print failure. This is the most common issue with FDM printing, especially with new operators. The first question to ask if a print fails is: “Is my build plate level/”
And prints will fail. FDM printing is a complicated mechanical process, and while you can tune a FDM printer to be very reliable, at some point you will have a failure and will come back to a print that looks like someone poured plastic spaghetti on your build plate. This is normal. Recalibrate, re-level, and try again.