3D printing engineering plastics

The Plastics of 3D Printing

By Jason Griffey |

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.

ABS
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
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.

Other Filament
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.

HIPS
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.

Nylon
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
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.

Polypropylene
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.

3D Printing Materials Guide: Plastics

Published on June 8, 2020 by Alexandrea P.

A plastic is a material made of synthetic or semi-synthetic compounds that has the property of being malleable (capable of changing its shape). Most plastics on the market are completely synthetic (most commonly derived from petrochemicals). However, given the growing environmental concern, plastics derived from renewable materials such as Polylactic Acid (PLA) are also popular on the market. Due to their low cost, ease of manufacture, versatility and water resistance, plastics are used in a multitude of products and sectors. In the AM sector, 3D printing plastics are also very popular.

In the following guide, we will take a look at the most common 3D printing plastics. As you may know, the most popular and affordable 3D printing process, FDM, produces parts through the extrusion of plastic filaments. However, the precision on FDM machines is not the same as other AM processes such as SLS or SLA. Plastics are often used with this technology to create prototypes. Therefore, for industrial and end-use parts, manufacturers might decide to opt for SLS (using plastic powders) or SLA (using plastic resins) technologies that offer more accuracy and part quality. Two other technologies that can print with plastics are Material Jetting and Multi Jet Fusion.

What plastics can be used in additive manufacturing? In filament or powder form, the plastic should melt to form the object you are printing layer by layer. In resin form, it should solidify to form the object. Each plastic will require different 3D printing parameters during the building process, and will give parts varying properties.

ABS

ABS filament is the most commonly used 3D printing plastics. It is used in the bodywork of cars, appliances, and mobile phone cases. It is a thermoplastic which contains a base of elastomers based on polybutadiene, making it more flexible, and resistant to shocks. ABS can also be found in powder form for powder bed processes such as SLS, and liquid form for SLA and PolyJet technologies.

ABS is used in 3D printing when heated between 230ºC and 260ºC. It is a tough material, able to easily withstand temperatures of -20ºC to 80ºC. In addition to its high strength, it is a reusable material and can be welded with chemical processes. However, ABS is not biodegradable and shrinks in contact with air, so the printing platform must be heated to prevent warping. Moreover, it is recommended to use a closed chamber 3D printer to limit particle emissions when printing with ABS. Learn more about ABS in our dedicated guide.

PLA

Known as polylactic acid, or PLA, this material has the benefit of being biodegradable, unlike ABS. PLA is manufactured using renewable raw materials such as corn starch. PLA is one of the easiest materials to print, though it does have a tendency to shrink slightly after 3D printing. You don’t require a heated platform when printing in PLA, unlike with ABS. PLA also prints at a lower temperature than ABS, between 190ºC to 230ºC.

PLA is a more difficult material to manipulate due to its high cooling and solidification speed. It is also important to mention that models can deteriorate when in contact with water. However, the material is consistent, simple to use, and comes in a wide variety of colors, making it suitable for FDM 3D printing. Learn more about PLA in our dedicated guide.

PLA 3D printing filament spools

ASA

ASA is a material that has similar properties to ABS, but has a greater resistance to UV rays. As with ABS, it is advised to print the material with a heated bed platform to prevent warping. When printing with ASA, similar print settings are used to ABS, but extra care must be taken to print with a closed chamber due to styrene emissions.

PET

Polyethylene terephthalate, or PET, is commonly seen in disposable plastic bottles. PET is the ideal filament for any pieces intended for contact with food. Moreover, the material is fairly rigid and has good chemical resistance. To obtain the best results when printing with PET, print between 75 – 90ºC. PET is commonly marketed as a translucent filament, with variants such as PETG, PETE, and PETT also sold. Advantages of PET include that the material doesn’t release any odours when printing, and is 100% recyclable.

PETG

PETG, or glycolized polyester, is a thermoplastic widely used in the additive manufacturing market, combining both the simplicity of PLA 3D printing and the strength of ABS. It is an amorphous plastic, which can be 100% recycled. It has the same chemical composition as polyethylene terephthalate, better known by its acronym PET. Glycol has been added to reduce its brittleness and therefore its fragility. Learn more about PETG in our dedicated guide.

Polycarbonate (PC)

Polycarbonate (PC) is a high strength material designed for engineering applications. The material has good temperature resistance, able to resist any physical deformation up to around 150ºC. However, PC is prone to absorbing moisture from the air, which can affect performance and printing resistance. Therefore, PC has to be stored in airtight containers. PC is highly valued by the AM industry for its strength and transparency. It has a much lower density than glass, making it particularly interesting for designing optical parts, protective screens or decorative objects. Learn more about PC in our dedicated guide.

A 3D printed part made from PC

High Performance Polymers (PEEK, PEKK, ULTEM)

The evolution of 3D printing technologies has led to extensive research work on printing materials, enabling the development of a whole range of high-performance filaments with mechanical characteristics similar to those of metals. There are several types of high-performance 3D printing plastics such as PEEK, PEKK or ULTEM – they are distinguished by family such as polyaryletherketones (PAEK) or polyetherimides (PEI). These filaments have a very high mechanical and thermal resistance, are very strong and at the same time much lighter than some metals. These properties make them very attractive in the aerospace, automotive and medical sectors.

Due to their characteristics, high performance polymers cannot be printed on all FDM machines on the market. Indeed, the 3D printer must have a heating plate capable of reaching at least 230°C, an extrusion at 350°C and a closed chamber. Today, about 65% of these materials are printed with FDM technology, but they are also found in powder form, compatible with SLS technology. Learn more in our dedicated guides on PEEK and PEKK.

Image via VisionMiner

Polypropylene (PP)

Polypropylene is another thermoplastic widely used in the automotive sector, professional textiles sector, and in the manufacturing of hundreds of everyday objects. PP is known for its resistance to abrasion and its ability to absorb shocks, as well as relative rigidity and flexibility. However, drawbacks of the material include its low temperature resistance, and sensitivity to UV rays which can cause it to expand. Due to this, several manufacturers have developed alternative types of PP, simili-propilenos, that are stronger both physically and mechanically.

Nylon

Objects made from polyamides (nylon) are usually created from a fine, white, granular powder with SLS technology. There are however some variants of the material such as nylon that are also available in filaments used in fused deposition modeling (FDM). Due to its biocompatibility, polyamides can be used to create parts that come into contact with food (except foods that contain alcohol).

Constituted of semi crystalline structures, polyamides have a good balance of chemical and mechanical characteristics that offer good stability, rigidity, flexibility, and shock resistance. These advantages mean that the material has many applications across sectors and offers a high level of detail. Due to its high quality, polyamides are used in the manufacture of gears, parts for the aerospace market, automotive market, robotics, medical prostheses, and injection molds. You can learn more in our dedicated guide on Nylon.

Image via Sculpteo

Composites

Composites are extremely beneficial when making lightweight yet strong parts. The fibers add strength to a part without adding weight, which is why we also refer to composites as fiber reinforced materials. There are two types of reinforcements, short fiber or continuous fiber. In the first case, chopped fibers, which consist of segments less than a millimeter in length, are mixed into traditional 3D printing plastics to increase the stiffness and to a lesser extent the strength of components. Chopped fibers can be mixed with thermoplastics such as nylon, ABS or PLA.

Alternatively, the fibers can be added to the thermoplastics continuously to arrive at a stronger part. The main fiber used in the 3D printing sector is carbon fiber, but there are also other fibers such as glass fiber or Kevlar. You can find more information in our dedicated guide.

Carbon fiber reinforced filament spool

Hybrid Materials

There are a variety of hybrid materials that mix base plastics with powders to give them a new color, finish or additional material properties. Often based on PLA, these materials are usually made of 70% PLA and 30% hybrid material. For example, wood-based filaments ranging from bamboo, cork, wood dust, and more are available. These wood-based materials mixed with PLA give the hybrid filament a more organic texture. Additionally, some hybrid materials incorporate metal powders to work with FDM-based technologies, to give parts a metal finish. They can be based on copper, bronze, silver, and more.

3D filaments based on wood.

Alumide

Alumide plastic objects are manufactured from a combination of polyamides and aluminium powder using the SLS process. The material has a large, slightly porous surface and a gritty, grainy appearance offering great strength and good temperature resistance (up to 172°C). However, some post-processing treatments are necessary, such as grinding, sanding, coating, or milling.

Alumide is used for complex models, design pieces, or for small series production of functional models that need high rigidity and an appearance similar to aluminium. This technique involves few geometric limits.

Soluble Materials

Soluble materials are materials printed with the intention of being dissolved in a future stage of the manufacturing process. The two most common soluble filament materials are HIPS (High Impact Polystyrene) and PVA (Polyvinyl Acetate). HIPS is associated with ABS, and can be dissolved with limonene, whereas PVA is associated with PLA and can be dissolved using just water.

There are also BVOH filaments which are becoming increasingly popular, especially in dual extruder printers. This is because the material is soluble in water, and according to experts has a higher solubility than PVA.

Flexible Materials

A newer type of filament, and one of the most successful, are flexible filaments. They are similar to PLA, but usually made out of TPE or TPU. The advantage of using these filaments for 3D printing is they allow for the creation of deformable objects, widely used in the fashion industry. Generally, these flexible filaments have the same printing characteristics as PLA, though they come in a variety of ranges based on their stiffness. It is worth finding out which type of extruder is best suited to the material to avoid jams when 3D printing.

Flexible materials are widely used in fashion and design

Resins (for photopolymerization-based 3D printing)

3D printing technologies based on photopolymerization use UV-sensitive resins to create objects layer by layer. In other words, they use a light source such as a laser or LCD screen to solidify a liquid photopolymer. Technologies include SLA, DLP, and even Material Jetting (PolyJet). Creating parts using resins results in high detail and smooth surface objects, nevertheless, the color range is still quite limited using this process. What differentiates resins from FDM filaments is that it is impossible to mix resins to obtain different results quite easily.

Standard resin has properties similar to ABS: the surface finish of the part will be good given the photopolymerization process, however mechanical properties will be moderate. More advanced resins do exist for technical applications such as in dentistry (also need to be biocompatible), or engineering. Additionally, flexible resins that offer greater flexibility and deformation can be used to make jewelry. Over the years, manufacturers have expanded their range of liquid photopolymers to answer manufacturing needs from various sectors. Therefore, you should be able to find resins that have high-temperature resistance, can withstand large impacts, or that have high elongation properties.

The 3D printing resin is poured in a tank

What do you think of our explanation of these 3D printing plastics? Let us know in a comment below or on our Facebook and Twitter pages! Don’t forget to sign up for our free weekly Newsletter, with all the latest news in 3D printing delivered straight to your inbox!

High Temperature 3D Printing to the Masses / Sudo Null IT News

There is an impressive variety of thermoplastics that can be printed on consumer grade desktop 3D printers. But, despite this, most often users turn to polylactide (PLA) threads. This is not only the cheapest of materials, but also the easiest to work with. Its extrusion can already be carried out at a temperature of 180 °C, and good results can be obtained even without preheating the table. The disadvantage of PLA-printed objects is that they are relatively brittle and do not tolerate high temperatures well. For prototyping or printing low-stress components, PLA is great. However, many users quickly go beyond its capabilities.

Polyethylene terephthalate (PETG) is usually the next step. It is not much harder to work with compared to PLA, while it is more reliable and can withstand higher temperatures. In general, it is better suited for creating mechanically loaded parts. But if you need to make even stronger and more heat resistant parts, you can switch to acrylonitrile butadiene styrene (ABS), polycarbonate (PC) or nylon. And this is where the problems begin. These materials are extruded at temperatures over 250°C and closed chambers are recommended for best results. These printers are at the top of the budget range that hobbyists are willing to work with.


Industrial 3D printers like this one, the Apium P220, start at around $30,000. (PAEK, PEEK, PEKK). Components made from these plastics are suitable for aerospace applications as they can replace metal while remaining much lighter.