From Multirotor Pilot Issue: 8
by Erick Royer
Since I got my first 3D printer, the number of uses that I find for this technology in the multirotor world seems to exponentially grow every day. One common question that I get a lot from people who know that I am a 3D printing guru, is “what material should I use for my project?”
In this article I will give you a quick overview of the most common filaments used in 3D printing and I will explain the main differences between them in terms that beginners will easily understand. Additionally, I am only focusing on consumer grade 3D printers that use fused deposition modeling (FDM) technology. To simplify, you can think of FDM much like a hot glue gun; the glue stick melts and the molten glue is deposited and once cooled it becomes hard and creates a bond. With 3D printing we are laying down layers of molten plastic fi lament that will bond to each other and create a solid part as it cools. Unlike a traditional inkjet printer that needs an ink cartridge to print, 3D printers use plastic filament. These consumables are widely available online and come in a wide variety of types (ABS, PLA, PVA, etc.), colors, diameters and lengths.
The most common sizes for desktop 3D printers are 1.75mm and 3mm. In this article we are going to focus on ABS, PLA and PVA filaments. I will visit some newer fi laments that are starting to emerge like nylon, carboninfused PLA, laywood, flexible and there was recently even a stainless steel fi lament released.
ABS, PLA OR PLA – HOW DO I CHOOSE?
ABS (Acrylonitrile Butadiene Styrene)
ABS is used in a large variety of applications in industry today. Some examples include: manufacturing of pipes (like drain, waste and vent pipes), electronic assemblies, kitchen appliances, protective carrying cases, automotive components, musical instruments and toys like Lego blocks.
ABS, for the most part, is durable and strong, slightly flexible and quite resistant to heat. The general operating temperature of the hot end (the heated part that melts the plastic and forces it through a print nozzle) of around 210-250 degrees C. Typically printers that are designed to work with ABS will have a heated print bed (the surface that the part is built on), in order to prevent warping and curling of the printed parts.
ABS tends to be the least expensive material of the three types of filaments mentioned in this article. It was also the most favored material up until the release of PLA filaments. ABS is suitable for a large variety of purposes. It can be easily sanded and painted and printed parts can be glued together with ABS glue and it is easily soluble in acetone (nail polish remover). ABS is generally available in white, black, red, blue, yellow and green as well as transparent. ABS that will typically have a matte appearance when the part has cured.
ABS does have some drawbacks. The main one is that it is very difficult to get a large flat part to successfully print without distortion even with a heated print bed. I have good luck with ABS on smaller parts, but when I have to print something large like a mini quad frame, I stay away from ABS and the stress that comes with it. ABS is also a petroleumbased nonbiodegradable plastic. While it can be recycled, if not properly disposed of it will be around forever in landfills. Another problem with ABS is that it does create mild fumes when it is melted which can irritate more sensitive persons. Because of this, I always run my printer in a well-ventilated area when printing this material. I know some people will even install a vented hood over the printer to be rid of the fumes. The last thing to note about ABS is that it will deteriorate with prolonged exposure to sunlight. That is not to say that it is not good to use on our machines outdoors, but if you plan to print something that will remain outside for a long time in direct sunlight, you may find this deterioration.
If you do not plan to use your ABS filament for a long period of time, it is wise to store it in an airtight container. ABS will attract moisture from ambient air, which can affect your future prints.
TIP 1 – ABS does not adhere well to bare glass. Even with heated glass build plates, you will often experience warping or curling of prints or failed prints due to the print breaking free.
TIP 2 – Do not use an extruder fan when printing with ABS. If you get a print that does not have a nice finish because of too much heat, try to print more than one at a time. This allows the first part to cool while the second is being printed. Some software programs have a filament-cooling feature where the extruder will lift off the print between layers, allowing the print to cool.
TIP 3 – Heated beds are recommended and depending on the part and bed adhesion method that you are using, 85-90 degrees C is a good bed temperature.
The following adhesion solutions can be used to try and obtain successful prints. ?
- Use PET or Kapton tape on the glass bed with an ABS slurry. ?
- ABS slurry is made from dissolving ABS in acetone. Use two ounces of acetone and six ounces of ABS to create a thicker-than-water, but thinner than milk solution that you will “paint” on your bed while it is hot. ?
- Try ABS slurry on both glass and PET/Kapton tape to see which gives the best results. ?
- Use a glue stick, such as Elmer’s. Apply a thin layer of glue in one direction to a cool print bed, then apply a second layer in another direction. Then bring the bed up to temperature and let dry before printing. ?
- Use hair spray. I have had good luck with Aquanet unscented extra hold. I apply a thin coat to a cool print bed and let it dry, then apply a second coat and let dry before bringing bed up to temperature.
TIP 4 – The size of the footprint of the part will play a large role in successful bed adhesion. The larger the footprint, the more chance of warping and curling of the part. It is best to position larger prints near the center of the bed (where it tends to be the hottest). I have a lot of success with hairspray, however, for larger prints that are more critical, I opt to use the ABS slurry method. The downside to this is that the parts are much more difficult to remove from the print bed and cleanup is challenging. ABS is a good material choice for many parts and I am confident that using some (or all) of these tips will help you realize successful ABS prints.
PLA (Polylactic Acid)
PLA tends to be the most common filament used by hobbyists today. It is a biodegradable thermoplastic, which is derived from renewable resources such as cornstarch, sugar cane, tapioca roots or even potato starch. Because of this, PLA is the most environmentally friendly solution in the world of 3D printing as compared to all the other petroleum-based plastics like ABS or PVA. In the medical world PLA is used for surgical implants and medical suturing as it possesses the ability to degrade into inoffensive lactic acid in the body. PLA is also used for food packaging, bags, upholstery, disposable garments, hygiene products and is even used in diapers. It is considered to be very safe. A word of caution for those looking to print parts that would be used in conjunction with food or drink; the coloring pigments that are used in the filament may not be as safe as the PLA filament itself.
PLA is tough, but can be brittle once it has cooled. The temperature threshold of PLA is less than ABS. It is normally extruded between 160 and 220 degrees C. PLA does not require a heated printbed. There are many that suggest that a heated bed (between 50-60 degrees C) aids the quality of the printed object, but I have been printing successfully for years without heat. I do, however, use 3M Blue Painters Tape on the bed, which promotes better adhesion when printing and a more stable first layer. PLA cools slowly, so the use of a fan pointed at the extruded material can help speed up the cooling process.
PLA will emit a slight odor once heated. It is best described as sweet corn, pancakes or maple syrup, which is not all that bad. Unlike ABS, PLA does not emit any fumes so you will not require a vented hood and PLA is safe to print within your house.
PLA can be sanded and painted with acrylic paint, but some people recommend using a primer. Gluing PLA is not as easy as ABS, though I have had good results with CA glue (i.e. super glue).
PLA has become one of the most popular plastic filaments in the 3D printing and hobby worlds. It has a low toxicity and is more environmentally friendly compared to petroleum-based fi laments. The main drawback is that PLA cannot stand too much heat, as standard PLA becomes soft at 50 degrees C. You can actually reheat your printed parts with a heat gun if necessary. Although for some, this is considered an advantage when it comes to making repairs or for bending and welding printed parts.
PLA is available in a wide variety of colors and types, from translucent and solids to flexible and specialty materials; there are even glow-inthe- dark varieties. As with ABS, PLA also attracts water molecules from the air and is more prone to water absorption than ABS. Water saturated PLA can become more brittle and difficult to print, requiring a higher extrusion temperature. You must take care to store your PLA spools in dry and airtight containers
PVA (Polyvinyl Alcohol)
PVA is a special type of plastic that is water-soluble. It is commonly used as paper adhesive, packaging film, as a mold release agent and in children’s play putty. Another use for PVA is in freshwater sport fishing, where PVA bags are filled with bait and thrown into the water. The bag rapidly dissolves, releasing the bait in order to attract fish.
In the 3D printing world, PVA is often used with dual extruder printers to provide a support structure for an object that has overhangs in the design. Many complex parts that involve many areas where there is no support under the upper layers (overhangs) can only be produced using these support structures. Without them, the part will warp and collapse. The finished object can be placed in water which will dissolve the PVA support structure leaving just the finished part. This is a preferred method over printing support structures with the same material, which requires some tedious post-print cleanup.
PVA is normally extruded at a temperature of 190 degrees C, but it can be difficult to use as it has a very high tendency to att ract moisture. PVA is best stored in a sealed box or container. PVA is tends to be more costly than ABS or PLA and it not as easy to find.
THE FINAL WORD
While 3D printing has come a long way in the last few years, it is still not a simple push-toprint operation like an inkjet printer. There are a lot of tricks that you need to know, especially when it comes to printer fi lament. As an example, I have purchased multiple spools of the same type of PVA filament in the same size and color at the same time and I found that I needed to vary the extrusion temperature as much as 10 degrees C from spool to spool. If you are a beginner, I strongly suggest sticking with PLA as it will give you the highest chance for successful prints and will give you the strength that you need for most projects. Please send me an email at firstname.lastname@example.org with photos of projects that you 3D print for your multirotor applications as I would love to include them in future articles.