3D printing - Types of materials
Types of materials
In the previous article, we spoke briefly about 3D printers in general and how they work. We also mentioned that plastic is the most common material used in conventional 3D printers. However, 3D printers are capable of printing using a wide variety of materials ranging from plastic to cement used in construction. In this article we will focus on the two most common plastic types used in 3D printing.
The most commonly used materials in popular desktop 3D printers include the following:
- PLA - Partly made from corn
- ABS - Same material used in Legos
- PVA - Dissolvable material
- TPE - Flexible material
3D printer material typically comes in the form of filament spools. The filaments are usually either 1.75mm or 3mm in diameter with 1.75 mm being the most common. They can come in different colors and material types ranging from brittle plastic to rubber like material to dissolvable material. Filament spools are usually sold according to their weight. They most commonly come in 1 kg and 0.5 kg weights. Some vendors sell smaller amounts that are meant for testing out the material before purchasing a large spool.
Figure 1: Plastic filament spools
PLA and ABS are the most commonly used types of plastic in 3D printing. Both are known as thermoplastics as they can be melted and cooled again into a desired shape, but more importantly, this process is repeatable which allows for manufacturing the filaments in the first place and then melting the plastic again while 3D printing. This even allows for recycling unwanted or failed prints into filaments again for reuse.
PLA (PolyLactic Acid) is a biodegradable plastic that is partly made from corn and has one of the highest consumption volumes in the world compared to any other type of plastic. It is the most common type of plastic using for 3D printing due to its practicality and ease of use.
Figure 2: PLA is partly made from corn. That’s why it has a sweet smell when printing.
Printing with PLA doesn’t require a heated build plate and nozzle temperatures tend to be slightly lower than those required for ABS. Hence, it is favored by a lot of 3D printing beginners. The current trend however is to use a slightly heated build plate (around 70° C) for improved adhesion.
Figure 3: A PLA print
Generally speaking, PLA offers better immediate results as it is easier to achieve accurate parts with. This means that mechanical and functional parts are easier to produce with PLA. For example, a 3D printed miniature transmission would perform better in PLA as compared to ABS. But when it comes to finishing the surface of the product or piece, PLA is overtaken by ABS. Lastly, the nature of PLA results in strong but brittle parts, therefore, PLA parts cannot withstand bending or high pressure impacts.
ABS (Acrylonitrile Butadiene Styrene) is one of the most widely used type of plastics. ABS parts can be found in almost every car and household item. The most recognizable product made from ABS is Legos. In 3D printing, it is usually one of the most popular materials used second only to PLA.
Figure 4: Legos are made from ABS plastic.
It is important to note that ABS releases toxic fumes when heated at high temperatures similar to the ones used for 3D printing. You need to make sure that the area you have your 3D printer in is well ventilated and that you don’t spend a long time next to the printer while printing. Ideally speaking, having a small exhaust fan that vents the fumes away from you and preferably outdoors is the best method of avoiding these toxic fumes. Those fumes usually become a concern only when you are printing for long stretches of time.
ABS is relatively harder to print with when compared to PLA. It requires higher nozzle temperatures and a heated build plate. The main problem of ABS when printing is warping of the first layer resulting in deformation of the printed object and even dislodgment of the print resulting in total print failure. That is why a heated build plate is required in this case and is usually heated between 100-120° C. Printing in ABS without a heated build plate is virtually impossible.
Figure 5: Warping of the first layers due to bad adhesion.
Figure 6: A failed 3D print
In addition to having the build plate heated, ABS requires certain types of build plate surfaces to adhere properly. These can range from a sprayed layer of hair-spray, to a layer of glue, and finally to a layer of tape. From personal experience, I personally recommend the use of kapton tape. Kapton tape provides excellent adhesion at printing temperatures provided that it is cleaned properly (preferably with high concentration acetone) before printing.
Figure 7: Kapton tape roll (left), build plate with kapton tape layer (right)
Although ABS is relatively harder to print with it can yield better final products after doing proper surface finishing. Using sand paper is the most popular method for smoothing out finished prints and can improve the final look dramatically. If you are willing to go the extra mile then doing an acetone bath is probably the best method for smoothing out ABS prints. It involves heating up a small amount of acetone in a container and then “dipping” the 3D printed object in the acetone vapor for a few seconds until the layers melt and disappear. This method results in smooth surfaces than can be comparable to injection molding quality.
Figure 8: A short comparison between PLA and ABS
Storing plastic filament spools in a dry space is important especially for long term storage as the filament can absorb humidity resulting in changes in filament diameter, material nature, and printing quality. If any of the aforementioned occur they can result in bubbling of the plastic when printing, a need to change the print temperatures, or even clogging the nozzle of the extruder. Hence it is important to store filament spools properly.
Figure 9: Storing filament spools in an Ikea box is my favorite method of preserving the plastic quality.
Keep in mind that due to different storage conditions and varying temperatures, a plastic filament might have a slightly different diameter than the one specified. The difference has to be corrected by entering the correct diameter into the slicing program after measuring it with a caliper. For example, a 1.75mm filament may actually measure 1.77mm. Such a small difference won’t result in drastic changes in print quality but will be noticeable.
A trick to differentiating ABS from PLA
Let’s say you have two unlabeled filament spools and you don’t know which one is ABS and which one is PLA. What do you do?
Apart from trying to differentiate them by their color and feel, which even experienced people mix up sometime, there is a trick to make sure which one is which.
*WARNING* The following method involves the use of fire and requires taking proper safety measures.
Here are the steps:
- Start by cutting off a small piece of the filament (around 5-10 cm in length).
- Using a lighter, start heating one end of the piece of filament with direct contact with the flame until the plastic catches on fire.
- Watch carefully as the color of the flame changes
- Observe what is left of the filament after it is burned.
PLA will burn with a blue flame and start melting and dripping drops of molten plastic that are still on fire.
ABS on the other hand will burn with a bright red flame and will leave a charred remnant of the filament after it has burned. It is important to note that ABS will release a ton of toxic fumes when burning and hence proper protective measures must be taken.
This concludes it for today’s article. We will discuss PVA and TPE in upcoming articles to understand where they can be used and how they can complement ABS and PLA. In the next article, we will start with the process of preparing a 3D model for printing.
Author: Muhammad B. Darwish
Muhammad Darwish is a self-taught 3D printing enthusiast that has considerable expertise in the world of 3D printing and 3D designing. Muhammad is currently studying medicine in Ras Al Khaimah and continues to practice his 3D printing hobby in his free time. He started his 3D printing journey 6 years ago with a DIY MakerBot Thing-O-Matic 3D printer that he assembled and fine-tuned at home. One of his recent projects include a RepRap Prusa Mendel i2 that he sourced and assembled himself. He now offers 3D printing tutorials and courses and can be reached at the following email: mdarwish3D(@)gmail.com