Plastic is today a well-used material for manufacturing technical products and is available in all possible colors, shapes, and functions.
There is a general perception that plastic is not durable and that plastic breaks easily. The fact that parts made of plastic break is usually due to incorrect use, aging or incorrect construction. It is the last part that can be influenced in the development stage when designing or constructing a plastic part. It is then important to understand the material plastic and be able to design the part or the 3D print after that material.
Therefore, we will present a series of articles on plastic in general, on design rules for plastic and what to keep in mind when printing 3D prints in plastic. We will also tell you more about what, for example, the abbreviations ABS, PLA or PA stand for and why they are often mentioned in connection with 3D printers and 3D prints. Below you can read part 1 of our article series.
A common problem with plastic parts and 3D prints in plastic is that they are designed without taking into account the properties of the material, the characteristics of the 3D printer or that the parts are designed as if they were made of metal. The next step to understand is that a 3D printed part does not work in the same way as a plastic part that is, for example, injection-molded because 3D prints are built up layer by layer.
The most important things to keep in mind with plastic material for 3D printing are:
1. Plastic details do not get better with increased goods
Source: plastics.com/
An important aspect with plastic is that plastic does not automatically become stronger with increased goods (how much material there is in a certain place in the detail). This is because plastic has non-linear force and elongation properties, which means that just because the thickness increases from 2 to 4 mm, for example, does not mean that the piece of plastic becomes twice as strong. Therefore, it is important to use ribs, sockets and other geometry to make the piece of plastic stronger. More about that in the next article.
2. Plastic details from a 3D printer need to be oriented correctly
The orientation is important. Source: 3dprinteresting.com/
Since a 3D printer builds the details layer by layer, it is important to think about how to orient a detail. For example, a beam printed horizontally may be stronger than if the same beam is printed vertically. This is because if it is printed upright, each layer is printed as the short side and breaks it there under load. The risk of breakage is greater than if the layers had been printed perpendicular to the load.
3. Plastic is temperature and load dependent
Glass transformation temperature is called the point where the plastic “softens”. Source: cad-resurs.se/
Another important aspect to remember is that plastics are temperature and load dependent. Most 3D printers use thermoplastics that have a melting point and soften as the temperature rises. This means that at a certain temperature the plastic part loses some rigidity and can therefore be deformed.
In addition, it is affected by the force to which it is subjected. It is even the case that if a plastic part is exposed to a force at room temperature, it will be extended in the same direction as the force pulls. This phenomenon is called creep and is due to the fact that the plastic molecules are affected by the force and move with time.
4. Plastic is affected by the environment
Black lacquered plastic, best withstands UV light. Source: pepctplastics.com/
Another important aspect to consider is that plastic is affected by both light and chemicals. This means that a plastic part that is exposed to UV light can have deteriorated properties. It may crack, lose luster, or weather.
One way to protect yourself from this is to paint the part or choose, for example, black color over white because white is more sensitive to UV light. In addition, plastics are sensitive to various chemicals. ABS, for example, is sensitive to acetone and “melts” while PLA is sensitive to bases such as dishwasher detergent and can therefore not be used in a dishwasher.
5. Plastic can change properties with additives
Aramide together with Polyamide can create the strong Kevlar composite. Source: germes-online.com
A unique property of plastics is that they can be mixed into additives to, for example, increase UV resistance. This means that the properties of plastics can vary incredibly much. A known additive is fibers and aramid fibers which together with plastic create a composite known as Kevlar. It is also possible to glass-reinforce and carbon fiber-reinforce plastics to increase strength.
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