- Eng. Antonio Montes de Oca
Printing parameters for parts with high mechanical performance.
3D printed parts have become notorious for sometimes not being durable enough for tasks that involve a considerable amount of mechanical stress. This is partly true, if adaptations or modifications to certain parameters are not taken into consideration at the time of design and/or in manufacturing to improve the durability of the parts. Like many things in engineering, 3D printer operators can make modifications to the manufacturing process to make parts perform as expected or correct in the field.
Continuing the format of previous blogs, below is a list of just a few of the parameters (for FDM printing) that we at Kenko Solutions customize to meet the needs of our customers:
Choice of thermoplastic: One of the main unknowns to be solved when manufacturing 3D printed parts. The main factor that intervenes in our choice is the temperature at which the printed parts will be exposed.
As a general rule, if the parts will not be exposed to sunny environments, we can choose to use PLA because of its ease of printing and availability in the market.
Secondly, if the parts will have light exposure to the sun, we recommend using PETG.
Thirdly, if the parts will be continuously in hot environments and in continuous exposure to UV sunlight, we could choose to use ASA.
As the printing temperature increases, the difficulty of successfully printing parts generally increases as well. A numerical way to determine which thermoplastic to use is to know the ambient temperature in advance. If the temperature is less than 50ºC, use PLA; if less than 70ºC, PETG; and for less than 100ºC, ASA. For higher temperatures, PEEK, ULTEM or PEI can be used.
Another characteristic that can influence the choice of thermoplastic is to look for different mechanical or commercial properties.
PLA: Higher availability, low price, easy printability, higher tolerated strength before rupture, low stringing, lower ductility and low glass transition temperature.
PETG: Medium availability, ductile rupture, medium glass transition temperature and medium stringing.
ASA: Low availability, higher ductility, high glass transition temperature, high stringing and hygroscopic material.
Print orientation: One of the most important factors that will determine whether the part fails or not. Parts that are printed when the axis that will carry the most mechanical stress is parallel to the X or Y axis of the print bed (XY or horizontal orientation) will have a better chance of withstanding the stress without breaking. The image below shows two scenarios for the same model, but with different printing shapes. In the bottom image would be the case with less support to breakage would have, the top right image would be the opposite case. The first image shows the intended use of the part with the red arrows symbolizing the axis that will have the highest mechanical stress.
Number of perimeters: Commonly people starting in the 3D printing world consider that modifying the infill percentage is the easiest and most direct way to improve the strength tolerated by the parts. However, the number of perimeters is actually the parameter that has the greatest impact on improving that property. To give an example, a part with 75% fill and 2 perimeters is 20% weaker than a part with 15% fill and 3 perimeters. This is the result of a ratio between the tolerated strength and the weight of the parts.
Printing temperatures and venting: Adjusting temperature and venting values to improve mechanical properties is less common. This could be used as one of the last resources to increase part stiffness. By printing parts with higher temperature and filament cooling fan speeds, it allows the deposited filament to fuse better with the lower plastic layers. The tolerated strength can be increased by up to 60% just by changing these two parameters. However, not cooling the lower plastic layers causes the new layers to be deposited on plastic that is not completely solid, so you will not have good cementation of the upper layers. This will affect the surface aesthetics of the parts. The dimensions of the printed model will deviate greatly from the model you intend to print and may even result in a complete failure of the print.
Change part design or mode of use: There will be situations where it will be more convenient or totally necessary to re-model the part and add reinforcement in the most critical or failure-prone parts. One possible option is to use generative design to optimize the parts given a force magnitude and direction.
These were some of the recommendations and factors we took into consideration when manufacturing 3D printed parts. The 3D models we receive sometimes need modifications in their design so that the parts meet the mechanical requirements that our customers want. It is important to know the environment where the parts will perform and the way they will be used. If you want some recommendations to improve your parts when modeling them, check the 3D printing modeling guide.
In Kenko Solutions we will make the necessary recommendations and we will make the necessary adjustments to your model so you can be confident that your parts will operate as expected.