Researchers from Laboratoire de thermique et énergie de Nantes uncover some of the challenges in 3D printing versus thermoplastic injection, releasing the findings of their recent study in ‘Heat Transfer and Adhesion Study for the FFF Additive Manufacturing Process.’
Mechanical properties are often the topic of study today—from researching helpful additives to studying the influences of color, to issues with porosity, and far more—as users attempt to improve the functionality of parts. Adhesion between layers is a common problem, usually leading to further examination of technique and materials. In this study, the researchers focused on heat exchanges in an attempt to improve 3D printing.
Temperature remains one of the most important settings for users, leading to good quality and performance in printed parts—or in other unfortunate cases, major structural issues.
“To find precisely the limit of this optimal processing area, the thermal history needs to be predicted accurately,” stated the researchers.
With a better understanding of thermal factors, users may be able to avoid macro-porosities and adhesion problems. During FFF 3D printing, the following heat transfers occur:
- Heat from the extruder
- Convection cooling of filament
- Exchanges between filaments
- Heat from the support plates
- Radiative losses
- Heat from exothermal crystallization for semi-crystalline polymers
While controlling the 3D printing process with high temperatures, the researchers also reinforced PEKK materials with short carbon fibers. In the beginning of the experiment, however, the team used ABS due to ‘greater ease of implementation.’ An experimental bench was 3D printed on a CR-10 3D Printer from Creality3D for measurements of temperature, and then a simulation model was created via COMSOL Multiphysics® v5.4 for predicting temperature and healing.
Before printing, the authors customized the 3D printer in their lab, modifying the hardware so it would be able to attain the proper temperatures of up to 400°C.
“The extruder was changed, for a full-metal unit, with a water-cooling closed circuit system. A closed insulated chamber maintains the part in a 200°C atmosphere. It does not block the three translation moving system of the 3D printer inside the chamber. Electronics and mechanical parts are kept outside the chamber. This heating chamber is mandatory for printing polymers like PEKK,” said the researchers.
The other specimen was a basic structure 3D printed with both ABS and PEKK, in the form of a 60×2.2×50 mm wall. For ABS, the researchers took qualitative measurements with a pyrometer, with quantitative measurements taken for both ABS and PEKK.
“Because of the poor knowledge of the rheological properties, the calculated degree of healing was found to be equal to 1 very quickly for ABS. However, this is the opposite for PEKK material, which reaches only a degree of healing of 0.45 after the cooling-down of the filament,” concluded the researchers.
“The bench was designed to handle high temperature and future work will consist in studying deposition of PEKK more precisely, and also for carbon fibers reinforced PEKK with different process parameters. The short-term perspectives are to use the model with the thermo-dependent thermal properties, which were characterized in the LTeN laboratory on PEKK polymer.”
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