3D printing has established itself in the 21st century as the process for producing prototypes and very small series. In the plastics sector, the fused filament fabrication (FFF) process is used in particular. A plastic filament is melted in a nozzle and a component is built up layer by layer. As with all manufacturing processes, there is an interest in continuously optimizing and improving the FFF process. One possibility is based on process simulations, which enable a better understanding of the entire process. Afterwards a validation of the simulation with the real process is always necessary. In the case of FFF, this validation was so far only possible to a limited extent. In this work, a method is presented that enables a non-destructive investigation of the melting behavior during the printing process. For this purpose, a 3D printer nozzle with an extruder was integrated into an X-ray computed tomography system. Thus, a computed tomography scan (CT scan) can be performed during the extrusion process. By using filaments with high absorbent tungsten, a sufficient contrast can be created between the metal nozzle and the plastic filament, which allows an analysis of the melting behavior. This setup allows to distinguish between the solid filament area and the melt area, as well as to determine contact between the filament and the nozzle wall. In this way, the simulations can be validated and nozzle geometries to be improved in the future by means of improved simulation tools.
The increasing requirements on plastic parts demand a rising use of combined functional and reinforcing materials. Therefore, often reinforcing particles with different aspect ratios are added to the plastic as additive mixtures. However, the engineering design process of reinforced parts requires an early knowledge of the expected orientation of the reinforcing particles. Numerous models try to predict the orientation of particles in polymer suspensions. However, the interaction coefficient strongly depends on the aspect ratio of the particles and a prediction of the orientation behavior of additive mixtures with differently shaped particles has not been validated using conventional methods. In this work, the orientation of differently shaped particle mixtures in polymer suspensions is investigated for different fluid channel geometries. Finally, the Folgar–Tucker model is applied to filler mixtures and implemented into OpenFOAM®, which enables the comparison of filler orientation in different fluid channel geometries. Regarding the experiments a characteristic increase of the interaction coefficient was observed at a filling level of 5%. Furthermore, it was shown that a balanced mixing ratio yields higher interaction coefficients. With regard to the performed simulations, it was possible to show qualitatively how a considered interaction between fibers and platelets affects the orientations.
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