Many factors impact the quality of 3D printed parts, and as the technology is used more and more for production of final parts rather than just prototyping, it is necessary to investigate those factors more thoroughly so that these final parts can be produced with optimal properties. In a paper entitled “Investigating the effect of fabrication temperature on mechanical properties of fused deposition modeling parts using X-ray computed tomography,” a group of researchers study the effect of printing temperature on the final quality of 3D printed parts.
Defects in 3D printed parts are not always visible, but internal defects can have even more of a negative effect than visible ones. In this study, the researchers used CT scanning to non-destructively study 3D printed parts and check their quality. An Ultimaker 2 3D printer was used to print several sample parts from black PLA. Nine sets of three samples each were printed, and the parameters for each part were identical except for the print temperature, which differed in degrees of 10 over a range from 180º to 260ºC.
The 3D printed samples were subjected to tensile tests, and then a CT system was used to test one out of each three-sample set. A 20-mm-long section from the middle of each sample was scanned, and the CT data was used to analyze the porosity of each sample. The researchers found that the weight of the samples was influenced by the temperature at which they had been printed – the higher the temperature, the heavier the part. Part quality also became higher at higher temperatures.
“An in-depth investigation was carried out on the internal geometry of the specimens at the ROI obtained from CT data,” the researchers state. “The lack of deposition resulting in bigger air gap was observed for the specimens fabricated at lower temperatures which confirms the results obtained from the weight measurement.”
The longitudinal filaments showed a lack of bonding at lower temperatures, as did the transverse filaments, although the transverse filaments had less of an effect on the strength of each part than the longitudinal ones. The porosity of each part decreased as temperature went up, as well.
“All the specimens were subjected to a uniaxial tensile load,” the researchers continue. “The results showed that the mechanical properties of PLA specimens are dependent on fabrication temperature. The specimens fabricated at lower temperatures had a higher percentage of elongation and lower yield stress. On the contrary, those fabricated at higher temperatures showed higher yield stress and lower strain at break.”
Overall, it was discovered that parts 3D printed at lower temperatures had greater air gaps in them, which decreased their strength, meaning that for strong parts, higher printing temperatures are ideal.
“Using CT, it was shown that the local density varies throughout the parts regardless of fabrication temperature,” the researchers add. “This means that FDM parts, even those printed at recommended temperature range with 100 % infill, do not achieve homogenous internal structure. Since the porosity is not distributed homogenously throughout the FDM parts, it is not the only parameter for assessing the strength of FDM parts; however, internal geometry features such as minimum cross-sectional area obtained from CT give better information for evaluating the expected strength of FDM parts.”
Authors of the paper include Amir Reza Zekavat, Anton Jansson, Joakim Larsson and Lars Pejryd.
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