Results: Tomography and Morphological Variations
Using an analysis software available with the scanner called CT-Analyser, it was possible to make measurements to determine the smallest of anomalies in the scanned objects. At first, the thickness of the layers of the scanned objects were measured. The results showed that the thickness was closer to the theoretical value. However, it also showed that each successive layer causes the print material to shrink , causing some layers to protrude outside the expected region, affecting the overall dimensions , and hence the surface quality, as seen in Fig. 8. The horizontal cross sections of 20% and 80% infill levels show that the infill doesn’t completely meet the wall of the object . As each successive layer is printed, the points where any two paths intersect show a higher amount of PLA deposition.
Fig 8 Uneven surface of a scanned hollow pink cone
The box plots of the average layer thickness in all the scanned objects and the average distance between consecutive edges in cones are compared as shown in Fig. 9. The horizontal lines in the middle of the plots indicate the median value. The layer thickness is a critical factor which directly affects the surface quality . The analysis shows that the layer thickness is close to the mean value, but always lesser than the expected value, indicating shrinkage; this is true for all scanned objects.
For a cone, each successive layer printed must be smaller than the previous layer under it, i.e., as they taper, their size gets consecutively smaller , hence the shape tends to worsen. The distances between the edges of two consecutive layers should be constant, since they are right circular cones. However, when this distance is measured using CT-Analyser, the values are highly inconsistent at all infill levels. This is especially visible in the upper layers of the cone in the scans, which can be seen in Fig. 8.
Fig. 9 Box plots of various measurements done on the scanned objects.
The tomographic images show irregularities in the final few layers of the cones, regardless of the infill. The pigmentation may influence certain properties , but they affect the surface quality the least. When the tomographic images from the natural PLA cylinder and pink PLA cylinder were compared, there was little to no difference in the surface evenness of their shell. However, it is to be noted that the insides of the hollow cylinders show the final layers sagging, in turn, leaving unnecessary frizzy material inside the shell, as seen in Fig. 5 and Fig. 6 in both pink and natural cylinders.
The infill doesn’t affect the surface quality of the object by much [3,21], as confirmed from the results in Table 2-4. The cylinder has an even surface. Even when it is hollow, the final layers are printed uniformly. The cones are uneven regardless of the infill, and their final layers tend to misalign. This is indicated by the tomographic scans, and the analysis from measuring the distances between two consecutive edges, which shows a high variability. The accompanied video shows the individual layers of a 20% infill pink cone. The transition of each layer (shown in light blue color) reveals unevenness in their edges since they are not perfectly circular, indicating surface roughness. The statistical experiment also repeatedly puts cones in the least ideal configuration, supporting the argument that tapered objects tend to have poorer surface quality.
References can be found in the Introduction section.