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Aihemaiti, et al.
of scheme 3 was 0.2 mm and the printing speed was the deposited line correlates with a greater deformation
50 mm/s, the deposited line was narrow and high, the of the thin plate, indicating a greater printing pressure.
high-temperature area was small (as shown in Figure 7), According to the width measurement of a single line
and the width was less than the print spacing. Thus, the printed in each scheme in Figure 5, the cross-sectional
adjacent materials could not be fully integrated, resulting widths of schemes 3, 5, and 9 were less than the outlet
in cracks along the height direction. diameter (0.4 mm) of the nozzle, indicating that the
extruded material fell on the sheet and was stretched
3.5. Analysis of printing pressure before solidifying. The sheet underwent only a relatively
Figure 8A shows the deformation contour of the sheet small deformation under the pressure of the filament
under the pressure of the extruded materials, which was extrusion.
captured by the 3DFSMS as detailed in Figure 1D. To In summary, the porosity was a key factor affecting
compare the deformation differences of each scheme the flexural strength. The cross-sectional geometries of the
directly, a section line was drawn perpendicular to the deposited lines printed by different process parameters were
movement direction of the nozzle. The displacement different, which led to different porosities. To be specific,
data on the section line were extracted for analysis. The the relationship between the widths of the deposited lines
process parameter with the maximum deformation of the and the center distance of two adjacent deposited lines
sheets showed a high bending strength. affected the specimen porosity. When the width of the
Figure 8 illustrates the pressure generation deposited line was less than the print spacing between
mechanism and sheet deformation when printing two adjacent deposited lines, a gap was created between
with different process parameters. The color cloud the two lines, and several parallel thin wall structures
diagram shows the deformation of the sheet captured were formed that were not connected after multiple-layer
by the 3DFSMS. The curve was a deformation curve stacking. Under the applied bending load, the thin-walled
corresponding to each scheme. The deposited line with structure was unstable, resulting in distortion and collapse
a flat cross-section extended to both sides of the nozzle of the specimen. When the cross-sectional width was
under the constraints of the surface around the nozzle greater than the print spacing, the two adjacent deposited
outlet. Under the pressure of the filament extrusion, lines could be fully fused, and when the cross-sectional
the molten material was squeezed into the previously width became larger, the porosity of the specimen became
deposited lines. The moving nozzle, which acted like an smaller. The printing temperature and pressure were
iron, was used to iron the molten filament. Therefore, the important factors for ensuring the full integration between
pressure that caused the deformation of the sheet included deposited lines. A higher temperature of the deposited lines
the pressure of the filament extrusion and the pressure of was more conducive to melting the surrounding solidified
the flowing melted material, which is called the printing materials. A higher printing pressure was more conducive
pressure in this paper. A larger cross-sectional width of to combining the melted materials.

A B C

D E F G

H I J K

Figure 7. (A) Schematic of temperature measurement on the bottom surface of the sheet. (B-K) Temperature measurement results and top
view appearance of the single deposited line of schemes 1-10.

International Journal of Bioprinting (2022)–Volume 8, Issue 1 161