Page 47 - MSAM-3-3

Materials Science in Additive Manufacturing MEX optimization printing of rHPDE from milk jugs

2.3.2. Printing at different speeds was set at 30 – 45°C at 5°C intervals. The 20 × 20 × 2 mm

A hot-pressed rHDPE sheet was placed over the PEI surface square models were printed using different combinations
of the print bed after identifying the suitable print bed of PBT and PT. Each square model was printed on two
material for printing rHDPE. All printing parameters were separate pieces of 60 × 60 mm vHDPE sheets (Figure 3).
generated based on the ABS standard profile in the slicer The ends of each specimen were then loaded into tensile
program. If the initial print is unsuccessful, adjustments grips (Figure 3). The specimens were pulled at 5 mm/min
would be made to the print parameters as indicated in the until either failure of the part or adhesion to the print
results to achieve better print outcomes. The PBT was set bed. In cases where adhesion to the print bed fails before
to 24°C (room temperature) and the PS was set to 5, 14,16 15, the part, the shear strength of the print bed adhesion is
and 50 mm/s. Notably, 5 mm/s is a reduced PS compared calculated using Equation I.
to the standard ABS profile for the LulzBot MEX 3D Peak shearing load
Printer, while 15 and 50 mm/s are considered as the PS Shear strength = Failure area (I)
for subsequent layers in the ABS profile. Finally, the test
was repeated at 5 mm/s PS and at an elevated PBT of 40°C, 2.4. Statistical analysis
following the recommendation of Sun et al., to determine
17
if elevated PBT can yield better print outcomes. Linear regression was utilized to determine the adequate fit
of relationships based on the R value obtained. Microsoft
2
2.3.3. Printing on print beds with different surface Excel was used to illustrate the analytical results obtained
roughness from the linear regression.
A vHDPE sheet of 4-mm thickness was applied over the 3. Results
PEI surface of the print bed. The Ra of the vHDPE sheet
was 0.075 μm, measured using TalyScan 150 (Taylor 3.1. Recycling milk jugs into filament for extrusion
Hobson, United Kingdom). All printing parameters were The process of extruding rHDPE filament with Filabot
generated based on the ABS standard profile in the slicer Original is challenging, as it was not originally designed
program. The PT was adjusted from 210 to 240°C at 10°C for HDPE or rHDPE extrusion. After several attempts
18
intervals, while the PBT was set at 24 (room temperature) using different flake sizes (3 – 10 mm), filaments were
and 50°C accordingly. Only 20 × 20 × 5 mm square successfully produced with a diameter of 2.85 – 3.00 mm at
17
models were printed using different combinations of PBTs an extruder temperature of 190°C. This was achieved using
and PTs. After each print, the part was manually peeled off small flakes of ≤6 mm while considering the effort required
to assess its removability by hand.
For the subsequent prints, another vHDPE sheet
of 4-mm thickness was layered over the PEI surface of
the print bed. This time, the vHDPE sheet surface was
manually roughened with grit 400 sandpaper, resulting in
a Ra of 0.696 μm. Similar to previous prints, all printing
parameters were generated based on the ABS standard
profile in the slicer program. The PT was set at a range
from 210 to 240°C at 10°C intervals, and the PBT was set
at 24 (room temperature) and 50°C accordingly. The 20
× 20 × 5 mm square models were printed using various
combinations of PBT and PT. After each print, the part was
manually peeled off to evaluate its removability by hand.

2.3.4. Printing on different print beds and PTs
This test investigated the effect of different PTs and PBTs
on print beds with different Ra. vHDPE sheets (60 × 60 ×
4 mm) were manually roughened with grit 400 sandpaper,
resulting in Ra levels of 0.4 – 1 μm, measured using
TalyScan 150. All printing parameters were generated
based on the ABS standard profile in the slicer program. PT Figure 3. Square models (20 × 20 × 2 mm) were printed on two separate
was adjusted from 220 to 235°C at 5°C intervals, while PBT pieces (60 × 60 mm) of the high-density polyethylene shear test setup

Volume 3 Issue 3 (2024) 4 doi: 10.36922/msam.4084