Page 48 - MSAM-3-3

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

for manual cutting. Initial attempts to extrude the filament used in the preliminary tests, which were found to have
were unsuccessful due to the excessive moisture absorbed impurities that could have affected the printing outcomes.
by the flakes from over-handling, thus affecting the melting For the smooth print surface (Table 2), only two
consistency in the heating chamber. It is important to keep permutations of settings successfully produced parts that
the flakes as dry as possible before feeding them into the meet the desired conditions. These conditions require
hopper to ensure a smooth, consistent flow. Throughout (i) the first print layer to adhere to the print bed during
the process, the Airpath was maintained at 39% of its printing and (ii) the part to be easily removed from the
maximum fan speed, and the temperature directly above print surface after printing (preferably by hand). For the
the Airpath was maintained at 21.8°C.
roughened print surface (Table 3), seven permutations of
3.2. Optimization of MEX print parameters for settings were found to meet both these desired conditions.
rHDPE
3.2.4. Printing with different print beds and PTs
The findings from the four tests conducted on various
types of print bed materials, PS, print quality on surfaces During these tests, a total of 16 permutations of PT and PBT
with different degrees of roughness, and variations in PBTs settings were explored. Out of these 16, 11 tests resulted
and PTs are described in the following sections. in print bed adhesion failure. The remaining five tests
reported part failure, which indicated that the adhesion
3.2.1. Printing on different print bed materials strength was greater than that of the part and thus was not

From testing on various surfaces, such as the PEI board, further examined. The peak shear load and failure area for
vHDPE sheet, hot-pressed rHDPE sheet, masking tape these prints were recorded (Tables 4 and 5, respectively).
backing on the PEI board, double-sided tape on PEI The resultant shear strength of the print bed adhesion
board, ABS board, and the paper side of the foam core, was then calculated using Equation I and summarized in
it was observed that print detachment from print bed Table 6.
occurred on all these surfaces after printing different 4. Discussion
number of layers, except for the prints on the rHDPE and
vHDPE surfaces, where complete prints were achieved 4.1. Recycling milk jugs into rHDPE filaments
(Table 1). After several attempts to extrude the filament using the
3.2.2. Printing at various speeds different flake sizes, it was observed that it is important to
maintain the spooling speed slightly faster or at a similar
A single layer of the model was printed at PS of 5, 15, and speed to the extrusion rate to achieve constant filament
50 mm/s, with varying degrees of success. It was observed diameters. However, inconsistencies in the feed material
that the printed path of materials began to break while can lead to erratic extrusion rates, highlighting the need to
printing the first layer at 50 mm/s. There was no breaking preprocess the flakes to an appropriate size before feeding
of filament while printing the first layer at 15 mm/s, but them in the hopper. Furthermore, keeping the hopper
the filament was sliding on the print bed during the print constantly filled during operation ensures a consistent
as the filament did not adhere sufficiently to the surface of material feed into the extruder and maintains a steady
the hot-pressed rHDPE sheet. At 5 mm/s, the sliding was extrusion rate.
reduced, but the print detached from the print bed soon
after being printed. When working with HDPE flakes, it is important
to prevent moisture from coming into contact with the
According to Sun et al., the temperature profile of surface. Excessive handling or touching the flakes with
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the print significantly affects bond formation and print bare hands can introduce unwanted moisture, adversely
bed adhesion. In a test where parts were printed at PS affecting melting consistency and extrusion rate. It is best
of 5 mm/s and PBT of 24 (room temperature) and 40°C, to keep the flakes as dry as possible while filling the hopper,
the prints at PBT of 24°C did not adhere well to the print and it is recommended to thoroughly dehydrate the flakes
bed, while complete prints were achieved with sufficient
adherence at PBT of 40°C. in the oven just before placing them into the hopper.
Using smaller flake sizes provides better consistency
3.2.3. Printing on print bed with different surface in terms of extrusion rate and filament diameter. Flakes
roughness larger than 6 mm cause more “popping” or expulsion from
A 4 mm vHDPE sheet was placed over the PEI surface the feeder and obstruction within the hopper, resulting
of the print bed to ensure better reliability of the results in a less smooth material feed and flow into the heating
compared to those of the hot-pressed rHDPE sheets chamber. In all subsequent tests, the selected flake size for

Volume 3 Issue 3 (2024) 5 doi: 10.36922/msam.4084