Page 132 - MSAM-2-3

Materials Science in Additive Manufacturing
Figure 16. Cumulative particle-size distribution measured for each zone. reduction in fine particles minimizes agglomeration effects,
Figure 17. Particle-size distribution measured for each zone (first
replicate for each zone).
Figure 18. D-values for each zone.
Volume 2 Issue 3 (2023)
Powder alteration caused by L-PBF process
a dramatic degradation in their morphology: partial
melting, hard sintering, and agglomerations. The results of
this experiment had also been confirmed by Sutton et al.
[10]
who concluded that heat affects particles located near the
melt pool (zone 1). Consequently, heat-affected particles
become irregular in shape and coarser than particle
coming from unused powder. Recent studies [10,11,22,34,36,38]
on the effects of reusing powder show that the PSD shifts
rightward toward large particles after reuse cycles. In
addition, the proportion of fine particles drops, whereas
the proportion of bigger particles grows. Consequently, we
can establish a similarity between the powder alteration
caused by the proximity of printed parts and reuse cycles;
the smaller the distance between printed parts, the more
the powder is altered. Many authors [1,5,25,27] claim that the
which improves powder flowability. However, a decrease in
the smallest particles and the presence of coarser particles
may be responsible for an increase in the percentage of
void within the powder bed so that the printed part can be
impacted by a lack of fusion [5,11] .
3.3. Results of experiment 3: PSD changes when
printing lattice structures of different cell sizes
Figure 4 shows the four lattice cylinders printed with varying
cell sizes of 2 mm, 3 mm, 4 mm, and 5 mm. The powder
samples are extracted from the lattices at the locations
indicated by the yellow arrows. As mentioned above, and
to evaluate the repeatability of the measurements, four
samples of the powder trapped in each lattice structure
were analyzed.
The PSD of the four different lattice cell sizes is not
superposed, as shown in Figure 19. The PSD of powder
trapped in the 2-mm-cell lattice shows a lower proportion
of tiny particles than in the 5-mm-cell lattice. This finding
is similar to the results of experiment 2, which reported
a relevant decrease in small particles as the distance of
spacing between parts was reduced.
Changing the cell size of the lattice, as described in
Table 2, varied the area and volume ratios of the printed lattice
cylinders. Figure 20 illustrates that increasing the cell size
from 2 mm to 5 mm decreased the average diameter D-values
D90, D50, and D10 by 6%, 12%, and 16%, respectively. The
coefficients of variation on the measurements of the four
samples for each lattice cell are <3.9%, <3.0%, and <4.2% on
Dv90, Dv50, and Dv10, respectively.
When printing the lattice cylinders, the powder had
already been recycled 11 times. Figure 21 illustrates the
evolution of powder diameter values when comparing
the diameter values of new powder with the diameter
9 https://doi.org/10.36922/msam.1781