Page 87 - MSAM-1-3

Materials Science in Additive Manufacturing Increasing density and strength in binder jetting

due to debinding caused by outgassing . A higher sinter (v) In the bimodal groups of this study, statistical
[19]
temperature should be considered to facilitate mass transport differences in density and UFS between the
and increase the part density . In addition, this study did groups were not observed.
[42]
not optimize binder saturation, rolling speed, and other (vi) It was found that in unimodal powders, density
process parameters. Based on other reported studies, higher decreases as particle size increases, despite the
density values have been obtained by appropriately selecting lack of statistical differences within the unimodal
specific process and thermal parameters that would enhance group. The 10 µm group had the highest density
the printing performance [2,14] . Future work should focus on and was found to be the only group having
finding different parameters and adjusting them for density statistically higher particle size compared to the
increases, as well as investigating the impact of sintering 30 µm group (by 11.18%). This indicates that
profiles and their effect on bimodal distributions as they are finer particles could result in higher density
directly affected by powder properties and packing state.
within unimodal particle sizes.
6. Conclusions (vii) UFS followed a similar trend to density within

The goal of this study was to evaluate the impact bimodal the unimodal group; as particle size increases,
distributions in binder jetting of SS316L feedstock. Six UFS decreases. The 10 µm group was found to
different particle distributions, that is, four unimodal have statistically higher UFS than the rest of the
(10 µm, 20 µm, 30 µm, and 40 µm) and two bimodal (30 unimodal groups.
+ 10 µm and 40 + 10 µm), were compared. An ExOne (viii) Slight variation in the trend among observed
Innovent + was used to print four cylinders and five unimodal density trend and across groups in
bars per particle size group. The samples were cured and UFS could have been caused by variability during
sintered; cylinders were used to calculate density and bars sintering.
were used for 3-point bending using weight and XCT data. Future work should optimize the printing parameters
Density and UFS (through 3-point bending tests) were of the bimodal groups to achieve the highest possible
used to compare the impact of the particle distribution. density and UFS. In addition to different sintering profiles
The measured UFS was compared with the MD simulations and sample position, the effects of gas flow rate during
using the ReaxFF potential. Based on the results, the main sintering should be further investigated. Finally, the effect
conclusions are as follows:
of powder binder interaction in bimodal distributions
(i) A bimodal powder distribution is preferred over could be investigated both through MD simulation and
unimodal distribution in binder jetting of SS316L, experimental efforts, including in-process monitoring.
for higher density and preferred mechanical
performance. Acknowledgments
(ii) Bimodal groups were statistically denser than the The authors acknowledge the support from the ExOne
unimodal groups, achieving an average increase Company, The Pennsylvania State University, Tim Stecko,
in density of 20%. and Verder Scientific for their assistance.
(iii) Bimodal groups showed a higher UFS than the Funding
unimodal groups. Both the 30 + 10 µm and
40+10 µm groups had an average increase of This work was funded by NSF CAREER CMMI #1944120
170% in UFS when compared to the 10 µm group, and partially by Manufacturing PA program.
which saw the highest UFS out of all unimodal
groups. According to the MD simulations, Conflict of interest
the fine powders in the bimodal groups filling There are no conflicts of interest to declare.
the interstitial space provided extra bonds to
strengthen the sintered part. Author contributions
(iv) UFS followed the same trend observed in Conceptualization: Ana Paula Clares, Adri C.T. van Duin,
ReaxFF-MD simulation of bimodal powder size and Guha Manogharan
distribution. The improvements in mechanical Formal analysis: Ana Paula Clares and Ryan Stebbins
strength was greater than predicted MD Funding acquisition: Guha Manogharan
simulation results which could be attributed to Investigation: Ana Paula Clares
higher number of fine particles in ASTM standard Methodology: Ana Paula Clares
size samples when compared to MD simulations. Project Administration: Guha Manogharan

Volume 1 Issue 3 (2022) 9 https://doi.org/10.18063/msam.v1i3.20