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@PHDTHESIS{LopezDAngelo:819672,
author = {Lopez-D'Angelo, Olfa},
othercontributors = {Brillo, Jürgen and Senk, Dieter and Meyer, Andreas},
title = {{P}owder-based additive manufacturing for space : from
granular rheology in varying gravitational environment to
the development of a gravity-independent powder handling
method},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2021-05200},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2021},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2021},
abstract = {As human reach into space expands, need arises for
versatile technologies, working under extreme conditions –
notably, in absence of gravity. In-Space Manufacturing (ISM)
would allow payload optimisation by enabling on-demand
production of tools, spare parts or building elements,
increasing self-sufficiency of long-endurance missions.
While powder-based three dimensional (3D) printing processes
offer high printing quality and adaptability to multiple raw
materials, for all techniques available today, constrains
remain on feedstock flow properties and recyclability of
base-material. The work presented here proposes a new method
for handling and additively manufacturing granular
materials, independently of the gravitational environment,
and emancipating from requirements on powder-feedstock flow
properties. Technical evolutions go hand in hand with an
understanding of the physical phenomena that underlie them.
The development of a powder-based Additive Manufacturing
(AM) process was hence preceded by a study of the factors
influencing granular rheological response. To be used as
demonstrator, a spherical polystyrene (PS) powder was
modified to increase its surface roughness, resulting in two
powders similar in all respects but their surface state. The
link between physical and rheological properties of powders
was explored, through typical rheometry tests (flow start-up
and stationary flow curves, powder-bed tensile strength),
but also through phenomenological testing methods found in
industrial applications (notably the flow energy test).
Observing and quantifying essential differences in
flow-behaviour emerging from this modification of the
frictional interactions between particles, allowed to
approach the ill-defined concept of powder flowability, to
propose a definition which encompasses not only the inherent
powder physical properties, but also the environmental
factors surrounding the material. To query the influence of
such environmental factors, the same powder was used to
study the effect of gravity (and absence thereof) on
piston-probing of granular material. Using parabolic flight
as a microgravity platform, this experiment revealed that,
in absence of the secondary force field provided by gravity,
powder flow deteriorates and packing fraction at jamming
lowers, with dramatic consequences for powder handling in
reduced gravity. Results from this first experimental
campaign led to the design of the mentioned AM process. To
deposit the granular base-material, this process uses solely
driving mechanisms in- dependent of gravity (namely shear
and shaking). To allow versatility in feedstock material’s
flow-behaviour, adaptability of the process printing
parameters was implemented through a control loop fed by
in-situ probing during powder handling. The material
deposition method was first validated through Discrete
Element Method (DEM) simulation, showing no dependence of
the process efficiency on the gravitational environment, nor
on the increased interparticle cohesive forces. Experimental
demonstration was also provided, through the construction of
two prototype 3D printers, used on-ground and on parabolic
flights to manufacture parts from the two powders mentioned
above: PS powders of high and mediocre flowability. The
successful manufacturing of parts under gravity as well as
in weightlessness, from both powders, regardless of their
flow properties, represents the main achievement of this
work. X-ray computed tomography (CT) analysis of the
sintered parts showed no systematic change in porosity
between the samples manufactured under different
gravitational environments, with near-perfect density and
isotropic porosities. Parts were also produced directly from
recycled material (under 1g), obtained by closed-loop
recycling of former 3D printed parts; an achievement that no
commercially available additive manufacturing process to
date could realise, and that will be a critical asset for
increasing the self-sustainability of space exploration
missions. The work presented lead to filing a patent in
September 2020, endorsed by the German Aerospace Center,
under the application number 10 2020 123 753.7 for an
“Apparatus and Method for Additive Manufacturing of
Components in Environments with Various Gravitation- levels
and with Materials of Different Flowability”.},
cin = {526110 / 520000},
ddc = {620},
cid = {$I:(DE-82)526110_20140620$ / $I:(DE-82)520000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2021-05200},
url = {https://publications.rwth-aachen.de/record/819672},
}
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