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TENSILE MECHANICAL PROPERTIES OF POLYPROPYLENE COMPOSITES
FABRICATED BY MATERIAL EXTRUSION
Narumi Watanabe1, Meisha L. Shofner2 and David W. Rosen1,3
1 George W. Woodruff School of Mechanical Engineering, Georgia
Institute of Technology, Atlanta, GA 30332,
[email protected], www.me.gatech.edu
2 School of Materials Science and Engineering, Georgia Institute
of Technology,
Atlanta, GA 30332, [email protected],
www.mse.gatech.edu
3 Engineering Product Development, Singapore University of
Technology and Design, Singapore 487372, [email protected],
epd.sutd.edu.sg
Keywords: Polypropylene composites, Material extrusion, Additive
manufacturing, Tensile
properties, Process simulation
ABSTRACT
In the material extrusion additive manufacturing process, a thin
filament of material is deposited in a layer-by-layer manner to
fabricate a three dimensional part. The filament deposition pattern
can result in voids and incomplete bonding between adjacent
filaments in a part, which leads to reduced mechanical properties.
Further, the layer-by-layer deposition procedure typically results
in mechanical property anisotropy, with higher properties in the
layer compared to those across layers. The study reported in this
paper explored various polypropylene composite formulations to
address these issues: low residual stress and warpage, good
mechanical properties, and reduced anisotropy. The reduction in
anisotropy will be the focus of this paper as a function of thermal
properties and process variable settings. A series of process
simulation models was developed to explore ranges of thermal
properties and process settings, which provided insights into
tensile specimen behaviors. Results demonstrate that anisotropy can
be reduced almost completely if the material can be formulated to
have low crystallinity, low coefficient of thermal expansion, and
moderate to high thermal conductivity (for a polymer).
1 INTRODUCTION
During the material extrusion (MEX) process, the part goes
through a repetition of heating and cooling as the filament is
liquefied in the liquefier chamber and is deposited onto a build
platform to fabricate a three-dimensional part [1]. This filament
deposition procedure causes voids to form in each layer, which
reduces mechanical properties in the part. Furthermore,
layer-to-layer bonding tends to be weaker than the filament
strength, causing significant variations in mechanical properties
in the layer vs. out-of-plane. In this paper, mechanical properties
in tension of material extrusion fabricated parts are investigated
as a function of process settings and material composition.
One of the challenges in material extrusion is the limited
availability of materials. With additive manufacturing (AM)
processes, many of the part geometries that are unachievable using
conventional manufacturing processes can be realized. As different
material compositions are investigated, AM technology will be
improved further by expanding the portfolio of available materials.
Polypropylene, a widely used thermoplastic that is inexpensive and
flexible compared to acrylonitrile-co-butadiene-co-styrene (ABS),
is the material of interest of this study. However, polypropylene
is a semicrystalline thermoplastic unlike ABS, which is an
amorphous thermoplastic, and there are processing issues associated
with material extrusion of polypropylene. The molecules in
semi-crystalline thermoplastics are drawn together and ordered
during the crystallization process, so they shrink more than
amorphous thermoplastics upon solidification [2]. This increased
shrinkage causes parts that are fabricated with polypropylene to
warp more and detach from the build platform, compared to those
with ABS.
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Solid Freeform Fabrication 2017: Proceedings of the 28th Annual
International Solid Freeform Fabrication Symposium – An Additive
Manufacturing Conference
Reviewed Paper
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Alternatives to reduce warpage are to create polypropylene-based
composite materials by combining polypropylene with additives
and/or investigate polypropylene copolymers with reduced
crystallinity. Several types of additives exist, such as particles,
fibers, and agents that affect viscosity and thermal conductivity.
In this study a total of 10 polypropylene formulations were
investigated, of which 5 showed promise as a MEX material and were
processable in our Hyrel System 30M machine [3]. Several composite
formulations for some of these five polypropylenes were tested. Two
materials were investigated further since they exhibited similar
lack of warpage for their 3D bonding and mechanical properties.
Although the materials processed equally well, they exhibited
substantially different surface finish and levels of anisotropy in
tensile mechanical properties. In this study, layer thickness,
deposition (extruder) temperature, and fill angle were varied for
the tensile specimens, while yield and ultimate strength and
elastic modulus were measured. Note that all specimens were
fabricated flat and horizontally.
2 LITERATURE SURVEY
Mechanical properties of parts fabricated using material
extrusion are of great interest, as is the reduction in anisotropy.
As is well recognized, properties are typically higher for parts
built in the XY plane, compared to properties in the Z direction,
since Z direction properties depend entirely on filament bond
strength. In this process, bonds are weaker than filaments. Many
researchers have investigated mechanical properties of MEX parts.
In an early study, Rodriguez et al. [4] quantified the effects of
mesostructure (road deposition pattern and pore size) on tensile
strength and compared with monofilament strength. They also related
process variables to pore size and mesostructure in order to
identify process settings that maximize part strength through an
understanding of bonding potential [5]. Sun et al. [6] showed that
a correlation exists among road-to-road neck radius and flexural
strength of test specimens which helps to explain these
results.
More recently, a group tested tensile properties of parts in a
Dimension system (Stratasys) with the ABS-M30 material [7].
Specimens were built flat, on edge, and vertically at various
angles and tests indicated that properties were anisotropic,
particularly for tensile strength. Parts built vertically were the
weakest, as expected, since their strength was primarily dependent
on bond strength between layers. Additionally, for the
perpendicular specimens, the high surface roughness caused by layer
boundaries and internal pores may have acted as stress
concentrations and fracture initiation sites, which caused lower
strength. Elastic modulus was fairly uniform across all sets of
specimens and all orientations; interestingly, the highest values
were for parts built vertically. It is important to note that
elongation at break was highly dependent on orientation, with
results of 7% for XZ orientation, while ZX orientations exhibited
elongation of only 2%. These results are consistent with the
Stratasys ABS-M30 specification sheet [8]. This trend indicated
that while vertically built specimens may be stiff, they failed
much earlier (lower load, less strain) than parts in other
orientations.
Another group investigated tensile and compressive properties,
as well as failure mechanisms, of ABS specimens built on a Zortrax
M200 machine [9]. Similar anisotropic properties were reported.
Failure mechanisms included ductile failures for some specimen and
fill orientations, while other orientations exhibited fracture
along filament interfaces, particularly for vertically built
specimens. Compression results also exhibited anisotropy.
Of interest in this paper is research on polypropylene (PP)
materials. One group compared tensile properties of two
commercially available PP homopolymer extrusion grade materials,
one a neat PP formulation and the other a glass fiber reinforced PP
[10]. Specimens were fabricated on a Prusa i3, available from the
RepRap platform. The authors reported significant part shrinkage
and warpage. They investigated various fill orientations, infill
percentages, and layer thicknesses; all specimens were built flat
and horizontally. Tensile properties for the neat PP exhibited
anisotropy for different fill orientations, which is consistent
with ABS results referenced above. In contrast to [9], a larger
layer thickness resulted in high ultimate strength. Little was
reported about the glass fiber PP, except to compare strength and
Young’s modulus to the neat PP; properties for the glass fiber PP
were significantly better. Another recent study [11] investigated
impact strength of a different PP homopolymer composite material,
where specimens were fabricated on a Makerbot Replicator 2X.
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Two different extrusion temperatures (200, 250 °C) and layer
thicknesses (0.1, 0.3 mm) were investigated. Results showed that
specimens fabricated at the lower extruder temperature had
significantly higher impact strength, which was comparable with
injection molded specimens of the same material. X-ray diffraction
experiments showed that the specimens extruded at 200 °C has high
β-crystal content (75%), compared to 5.6% (0.3 mm layers), 11.4%
(0.1 mm layers), and 4.6% (injection molding). Apparently, the
higher crystallinity of the specimens extruded at the lower
temperature compensated for the higher density of the injection
molded specimens.
3 MATERIAL FORMULATIONS
During this research, ten different neat polypropylene-based
polymers were investigated. Out of those, test specimens were
successfully fabricated on our HYREL System 30M (HYREL 3D) with
five of the polypropylenes (Polypropylenes A through E). The top
and side views of the test specimens as well as percent
crystallinity are presented in Table 1. Process variables under
investigation included layer height, deposition temperature, and
filament deposition angle. These five polypropylenes (two
homopolymers and three copolymers) were studied and various
composite materials were formulated with them using common filler
materials. Note that sponsor restrictions prohibit publishing the
specific material formulations. After screening based on printed
part quality, two copolymer polypropylenes (C and D) were
identified as favorable for further study. Although PP E had the
smallest crystallinity and little warpage, printed parts did not
exhibit good dimensional integrity; hence PP E was not selected for
further study.
Table 1. Test specimens and percent crystallinities of candidate
neat polypropylenes
Polypropylene Test Specimen % Crystallinity
Polypropylene A
52
Polypropylene B
39
Polypropylene C
34
Polypropylene D
13
Polypropylene E
10
Since polypropylene is a semi-crystalline thermoplastic polymer,
it experiences a higher degree of
shrinkage upon cooling than ABS, which is amorphous. This
increased shrinkage led to increased part warpage, so polypropylene
polymers with different levels of crystallinity were explored.
Table 1 shows that warpage was indeed related to the percent
crystallinity of the material. Polypropylene A had the highest
percent crystallinity, and its test specimen showed the most
warpage. In fact, the part fabrication with Polypropylene A could
not be completed since it detached from the build platform
completely during the fabrication process. In contrast,
Polypropylene D and E had the lowest percent crystallinity and
their test specimens showed the least warpage.
The addition of additives, such as particles and fibers, can
reduce shrinkage, warpage, and residual
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stress. Two mechanisms are typically credited with these
reductions: mechanical interference with shrinkage and prevention
of crystal formation. Several types of additives were explored in
Polypropylenes C and D, such as particles, fibers and agents that
affect viscosity and thermal conductivity. One composite material
(Polypropylene C1) was created with Polypropylene C as the base
material, and three composite materials (Polypropylenes D1 through
D3) were created with Polypropylene D as the base material. Test
specimens were fabricated with these composite materials as well,
but no significant differences in warpage were observed with
respect to each other. Polypropylenes D1 and D2 will be explored
further in this paper.
4 MATERIAL EXTRUSION SIMULATION
A series of simulation models has been developed and validated
in our lab recently [12], which built on the work of others, e.g.,
[13, 14]. The objective of these models is to predict temperature
distributions, deposited filament shapes, residual stresses, and
warpages/deformations of fabricated parts. Inputs include material
properties, process variable settings, and process conditions. A
commercially available polypropylene-based polymer was used here as
a model system for study. The simulation model overview is
presented in Figure 1.
The simulations were developed using ANSYS® Polyflow and
Mechanical. To capture the thermal processes experienced during
material deposition, several simulations were developed, and these
sequential simulations were linked to one another through the
temperature profiles developed in previous steps. A final
simulation was developed using ANSYS Mechanical to predict residual
stresses and warpage. Each simulation model will be summarized
here; additional information is available in references [12,
15].
The first simulation model was the deposition and cooling of the
first layer of filament. The first layer was deposited onto a build
platform, which was assumed to be at a constant temperature of 80
°C. By applying the calculated volumetric flow rate at the nozzle
entrance and gravitational force, and using the remeshing technique
in ANSYS® Polyflow, the deposition of the first layer was
performed. In this simulation model, the filament was extruded
through the nozzle in the vertical direction, while the deposition
velocity was applied in the horizontal direction. In order to
simulate the relative motion between the nozzle and the build
platform, the nozzle was maintained in a fixed position, while the
build platform translated in the horizontal direction with a
deposition velocity.
The second simulation model was the deposition of the second
layer of filament on top of the first layer and the cooling of both
layers. The temperature distribution after the first layer cooling
was exported from the previous simulation. Conduction heat transfer
between the two layers was accomplished using the fluid-to-fluid
contact capability in ANSYS® Polyflow.
Figure 1. Overview of material extrusion process simulation
models
5 MATERIAL PROPERTIES
Although test specimens with polypropylene-based composite
materials showed no significant differences in warpage with respect
to each other, differences in surface finish were observed, which
was related to the bonding between the extruded filaments. The
surface topography of test specimen
Inputs•Material Compositions and Properties
•Process Variable Settings•Process Conditions (Initial and
Boundary Conditions)
Outputs•Temperature Distributions•Deposited Filament
Shapes•Residual Stresses•Warpages/Deformations
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was examined for each composite material using a SEM. The two
extreme cases of surface finish are shown in Figure 2. The
topographies are shown of the top surface and the cross section of
the test specimens fabricated with Polypropylenes D2 and D1. The
surface finish and bonding quality of Polypropylene D2 were
remarkable as all of the extruded filaments seemed to have
coalesced. The lumps on the top surface indicated each extruded
filament, but no voids were visible from the SEM image. In
contrast, the surface finish and bonding quality of Polypropylene
D1 were poor as each extruded filament could be distinguished in
the SEM image and broke during SEM specimen preparation.
(a)
(b)
Figure 2. Images of (a) top surface of Polypropylene D2 and (b)
cross section of Polypropylene D1
One of the disadvantages of MEX is known to be the pronounced
anisotropy of mechanical
properties of fabricated parts that is caused by incomplete
bonding between the extruded filaments as well as preferred
orientation of polymer chains and crystals due to the imposed flow
[4, 16]. However, no voids were observed in the test specimen
fabricated with Polypropylene D2, which meant that a complete
bonding was accomplished between the extruded filaments and a solid
part was created. This suggested that anisotropy was perhaps
reduced with this composite material. In order to investigate this
phenomenon further, tensile tests were conducted using
Polypropylene D2.
For completeness, properties of Polypropylene D2 are presented
in Table 2 [12].
Table 2. Material properties of polypropylene copolymer
Viscosity Expression 𝜂𝜂 = 𝑒𝑒�1318.9�1𝑇𝑇−
1503.15��3346.4(�̇�𝛾)−0.54
Coefficient of Thermal Expression 1.50 x 10-4 m/(m-°C) Thermal
Conductivity 0.2 W/(m-°C)
Specific Heat 1920 J/(kg-°C) Density 900 kg/m3
Melting Temperature (Tm) 151.0 °C Crystallization Temperature
(Tc) 104.0 °C
6 MECHANICAL PROPERTY ANISOTROPY
Tensile experiments were performed to determine tensile strength
at yield, tensile strength at failure, and elastic modulus for
Polypropylene D2. Correlations between mechanical property
anisotropy and the bonding quality of extruded filaments were
examined experimentally by producing tensile property data of
fabricated parts with different fill angles. The efficacy of the
process
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simulation models was evaluated by comparing the experimental
and simulation model results.
By producing tensile property data with different fill angles,
the filament bonding performance can be tested and the degree of
anisotropy can be assessed. Thin flat strips of material (12.5 mm x
87.5 mm) having a constant rectangular cross section were
fabricated with two fill angles, 0° and 90° and were tested
following a method similar to ASTM D3039/D3039M-14 [17]. Standard
“dog bone” specimens were not used in order to avoid the stress
concentrations that occur where along the curved regions between
the gauge and grip regions of the specimen. The 0° fill angle
specimens were fabricated without perimeters, but the 90° fill
angle specimens required three perimeters since the fabrication
process was unsuccessful without them. The schematics of fill
angles are shown in Figure 3. Five specimens were tested using an
Instron 5566 at a speed of 20 mm/min in order to produce failure
within approximately 1 to 10 minutes.
Representative stress-strain curves with yield and filament
failure points with 0° and 90° fill angles are shown in Figures 4
and 5, respectively. Yield point was defined according to the
testing standard as the first point on the stress-strain curve at
which an increase in strain occurs without an increase in stress.
The filament failure point was estimated to be the point where
filaments began to fail during the test. Since these test specimens
deformed differently over the entire length of the sample between
the grips, the nominal strain was calculated and was used on the
stress-strain curves. The nominal strain was calculated by dividing
the crosshead extension by the distance between grips, which was
62.5 mm. It should be noted that the test specimens with a 0° fill
angle never failed during this test. Instead, the specimens
continued to extend until they were too thin for the Instron
machine to grip.
(a) (b)
Figure 3. Anisotropy test specimens: (a) 0° fill angle and (b)
90° fill angle
Figure 4. Stress-strain curve of Polypropylene D2 with a 0° fill
angle
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Figure 5. Stress-strain curve of Polypropylene D2 with a 90°
fill angle
Various deposition temperatures and layer heights were also
explored to see if these process variable settings affect
mechanical property anisotropy and filament bonding performance.
The settings are summarized in Table 2.
Table 2. Process variable settings for mechanical property
anisotropy
Process Variable Settings Values
Deposition Temperature 240 °C 260 °C 280 °C Layer Height 0.1 mm
0.2 mm -
6.1 Deposition Temperature
From the stress-strain curves, tensile stress at yield point,
tensile stress and nominal strain at filament failure point and
modulus of elasticity were determined with various deposition
temperatures, and are shown in Figures 6-9, respectively. In this
case, the layer height was kept constant at 0.2 mm. Since there
were overlaps of the error bars, statistical analyses were
performed on these experimental results. Single factor analysis of
variance (ANOVA) was run to test the null hypothesis that the means
are all equal. For all four plots, the means were determined to be
statistically equal for each fill angle. Tensile stress, nominal
strain and modulus of elasticity with both 0° and 90° fill angles
were not dependent on temperature.
At 240 °C, the tensile stress at yield point was higher with a
0° fill angle than with a 90° fill angle, which implied that
anisotropy existed at this temperature. When the deposition
temperature was increased to 260 °C and 280 °C, the tensile
stresses at yield point were determined to be statistically equal.
A similar trend was observed with the tensile stress at filament
failure point in Figure 7. At 240 °C and 260 °C, the tensile
stresses were higher with a 0° fill angle compared to a 90° fill
angle. However, statistical analysis showed that they are equal at
280 °C. Therefore, a reduction in anisotropy was accomplished by
increasing the deposition temperature. In addition, the typical
value of tensile stress at yield point of Polypropylene D is 15.8
MPa, which is slightly lower than the base polypropylene.
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Figure 6. Tensile stress at yield point with various deposition
temperatures
It can be observed from Figure 8 that the tensile nominal strain
at filament failure point was highly dependent on fill angle. The
nominal strain with 0° fill angle was approximately 5.1 mm/mm, and
that with 90° fill angle was approximately 0.2 mm/mm. Although
there were differences between the strain values, those with a 0°
fill angle were significantly higher compared to those with a 90°
fill angle. In addition, the typical value of elongation at break
of Polypropylene D was reported to be 617%; the elongation at break
for Polypropylene D2 with 0° fill angle was approximately 17% lower
than the base polypropylene.
Figure 7. Tensile stress at filament failure point with various
deposition temperatures
Figure 9 shows that the modulus of elasticity was fairly uniform
and was not dependent on fill angle, although tensile nominal
strain at filament failure point is highly dependent on fill angle
as previously stated. It was determined that the moduli of
elasticity with different fill angles were statistically equal at
each temperature as well. This was due to consistent nominal strain
values in the elastic region, and the range of nominal strain was
approximately 0.005 and 0.015 mm/mm in all cases. However, the
average value of modulus of elasticity with 0° fill angle was
approximately 383 MPa, and that with 90° fill angle was
approximately 357 MPa, which was a 7% decrease. The flexural
0
2
4
6
8
10
12
14
16
240 °C 260 °C 280 °CTen
sile
Str
ess a
t Yie
ld P
oint
[MPa
]
Temperature [°C]
0° Fill Angle
90° Fill Angle
0
2
4
6
8
10
12
14
16
240 °C 260 °C 280 °C
Tens
ile S
tres
s at F
ilam
ent F
ailu
re
Poin
t [M
Pa]
Temperature
0° Fill Angle
90° Fill Angle
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modulus of Polypropylene D, the base material of this composite
material, was slightly higher than the experimental data of the
fabricated parts with a reported value of 393 MPa. In addition,
Stratasys reported the tensile modulus of ABS-M30 was 2,230 MPA for
0° fill angle, while 90° fill angle exhibited tensile modulus of
2,180 MPa, which was a 2% difference [8].
Figure 8. Tensile nominal strain at filament failure point with
various deposition temperatures
Using the material extrusion process simulation models, the
temperature distributions of two layers of filaments were
determined and are shown in Figure 10. The difference in fill
angles was simulated by changing the deposition length. In order
for the deposition length to be directly proportional to the
anisotropy test specimen dimensions shown in F, it was set to 5.0
mm for 0° fill angle and 0.7 mm for 90° fill angle. The temperature
contour plots are shown in two colors only, in which green
represents below melting temperature (108 °C) and red represents
above melting temperature. In all cases, the temperature at the
interface between the first and second layers was above melting
temperature, which means that good bonding was achieved. In
addition, no significant differences in the contour plots could be
observed at different temperatures. This agreed with the
experimental results that tensile stress, nominal strain and
modulus of elasticity were not dependent on temperature.
Figure 9. Modulus of elasticity with various deposition
temperatures
0
1
2
3
4
5
6
240 °C 260 °C 280 °C
Tens
ile N
omin
al S
trai
n at
Fi
lam
ent F
ailu
re P
oint
[mm
/mm
]
Temperature
0° Fill Angle
90° Fill Angle
050
100150200250300350400450
240 °C 260 °C 280 °C
Mod
ulus
of E
last
icity
[MPa
]
Temperature [°C]
0° Fill Angle
90° Fill Angle
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Fill Angle 0° 90° D
epos
ition
Tem
pera
ture
240 °C
260 °C
280 °C
Figure 10. Temperature distributions from process simulation
models with various fill angles and deposition temperatures
6.2 Layer Height
Tensile stress at yield point, tensile stress and nominal strain
at filament failure point and modulus of elasticity were determined
with various layer heights, and are shown in Figures 11-14,
respectively. In this case, the deposition temperature was kept
constant at 260 °C. Statistical analyses were performed on these
experimental results as well due to the error bar overlaps. For all
four plots, the means were determined to be statistically equal for
the 0° fill angle, however, the means were determined to be
statistically not equal for the 90° fill angle. In fact, the values
with a layer height of 0.1 mm were determined to be higher than
those with a layer height of 0.2 mm in all cases. Tensile stress,
nominal strain and modulus of elasticity with a 0° fill angle were
not dependent on layer height, but those with a 90° fill angle were
dependent on layer height.
The tensile stresses with two different fill angles were also
compared at each layer height. From the experimental results shown
in Figure 12, the tensile stresses at yield point with a layer
height of 0.1 mm were statistically equal, and those with a layer
height of 0.2 mm were statistically equal. The same trend was
observed with the tensile stresses at filament failure point, which
implied that statistical anisotropy did not exist at each layer
height. However, slightly larger differences in the average tensile
stress values were observed with a 0.2 mm layer height from the two
plots. Therefore, a reduction in anisotropy was perhaps
accomplished by decreasing the layer height.
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Figure 11. Tensile stress at yield point with various layer
heights
Figure 12. Tensile stress at filament failure point with various
layer heights
It can be observed from Figure 13 that tensile nominal strain at
filament failure point was highly dependent on fill angle. Although
the nominal strains for the 0° fill angle specimens were higher
than those for the 90° fill angle for both layer heights, the value
with a 0.1 mm layer height was significantly higher than that with
a 0.2 mm layer height for the 90° fill angle specimens. This
indicated that a reduction in anisotropy in nominal strain was
achieved by decreasing the layer height.
The moduli of elasticity with two different fill angles were
compared at each layer height. From the experimental results shown
in Figure 14, the moduli of elasticity with a layer height of 0.1
mm were statistically equal, and those with a layer height of 0.2
mm were statistically equal. This suggested that the modulus of
elasticity was fairly uniform and was not dependent on fill angle.
However, once again, the difference between the average modulus of
elasticity with a 0.2 mm layer height was larger compared to that
with a 0.1 mm layer height. This supported the hypothesis that
anisotropy could be reduced with a lower layer height.
0
2
4
6
8
10
12
14
16
0.1 mm 0.2 mmTen
sile
Str
ess a
t Yie
ld P
oint
[MPa
]
Layer Height [mm]
0° Fill Angle
90° Fill Angle
02468
10121416
0.1 mm 0.2 mmTens
ile S
tres
s at F
ilam
ent F
ailu
re
Poin
t [M
Pa]
Layer Height
0° Fill Angle
90° Fill Angle
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Figure 13. Tensile nominal strain at filament failure point with
various layer heights
Figure 14. Modulus of elasticity with various layer heights
The temperature distributions of two layers of filaments with
different layer height values were
determined from the process simulation models, and the results
are shown in Figure 15. Since the number of layers was kept
constant, this led to differences in part thickness. Therefore,
when comparing the red region in the vertical direction, the
results needed to be normalized to the part thickness. It was
determined that a larger percentage of the thickness was at a
higher temperature with a lower layer height. This meant that a
greater portion of the first layer with a 0.1 mm layer height was
re-liquefied and a better diffusion across the interface was
obtained. It can be concluded that a better bonding was achieved
with filaments with a lower layer height. This agreed with the
experimental results that tensile stress, nominal strain and
modulus of elasticity with a layer height of 0.1 mm were higher
than those with a layer height of 0.2 mm for the 90° fill angle
specimens. It can also be observed that there was a large green
region for the 0° fill angle specimen with a layer height of 0.1
mm. This was most likely due to this specimen being thinner than
the specimen with a layer height of 0.2 mm. The simulation result
indicated that the green region had cooled down at this instant but
a good bonding between the layers had already been achieved as it
can be observed from the red region in the current time step.
0
1
2
3
4
5
6
0.1 mm 0.2 mmTen
sile
Nom
inal
Str
ain
at F
ilam
ent
Failu
re P
oint
[mm
/mm
]
Layer Height [mm]
0° Fill Angle
90° Fill Angle
050
100150200250300350400450
0.1 mm 0.2 mm
Mod
ulus
of E
last
icity
[MPa
]
Layer Height [mm]
0° Fill Angle
90° Fill Angle
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Fill Angle 0° 90° La
yer H
eigh
t
0.1 mm
0.2 mm
Figure 15. Temperature distributions from process simulation
models with various fill angles and
deposition temperatures
7 CONCLUSIONS
Tensile mechanical properties of polypropylene composite
formulations were investigated as a function of some material
extrusion process variables and the thermal properties of these
formulations. Results demonstrated three main conclusions for
tensile specimens fabricated horizontally and flat, with two
different fill angles:
• Results demonstrate that anisotropy can be reduced almost
completely if the material can be formulated to have low
crystallinity, low coefficient of thermal expansion, and moderate
to high thermal conductivity (for a polymer). Low crystallinity is
critically important for good MEX processibility.
• Tensile stress, nominal strain and modulus of elasticity were
not dependent on temperature with both the 0° and 90° fill angle
specimens. However, a reduction in tensile stress anisotropy was
achieved with an increase in deposition temperature. In addition,
the tensile properties with a 0° fill angle test specimens were not
dependent on layer height, but those with a 90° fill angle test
specimens were dependent on layer height. The experimental results
also showed that a reduction in tensile property anisotropy was
accomplished with a decrease in layer height.
• Simulation model results exhibited good correlations with
experimental results. Temperature contour plots at various
deposition temperatures depicted no significant differences, which
agreed with the experimental results that tensile properties were
not dependent on temperature. The temperature contour plots with
various layer heights showed that there is a greater region with
higher temperature in the vertical direction with a lower layer
height. This represented that a better bonding was achieved between
the extruded filaments with a lower layer height, which leads to a
reduction in mechanical property anisotropy. This agreed with the
experimental results that tensile properties with a lower layer
height were higher than those with a higher layer height for the
90° fill angle specimens.
ACKNOWLEDGEMENTS
The authors acknowledge support from Imerys Filtration &
Performance Additives.
645
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646
http://www.hyrel3d.com/
WelcomeTitle PagePrefaceOrganizing CommitteePapers to
JournalsTable of ContentsMaterialsScanning Strategies in Electron
Beam Melting to Influence Microstructure DevelopmentRelating
Processing of Selective Laser Melted Structures to Their Material
and Modal PropertiesThermal Property Measurement Methods and
Analysis for Additive Manufacturing Solids and PowdersPrediction of
Fatigue Lives in Additively Manufactured Alloys Based on the
Crack-Growth ConceptFatigue Behavior of Additive Manufactured Parts
in Different Process Chains – An Experimental StudyEffect of
Process Parameter Variation on Microstructure and Mechanical
Properties of Additively Manufactured Ti-6Al-4VOptimal Process
Parameters for In Situ Alloyed Ti15Mo Structures by Laser Powder
Bed FusionEfficient Fabrication of Ti6Al4V Alloy by Means of
Multi-Laser Beam Selective Laser MeltingEffect of Heat Treatment
and Hot Isostatic Pressing on the Morphology and Size of Pores in
Additive Manufactured Ti-6Al-4V PartsEffect of Build Orientation on
Fatigue Performance of Ti-6Al-4V Parts Fabricated via Laser-Based
Powder Bed FusionEffect of Specimen Surface Area Size on Fatigue
Strength of Additively Manufactured Ti-6Al-4V PartsSmall-Scale
Mechanical Properties of Additively Manufactured Ti-6Al-4VDesign
and Fabrication of Functionally Graded Material from Ti to Γ-Tial
by Laser Metal DepositionTailoring Commercially Pure Titanium Using
Mo₂C during Selective Laser MeltingCharacterization of MAR-M247
Deposits Fabricated through Scanning Laser Epitaxy (SLE)Mechanical
Assessment of a LPBF Nickel Superalloy Using the Small Punch Test
MethodEffects of Processing Parameters on the Mechanical Properties
of CMSX-4® Additively Fabricated through Scanning Laser Epitaxy
(SLE)Effect of Heat Treatment on the Microstructures of CMSX-4®
Processed through Scanning Laser Epitaxy (SLE)On the Use of X-Ray
Computed Tomography for Monitoring the Failure of an Inconel 718
Two-Bar Specimen Manufactured by Laser Powder Bed FusionLaser
Powder Bed Fusion Fabrication and Characterization of Crack-Free
Aluminum Alloy 6061 Using In-Process Powder Bed Induction
HeatingPorosity Development and Cracking Behavior of Al-Zn-Mg-Cu
Alloys Fabricated by Selective Laser MeltingEffect of Optimizing
Particle Size in Laser Metal Deposition with Blown Pre-Mixed
PowdersAluminum Matrix Syntactic Foam Fabricated with Additive
ManufacturingBinderless Jetting: Additive Manufacturing of Metal
Parts via Jetting NanoparticlesCharacterization of Heat-Affected
Powder Generated during the Selective Laser Melting of 304L
Stainless Steel PowderEffects of Area Fraction and Part Spacing on
Degradation of 304L Stainless Steel Powder in Selective Laser
MeltingInfluence of Gage Length on Miniature Tensile
Characterization of Powder Bed Fabricated 304L Stainless SteelStudy
of Selective Laser Melting for Bonding of 304L Stainless Steel to
Grey Cast IronMechanical Performance of Selective Laser Melted 17-4
PH Stainless Steel under Compressive LoadingMicrostructure and
Mechanical Properties Comparison of 316L Parts Produced by
Different Additive Manufacturing ProcessesA Parametric Study on
Grain Structure in Selective Laser Melting Process for Stainless
Steel 316L316L Powder Reuse for Metal Additive
ManufacturingCompeting Influence of Porosity and Microstructure on
the Fatigue Property of Laser Powder Bed Fusion Stainless Steel
316LStudying Chromium and Nickel Equivalency to Identify Viable
Additive Manufacturing Stainless Steel ChemistriesInvestigation of
the Mechanical Properties on Hybrid Deposition and Micro-Rolling of
Bainite SteelProcess – Property Relationships in Additive
Manufacturing of Nylon-Fiberglass Composites Using Taguchi Design
of ExperimentsDigital Light Processing (DLP): Anisotropic Tensile
ConsiderationsDetermining the Complex Young’s Modulus of Polymer
Materials Fabricated with MicrostereolithographyEffect of Process
Parameters and Shot Peening on Mechanical Behavior of ABS Parts
Manufactured by Fused Filament Fabrication (FFF)Expanding Material
Property Space Maps with Functionally Graded Materials for Large
Scale Additive ManufacturingConsidering Machine- and
Process-Specific Influences to Create Custom-Built Specimens for
the Fused Deposition Modeling ProcessRheological Evaluation of High
Temperature Polymers to Identify Successful Extrusion ParametersA
Viscoelastic Model for Evaluating Extrusion-Based Print
ConditionsTowards a Robust Production of FFF End-User Parts with
Improved Tensile PropertiesInvestigating Material Degradation
through the Recycling of PLA in Additively Manufactured
PartsEcoprinting: Investigating the Use of 100% Recycled
Acrylonitrile Butadiene Styrene (ABS) for Additive
ManufacturingMicrowave Measurements of Nylon-12 Powder Ageing for
Additive ManufacturingImprovement of Recycle Rate in Laser
Sintering by Low Temperature ProcessDevelopment of an Experimental
Laser Sintering Machine to Process New Materials like Nylon
6Optimization of Adhesively Joined Laser-Sintered
PartsInvestigating the Impact of Functionally Graded Materials on
Fatigue Life of Material Jetted SpecimensFabrication and
Characterization of Graphite/Nylon 12 Composite via Binder Jetting
Additive Manufacturing ProcessFabricating Zirconia Parts with
Organic Support Material by the Ceramic On-Demand Extrusion
ProcessThe Application of Composite Through-Thickness Assessment to
Additively Manufactured StructuresTensile Mechanical Properties of
Polypropylene Composites Fabricated by Material ExtrusionPneumatic
System Design for Direct Write 3D PrintingCeramic Additive
Manufacturing: A Review of Current Status and
ChallengesRecapitulation on Laser Melting of Ceramics and
Glass-CeramicsA Trade-Off Analysis of Recoating Methods for Vat
Photopolymerization of CeramicsAdditive Manufacturing of
High-Entropy Alloys – A ReviewMicrostructure and Mechanical
Behavior of AlCoCuFeNi High-Entropy Alloy Fabricated by Selective
Laser MeltingSelective Laser Melting of AlCu5MnCdVA: Formability,
Microstructure and Mechanical PropertiesMicrostructure and Crack
Distribution of Fe-Based Amorphous Alloys Manufactured by Selective
Laser MeltingConstruction of Metallic Glass Structures by
Laser-Foil-Printing TechnologyBuilding Zr-Based Metallic Glass Part
on Ti-6Al-4V Substrate by Laser-Foil-Printing Additive
ManufacturingOptimising Thermoplastic Polyurethane for Desktop
Laser Sintering
ModelingReal-Time Process Measurement and Feedback Control for
Exposure Controlled Projection LithographyOptimization of Build
Orientation for Minimum Thermal Distortion in DMLS Metallic
Additive ManufacturingUsing Skeletons for Void Filling in
Large-Scale Additive ManufacturingImplicit Slicing Method for
Additive Manufacturing ProcessesTime-Optimal Scan Path Planning
Based on Analysis of Sliced GeometryA Slicer and Simulator for
Cooperative 3D PrintingStudy on STL-Based Slicing Process for 3D
PrintingORNL Slicer 2: A Novel Approach for Additive Manufacturing
Tool Path PlanningComputer Integration for Geometry Generation for
Product Optimization with Additive ManufacturingMulti-Level
Uncertainty Quantification in Additive ManufacturingComputed Axial
Lithography for Rapid Volumetric 3D Additive ManufacturingEfficient
Sampling for Design Optimization of an SLS ProductReview of AM
Simulation Validation TechniquesGeneration of Deposition Paths and
Quadrilateral Meshes in Additive ManufacturingAnalytical and
Experimental Characterization of Anisotropic Mechanical Behaviour
of Infill Building Strategies for Fused Deposition Modelling
ObjectsFlexural Behavior of FDM Parts: Experimental, Analytical and
Numerical StudySimulation of Spot Melting Scan Strategy to Predict
Columnar to Equiaxed Transition in Metal Additive
ManufacturingModelling Nanoparticle Sintering in a Microscale
Selective Laser Sintering Process3-Dimensional Cellular Automata
Simulation of Grain Structure in Metal Additive Manufacturing
ProcessesNumerical Simulation of Solidification in Additive
Manufacturing of Ti Alloy by Multi-Phase Field MethodThe Effect of
Process Parameters and Mechanical Properties Oof Direct Energy
Deposited Stainless Steel 316Thermal Modeling of 304L Stainless
Steel Selective Laser MeltingThe Effect of Polymer Melt Rheology on
Predicted Die Swell and Fiber Orientation in Fused Filament
Fabrication Nozzle FlowSimulation of Planar Deposition Polymer Melt
Flow and Fiber Orientaiton in Fused Filament FabricationNumerical
Investigation of Stiffness Properties of FDM Parts as a Function of
Raster OrientationA Two-Dimensional Simulation of Grain Structure
Growth within Substrate and Fusion Zone during Direct Metal
DepositionNumerical Simulation of Temperature Fields in Powder Bed
Fusion Process by Using Hybrid Heat Source ModelThermal Simulation
and Experiment Validation of Cooldown Phase of Selective Laser
Sintering (SLS)Numerical Modeling of High Resolution
Electrohydrodynamic Jet Printing Using OpenFOAMMesoscopic
Multilayer Simulation of Selective Laser Melting ProcessA Study
into the Effects of Gas Flow Inlet Design of the Renishaw AM250
Laser Powder Bed Fusion Machine Using Computational
ModellingDevelopment of Simulation Tools for Selective Laser
Melting Additive ManufacturingMachine Learning Enabled Powder
Spreading Process Map for Metal Additive Manufacturing (AM)
Process DevelopmentMelt Pool Dimension Measurement in Selective
Laser Melting Using Thermal ImagingIn-Process Condition Monitoring
in Laser Powder Bed Fusion (LPBF)Performance Characterization of
Process Monitoring Sensors on the NIST Additive Manufacturing
Metrology TestbedMicroheater Array Powder Sintering: A Novel
Additive Manufacturing ProcessFabrication and Control of a
Microheater Array for Microheater Array Powder SinteringInitial
Investigation of Selective Laser Sintering Laser Power vs. Part
Porosity Using In-Situ Optical Coherence TomographyThe Effect of
Powder on Cooling Rate and Melt Pool Length Measurements Using In
Situ Thermographic TecniquesMonitoring of Single-Track Degradation
in the Process of Selective Laser MeltingMachine Learning for
Defect Detection for PBFAM Using High Resolution Layerwise Imaging
Coupled with Post-Build CT ScansSelection and Installation of High
Resolution Imaging to Monitor the PBFAM Process, and
Synchronization to Post-Build 3D Computed TomographyMultisystem
Modeling and Optimization of Solar Sintering SystemContinuous Laser
Scan Strategy for Faster Build Speeds in Laser Powder Bed Fusion
SystemInfluence of the Ratio between the Translation and
Contra-Rotating Coating Mechanism on Different Laser Sintering
Materials and Their Packing DensityThermal History Correlation with
Mechanical Properties for Polymer Selective Laser Sintering
(SLS)Post Processing Treatments on Laser Sintered Nylon
12Development of an Experimental Test Setup for In Situ Strain
Evaluation during Selective Laser MeltingIn Situ Melt Pool
Monitoring and the Correlation to Part Density of Inconel® 718 for
Quality Assurance in Selective Laser MeltingInfluence of Process
Time and Geometry on Part Quality of Low Temperature Laser
SinteringIncreasing Process Speed in the Laser Melting Process of
Ti6Al4V and the Reduction of Pores during Hot Isostatic PressingA
Method for Metal AM Support Structure Design to Facilitate
RemovalExpert Survey to Understand and Optimize Part Orientation in
Direct Metal Laser SinteringFabrication of 3D Multi-Material Parts
Using Laser-Based Powder Bed FusionMelt Pool Image Process
Acceleration Using General Purpose Computing on Graphics Processing
UnitsBlown Powder Laser Cladding with Novel Processing Parameters
for Isotropic Material PropertiesThe Effect of Arc-Based Direct
Metal Energy Deposition on PBF Maraging SteelFiber-Fed Laser-Heated
Process for Printing Transparent GlassReducing Mechanical
Anisotropy in Extrusion-Based Printed PartsExploring the
Manufacturability and Resistivity of Conductive Filament Used in
Material Extrusion Additive ManufacturingActive - Z Printing: A New
Approach to Increasing 3D Printed Part StrengthA Mobile 3D Printer
for Cooperative 3D PrintingA Floor Power Module for Cooperative 3D
PrintingChanging Print Resolution on BAAM via Selectable
NozzlesPredicting Sharkskin Instability in Extrusion Additive
Manufacturing of Reinforced ThermoplasticsDesign of a Desktop
Wire-Feed Prototyping MachineProcess Modeling and In-Situ
Monitoring of Photopolymerization for Exposure Controlled
Projection Lithography (ECPL)Effect of Constrained Surface
Texturing on Separation Force in Projection
StereolithographyModeling of Low One-Photon Polymerization for 3D
Printing of UV-Curable SiliconesEffect of Process Parameters and
Shot Peening on the Tensile Strength and Deflection of Polymer
Parts Made Using Mask Image Projection Stereolithography
(MIP-SLA)Additive Manufacturing Utilizing Stock Ultraviolet Curable
SiliconeTemperature and Humidity Variation Effect on Process
Behavior in Electrohydrodynamic Jet Printing of a Class of Optical
AdhesivesReactive Inkjet Printing Approach towards 3D Silcione
Elastomeric Structures FabricationMagnetohydrodynamic
Drop-On-Demand Liquid Metal 3D PrintingSelective Separation Shaping
of Polymeric PartsSelective Separation Shaping (SSS) – Large-Scale
Fabrication PotentialsMechanical Properties of 304L Metal Parts
Made by Laser-Foil-Printing ProcessInvestigation of Build
Strategies for a Hybrid Manufacturing Process Progress on
Ti-6Al-4VDirect Additive Subtractive Hybrid Manufacturing (DASH) –
An Out of Envelope MethodMetallic Components Repair Strategies
Using the Hybrid Manufacturing ProcessRapid Prototyping of EPS
Pattern for Complicated Casting5-Axis Slicing Methods for Additive
Manufacturing ProcessA Hybrid Method for Additive Manufacturing of
Silicone StructuresAnalysis of Hybrid Manufacturing Systems Based
on Additive Manufacturing TechnologyFabrication and
Characterization of Ti6Al4V by Selective Electron Beam and Laser
Hybrid MeltingDevelopment of a Hybrid Manufacturing Process for
Precision Metal PartsDefects Classification of Laser Metal
Deposition Using Acoustic Emission SensorAn Online Surface Defects
Detection System for AWAM Based on Deep LearningDevelopment of
Automatic Smoothing Station Based on Solvent Vapour Attack for Low
Cost 3D PrintersCasting - Forging - Milling Composite Additive
Manufacturing ThechnologyDesign and Development of a Multi-Tool
Additive Manufacturing SystemChallenges in Making Complex Metal
Large-Scale Parts for Additive Manufacturing: A Case Study Based on
the Additive Manufacturing ExcavatorVisual Sensing and Image
Processing for Error Detection in Laser Metal Wire Deposition
ApplicationsEmbedding of Liquids into Water Soluble Materials
via Additive Manufacturing for Timed ReleasePrediction of the
Elastic Response of TPMS Cellular Lattice Structures Using Finite
Element MethodMultiscale Analysis of Cellular Solids Fabricated by
EBMAn Investigation of Anisotropy of 3D Periodic Cellular Structure
DesignsModeling of Crack Propagation in 2D Brittle Finite Lattice
Structures Assisted by Additive ManufacturingEstimating Strength of
Lattice Structure Using Material Extrusion Based on Deposition
Modeling and Fracture MechanicsControlling Thermal Expansion with
Lattice Structures Using Laser Powder Bed FusionDetermination of a
Shape and Size Independent Material Modulus for Honeycomb
Structures in Additive ManufacturingAdditively Manufactured
Conformal Negative Stiffness HoneycombsA Framework for the Design
of Biomimetic Cellular Materials for Additive ManufacturingA
Post-Processing Procedure for Level Set Based Topology
OptimizationMulti-Material Structural Topology Optimization under
Uncertainty via a Stochastic Reduced Order Model ApproachTopology
Optimization for 3D Material Distribution and Orientation in
Additive ManufacturingTopological Optimization and Methodology for
Fabricating Additively Manufactured Lightweight Metallic
MirrorsTopology Optimization of an Additively Manufactured
BeamQuantifying Accuracy of Metal Additive Processes through a
Standardized Test ArtifactIntegrating Interactive Design and
Simulation for Mass Customized 3D-Printed Objects – A Cup Holder
ExampleHigh-Resolution Electrohydrodynamic Jet Printing of Molten
Polycaprolactone3D Bioprinting of Scaffold Structure Using
Micro-Extrusion TechnologyFracture Mechanism Analysis of Schoen
Gyroid Cellular Structures Manufactured by Selective Laser
MeltingAn Investigation of Build Orientation on Shrinkage in
Sintered Bioceramic Parts Fabricated by Vat
PhotopolymerizationHypervelocity Impact of Additively Manufactured
A356/316L Interpenetrating Phase CompositesUnderstanding and
Engineering of Natural Surfaces with Additive ManufacturingAdditive
Fabrication of Polymer-Ceramic Composite for Bone Tissue
EngineeringBinder Jet Additive Manufacturing of Stainless Steel -
Tricalcium Phosphate Biocomposite for Bone Scaffold and Implant
ApplicationsSelective Laser Melting of Novel Titanium-Tantalum
Alloy as Orthopedic BiomaterialDevelopment of Virtual Surgical
Planning Models and a Patient Specific Surgical Resection Guide for
Treatment of a Distal Radius Osteosarcoma Using Medical 3D
Modelling and Additive Manufacturing ProcessesDesign Optimisation
of a Thermoplastic SplintReverse Engineering a Transhumeral
Prosthetic Design for Additive ManufacturingBig Area Additive
Manufacturing Application in Wind Turbine MoldsDesign, Fabrication,
and Qualification of a 3D Printed Metal Quadruped Body: Combination
Hydraulic Manifold, Structure and Mechanical InterfaceSmart Parts
Fabrication Using Powder Bed Fusion Additive Manufacturing
TechnologiesDesign for Protection: Systematic Approach to Prevent
Product Piracy during Product Development Using AMThe Use of
Electropolishing Surface Treatment on IN718 Parts Fabricated by
Laser Powder Bed Fusion ProcessTowards Defect Detection in Metal
SLM Parts Using Modal Analysis “Fingerprinting”Electrochemical
Enhancement of the Surface Morphology and the Fatigue Performance
of Ti-6Al-4V Parts Manufactured by Laser Beam MeltingFabrication of
Metallic Multi-Material Components Using Laser Metal DepositionA
Modified Inherent Strain Method for Fast Prediction of Residual
Deformation in Additive Manufacturing of Metal Parts 2539Effects of
Scanning Strategy on Residual Stress Formation in Additively
Manufactured Ti-6Al-4V PartsHow Significant Is the Cost Impact of
Part Consolidation within AM Adoption?Method for the Evaluation of
Economic Efficiency of Additive and Conventional
ManufacturingIntegrating AM into Existing Companies - Selection of
Existing Parts for Increase of AcceptanceRamp-Up-Management in
Additive Manufacturing – Technology Integration in Existing
Business ProcessesRational Decision-Making for the Beneficial
Application of Additive ManufacturingApproaching Rectangular
Extrudate in 3D Printing for Building and Construction by
Experimental Iteration of Nozzle DesignAreal Surface
Characterization of Laser Sintered Parts for Various Process
ParametersDesign and Process Considerations for Effective Additive
Manufacturing of Heat ExchangersDesign and Additive Manufacturing
of a Composite Crossflow Heat ExchangerFabrication and Quality
Assessment of Thin Fins Built Using Metal Powder Bed Fusion
Additive ManufacturingA Mobile Robot Gripper for Cooperative 3D
PrintingTechnological Challenges for Automotive Series Production
in Laser Beam MeltingQualification Challenges with Additive
Manufacturing in Space ApplicationsMaterial Selection on Laser
Sintered Stab Resistance Body ArmorInvestigation of Optical
Coherence Tomography Imaging in Nylon 12 PowderPowder Bed Fusion
Metrology for Additive Manufacturing Design GuidanceGeometrical
Accuracy of Holes and Cylinders Manufactured with Fused Deposition
ModelingNew Filament Deposition Technique for High Strength,
Ductile 3D Printed PartsApplied Solvent-Based Slurry
Stereolithography Process to Fabricate High-Performance Ceramic
Earrings with Exquisite DetailsDesign and Preliminary Evaluation of
a Deployable Mobile Makerspace for Informal Additive Manufacturing
EducationComparative Costs of Additive Manufacturing vs. Machining:
The Case Study of the Production of Forming Dies for Tube
Bending
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