U.S. patent application number 16/604384 was filed with the patent office on 2021-04-29 for three-dimensional printing.
The applicant listed for this patent is HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P.. Invention is credited to Vladek Kasperchik, Mark H. Kowalski, Mohammed S. Shaarawi.
Application Number | 20210121951 16/604384 |
Document ID | / |
Family ID | 1000005327812 |
Filed Date | 2021-04-29 |
![](/patent/app/20210121951/US20210121951A1-20210429\US20210121951A1-2021042)
United States Patent
Application |
20210121951 |
Kind Code |
A1 |
Kowalski; Mark H. ; et
al. |
April 29, 2021 |
THREE-DIMENSIONAL PRINTING
Abstract
An example of a kit for three-dimensional (3D) printing includes
a host metal and fumed flow additive aggregates to be mixed with
the host metal. The fumed flow additive aggregates include flow
additive nanoparticles and partially fused necks between at least
some of the flow additive nanoparticles. Each of the flow additive
nanoparticles consists of a metal containing compound that is
reducible to an elemental metal in a reducing environment at a
reducing temperature less than or equal to a sintering temperature
of the host metal.
Inventors: |
Kowalski; Mark H.; (San
Diego, CA) ; Kasperchik; Vladek; (Corvallis, OR)
; Shaarawi; Mohammed S.; (Corvallis, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P. |
Spring |
TX |
US |
|
|
Family ID: |
1000005327812 |
Appl. No.: |
16/604384 |
Filed: |
October 10, 2018 |
PCT Filed: |
October 10, 2018 |
PCT NO: |
PCT/US18/55246 |
371 Date: |
October 10, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US18/28341 |
Apr 19, 2018 |
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16604384 |
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PCT/US18/27286 |
Apr 12, 2018 |
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PCT/US18/28341 |
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PCT/US18/22684 |
Mar 15, 2018 |
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PCT/US18/27286 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 1/0059 20130101;
B33Y 70/00 20141201; B22F 10/14 20210101; B33Y 10/00 20141201 |
International
Class: |
B22F 1/00 20060101
B22F001/00; B22F 10/14 20060101 B22F010/14; B33Y 70/00 20060101
B33Y070/00 |
Claims
1. A kit for three-dimensional (3D) printing, comprising: a host
metal; and fumed flow additive aggregates to be mixed with the host
metal, the fumed flow additive aggregates including flow additive
nanoparticles and partially fused necks between at least some of
the flow additive nanoparticles, each of the flow additive
nanoparticles consisting of a metal containing compound that is
reducible to an elemental metal in a reducing environment at a
reducing temperature less than or equal to a sintering temperature
of the host metal.
2. The kit as defined in claim 1 wherein the fumed flow additive
aggregates have a surface area greater than 50 m.sup.2/g.
3. The kit as defined in claim 1 wherein the fumed flow additive
aggregates have a surface area greater than 100 m.sup.2/g.
4. The kit as defined in claim 1 wherein: the average host metal
particle size is less than 20 .mu.m; and the average flow additive
nanoparticle size ranges from about 3 nm to about 200 nm.
5. The kit as defined in claim 1 wherein: the fumed flow additive
aggregates, when mixed with the host metal, break into individual
flow additive nanoparticles, aggregate fragments, or a combination
thereof; and the individual flow additive nanoparticles, the
aggregate fragments, or the combination thereof become disposed on
a surface of particles of the host metal.
6. The kit as defined in claim 1 wherein at least one of: the fumed
flow additive aggregates have an average flow additive aggregate
particle size ranging from about 50 nm to about 1000 .mu.m; or the
fumed flow additive aggregates have meso-sized pores; or the fumed
flow additive aggregates have a density ranging from about 0.1% to
20% of a bulk density of a material of the flow additive
nanoparticles.
7. The kit as defined in claim 1 wherein the metal containing
compound is selected from the group consisting of vanadium oxides,
chromium oxides, iron oxides, cobalt oxides, nickel oxides,
manganese oxides, copper oxides, and mixed transition metal
oxides.
8. The kit as defined in claim 1 wherein at least some of the fumed
flow additive aggregates are agglomerated together.
9. A method for making a build material composition for
three-dimensional (3D) printing, comprising: spraying a precursor
liquid into a combustion chamber, wherein the precursor liquid is
exposed to an external flame or is ignited to generate a flame,
whereby fumed flow additive aggregates are formed, the flow
additive aggregates including flow additive nanoparticles and
partially fused necks between at least some of the flow additive
nanoparticles, each of the flow additive nanoparticles consisting
of a metal containing compound that is reducible to an elemental
metal in a reducing environment at a reducing temperature less than
or equal to a sintering temperature of a host metal; and mixing the
fumed flow additive aggregates with the host metal; wherein the
flow additive nanoparticles have an average flow additive particle
size ranging from about 1 to about 3 orders of magnitude smaller
than an average host metal particle size of the host metal.
10. The method as defined in claim 9 wherein the precursor liquid
includes a solvent and i) a precursor of a transition metal oxide
selected from the group consisting of vanadium oxides, chromium
oxides, iron oxides, cobalt oxides, nickel oxides, manganese
oxides, and copper oxides, or ii) a precursor of a mixed transition
metal oxide.
11. The method as defined in claim 10 wherein the precursor is a
metal salt that is soluble in the solvent, the metal salt
including: a cation selected from the group consisting of vanadium,
chromium, iron, cobalt, nickel, manganese, and copper; and an anion
selected from the group consisting of nitrate, sulfate, halide, an
organic carboxylate, and an alkoxide.
12. The method as defined in claim 10 wherein the precursor is
present in the precursor liquid in an amount ranging from about 0.1
wt % to about 5 wt %, based on the total weight of the precursor
liquid.
13. The method as defined in claim 9 wherein: the mixing breaks the
flow additive aggregates into individual flow additive
nanoparticles, aggregate fragments, or a combination thereof; the
individual flow additive nanoparticles, the aggregate fragments, or
the combination thereof become disposed on a surface of particles
of the host metal; and the mixing forms the build material
composition including: the host metal present in an amount of at
least 99 wt % based on a total weight of the build material
composition; and the individual flow additive nanoparticles, the
aggregate fragments, or the combination thereof present in an
amount of less than 1 wt % based on the total weight of the build
material composition.
14. The method as defined in claim 9, further comprising stopping
mixing when the build material composition has a Hausner Ratio less
than 1.25.
15. A method for three-dimensional (3D) printing, comprising:
applying a build material composition including: a host metal
present in an amount of at least 99 wt %, based on a total weight
of the build material composition; and a flow additive present in
an amount of less than 1 wt % based on the total weight of the
build material composition, the flow additive including flow
additive primary particles that: have an average flow additive
primary particle size ranging from about 1 to about 3 orders of
magnitude smaller than an average host metal particle size; and are
metal oxide particles that are reducible to at least one elemental
metal in a reducing environment at a reducing temperature less than
or equal to a sintering temperature of the host metal, wherein the
at least one elemental metal is capable of being incorporated into
a bulk metal phase of the host metal in a final metal object;
wherein the build material composition is spreadable, having a
Hausner Ratio less than 1.25; and selectively applying a binder
agent on at least a portion of the build material composition.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to International Patent
Application Number PCT/US2018/028341, filed Apr. 19, 2018; which
itself claims priority to International Patent Application Number
PCT/US2018/022684, filed Mar. 15, 2018, and to International Patent
Application Number PCT/US2018/027286, filed Apr. 12, 2018, which
claims priority to International Patent Application Number
PCT/US2018/022684, filed Mar. 15, 2018; the disclosure of each of
which is incorporated by reference herein in its entirety.
BACKGROUND
[0002] Three-dimensional (3D) printing may be an additive printing
process used to make three-dimensional solid parts from a digital
model. 3D printing is often used in rapid product prototyping, mold
generation, mold master generation, and short run manufacturing.
Some 3D printing techniques are considered additive processes
because they involve the application of successive layers of
material (which, in some examples, may include build material,
binder and/or other printing liquid(s), or combinations thereof).
This is unlike traditional machining processes, which often rely
upon the removal of material to create the final part. Some 3D
printing methods use chemical binders or adhesives to bind build
materials together. Other 3D printing methods involve at least
partial curing, thermal merging/fusing, melting, sintering, etc. of
the build material, and the mechanism for material coalescence may
depend upon the type of build material used. For some materials, at
least partial melting may be accomplished using heat-assisted
extrusion, and for some other materials (e.g., polymerizable
materials), curing or fusing may be accomplished using, for
example, ultra-violet light or infrared light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Features of examples of the present disclosure will become
apparent by reference to the following detailed description and
drawings, in which like reference numerals correspond to similar,
though perhaps not identical, components. For the sake of brevity,
reference numerals or features having a previously described
function may or may not be described in connection with other
drawings in which they appear.
[0004] FIG. 1 depicts a graph of Hausner Ratio as a function of
flow additive weight percentage for a mixture of a comparative
fumed silica flow aid in 316L stainless steel powder;
[0005] FIG. 2 is a schematic diagram depicting an example method
for forming example fumed flow additive aggregates;
[0006] FIG. 3 is a flow diagram depicting an example of a method
for making a build material composition according to the present
disclosure;
[0007] FIG. 4 is a flow diagram depicting another example of a
method for making a build material composition according to the
present disclosure;
[0008] FIG. 5 is a block diagram that depicts components of a build
material composition and a three-dimensional (3D) printing kit as
disclosed herein;
[0009] FIG. 6 is a schematic diagram depicting effects of
processing on examples of the composition disclosed herein;
[0010] FIG. 7 is a flow diagram depicting an example of a 3D
printing method;
[0011] FIG. 8 depicts semi-schematic, partially cross-sectional
views illustrating an example of a 3D printing method applying an
example of the composition disclosed herein;
[0012] FIG. 9 is a block diagram illustrating a portion of a 3D
printing system that can use an example of the composition
disclosed herein;
[0013] FIG. 10 is a column graph depicting Hausner Ratio test
results of a comparative example build material composition and
example build material compositions as disclosed herein;
[0014] FIG. 11 depicts a graph of Hausner Ratio as a function of
flow additive weight percentage for comparative example build
material compositions and example build material compositions as
disclosed herein;
[0015] FIG. 12 is a scanning electron microscope (SEM) image (at
250,000 times magnification), with a scale bar of 500 nm, of an
example fumed flow additive aggregate disclosed herein; and
[0016] FIG. 13 is a SEM image (at 250,000 times magnification),
with a scale bar of 1 .mu.m, of a comparative example flow additive
aggregate.
DETAILED DESCRIPTION
[0017] Disclosed herein is a method for making a build material
composition, which includes a custom flow additive. The custom flow
additive is formed by liquid-feed flame spray pyrolysis. During
this process, a precursor liquid is sprayed into a combustion
chamber, where it is introduced into an external flame or is
ignited to form a flame. The flame decomposes a precursor in the
precursor liquid to form flow additive nanoparticles. The flow
additive nanoparticles are primary particles, which aggregate to
form fumed flow additive aggregates. The fumed flow additive
aggregates include the flow additive nanoparticles and partially
fused necks between at least some of the flow additive
nanoparticles. The partially fused necks weakly attach the flow
additive nanoparticles, and thus the fumed flow additive aggregates
are easily broken. When combined with host build materials, the
fumed aggregates readily break apart into individual flow additive
nanoparticles and/or aggregate fragments that stick to surfaces of
the host build material. This improves the flowability and
spreadability of the host build material.
[0018] The flow additive nanoparticles consist of a metal
containing compound that is reducible to an elemental metal in a
reducing environment at a reducing temperature less than or equal
to a sintering temperature of the host metal. As used herein, the
term "elemental metal" means one or more metals obtained from the
reduction, decomposition, or decomposition and reduction of a metal
containing compound. The number of elemental metals obtained will
depend upon the metal containing compound and the reaction(s) it
undergoes. For examples, a transition metal oxide may reduce to a
single elemental metal (that corresponds to the transition metal
cation), while mixed transition metal oxides may reduce to two or
more elemental metals (that correspond to the transition metal
cations). Unlike the elemental metal, the metal containing compound
contains a non-metal component, such as oxygen, or oxygen and
hydrogen (for hydroxides), etc. in accordance with the examples
disclosed herein. The elemental metal produced can be integrated
into a 3D object being formed without deleteriously affecting the
mechanical properties of the 3D object. As such, the custom flow
additive is suitable for a 3D printing process.
[0019] In some examples, the 3D printing process may include
patterning of uniformly spread layers of the build material
composition with liquid binder agent applied by means of an inkjet
printhead. Each patterned layer of the composition forms an
individual cross-section of the final metal object. Stacking of the
binder-patterned layers produces an intermediate part which can be
extracted from the powderbed (or other build surface) after the
patterning has been finished. The extracted intermediate part may
be subjected to post-printing processing (e.g., heating via
sintering), leading to consolidation of the particles of the
composition into a mechanically stronger final metal object.
[0020] In other examples, the 3D printing process may include
Selective Laser Melting (SLM). In these examples, uniformly spread
layers of the build material composition are individually exposed
to a laser beam of high energy density. The laser spot scans the
spread metal powder surface, heats the metal particles, melts the
metal particles and fuses the molten metal into continuous layers.
During a SLM printing process, stacked fused layers (each layer
representing a portion of the printed part) produce the final metal
part (i.e., each subsequent laser-patterned layer is fused on top
of the previous one). With SLM, the final metal part is produced
without printing an intermediate part and without sintering the
intermediate part. Therefore the sintering-related advantages of
smaller particles size are not applicable to SLM; however, the flow
additives disclosed herein enable non-classified, lower cost metal
powders with wide particle size distribution to be used with
SLM.
[0021] Examples of the build material composition disclosed herein
may be used in a 3D printing kit, a 3D printing system, and a 3D
printing method. While some of the examples provided herein relate
to 3D printing, it is to be understood that the flow additives
disclosed herein and the compositions including the flow additives
may also be used in other methods and applications. When the custom
flow additives disclosed herein are used in applications other than
3D printing, it is to be understood that the metal containing
compound may be suitable for the particular application (i.e., the
flow additive does not deleteriously affect the host material or
any aspect of the application).
[0022] As used herein, "material set" or "kit" is understood to be
synonymous with "composition." Further, "material set" and "kit"
are understood to be compositions comprising one or more components
where the different components in the compositions are each
contained in one or more containers, separately or in any
combination, prior to and during printing but these components can
be combined together during printing. The containers can be any
type of a vessel, box, or receptacle made of any material.
[0023] Throughout this disclosure, a weight percentage that is
referred to as "wt % active" refers to the loading of an active
component of a dispersion or other formulation that is present in
the precursor liquid, and/or binder agent. For example, binder
polymer particles may be present in a water-based formulation
(e.g., a stock solution or dispersion) before being incorporated
into the binder agent. In this example, the wt % actives of the
binder polymer particles accounts for the loading (as a weight
percent) of the binder polymer particles solids that are present in
the binder agent, and does not account for the weight of the other
components (e.g., water, etc.) that are present in the stock
solution or dispersion with the binder polymer particles. The term
"wt %," without the term actives, refers to either i) the loading
(in the precursor liquid, or binder agent) of a 100% active
component that does not include other non-active components
therein, or ii) the loading (in the precursor liquid or binder
agent) of a material or component that is used "as is" and thus the
wt % accounts for both active and non-active components.
[0024] The build material compositions include the host metal and
the custom flow additive formed by flame spray pyrolysis. In
example compositions, the host metal is present in an amount of at
least 99 wt % based on a total weight of the build material
composition; and the individual flow additive nanoparticles, the
aggregate fragments, or the combination thereof is present in an
amount of less than 1 wt % based on the total weight of the build
material composition. In an example, the individual flow additive
nanoparticles, the aggregate fragments, or the combination thereof
is/are present in an amount ranging from about 0.02 wt % to about 1
wt % based on the total weight of the build material composition.
In another example, the individual flow additive nanoparticles, the
aggregate fragments, or the combination thereof is/are present in
an amount ranging from about 0.02 wt % to about 0.1 wt % based on
the total weight of the build material composition. In still
another example, the individual flow additive nanoparticles, the
aggregate fragments, or the combination thereof is/are present in
an amount of about 0.1 wt % based on the total weight of the build
material composition. In yet another example, the individual flow
additive nanoparticles, the aggregate fragments, or the combination
thereof is/are present in an amount of about 0.02 wt % based on the
total weight of the build material composition.
[0025] As such, in examples of the present disclosure, the
composition is mainly the host metal. The host metal may be in
powder form, i.e., particles. In the present disclosure, the term
"particles" means discrete solid pieces of components of the build
material composition. As used herein, the term "particles" does not
convey a limitation on the shape of the particles. As examples,
particles may be spherical beads or irregularly shaped beads of
lower aspect ratio.
[0026] Sintering of the host metal particles usually happens below
a melting temperature of the host metal. The sintering temperature
of the host metal particles may be dependent, in part, on the size
of the host metal particles. A host metal with a smaller average
particle size will experience a faster sintering rate than a host
metal having a larger average particle size. The rate of sintering
of solid crystalline powders obeys Herring scaling law and is
inversely proportional to the particle size by a power of between 2
and 4. Therefore, reducing a metal particle size may allow faster
sintering at a lower sintering temperature. Both the speed of
sintering and the sintering temperature may beneficially alter a
structure of the sintered part. For example, a fast sintering rate
at a lower temperature may prevent large grain growth. The
prevention of large grain growth may improve ultimate tensile
strength, yield strength, ductility and other mechanical properties
of the final metal objects.
[0027] Thus, it may be desirable to use metal powders with the
smallest particle size possible in 3D printing processes involving
sintering. However, spreading of a powder into uniform thin layers
of well-controlled thickness becomes increasingly difficult with
decreased particle size. Without being held bound to any theory, it
is believed that the reduced spreadability with decreasing particle
size is due to inter-particle forces (i.e., van der Waals,
electrostatic attraction, etc.) becoming significantly stronger
than gravitational pull. Therefore, in general, powders become
increasingly cohesive when a particle size of the powder is well
below 100 .mu.m. As such, smaller particles agglomerate together
and the powders lose flowability. In the case of metals, even
powders with spherical particles become non-spreadable into thin
layers when the average particle size of the metal particles is
within or below the range of about 12 .mu.m to about 20 .mu.m;
especially when a fraction of particles present in the powder is
within or smaller than the range of about 7 .mu.m to about 10
.mu.m. It is possible to remove the small particles from a metal
powder by classification; however, classification is an additional
process that adds to cost and removes the beneficial effects of
small particles discussed above.
[0028] Comparative flow additives include fumed silica or alumina
powders, which have been used to decrease the inter-particle
cohesive forces in difficult-to-flow powders. It is believed that
many, if not all, current commercially available comparative flow
additives are based on different grades of fumed silica and, in
some cases, fumed aluminum oxides. In some cases, precipitated
colloidal silica powders have been used as comparative flow
additives after surface modification.
[0029] These comparative flow additives are very low density
powders made of loosely aggregated nano-particles. A typical
primary particle size for the comparative flow additives ranges
from about 1.5 to about 3 orders of magnitude smaller than the
particle size of the cohesive powders to which the comparative flow
additives are added. When added and mixed with cohesive host
powders, these comparative flow additive nano-particles or their
small aggregates stick to surfaces of the host particles. The host
particle surfaces are coated with flow additive nano-spacers,
thereby preventing agglomeration of the cohesive powder particles.
Thus, formerly cohesive powders treated with an effective amount of
the comparative flow additive (about 0.01 weight percent to 1.0
weight percent of the host powder) may be made flowable, with the
potential of being spread in thin uniform layers. As used herein,
better flowability of a composition means that the composition has
better spreadability.
[0030] FIG. 1 depicts a graph of Hausner Ratio as a function of
weight percentage for a mixture of a fumed silica flow aid in 316L
stainless steel powder. The 316L stainless steel powder had an "as
is" Hausner Ratio of about 1.37. Hausner Ratio (H[n]) is a powder
flowability metric that can be measured by a tap density test. More
specifically, the Hausner Ratio is a ratio of powder densities
after and before compaction by tapping. A lower H[n] correlates to
better flowability. Metal powders with a spherical particle shape
and a Hausner Ratio of less than or equal to about 1.20 may be
suitable for 3D printing applications with. In some cases, suitable
flowability may be found with a Hausner Ratio up to about 1.25. The
function depicted in FIG. 1 was determined from laboratory test
results. The stainless steel powder was SAE 316L, grade -22 .mu.m
(80%) powder from "Sandvik", (average particle diameter is
approximately 11 .mu.m). The fumed silica flow aid was Aerosil
R812, available from Evonik.
[0031] It has been found that the comparative flow additives based
on fumed oxides of silicon and aluminum discussed above cannot be
used to improve flowability of metal powders used in certain
additive manufacturing processes (e.g., those involving sintering)
without negatively affecting strength-related structural properties
of the final metal objects produced during the sintering process.
Silica and alumina are not reduced during sintering processes with
or without a reducing atmosphere. As such, both silica and alumina
flow additive nano-particles become part of the structure of the
final metal object. More particularly, the silica and alumina flow
additive nano-particles get incorporated into grain boundary space
of the final metal object structure. The presence of silica and/or
alumina inclusions in a metal object structure diminishes the
mechanical strength and ductility of the metal object. Thus,
although comparative flow additives may improve flowability of
certain metal powders, the comparative flow additives deleteriously
affect mechanical properties of 3D objects formed therefrom.
[0032] The examples of the method disclosed herein generate low
density, loosely aggregated flow additive aggregates, which have a
structure similar to comparative flow additives based on fumed
oxides of silicon and aluminum. The fumed flow additive aggregates
disclosed herein include flow additive nanoparticles (primary
particles), at least some of which are connected by partially fused
necks. The partially fused necks between the flow additive
nanoparticles are sufficiently fused so that the primary particles
are held together in the form of rigid secondary aggregates having
a fractal structure. The partial fusing, however, enables the
secondary aggregates to be easily broken. In some examples, the
flow additive (secondary) aggregates can agglomerate into even
larger loose agglomerates (up to 1000 .mu.m), where the flow
additive (secondary) aggregates are held together by weak Van der
Waals forces. These loose agglomerates are multi-level, highly
structured materials, that can be easily broken apart when mixed
with the host metal. The Van der Waals forces of the loose
agglomerates can be easily broken, resulting in the flow additive
(secondary) aggregates, and the partially fused necks between the
flow additive nanoparticles are not completely fused so that the
secondary aggregates can be easily broken, resulting in the primary
particles. As such, the fumed flow additive aggregates disclosed
herein, whether present as secondary aggregates or larger
agglomerates of the secondary aggregates, can easily break down to
flow additive nanoparticles (the primary particles) when mixed with
a host metal, and thus improve host metal flowability in a manner
similar to or better than comparative flow additives based on fumed
oxides of silicon and aluminum. For example, the build material
composition disclosed herein is spreadable, having a Hausner Ratio
less than 1.25. In some examples, the build material composition
has a Hausner Ratio less than 1.2.
[0033] Moreover, unlike the comparative flow additives based on
fumed oxides of silicon and aluminum, the flow additive formed by
the method disclosed herein is a metal containing compound that is
reducible to an elemental metal in a reducing environment at a
reducing temperature less than or equal to a sintering temperature
of the host metal. In some examples, the metal containing compound
is selected from the group consisting of vanadium oxides, chromium
oxides, iron oxides, cobalt oxides, nickel oxides, manganese
oxides, copper oxides, and mixed transition metal oxides. As such,
the elemental metal(s) is/are capable of being incorporated into a
bulk metal phase of the host metal in a final metal object. It is
to be understood that incorporation into a bulk metal phase may
include dissolution into the bulk metal phase, and/or alloying with
a bulk metal phase. Further, incorporation into a grain boundary
space, as occurs with comparative silica and alumina flow additive
nano-particles, is not a form of incorporation into a bulk metal
phase. Thus, unlike the build compositions that have the
comparative flow additives discussed above, the build composition
of the present disclosure has better spreadability/flowability and
is able to be incorporated into the bulk metal phase. Further,
final metal objects made from the build composition of the present
disclosure have comparable strength properties to parts made from
sintered powdered metal without flow additives. Therefore, the flow
additives formed by the methods disclosed herein include
metallurgy-friendly flow additives based on reducible metal oxide
nano-powders that enable using small particle metal powder with low
inherent flowability in additive manufacturing processes to yield
final metal objects with comparable strength properties to parts
made from sintered powdered metal without flow additives.
[0034] Referring now to FIG. 2, an example of a method for making
the fumed flow additive aggregates 21' is depicted.
[0035] At the outset of the method, a precursor liquid 58 (which is
shown at the bottom of FIG. 2) is prepared or purchased. The
precursor liquid 58 includes a solvent and a precursor of the metal
containing compound. Because the metal containing compound is a
transition metal oxide or a mixed transition metal oxide, the
precursor liquid includes, in some examples, a solvent and i) a
precursor of a transition metal oxide selected from the group
consisting of vanadium oxides, chromium oxides, iron oxides, cobalt
oxides, nickel oxides, manganese oxides, and copper oxides, or ii)
a precursor of mixed transition metal oxide.
[0036] The solvent may be water, an organic solvent, or a
combination thereof. Examples of suitable organic solvents include
alcohols (e.g., primary aliphatic alcohols, secondary aliphatic
alcohols, aromatic alcohols, 1,2-alcohols, 1,3-alcohols,
1,5-alcohols, etc.) and aromatic hydrocarbons. Suitable aromatic
hydrocarbons are commercially available as part of the
SOLVESSO.RTM. Series from ExxonMobile.
[0037] In some examples, the solvent includes a combination of
water and an organic solvent. In these examples, the solvent may be
a water-based solvent mixture (e.g., 50 wt % or more of the solvent
mixture is water) or an organic solvent-based solvent mixture
(e.g., 50 wt % or more of the solvent mixture is an organic
solvent). When the solvent is a water-based solvent mixture, the
organic solvent may be selected so that it is miscible with water
and so that the precursor is not precipitated.
[0038] The precursor may be any component that is i) able to form
the flow additive nanoparticles 21 when exposed to the flame 60,
and ii) soluble in the solvent of the precursor liquid 58.
[0039] Each of the flow additive nanoparticles 21 consists of a
metal containing compound that is reducible to an elemental metal
in a reducing environment at a reducing temperature less than or
equal to a sintering temperature of a host metal 15, and thus any
component that is a precursor of the metal containing compound may
be used. In some examples, the metal containing compound is
selected from the group consisting of vanadium oxide nanoparticles,
chromium oxide nanoparticles, iron oxide nanoparticles, cobalt
oxide nanoparticles, nickel oxide nanoparticles, manganese oxide
nanoparticles, copper oxide nanoparticles, and mixed transition
metal oxide nanoparticles. In examples, the iron oxide may be
selected from the group consisting of ferrous oxide (FeO), ferric
oxide (Fe.sub.2O.sub.3), and magnetite (Fe.sub.3O.sub.4). The mixed
transition metal oxide may be a spinel, i.e.,
A.sup.2+B.sub.2.sup.3+O.sub.4.sup.2-, where A and B are
independently selected from the group consisting of chromium,
cobalt, iron, manganese, nickel, copper, vanadium and zinc, or many
other mixed oxides of the ferrite type not necessarily limited to
the spinel structure. In an example, the mixed transition metal
oxide is nickel iron oxide. As such, any precursor of the listed
transition metal oxides or mixed transition metal oxides may be
used in the precursor liquid 58.
[0040] In some examples, the precursor is a metal salt that is
soluble in the solvent. In some of these examples, the precursor
has a high enough solubility in the solvent that it may be fully
dissolved.
[0041] The cation of the metal salt may be selected from the group
consisting of vanadium, chromium, iron, cobalt, nickel, manganese,
and copper. The anion of the metal salt may be selected from the
group consisting of nitrate, sulfate, a halide (e.g., chloride,
bromide, fluoride, iodide), an organic carboxylate (e.g.,
propionate, acetate, ethylhexanoate, etc.), and an alkoxide (e.g.,
methoxide, ethoxide, etc.). The anion of the metal salt may be
selected so that the metal salt is/are soluble in the solvent. For
example, when the solvent is water or a water-based solvent mixture
(e.g., 50 wt % or more of the solvent mixture is water), the anion
may be nitrate, sulfate, or chloride. For another example, when the
solvent is an organic solvent or an organic solvent-based solvent
mixture (e.g., 50 wt % or more of the solvent mixture is an organic
solvent), the anion may be an organic carboxylate or an alkoxide.
Examples of suitable metal salts include Ni(NO.sub.3).sub.2 (nickel
(II) nitrate), NiSO.sub.4 (nickel (II) sulfate), Co(NO.sub.3).sub.2
(cobalt (II) nitrate), CoSO.sub.4 (cobalt (II) sulfate),
Cr(NO.sub.3).sub.3 (chromium (III) nitrate), CrSO.sub.4 (chromium
(II) sulfate), VSO.sub.4 (vanadium (II) sulfate),
C.sub.40H.sub.75O.sub.10V (vanadium 2-ethylhexanoate), CuCl.sub.2
(copper (II) chloride), CuSO.sub.4 (copper (II) sulfate),
Cu(NO.sub.3).sub.2 (copper (II) nitrate),
Mn(CH.sub.3CO.sub.2).sub.2 (manganese (II) acetate),
C.sub.2H.sub.6MnO.sub.2 (manganese (II) methoxide),
C.sub.6H.sub.10FeO.sub.4 (iron propionate),
[Fe.sub.3O(OAc).sub.6(H.sub.2O).sub.3]OAc (OAc.sup.- is
CH.sub.3CO.sub.2.sup.-) (iron (III) acetate), etc.
[0042] In some examples, the precursor is present in the precursor
liquid 58 in an amount ranging from about 0.1 wt % to about 5 wt %,
based on the total weight of the precursor liquid 58.
[0043] In one specific example, the precursor liquid 58 includes a
solvent and a transition metal salt precursor having: a cation
selected from the group consisting of vanadium, chromium, iron,
cobalt, nickel, manganese, and copper; and an anion selected from
the group consisting of nitrate, sulfate, halide, an organic
carboxylate, and an alkoxide; and the precursor is present in the
precursor liquid in an amount ranging from about 0.1 wt % to about
5 wt %, based on a total weight of the precursor liquid.
[0044] Still referring to FIG. 2, after the precursor liquid 58 is
prepared or purchased, the precursor liquid 58 is atomized so that
it can be sprayed into a combustion chamber 36. The precursor
liquid 58 may be atomized by an aerosol generator, such as an
ultrasonic nebulizer (using high-frequency vibration to form a mist
of the precursor liquid 58), a two-fluid nozzle (using an atomizing
gas, such as oxygen gas, to disperse the precursor liquid 58), or
an electro-sprayer (using high voltage to convert the precursor
liquid 58 into an aerosol). The mist/spray/aerosol is introduced
into the combustion chamber 36 where it can be introduced into an
external flame 60, or where it can be ignited to form a flame 60'.
A precursor liquid 58 containing water or an aqueous-based mixture
as the solvent cannot form a self-sustaining flame due to the low
combustion enthalpy (<50% of total energy of combustion) of the
solution. In these instances, an external flame source (e.g., an
oxy-hydrogen or oxyhydrocarbon) may be used to generate the
external flame 60 to support the combustion of the precursor liquid
58. In contrast, a precursor liquid 58 containing an organic
solvent or an organic-based mixture as the solvent can form a
self-sustaining flame 60' due to the high combustion enthalpy
(>50% of total energy of combustion) of the solution. In these
instances, pilot torches or flamelets 38 may be used to ignite the
mist/spray/aerosol, which generates the self-sustaining flame
60'.
[0045] The flame 60 or 60' may have any temperature suitable for
the conversion of the precursor to the primary flow additive
nanoparticles 21, and ultimately to the fumed flow additive
aggregates 21'. In an example, the flame 60 or 60' has a
temperature ranging from about 1000.degree. C. to about
3000.degree. C.
[0046] Within the external flame 60 or the self-sustaining flame
60', the primary flow additive nanoparticles 21, and ultimately to
the fumed flow additive aggregates 21', are formed. The mechanism
for particle formation taking place in the flame 60 or 60' may
depend upon the components of the precursor liquid 58. With some
precursor liquids 58, the solvent evaporates and the precursor is
dispersed. The dispersed precursor reacts with a carrier gas (e.g.,
oxygen, air, or a mixture of an oxidizing and reducing gas) to form
particles (e.g., metal oxide particles). With other precursor
liquids 58 (e.g., organometallic salts), the precursor evaporates
and decomposes to form metal vapor and gaseous oxyanion species,
which co-react to nucleate as a result of supersaturation. This
forms sub-nano-size proto-particles. Growth continues to form
clusters of metal oxide bonds by coalescence and sintering
processes taking place in the high temperature environment of the
flame 60, 60' (which forms the primary flow additive nanoparticles
21). These particles 21 can then aggregate or fuse to form necks
between the particles (i.e., the fumed flow additive (secondary)
aggregates 21'). With either mechanism, the oxygen abundance in the
system and the high temperature of the flame 60, 60' may result in
fully oxidized and crystalline nanoparticles 21 and aggregates
21'.
[0047] The aggregates 21' formed have low density, fractal
structures that are easily broken when mixed with the host metal
15. The low density, fractal structures or fumed flow additive
aggregates 21' are shown at the top of FIG. 2.
[0048] The fumed flow additive aggregates 21' may be collected
using a suitable filtering system place above the flame 60, 60'.
The fumed flow additive aggregates 21' are ready to use, and thus
no additional post-processing is used.
[0049] The flow additive nanoparticles 21 may have an average flow
additive particle size (i.e., a primary particle size) ranging from
about 3 nanometers to about 200 nanometers. As used herein, the
term "particle size" or "average particle size" refers to the
volume-weighted mean diameter (i.e., the average diameter of
particles in a distribution normalized by the volume of the
particles). The size of the nanoparticles 21 formed through flame
spray pyrolysis may be affected by various parameters, such as the
composition of the precursor liquid 58, the fuel used to generate
the flame 60, the mist/spray/aerosol and/or oxidant flow rates, the
size of the mist/spray/aerosol droplets, and the temperature of
flame 60, or 60'. In an example, the flow additive nanoparticles 21
may have an average flow additive particle size ranging from about
3 nm to about 15 nm. In another example, the flow additive
nanoparticles 21 may have an average flow additive particle size
ranging from about 3 nm to about 10 nm. In still another example,
the flow additive nanoparticles 21 may have an average flow
additive particle size of about 10 nm. In yet another example, the
flow additive nanoparticles 21 may have an average flow additive
particle size ranging of about 7 nm.
[0050] The fumed flow additive aggregates 21' are highly structured
aggregates of the flow additive nanoparticles 21. The fumed flow
additive aggregates 21' have a relatively high porosity. As such,
the fumed flow additive aggregates 21' may have a surface area
greater than 50 m.sup.2/g. In another example, the fumed flow
additive aggregates 21' have a surface area greater than 70
m.sup.2/g. In still another example, the fumed flow additive
aggregates 21' have a surface area greater than 100 m.sup.2/g. In
yet another example, the fumed flow additive aggregates 21' have a
surface area of about 150 m.sup.2/g.
[0051] The fumed flow additive (secondary) aggregates 21' have a
relatively low density ranging from about 0.1% to 20% of a bulk
density of the material of the flow additive nanoparticles 21. In
another example, the fumed flow additive aggregates 21' have a
relatively low density ranging from about 0.5% to 20% of a bulk
density of the material of the flow additive nanoparticles 21. In
some examples, the highly structured fumed flow additive aggregates
21' may have an average flow additive aggregate particle size
ranging from about 50 nm to about 1000 .mu.m, or 100 nm to about
300 .mu.m, or from about 1 .mu.m to about 300 .mu.m, or from about
1 .mu.m to about 200 .mu.m. At the higher end of these ranges
(e.g., 300 .mu.m or more), it is to be understood that the fumed
flow additive (secondary) aggregates 21' may be agglomerated
together as described herein. The secondary aggregates 21' are
composed from primary particles (i.e., the flow additive
nanoparticles 21) having a primary particle size in the nano-range,
as mentioned hereinabove. The aggregates 21' also have meso-sized
pores. These mesopores may range in size from about 10 nm to about
1 .mu.m, and are present between the loosely aggregated flow
additive nanoparticles 21. In some examples, at least one of: the
fumed flow additive aggregates 21' have an average flow additive
aggregate particle size ranging from about 50 nm to about 1000
.mu.m; or the fumed flow additive aggregates 21' have meso-sized
pores; or the fumed flow additive aggregates have a density ranging
from about 0.1% to 20% of a bulk density of a material of the flow
additive nanoparticles. In a container of the flow additive formed
by this method, the primary flow additive nanoparticles 21 may be
encountered as low density, often fractal structures or aggregates
21' and/or as loose agglomerates of the aggregates 21'.
[0052] The fumed flow additive aggregates 21' (whether present as
secondary aggregates and/or as larger agglomerates of the secondary
aggregates), when mixed with the host metal 15, break into
individual flow additive nanoparticles 21, aggregate fragments, or
a combination thereof; and the individual flow additive
nanoparticles 21, the aggregate fragments, or the combination
thereof become disposed on a surface of particles of the host metal
15. The relatively high porosity and the relatively low density of
the fumed flow additive aggregates 21' may contribute to the
ability of the fumed flow additive aggregates 21' to break into
individual flow additive nanoparticles 21, aggregate fragments, or
a combination thereof when mixed with the host metal 15.
[0053] The method described in reference to FIG. 2 may be
accomplished in an environment including an oxidizing gas (e.g.,
oxygen gas (O.sub.2) or air). The oxidizing gas may oxidize the
precursor in the presence of the flame 60, 60' to form the metal
oxide. The oxidizing gas may also participate in the combustion to
form the self-sustaining flame 60'. In some examples, the method
may be accomplished in an air environment (i.e., an environment
including at least 20 vol. % oxygen gas (O.sub.2)). In other
examples, the method may be accomplished in an environment that
includes a reducing component (e.g., hydrogen gas (H.sub.2)), in
addition to the oxidizing gas. In these examples, the reducing
component may convert the precursor into an oxide. As an example,
when the precursor is a halide, a reducing component may convert
the halide into an oxide.
[0054] The method described in reference to FIG. 2 may be used in a
method for making a build material composition for 3D printing,
examples of which are depicted in FIGS. 3 and 4.
[0055] In the example shown in FIG. 3, the method 200 for making a
build material composition 12 for three-dimensional (3D) printing
comprises: spraying a precursor liquid 58 into a combustion chamber
36, wherein the precursor liquid 58 is exposed to an external flame
60 or is ignited to generate a flame 60', whereby fumed flow
additive aggregates 21' are formed, the fumed flow additive
aggregates 21' including flow additive nanoparticles 21 and
partially fused necks between at least some of the flow additive
nanoparticles, each of the flow additive nanoparticles 21
consisting of a metal containing compound that is reducible to an
elemental metal in a reducing environment at a reducing temperature
less than or equal to a sintering temperature of a host metal 15
(as shown at reference numeral 210); and mixing the flow additive
aggregates 21' with the host metal 15 (shown in FIGS. 5 and 6);
wherein the fumed flow additive nanoparticles 21 have an average
flow additive particle size ranging from about 1 to about 3 orders
of magnitude smaller than an average host metal particle size of
the host metal 15 (as shown at reference numeral 212).
[0056] The formation of the fumed flow additive aggregates 21' may
be performed as described in reference to FIG. 2. Any of the
materials, amounts of materials, conditions (for the flame 60,
60'), etc. may be used in the method 200.
[0057] Once the fumed flow additive aggregates 21' are formed, they
may be mixed with the host metal 15. In an example, the host metal
15 may be a single phase metallic material composed of one element.
In this example, the sintering temperature of the build material
composition 12 may be below the melting point of the single
element. In another example, the host metal 15 may be composed of
two or more elements, which may be in the form of a single phase
metallic alloy or a multiple phase metallic alloy. In these other
examples, sintering generally occurs over a range of
temperatures.
[0058] Some examples of the host metal 15 include steels, stainless
steel, bronzes, titanium (Ti) and alloys thereof, aluminum (Al) and
alloys thereof, nickel (Ni) and alloys thereof, cobalt (Co) and
alloys thereof, iron (Fe) and alloys thereof, nickel cobalt (NiCo)
alloys, gold (Au) and alloys thereof, silver (Ag) and alloys
thereof, platinum (Pt) and alloys thereof, tungsten (W) and alloys
thereof, and copper (Cu) and alloys thereof. Some specific examples
include AlSi10Mg, 2xxx series aluminum, 4xxx series aluminum, CoCr
MP1, CoCr SP2, MaragingSteel MS1, Hastelloy C, Hastelloy X,
NickelAlloy HX, Inconel IN625, Inconel IN718, SS GP1, SS 17-4PH, SS
316L, SS 430L, Ti6Al4V, and Ti-6Al-4V ELI7. While several example
alloys have been provided, it is to be understood that other alloys
may be used.
[0059] In some examples, the particles of the host metal 15 may
have an average host metal particle size less than 20 .mu.m. In
some examples, some host metal particles in a mixture of host metal
particles may be as small as about 1 .mu.m. The flow additive
nanoparticles 21 have an average flow additive particle size
ranging from about 1 to about 3 orders of magnitude smaller than
the average host metal particle size. In some examples, the average
host metal particle size is less than 20 .mu.m; and the average
flow additive particle size may range from about 3 nm to about 200
nm. In other examples, the average host metal particle size is less
than 20 .mu.m, and the average flow additive primary particle size
is 50 nm or less.
[0060] Any suitable conditions may be used to mix the host metal 15
with the fumed flow additive aggregates 21'. As examples, mixing
may be accomplished in a rotating container, using a mechanical
mixer, or using a hand mixer. Mixing may also be accomplished at
ambient temperatures, which may range from about 18.degree. C. to
about 25.degree. C. In some examples (as described further in
reference to FIG. 4), mixing may be accomplished for a suitable
time period, which may depend, at least in part, upon how long it
takes for the mixture to obtain a desirable Hausner Ratio (which
indicates good flowability). As such, some examples of the method
200 include stopping mixing when the build material composition 12
has a Hausner Ratio less than 1.25. Other examples, of the method
200 include stopping mixing when the build material composition 12
has a Hausner Ratio less than 1.2.
[0061] The mixing breaks the fumed flow additive aggregates 21'
into either individual flow additive nanoparticles 21, aggregate
fragments, or combinations thereof; the individual flow additive
nanoparticles 21, the aggregate fragments, or the combination
thereof become disposed on a surface of the particles of the host
metal 15; and the mixing forms the build material composition 12
including: the host metal 15 present in an amount of at least 99 wt
% based on a total weight of the build material composition 12; and
the individual flow additive nanoparticles 21, the aggregate
fragments, or the combination thereof present in an amount of less
than 1 wt % based on the total weight of the build material
composition 12. As used herein, the term "aggregate fragments"
refers to a few flow additive nanoparticles 21 that are stuck
together, but are smaller than the fumed flow additive aggregates
21'. The flow additive nanoparticles 21 and/or the aggregate
fragments stick to a surface of the host metal 15 particles and
improve the flowability of the host metal 15.
[0062] Referring now to FIG. 4, another example of the method,
shown as 300, is depicted. In this example, the method 300 for
making a build material composition for three-dimensional (3D)
printing comprises: spraying a precursor liquid 58 into combustion
chamber 36, wherein the precursor liquid 58 is exposed to an
external flame 60 or is ignited to generate a flame 60', whereby
fumed flow additive aggregates 21' are formed, the flow additive
aggregates 21' including flow additive nanoparticles 21 and
partially fused necks between at least some of the flow additive
nanoparticles, each of the flow additive nanoparticles 21
consisting of a metal containing compound that is reducible to an
elemental metal in a reducing environment at a reducing temperature
less than or equal to a sintering temperature of a host metal 15
(as shown at reference numeral 310); mixing the fumed flow additive
aggregates 21' with the host metal 15 to form a build material
mixture (as shown at reference numeral 312); during mixing,
monitoring a Hausner Ratio of the build material mixture (as shown
at reference numeral 314); and stopping mixing when a build
material composition 12 having a Hausner Ratio less than 1.25 is
formed (as shown at reference numeral 316).
[0063] The formation of the fumed flow additive aggregates 21' may
be performed as described in reference to FIG. 2. Any of the
materials, amounts of materials, conditions (for the flame 60,
60'), etc. may be used in the method 300.
[0064] The mixing of the host metal 15 and the fumed flow additive
aggregates 21' may be performed as described in reference to FIG.
3.
[0065] In examples of the method 300, the Hausner Ratio may be
monitored throughout the mixing process to determine when the
desirable Hausner Ratio has been obtained. Monitoring the Hausner
Ratio may be accomplished by periodically testing the Hausner Ratio
of the mixture throughout the mixing process. In an example, simple
mixing of the host metal 15 with the fumed flow additive aggregates
21' in a rotating container for about 1 hour to about 2 hours may
be sufficient mixing to obtain a uniform Hausner Ratio throughout
the mixture. Very long mixing, (e.g., 2 days or more) may result in
flowability degradation (i.e., an increase in the Hausner Ratio
over the Hausner Ratio that is achieved by an amount of mixing that
has a duration at a threshold of sufficiency to be effective).
[0066] In some examples, the fumed flow additive aggregates 21'
(which may or may not agglomerate into larger loose agglomerate)
are included in a 3D printing kit, such as the build material
composition kit 13 shown in FIG. 5. In an example, the kit 13
includes the host metal 15 and the fumed flow additive aggregates
21' (formed by the method described in reference to FIG. 2) that
are to be mixed with the host metal 15. In one example, the kit for
three-dimensional (3D) printing, comprises: the host metal 15 and
the fumed flow additive aggregates 21' to be mixed with the host
metal 15, the fumed flow additive aggregates 21' including flow
additive nanoparticles 21 and partially fused necks between at
least some of the flow additive nanoparticles 21, each of the flow
additive nanoparticles 21 consisting of a metal containing compound
that is reducible to an elemental metal in a reducing environment
at a reducing temperature less than or equal to a sintering
temperature of the host metal 15.
[0067] The components 15, 21' of this kit 13 may be used to form a
build material composition 12 for use in 3D printing, or to form
another composition that is to be used in an application that
involves spreading of the composition 12. The components of the
build material composition kit 13 may be maintained separately
until used together in examples of the 3D printing method disclosed
herein.
[0068] In some examples, the kit 13 may consist of the fumed flow
additive aggregates 21' and the metal host 15 with no other
components. In other examples, the build material composition kit
13 may further include a binder agent 14 to be applied, via an
inkjet printhead, to at least a portion of a layer of a build
material composition 12 formed from mixing the fumed flow additive
aggregates 21' with the host metal 15.
[0069] As shown in FIG. 5, the fumed flow additive aggregates 21'
and the metal host 15 are mixed together to form the build material
composition 12. The build material composition 12 may be included
in another example of a 3D printing kit 23. In this example, the
kit 23 includes the build material composition 12 and a binder
agent 14 to be applied to at least a portion of a layer of the
build material composition 12 via an inkjet printhead to pattern a
cross-section of an intermediate part. The kit 23 may consist of
the build material composition 12 and the binder agent 14 with no
other components. The components of the kit 23 may be maintained
separately until used together in examples of the 3D printing
method disclosed herein.
[0070] As mentioned herein, the fumed flow additive aggregates 21'
and the host metal 15 are mixed to form a build material
composition 12 for an additive manufacturing process. FIG. 6 is a
diagram depicting the components (15, 21', 21) of the build
material composition 12 going through certain steps of an example
of an additive manufacturing process. FIG. 6 begins with the host
metal particles 15 being mixed with the fumed flow additive
aggregates 21'. As a result of mixing, the fumed flow additive
aggregates 21' (or larger agglomerates thereof) break up to form
individual flow additive nanoparticles 21 and/or aggregate
fragments that stick to the host metal 15. This forms the build
material composition 12. The build material composition 12 may be
spread into a layer and patterned with a binder fluid 14 (not shown
in FIG. 6) to form a portion of an intermediate part 31. During
initial heating stages after patterning, the example flow aid 21
decomposes (e.g., by reduction), and is removed from the
intermediate part 31. The vapor cloud 19 shown in FIG. 6 represents
the flow additive nanoparticles 21 being removed from the build
material composition 12. The remaining intermediate part 31' is
then sintered to form the final 3D object or part 35.
[0071] An example of a printing method 400 that utilizes the build
material composition 12 disclosed herein is shown in FIG. 7. In
this example, the method 400 for three-dimensional (3D) printing
comprises: applying a build material composition 12 including: a
host metal 15 present in an amount of at least 99 wt %, based on a
total weight of the build material composition 12; and a flow
additive present in an amount of less than 1 wt % based on the
total weight of the build material composition 12, the flow
additive including flow additive primary particles 21 that: have an
average flow additive primary particle size ranging from about 1 to
about 3 orders of magnitude smaller than an average host metal
particle size; and are metal oxide particles that are reducible to
at least one elemental metal in a reducing environment at a
reducing temperature less than or equal to a sintering temperature
of the host metal 15, wherein the at least one elemental metal is
capable of being incorporated into a bulk metal phase of the host
metal 15 in a final metal object; wherein the build material
composition 12 is spreadable, having a Hausner Ratio less than
1.25; and selectively applying a binder agent 14 on at least a
portion of the build material composition 12.
[0072] In some examples of the method 400, prior to the applying of
the build material composition 12, the method further comprises:
spraying a precursor liquid 58 into a combustion chamber 36,
wherein the precursor liquid 58 is exposed to an external flame 60
or is ignited to generate a flame 60', whereby fumed flow additive
aggregates 21' are formed, the flow additive aggregates 21'
including the flow additive 21; and mixing the flow additive
aggregates 21' with the host metal 15 to form the build material
composition 12.
[0073] In the examples of the printing method 400 disclosed herein,
the binder agent 14 may include a binder and a liquid vehicle.
[0074] Examples of suitable binders include latexes (i.e., an
aqueous dispersion of polymer particles), polyvinyl alcohol,
polyvinylpyrrolidone, and combinations thereof.
[0075] Examples of polyvinyl alcohol include low weight average
molecular weight polyvinyl alcohols (e.g., from about 13,000 to
about 50,000), such as SELVOL.TM. PVOH 17 from Sekisui. Examples of
polyvinylpyrrolidones include low weight average molecular weight
polyvinylpyrrolidones (e.g., from about 15,000 to about 19,000),
such as LUVITEC.TM. K 17 from BASF Corp.
[0076] The binder polymer particles may be any latex polymer (i.e.,
polymer that is capable of being dispersed in an aqueous medium)
that is jettable via inkjet printing (e.g., thermal inkjet printing
or piezoelectric inkjet printing). In some examples disclosed
herein, the binder polymer particles are heteropolymers or
co-polymers. The heteropolymers may include a more hydrophobic
component and a more hydrophilic component. In these examples, the
hydrophilic component renders the particles dispersible in the
binder agent 14, while the hydrophobic component is capable of
coalescing upon exposure to heat in order to temporarily bind the
host metal particles 15.
[0077] The binder polymer particles of the latex may have several
different morphologies. The binder polymer particles may include
two different copolymer compositions, which may be fully separated
core-shell polymers, partially occluded mixtures, or intimately
comingled as a polymer solution. In an example, the polymer
particles may be individual spherical particles containing polymer
compositions of hydrophilic (hard) component(s) and/or hydrophobic
(soft) component(s) that may be interdispersed according to IPN
(interpenetrating networks), although it is contemplated that the
hydrophilic and hydrophobic components may be interdispersed in
other ways. For another example, the polymer particles may be made
of a hydrophobic core surrounded by a continuous or discontinuous
hydrophilic shell. This may lead to good water dispersibility and
jetting reliability. For another example, the polymer particle
morphology may resemble a raspberry, in which a hydrophobic core is
surrounded by several smaller hydrophilic particles that are
attached to the core. For still another example, the polymer
particles may include 2, 3, or 4 or more relatively large particles
(i.e., lobes) that are at least partially attached to one another
or that surround a smaller polymer core. The latex polymer
particles may have a single phase morphology, may be partially
occluded, may be multiple-lobed, or may include any combination of
the morphologies disclosed herein.
[0078] The latex polymer particles may have a weight average
molecular weight ranging from about 5,000 to about 500,000. As
examples, the weight average molecular weight of the latex
particles may range from about 10,000 to about 500,000, from about
100,000 to about 500,000, or from about 150,000 to about
300,000.
[0079] Latex particles may include a heteropolymer including a
hydrophobic component that makes up from about 65% to about 99.9%
(by weight) of the heteropolymer, and a hydrophilic component that
makes up from about 0.1% to about 35% (by weight) of the
heteropolymer, where the hydrophobic component may have a lower
glass transition temperature than the hydrophilic component. In
general, a lower content of the hydrophilic component is associated
with easier use of the latex particles under typical ambient
conditions. The glass transition temperature of the latex particles
may range from about -20.degree. C. to about 130.degree. C., or in
a specific example, from about 60.degree. C. to about 105.degree.
C. The particle size of the latex particles may range from about 10
nm to about 300 nm.
[0080] Examples of monomers that may be used to form the
hydrophobic component of the binder polymer particles may include
C4 to C8 alkyl acrylates or methacrylates, styrene, substituted
methyl styrenes, polyol acrylates or methacrylates, vinyl monomers,
vinyl esters, ethylene, maleate esters, fumarate esters, itaconate
esters, or the like. Some specific examples include methyl
methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate,
hexyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl
acrylate, propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexy
methacrylate, hydroxyethyl acrylate, lauryl acrylate, lauryl
methacrylate, octadecyl acrylate, octadecyl methacrylate, isobornyl
acrylate, isobornyl methacrylate, stearyl methacrylate, ethylene
glycol dimethacrylate, diethylene glycol dimethacrylate,
triethylene glycol dimethacrylate, tetrahydrofurfuryl acrylate,
alkoxylated tetrahydrofurfuryl acrylate, 2-phenoxyethyl
methacrylate, benzyl acrylate, ethoxylated nonyl phenol
methacrylate, cyclohexyl methacrylate, trimethyl cyclohexyl
methacrylate, t-butyl methacrylate, n-octyl methacrylate, tridecyl
methacrylate, isodecyl acrylate, dimethyl maleate, dioctyl maleate,
acetoacetoxyethyl methacrylate, diacetone acrylamide,
pentaerythritol tri-acrylate, pentaerythritol tetra-acrylate,
pentaerythritol tri-methacrylate, pentaerythritol
tetra-methacrylate, divinylbenzene, styrene, methylstyrenes (e.g.,
.alpha.-methyl styrene, p-methyl styrene), 1,3-butadiene, vinyl
chloride, vinylidene chloride, vinylbenzyl chloride, acrylonitrile,
methacrylonitrile, N-vinyl imidazole, N-vinylcarbazole,
N-vinyl-caprolactam, combinations thereof, derivatives thereof, or
mixtures thereof.
[0081] The heteropolymer may be formed of at least two of the
previously listed monomers, or at least one of the previously
listed monomers and a higher T.sub.g hydrophilic monomer, such as
an acidic monomer. Examples of acidic monomers that can be
polymerized in forming the latex polymer particles include acrylic
acid, methacrylic acid, ethacrylic acid, dimethylacrylic acid,
maleic anhydride, maleic acid, vinylsulfonate, cyanoacrylic acid,
vinylacetic acid, allylacetic acid, ethylidineacetic acid,
propylidineacetic acid, crotonoic acid, fumaric acid, itaconic
acid, sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid,
citraconic acid, glutaconic acid, aconitic acid, phenylacrylic
acid, acryloxypropionic acid, aconitic acid, phenylacrylic acid,
acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidic
acid, mesaconic acid, methacroylalanine, acryloylhydroxyglycine,
sulfoethyl methacrylic acid, sulfopropyl acrylic acid, styrene
sulfonic acid, sulfoethylacrylic acid,
2-methacryloyloxymethane-1-sulfonic acid,
3-methacryoyloxypropane-1-sulfonic acid,
3-(vinyloxy)propane-1-sulfonic acid, ethylenesulfonic acid, vinyl
sulfuric acid, 4-vinylphenyl sulfuric acid, ethylene phosphonic
acid, vinyl phosphoric acid, vinyl benzoic acid, 2
acrylamido-2-methyl-1-propanesulfonic acid, combinations thereof,
derivatives thereof, or mixtures thereof. Other examples of high
T.sub.g hydrophilic monomers include acrylamide, methacrylamide,
monohydroxylated monomers, monoethoxylated monomers,
polyhydroxylated monomers, or polyethoxylated monomers.
[0082] In an example, the selected monomer(s) is/are polymerized to
form a polymer, heteropolymer, or copolymer. In some examples, the
monomer(s) are polymerized with a co-polymerizable surfactant. In
some examples, the co-polymerizable surfactant can be a
polyoxyethylene compound. In some examples, the co-polymerizable
surfactant can be a HITENOL.RTM. compound e.g., polyoxyethylene
alkylphenyl ether ammonium sulfate, sodium polyoxyethylene
alkylether sulfuric ester, polyoxyethylene styrenated phenyl ether
ammonium sulfate, or mixtures thereof.
[0083] The binder polymer particles may have a particle size that
can be jetted via thermal inkjet printing or piezoelectric printing
or continuous inkjet printing. In an example, the particle size of
the binder polymer particles ranges from about 10 nm to about 300
nm.
[0084] Any suitable polymerization process may be used to prepare
the binder polymer particles. In examples, the aqueous dispersion
of polymer particles (latexes) may be produced by emulsion
polymerization or co-polymerization of any of the previously listed
monomers.
[0085] In an example, the polymer particles may be prepared by
polymerizing hydrophilic monomers to form the hydrophilic component
and attaching the hydrophilic component onto the surface of the
hydrophobic component.
[0086] In another example, each of the polymer particles may be
prepared by polymerizing the hydrophobic monomers and the
hydrophilic monomers at a ratio of the hydrophobic monomers to the
hydrophilic monomers that ranges from 5:95 to 30:70. In this
example, the hydrophobic monomers may dissolve in the hydrophilic
monomers.
[0087] In still another example, each of the binder polymer
particles may be prepared by starting the polymerization process
with the hydrophobic monomers, then adding the hydrophilic
monomers, and then finishing the polymerization process. In this
example, the polymerization process may cause a higher
concentration of the hydrophilic monomers to polymerize at or near
the surface of the hydrophobic component.
[0088] In still another example, each of the polymer particles may
be prepared by starting a copolymerization process with the
hydrophobic monomers and the hydrophilic monomers, then adding
additional hydrophilic monomers, and then finishing the
copolymerization process. In this example, the copolymerization
process may cause a higher concentration of the hydrophilic
monomers to copolymerize at or near the surface of the hydrophobic
component.
[0089] Other suitable techniques, specifically for generating a
core-shell structure, may be used, such as: i) grafting a
hydrophilic shell onto the surface of a hydrophobic core, ii)
copolymerizing hydrophobic and hydrophilic monomers using ratios
that lead to a more hydrophilic shell, iii) adding hydrophilic
monomer (or excess hydrophilic monomer) toward the end of the
copolymerization process so there is a higher concentration of
hydrophilic monomer copolymerized at or near the surface, or iv)
any other method known in the art to generate a more hydrophilic
shell relative to the core.
[0090] The hydrophobic monomers and/or the hydrophilic monomers
used in any of these example methods may be any of the hydrophobic
monomers and/or the hydrophilic monomers (respectively) listed
above. In an example, the hydrophobic monomers are selected from
the group consisting of C4 to C8 alkyl acrylate monomers, C4 to C8
alkyl methacrylate monomers, styrene monomers, substituted methyl
styrene monomers, vinyl monomers, vinyl ester monomers, and
combinations thereof; and the hydrophilic monomers are selected
from the group consisting of acidic monomers, unsubstituted amide
monomers, alcoholic acrylate monomers, alcoholic methacrylate
monomers, C1 to C2 alkyl acrylate monomers, C1 to C2 alkyl
methacrylate monomers, and combinations thereof.
[0091] The resulting binder polymer particles may exhibit a
core-shell structure, a mixed or intermingled polymeric structure,
or some other morphology.
[0092] In some examples, the binder polymer particles have a MFFT
or a glass transition temperature (T.sub.g) that is greater (e.g.,
>) than ambient temperature. In other examples, the binder
polymer particles have a MFFT or T.sub.g that is much greater
(e.g., >>) than ambient temperature (i.e., at least
15.degree. higher than ambient). As mentioned herein, "ambient
temperature" may refer to room temperature (e.g., ranging about
18.degree. C. to about 22.degree. C.), or to the temperature of the
environment in which the 3D printing method is performed. Examples
of the 3D printing environment ambient temperature may range from
about 40.degree. C. to about 50.degree. C. The MFFT or the T.sub.g
of the bulk material (e.g., the more hydrophobic portion) of the
polymer particles may range from 25.degree. C. to about 125.degree.
C. In an example, the MFFT or the T.sub.g of the bulk material
(e.g., the more hydrophobic portion) of the polymer particles is
about 40.degree. C. or higher. The MFFT or the T.sub.g of the bulk
material may be any temperature that enables the polymer particles
to be inkjet printed without becoming too soft at the printer
operating temperatures.
[0093] The binder polymer particles may have a MFFT or T.sub.g
ranging from about 125.degree. C. to about 200.degree. C. In an
example, the binder polymer particles may have a MFFT or T.sub.g of
about 160.degree. C.
[0094] In an example, the binder is present in the binder agent 14
in an amount ranging from about 1 wt % active to about 40 wt %
active based on a total weight of the binder agent. In another
example, the binder is present in the binder agent 14 in an amount
ranging from about 2 wt % active to about 30 wt % active based on
the total weight of binder agent 14.
[0095] In addition to the binder, the binder agent 14 may also
include water, co-solvent(s), surfactant(s) and/or dispersing
aid(s), antimicrobial agent(s), and/or anti-kogation agent(s).
[0096] The co-solvent may be an organic co-solvent present in an
amount ranging from about 0.5 wt % to about 40 wt % (based on the
total weight of the binder agent 14). It is to be understood that
other amounts outside of this range may also be used depending, at
least in part, on the jetting architecture used to dispense the
binder agent 14. The organic co-solvent may be any water miscible,
high-boiling point solvent, which has a boiling point of at least
120.degree. C. Classes of organic co-solvents that may be used
include aliphatic alcohols, aromatic alcohols, diols, glycol
ethers, polyglycol ethers, 2-pyrrolidones/pyrrolidinones,
caprolactams, formamides, acetamides, glycols, and long chain
alcohols. Examples of these co-solvents include primary aliphatic
alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols,
1,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl
ethers, higher homologs (C.sub.6-C.sub.12) of polyethylene glycol
alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams,
both substituted and unsubstituted formamides, both substituted and
unsubstituted acetamides, and the like. In some examples, the gas
generating liquid functional agent may include 2-pyrrolidone,
2-methyl-1,3-propanediol, 1-(2-hydroxyethyl)-2-pyrrolidone,
1,2-butanediol, or combinations thereof.
[0097] The binder agent 14 may also include surfactant(s) and/or
dispersing aid(s). Surfactant(s) and/or dispersing aid(s) may be
used to improve the wetting properties and the jettability of the
binder agent 14. Examples of suitable surfactants and dispersing
aids include those that are non-ionic, cationic, or anionic.
Examples of suitable surfactants/wetting agents include a
self-emulsifiable, non-ionic wetting agent based on acetylenic diol
chemistry (e.g., SURFYNOL.RTM. SEF from Evonik Degussa), a
non-ionic fluorosurfactant (e.g., CAPSTONE.RTM. fluorosurfactants
from DuPont, previously known as ZONYL FSO), and combinations
thereof. In a specific example, the surfactant is a non-ionic,
ethoxylated acetylenic diol (e.g., SURFYNOL.RTM. 465 from Evonik
Degussa). In other examples, the surfactant is an ethoxylated
low-foam wetting agent (e.g., SURFYNOL.RTM. 440 or SURFYNOL.RTM.
CT-111 from Evonik Degussa) or an ethoxylated wetting agent and
molecular defoamer (e.g., SURFYNOL.RTM. 420 from Evonik Degussa).
Still other suitable surfactants include non-ionic wetting agents
and molecular defoamers (e.g., SURFYNOL.RTM. 104E from Evonik
Degussa) or secondary alcohol ethoxylates (commercially available
as TERGITOL.RTM. TMN-6, TERGITOL.RTM. 15-S-7, TERGITOL.RTM. 15-S-9,
etc. from The Dow Chemical Co.). In some examples, it may be
desirable to utilize a surfactant having a hydrophilic-lipophilic
balance (HLB) less than 10. Examples of suitable dispersing aid(s)
include those of the SILQUEST.TM. series from Momentive, including
SILQUEST.TM. A-1230. Whether a single surfactant or dispersing aid
is used or a combination of surfactants and/or dispersing aids is
used, the total amount of surfactant(s) and/or dispersing aid(s)
may range from about 0.01 wt % active to about 6 wt % active based
on the total weight of the binder agent 14.
[0098] The binder agent 14 may also include antimicrobial agent(s).
Suitable antimicrobial agents include biocides and fungicides.
Example antimicrobial agents may include the NUOSEPT.RTM. (Ashland
Inc.), UCARCIDE.TM. or KORDEK.TM. or ROCIMA.TM. (Dow Chemical Co.),
PROXEL.RTM. (Arch Chemicals) series, ACTICIDE.RTM. B20 and
ACTICIDE.RTM. M20 and ACTICIDE.RTM. MBL (blends of
2-methyl-4-isothiazolin-3-one (MIT), 1,2-benzisothiazolin-3-one
(BIT), and Bronopol) (Thor Chemicals), AXIDE.TM. (Planet Chemical),
NIPACIDE.TM. (Clariant), blends of
5-chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under
the tradename KATHON.TM. (Dow Chemical Co.), and combinations
thereof. In an example, the binder agent 14 may include a total
amount of antimicrobial agents that ranges from about 0.1 wt %
active to about 1 wt % active.
[0099] An anti-kogation agent may also be included in the binder
agent 14. Kogation refers to the deposit of dried solids on a
heating element of a thermal inkjet printhead. Anti-kogation
agent(s) is/are included to assist in preventing the buildup of
kogation, and thus may be included when the binder agent 14 is to
be dispensed using a thermal inkjet printhead. Examples of suitable
anti-kogation agents include oleth-3-phosphate (e.g., commercially
available as CRODAFOS.RTM. O3A or CRODAFOS.RTM. N-3 acid from
Croda), dextran 500k, CRODAFOS.TM. HCE (phosphate-ester from Croda
Int.), CRODAFOS.RTM. N10 (oleth-10-phosphate from Croda Int.),
DISPERSOGEN.RTM. LFH (polymeric dispersing agent with aromatic
anchoring groups, acid form, anionic, from Clariant), or a
combination of oleth-3-phosphate and a low molecular weight (e.g.,
<5,000) acrylic acid polymer (e.g., commercially available as
CARBOSPERSE.TM. K-7028 Polyacrylate from Lubrizol). The
anti-kogation agent may be present in the binder agent 14 in an
amount ranging from about 0.1 wt % active to about 1 wt % active,
based on the total weight of the binder agent 14.
[0100] The balance of the binder agent 14 is water (e.g., deionized
water). As such, the amount of water may vary depending upon the
weight percent of the other binder agent 14 components.
[0101] Examples of a printing method 100 and system 10, which
include the build material composition 12 and the binder agent 14
are shown in FIG. 8.
[0102] As depicted in FIG. 8 at reference numeral 102, the 3D
printing system 10 may include an inkjet applicator 16, a supply
bed 20 (including a supply of build material composition 12), a
delivery piston 26, a spreader 24, a fabrication bed 22, and a
fabrication piston 28. The delivery piston 26 and the fabrication
piston 28 may be the same type of piston, but are programmed to
move in opposite directions. In an example, when a layer of the 3D
part 35 is to be formed, the delivery piston 26 may be programmed
to push a predetermined amount of the build material composition 12
out of the opening in the supply bed 20 and the fabrication piston
28 may be programmed to move in the opposite direction of the
delivery piston 26 in order to increase the depth of the
fabrication bed 22. The delivery piston 26 will advance enough so
that when the spreader 24 pushes the build material composition 12
into the fabrication bed 22 and onto the build surface 18 or the
previously formed layer, the depth of the fabrication bed 22 is
sufficient so that a layer 34 of the build material composition 12
and the binder agent 14 may be formed in the fabrication bed 22.
The spreader 24 is capable of spreading the build material
composition 12 into the fabrication bed 22 to form the build
material layer 34, which is relatively uniform in thickness.
[0103] In an example, the thickness of the build material layer 34
ranges from about 10 .mu.m to about 70 .mu.m, although thinner or
thicker layers may also be used. For example, the thickness of the
layer may range from about 20 .mu.m to about 1000 .mu.m. Depending
upon the desired thickness for the layer 34 and the particle
size(s) within the build material composition 12, the layer 34 that
is formed in a single build material application may be made up of
a single row of the build material composition 12 or several rows
of build material composition 12.
[0104] While the system 10 is depicted, it is to be understood that
other printing systems 10 may also be used. For example, another
support member, such as a build area platform, a platen, a glass
plate, or another build surface may be used instead of the
fabrication bed 22. The build material composition 12 may be
delivered from another source, such as a hopper, an auger conveyer,
or the like. It is to be understood that the spreader 24 may be a
rigid or flexible blade, which is a more common spreader for
metal/metal alloy build materials. However, the spreader may also
be replaced by other tools, such as a roller, or a combination of a
roller and a blade.
[0105] Each of these physical elements of the 3D printing system 10
may be operatively connected to a central processing unit 46 (see
FIG. 9) of the 3D printing system 10. The central processing unit
46 (e.g., running computer readable instructions 48 stored on a
non-transitory, tangible computer readable storage medium)
manipulates and transforms data represented as physical
(electronic) quantities within the printer's registers and memories
50 in order to control the physical elements to create the 3D part
35. The data for the selective delivery of the binder agent 14, the
build material composition 12, etc. may be derived from a 3D model
of the 3D part 35 to be formed. For example, the instructions 48
may cause the controller to utilize an applicator (e.g., an inkjet
applicator 16) to selectively dispense the binder agent 14, and to
utilize a build material distributor (spreader 24) to dispense the
build material composition 12. The central processing unit 46
controls the selective delivery (i.e. dispensing) of the binder
agent 14 in accordance with delivery control data 52.
[0106] The binder agent 14 may be dispensed from any suitable
applicator. As illustrated in FIG. 8 at reference number 102, the
binder agent 14 may be dispensed from an inkjet applicator, such as
a thermal inkjet printhead or a piezoelectric inkjet printhead. The
printhead may be a drop-on-demand printhead or a continuous drop
printhead. The inkjet applicator 16 may be selected to deliver
drops of binder agent 14 at a resolution ranging from about 300
dots per inch (DPI) to about 1200 DPI. In other examples, the
inkjet applicator 16 may be selected to be able to deliver drops of
the binder agent 14 at a higher or lower resolution. The drop
velocity may range from about 5 m/s to about 24 m/s and the firing
frequency may range from about 1 kHz to about 100 kHz. The inkjet
applicator 16 may include an array of nozzles through which it is
able to selectively eject drops of fluid. In one example, each drop
may be in the order of about 5 ng per drop, although it is
contemplated that a higher (e.g., 100 ng) or lower (e.g., 1 ng)
drop size may be used. In some examples, inkjet applicator 16 is
able to deliver variable size drops of the binder agent 14.
[0107] The inkjet applicator(s) 16 may be attached to a moving XY
stage or a translational carriage (neither of which is shown) that
moves the inkjet applicator(s) 16 adjacent to the build surface 18
in order to deposit the binder agent 14 in desirable area(s) 30. In
other examples, the applicator(s) 16 may be fixed while a support
member (supporting the build surface 18) is configured to move
relative thereto.
[0108] The inkjet applicator(s) 16 may be programmed to receive
commands from the central processing unit 46 and to deposit the
binder agent 14 according to a pattern of the layer 34 to be
achieved. In an example, a computer model of the part 35 to be
printed is generated using a computer aided design (CAD) program.
The computer model of the 3D part 35 is sliced into N layers, which
are then divided into voxels. The printing parameters for each
voxel are computed based on the desired composition and physical
properties of the part 35 to be printed. The printing parameters
for each voxel may include the X, Y, and Z coordinates that define
its location and the amount of the binder agent 14 (if any) that is
to be received. The central processing unit 46 may then use this
information to instruct the inkjet applicator(s) 16 as to how much
(if any) of the binder agent 14 should be jetted into each
voxel.
[0109] The inkjet applicator 16 selectively applies the binder
agent 14 on those portions 30 of the layer 34 of the build material
composition 12 that is to form the intermediate part, and
ultimately the final 3D part 35. The binder agent 14 may not be
applied on the entire layer 34, as shown at the portions 32.
[0110] After the binder agent 14 is selectively applied in a
pattern on the desired portion(s) 30 of the layer 34 of build
material composition 12, another layer of the build material
composition 12 is applied, as shown at reference numeral 104 in
FIG. 5, and patterned with the binder agent 14, as shown at
reference numeral 106. The formation and patterning of additional
layers may be repeated in order to form the intermediate part
31.
[0111] During and/or after formation of the intermediate part 31,
liquid components of the binder agent 14 may be evaporated. At
least substantially evaporation (with or without the application of
heat) activates the binder, and the activated binder provides
enough adhesive strength to hold the intermediate part 31 together
with enough mechanical stability to survive removal from any
non-patterned build material composition 12.
[0112] The intermediate part 31 may be extracted or separated from
the non-patterned build material composition 12 (e.g., in
portion(s) 32) by any suitable means. In an example, the
intermediate part 31 may be extracted by lifting the intermediate
part 31 from the non-patterned build material composition 12. Any
suitable extraction tool may be used. In some examples, the
intermediate part 31 may be cleaned to remove non-patterned build
material composition 12 from its surface. In an example, the
intermediate part 31 may be cleaned with a brush and/or an air jet,
may be exposed to mechanical shaking, or may be exposed to other
techniques that can remove the non-patterned build material
composition 12.
[0113] The intermediate part 31 may then be placed in a heating
mechanism (not shown). Examples of the heating mechanism include a
conventional furnace or oven, a microwave, or devices capable of
hybrid heating (i.e., conventional heating and microwave
heating).
[0114] The heating mechanism may be used to perform a heating
sequence, which involves exposing the intermediate part 31 to a
decomposition/reduction temperature or a pyrolysis temperature that
decomposes the flow additive 21. The heating sequence may form the
3D object 35 (see FIG. 6). In some examples, heating involves
exposure to a series of temperatures.
[0115] The series of temperatures may involve heating the
intermediate structure 31 to the decomposition/reduction or
pyrolysis temperature, a de-binding temperature, and then to the
sintering temperature. Briefly, the decomposition/reduction
temperature decomposes/reduces the flow additive nanoparticle 21 to
the elemental metal or the pyrolysis temperature removes the flow
additive nanoparticle 21, and the de-binding temperature removes
the binder, from the intermediate structure 31 to produce a
binder-free intermediate structure 31', and the structure 31' may
be sintered to form the final 3D object 35. Heating to
decompose/pyrolyze, de-bind, and sinter may take place at several
different temperatures, where the temperatures for
decomposing/pyrolyzing and de-binding are lower than the
temperature(s) for sintering. In some instances, heating to de-bind
and heating to decompose/pyrolyze may take place at the same
temperature or within the same temperature range (e.g., from about
300.degree. C. to about 500.degree. C.).
[0116] Heating to decompose/reduce is accomplished at a reducing
temperature that is sufficient to thermally decompose/reduce the
flow additive 21. As such, the reducing temperature depends upon
the flow additive 21 used. In an example, the reducing temperature
ranges from about 250.degree. C. to about 600.degree. C. In another
example, the reducing temperature ranges from about 300.degree. C.
to about 550.degree. C.
[0117] Heating to pyrolyze is accomplished at a thermal
decomposition temperature that is sufficient to thermally decompose
the flow additive 21. As such, the temperature for pyrolysis
depends upon the flow additive 21 used. In an example, the thermal
decomposition temperature ranges from about 250.degree. C. to about
600.degree. C. In another example, the pyrolysis temperature ranges
from about 300.degree. C. to about 550.degree. C. The flow additive
21 may have a clean thermal decomposition mechanism (e.g., leaves
non-volatile residue in an amount <5 wt % of the initial binder,
and in some instances non-volatile residue in an amount <<1
wt % of the initial binder). Since the amount of flow additive 21
in the build material composition 12 is low, any carbon residue
that is formed and remains in the part is in a very small amount
that does not deleteriously affect the part.
[0118] Heating to de-bind is accomplished at a thermal
decomposition temperature that is sufficient to thermally decompose
the binder. As such, the temperature for de-binding depends upon
the binder in the agent 14. In an example, the thermal
decomposition temperature ranges from about 250.degree. C. to about
600.degree. C. In another example, the thermal decomposition
temperature ranges from about 300.degree. C. to about 550.degree.
C. The binder may have a clean thermal decomposition mechanism
(e.g., leaves non-volatile residue in an amount <5 wt % of the
initial binder, and in some instances non-volatile residue in an
amount <<1 wt % of the initial binder). The smaller residue
percentage (e.g., close to 0%) is more desirable.
[0119] While not being bound to any theory, it is believed that the
binder-free intermediate structure 31' may maintain its shape due,
for example, to one or more of: i) the low amount of stress
experience by the part 31' due to it not being physically handled,
and/or ii) low level necking occurring between the host metal
particles 15 at the decomposition/reducing temperature or the
pyrolysis temperature and at the thermal decomposition temperature
of the binder. The at least substantially flow additive and
binder-free intermediate structure 31' may maintain its shape
although the binder is at least substantially removed and the host
metal particles 15 are not yet sintered.
[0120] The temperature may be raised to sinter the binder-free
intermediate structure 31', which can result in the formation of
weak bonds that are strengthened throughout sintering. During
sintering, the host metal particles 15 coalesce to form the 3D
object 35, and so that a desired density of the 3D object 35 is
achieved. The sintering temperature is a temperature that is
sufficient to sinter the remaining host metal particles 15. The
sintering temperature is highly depending upon the composition of
the host metal particles 15. During sintering, the at least
substantially flow additive and binder-free intermediate structure
31' may be heated to a temperature ranging from about 80% to about
99.9% of the melting point of the host metal particles 15. In
another example, the at least substantially flow additive and
binder-free intermediate structure 31' may be heated to a
temperature ranging from about 90% to about 95% of the melting
point of the host metal particles 15. In still another example, the
at least substantially flow additive and binder-free intermediate
structure 31' may be heated to a temperature ranging from about 60%
to about 90% of the melting point of the host metal particles 15.
In still another example, the sintering temperature may range from
about 50.degree. C. below the melting temperature of host metal
particles 15 to about 200.degree. C. below the melting temperature
of the host metal particles 15. The sintering temperature may also
depend upon the particle size and time for sintering (i.e., high
temperature exposure time). As an example, the sintering
temperature may range from about 500.degree. C. to about
1800.degree. C. In another example, the sintering temperature is at
least 900.degree. C. An example of a sintering temperature for
bronze is about 850.degree. C., and an example of a sintering
temperature for stainless steel is between about 1300.degree. C.
and about 1400.degree. C. While these temperatures are provided as
sintering temperature examples, it is to be understood that the
sintering temperature depends upon the host metal particles 15 that
are utilized, and may be higher or lower than the provided
examples. Heating at a suitable sintering temperature sinters and
coalesces the host metal particles 15 to form a completed 3D object
35. As a result of final sintering, the density may go from 50%
density to over 90%, and in some cases very close to 100% of the
theoretical density.
[0121] The length of time at which the heat (for each of
decomposition/reduction or pyrolysis, de-binding, and sintering) is
applied and the rate at which the structure 31, 31' is heated may
be dependent, for example, on one or more of: characteristics of
the heating mechanism, characteristics of the flow additive 21 and
binder, characteristics of the host metal particles 15 (e.g., metal
type, particle size, etc.), and/or the characteristics of the 3D
object/part 46 (e.g., wall thickness).
[0122] Heating, respectively, at the decomposition/reduction or
pyrolysis temperature and de-binding temperature may occur for a
time period ranging from about 10 minutes to about 72 hours. When
the structure 31 contains open porosity to vent out binder and/or
flow aid 21 pyrolysis, and/or the amount of the binder and/or flow
aid 21 is low, and/or the wall thickness of the structure 31 is
relatively thin, the time period for de-binding and
decomposition/reduction or pyrolysis may be 3 hours (180 minutes)
or less. Longer times may be used if the structure 31 has less open
porosity, if the structure 31 has thicker walls, and/or if the
structure 31 has a higher concentration of binder. In an example,
the decomposition/reduction or pyrolysis and de-binding time period
is about 60 minutes. In another example, the de-binding time period
is about 180 minutes. The intermediate part 31 may be heated to the
decomposition/reduction or pyrolysis and/or de-binding temperatures
at a heating rate ranging from about 0.5.degree. C./minute to about
20.degree. C./minute. The heating rate (i.e. temperature rise rate)
may depend, in part, on one or more of: the amount of the flow
additive and/or binder and/or the porosity of the intermediate part
31.
[0123] The binder-free intermediate structure 31' may be heated at
the sintering temperature for a time period ranging from about 20
minutes to about 15 hours. In an example, the sintering time period
is 60 minutes. In another example, the sintering time period is 90
minutes. In still another example, the sintering time period is
less than or equal to 3 hours. The at least substantially flow
additive and binder-free intermediate structure 31' may be heated
to the sintering temperature at a heating rate ranging from about
1.degree. C./minute to about 20.degree. C./minute.
[0124] While FIGS. 7 and 8 illustrate example 3D printing
processes, it is to be understood that the build material
composition 12 may be used in other additive manufacturing
processes. An example of another additive manufacturing process is
direct metal laser sintering (DMLS). During DMLS, an energy beam is
aimed at a selected region (in some instances less than the entire
layer) of a layer of the build material composition 12. The energy
beam may first applied to cause the flow additive 21 in the build
material composition 12 to decompose, and then the intensity may be
increased to raise the temperature so that the remaining host metal
particles 15, which are exposed to the energy beam, sinter to form
the layer of the 3D part. The application of additional build
material composition 12 layers and the selective energy beam
exposure may be repeated to build up the 3D part layer by layer. In
examples that use DMLS, a binder agent 14 may be omitted from the
process.
[0125] To further illustrate the present disclosure, examples are
given herein. It is to be understood that these examples are
provided for illustrative purposes and are not to be construed as
limiting the scope of the present disclosure.
EXAMPLES
Example 1
[0126] Four examples of the build material composition were
prepared according to examples of the methods disclosed herein. One
comparative build material composition was also prepared according
to a comparative method. The host metal used in each of the build
material compositions was stainless steel, 316L, grade -22 .mu.m
(80%) powder from "Sandvik", (average particle diameter was about
11 .mu.m).
[0127] The comparative build material composition was a baseline
build material composition, which included the stainless steel host
particles without any flow additive.
[0128] Iron oxide flow additives prepared according to different
examples of the methods disclosed here were used as the example
flow additives in the example build material compositions.
[0129] To prepare the first example build material composition,
fumed flow additive aggregates including iron oxide nanoparticles
that had an average flow additive primary particle size of about 30
nm were obtained.
[0130] The iron oxide flow additive aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The first example build material composition included 0.1 wt % of
the first example iron oxide flow additive.
[0131] To prepare the second example build material composition,
fumed flow additive aggregates including iron oxide nanoparticles
that had an average flow additive primary particle size of about 20
nm were obtained.
[0132] The iron oxide flow additive aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The second example build material composition included 0.1 wt % of
the second example iron oxide flow additive.
[0133] To prepare the third example build material composition,
fumed flow additive aggregates including iron oxide nanoparticles
that had an average flow additive primary particle size of about 10
nm were obtained.
[0134] The iron oxide flow additive aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The third example build material composition included 0.1 wt % of
the third example iron oxide flow additive.
[0135] To prepare the fourth example build material composition,
fumed flow additive aggregates included iron oxide nanoparticles
that had an average flow additive primary particle size of about 7
nm.
[0136] The iron oxide flow additive aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The fourth example build material composition included 0.1 wt % of
the fourth example iron oxide flow additive.
[0137] The flowability of each of the build material compositions
was evaluated using a Granupack density tester tap (available from
Granutools, www.granutools.com). The results of flowability tests
are shown in FIG. 10. In FIG. 10, the Hausner Ratio values are
shown on the y-axis, and the build material compositions are
identified on the x-axis.
[0138] The comparative build material composition (labeled
"Control" in FIG. 10) demonstrated poor flowability and thus poor
spreadability, with a Hausner ratio of about 1.29. The first
example build material (labeled "30 nm" in FIG. 10) had a Hausner
Ratio of about 1.25. The first example build material had a lower
Hausner Ratio than the baseline (comparative) build material
composition. It is believed that including a larger amount of the
first example iron oxide flow additive may result in a lower
Hausner ratio and a greater spreadability. The second example build
material (labeled "20 nm" in FIG. 10) had a Hausner Ratio of about
1.27. The second example build material had a lower Hausner Ratio
than the baseline (comparative) build material composition. It is
believed that including a larger amount of the second example iron
oxide flow additive may result in a lower Hausner ratio and a
greater spreadability. The third example build material (labeled
"10 nm" in FIG. 10) had a Hausner Ratio of about 1.165. The third
example build material had a lower Hausner Ratio than the baseline
(comparative) build material composition, and was considered
spreadable. The fourth example build material (labeled "7 nm" in
FIG. 10) had a Hausner Ratio of about 1.145. The fourth example
build material had a lower Hausner Ratio than the baseline
(comparative) build material composition, and was considered
spreadable.
[0139] As shown in FIG. 10, the addition of example iron oxide flow
additives that were prepared according to examples of the methods
disclosed herein lowered the Hausner Ratio of the example build
material compositions compared to the host metal particles without
any flow additive (the comparative build material composition).
These results indicate that method of making the build material
composition (and in particular the method of making the flow
additive) impacts the flowability/speadability of the build
material composition.
Example 2
[0140] Four additional examples of the build material composition
were prepared according to examples of the methods disclosed
herein. The host metal used in each of the additional example build
material compositions was stainless steel, 316L, grade -22 .mu.m
(80%) powder from "Sandvik", (average particle diameter was about
11 .mu.m). The fourth example iron oxide flow additive used in the
fourth example build material composition (in Example 1) was also
used in each of the additional example build material
compositions.
[0141] To prepare the fifth example build material composition, the
fourth example iron oxide flow aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The fifth example build material composition included 0.05 wt % of
the fourth example iron oxide flow additive.
[0142] To prepare the sixth example build material composition, the
fourth example iron oxide flow aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The sixth example build material composition included 0.03 wt % of
the fourth example iron oxide flow additive.
[0143] To prepare the seventh example build material composition,
the fourth example iron oxide flow aggregates were mixed with the
stainless steel host particles via rolling the powder mix in a
plastic container for about 2 hours. Mixing broke the iron oxide
flow additive aggregates into individual nanoparticles and
aggregate fragments, and disposed the individual nanoparticles and
aggregate fragments on the stainless steel host metal particles.
The seventh example build material composition included 0.02 wt %
of the fourth example iron oxide flow additive.
[0144] The flowability of each of the additional build material
compositions was evaluated using a Granupack density tester tap.
The results of flowability tests are shown in FIG. 11. Also shown
in FIG. 11 are the results of flowability tests of the fourth
example build material composition (including 0.1 wt % of the flow
additive, from Example 1), the comparative build material
composition (including 0 wt % of a flow additive, from Example 1),
and the host metal with different amounts of a fumed silica flow
aid (also shown in FIG. 1). In FIG. 11, the Hausner Ratio values
are shown on the y-axis, and amounts (in wt %) of flow additive
present in the build material compositions are shown on the
x-axis.
[0145] Again, the comparative build material composition
(corresponding with "0.00%" in FIG. 11) demonstrated poor
flowability, with a Hausner ratio of about 1.29. The fourth example
build material (corresponding with "0.10%" of "Fumed FeOx 7 nm" in
FIG. 11) had a Hausner Ratio of about 1.145. The fourth example
build material had a lower Hausner Ratio than the baseline
(comparative) build material composition, had a lower Hausner Ratio
than the build material including the same amount of the silica
flow aid, and was considered spreadable. The fifth example build
material (corresponding with "0.05%" of "Fumed FeOx 7 nm" in FIG.
11) had a Hausner Ratio of about 1.142. The fifth example build
material had a lower Hausner Ratio than the baseline (comparative)
build material composition, had a lower Hausner Ratio than the
build material including the same amount of the silica flow aid,
and was considered spreadable. The sixth example build material
(corresponding with "0.03%" of "Fumed FeOx 7 nm" in FIG. 11) had a
Hausner Ratio of about 1.15. The sixth example build material had a
lower Hausner Ratio than the baseline (comparative) build material
composition, had a lower Hausner Ratio than the build materials
including the similar amounts of the silica flow aid, and was
considered spreadable. The seventh example build material
(corresponding with "0.02%" of "Fumed FeOx 7 nm" in FIG. 11) had a
Hausner Ratio of about 1.155. The seventh example build material
had a lower Hausner Ratio than the baseline (comparative) build
material composition, had a lower Hausner Ratio than the build
material including the same amount of the silica flow aid, and was
considered spreadable.
[0146] As shown in FIG. 11, the addition of example iron oxide flow
additives that were prepared according to examples of the methods
disclosed herein lowered the Hausner Ratio of the example build
material compositions compared to the host metal particles without
any flow additive (the comparative build material composition). As
also shown in FIG. 11, the addition of example iron oxide flow
additives also lowered the Hausner Ratio of the example build
material compositions compared to the host metal particles with a
comparative fumed silica flow aid. These results indicate that
method of making the build material composition (and in particular
the method of making the flow additive) impacts the
flowability/speadability of the build material composition.
[0147] Further, the seventh example build material was used in an
example of a 3D printing method disclosed herein. The seventh
example build material composition was able to be spread into
substantially uniform build material layers. Thus, the seventh
example build material composition was shown to be a suitable build
material composition for the 3D printing methods disclosed
herein.
Example 3
[0148] The structure of the fourth example iron oxide flow additive
was compared to the structure of a comparative iron oxide flow
additive using SEM imaging. The comparative iron oxide flow
additive was obtained by freezing a dispersion of iron oxide
nanoparticles and lyophilizing the frozen dispersion.
[0149] The fourth example iron oxide flow additive is shown in FIG.
12. The comparative iron oxide flow additive is shown in FIG. 13.
Comparing FIGS. 12 and 13, it is shown that an iron oxide flow
additive prepared according to the method disclosed herein (FIG.
12) has a less dense structure with a higher porosity that is more
easily broken into smaller fragments than an iron oxide flow
additive prepared according to a comparative freeze-drying method
(FIG. 13).
[0150] The fourth example iron oxide flow additive and the
comparative freeze-dried flow additive were mixed with the 316L
stainless steel powder, and the build material composition with the
fourth example iron oxide flow additive was 3 to 5 times more
spreadable than the comparative build material composition.
[0151] It is to be understood that the ranges provided herein
include the stated range and any value or sub-range within the
stated range, as if the value(s) or sub-range(s) within the stated
range were explicitly recited. For example, a range from about 0.1
wt % to about 5 wt % should be interpreted to include the
explicitly recited limits of about 0.1 wt % to about 5 wt %, as
well as individual values, such as 0.73 wt %, 2.6 wt %, 4.2 wt %,
etc., and sub-ranges, such as from about 0.25 wt % to about 3.25 wt
%, from about 1.5 wt % to about 3.85 wt %, from about 2.0 wt % to
about 4.95 wt %, etc. Furthermore, when "about" is utilized to
describe a value, this is meant to encompass minor variations (up
to +/-10%) from the stated value. As used herein, the term "few"
means about three.
[0152] Reference throughout the specification to "one example",
"another example", "an example", and so forth, means that a
particular element (e.g., feature, structure, and/or
characteristic) described in connection with the example is
included in at least one example described herein, and may or may
not be present in other examples. In addition, it is to be
understood that the described elements for any example may be
combined in any suitable manner in the various examples unless the
context clearly dictates otherwise.
[0153] In describing and claiming the examples disclosed herein,
the singular forms "a", "an", and "the" include plural referents
unless the context clearly dictates otherwise.
[0154] While several examples have been described in detail, it is
to be understood that the disclosed examples may be modified.
Therefore, the foregoing description is to be considered
non-limiting.
* * * * *
References