U.S. patent application number 17/401026 was filed with the patent office on 2021-12-02 for additive manufacturing.
The applicant listed for this patent is Hewlett-Packard Development Company, L.P.. Invention is credited to Alejandro Manuel De Pena, Hou T. Ng.
Application Number | 20210370597 17/401026 |
Document ID | / |
Family ID | 1000005771623 |
Filed Date | 2021-12-02 |
United States Patent
Application |
20210370597 |
Kind Code |
A1 |
Ng; Hou T. ; et al. |
December 2, 2021 |
ADDITIVE MANUFACTURING
Abstract
In one example, a non-transitory processor readable medium with
instructions thereon that when executed cause an additive
manufacturing machine to inhibit build material in an overlying
layer of build material from fusing with a first slice formed in an
underlying layer of build material.
Inventors: |
Ng; Hou T.; (Campbell,
CA) ; De Pena; Alejandro Manuel; (Sant Cugat del
Valles, ES) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hewlett-Packard Development Company, L.P. |
Spring |
TX |
US |
|
|
Family ID: |
1000005771623 |
Appl. No.: |
17/401026 |
Filed: |
August 12, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15520826 |
Apr 20, 2017 |
11117322 |
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PCT/US2015/011368 |
Jan 14, 2015 |
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17401026 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 64/291 20170801;
B29C 64/393 20170801; B33Y 70/00 20141201; B29C 64/188 20170801;
B33Y 30/00 20141201; B29C 64/153 20170801; B29C 64/165 20170801;
B33Y 40/00 20141201; B33Y 10/00 20141201; B33Y 50/02 20141201 |
International
Class: |
B29C 64/291 20060101
B29C064/291; B33Y 10/00 20060101 B33Y010/00; B33Y 70/00 20060101
B33Y070/00; B29C 64/165 20060101 B29C064/165; B33Y 30/00 20060101
B33Y030/00; B33Y 40/00 20060101 B33Y040/00; B33Y 50/02 20060101
B33Y050/02; B29C 64/153 20060101 B29C064/153; B29C 64/188 20060101
B29C064/188; B29C 64/393 20060101 B29C064/393 |
Claims
1-4. (canceled)
5. A non-transitory processor readable medium having instructions
thereon that when executed cause an additive manufacturing machine
to form a physical barrier on an underlying object slice to
overlying build material fusing with the underlying object
slice.
6-7. (canceled)
8. The medium of claim 5, where the instructions to form a physical
barrier include instructions to dispense a liquid coalescence
modifier agent on to the underlying object slice bordering an area
where an overlying object slice in the overlying build material
will cover the underlying object slice.
9. A computer program product that includes the processor readable
medium of claim 5.
10. An additive manufacturing machine controller that includes the
processor readable medium of claim 5.
11-14. (canceled)
15. The medium of claim 5, where the instructions to form a
physical barrier include instructions to dry the modifier agent
dispensed on to the underlying object slice before forming the
overlying build material.
16. An additive manufacturing machine, comprising: an apparatus for
form slices of an object; and a controller having instructions
thereon that when executed: cause the apparatus to form an
underlying object slice; cause the apparatus to form a physical
barrier on the underlying object slice to overlying build material
fusing with the underlying object slice; and cause the apparatus
to, in the overlying build material, form an overlying object slice
on the underlying object slice.
17. The machine of claim 16, wherein: the apparatus comprises: a
first device to layer powdered build material; a second device to
dispense a liquid, light absorbing coalescing agent on to build
material; a third device to dispense a liquid coalescence modifier
agent on to build material; a light source to apply light energy to
build material; the instructions to cause the apparatus to form the
underlying object slice include instructions to: cause the first
device to layer build material in a first layer; cause the second
device to dispense a liquid, light absorbing coalescing agent on to
build material in the first layer in a first pattern of the
underlying object slice; and cause the light source to apply light
energy to build material in the first layer patterned with
coalescing agent to generate heat to melt patterned build material
in the first layer, to form the underlying object slice; the
instructions to cause the apparatus to form the physical barrier
include instructions to cause the third device to dispense a liquid
coalescence modifier agent on to the underlying object slice
bordering an area where the overlying object slice will cover the
underlying object slice; and the instructions to cause the
apparatus to form the overlying object slice include instructions
to: cause the first device to layer build material in a second
layer over the underlying object slice; cause the second device to
dispense a liquid, light absorbing coalescing agent on to build
material in the second layer in a second pattern of the overlying
object slice; and cause the light source to apply light energy to
build material in the second layer patterned with coalescing agent
to generate heat to melt patterned build material in the second
layer, to form the overlying object slice on the underlying object
slice.
18. The machine of claim 17, wherein the instructions to cause the
apparatus form the barrier include instructions to dry the modifier
agent dispensed on to the underlying object slice before layering
build material over the underlying object slice.
19. A non-transitory processor readable medium having instructions
thereon that when executed cause an additive manufacturing machine
to: form a first layer of build material; dispense a liquid, light
absorbing coalescing agent on to build material in the first layer
in a pattern of a first slice of an object; expose build material
in the first layer patterned with coalescing agent to light to
generate heat to melt patterned build material in the first layer
to form the first slice; dispense a liquid coalescence modifier
agent on to the first slice covering an area where the first slice
will underhang a second slice of the object; form a second layer of
build material on the first slice; dispense a liquid, light
absorbing coalescing agent on to build material in the second layer
in a pattern of the second slice; and expose build material in the
second layer patterned with coalescing agent to light to generate
heat to melt patterned build material in the second layer to form
the second slice on the first slice.
20. The medium of claim 19, having instructions to dry the modifier
agent on the first slice before forming the second layer of build
material.
21. The medium of claim 20, wherein the instructions to dry the
modifier agent include instructions to heat the modifier agent.
Description
BACKGROUND
[0001] Additive manufacturing machines produce 3D
(three-dimensional) objects by building up layers of material. Some
additive manufacturing machines are commonly referred to as "3D
printers" because they often use inkjet or other printing
technology to apply some of the manufacturing materials. 3D
printers and other additive manufacturing machines make it possible
to convert a CAD (computer aided design) model or other digital
representation of an object directly into the physical object.
DRAWINGS
[0002] FIGS. 1A-9A and 1B-9B present a sequence of sections and
perspectives illustrating one example for additive manufacturing an
object with an underhang.
[0003] FIGS. 10 and 11 are flow diagrams that illustrate example
additive manufacturing processes.
[0004] FIG. 12 is a block diagram illustrating one example of a
processor readable medium with instructions to help form an
underhang during the additive manufacture of an object.
[0005] FIG. 13 is a block diagram illustrating one example of an
additive manufacturing machine implementing a controller with a
processor readable medium with underhang instructions, such as the
medium shown in FIG. 12.
[0006] FIG. 14 is a block diagram illustrating one example of an
additive manufacturing system implementing a CAD computer program
product with a processor readable medium with underhang
instructions, such as the medium shown in FIG. 12.
[0007] The same part numbers designate the same or similar parts
throughout the figures.
DESCRIPTION
[0008] Some additive manufacturing machines make a 3D object by
coalescing layers of powdered build material. Additive
manufacturing machines make objects based on data in a 3D model
created, for example, with a CAD computer program product. The
model data is processed into slices, each defining that part of a
layer or layers of build material to be coalesced. The examples of
additive manufacturing described below use a technique in which a
light absorbing ink or other suitable coalescing agent is "printed"
on to a layer of build material in the desired pattern and then
exposed to light to coalesce the patterned build material.
Coalescing agents increase light absorption to generate sufficient
heat to sinter, melt or otherwise coalesce the patterned build
material for solidification directly (as in sintering) or
indirectly through cooling (as in melting).
[0009] Coalescing agent may bleed into build material outside the
desired pattern, causing the unwanted coalescence and
solidification of build material. Also, heat generated in the
patterned build material can, under some circumstances, propagate
into and solidify surrounding, unpatterned build material. The
unwanted solidification of build material can degrade the overall
dimensional accuracy and appearance of the manufactured object.
Such degradation is often manifested, for example, in poorly
defined edges. Modifier agents have been developed to block or
neutralize the effects of a coalescing agent. The unwanted
solidification of build material may be controlled by dispensing a
coalescence modifier agent on to unpatterned build material
surrounding build material patterned with a coalescing agent. For
example, modifier agents and additive manufacturing processes are
described in international patent application no. PCT/US2014/036169
filed Apr. 30, 2014, titled Three Dimensional Printing Method, to
prevent or reduce the degree of coalescence of targeted areas of
build material to help control dimensional accuracy and surface
roughness along the edges in each layer of the manufactured
object.
[0010] It has been discovered that coalescence modifier agents may
also be used to control unwanted fusing between build material and
object slices, fusing that can lead to excessive surface roughness
in objects with an underhang (that part of an underlying slice that
extends past an overlying slice). Accordingly, a new additive
manufacturing process has been developed to inhibit or prevent
interlayer fusing to obtain smooth, well defined underhangs.
[0011] In one example, the new process includes applying a
coalescence modifier agent on to a first object slice formed in a
first layer of build material as a fusion barrier to protect the
top surface of the first slice during formation of a second slice.
The modifier agent is applied at locations bordering the area where
the second slice will cover the first slice, covering at least part
of the underhang. Then, when build material in a second, overlying
layer is heated to form the second slice, the fusion barrier
prevents, or at least inhibits, heated build material in the second
layer from fusing with the first slice in the underhang area so
that the top of the underhang on the second slice will remain
smooth and well defined. A processor readable medium with
instructions for underhang surface control using a coalescence
modifier agent may be implemented, for example, in a CAD computer
program product, in an object model processor, or in the controller
for the additive manufacturing machine.
[0012] As used in this document: a "coalescing agent" means a
substance that causes or helps cause a build material to coalesce;
a "coalescence modifier agent" means a substance that inhibits or
prevents coalescence of a build material including, for example,
modifying the effect of a coalescing agent; a "slice" means a slice
of a multi-slice object; and an "underhang" means that part of an
underlying slice that extends past an overlying slice (i.e., an
upside down overhang).
[0013] The sequence of sections and perspectives presented in FIGS.
1A-9A and 1B-9B illustrate one example for additive manufacturing
an object with an underhang. FIG. 10 is a flow diagram illustrating
one example of an additive manufacturing process 100 implemented in
FIGS. 1A-9A, 1B-9B. Referring to FIGS. 1A-9A, 1B-9B and FIG. 10, a
first layer 12 of build material 14 is formed, as shown in FIGS.
1A, 1B (block 102 in FIG. 10). A coalescing agent 16 is dispensed
on to build material 14, as shown in FIGS. 2A, 2B, in a pattern 20
corresponding to an object slice, for example with an inkjet type
dispenser 18 (block 104 in FIG. 13). Coalescing agent pattern 20 is
depicted by dense stippling in the figures. Any suitable build
material 14 may be used to make object 10, shown in FIGS. 9A and
9B, which may be hard or soft, rigid or flexible, elastic or
inelastic. Also, while a powdered build material 14 is depicted by
particles 22 in this example, suitable non-powdered build materials
could also be used.
[0014] In FIGS. 3A, 3B, the area 20 of layer 12 patterned with
coalescing agent is exposed to light 24 from a light source 26 to
coalesce build material and, upon solidification, form a first
object slice 28 (block 106 in FIG. 10). Depending on the
characteristics of build material 14, coalescing agent 16 and light
24, the build material may coalesce, for example, by melting to a
liquid or by sintering to a solid. If the build material melts,
then solidification occurs upon cooling.
[0015] In FIGS. 4A, 4B, a coalescence modifier agent 30 is
dispensed on to slice 28 in a pattern 32 covering an area 34 where
a second object slice will underhang the first slice (block 108 in
FIG. 10), for example with an inkjet type dispenser 36. Modifier
agent pattern 32 is depicted by sparse stippling in the figures. In
the example shown, the pattern 32 for modifier agent 30 is
co-extensive with underhang area 34. Other underhang patterns 32
are possible. For example, if light source 26 is configured to
selectively illuminate only those portions of build material
patterned with coalescing agent, then it may be desirable to limit
pattern 32 to locations immediately bordering the second slice
pattern in the underhang areas. (Second slice pattern 44 is shown
in FIGS. 7A, 7B.) If, however, light source 26 is configured to
illuminate most or all of each layer of build material, then it
usually will be desirable for modifier agent pattern 32 to
completely cover underhang area 34 as shown in FIGS. 4A and 4B.
[0016] Coalescence modifier agent 30 may also be dispensed on to
other areas of build material in each layer to help define other
aspects of the object slices including, for example, interspersed
with the pattern of the coalescing agent to change the material
characteristics of the slice. Although two distinct dispensers 18,
36 are shown, agents 16 and 30 could be dispensed from the same
dispensers integrated into a single device, for example using
different printheads (or groups of printheads) in a single inkjet
printhead assembly.
[0017] For a liquid modifier agent 30, it may be desirable to dry
the patterned area 32 before forming the next layer of build
material. In the example shown in FIGS. 5A, 5B, the area of slice
28 patterned with modifier agent is heated to dry the modifier
agent and form a solid fusion barrier 38. In other examples, it may
be desirable to allow a liquid modifier agent 30 to dry without
added heating. Heater 40 in FIG. 5A represents generally any
suitable heater, which may include one or more of thermal
radiation, convection and conduction.
[0018] In FIGS. 6A, 6B, a second layer 42 of build material 14 is
formed over first layer 12 covering first slice 28 (block 110 in
FIG. 10). In FIGS. 7A, 7B, a coalescing agent 16 is dispensed on to
build material 14 in layer 42 in a pattern 44 corresponding to a
second object slice underhanging first slice 28 (block 112 in FIG.
10). In FIGS. 8A, 8B, area 44 patterned with coalescing agent is
exposed to light 24 to coalesce build material and, upon
solidification, form a second object slice 46 (block 114 in FIG.
10). While distinct first and second slices 28, 46 are shown in
FIGS. 8A, 8B, the two slices actually fuse together into a single
part. The now fused slices 28, 46 are separated from the build
material and the fusion barrier, in a process sometimes referred to
as "uncaking", as a finished object 10 shown in FIGS. 9A and 9B.
Second slice 46 includes part 48 that underhangs first slice 46.
While a simple two-slice object 10 is shown, the same process steps
may be used to form more complex, multi-slice objects.
[0019] FIG. 11 is a flow diagram illustrating another example of an
additive manufacturing process 120. Referring to FIG. 11, a first
layer of build material is formed (block 122) and build material in
the first layer solidified to form a first slice (block 124), for
example as described above with reference to FIGS. 1A-3A, 1B-3B. A
coalescence modifier agent is dispensed on to the first slice
covering an area where the first slice will underhang the second
slice (block 126), for example as described above with reference to
FIGS. 4A and 4B. A second layer of build material is formed on the
first layer of build material (block 128) and build material in the
second layer is solidified to form a second slice on the first
slice (block 130), for example as described above with reference to
FIGS. 6A-8A, 6B-8B. If a liquid coalescence modifier agent is used,
the modifier agent may be dried before forming the second layer of
build material, for example by actively heating the modifier agent
as shown in FIGS. 5A and 5B. In another example, the heat in a
newly formed slice may be sufficient to dry the liquid modifier
agent without additional heating.
[0020] FIG. 12 is a block diagram illustrating a processor readable
medium 50 with instructions 52 to help form an underhang during the
manufacture of a 3D object. A processor readable medium 50 is any
non-transitory tangible medium that can embody, contain, store, or
maintain instructions for use by a processor. Processor readable
media include, for example, electronic, magnetic, optical,
electromagnetic, or semiconductor media. More specific examples of
suitable processor readable media include a hard drive, a random
access memory (RAM), a read-only memory (ROM), memory cards and
sticks and other portable storage devices.
[0021] Underhang instructions 52 include instructions to inhibit
build material in an overlying layer of build material from fusing
with a first slice formed in an underlying layer of build material,
for example by dispensing a coalescing modifier agent at block 126
in FIG. 11. Instructions 52 may include other additive
manufacturing instructions, for example instructions to form and
solidify shown at blocks 122, 124, 128 and 130 in FIG. 11.
Processor readable medium 50 with instructions 52 may be
implemented, for example, in a CAD computer program product, in an
object model processor, or in a controller for an additive
manufacturing machine. Control data to inhibit fusing can be
generated, for example, by processor readable instructions on the
source application, usually a CAD computer program product, in an
object model processor, or by processor readable instructions on
the additive manufacturing machine.
[0022] FIG. 13 is a block diagram illustrating one example of an
additive manufacturing machine 54 implementing a controller 56 with
overhang instructions 52. Referring to FIG. 13, machine 54 includes
controller 56, a manufacturing bed or other suitable support 58, a
roller or other suitable build material layering device 60, a
coalescing agent dispenser 18, a coalescence modifier agent
dispenser 36, a heater 40 and a light source 26. The in-process
object structure is supported on support 58 during manufacturing.
In some machines 54, support 58 may be movable at the urging of
controller 56 to compensate for the changing thickness of the
in-process structure, for example as layers of build material are
added during manufacturing.
[0023] Build material layering device 60 layers build material on
support 58 and on the in-process structures and may include, for
example, a device to dispense the build material and a blade or
roller to distribute the build material uniformly to the desired
thickness for each layer. Coalescing agent dispenser 18 dispenses
coalescing agent selectively at the direction of controller 56 on
to build material, for example as described above with reference to
FIGS. 2A and 7A. Coalescence modifier agent dispenser 36 dispenses
modifier agent selectively at the direction of controller 56 on to
build material, for example as described above with reference to
FIG. 4A. While any suitable dispensers 18, 36 may be used, inkjet
printheads are often used in additive manufacturing machines
because of the precision with which they can dispense agents and
their flexibility to dispense different types and formulations of
agents. Manufacturing machine 54 may include a heater 40 if it is
desired to pre-heat build material or to heat modifier agent. Light
source 26 applies light 24 selectively at the direction of
controller 56 to coalesce build material treated with coalescing
agent, for example as described above with reference to FIGS. 3A
and 8A.
[0024] Controller 56 represents the processor (or multiple
processors), the associated memory (or multiple memories) and
instructions, and the electronic circuitry and components needed to
control the operative elements of machine 54. In particular,
controller 56 includes a memory 62 having a processor readable
medium 50 with underhang instructions 52, and a processor 64 to
read and execute instructions 52. For example, controller 56 would
receive control data and other instructions from a CAD program to
make an object that includes an overhang and execute local
underhang instructions 52 as part of the process of making the
object.
[0025] Alternatively, underhang instructions 52 may be embodied in
a processor readable medium 50 separate from controller 56, for
example as part of a CAD computer program product shown in FIG. 14.
Referring to FIG. 14, an additive manufacturing system 66 includes
an additive manufacturing machine 54 operatively connected to a CAD
computer program product 68 with underhang instructions 52 residing
on a processor readable medium 50. Any suitable connection between
machine 54 and CAD program product 68 may be used to communicate
instructions and control data to machine 54 including, for example,
a wired link, a wireless link, and a portable connection such as a
flash drive or compact disk.
[0026] Light source 26 applies light energy to build material to
cause the coalescence of portions of the build material according
to where coalescing agent has been delivered or has penetrated. In
some examples, light source 26 is an infra-red (IR) or near
infra-red light source, or a halogen light source. Light source 26
may be a single light source or an array of multiple light sources.
In some examples, light source 26 is configured to apply light
energy in a substantially uniform manner simultaneously to the
whole surface of a layer of build material. In other examples,
light source 26 is configured to apply energy to only select areas
of the whole surface of a layer of build material.
[0027] Build material may be a powder, a liquid, a paste, or a gel.
Examples of build material include semi-crystalline thermoplastic
materials with a processing window of greater than 5.degree. C.
(i.e., the temperature range between the melting point and the
re-crystallization temperature). Suitable build materials may
include polyamides (e.g., PA or nylon 11, PA or nylon 12, PA or
nylon 6, PA or nylon 8, PA or nylon 9, PA or nylon 66, PA or nylon
612, PA or nylon 812, PA or nylon 912), polyethylene, polyethylene
terephthalate (PET), polystyrene, polyacetals, polypropylene,
polycarbonate, polyester, thermal polyurethanes, other engineering
plastics, and blends of any two or more of the polymers listed.
Core shell polymer particles of these materials may also be
used.
[0028] Build material may have a melting point ranging from about
50.degree. C. to about 400.degree. C. In some implementations, it
is desirable that the melting point of the build material be less
than (lower than) the melting point of an inorganic salt used in
the modifier agent. As examples, polyamide 12 having a melting
point of 180.degree. may be used, or thermal polyurethanes having a
melting point ranging from about 100.degree. C. to about
165.degree. C. may be used. In one example, when a combination of
polymer particles is used in the build material, at least one of
the particles has a melting point below the melting point of the
inorganic salt in the modifier agent.
[0029] The build material may be made up of similarly sized
particles or differently sized particles. In the example shown in
the figures, the build material includes particles of three
different sizes. As one example of the different sizes for each of
the build material particles, the average of each size particle may
be greater than 50 .mu.m, between 10 .mu.m and 30 .mu.m, and less
than 10 .mu.m. In an example, the largest particles are present in
an amount ranging from 70 wt % to 95 wt %, the medium particles
present in an amount ranging from 0.5 wt % to 21 wt %, and the
smallest particles present in an amount ranging from greater than 0
wt % up to 21 wt %.
[0030] Build material may include, in addition to polymer
particles, a charging agent and a flow aid. A charging agent may be
added to suppress tribo-charging. Suitable charging agents may
include aliphatic amines (which may be ethoxylated), aliphatic
amides, quaternary ammonium salts (e.g., behentrimonium chloride or
cocamidopropyl betaine), esters of phosphoric acid, polyethylene
glycol esters, or polyols. Some suitable commercially available
charging agents include HOSTASTAT.RTM. FA 38 (natural based
ethoxylated alkylamine), HOSTASTAT.RTM. FE2 (fatty acid ester), and
HOSTASTAT.RTM. HS 1 (alkane sulfonate), each of which is available
from Clariant Int. Ltd.). In an example, the charging agent is
added in an amount ranging from greater than 0 wt % to less than 5
wt % based upon the total wt % of the polymer particles. A flow aid
improves the flowability of build material by reducing friction,
lateral drag, and tribo-charging, and may be particularly desirable
when build material particles are less than 25 .mu.m in size.
Examples of suitable flow aids include tricalcium phosphate (E341),
powdered cellulose (E460(ii)), magnesium stearate (E470b), sodium
bicarbonate (E500), sodium ferrocyanide (E535), potassium
ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate
(E542), sodium silicate (E550), silicon dioxide (E551), calcium
silicate (E552), magnesium trisilicate (E553a), talcum powder
(E553b), sodium aluminosilicate (E554), potassium aluminium
silicate (E555), calcium aluminosilicate (E556), bentonite (E558),
aluminium silicate (E559), stearic acid (E570), or
polydimethylsiloxane (E900). In an example, the flow aid is added
in an amount ranging from greater than 0 wt % to less than 5 wt %
based upon the total wt % of the particles.
[0031] Suitable coalescing agents include water-based dispersions
with an active, radiation absorbing binding agent. The active agent
may be, for example, an infrared light absorber, a near infrared
light absorber, or a visible light absorber. As one example, the
coalescing agent may be an ink-type formulation including carbon
black as the active material. An example of this ink-type
formulation is commercially known as CM997A available from
Hewlett-Packard Company. Examples of inks including visible light
enhancers as the active agent are dye based colored ink and pigment
based colored ink. Examples of pigment based inks include the
commercially available inks CM993A and CE042A, available from
Hewlett-Packard Company. The aqueous nature of some coalescing
agent enables the coalescing agent to penetrate the layer of build
material. For hydrophobic build materials the presence of a
co-solvent and/or a surfactant in the coalescing agent may assist
in obtaining the desired wetting. One or more coalescing agents may
be dispensed to form each slice.
[0032] Suitable coalescence modifier agents may separate individual
particles of the build material to prevent the particles from
coalescing. Examples of this type of modifier agent include
colloidal, dye-based, and polymer-based inks, as well as solid
particles that have an average size less than the average size of
particles of the build material. The molecular mass of the modifier
agent and its surface tension may be such that it enables the agent
to penetrate sufficiently into the build material to achieve the
desired mechanical separation. In one example, a salt solution may
be used as a coalescence modifier agent. In other examples, inks
commercially known as CM996A and CN673A available from
Hewlett-Packard Company may be used as a coalescence modifier
agent.
[0033] Suitable coalescence modifier agents may act to modify the
effects of a coalescing agent by preventing build material from
reaching the melting point. A fluid that exhibits a suitable
cooling effect may be used as this type of coalescence modifier
agent. For example, when build material is treated with a cooling
fluid, energy applied to the build material may be absorbed
evaporating the fluid to help prevent build material from reaching
its melting point. Thus, for example, a fluid with a high water
content may be a suitable coalescence modifier agent.
[0034] "A" and "an" used in the claims means one or more.
[0035] The examples shown in the figures and described above
illustrate but do not limit the scope of the patent, which is
defined in the following Claims.
* * * * *