U.S. patent application number 11/453695 was filed with the patent office on 2006-10-19 for three dimensional printing material system and method.
This patent application is currently assigned to Z Corporation. Invention is credited to James F. Bredt, Sarah L. Clark, Grieta Gilchrist.
Application Number | 20060230984 11/453695 |
Document ID | / |
Family ID | 31993437 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060230984 |
Kind Code |
A1 |
Bredt; James F. ; et
al. |
October 19, 2006 |
Three dimensional printing material system and method
Abstract
The present invention is directed to a three-dimensional
printing system and method, and an article made therefrom. The
method of the present invention includes building cross-sectional
portions of a three dimensional article, and assembling the
individual cross-sectional areas in a layer-wise fashion to form a
final article. The individual cross-sectional areas are built using
an ink-jet printhead to deliver an aqueous fluid to a particle
material that includes a first particulate material, a second
particulate material, and a third particulate material, wherein the
first and second particulate materials react in the presence of the
fluid in a period of time, and the third particulate material
reacts in the presence of the fluid to form a solid in a longer
period of time.
Inventors: |
Bredt; James F.; (Watertown,
MA) ; Clark; Sarah L.; (Somerville, MA) ;
Gilchrist; Grieta; (Alburquerque, NM) |
Correspondence
Address: |
GOODWIN PROCTER LLP;PATENT ADMINISTRATOR
EXCHANGE PLACE
BOSTON
MA
02109-2881
US
|
Assignee: |
Z Corporation
Burlington
MA
|
Family ID: |
31993437 |
Appl. No.: |
11/453695 |
Filed: |
June 15, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10255139 |
Sep 25, 2002 |
7087109 |
|
|
11453695 |
Jun 15, 2006 |
|
|
|
Current U.S.
Class: |
106/690 ;
106/683; 106/689; 106/691; 524/4; 524/5 |
Current CPC
Class: |
C04B 28/30 20130101;
B28B 1/001 20130101; B33Y 70/00 20141201; B28B 7/465 20130101; C04B
28/14 20130101; B33Y 80/00 20141201; C04B 28/34 20130101; B29C
64/165 20170801; C04B 2111/00181 20130101; C04B 28/34 20130101;
C04B 14/02 20130101; C04B 14/30 20130101; C04B 22/064 20130101;
C04B 24/122 20130101; C04B 2103/0092 20130101; C04B 28/30 20130101;
C04B 14/02 20130101; C04B 24/122 20130101; C04B 2103/0092 20130101;
C04B 28/14 20130101; C04B 2103/0092 20130101; C04B 2103/10
20130101 |
Class at
Publication: |
106/690 ;
106/691; 106/683; 106/689; 524/004; 524/005 |
International
Class: |
C04B 28/02 20060101
C04B028/02; C04B 24/26 20060101 C04B024/26; C04B 9/00 20060101
C04B009/00; C04B 28/34 20060101 C04B028/34 |
Claims
1. A solid article comprising: a product of a mixture of a
plurality of particles of: a first particulate material comprising
a phosphate; a second particulate material comprising an oxide; and
a third particulate material comprising an adhesive, wherein the
first particulate material and the second particulate material can
react to form a solid in a period of time, and the third
particulate material can solidify in a longer period of time when
the mixture is contacted by a fluid during three-dimensional
printing, the article having been formed by three-dimensional
printing and comprising a plurality of layers of the mixture.
2. The article of claim 1, wherein the first particulate material
and the second particulate material react in the presence of a
fluid.
3. The article of claim 2, wherein at least one of the first
particulate material and the second particulate material is
substantially soluble in the fluid.
4. (canceled)
5. The article of claim 1, wherein the phosphate is selected from
the group consisting of monoammonium phosphate; sodium aluminum
phosphate, acidic; monocalcium phosphate, anhydrous; monopotassium
phosphate; monosodium phosphate; and aluminum acid phosphate.
6. The article of claim 1, wherein the phosphate is selected from
the group consisting of: sodium tripolyphosphate; sodium
hexametaphosphate; sodium polyphosphate, anhydrous; phosphoric
acid, sodium salt; sodium trimetaphosphate; and ammonium
polyphosphate.
7. The article of claim 1, wherein the phosphate is selected from
the group consisting of diammonium phosphate; dipotassium
phosphate; disodium phosphate; monocalcium phosphate dihydrate;
monocalcium phosphate, monohydrate; dicalcium phosphate, dihydrate;
dicalcium phosphate, anhydrous; tricalcium phosphate; disodium
phosphate; and tripotassium phosphate.
8. The article of claim 1, wherein the phosphate is selected from
the group consisting of sodium acid pyrophosphate; tetrasodium
pyrophosphate; and tetrapotassium pyrophosphate.
9. (canceled)
10. The article of claim 1, wherein the second particulate material
comprises at least one of an alkaline oxide, an alkaline hydroxide,
and a combination thereof.
11. The article of claim 10, wherein the alkaline oxide is selected
from the group consisting of: zinc oxide; magnesium oxide; calcium
oxide; copper oxide; bismuth oxide; cadmium oxide; tin oxide; red
lead oxide; and combinations thereof.
12. The article of claim 10, wherein the alkaline hydroxide is
selected from the group consisting of: magnesium hydroxide; cobalt
trihydroxide; beryllium dihydroxide and combinations thereof.
13. The article of claim 10, wherein the alkaline oxide comprises
magnesium oxide.
14-15. (canceled)
16. The article of claim 1, wherein the adhesive is selected from
the group consisting of: copolymer of
octylacrylamide/acrylates/butylaminoethyl methacrylate; polyvinyl
alcohol; polyethylene oxide; sodium polystyrene sulfonate;
polyacrylic acid; polyvinyl pyrrolidone; maltodextrine; hydrolyzed
gelatin; sugar; hydrolyzed starch; sodium salt of polymethacrylic
acid; ammonium salt of polymethacrylic acid; polyvinyl sulfonic
acid; sulfonated polyester; poly(2-ethyl-2-oxazoline);
polymethacrylic acid; sodium salt of polyacrylic acid; ammonium
salt of polyacrylic acid; and combinations thereof.
17. The article of claim 1, wherein the mixture of plurality of
particles further comprises a filler.
18. The article of claim 17, wherein the filler is selected from
the group consisting of: limestone, staurolite, silica sand, zircon
sand, olivine sand, chromite sand, magnesite, alumina silicate,
calcium silicate, fused silica, calcium phosphate, rutile,
bentonite, montmorillonite, glass, chamotte, fireclay, and mixtures
thereof.
19. The article of claim 2, wherein the fluid is aqueous.
20-27. (canceled)
28. A compound used in three dimensional printing comprising: a dry
particulate mixture of: a first particulate material comprising a
phosphate; a second particulate material comprising an oxide; and a
third particulate material comprising an adhesive, wherein the dry
particulate mixture can be used in three-dimensional printing to
form an article comprised of a plurality of layers, the first
particulate material and the second particulate material can react
to form a solid in a period of time, and the third particulate
material can solidify in a longer period of time when the mixture
is contacted by a fluid during three-dimensional printing.
29. The compound of claim 28, wherein the first particulate
material and the second particulate material react in the presence
of the fluid.
30. The compound of claim 29, wherein at least one of the first
particulate material and the second particulate material is
substantially soluble in the fluid.
31. (canceled)
32. The compound of claim 28, wherein the phosphate is selected
from the group consisting of monoammonium phosphate; sodium
aluminum phosphate, acidic; monocalcium phosphate, anhydrous;
monopotassium phosphate; monosodium phosphate; and aluminum acid
phosphate.
33. The compound of claim 28, wherein the phosphate is selected
from the group consisting of: sodium tripolyphosphate; sodium
hexametaphosphate; sodium polyphosphate, anhydrous; phosphoric
acid, sodium salt; sodium trimetaphosphate; and ammonium
polyphosphate.
34. The compound of claim 28, wherein the phosphate is selected
from the group consisting of diammonium phosphate; dipotassium
phosphate; disodium phosphate; monocalcium phosphate dihydrate;
monocalcium phosphate, monohydrate; dicalcium phosphate, dihydrate;
dicalcium phosphate, anhydrous; tricalcium phosphate; disodium
phosphate; and tripotassium phosphate.
35. The compound of claim 28, wherein the phosphate is selected
from the group consisting of sodium acid pyrophosphate; tetrasodium
pyrophosphate; and tetrapotassium pyrophosphate.
36. (canceled)
37. The compound of claim 28, wherein the second particulate
material comprises at least one of an alkaline oxide, an alkaline
hydroxide, and a combination thereof.
38. The compound of claim 37, wherein the alkaline oxide is
selected from the group consisting of: zinc oxide; magnesium oxide;
calcium oxide; copper oxide; bismuth oxide; cadmium oxide; tin
oxide; red lead oxide; and combinations thereof.
39. The compound of claim 37, wherein the alkaline hydroxide is
selected from the group consisting of: magnesium hydroxide; cobalt
trihydroxide; beryllium dihydroxide and combinations thereof.
40. The compound of claim 37, wherein the alkaline oxide comprises
magnesium oxide.
41-42. (canceled)
43. The compound of claim 28, wherein the adhesive is selected from
the group consisting of: copolymer of
octylacrylamide/acrylates/butylaminoethyl methacrylate; polyvinyl
alcohol; polyethylene oxide; sodium polystyrene sulfonate;
polyacrylic acid; polyvinyl pyrrolidone; maltodextrine; hydrolyzed
gelatin; sugar; hydrolyzed starch; sodium salt of polymethacrylic
acid; ammonium salt of polymethacrylic acid; polyvinyl sulfonic
acid; sulfonated polyester; poly(2-ethyl-2-oxazoline);
polymethacrylic acid; sodium salt of polyacrylic acid; ammonium
salt of polyacrylic acid; and combinations thereof.
44. The compound of claim 28, wherein the mixture of plurality of
particles further comprises a filler.
45. The compound of claim 44, wherein the filler is selected from
the group consisting of: limestone, staurolite, silica sand, zircon
sand, olivine sand, chromite sand, magnesite, alumina silicate,
calcium silicate, fused silica, calcium phosphate, rutile,
bentonite, montmorillonite, glass, chamotte, fireclay, and mixtures
thereof.
46. The compound of claim 29, wherein the fluid is aqueous.
47-83. (canceled)
84. A dry particulate mixture of solids used for three dimensional
printing that, when contacted by a fluid during three-dimensional
printing to form an article composed of a plurality of layers,
undergoes a first solidification reaction beginning with the fluid
contact and occurring at a first rate, and also undergoes a second
solidification reaction beginning with the fluid contact and
occurring at a second rate slower than the first rate, wherein the
dry particulate mixture comprises: a first particulate material
comprising a phosphate; a second particulate material comprising an
oxide; and a third particulate material comprising an adhesive.
85. The compound of claim 84, wherein the phosphate is selected
from the group consisting of monoammonium phosphate; sodium
aluminum phosphate, acidic; monocalcium phosphate, anhydrous;
monopotassium phosphate; monosodium phosphate; and aluminum acid
phosphate.
86. The compound of claim 84, wherein the phosphate is selected
from the group consisting of: sodium tripolyphosphate; sodium
hexametaphosphate; sodium polyphosphate, anhydrous; phosphoric
acid, sodium salt; sodium trimetaphosphate; and ammonium
polyphosphate.
87. The compound of claim 84, wherein the phosphate is selected
from the group consisting of diammonium phosphate; dipotassium
phosphate; disodium phosphate; monocalcium phosphate dihydrate;
monocalcium phosphate, monohydrate; dicalcium phosphate, dihydrate;
dicalcium phosphate, anhydrous; tricalcium phosphate; disodium
phosphate; and tripotassium phosphate.
88. The compound of claim 84, wherein the phosphate is selected
from the group consisting of sodium acid pyrophosphate; tetrasodium
pyrophosphate; and tetrapotassium pyrophosphate.
89. The compound of claim 84, wherein the second particulate
material comprises at least one of an alkaline oxide, an alkaline
hydroxide, and a combination thereof.
90. The compound of claim 89, wherein the alkaline oxide is
selected from the group consisting of: zinc oxide; magnesium oxide;
calcium oxide; copper oxide; bismuth oxide; cadmium oxide; tin
oxide; red lead oxide; and combinations thereof.
91. The compound of claim 89, wherein the alkaline hydroxide is
selected from the group consisting of: magnesium hydroxide; cobalt
trihydroxide; beryllium dihydroxide and combinations thereof.
92. The compound of claim 89, wherein the alkaline oxide comprises
magnesium oxide.
93. The compound of claim 84, wherein the adhesive is selected from
the group consisting of: copolymer of
octylacrylamide/acrylates/butylaminoethyl methacrylate; polyvinyl
alcohol; polyethylene oxide; sodium polystyrene sulfonate;
polyacrylic acid; polyvinyl pyrrolidone; maltodextrine; hydrolyzed
gelatin; sugar; hydrolyzed starch; sodium salt of polymethacrylic
acid; ammonium salt of polymethacrylic acid; polyvinyl sulfonic
acid; sulfonated polyester; poly(2-ethyl-2-oxazoline);
polymethacrylic acid; sodium salt of polyacrylic acid; ammonium
salt of polyacrylic acid; and combinations thereof.
Description
BACKGROUND
[0001] This application relates generally to rapid prototyping
techniques and, more particularly to a Three. Dimensional Printing
material and method using particulate mixtures.
[0002] The field of rapid prototyping involves the production of
prototype articles and small quantities of functional parts, as
well as structural ceramics and ceramic shell molds for metal
casting, directly from computer-generated design data.
[0003] Two well-known methods for rapid prototyping include a
selective laser sintering process and a liquid binder Three
Dimensional Printing process. The techniques are similar to the
extent that they both use layering techniques to build
three-dimensional articles. Both methods form successive thin cross
sections of the desired article. The individual cross sections are
formed by bonding together grains of a granular material on a flat
surface of a bed of the granular material. Each layer is bonded to
a previously formed layer to form the desired three-dimensional
article at the same time as the grains of each layer are bonded
together. The laser-sintering and liquid binder techniques are
advantageous because they create parts directly from
computer-generated design data and can produce parts having complex
geometries. Moreover, Three Dimensional Printing can be quicker and
less expensive than conventional machining of prototype parts or
production of cast or molded parts by conventional "hard" or "soft"
tooling techniques which can take from a few weeks to several
months, depending on the complexity of the item.
[0004] Three Dimensional Printing has been used to make ceramic
molds for investment casting, thereby generating fully-functional
metal parts. Additional uses have been contemplated for Three
Dimensional Printing.
[0005] For example, three Dimensional Printing may be useful in
design-related fields where it is used for visualization,
demonstration and mechanical prototyping. It may also be useful for
making patterns for molding processes. Three Dimensional Printing
techniques may be further useful, for example, in the fields of
medicine and dentistry, where expected outcomes may be modeled
prior to performing procedures. Other businesses that could benefit
from rapid prototyping technology include architectural firms, as
well as others in which visualization of a design is useful.
[0006] A selective laser sintering process is described in U.S.
Pat. No. 4,863,538 to Deckard, which is incorporated herein by
reference for all purposes. The selective laser sintering process
was commercialized by DTM and acquired by 3D Systems. The selective
laser sintering process involves spreading a thin layer of powder
onto a flat surface. The powder is spread using a tool developed
for use with the selective laser sintering process, known in the
art as a counter-rolling mechanism (hereinafter "counter-roller").
Using the counter-roller allows thin layers of material to be
spread evenly, without disturbing previous layers. After the layer
of powder is spread onto the surface, a laser directs laser energy
onto the powder in a predetermined two-dimensional pattern. The
laser sinters or fuses the powder together in the areas struck by
its energy. The powder can be plastic, metal, polymer, ceramic or a
composite. Successive layers of powder are spread over previous
layers using the counter-roller, followed by sintering or fusing
with the laser. The process is essentially thermal, requiring
delivery by the laser of a sufficient amount of energy to sinter
the powder together, and to previous layers, to form the final
article.
[0007] U.S. Pat. No. 5,639,402 to Barlow, incorporated herein by
reference for all purposes, discloses a method for selectively
fusing calcium phosphate particles that are coated, or
alternatively mixed with, a polymeric binder material.
[0008] U.S. Pat. No. 5,204,055, to Sachs et al. incorporated herein
by reference for all purposes, describes an early Three Dimensional
Printing technique which involves the use of an ink-jet printing
head to deliver a liquid or colloidal binder material to layers of
powdered material. The Three Dimensional inkjet printing technique
(hereafter "liquid binder method") involves applying a layer of a
powdered material to a surface using a counter-roller. After the
powdered material is applied to the surface, the ink-jet printhead
delivers a liquid binder to the layer of powder. The binder
infiltrates into gaps in the powder material, hardening to bond the
powder material into a solidified layer. The hardened binder also
bonds each layer to the previous layer. After the first
cross-sectional portion is formed, the previous steps are repeated,
building successive cross-sectional portions until the final
article is formed. Optionally, the binder can be suspended in a
carrier which evaporates, leaving the hardened binder behind. The
powdered material can be ceramic, metal, plastic or a composite
material, and can also include fiber. The liquid binder material
can be organic or inorganic. Typical organic binder materials used
are polymeric resins, or ceramic precursors such as
polycarbosilazane. Inorganic binders are used where the binder is
incorporated into the fmal articles; silica is typically used in
such an application.
[0009] U.S. Pat. No. 5,490,962 to Cima, incorporated herein by
reference for all purposes, discloses solid free-form techniques
for making medical devices for controlled release of bioactive
agents.
[0010] U.S. Pat. No. 6,397,922 to Sachs et al., incorporated herein
by reference for all purposes, discloses a layered fabrication
technique used to create a ceramic mold and is incorporated herein
by reference for all purposes.
[0011] One advantage of using an inkjet printhead rather than a
laser is that a plurality of spray nozzles used to deliver binder
to the powder can be arranged side-by-side in a single printhead.
In selective laser sintering machines, only one laser, which
delivers energy to the powder, is conventionally used. The
combination of several spray nozzles increases the speed of liquid
binder printing compared to laser-sintering by allowing a wider
area to be printed at one time. In addition, the liquid binder
printing equipment is much less expensive than the laser equipment
due to the high cost of the laser and the high cost of the related
beam deflection optics and controls.
[0012] However, three-dimensional printing materials may be
susceptible to deformation during and after the printing process if
sufficient bond strength within and between layers has not
adequately developed.
[0013] In addition, the powders, especially metallic powders, used
in both selective laser sintering and liquid binder techniques
present safety issues that render them undesirable for use in an
office environment. These safety issues may require special
clothing and processing facilities to prevent, for example, skin
contact or inhalation of toxic materials. In addition, more expense
may be incurred through complying with regulations for the disposal
of toxic materials.
SUMMARY
[0014] One aspect of the invention is directed to an article
comprising a product of a mixture of a plurality of particles of a
first particulate material, a second particulate material and a
third particulate material. The first particulate material and the
second particulate material can react to form a solid in a period
of time, and the third particulate material can solidify in a
longer period of time. In another embodiment, the mixture of the
plurality of particles may also include a filler. In another
embodiment, the first particulate material is a phosphate. In
another embodiment, the second particulate material is an alkaline
oxide. In yet another embodiment, the first particulate material is
a plaster. In another embodiment, the second particulate material
is an accelerator. In yet another embodiment, the third particulate
material is an adhesive.
[0015] Another aspect of the invention is directed to a compound
used in three dimensional printing. The compound comprises a first
particulate material, a second particulate material, and a third
particulate, wherein the first particulate material and the second
particulate material can react to form a solid in a period of time,
and the third particulate material can solidify in a longer period
of time. In another embodiment, the compound may also include a
filler. In another embodiment, the first particulate material is a
phosphate. In another embodiment, the second particulate material
is an alkaline oxide. In yet another embodiment, the first
particulate material is a plaster. In another embodiment, the
second particulate material is an accelerator. In yet another
embodiment, the third particulate material is an adhesive.
[0016] Another aspect of the invention is directed to a method of
three-dimensional printing, comprising providing a layer of a dry
particulate material comprising a first particulate material, a
second particulate material, and a third particulate material and
dispensing a fluid onto a region of the first layer. The fluid
causes a reaction between the first and second particulate
materials to occur, the reaction causing a solidified material to
form in the region, and causes the third particulate material to
solidify in the region. The reaction between the first and second
particulate materials occurs in a period of time, and the third
particulate material solidifies in a longer period of time. In
another embodiment, the layer of dry particulate material may also
include a filler. In another embodiment, the first particulate
material is a phosphate. In another embodiment, the second
particulate material is an alkaline oxide. In yet another
embodiment, the first particulate material is a plaster. In another
embodiment, the second particulate material is an accelerator. In
yet another embodiment, the third particulate material is an
adhesive.
[0017] Another aspect of the invention is directed to a mixture of
solids used in three dimensional printing that, when contacted by a
fluid, undergoes a first solidification reaction occurring at a
first rate, and simultaneously undergoes a second solidification
reaction occurring at a second rate slower than the first rate.
[0018] Other advantages, novel features, and objects of the
invention will become apparent from the following detailed
description of non-limiting embodiments of the invention when
considered in conjunction with the accompanying drawings, which are
schematic and which are not intended to be drawn to scale. In the
figures, each identical or nearly identical component that is
illustrated in various figures typically is represented by a single
numeral. For purposes of clarity, not every component is labeled in
every figure, nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. In cases
where the present specification and a document incorporated by
reference include conflicting disclosure, the present specification
shall control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Preferred non limiting embodiments of the present invention
will be described by way of example with reference to the
accompanying drawings, in which:
[0020] FIG. 1 illustrates schematically a first layer of a mixture
of particulate material of the invention deposited onto a
downwardly movable surface on which an article is to built, before
any fluid has been delivered;
[0021] FIG. 2 illustrates schematically an ink-jet nozzle
delivering a fluid to a portion of the layer of particulate
material of FIG. 1 in a predetermined pattern;
[0022] FIG. 3 illustrates schematically a view of a fmal article
made from a series of steps illustrated in FIG. 2 enclosed in the
container while it is still immersed in the loose unactivated
particles;
[0023] FIG. 4 illustrates schematically a view of the final article
from FIG. 3.
[0024] FIG. 5 illustrates schematically a cross-sectional view of a
mold, including a support structure, for fabricating a casting.
DETAILED DESCRIPTION
[0025] The present invention relates to a Three Dimensional
Printing material system useful, among other things, for preparing
molds for casting, such as molds for metal casting. A large number
of metal castings are made by pouring molten metal into a ceramic
mold. For sand casting, the mold may be made of sand held together
with binders. For investment casting, the mold may be made of
refractories, such a alumina powder, held together by silica.
[0026] Molds prepared for casting should be sufficiently strong to
withstand pouring of a molten material, such as metal, into a mold
cavity. However, the mold should also be able to break during the
cooling process, or be broken after the cooling process, to allow
removal of the molded product.
[0027] In a Three Dimensional Printing material system, it is
desired to have good depowderablility, sufficient strength, and a
quick solidification mechanism when preparing a mold or an
appearance model. As used herein, the term `depowderability" is
defined as the ability to clean loose powder from a printed article
after it has solidified. While the exemplary embodiments described
herein are particularly advantageous for molds because of their
strength, heat resistance and other characteristics, they can also
be used to make appearance models and other articles.
[0028] The present invention relates to a Three Dimensional
Printing material system comprising a mixture of a first
particulate material, a second particulate material, a third
particulate material, and a filler. A fluid causes the first
particulate material and the second particulate material to react
to form a solid in a first period of time, and causes the third
particulate material to solidify in a second period of time that is
longer than the first period of time. The reaction between the
first particulate material and the second particulate material
provides initial strength to the printed part during and after the
printing process and may promote high accuracy, allow for a shorter
time from the end of the print stage to handling and may reduce or
eliminate part deformation. Solidification of the third particulate
material provides strength to the final product. As used herein,
the term "solid" is intended to mean a substance that has a
definite volume and shape and resists forces that tend to alter its
volume or shape, as well as to include solid-like substances, such
as gels. The present invention also relates to a method of use for
such a materials system, and to an article made by the method of
the invention.
[0029] Referring now to FIG. 1, a schematic representation of a
printing method using the materials system of the present invention
is presented. According to the method, a layer or film of
particulate material 20 is applied on a downwardly movable surface
22 of a container 24. The layer or film of particulate material can
be formed in any manner, and preferably is applied using a
counter-roller. The particulate material applied to the surface
includes a first particulate material, a second particulate
material, a third particulate material, and a filler. As used
herein, "filler" is meant to define an inert material that is solid
prior to application of the fluid, which is substantially insoluble
in the fluid, and which gives structure to the final article. The
first and second particulate materials react in the presence of a
fluid to provide initial bond strength to the part being built,
while the third particulate material solidifies in a longer period
of time to provide final part strength.
[0030] For purposes of the present invention, "particulate
material" is meant to define any dry material containing
significant amounts of particulate material. The particulate
material may be soluble in, or interact with the fluid material, or
any portion thereof, depending upon the particular embodiment of
the invention that is being practiced. For example, in certain
embodiments, it may be desirable that the particulate material
dissolve in the fluid material.
[0031] Generally, the size of the particles in the particulate
material is limited by the thickness of the layers to be printed.
That is, the particles are preferably approximately smaller than
the thickness of the layers to be printed. The particulate
materials may have any regular or irregular shape. Using smaller
particles may provide advantages such as smaller feature size, the
ability to use thinner layers, and the ability to reduce what is
known in the art as a "stair stepping" effect. In preferred
embodiments, the material systems include particulate material
having particles with a mean diameter ranging from about 1 .mu.m to
about 300 .mu.m, preferably ranging from about 2 .mu.m to about 250
.mu.m, more preferably ranging from about 10 .mu.m to about 100
.mu.m, and more preferably ranging from about 10 .mu.m to about 50
.mu.m.
[0032] The particulate material may include impurities and/or inert
particles. The inert particles or any portion of the particulate
material can comprise granular, powdered or fibrous materials.
Classes of inert particles include a polymer, a ceramic, a metal,
an organic material, an inorganic material, a mineral, clay and a
salt.
[0033] Choosing a suitable particulate material for the material
systems of the present invention involves various qualitative
evaluations, which may easily be accomplished through routine
experimentation by those of ordinary skill in the art. First, a
small mound of particulate material is formed, a small depression
is formed in the mound, and a small amount of fluid is placed in
the depression. Visual observations are made regarding, among other
things, the rate at which the fluid diffuses into the particulate
material, the viscosity of the particulate material introduction of
the fluid, and whether a membrane is formed around the fluid. Next,
line testing is performed by filling a syringe filled with fluid
and strafing the mounds of particulate material. After a period of
about 24 hours, the mounds of particulate material are examined.
Those in which pebbles of particulate material have formed are
suitable, as it means that the particulate material and fluid react
more quickly than the fluid can evaporate or diffuse into the
surrounding dry powder. Those in which both pebbles and rods of
hardened material have formed are the yet more suitable, indicating
that the rate at which the fluid and particulate material harden is
greater than the rate at which fluid evaporates or diffuses into
the surrounding dry powder. In some instances, the rods of hardened
material will shrink, indicating that the particulate material may
give rise to problems with distortions. As described above, various
additives may be included in the particulate material and/or fluid
to accelerate the rate at which the particulate material
hardens.
[0034] The particulate material may also be evaluated to determine
the ease of spreading. Simple test parts may also be formed to
determine, inter alias, the flexural strength, the distortion, the
rate of hardening, the optimum layer thickness, and the optimum
ratio of fluid to particulate material. Material systems suitable
for use in the three-dimensional printing method include those
hardening with minimal distortion, in addition to relatively high
flexural strength. Hardened products with high flexural strength
values may not be suitable for use in the three-dimensional
printing method, if distortions compromise the accuracy of the
final printed articles; this is especially applicable where
relatively fine features are desired.
[0035] After a material has been identified as a potential material
through line testing, the formula may be further developed by
printing test patterns on a three dimensional printer. The
strength, accuracy, and degree of difficulty in handling may all be
characterized with a set of test parts (e.g., breaking bars for
strength and gauge blocks for accuracy). These tests may be
repeated as much as necessary, and powder formulas are iterated
until optimum characteristics are obtained.
[0036] According to aspects of embodiments of the present
invention, an additional criterion for selecting the particulate
materials are the relative rates of reaction and/or solidification
in the presence of a fluid. The first particulate material and the
second particulate material are selected to react and solidify in
the presence of the fluid in a period of time shorter than the
solidification of the third particulate material in the presence of
the fluid. Solidification of the reaction product of the first and
second particulate materials in the presence of the fluid could
occur within about 20 minutes. In another embodiment, the first
particulate material and the second particulate material react to
form a solid within about 10 minutes, preferably within about 5
minutes, more preferably within about 2 minutes, and most
preferably within about 1 minute of application of the fluid. The
solidification of the third particulate material occurs at a time
longer than the reaction between the first particulate material and
the second particulate material. In one embodiment, the third
particulate material solidifies in a time ranging from about 10
minutes to about 2 hours or more. The absolute period of time for
the solidification of the first and second particulate materials
and the absolute period of time for solidification of the third
particulate material can each vary over a wide range, however, the
period of time for solidification of the third particulate material
will be at least longer than period of time for solidification of
the first particulate material and the second particulate
material.
[0037] In one embodiment, the first particulate material may be an
acid and second particulate material may be a base that react with
one another in the presence of a fluid. For example, the first
particulate material may be a phosphate while the second
particulate material may be an alkaline oxide, and/or an alkaline
hydroxide. When an aqueous fluid is printed on a powder that
contains these materials, the phosphate dissolves and acts on the
alkaline oxide and/or an alkaline hydroxide to form a cement.
[0038] The phosphates used in the embodiments of the invention
include a salt of an oxygen acid of phosphorus including salts of
phosphoric acids such as orthophosphoric acid, polyphosphoric acid,
pyrophosphoric acid, and metaphosphoric acid.
[0039] As used herein, the term "phosphate" is generic and includes
both crystalline and amorphous inorganic phosphates. Further,
"phosphate" includes, but is not limited to, orthophosphates and
condensed phosphates. Orthophosphates are compounds having a
monomeric tetrahedral ion unit (PO.sub.4).sup.3-. Typical
orthophosphates include sodium orthophosphates, such as, monosodium
phosphate, disodium phosphate, trisodium phosphate, potassium
orthophosphates and ammonium orthophosphates. Phosphates are
further described in U.S. Pat. No. 6,299,677 to Johnson et al. and
incorporated by reference in its entirety for all purposes.
[0040] Examples of acid phosphates that may be used in embodiments
of the invention include, but are not limited to, monoammonium
phosphate; sodium aluminum phosphate, acidic; monocalcium
phosphate, anhydrous; monopotassium phosphate; monosodium
phosphate; and aluminum acid phosphate. Examples of acid
polyphosphates that may be used in embodiments of the invention
include, but are not limited to, sodium tripolyphosphate; sodium
hexametaphosphate; sodium polyphosphate, anhydrous; and ammonium
polyphosphate. Examples of acid pyrophosphates that may be used in
embodiments of the invention include, but are not limited to,
sodium acid pyrophosphate; tetrasodium pyrophosphate;
tetrapotassium pyrophosphate. Examples of other phosphates that may
be used in embodiments of the invention include, but are not
limited to, diammonium phosphate; dipotassium phosphate; disodium
phosphate; monocalcium phosphate, monhydrate; dicalcium phosphate,
dihydrate; dicalcium phosphate, anhydrous; tricalcium phosphate;
disodium phosphate; and tripotassium phosphate. In a preferred
embodiment, the phosphate is a phosphate salt, such as, monocalcium
phosphate, anhydrous; sodium aluminum phosphate, acidic; aluminum
acid phosphate; monoammonium phosphate; monopotassium phosphate;
and combinations thereof.
[0041] Alkaline oxides that may be used as the second particulate
material include, but are not limited to, zinc oxide; magnesium
oxide; calcium oxide; copper oxide; beryllium oxide; bismuth oxide;
cadmium oxide; tin oxide; red lead oxide; and combinations thereof.
Examples of alkaline hydroxides that may be used as the second
particulate material include, but are not limited to, magnesium
hydroxide, beryllium dihydroxide, cobalt trihydroxide, and
combinations thereof. In one embodiment, the second particulate
material is an alkaline oxide. In a preferred embodiment, the
alkaline oxide is magnesium oxide. Magnesium oxide may react with
phosphate compounds to form magnesium phosphate cement. In one
embodiment, the ratio of magnesium oxide and acid phosphate salt
may be varied to accommodate a variety of resin, filler, and binder
chemistries.
[0042] In another embodiment, magnesium oxide may react with
sulfate containing compounds to form magnesium oxysulfate cement,
or react with chloride containing compounds to form magnesium
oxychloride cement. In another embodiment, zinc oxide may react
with sulfate containing compounds or chloride containing compounds.
Examples of sulfate containing compounds include, but are not
limited to, magnesium sulfate and zinc sulfate. Examples of
chloride containing compounds include, but are not limited to,
magnesium chloride, zinc chloride, and calcium chloride.
[0043] In another embodiment, the first particulate material may be
plaster, and the second particulate material may be an accelerator.
Plaster is frequently called "Plaster of Paris," a name derived
from the earths of Paris and its surrounding regions, which contain
an abundance of the mineral gypsum, from which Plaster of Paris is
manufactured. Plaster is also referred to by many other names,
including, but not limited to, sulphate of lime, semihydrate of
calcium sulfate, casting plaster, gypsum plaster, hydrated sulphate
of lime, hydrated calcium sulphate, and dental plaster, as well as
a variety of trade names. The term "plaster," as used herein, is
meant to define any variety of material including a substantial
amount of CaSO.sub.4.1/2H.sub.2O that is in powder form prior to
the application of an aqueous fluid. The terms "hydrated plaster"
and "set plaster" are used interchangeably herein, and are meant to
include any variety of plaster that includes a substantial amount
of CaSO.sub.4.2H.sub.2O after setting, or rehydration. Many
varieties of plaster are commercially available, varying, for
example, in structural strength, the time required for setting, and
in volume changes that occur during the setting. Typically,
commercially available plasters include other ingredients such as,
but not limited to, silica, powdered limestone, starch, Terra Alba,
and lime. Examples of commercially available plaster materials that
may be suitable for the embodiments of the present invention
include, but are not limited to, white hydrocal cement, durabond
90, and drystone (each available from U.S. Gypsum, located in
Chicago, Ill.), as well as most brands of casting plaster, molding
plaster, and spackling compound.
[0044] An accelerator may be used as the second particulate
material. "Accelerator," as used herein, is meant to define any
material that increases the rate at which plaster sets. Examples of
ways to accelerate the rate of plaster include, but are not limited
to, increasing the solubility of plaster in water, by providing
additional nucleation sites for crystal formation or increasing the
growth rate of crystals. Accelerators are generally used sparingly
in conventional plaster processing, as they may adversely affect
the strength characteristics of the plaster. However, accelerators
are preferred in some embodiments of the present invention because
they help produce a relatively quick set during printing and
further processing. The potential adverse effect to the strength
characteristics of the plaster is of less importance since the
third particulate material is present to provide strength to the
fmal part. Suitable accelerators include, but are not limited to,
Terra Alba, potassium sulfate, barium sulfate, ammonium sulfate,
sodium chloride, under calcined-plaster, alum, potassium alum,
lime, calcined lime, and combinations thereof. Terra Alba, which is
raw ground gypsum, is a preferred accelerator, and works by
providing additional nucleation sites for gypsum crystal formation.
Another preferred accelerator is potassium sulfate, which is
thought to work by increasing the solubility of the plaster in the
water. Both Terra Alba and potassium sulfate also increase the
final strength of the article. In one embodiment, at least one
accelerator is preferably used as a second particulate material in
order to increase the rate at which the plaster sets. Plaster
chemistry is further described in U.S. patent application Ser. No.
09/832,309 filed Apr. 10, 2001 which is a continuation of U.S.
patent application Ser. No. 09/182,295 filed Oct. 29, 1998, and is
incorporated herein by reference in its entirety for all purposes.
The third particulate material of the embodiments of the invention
reacts in the presence of an fluid to solidify at a rate slower
than that of the reaction between the first particulate material
and the second particulate material, and imparts strength to the
final part. In one embodiment, the third particulate material is an
adhesive. In another embodiment, the third particulate material is
a filler coated with an adhesive.
[0045] The adhesive is a compound selected for the characteristics
of high solubility in the fluid, low solution viscosity, low
hygroscopicity, and high bonding strength. The adhesive should be
highly soluble in the fluid in order ensure that it is incorporated
rapidly and completely into the fluid. Low solution viscosity is
preferred to ensure that once dissolved in the fluid, the solution
migrates quickly to sites in the powder bed to adhesively bond
together the reinforcing materials. The adhesive is preferably
milled as finely as possible prior to admixture with the filler
and/or prior to coating the filler particles in order to increase
the available surface area, enhancing dissolution in the solvent,
without being so fine as to cause "caking," an undesirable article
characteristic. Typical adhesive particle grain sizes are about
10-40 .mu.m. Low hygroscopicity of the adhesive avoids absorption
of excessive moisture from the air and evaporating fluid in printed
regions of the powder bed which causes "caking", in which
unactivated powder spuriously adheres to the outside surface of the
part, resulting in poor surface definition.
[0046] Water-soluble compounds are preferred for the adhesive in
embodiments of the present invention, although other compounds can
be used. Compounds suitable for use as the adhesive in embodiments
of the present invention may be selected from the following
non-limiting list: water-soluble polymers, carbohydrates, sugars,
sugar alcohols, proteins, and some inorganic compounds.
Water-soluble polymers with low molecular weights dissolve more
quickly because smaller molecules diffuse more rapidly in solution.
Suitable water-soluble polymers include but are not limited to,
polyethylene glycol, sodium polyacrylate, polyacrylic acid,
polyvinyl alcohol, polyvinyl pyrrolidone, sodium polyacrylate
copolymer with maleic acid, polyvinyl alcohol copolymer with
polyvinyl acetate, and polyvinyl pyrrolidone copolymer with vinyl
acetate, a copolymer of octylacrylamide/acrylate/butylaminoethyl
methacrylate, polyethylene oxide, sodium polystyrene sulfonate,
polyacrylic acid, polymethacrylic acid, copolymers of polyacrylic
acid and methacrylic acid with maleic acid, and alkali salts
thereof, maltodextrine, hydrolyzed gelatin, sugar, polymethacrylic
acid, polyvinyl sulfonic acid, sulfonated polyester,
poly(2-ethyl-2-oxazoline), polymers incorporating maleic acid
functionalities, and combinations thereof. Carbohydrates include,
but are not limited to, acacia gum, locust bean gum, pregelatinized
starch, acid-modified starch, hydrolyzed starch, sodium
carboxymethylcellulose, sodium alginate and hydroxypropyl
cellulose. Suitable sugars and sugar alcohols include sucrose,
dextrose, fructose, lactose, polydextrose, sorbitol and xylitol.
Organic compounds including organic acids and proteins can also be
used, including citric acid, succinic acid, polyacrylic acid,
gelatin, rabbit-skin glue, soy protein, and urea. Inorganic
compounds include plaster, bentonite, sodium silicate and salt.
[0047] In another embodiment, a mixture of solid material is
contacted by a fluid, and undergoes a first solidification
beginning with the fluid contact and occurring at a first rate, and
also undergoes a second solidification reaction beginning with the
fluid contact and occurring at a second rate slower than the first
rate. As used herein, the term "solid material" includes
particulate material, aggregates, and the like. In one embodiment
of the invention, a solid material may include more than one type
of material, such as, a particulate material having a coating that
is activated by the fluid causing a solidification reaction to
occur within the solid material and among adjacent solid material.
As used herein, the term "solidification reaction" is defined as
any chemical, thermal, or physical process wherein free flowing
solid material are hardened, bonded, or firmly fixed in relation to
other adjacent solids.
[0048] In one embodiment, the mixture may be a mixture of two solid
materials, wherein one of the solid materials is present in excess
of a quantity that will react with the other solid material. In
this embodiment, when contacted by a fluid, the two solids
materials react and solidify in a first period of time, and the
excess of one of the solid materials left over from the reaction
with the other solid material reacts when contacted by a fluid in a
second period of time that is longer than the first period of time.
For example, the mixture may comprise an alkaline oxide, such as
magnesium oxide, and at least one of polyacrylic acid,
polymethacrylic acid, copolymers of polyacrylic acid and
methacrylic acid with maleic acid, and alkali salts thereof. In the
presence of a fluid, the alkaline oxide reacts with a portion of
the at least one of polyacrylic acid, polymethacrylic acid, citric
acid, succinic acid, malic acid, copolymers of polyacrylic acid and
methacrylic acid with maleic acid, and alkali salts thereof to form
a solid. The remaining portion of the at least one of polyacrylic
acid, polymethacrylic acid, citric acid, succinic acid, malic acid,
copolymers of polyacrylic acid and methacrylic acid with maleic
acid, and alkali salts thereof left over from the reaction with the
alkaline oxide may then solidify in the presence of a fluid in a
longer period of time.
[0049] In another embodiment, the mixture may comprise two solids,
wherein one solid material solidifies in the presence of a fluid in
one period of time, while the other particulate material solidifies
in the presence of a fluid in a second period of time that is
longer than the first period of time.
[0050] In another embodiment, the mixture may comprise three solid
materials, wherein a first and second solid material react in the
presence of a fluid to form a solid in one period of time, and the
third solid material solidifies in the presence of a fluid in a
longer period of time. In an alternative embodiment, a first solid
material may solidify in the presence of a fluid in one period of
time, and a second solid material and third solid material may
react to form a solid in the presence of a fluid in a second period
of time that is longer than the first period of time.
[0051] In another embodiment, the mixture may comprise a first
coated particulate material and a second particulate material. In
one embodiment, the first coated particulate material reacts to
form a solid in one period of time when contacted by a fluid and
the second particulate material solidifies when contacted by a
fluid in longer period of time. In another embodiment, a first
coated particulate material reacts to form a solid in one period of
time when contacted by a fluid and a second particulate material
solidifies when contacted by a fluid in a shorter period of time.
In another embodiment, one or more particulate material may be
encapsulated, or present in an aggregate.
[0052] The fluid in embodiments of the present invention is
selected to comport with the degree of solubility required for the
various particulate components of the mixture, as described above.
The fluid comprises a solvent in which the third particulate
material and at least one of the first particulate material and the
second particulate material are active, preferably soluble, and may
include processing aids such as a humectant, a flowrate enhancer,
and a dye. An ideal solvent is one in which the third particulate
material and at least one of the first particulate material, the
second particulate material, and the third particulate material is
highly soluble, and in which the filler is insoluble or
substantially less soluble. The fluid can be aqueous or
non-aqueous. In a preferred embodiment, an aqueous fluid comprises
at least one cosolvent. Suitable solvents and cosolvents may be
selected from the following non-limiting list: water; methyl
alcohol; ethyl alcohol; isopropyl alcohol; acetone; methylene
chloride; acetic acid; ethyl acetoacetate; dimethylsulfoxide;
n-methyl pyrrolidone; 2-amino-2-methyl-1-propanol;
1-amino-2-propanol; 2-dimethylamino-2-methyl-1-propanol;
N,N-diethylethanolamine; N-methyldiethanolamine;
N,N-dimethylethanolamine; triethanolamine; 2-aminoethanol;
1-[bis[3-(dimethylamino)propyl]amino]-2-propanol;
3-amino-1-propanol; 2-(2-aminoethylamino)ethanol;
tris(hydroxymethyl)aminomethane; 2-amino-2-ethyl-1,3-propanediol;
2-amino-2-methyl-1,3-propanediol; diethanolamine;
1,3-bis(dimethylamino)-2-propanol; and combinations thereof. Other
polar organic compounds will be obvious to one skilled in the art.
In a preferred embodiment, the fluid is an aqueous solution of
2-amino-2-methyl-1-propanol, with isopropanol, ethanol, or a
combination of both.
[0053] The filler in embodiments of the present invention is a
compound selected for the characteristics of insolubility, or
extremely low solubility in the fluid, rapid wetting, low
hygroscopicity, and high bonding strength. The filler provides
mechanical structure to the hardened composition. Sparingly soluble
filler material may be used, but insoluble filler material is
preferred. The filler particles become adhesively bonded together
when the first particulate material and the second particulate
material interact upon application of the fluid. The filler
particles are further bonded together when the third particulate
material dries/hardens after the fluid has been applied.
Preferably, the filler includes a distribution of particle grain
sizes, ranging from the practical maximum of about 250-300 .mu.m
downward, to the practical minimum of about 1 .mu.m. Large grain
sizes appear to improve the final article quality by forming large
pores in the powder through which the fluid can migrate rapidly,
permitting production of a more homogeneous material. Smaller grain
sizes serve to reinforce article strength.
[0054] Compounds suitable for use as the filler in embodiments of
the present invention may be selected from the same general groups
from which the third particulate material is selected, provided
that the solubility, hygroscopicity and bonding strength criteria
described above are met. Examples of fillers include, but are not
limited to, limestone, olivine, zircon, alumina, staurolite, and
fused silica. In one embodiment, the filler may be a granular
refractory particulate, including, but not limited to, limestone,
staurolite, silica sand, zircon sand, olivine sand, chromite sand,
magnesite, alumina silicate, calcium silicate, fused silica,
calcium phosphate, rutile, bentonite, montmorillonite, glass,
chamotte, fireclay, and mixtures thereof. In a preferred
embodiment, the filler is olivine, a mineral used for foundry sand
((Mg--Fe).sub.2SiO.sub.4) that is low in crystalline silica and
possesses a low coefficient of thermal expansion. In another
preferred embodiment, the filler is zircon (ZrSiO.sub.4).
[0055] Various processing aids may be added to the particulate
material, the fluid, or both, including, but not limited to,
accelerators, adhesives, flowrate enhancers, humectants, visible
dyes, fiber, filler, and combinations thereof. Examples of these
and other additives may be found in U.S. Pat. Nos. 5,902,441 to
Bredt et al. and 6,416,850 to Bredt et al., both incorporated by
reference in their entirety for all purposes
[0056] FIG. 2 is a schematic representation of an inkjet nozzle 28
delivering fluid 26 to a portion 30 of the layer or film 20 of the
particulate mixture in a two-dimensional pattern. According to the
method, the fluid 26 is delivered to the layer or film of
particulate material in any predetermined two-dimensional pattern
(circular, in the figures, for purposes of illustration only),
using any convenient mechanism, such as a Drop-On-Demand
(hereinafter "DOD") printhead driven by customized software which
receives data from a computer-assisted-design hereinafter "CAD")
system, a process which is known in the art. The first portion 30
of the particulate mixture is by the fluid, causing the first
particulate material and the second particulate material to adhere
together and the third particulate material to adhere to form an
essentially solid circular layer that becomes a cross-sectional
portion of the final article. As used herein, "activates" is meant
to define a change in state from essentially inert to adhesive.
When the fluid initially comes into contact with the particulate
mixture, it immediately flows outward (on the microscopic scale)
from the point of impact by capillary action, dissolving the
adhesive within the first few seconds. A droplet of fluid,
typically having a volume of about 100 .mu.l, may spread to a
surface area of about 100 .mu.m once it comes into contact with the
particulate mixture. As the solvent dissolves the third particulate
material and at least one of the first particulate material and
second particulate material, the fluid viscosity increases
dramatically, arresting further migration of the fluid from the
initial point of impact. Within a few minutes, the fluid with
dissolved particulate material therein infiltrates the less soluble
and slightly porous particles, forming bonds between the filler
particles. The fluid is capable of bonding together the particulate
mixture in an amount that is several times the mass of a droplet of
the fluid. As volatile components of the fluid evaporate, the
adhesives harden, joining the filler into a rigid structure, which
becomes a cross-sectional portion of the finished article.
[0057] Any unactivated particulate mixture 32 that was not exposed
to the fluid remains loose and free-flowing on the movable surface.
Preferably, the unactivated particulate mixture is left in place
until formation of the final article is complete. Leaving the
unactivated, loose particulate mixture in place ensures that the
article is supported during processing, allowing features such as
overhangs, undercuts, and cavities (not illustrated, but
conventional) to be defined without using support structures. After
formation of the first cross-sectional portion of the final
article, the movable surface is indexed downward.
[0058] Using, for example, a counter-rolling mechanism, a second
film or layer of the particulate mixture is then applied over the
first, covering both the rigid first cross-sectional portion, and
any loose particulate mixture by which it is surrounded. A second
application of fluid follows in the manner described above,
dissolving the adhesive and forming adhesive bonds between a
portion of the previous cross-sectional portion, the filler, and,
optionally, fiber of the second layer, and hardening to form a
second rigid cross-sectional portion added to the first rigid
cross-sectional portion of the final article. The movable surface
is again indexed downward.
[0059] Applying a layer of particulate mixture, including the
adhesive, applying the fluid, and indexing the movable surface
downward are repeated until the final article is completed. FIG. 3
is a schematic representation of the final cylindrical article
after it has been completely formed. At the end of the process,
only the top surface 34 of a final article 38 is visible in the
container. The final article is preferably completely immersed in a
bed 36 of unactivated particulate material. Alternatively, those
skilled in this art would know how to build an article in layers
upward from an immovable platform, by successively depositing,
smoothing and printing a series of such layers.
[0060] FIG. 4 is a schematic representation of the final
cylindrical article 38. The unactivated particulate material is
preferably removed by blown air or a vacuum. After removal of the
unactivated particulate material from the final article 38,
post-processing treatment may be performed, including cleaning,
infiltration with stabilizing materials, painting, etc.
[0061] FIG. 5 illustrates a mold prepared using the
three-dimensional printing techniques of on embodiment of the
present invention. Mold 40 comprises an inner shell 42, an outer
shell 44, and supports 46 to provide added strength to the inner
shell during the casting process. After three-dimensional printing
is completed, unactivated particulate material is removed from
cavity 48, thus providing a casting surface. Unactivated
particulate material may, but need not be, removed from
interstitial spaces 50. Unactivated particulate material remaining
in the interstitial spaces may provide additional strength to the
inner shell during subsequent casting.
[0062] Embodiments of the present invention is further illustrated
by the following Examples which in no way should be construed as
further limiting. The following representative formulas are
directed to preparing molds for investment casting.
Particulate Formulation I
67% Olivine sand (-140 mesh)
[0063] 29.6% Plaster [0064] 3% PVA [0065] 0.3% Terra alba [0066]
0.1% K.sub.2SO.sub.4.
[0067] In Formulation I, Olivine is a mineral used for foundry sand
((Mg--Fe).sub.2 SiO.sub.4) that is low in crystalline silica and
possesses a low coefficient of thermal expansion. Olivine sand
(-140 mesh) is bonded with plaster (Hydrocal) and PVA, but the bond
between PVA and olivine is sufficiently strong that much less resin
is needed. The reduced organic content causes molds made with the
formulation of Example II, to emit less smoke during casting. This
improves the environmental conditions during casting, and leads to
higher quality castings due to the formation of less gas bubbling.
The mold resulting from this formulation is suitable for
low-temperature casting, such as casting Aluminum, Magnesium and
Zinc.
Fluid I
[0068] 92.6% Water [0069] 6.0% glycerol [0070] 0.5% isopropanol
[0071] 0.5% polyvinyl pyrrolidone [0072] 0.2%
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate [0073] 0.2%
potassium sorbate
[0074] Fluid I is a preferred fluid for particulate formulation
I.
[0075] Particulate Formulations II and III are intended for high
temperature material casting such as for brass, cast iron, and
steel. Because plaster decomposes at around 1200.degree. C. and
releases sulfur dioxide, it is not desirable to use it for high
temperature casting.
Particulate Formulation II
[0076] 83.9% Zircon [0077] 2.5%
octacrylamide/acrylatelbutylaminoethyl methacrylate copolymer
[0078] 1.5% Zinc oxide [0079] 10% limestone [0080] 1.28% MgO [0081]
0.72% monocalcium phosphate, anhydrate [0082] 0.1% ethylene glycol
octyl/decyl diester
[0083] Magnesium phosphate cement forms bonds early in the curing
process to resist the drying stresses and attendant part
distortion. The active cement filler is formed by the combination
of magnesium oxide with monocalcium phosphate, anhydrate. Any
commercially available grade of magnesium oxide or monocalcium
phosphate, anhydrate may be used. This material rapidly forms a gel
that maintains the dimensional stability of the part while the
octylacrylamide/acrylate/butylaminoethyl methacrylate copolymer,
having a particle size of less than about 70 .mu.m, dissolves and
deposits itself into the pores of the granular solid, forming
stronger bonds that support the material during handling up the
casting stage. Zircon (ZrSiO.sub.4) having a 140 mesh particle size
is a very refractory (foundry sand) filler that has a very low
coefficient of thermal expansion. The remaining ingredients: Zinc
oxide having a particle size of about 10 microns, limestone having
a particle size of less than about 40 microns, and ethylene glycol
octyl/decyl diester are added in order to control the flow of
powder during spreading and printing. Any commercially available
grade of ethylene glycol octyl/decyl diester may be used.
Particulate Formulation III
[0084] 75.9% Olivine [0085] 2.0%
octacrylamide/acrylate/butylaminoethyl methacrylate copolymer
[0086] 2.4% ZnO [0087] 15.9% fused silica (SiO.sub.2) [0088] 2.2%
MgO [0089] 1.4% monocalcium phosphate, anhydrous [0090] 0.18%
ethylene glycol octyl/decyl diester [0091] 0.02% sorbitan trioleate
(SPAN 85)
[0092] In this formula, olivine replaces zircon as the refractory
filler. Olivine has a slightly higher thermal expansion than
zircon, but since it is lower density, the printed parts are
lighter and easier to manipulate. The magnesium oxide/monocalcium
phosphate cement enables parts to be built and removed from the
machine rapidly, and placed in a drying oven to harden the organic
copolymer to full strength. Zinc oxide and fused silica, having a
particle size of about 200 mesh, are fine powdered additives.
Ethylene glycol octyl/decyl diester and sorbitan trioleate are oily
liquids that give the powder a small degree of cohesion, further
improving the friction characteristics.
Fluid II
[0093] 86.5% water [0094] 10.0% isopropanol [0095] 2.5%
2-amino-2-methyl-1-propanol [0096] 1%
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate
[0097] In Fluid II, the water component dissolves the phosphate
allowing the phosphate to act on the magnesium oxide to form a
cement. Fluid II includes 2-amino-2-methyl-1-propanol, an organic
alkali that is compatible with the
octylacrylonitrile/acrylate/butylaminoethyl methacrylate copolymer
and dissolves the copolymer. Isopropanol and
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate facilitate wetting
of the fluid in the powder.
[0098] Further considerations when selecting the adhesive, filler
and fiber depend on the desired properties of the fmal article. The
fmal strength of the finished article depends largely on the
quality of the adhesive contacts between the particles of the
mixture, and the size of the empty pores that persist in the
material after the adhesive has hardened; both of these factors
vary with the grain size of the particulate material. In general,
the mean size of the grains of particulate material is preferably
not larger than the layer thickness. A distribution of grain sizes
increases the packing density of the particulate material, which in
turn increases both article strength and dimensional control.
[0099] The materials and method of the illustrative embodiments of
the present invention present several advantages over prior Three
Dimensional Printing methods. The particulate materials provide a
relatively rapid binding reaction in addition to a relatively
longer reaction time for preparing the fmal part. The additional
rapid binding mechanism may provide high accuracy, allow for
shorter printing and handling time and may reduce or eliminate part
deformation. The materials used in embodiments of the present
invention are relatively non-toxic and inexpensive. Because the
binding particles are added directly to the particulate mixture,
adhesive, particularly adhesive including high levels of suspended
solids, need not be sprayed through the printhead. Instead,
embodiments of the present invention involves spraying preferably
an aqueous solvent, which overcomes problems such as clogging
associated with prior art methods that involve spraying a binder to
a layer of powder.
[0100] Those skilled in the art will readily appreciate that all
parameters listed herein are meant to be exemplary and actual
parameters depend upon the specific application for which the
methods and materials of the present invention are used. It is,
therefore, to be understood that the foregoing embodiments are
presented by way of example only and that, within the scope of the
appended claims and equivalents thereto, the invention can be
practiced otherwise than as specifically described.
[0101] While several embodiments of the invention have been
described and illustrated herein, those of ordinary skill in the
art will readily envision a variety of other means and structures
for performing the functions and/or obtaining the results or
advantages described herein, and each of such variations or
modifications is deemed to be within the scope of the present
invention. More generally, those skilled in the art would readily
appreciate that all parameters, dimensions, materials, and
configurations described herein are meant to be exemplary and that
actual parameters, dimensions, materials, and configurations will
depend upon specific applications for which the teachings of the
present invention are used. Those skilled in the art will
recognize, or be able to ascertain using no more than routine
experimentation, many equivalents to the specific embodiments of
the invention described herein. It is, therefore, to be understood
that the foregoing embodiments are presented by way of example only
and that, within the scope of the appended claims and equivalents
thereto, the invention may be practiced otherwise than as
specifically described. The present invention is directed to each
individual feature, system, material and/or method described
herein. In addition, any combination of two or more such features,
systems, materials and/or methods, if such features, systems,
materials and/or methods are not mutually inconsistent, is included
within the scope of the present invention.
[0102] In the claims (as well as in the specification above), all
transitional phrases such as "comprising", "including", "carrying",
"having", "containing", "involving", and the like are to be
understood to be open-ended, i.e. to mean including but not limited
to. Only the transitional phrases "consisting of" and "consisting
essentially of" shall be closed or semi-closed transitional
phrases, respectively, as set forth in the United States Patent
Office Manual of Patent Examining Procedures, section 2111.03.
* * * * *