U.S. patent application number 17/393864 was filed with the patent office on 2021-11-25 for method and device for 3d printing using temperature-controlled processing.
The applicant listed for this patent is VOXELJET AG. Invention is credited to Ingo Gnuchtel, Daniel Gunther, Johannes Gunther, Massimo Russo.
Application Number | 20210362409 17/393864 |
Document ID | / |
Family ID | 1000005756530 |
Filed Date | 2021-11-25 |
United States Patent
Application |
20210362409 |
Kind Code |
A1 |
Gunther; Daniel ; et
al. |
November 25, 2021 |
METHOD AND DEVICE FOR 3D PRINTING USING TEMPERATURE-CONTROLLED
PROCESSING
Abstract
The invention relates to a method for producing 3D components,
particulate material being applied in layers to a building platform
in a closed build space and printing fluid being selectively
applied, and these steps being repeated until a three-dimensional
component is obtained, the relative humidity or the relative
solvent concentration in the atmosphere in the build space being
set to a selected value, and/or the temperature in the build space
being set to a selected temperature.
Inventors: |
Gunther; Daniel; (Munchen,
DE) ; Gunther; Johannes; (Martinsried, DE) ;
Gnuchtel; Ingo; (Villenbach, DE) ; Russo;
Massimo; (Augsburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOXELJET AG |
Friedberg |
|
DE |
|
|
Family ID: |
1000005756530 |
Appl. No.: |
17/393864 |
Filed: |
August 4, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15128640 |
Sep 23, 2016 |
11097471 |
|
|
PCT/DE2015/000151 |
Mar 27, 2015 |
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17393864 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 50/02 20141201;
B29C 64/165 20170801; B33Y 30/00 20141201; B33Y 40/00 20141201;
B33Y 10/00 20141201 |
International
Class: |
B29C 64/165 20060101
B29C064/165; B33Y 10/00 20060101 B33Y010/00; B33Y 30/00 20060101
B33Y030/00; B33Y 40/00 20060101 B33Y040/00; B33Y 50/02 20060101
B33Y050/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2014 |
DE |
10 2014 004 692.3 |
Claims
1-8. (canceled)
9. A device, suitable for 3D printing methods, comprising a. a
closed build space; b. a coater for applying a layer of particulate
material to a building platform in the closed build space; c. a
printer for selectively applying a printing fluid to the layer of
particulate material; d. a sensor for measuring a temperature of an
air in the closed build space; e. an air conditioner for regulating
a temperature and a humidity of the air in the closed build space
and for flowing a processed air into the closed build space,
wherein the temperature is regulated to -18.degree. C. to
40.degree. C.; and f. a diffusor or a baffle plate for controlling
or eliminating eliminating air currents from the processed air in
the closed build space.
10. The device according to claim 9, wherein the build space is
essentially tightly sealable.
11-17. (canceled)
18. The device of claim 10, wherein the device includes a
water-based humidifier for regulating the humidity of the air in
the closed build space.
19-20. (canceled)
21. The device of claim 10, wherein the closed build space is
insulated.
22. The device of claim 10, wherein the device includes an IR
emitting unit.
23. The device of claim 10, wherein a reservoir of the coater
includes a water-insoluble particulate material.
24. The device of claim 10, wherein the device includes a removable
build container.
25. The device of claim 10, wherein the device includes a 3D part
having particulate material joined by bridges of a dried water
glass binder, wherein the 3D part is embedded in loose particulate
material.
26. The device of claim 23, wherein the reservoir of the coater
further includes a dried water glass binder.
27. The device of claim 26, wherein the printer includes the
printing fluid, wherein the printing fluid includes or consists of
water.
28. The device of claim 27, wherein the device includes a humidity
sensor.
Description
FIELD
[0001] The invention relates to a method and a device for producing
three-dimensional models by means of settable method
parameters.
BACKGROUND
[0002] A method for producing three-dimensional objects from
computer data is described in the European patent specification EP
0 431 924 B1. In this method, a particulate material is applied in
a thin layer to a platform, and a binder material is selectively
printed onto the particulate material, using a print head. The
particle area onto which the binder is printed sticks together and
solidifies under the influence of the binder and, if necessary, an
additional hardener. The platform is then lowered by a distance of
one layer thickness into a build cylinder and provided with a new
layer of particulate material, which is also printed as described
above. These steps are repeated until a certain, desired height of
the object is reached. A three-dimensional object (also referred to
as a molded part or model) is thereby produced from the printed and
solidified areas.
[0003] After it is completed, this object produced from solidified
particulate material is embedded in loose particulate material and
is subsequently removed therefrom. This is done, for example, using
an extractor. This leaves the desired objects, from which powder
deposits are removed, for example by manual brushing. This method
may be used to process different particulate materials, including
natural biological raw materials, polymers, metals, ceramics and
sands (not an exhaustive list).
[0004] For example, a solid in the particulate material may be used
as the binding system. This solid is dissolved by means of a
solvent which is expelled from the ink-jet print head. After the
solvent evaporates, the particles stick together in the desired
locations. The component may be removed from the remaining loose
powder after a certain waiting period.
[0005] Among other things, powdered water glass (sodium silicate)
may also be used as the binding system. This material is dissolved
by printing a water-based fluid. Depending on the quantity, this
liquid water glass now settles between the particles. Hardening
takes place by means of various mechanisms. However, drying the
binding fluid is predominantly used. The water glass hardens
physically. Other combinations of particulate materials, binders
and fluids are also known to those skilled in the art. Drying or
evaporating the fluid in 3D printing processes of this type also
results in a solidification and formation of a molded part.
[0006] The process execution is problematic during the hardening
process or drying or evaporating of the fluid. A 3D printing
process of this type often results in components having inadequate
strength and extreme geometric deviations.
[0007] In known 3D printing methods, a process parameter is
changed, on the one hand, and the material system is adapted, on
the other hand, for the purpose of increasing the strength and
improving the surface quality.
[0008] WO2012/175072 A1 describes, for example, a method for
controlling deposits on the component using various aggregates. For
example, cement which absorbs excess water may be used. The water
glass content may also be increased.
[0009] Both methods have certain disadvantages. The cement absorbs
a certain amount of moisture and acts, to a certain extent, as a
premature drying process. This is detrimental to the strength.
[0010] It is also useful to increase the water glass content in
order to positively influence the surface qualities. However, the
amount that can be added is technologically limited, and the
economic feasibility of the method is negatively influenced.
[0011] SUMMARY
[0012] The object of the invention is therefore to mitigate the
disadvantages of the known 3D methods or to avoid them entirely. In
particular, one objective of the invention is to increase the
strength of the molded parts produced thereby while maintaining a
good size accuracy and/or reducing the variance of the
aforementioned properties in components of this type.
[0013] This object is achieved by a method for producing 3D
components, particulate material being applied in layers to a
building platform in a closed build space and printing fluid being
selectively applied, and these steps being repeated until a
three-dimensional component is obtained, the relative humidity or
the relative solvent concentration in the atmosphere in the build
space being set to a selected value, and/or the temperature in the
build space being set to a selected temperature.
[0014] In another aspect, the achievement of the object relates to
a device, suitable for 3D printing methods, comprising [0015] a. a
closed build space; [0016] b. means for setting the relative
humidity or the relative solvent concentration in the atmosphere;
and/or [0017] c. means for controlling the temperature of the build
space interior.
[0018] In principle, the object of the invention is achieved in
that the aqueous or fluid solution and the drying or evaporation
are controlled by a targeted guidance of the humidity or the
solvent. A favorable hardening development is achieved thereby, and
components having a desired and regulatable strength are
obtained.
[0019] The inventors have developed an advantageous method, with
the aid of which molded parts having water-based or other
fluid-based materials may be produced, which have both advantageous
strengths and satisfactory surface qualities.
[0020] A number of terms in the invention are explained in greater
detail below.
[0021] Within the meaning of the invention, "3D printing methods"
are all methods known from the prior art which facilitate the
construction of components in three-dimensional molds and are
compatible with the described process components and devices. In
particular, they are powder-based methods, which contain, as one
constituent, aqueous solutions and/or other fluid components or
solvents which must be removed from the molded part or which escape
from the molded part to be produced during or for the
solidification thereof. The solidification and quality of the
molded part may be influenced by the invention in a targeted
manner, other quality features remaining the same or even being
positively influenced.
[0022] "Printing fluid" is understood to be an essentially aqueous
or fluid liquid, which is printable with the aid of ink-jet
devices. The printing fluid may be a material mixture, which
consists of water and other additives, which influence, for
example, the viscosity and surface tension. Agents for preventing
the growth of fungal and vegetable matter may also be contained in
the printing fluid. Not least, the printing fluid may also contain
bindable materials, which result in a certain binding effect in the
filler after drying.
[0023] All materials known for powder-based 3D printing, in
particular sands, ceramic powders, metal powders, plastics, wood
particles, fibrous materials, celluloses and/or lactose powders,
may be used as "fillers." The filler is preferably a dry,
free-flowing powder, although a cohesive, firm powder may also be
used.
[0024] Within the meaning of the invention, "selective binder
application" or "selective binder system application" or "binder
fluid application" or "application of the binder fluid" may take
place after each particulate material application or irregularly,
depending on the requirements of the molded body and for the
purpose of optimizing the production of the molded body, i.e.,
non-linearly and not in parallel after each particulate material
application. "Selective binder application" or "selective binder
system application" may thus be set individually and during the
course of producing the molded body.
[0025] "Binder system" is understood to be a material system that
is able to bind the particulate material. The binder system
comprises at least one "binder fluid" to be printed and possibly
other liquid or solid components, which may be present in the
binder fluid as well as in the particulate material. The binder
system may bind chemically or physically or by means of a
combination of a chemical and physical process. The binding action
may be triggered or accelerated by adding energy, e.g., in the form
of heat or light. In general, all material systems known to those
skilled in the art in this connection may be considered as the
binder system. For example, a binder system may include a "binder
fluid" and a solid "binder," which is contained in the particulate
material (build material) and is soluble in the binder fluid. In
this case, the solid is dissolved by the solvent, which is expelled
from the ink-jet print head and applied to the particulate
material. After the essential evaporation or drying of the binder
fluid, the selectively printed areas of the build material are
bound together. A selective solidification may likewise be produced
in the binder fluid and/or the particulate material with the aid of
chemical systems known to those skilled in the art.
[0026] "Binding agent" is understood to be a powdered component
which is essentially soluble in the printing fluid and induces a
binding action in the dissolved state, in particular if the binder
is in the filler. For example, water glass as well as cement
binders are suitable as the binding agent.
[0027] "Molded body," "model," "3D molded part" or "component"
within the meaning of the invention are all three-dimensional
objects that are produced with the aid of the method according to
the invention and/or the device according to the invention and
which have a nondeformability.
[0028] Any known 3D printing device that contains the necessary
components may be used as the "device" for carrying out the method
according to the invention. Common components include a coater, a
build space, a means for moving the build space or other
components, a dosing device, a print head, a heat means, a
positioning means for batch processes or continuous processes and
other components which are known to those skilled in the art and
therefore do not need to be listed in greater detail here.
[0029] All materials known for powder-based 3D printing, in
particular sands, ceramic powders, metal powders, plastics, wood
particles, fibrous materials, celluloses and/or lactose powders,
may be used as "particulate materials" or as "build materials." The
particulate material is preferably a dry, free-flowing powder,
although a cohesive, firm powder may also be used.
[0030] "Build space" within the meaning of the invention is the
geometric place in which the particulate material feedstock grows
during the build process by repeated coating with particulate
material. The build space is generally delimited by a base, the
building platform, by walls and an open cover surface, the build
plane. The build plane may be horizontal but also form an angle,
for example in continuous methods, so that the layer application
takes place obliquely at an angle.
[0031] A "build container" within the meaning of the invention
implements a build space. It therefore has a base, walls and an
open access area, the build plane. The build container always
includes parts which do not move relative to the frame of the 3D
printing device. Removable build containers, so-called job boxes,
make it possible to operate the machine more or less continuously,
since the job box may be inserted into and removed from the
machine. The parts in a first build operation may thus be unpacked
outside the 3D printing device, while new parts may be printed
within the machine in a second build container.
[0032] According to the invention, the "printing and coater plane"
is the abstraction of the location of the building process
currently in progress. Since the dosing unit and the coater are
structurally moved in the device on a positioning unit with shared
components at nearly one height, the "printing and coater plane" is
viewed in this description as being situated at the upper edge of a
newly applied layer. It may form a horizontal plane or be disposed
at an angle.
[0033] According to the invention, a "building platform" moves
relative to the printing and coater plane. This relative movement
takes place during the building process in interrupted movements in
the layer thickness. It defines the layer thickness.
[0034] "Container wall" or "wall" designates a barrier to the
particulate material. The particulate material is unable to travel
from one side of the wall to the other.
[0035] In this publication, a "seal" designates two structural
elements which prevent a passage of the particulate material
through contact points between walls moving relative to each other
or between walls and the building platform.
[0036] The "geometric component limit" designates an abstraction of
a component in the build material. The part produced during the
build process deviates from the geometric component limit, due to
the discrete nature of the build material particles.
[0037] The "retention system" is located at the interface between
the ventilation system and the particulate material feedstock. Its
function is to trap the particles present in the air current. It
may be designed as a screen mesh or as a porous body. 3D-printed
bodies may also be used as a retention system. It is immaterial
whether they have already been completely dried. Bodies of this
type may also be produced by the building process.
[0038] A "controlled air flow" within the meaning of the invention
is an air current, which is conducted through the build material in
a defined manner or, in any case, is purposefully introduced into
the applied build material from the outside and flows through the
applied build material for the purpose of more quickly removing the
solvent vapors (binder fluid vapors). This reduces or essentially
dries the binder fluid in the applied build material. The
"controlled air flow" may be simple ambient air, which is
preferably temperature-controlled, preferably heated, or it may be
a defined gas mixture.
[0039] "Controlled air current" or "controlled air flow" may also
be referred to as "forced ventilation" and is a particular form of
controlled air flow. The free convection in the build material is,
in a sense, the opposite of forced ventilation. In this case,
vapors may be removed only through diffusion, due to concentration
gradients. In the case of forced ventilation, the vapors, i.e. the
solvent vapors or binder fluid vapors, are controlled by an air
current and selectively moved or removed from the build
material.
[0040] "Temperature control" or "temperature control of the air
current" means that the air introduced into the build space or the
gas mixture is set to a specific temperature, or the build space is
set to a selected temperature.
[0041] According to the invention, "relative humidity" refers to
the fact that the air or gas flow present in, introduced into or
conducted through the build space has a humidity which is set to a
desired value. This may affect not only the humidity but also the
relative solvent content.
[0042] "Reduced or essentially dried" with regard to the binder
fluid means that the quantity of binder fluid is reduced during the
selective application, compared to the direct application of binder
fluid. The binder fluid is preferably reduced to the extent that
the produced component has a strength that makes it stable to the
extent that it may be unpacked easily and without problems.
"Essentially dried" means that the component does not contain any
binder fluid or only remnants thereof. According to the invention,
the process of "reducing" or "drying" the binder fluid is
advantageously accelerated and purposefully controlled with the aid
of a "controlled air flow" with regard to the time and quantity of
the binder fluid reduction.
[0043] "Proceed layer by layer" within the meaning of the invention
designates the process of lowering the build space by the thickness
of one layer or raising device parts located above the build space
by the thickness of one layer in a job box or in another horizontal
build plane. In a continuous method, "proceed layer by layer"
designates the moving of the applied build material (the build
material block in the print machine) by the thickness of one layer,
so that a new layer of particulate material may be applied and a
layer application and selective binder fluid application may thus
take place continuously.
[0044] "Flow through in a time-controlled manner" within the
meaning of the invention means that the controlled air flow during
the method is carried out at a defined point in time and over a
defined period of time, and the controlled air flow may take place
regularly or irregularly during the method.
[0045] "IR heating" in this publication means an irradiation of the
build space using an IR emitter. The emitter may be static, or it
may be moved over the build space with the aid of a positioning
unit.
[0046] "Drying" is understood to be a loss of a certain volume of
water or another fluid substance. This drying is brought about by
the release of moisture or another fluid substance to the ambient
air. The drying action may be combined with a hardening.
[0047] "Hardening" is the term for the increase in the strength of
a component. Hardening in water glass-based systems may take place
by drying or chemical hardening.
[0048] According to the invention, the terms drying and hardening
are not understood to be synonymous.
[0049] "Dissolution" is understood to be the process of dissolving
or beginning to dissolve the binding agent in the printing fluid.
The dissolution process is dependent on different factors, for
example the reaction duration, the temperature, the relative water
quantity and, e.g., the type of water glass.
[0050] "Setting the climatic conditions in the build space" means
that the temperature and/or the relative humidity or the relative
solvent concentration in the atmosphere in the build space is
varied or selected in such a way and set through suitable means in
such a way that the drying or hardening process in the component to
be produced proceeds within a desired time window, and advantageous
component properties are thus achieved.
[0051] In one preferred specific embodiment of the method according
to the invention, the climatic conditions in the build space may be
set in such a way that the evaporation rate of a printed binder
fluid or a volatile constituent is controllable in the 3D component
to be produced. The temperature is preferably set to a suitable
range or a particular temperature in the build space with the aid
of suitable means, and/or the atmosphere of the build space is
enriched with a suitable agent, an air current enriched with the
agent evaporating from the 3D molded part to be produced (water or
another volatile substance, preferably a known solvent used in 3D
printing) is preferably introduced into the atmosphere of the build
space. The evaporation rate may thus be advantageously
controlled.
[0052] In the method according to the invention, the evaporation
rate of the printed binder fluid or a volatile constituent thereof
is furthermore advantageously reduced with respect to the
conditions at room temperature (preferably 21.degree. C.) and the
ambient humidity. The reduction or, alternatively, the increase is
preferably at least 50%, preferably 50%-90%, more preferably
50%-70%, even more preferably 60%-80%.
[0053] In another preferred specific embodiment, the relative
humidity or the relative solvent concentration is set to a value of
more than 40%, preferably between 50% and 90%, more preferably 50%
and 80%, even more preferably 55% and 70% of the relative humidity
or relative solvent concentration.
[0054] It may furthermore be advantageous if the temperature in the
build space is regulated. The same temperature may be retained
throughout the entire manufacturing process, or [sic; it] may be
varied in steps during the course of production. The temperature is
preferably set to a value from 10.degree. C. to 50.degree. C.,
preferably from 15.degree. C. to 40.degree. C., more preferably
from 30.degree. C. to 35.degree. C.
[0055] Air currents oriented in the build space are preferably
applied, which preferably have a predetermined temperature and/or a
predetermined relative humidity or a relative solvent
concentration, as described above.
[0056] In principle, the method according to the invention may be
used with all known 3D printing methods and material systems which
contain an aqueous or volatile component, and demonstrates
advantages in the 3D components obtained thereby. The particulate
material is preferably selected from the group comprising sand,
metal, polymers, ceramic, wood, cellulose, lactose, salts, carbon,
hard materials (WC), glasses, cement and gypsum.
[0057] In the method according to the invention, any known fluid
substance may also be used as the printing fluid or the binder
fluid. The printing fluid is preferably selected from the group
comprising water, alcohols, esters, ethers, acetates, ketones,
amides, aldehydes, benzene, acrylates, styrene, epoxies, polyols,
isocyanates, novolaks, resols, polyesters, peroxides, succinates,
aromatics, aliphatics and hydrocarbons.
[0058] A material system is preferably used in the method according
to the invention, which includes a water-soluble binder as the
powdered binding agent and water-insoluble particles and a
water-based binder fluid in the particulate material.
[0059] The device which may be used for the method according to the
invention has already been described above and may have the
following preferred features:
[0060] The build space is preferably tightly sealable, whereby the
regulation of the temperature and/or the relative humidity or the
relative portion of another component may be set more easily and
more constantly.
[0061] Means known to those skilled in the art may be used to
regulate the temperature and set the relative humidity in the build
space. The means for setting the relative humidity may be
preferably selected from the group comprising a water-based
humidifier or a solvent evaporator.
[0062] The means for controlling the temperature of the build space
interior is preferably selected from the group comprising an air
heating unit or an IR emitting unit.
[0063] The device according to the invention may furthermore
include means for controlling one or multiple air currents in the
build space interior, preferably for controlling one or more air
currents over the build space.
[0064] Means for controlling one or multiple air currents in the
build space interior may be selected from pipes, diffusors, nozzles
and/or baffle plates.
[0065] The device according to the invention is designed in such a
way that it is suitable for the material systems described above as
well as for the stated materials and their combinations.
[0066] The device according to the invention may preferably also
include an insulation for minimizing or avoiding undesirable
convection movements.
BRIEF DESCRIPTION OF THE FIGURES
[0067] FIG. 1: shows a schematic representation of the components
of a powder-based 3D printer as a sectional isometric view;
[0068] FIG. 2: shows a diagram of the sequence of a conventional 3D
printing process;
[0069] FIG. 3: shows the drying process using forced
convection;
[0070] FIG. 4: shows an illustration of the dissolution
process;
[0071] FIG. 5: shows different binder bridge designs.
DETAILED DESCRIPTION
[0072] The basic components correspond to a system for building
models in layers with the aid of ink-jet printing technology, as
known to those skilled in the art and which therefore do not need
to be repeated in every detail here.
[0073] The sequence is preferably organized as follows: A layer of
particulate material is applied to a building platform and leveled.
A printing fluid is then printed onto the layer according to the
layer data of the 3D model. The essential portion of the material
for bonding the particles is provided in the powder in the form of
dry particles. The dissolution process may now be accelerated by
heating with an IR lamp. After the printing and heating process,
the building platform is lowered, and the process begins all over
again.
[0074] These steps are repeated until the component is completely
present in the constructed powder cake.
[0075] The quality of the components produced in this manner is
evaluated on the basis of different criteria. For example, the
strength is of critical importance for later use as a core or mold
in a foundry. It determines how easy it is to handle the component
or whether the core will survive the casting process without
breaking.
[0076] Another essential variable is the surface quality. During
the foundry application, for example, the surface of the printed
component is reproduced directly on the cast part. The size
accuracy is also important. Only size-accurate components may be
processed into an industrially useable part in the remaining
steps.
[0077] In a so-called water glass material system, the strength and
surface properties are in a certain opposition to each other, as
tests have shown. Very strong components are easily achievable
using the procedure described. These parts are printed with a high
proportion of liquid and have poor surfaces after the process.
[0078] Good surfaces may also be achieved. However, the component
is then very fragile and may be handled or shipped only with
difficulty.
[0079] This contradiction arises from the circumstance that the
water glass takes time to dissolve. During this time, the printed
liquid may travel across the boundaries of the geometrically
desired shape, due to the capillary effect in the component, and
generate undesirable deposits on the component. These deposits
occur in the form of efflorescence on the component wall. If the
dissolution were to take place faster, the viscosity of the
printing fluid would increase more rapidly in the particulate
material, the penetration of the printing fluid into adjacent areas
would decrease, and better surfaces would thus be achievable.
[0080] In devices according to the prior art, the particulate
material is heated with an IR lamp after being applied to increase
the dissolution speed. As shown in tests involving dry water glass,
this causes the viscosity of the printing fluid to increase
rapidly, and the components have better surfaces.
[0081] Despite this procedure, some particulate materials (e.g.,
some sand types) may not be satisfactorily processed using this
method.
[0082] Tests involving devices according to the prior art have
shown that drafts may have a significant negative impact on the
process. The customary strengths may not be achieved. The surfaces,
however, appear to be good.
[0083] The inventors have now determined that this is due to the
fluid drying out too fast. In this case, only a small portion of
the printing fluid is active during the dissolution, and
insufficient strength results.
[0084] The inventors have now developed a method in which the
drying of the printing fluid from the particulate material is
decelerated by means of additional humidity in the process chamber.
The temperature may be preferably increased with the aid of an IR
lamp or other suitable means, and even more material may be caused
to dissolve. A controlled air current is preferably conducted over
the build space.
[0085] Tests have shown that improved strengths may be achieved,
compared to the prior art, by using a system of this type. Very
good surfaces may simultaneously be achieved, despite the high
strengths.
[0086] The process window may be greatly enlarged with the aid of
the invention by combining a heat source, such as an IR lamp for
heating the fluid, with the creation of a moist atmosphere.
[0087] With the aid of the invention, and by increasing the
humidity, materials may thus be processed which previously were
unable to be used or only with a reduced quality of the molded
parts. These materials include fine sands, sands having an unusual
grain shape and special fillers having a high specific weight.
[0088] The system according to the invention draws heavily on
powder-based 3D printing. The mechanical engineering is augmented
to meet the requirements according to the invention.
[0089] The device according to the invention includes a powder
coater (101). Particulate material is applied thereby to a building
platform (102) and smoothed (FIG. 2(a)). The applied particulate
material may comprise a wide range of materials. For example,
fillers such as sands, artificial sands and ceramic particles may
be used. The flow characteristics of these materials may vary
enormously. Different coater techniques permit layering, from dry,
free-flowing powders and cohesive, firm powders to fluid-based
dispersions. The height of powder layers (107) is determined by
building platform (102). It is lowered after one layer has been
applied. During the next coating operation, the resulting volume is
filled and the excess smoothed. The result is a nearly perfectly
parallel and smooth layer of a defined height.
[0090] After a coating process, a printing fluid is printed onto
the layer with the aid of an ink-jet print head (100) (FIG. 2(b)).
The print image corresponds to the section of the component at the
present build height of the device. The fluid strikes and slowly
diffuses into the particulate material.
[0091] After the binder is printed, the layer may be heated (FIG.
2(c)). For this purpose, an IR emitter (200), for example, may be
passed over the build space. This IR emitter may be coupled with
the axis of the coating system. Part of the liquid binding agent is
evaporated during heating.
[0092] At the end of this heating process, building platform (102)
is lowered by the thickness of one layer. The steps of layer
construction, printing, heating and lowering are now repeated until
desired component (103) is completely produced.
[0093] Component (103) is now completely present in powder cake
(602). Depending on the physical or chemical process on which the
binding of particles (303) is based, the component is now more or
less solidified. The component is usually in a soft state
immediately after printing.
[0094] This state is not a problem as long as component (103)
remains in powder (107), supported by the surrounding particulate
material. However, once the component is unpacked from the powder,
a geometric deformation is unavoidable, due to gravity and other
effects of force.
[0095] The component is therefore typically left in the powder.
Excess binding agent (301), which does not allow component (103) to
solidify, now evaporates via various vapor channels (302) in
unbound particulate material (303). The bonds of bound particulate
material (304) in geometric component limit (305) solidify more and
more. After a certain waiting time, body (103) is sufficiently
solid to be able to be unpacked.
[0096] With a material system according to the invention, which has
a water glass-based binding agent, the parts may be unpacked
relatively quickly after printing. Waiting periods of less than 2
hours have to be maintained in this case, thanks to the heating
with IR lamp (200).
[0097] The solidification process takes place as follows: Printing
fluid (400) strikes particulate material (304, 401) and penetrates
the powder, due to the capillary action. The printing fluid
continues to penetrate farther and farther in a space to be
approximated as a sphere (403).
[0098] Within the particulate material, the printing fluid wets
both passive filler particles (304) and water glass grains (401).
The water glass is present in fine, discrete particles (401), which
are nearly evenly distributed, due to an intensive mixing of the
material.
[0099] The wetted water glass grains (404) gradually begin to
dissolve, due to the liquid binder, lose diameter (405) in the
process and increase the viscosity of the printing fluid. In this
stage, the dissemination speed of the fluid quantity decreases.
[0100] The wetting in this stage, with an adapted quantity of
printing fluid, is sufficient to the extent that the individual
gaps between the filler particles are in contact with each other
via the printing fluid (404). The entire water glass ideally
dissolves, and a homogeneous liquid (406) results.
[0101] In the next stage, moisture is removed from the thickened
printing fluid by storing the component in the particulate
material. This fluid is partially absorbed by the very dry powder
environment.
[0102] The removal of moisture ensures that the fluid continues to
thicken. This moisture is drawn back into the areas between the
filler particles, due to the capillary action. It continues to dry
out here, until a solid water glass bridge (407) remains in the
end. Particles (304) are thus bound, and a solid body is
produced.
[0103] While the water glass grains are in most cases partly
dissolved, the increase in viscosity is not sufficient to prevent
the further dissemination of the fluid. This results in deposits on
the component. Counteracting this effect by adding less fluid is
not expedient, since no sufficient binder bridges (500) and thus
strengths are then able to form. Instead, this effect may not be
counteracted by varying the quantity of printing fluid, since
coordinated quantities of water with regard to the total quantity
of water glass may be reasonably defined only in the fully
dissolved state. In the initial stage when little material has been
dissolved, an excess of water [sic; is] always present.
[0104] It is therefore reasonable to increase the dissolution
speed. Heating with the aid of an IR lamp is effective here. The
phase of water excess is now much shorter than before. On the other
hand, the influence on the viscosity may be disregarded.
[0105] However, the steam pressure of the printing fluid is also
increased by the heating. A large quantity of printing fluid
evaporates as early as during the creation of the layers. Likewise,
moisture is rapidly removed from the component by the dry,
surrounding powder. The accelerated dissolution process is aborted
too quickly, due to an excessively massive thickening of the
printing fluid, and incomplete bindings between particles (500)
occur. Part of the water glass is still in particulate form in
places, which do not contribute to the strength of the component
(501, 502).
[0106] This evaporation process may be counteracted by regulating
the humidity and the temperature in the build space according to
the invention. This means that the air in the closed build space is
regulated to a temperature range of 18.degree. C.-40.degree. C.,
preferably 30.degree. C.-35.degree. C., and the relative humidity
is then regulated within a range of 40%-70%, preferably 60%-70%.
The temperature and humidity may be regulated, for example, by
means of an external air conditioning unit, corresponding sensors
for temperature and humidity being accommodated in the process
chamber. The process air guided via the air conditioning unit
should then be preferably blown into the process chamber draft-free
via corresponding diffusors.
[0107] Due to the high partial pressure of the water in the ambient
air, the rate of evaporation from the particulate material
decreases. In addition, the particulate material is continuously
humidified, since the water glass particles have a highly
hygroscopic effect.
[0108] This prevented evaporation makes it possible to be able to
quickly dissolve large amounts of water glass due to the
temperature. Nearly ideal bindings (407) may occur. The ratio
between strength and surface quality is much better than without
the humidification, as the tests show.
[0109] Up to now, only special sands have been suitable for binding
with dry water glass. For example, spherical river sands having a
special surface texture are suitable. Artificial sands may also be
processed. Both materials are expensive to procure and are
therefore not suitable for widespread use.
[0110] A much broader range of particulate materials may now be
processed using the method according to the invention. These
include sand of the Strobel GS14 and GS09 type, which deliver too
little strength with an acceptable surface without the method
according to the invention. In conventional printing methods and
with an acceptable surface, the flexural strengths of these sands
are less than 90 N/cm.sup.2. This strength is insufficient for safe
cleaning and transport of the components. With the humidification
according to the invention, and without any changes to the sand
recipe, the same sands may achieve a strength of 290-300
N/cm.sup.2.
[0111] Particularly sharp-edged, broken materials benefit from this
increase in strength. The use of olivine sand is thus possible only
by means of this measure.
[0112] However, the measure is equally effective in the case of
special molding materials. In this case, significant strength
increases may also be achieved, which expand the range of
applications to more and more complex shapes.
[0113] The device according to the invention is based on a 3D
printer according to the prior art. At least one mobile or
stationary IR emission source must be present.
[0114] The air conditioning of the build space goes beyond the
prior art. A regulated humidification system must be used here. A
heating element in water may be used as the moisture source. The
moisture measured in the build space then determines the power of
the heating element.
[0115] The moist air is distributed, for example, via fans. Drafts
over the build space should be minimized. Otherwise, too much water
will be removed from the freshly printed layer, despite the high
humidity.
[0116] The moist air is guided to the vicinity of the build space
via pipes or guide plates.
[0117] A coupling of this regulating system with the print
controller of the machine is particularly preferred. The droplets
generated by the ink-jet print head may be included in the moisture
regulation.
[0118] Combining the moisture regulation with a temperature
regulation is also preferred. The temperature in the powder bed may
thus be controlled much more precisely with the aid of the IR lamp.
Better reproducible print results are thus possible.
[0119] The advantages of the process according to the invention may
be used for all material mixtures in which water-based printing
fluids are used, for the purpose of selectively dissolving
essentially water-soluble, powdered binding agents to bind
surrounding fillers with the aid of a subsequent drying process.
The invention is therefore not limited to water glass-based binders
but may also be used, for example, for gypsum-based or cement-based
binders.
LIST OF REFERENCE NUMERALS
[0120] 100 Print head
[0121] 101 Coater
[0122] 102 Building platform
[0123] 103 Component
[0124] 104 Build container
[0125] 105 Print head path
[0126] 106 Coater path
[0127] 107 Powder layers
[0128] 108 Direction of building platform movement
[0129] 109 Dosed droplets
[0130] 110 Powder roll
[0131] 111 Build space boundary
[0132] 112 Coater gap
[0133] 113 Coater stock
[0134] 200 IR emitter
[0135] 300 Evaporating material in an open layer
[0136] 301 Material evaporating into the powder
[0137] 302 Possible vapor channel
[0138] 303 Unbound particle
[0139] 304 Bound particle
[0140] 305 Geometric component limit
[0141] 400 Fluid droplets
[0142] 401 Water glass particles
[0143] 402 Gaps between passive particles
[0144] 403 Diffusion direction of the fluid
[0145] 404 Liquid film with connection between the water glass
grains
[0146] 405 Water glass particle reduced in size by dissolution
[0147] 406 Thickened solution
[0148] 407 Solid binding
[0149] 500 Weak binder bridge
[0150] 501 Bridge with water glass particles not involved in the
binding
[0151] 502 Ineffective drying
* * * * *