U.S. patent application number 16/561689 was filed with the patent office on 2020-02-27 for debinding of 3d objects.
This patent application is currently assigned to Desktop Metal, Inc.. The applicant listed for this patent is Desktop Metal, Inc.. Invention is credited to Alexander C. Barbati, Michael A. Gibson.
Application Number | 20200061706 16/561689 |
Document ID | / |
Family ID | 65024004 |
Filed Date | 2020-02-27 |
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United States Patent
Application |
20200061706 |
Kind Code |
A1 |
Gibson; Michael A. ; et
al. |
February 27, 2020 |
DEBINDING OF 3D OBJECTS
Abstract
3D-printed parts may include binding agents to be removed
following an additive manufacturing process. A debinding process
removes the binding agents by immersing the part in a solvent bath
causing chemical dissolution of the binding agents. The time of
exposure of the 3D-printed part to the solvent is determined based
on the geometry of the part, wherein the geometry is applied to
predict the diffusion of the solvent through the 3D-printed part.
The 3D-printed part is then immersed in the solvent bath to remove
the binding agent, and is removed from the solvent bath after the
time of exposure.
Inventors: |
Gibson; Michael A.;
(Burlington, MA) ; Barbati; Alexander C.;
(Cambridge, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Desktop Metal, Inc. |
Burlington |
MA |
US |
|
|
Assignee: |
Desktop Metal, Inc.
Burlington
MA
|
Family ID: |
65024004 |
Appl. No.: |
16/561689 |
Filed: |
September 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16221190 |
Dec 14, 2018 |
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16561689 |
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62599582 |
Dec 15, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 1/0059 20130101;
B22F 3/1025 20130101; B22F 3/008 20130101; B33Y 50/02 20141201;
B29C 64/357 20170801; B33Y 50/00 20141201; B29C 64/40 20170801;
B22F 2998/10 20130101; B22F 2003/1058 20130101; G05B 19/4099
20130101; B22F 5/10 20130101; B08B 3/08 20130101; B29C 64/35
20170801; G01B 21/08 20130101; B33Y 40/00 20141201; B22F 3/1055
20130101; B33Y 30/00 20141201; B22F 2999/00 20130101; B22F
2003/1059 20130101; B29C 64/393 20170801; B29C 64/386 20170801;
B22F 3/1021 20130101; B33Y 80/00 20141201; B33Y 10/00 20141201;
B29C 64/165 20170801; B29C 71/0009 20130101; B22F 2203/00 20130101;
B22F 2202/01 20130101; B22F 2202/07 20130101; B22F 2003/1057
20130101; B22F 2999/00 20130101; B22F 3/1055 20130101; B22F 3/24
20130101; B22F 2998/10 20130101; B22F 3/1055 20130101; B22F 3/1021
20130101; B22F 3/10 20130101; B22F 2998/10 20130101; B22F 3/1055
20130101; B22F 3/1021 20130101; B22F 3/15 20130101; B22F 2999/00
20130101; B22F 2203/00 20130101; B22F 3/1021 20130101; B22F
2003/244 20130101; B22F 2999/00 20130101; B22F 2003/1057 20130101;
B22F 3/1021 20130101; B22F 2003/244 20130101; B22F 2999/00
20130101; B22F 3/1055 20130101; B22F 3/10 20130101; B22F 2999/00
20130101; B22F 3/1055 20130101; B22F 3/1115 20130101; B22F 2999/00
20130101; B22F 2003/1057 20130101; B22F 2003/1059 20130101; B22F
2999/00 20130101; B22F 3/1055 20130101; B22F 3/225 20130101 |
International
Class: |
B22F 3/10 20060101
B22F003/10; B33Y 40/00 20060101 B33Y040/00; B29C 64/165 20060101
B29C064/165; B29C 64/35 20060101 B29C064/35; B33Y 50/00 20060101
B33Y050/00; B33Y 80/00 20060101 B33Y080/00; B29C 64/386 20060101
B29C064/386; B22F 3/105 20060101 B22F003/105 |
Claims
1-20. (canceled)
21. A method of determining a debinding time of a printed part or a
model of a part, the method comprising: receiving data about the
printed part or the model of the part, wherein the printed part or
the model of the part includes an outer shell and an interior
structure having a plurality of cells forming a honeycomb structure
having an axis of symmetry; determining a length of a longest cell
of the plurality of cells along the axis of symmetry of the
honeycomb structure; and calculating a debinding time based on the
length of the longest cell.
22. The method of claim 21, wherein determining the debinding time
further includes a proportional scaling relative to an inverse of a
thickness of the outer shell.
23. The method of claim 21, wherein determining the debinding time
further includes a proportional scaling relative to an area of
solid material in a plane of symmetry of the honeycomb
structure.
24. The method of claim 21, wherein determining the length of the
longest cell of the plurality of cells along the axis of symmetry
of the honeycomb structure includes calculating a distance field in
a geometry of the printed part or the model of the part.
25. The method of claim 24, wherein calculating the distance field
in the geometry of the printed part or the model of the part
includes calculating a vertical distance field in the geometry by:
calculating distances in a vertically downward direction between
all upward facing surfaces to another surface of the printed part
or the model of the part; and determining a maximum distance of the
calculated distances.
26. The method of claim 25, wherein calculating the length of the
longest cell of the plurality of cells along the axis of symmetry
of the honeycomb structure further includes subtracting thicknesses
of top and bottom layers of the plurality of cells.
27. The method of claim 21, wherein each of the cells forming the
honeycomb structure include cellular walls with a uniform size or a
uniform shape.
28. The method of claim 21, wherein the plurality of cells each
include a hexagonal cell shape in a plane.
29. The method of claim 21, wherein calculating the debinding time
based on the length of the longest cell includes raising the length
of the longest cell to an exponential power that is greater than or
equal to 1 and less than or equal to 2.4, and calculating the
debinding time proportional to the length of the longest cell
raised to the exponential power.
30. The method of claim 21, comprising receiving data about a
plurality of printed parts or a plurality of models of parts, and
wherein calculating the debinding time is based on the length of
the longest cell of the plurality of printed parts or the plurality
of models of parts.
31. A system for debinding a printed part, comprising: a chamber
configured to receive the printed part; a storage chamber fluidly
connected to the process chamber and configured to store a
debinding solution; and a controller configured to calculate a
debinding time for the printed part or a model of a part, wherein
the printed part or the model of the part includes an outer shell
and an interior structure having a plurality of cells forming a
honeycomb structure having an axis of symmetry, wherein calculating
the debinding time includes: determining a length of a longest cell
of the plurality of cells along the axis of symmetry of the
honeycomb structure; and calculating a debinding time based on the
length of the longest cell.
32. The system of claim 31, wherein determining the length of the
longest cell of the plurality of cells along the axis of symmetry
of the honeycomb structure includes calculating a distance field in
a geometry of the printed part or the model of the part by:
calculating distances in a vertically downward direction between
all upward facing surfaces to another surface of the printed part
or the model of the part and subtracting thicknesses of top and
bottom layers of the plurality of cells; and determining a maximum
distance of the calculated distances.
33. The system of claim 31, wherein determining the debinding time
further includes a proportional scaling relative to an inverse of a
thickness of the outer shell.
34. The system of claim 31, wherein determining the debinding time
further includes a proportional scaling relative to an area of
solid material in a plane of symmetry of the honeycomb
structure.
35. The system of claim 31, wherein the controller is configured to
calculate a debinding time for a plurality of printed parts or a
plurality of models of parts, and wherein the controller is
configured to determine the debinding time by determining a longest
debinding time of the debinding times for each of the plurality of
printed parts or the plurality of models of parts.
36. The system of claim 31, further comprising: a user interface,
wherein the controller is configured to signal the user interface
to display one or more indications of the debinding.
37. A non-transitory computer readable medium for use on a computer
system containing computer-executable programming instructions for
performing a method of determining a debinding time of a printed
part or a model of a part, the method comprising: receiving data
about the printed part or the model of the part, wherein the
printed part or the model of the part includes an outer shell and
an interior structure having a plurality of cells forming a
honeycomb structure having an axis of symmetry; determining a
length of a longest cell of the plurality of cells along the axis
of symmetry of the honeycomb structure; and calculating a debinding
time based on the length of the longest cell.
38. The non-transitory computer readable medium of claim 37,
wherein determining the debinding time further includes a
proportional scaling relative to an inverse of a thickness of the
outer shell and a proportional scaling relative to an area of solid
material in a plane of symmetry of the honeycomb structure.
39. The non-transitory computer readable medium of claim 37,
wherein determining the length of the longest cell of the plurality
of cells along the axis of symmetry of the honeycomb structure
includes calculating a distance field in a geometry of the printed
part or the model of the part by: calculating distances in a
vertically downward direction between all upward facing surfaces to
another surface of the printed part or the part to be printed and
subtracting thicknesses of top and bottom layers of the plurality
of cells; and determining a maximum distance of the calculated
distances.
40. The non-transitory computer readable medium of claim 37,
further comprising: raising the length of the longest cell to a
power having an exponent greater than or equal to 1 and less than
or equal to 2.4; and calculating a time proportional to the length
of the longest cell raised to the exponent.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/599,582, filed on Dec. 15, 2017. The entire
teachings of the above application are incorporated herein by
reference.
BACKGROUND
[0002] Metal injection molding (MIM) is a metalworking process
useful in creating a variety of metal objects. A mixture of
powdered metal and binder (e.g., a polymer such as polypropylene)
forms a "feedstock" capable of being molded, at a high temperature,
into the shape of a desired object or part. The initial molded
part, also referred to as a "green part," then undergoes a
debinding process to remove the binder, followed by a sintering
process. During sintering, the part is brought to a temperature
near the melting point of the powdered metal, which evaporates any
remaining binder and forms the metal powder into a solid mass,
thereby producing the desired metal object.
[0003] Additive manufacturing, also referred to as 3D printing,
includes a variety of techniques for manufacturing a
three-dimensional object via an automated process of forming
successive layers of the object. 3D printers may utilize a
feedstock comparable to that used in MIM, thereby creating a green
part without the need for a mold. The green part may then undergo
comparable debinding and sintering processes to produce the
finished object.
SUMMARY
[0004] Example embodiments provide for removal of binding agents
from 3D-printed parts. A 3D-printed part, including a build
material and a binding agent, may be provided. The time of exposure
of the 3D-printed part to the solvent may be determined by a)
computing an effective thickness of the 3D-printed part, and b)
scaling the time of exposure according to the effective thickness
raised to a power having an exponent greater than 1. The 3D-printed
part may then be immersed in a solvent bath that removes at least
some of the binding agent from the 3D-printed part. The 3D-printed
part may be removed from the solvent bath after the time of
exposure.
[0005] The effective thickness may correspond to a distance from a
deepest point to a nearest surface of the 3D-printed part, where
the deepest point is a point interior to the 3D-printed part that
is a maximum distance from any surface of the 3D-printed part. The
3D-printed part may retain less than 10% of the binding agent upon
removal from the solvent bath. The effective thickness may be
computed by identifying a point interior to a representation of the
3D-printed part that is a maximum distance from any surface of the
representation, wherein the effective thickness may be a linear
function of the maximum distance.
[0006] The effective thickness may be determined by a) defining
geometry of a sphere, the sphere having a volume that is entirely
encompassed by an internal volume of a representation of the
3D-printed part; and b) determining the effective thickness based
on a radius of the sphere. The sphere may be the largest sphere
that can be entirely encompassed by the internal volume. The
geometry of the sphere may be defined by a) producing a random
sampling of points from the representation; b) calculating, for
each of the points, a distance from the point to a closest surface;
and c) determining the radius of the sphere as a maximum of the
calculated distances. Alternatively, the geometry of the sphere may
be defined by a) generating a uniform grid sampling of points at
the representation; b) calculating, for each of the points, a
distance from the point to a closest surface; and c) determining
the radius of the sphere as a maximum of the calculated distances.
The center of the sphere may coincide with a point interior to the
3D-printed part that is a maximum distance from any surface of the
3D-printed part.
[0007] The effective thickness may be computed by a) defining
geometry of a succession of reduced parts based on a representation
of the 3D-printed part, where each of the reduced parts 1) occupies
an internal volume of the representation of the 3D-printed part and
2) has a geometry corresponding to a displacement of a surface
inward along its local normal vector relative to a geometry of a
preceding reduced part; b) identifying a minimum distance from a
surface of the part to a last one of the succession of reduced
parts; and c) determining the effective thickness based on the
minimum distance.
[0008] The exponent may be a value within a range, such as the
range of 1.6-2.4. The build material may include a powdered metal,
and the binding agent may include a polymer, wherein the solvent
bath causes chemical dissolution of the polymer during the
immersion.
[0009] Further embodiments include a method of removing binding
agents from 3D-printed parts having a shell encompassing an
interior honeycomb structure comprising a plurality of cells. A
3D-printed part, including a build material and a binding agent,
may be provided. A time of exposure of the 3D-printed part to the
solvent may be determined by a) computing a length of a longest
cell along an axis of symmetry of the honeycomb structure, and b)
scaling the time of exposure according to the length of the longest
cell raised to a power. The 3D-printed part may then be immersed in
a solvent bath that removes at least some of the binding agent from
the 3D-printed part. The 3D-printed part may be removed from the
solvent bath after the time of exposure.
[0010] The power may have an exponent of 1. A pore of each
honeycomb cell may be in geometric contact with the shell. The time
of exposure may be further scaled proportionally to the shell
thickness and/or the area fraction of solid material in the plane
of symmetry of the honeycomb. A void space of each of the plurality
of cells may be connected to the shell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing will be apparent from the following more
particular description of example embodiments, as illustrated in
the accompanying drawings in which like reference characters refer
to the same parts throughout the different views. The drawings are
not necessarily to scale, emphasis instead being placed upon
illustrating embodiments.
[0012] FIG. 1 is a block diagram of an additive manufacturing
system.
[0013] FIG. 2 is a flow chart of a method for printing with
composites.
[0014] FIG. 3 illustrates an additive manufacturing system for use
with metal injection molding materials.
[0015] FIG. 4 is a block diagram of an additive manufacturing
system.
[0016] FIG. 5 is a flow diagram of a process of fabricating a
part.
[0017] FIGS. 6A-B illustrate orientation of a printed part on a
build plate.
[0018] FIG. 7 illustrates a user interface configured to guide a
debind process.
[0019] FIG. 8 is a block diagram of a debinder system for debinding
printed parts.
[0020] FIG. 9 is a flow diagram of a debinding process.
[0021] FIG. 10 is a flow diagram of a process of determining a time
to debind a part in one embodiment.
[0022] FIGS. 11A-B illustrates a geometry of a full-filled part in
one embodiment.
[0023] FIG. 12 is a flow diagram of a process of determining an
effective thickness of a part.
[0024] FIGS. 13A-B illustrate parts in one embodiment.
[0025] FIGS. 14A-B illustrate a part in a further embodiment,
[0026] FIGS. 15A-B illustrate representations of a single cell of
an infilled part.
[0027] FIG. 16 is a flow diagram of a process for determining a
tallest infill cell height of a part.
[0028] FIG. 17 is a block diagram of a processing system in which
example embodiments may be implemented.
DETAILED DESCRIPTION
[0029] A description of example embodiments follows.
[0030] In metal-injection molding (MIM) manufacturing, molded
objects may be debound in a process comparable to the debinding
process described above. However, in contrast to additive
manufacturing, MIM-manufactured objects tend to be small, and are
left to debind in the solvent for extended periods of time to
guarantee that all of the primary binder is removed. Regardless of
this extended debind time, debinding in MIM manufacturing does not
typically require an excessive amount of time. Typical debinding
times for parts produced in MIM processes are between 2 and 10
hours, with typical wall thicknesses from several hundred microns
to several millimeters. The cost of waiting an extra hour or an
extra 10-20% longer than needed is not highly costly for such
debinding times. Further, in MIM processing, one can run an
engineering study for each part, and thus determine the debinding
time for that part by interrupting the debinding process. Because
debind time is dependent on part geometry, performing an
engineering study to determine and optimize the debind time of a
part is cost-effective when many parts (e.g., 10,000) are going to
be produced of identical geometry.
[0031] In contrast, 3D printing of objects using a MIM-like
feedstock allows production of articles that are much larger in
size, to a point where debinding may become an incredibly slow
step, and thus rate-limiting to the process. Thicknesses for
3D-printed articles may be an order of magnitude larger than those
for MIM-produced parts, with part cross sections sometimes
measuring tens of millimeters. As the debind time scales
non-linearly with the part thickness, debind times of 100 hours can
be common for the largest parts. Allowing the part to debind for
longer than needed would only add time to this already slow step,
and a 20% margin of safety could add an entire day to the
manufacturing process.
[0032] Further, a key advantage of a 3D printing process is that
each part produced may be unique. Thus, it may not be possible nor
cost-effective to run an engineering study to determine the
debinding time of the part through interrupted measurements in the
process.
[0033] Example embodiment enable the time to debind a part to be
determined without a costly or time-consuming engineering study. In
particular, the time to debind a part can be determined based on
the geometry of the part, which can be derived from CAD drawings,
print instructions such as toolpaths, or other information defining
the part. From this geometry, example embodiments can predict the
time required for a binding agent of a part to be substantially or
fully removed from the part through chemical dissolution when the
part is immersed in a solvent. As a result, the debind process can
be terminated immediately or shortly after the part is debound,
thereby minimizing the occupation time of the debinder and
improving the speed of the additive manufacturing process. Further,
the debind completion time can be predicted, and an indication of
the completion time, as well as the current progress of the debind,
can be reported to the user. Although embodiments below describe
chemical debinding, in further embodiments, the time to debind a
part via thermal debinding may be determined alternatively or in
addition to a chemical debinding.
[0034] Example embodiments providing for debinding a part are
described in further detail below with reference to FIGS. 9-16.
First, a description of an additive manufacturing process,
including printing, debinding and sintering, is provided below.
[0035] FIG. 1 is a block diagram of an additive manufacturing
system for use with composites. The additive manufacturing system
may include a three-dimensional printer 100 (or simply printer 100)
that deposits metal using fused filament fabrication. Fused
filament fabrication is well known in the art, and may be usefully
employed for additive manufacturing with suitable adaptations to
accommodate the forces, temperatures and other environmental
requirements typical of the metallic injection molding materials
described herein. In general, the printer 100 may include a build
material 102 that is propelled by a drive train 104 and heated to a
workable state by a liquefaction system 106, and then dispensed
through one or more nozzles 110. By concurrently controlling
robotic system 108 to position the nozzle(s) along an extrusion
path, an object 112 (also referred to as a part) may be fabricated
on a build plate 114 within a build chamber 116. In general, a
control system 118 manages operation of the printer 100 to
fabricate the object 112 according to a three-dimensional model
using a fused filament fabrication process or the like.
[0036] A variety of commercially available compositions have been
engineered for metal injection molding ("MIM"). These highly
engineered materials can also be adapted for use as a build
material 102 in printing techniques such as fused filament
fabrication. For example, MIM feedstock materials, when suitably
shaped, may be usefully extruded through nozzles typical of
commercially available FFF machines, and are generally flowable or
extrudable within typical operating temperatures (e.g., 160-250
degrees Celsius) of such machines. This temperature range may
depend on the binder--e.g., some binders achieve appropriate
viscosities at about 205 degrees Celsius, while others achieve
appropriate viscosities at lower temperatures such as about 160-180
C degrees Celsius. One of ordinary skill will recognize that these
ranges (and all ranges listed herein) are provided by way of
example and not of limitation. Further, while there are no formal
limits on the dimensions for powder metallurgy materials, parts
with dimensions of around 100 millimeters on each side have been
demonstrated to perform well for FFF fabrication of net shape green
bodies. Any smaller dimensions may be usefully employed, and larger
dimensions may also be employed provided they are consistent with
processing dimensions such as the print resolution and the
extrusion orifice diameter. For example, implementations target
about a 0.300 m diameter extrusion, and the MIM metal powder may
typically be about 1-22 m diameter, although nano sized powders can
be used. The term metal injection molding material, as used herein,
may include any such engineered materials, as well as other fine
powder bases such as ceramics in a similar binder suitable for
injection molding. Thus, where the term metal injection molding or
the commonly used abbreviation, MIM, is used, the term may include
injection molding materials using powders other than, or in
addition to, metals and, thus, may include ceramics. Also, any
reference to "MIM materials," "powder metallurgy materials," "MIM
feedstocks," or the like may generally refer to metal powder and/or
ceramic powder mixed with one or more binding materials, e.g., a
backbone binder that holds everything together and a bulk binder
that carries the metal and backbone into position within a mold or
print. Other material systems may be suitable for fabricating metal
parts using fabrication techniques such as stereolithography or
binder jetting, some of which are discussed in greater detail
below. Such fabrication techniques may, in some applications, be
identical to techniques for fabricating parts from ceramic
material.
[0037] In general, fabrication of such materials may proceed as
with a conventional FFF process, except that after the net shape is
created, the green part may be optionally machined or finished
while in a more easily workable state, and then debound and
sintered into a final, dense object using any of the methods common
in the art for MIM materials. The final object, as described above,
may include a metal, a metal alloy, a ceramic, or another suitable
combination of materials.
[0038] The build material 102 may be fed from a carrier 103
configured to dispense the build material to the three-dimensional
printer either in a continuous (e.g., wire) or discrete (e.g.,
billet) form. The build material 102 may for example be supplied in
discrete units one by one as billets or the like into an
intermediate chamber for delivery into the build chamber 118 and
subsequent melt and deposition. The carrier 103 may include a spool
or cartridge containing the build material 102 in a wire form.
Where a vacuum or other controlled environment is desired, the wire
may be fed through a vacuum gasket into the build chamber 118 in a
continuous fashion, however, typical MIM materials can be heated to
a workable plastic state under normal atmospheric conditions,
except perhaps for filtering or the like to remove particles from
the build chamber 116. Thus, a MIM build material may be formed
into a wire, the build material including an engineered composite
of metal powder and a polymeric binder or the like, wherein the
carrier 103 is configured to dispense the build material in a
continuous feed to a three-dimensional printer. For environmentally
sensitive materials, the carrier 103 may provide a vacuum
environment for the build material 102 that can be directly or
indirectly coupled to the vacuum environment of the build chamber
118. More generally, the build chamber 118 (and the carrier 103)
may maintain any suitably inert environment for handling of the
build material 102, such as a vacuum, and oxygen-depleted
environment, an inert gas environment, or some gas or combination
of gasses that are not reactive with the build material 102 where
such conditions are necessary or beneficial during
three-dimensional fabrication.
[0039] A drive train 104 may include any suitable gears,
compression pistons, or the like for continuous or indexed feeding
of the build material 116 into the liquefaction system 106. The
drive train 104 may include gear shaped to mesh with corresponding
features in the build material such as ridges, notches, or other
positive or negative detents. The drive train 104 may use heated
gears or screw mechanisms to deform and engage with the build
material. Thus, a printer for a fused filament fabrication process
can heats a build material to a working temperature, and that heats
a gear that engages with, deforms, and drives the composite in a
feed path. A screw feed may also or instead be used.
[0040] For more brittle MIM materials, a fine-toothed drive gear of
a material such as a hard resin or plastic may be used to grip the
material without excessive cutting or stress concentrations that
might otherwise crack, strip, or otherwise compromise the build
material.
[0041] The drive train 104 may use bellows, or any other
collapsible or telescoping press to drive rods, billets, or similar
units of build material into the liquefaction system 106.
Similarly, a piezoelectric or linear stepper drive may be used to
advance a unit of build media in a non-continuous, stepped method
with discrete, high-powered mechanical increments. Further, the
drive train 104 may include multiple stages. In a first stage, the
drive train 104 may heat the composite material and form threads or
other features that can supply positive gripping traction into the
material. In the next stage, a gear or the like matching these
features can be used to advance the build material along the feed
path. A collet feed may be used (e.g., similar to those on a
mechanical pencil). A soft wheel or belt drive may also or instead
be used. A shape forming wheel drive may be used to ensure accuracy
of size and thus the build. More generally, the drive train 104 may
include any mechanism or combination of mechanisms used to advance
build material 102 for deposition in a three-dimensional
fabrication process.
[0042] The liquefaction system 106 may be any liquefaction system
configured to heat the composite to a working temperature in a
range suitable for extrusion in a fused filament fabrication
process. Any number of heating techniques may be used. Electrical
techniques such as inductive or resistive heating may be usefully
applied to liquefy the build material 102. This may, for example
include inductively or resistively heating a chamber around the
build material 102 to a temperature at or near the glass transition
temperature of the build material 102, or some other temperature
where the binder or other matrix becomes workable, extrudable, or
flowable for deposition as described herein. Where the contemplated
build materials are sufficiently conductive, they may be directly
heated through contact methods (e.g., resistive heating with
applied current) or non-contact methods (e.g., induction heating
using an external electromagnet to drive eddy currents within the
material). The choice of additives may further be advantageously
selected to provide bulk electrical characteristics (e.g.,
conductance/resistivity) to improve heating. When directly heating
the build material 102, it may be useful to model the shape and
size of the build material 102 in order to better control
electrically-induced heating. This may include estimates or actual
measurements of shape, size, mass, etc.
[0043] In the above context, "liquefaction" does not require
complete liquefaction. That is, the media to be used in printing
may be in a multi-phase state, and/or form a paste or the like
having highly viscous and/or non-Newtonian fluid properties. Thus
the liquefaction system 106 may include, more generally, any system
that places a build material 102 in condition for use in
fabrication.
[0044] In order to facilitate resistive heating of the build
material 102, one or more contact pads, probes or the like may be
positioned within the feed path for the material in order to
provide locations for forming a circuit through the material at the
appropriate location(s). In order to facilitate induction heating,
one or more electromagnets may be positioned at suitable locations
adjacent to the feed path and operated, e.g., by the control system
118, to heat the build material internally through the creation of
eddy currents. Both of these techniques may be used concurrently to
achieve a more tightly controlled or more evenly distributed
electrical heating within the build material. The printer 100 may
also be instrumented to monitor the resulting heating in a variety
of ways. For example, the printer 100 may monitor power delivered
to the inductive or resistive circuits. The printer 100 may also or
instead measure temperature of the build material 102 or
surrounding environment at any number of locations. The temperature
of the build material 102 may be inferred by measuring, e.g., the
amount of force required to drive the build material 102 through a
nozzle 110 or other portion of the feed path, which may be used as
a proxy for the viscosity of the build material 102. More
generally, any techniques suitable for measuring temperature or
viscosity of the build material 102 and responsively controlling
applied electrical energy may be used to control liquefaction for a
fabrication process using composites as described herein.
[0045] The liquefaction system 106 may also or instead include any
other heating systems suitable for applying heat to the build
material 102 to a suitable temperature for extrusion. This may, for
example include techniques for locally or globally augmenting
heating using, e.g., chemical heating, combustion, ultrasound
heating, laser heating, electron beam heating or other optical or
mechanical heating techniques and so forth.
[0046] The liquefaction system 106 may include a shearing engine.
The shearing engine may create shear within the composite as it is
heated in order to maintain a mixture of the metallic base and a
binder or other matrix, or to maintain a mixture of various
materials in a paste or other build material. A variety of
techniques may be employed by the shearing engine. The bulk media
may be axially rotated as it is fed along the feed path into the
liquefaction system 106. Further, one or more ultrasonic
transducers may be used to introduce shear within the heated
material. Similarly, a screw, post, arm, or other physical element
may be placed within the heated media and rotated or otherwise
actuated to mix the heated material. Bulk build material may
include individual pellets, rods, or coils (e.g., of consistent
size) and fed into a screw, a plunger, a rod extruder, or the like.
For example, a coiled build material can be uncoiled with a heater
system including a heated box, heated tube, or heater from the
printer head. Also, a direct feed with no heat that feeds right
into the print head is also possible.
[0047] The robotic system 108 may include a robotic system
configured to three-dimensionally position the nozzle 110 within
the working volume 115 of the build chamber 116. This may, for
example, include any robotic components or systems suitable for
positioning the nozzle 110 relative to the build plate 114 while
depositing the composite in a pattern to fabricate the object 112.
A variety of robotics systems are known in the art and suitable for
use as the robotic system 108 described herein. For example, the
robotics may include a Cartesian or xy-z robotics system employing
a number of linear controls to move independently in the x-axis,
the y-axis, and the z-axis within the build chamber 116. Delta
robots may also or instead be usefully employed, which can, if
properly configured, provide significant advantages in terms of
speed and stiffness, as well as offering the design convenience of
fixed motors or drive elements. Other configurations such as double
or triple delta robots can increase range of motion using multiple
linkages. More generally, any robotics suitable for controlled
positioning of the nozzle 110 relative to the build plate 114,
especially within a vacuum or similar environment, may be usefully
employed including any mechanism or combination of mechanisms
suitable for actuation, manipulation, locomotion and the like
within the build chamber 116.
[0048] The nozzle(s) 110 may include one or more nozzles for
dispensing the build material 102 that has been propelled with the
drive train 104 and heated with the liquefaction system 106 to a
suitable working temperature. In a multiphase extrusion this may
include a working temperature above the melting temperature of the
metallic base of the composite, or more specifically between a
first temperature at which the metallic base melts and the second
temperature (above the first temperature) at which a second phase
of the composite remains inert.
[0049] The nozzles 110 may, for example, be used to dispense
different types of material so that, for example, one nozzle 110
dispenses a composite build material while another nozzle 110
dispenses a support material in order to support bridges,
overhangs, and other structural features of the object 112 that
would otherwise violate design rules for fabrication with the
composite build material. Further, one of the nozzles 110 may
deposit a different type of material, such as a thermally
compatible polymer or a metal or polymer loaded with fibers of one
or more materials to increase tensile strength or otherwise improve
mechanical properties of the resulting object 112. Two types of
supports may be used--(1) build supports and (2) sinter
supports--e.g., using different materials printed into the same
part to achieve these supports, or to create a distinguishing
junction between these supports and the part.
[0050] The nozzle 110 may preferably be formed of a material or
combination of materials with suitable mechanical and thermal
properties. For example, the nozzle 110 will preferably not degrade
at the temperatures wherein the composite material is to be
dispensed, or due to the passage of metallic particles through a
dispensing orifice therein. While nozzles for traditional
polymer-based fused filament fabrication may be made from brass or
aluminum alloys, a nozzle that dispenses metal particles may be
formed of harder materials, or materials compatible with more
elevated working temperatures such as a high carbon steel that is
hardened and tempered. Other materials such as a refractory metal
(e.g. molybdenum, tungsten) or refractory ceramic (e.g. mullite,
corundum, magnesia) may also or instead be employed. In some
instances, aluminum nozzles may instead be used for MIM extrusion
of certain MIM materials. Further, a softer thermally conductive
material with a hard, wear-resistant coating may be used, such as
copper with a hard nickel plating.
[0051] The nozzle 110 may include one or more ultrasound
transducers 130 as described herein. Ultrasound may be usefully
applied for a variety of purposes in this context. The ultrasound
energy may facilitate extrusion by mitigating clogging by reducing
adhesion of a build material to an interior surface of the nozzle
110. A variety of energy director techniques may be used to improve
this general approach. For example, a deposited layer may include
one or more ridges, which may be imposed by an exit shape of the
nozzle 110, to present a focused area to receive ultrasound energy
introduced into the interface between the deposited layer and an
adjacent layer.
[0052] The nozzle 110 may include an induction heating element,
resistive heating element, or similar components to directly
control the temperature of the nozzle 110. This may be used to
augment a more general liquefaction process along the feed path
through the printer 100, e.g., to maintain a temperature of the
build material 102 during fabrication, or this may be used for more
specific functions, such as declogging a print head by heating the
build material 102 substantially above the working range, e.g., to
a temperature where the composite is liquid. While it may be
difficult or impossible to control deposition in this liquid state,
the heating can provide a convenient technique to reset the nozzle
110 without more severe physical intervention such as removing
vacuum to disassemble, clean, and replace the affected
components.
[0053] The nozzle 110 may include an inlet gas or fan, e.g., an
inert gas, to cool media at the moment it exits the nozzle 110. The
resulting gas jet may, for example, immediately stiffen the
dispensed material to facilitate extended bridging, larger
overhangs, or other structures that might otherwise require support
structures underneath.
[0054] The object 112 may be any object suitable for fabrication
using the techniques described herein. This may include functional
objects such as machine parts, aesthetic objects such as
sculptures, or any other type of objects, as well as combinations
of objects that can be fit within the physical constraints of the
build chamber 116 and build plate 114. Some structures such as
large bridges and overhangs cannot be fabricated directly using
fused filament fabrication or the like because there is no
underlying physical surface onto which a material can be deposited.
In these instances, a support structure 113 may be fabricated,
preferably of a soluble or otherwise readily removable material, in
order to support the corresponding feature.
[0055] Where multiple nozzles 110 are provided, a second nozzle may
usefully provide any of a variety of additional build materials.
This may, for example, include other composites, alloys, bulk
metallic glass's, thermally matched polymers and so forth to
support fabrication of suitable support structures. One of the
nozzles 110 may dispense a bulk metallic glass that is deposited at
one temperature to fabricate a support structure 113, and a second,
higher temperature at an interface to a printed object 112 where
the bulk metallic glass can be crystallized at the interface to
become more brittle and facilitate mechanical removal of the
support structure 113 from the object 112. Conveniently, the bulk
form of the support structure 113 can be left in the super-cooled
state so that it can retain its bulk structure and be removed in a
single piece. Thus, a printer may fabricate a portion of a support
structure 113 with a bulk metallic glass in a super-cooled liquid
region, and may fabricate a layer of the support structure adjacent
to a printed object at a greater temperature in order to crystalize
the build material 102 into a non-amorphous alloy. The bulk
metallic glass particles may thus be loaded into a MIM feedstock
binder system and may provide a support. Pure binding or polymer
materials (e.g., without any loading) may also or instead provide a
support. A similar metal MIM feedstock may be used for
multi-material part creation. Ceramic or dissimilar metal MIM
feedstock may be used for a support interface material.
[0056] The build plate 114 within the working volume 115 of the
build chamber 116 may include a rigid and substantially planar
surface formed of any substance suitable for receiving deposited
composite or other material(s)s from the nozzles 110. The build
plate 114 may be heated, e.g., resistively or inductively, to
control a temperature of the build chamber 116 or the surface upon
which the object 112 is being fabricated. This may, for example,
improve adhesion, prevent thermally induced deformation or failure,
and facilitate relaxation of stresses within the fabricated object.
Further, the build plate 114 may be a deformable build plate that
can bend or otherwise physical deform in order to detach from the
rigid object 112 formed thereon.
[0057] The build chamber 116 may be any chamber suitable for
containing the build plate 114, an object 112, and any other
components of the printer 100 used within the build chamber 116 to
fabricate the object 112. The build chamber 116 may be an
environmentally sealed chamber that can be evacuated with a vacuum
pump 124 or similar device in order to provide a vacuum environment
for fabrication. This may be particularly useful where oxygen
causes a passivation layer that might weaken layer-to-layer bonds
in a fused filament fabrication process as described herein, or
where particles in the atmosphere might otherwise interfere with
the integrity of a fabricated object, or where the build chamber
116 is the same as the sintering chamber. Alternatively, only
oxygen may be removed from the build chamber 116.
[0058] Similarly, one or more passive or active oxygen getters 126
or other similar oxygen absorbing material or system may usefully
be employed within the build chamber 116 to take up free oxygen
within the build chamber 116. The oxygen getter 126 may, for
example, include a deposit of a reactive material coating an inside
surface of the build chamber 116 or a separate object placed
therein that completes and maintains the vacuum by combining with
or adsorbing residual gas molecules. The oxygen getters 126, or
more generally, gas getters, may be deposited as a support material
using one of the nozzles 110, which facilitates replacement of the
gas getter with each new fabrication run and can advantageously
position the gas getter(s) near printed media in order to more
locally remove passivating gasses where new material is being
deposited onto the fabricated object. The oxygen getters 126 may
include any of a variety of materials that preferentially react
with oxygen including, e.g., materials based on titanium, aluminum,
and so forth. Further, the oxygen getters 126 may include a
chemical energy source such as a combustible gas, gas torch,
catalytic heater, Bunsen burner, or other chemical and/or
combustion source that reacts to extract oxygen from the
environment. There are a variety of low-CO and NOx catalytic
burners that may be suitably employed for this purpose without
CO.
[0059] The oxygen getter 126 may be deposited as a separate
material during a build process. Thus, a three-dimensional object
may be fabricated from a metallic composite, including a physically
adjacent structure (which may or may not directly contact the
three-dimensional object) fabricated to contain an agent to remove
passivating gasses around the three-dimensional object. Other
techniques may be similarly employed to control reactivity of the
environment within the build chamber 116, or within post-processing
chambers or the like as described below. For example, the build
chamber 116 may be filled with an inert gas or the like to prevent
oxidation.
[0060] The control system 118 may include a processor and memory,
as well as any other co-processors, signal processors, inputs and
outputs, digital-to-analog or analog-to-digital converters and
other processing circuitry useful for monitoring and controlling a
fabrication process executing on the printer 100. The control
system 118 may be coupled in a communicating relationship with a
supply of the build material 102, the drive train 104, the
liquefaction system 106, the nozzles 110, the build plate 114, the
robotic system 108, and any other instrumentation or control
components associated with the build process such as temperature
sensors, pressure sensors, oxygen sensors, vacuum pumps, and so
forth. The control system 118 may be operable to control the
robotic system 108, the liquefaction system 106 and other
components to fabricate an object 112 from the build material 102
in three dimensions within the working volume 115 of the build
chamber 116.
[0061] The control system 118 may generate machine ready code for
execution by the printer 100 to fabricate the object 112 from the
three-dimensional model 122 stored to a database 120. The control
system 118 may deploy a number of strategies to improve the
resulting physical object structurally or aesthetically. For
example, the control system 118 may use plowing, ironing, planing,
or similar techniques where the nozzle 110 runs over existing
layers of deposited material, e.g., to level the material, remove
passivation layers, apply an energy director topography of peaks or
ridges to improve layer-to-layer bonding, or otherwise prepare the
current layer for a next layer of material. The nozzle 110 may
include a low-friction or non-stick surface such as Teflon, TiN or
the like to facilitate this plowing process, and the nozzle 110 may
be heated and/or vibrated (e.g., using an ultrasound transducer) to
improve the smoothing effect. This surface preparation may be
incorporated into the initially-generated machine ready code.
Alternatively, the printer 100 may dynamically monitor deposited
layers and determine, on a layer-bylayer basis, whether additional
surface preparation is necessary or helpful for successful
completion of the object.
[0062] FIG. 2 shows a flow chart of a method for printing with
composites, e.g., metal injection molding materials. As shown in
step 202, the process 200 may include providing a build material
including an injection molding material, or where a support
interface is being fabricated, a MIM binder (e.g., a MIM binder
with similar thermal characteristics). The material may include,
for example, any of the MIM materials described herein. The
material may be provided as a build material in a billet, a wire,
or any other cast, drawn, extruded or otherwise shaped bulk form.
As described above, the build material may be further packaged in a
cartridge, spool, or other suitable carrier that can be attached to
an additive manufacturing system for use.
[0063] As shown in step 204, the process may include fabricating a
layer of an object. This may include any techniques that can be
adapted for use with MIM materials. For example, this may include
fused filament fabrication, jet printing or any other techniques
for forming a net shape from a MIM material (and more specifically
for techniques used for forming a net shape from a polymeric
material loaded with a second phase powder).
[0064] As shown in step 211, this process may be continued and
repeated as necessary to fabricate an object within the working
volume. While the process may vary according to the underlying
fabrication technology, an object can generally be fabricated layer
by layer based on a three-dimensional model of the desired object.
As shown in step 212, the process 200 may include shaping the net
shape object after the additive process is complete. Before
debinding or sintering, the green body form of the object is
usefully in a soft, workable state where defects and printing
artifacts can be easily removed, either manually or automatically.
Thus the process 200 may take advantage of this workable,
intermediate state to facilitate quality control or other
process-related steps, such as removal of supports that are
required for previous printing steps, but not for debinding or
sintering.
[0065] As shown in step 214, the process 200 may include debinding
the printed object. In general debinding may be performed
chemically or thermally to remove a binder that retains a metal (or
ceramic or other) powder in a net shape. Contemporary injection
molding materials are often engineered for thermal debinding, which
advantageously permits debinding and sintering to be performed in a
single baking operation, or in two similar baking operations. In
general, the debinding process functions to remove binder from the
net shape green object, thus leaving a very dense structure of
metal (or ceramic or other) particles that can be sintered into the
final form.
[0066] As shown in step 216, the process 200 may include sintering
the printed and debound object into a final form. In general,
sintering may be any process of compacting and forming a solid mass
of material by heating without liquefaction. During a sintering
process, atoms can diffuse across particle boundaries to fuse into
a solid piece. Because sintering can be performed at temperatures
below the melting temperature, this advantageously permits
fabrication with very high melting point materials such as tungsten
and molybdenum.
[0067] Numerous sintering techniques are known in the art, and the
selection of a particular technique may depend upon the build
material used, and the desired structural, functional or aesthetic
result for the fabricated object. For example, in solid-state
(non-activated) sintering, metal powder particles are heated to
form connections (or "necks") where they are in contact. Over time,
these necks thicken and create a dense part, leaving small,
interstitial voids that can be closed, e.g., by hot isostatic
pressing (HIP) or similar processes. Other techniques may also or
instead be employed. For example, solid state activated sintering
uses a film between powder particles to improve mobility of atoms
between particles and accelerate the formation and thickening of
necks. As another example, liquid phase sintering may be used, in
which a liquid forms around metal particles. This can improve
diffusion and joining between particles, but also may leave
lower-melting phase within the sintered object that impairs
structural integrity. Other advanced techniques such as nano-phase
separation sintering may be used, for example to form a
high-diffusivity solid at the necks to improve the transport of
metal atoms at the contact point
[0068] Debinding and sintering may result in material loss and
compaction, and the resulting object may be significantly smaller
than the printed object. However, these effects are generally
linear in the aggregate, and net shape objects can be usefully
scaled up when printing to create a corresponding shape after
debinding and sintering.
[0069] FIG. 3 shows an additive manufacturing system for use with
metal injection molding materials. The system 300 may include a
printer 302, a conveyor 304, and a postprocessing station 306. In
general, the printer 302 may be any of the printers described above
including, for example a fused filament fabrication system, a
stereolithography system, a selective laser sintering system, or
any other system that can be usefully adapted to form a net shape
object under computer control using injection molding build
materials. The output of the printer 302 may be an object 303 that
is a green body including any suitable powder (e.g., metal, metal
alloy, ceramic, and so forth, as well as combinations of the
foregoing), along with a binder that retains the powder in a net
shape produced by the printer 302.
[0070] The conveyor 304 may be used to transport the object 303
from the printer 302 to a post-processing station 306 where
debinding and sintering can be performed. The conveyor 304 may be
any suitable device or combination of devices suitable for
physically transporting the object 303. This may, for example,
include robotics and a machine vision system or the like on the
printer side for detaching the object 303 from a build platform or
the like, as well as robotics and a machine vision system or the
like on the post-processing side to accurately place the object 303
within the post-processing station 306. Further, the
post-processing station 306 may serve multiple printers so that a
number of objects can be debound and sintered concurrently, and the
conveyor 304 may interconnect the printers and post-processing
station so that multiple print jobs can be coordinated and
automatically completed in parallel. Alternatively, the object 303
may be manually transported between the two corresponding
stations.
[0071] The post-processing station 306 may be any system or
combination of systems useful for converting a green part formed
into a desired net shape from a metal injection molding build
material by the printer 302 into a final object. The
post-processing station 306 may, for example, include a chemical
debinding station and a thermal sintering station that can be used
in sequence to produce a final object. Some contemporary injection
molding materials are engineered for thermal debinding, which makes
it possible to perform a combination of debinding and sintering
steps with a single oven or similar device. While the thermal
specifications of a sintering furnace may depend upon the powder to
be sintered, the binder system, the loading, and other properties
of the green object and the materials used to manufacture same,
commercial sintering furnaces for thermally debound and sintered
MIM parts may typically operate with an accuracy of +/-5 degrees
Celsius or better, and temperatures of at least 600 degrees C., or
from about 200 degrees C. to about 1900 degrees C. for extended
times. Any such furnace or similar heating device may be usefully
employed as the post-processing station 306 as described herein.
Vacuum or pressure treatment may also or instead be used. Identical
or similar material beads with a non-binding coating may be used
for a furnace support--e.g., packing in a bed of this material that
shrinks similar to the part, except that it will not bond to the
part.
[0072] Embodiments may be implemented with a wide range of other
debinding and sintering processes. For example, the binder may be
removed in a chemical debind, thermal debind, or some combination
of these. Other debinding processes are also known in the art (such
as supercritical or catalytic debinding), any of which may also or
instead be employed by the post-processing station 306 as described
herein. For example, in a common process, a green part is first
debound using a chemical debind, which is following by a thermal
debind at a moderately high temperature (in this context, around
700-800 C) to remove organic binder and create enough necks among a
powdered material to permit handling. From this stage, the object
may be moved to a sintering furnace to remove any remaining
components of a binder system densify the object. Alternatively, a
pure thermal debind may be used to remove the organic binder. More
general, any technique or combination of techniques may be usefully
employed to debind an object as described herein.
[0073] Similarly, a wide range of sintering techniques may be
usefully employed by the post-processing station. For example, an
object may be consolidated in a furnace to a high theoretical
density using vacuum sintering. Alternatively, the furnace may use
a combination of flowing gas (e.g., at below atmosphere, slightly
above atmosphere, or some other suitable pressure) and vacuum
sintering. More generally, any sintering or other process suitable
for improving object density may be used, preferably where the
process yields a near-theoretical density part with little or no
porosity. Hot-isostatic pressing ("HIP") may also (e.g., as a
postsinter finishing step) or instead be employed, e.g., by
applying elevated temperatures and pressures of 10-50 ksi, or
between about 15 and 30 ksi. Alternatively, the object may be
processed using any of the foregoing, followed by a moderate
overpressure (greater than the sintering pressure, but lower than
HIP pressures). In this latter process, gas may be pressurized at
100-1500 psi and maintained at elevated temperatures within the
furnace or some other supplemental chamber. Alternatively, the
object may be separately heated in one furnace, and then immersed
in a hot granular media inside a die, with pressure applied to the
media so that it can be transmitted to the object to drive more
rapid consolidation to near full density. More generally, any
technique or combination of techniques suitable for removing binder
systems and driving a powdered material toward consolidation and
densification may be used by the post-processing station 306 to
process a fabricated green part as described herein.
[0074] The post-processing station 306 may be incorporated into the
printer 302, thus removing a need for a conveyor 304 to physically
transport the object 303. The build volume of the printer 302 and
components therein may be fabricated to withstand the elevated
debinding/sintering temperatures. Alternatively, the printer 302
may provide movable walls, barriers, or other enclosure(s) within
the build volume so that the debind/sinter can be performed while
the object 303 is on a build platform within the printer 302, but
thermally isolated from any thermally sensitive components or
materials.
[0075] The post-processing station 306 may be optimized in a
variety of ways for use in an office environment. The
post-processing station 306 may include an inert gas source 308.
The inert gas source 308 may, for example, include argon or other
inert gas (or other gas that is inert to the sintered material),
and may be housed in a removable and replaceable cartridge that can
be coupled to the post-processing station 306 for discharge into
the interior of the post-processing station 306, and then removed
and replaced when the contents are exhausted. The post-processing
station 306 may also or instead include a filter 310 such as a
charcoal filter or the like for exhausting gasses that can be
outgassed into an office environment in an unfiltered form. For
other gasses, an exterior exhaust, or a gas container or the like
may be provided to permit use in unventilated areas. For
reclaimable materials, a closed system may also or instead be used,
particularly where the environmental materials are expensive or
dangerous.
[0076] The post-processing station 306 may be coupled to other
system components. For example, the post-processing station 306 may
include information from the printer 302, or from a controller for
the printer, about the geometry, size, mass and other physical
characteristics of the object 303 in order to generate a suitable
debinding and sintering profile. Optionally, the profile may be
created independently by the controller or other resource and
transmitted to the post-processing station 306 when the object 303
is conveyed. Further, the post-processing station 306 may monitor
the debinding and sintering process and provide feedback, e.g., to
a smart phone or other remote device 312, about a status of the
object, a time to completion, and other processing metrics and
information. The post-processing station 306 may include a camera
314 or other monitoring device to provide feedback to the remote
device 312, and may provide time lapse animation or the like to
graphically show sintering on a compressed time scale.
Post-processing may also or instead include finishing with heat, a
hot knife, tools, or similar, and may include applying a finish
coat.
[0077] FIG. 4 is a block diagram of an additive manufacturing
system 400. The system 400 may include a printer 420, a debinder
430, and a furnace 440 operating in series to manufacture a
finished part 460. In particular, the printer may produce a
fabricated green part 491, the debinder 430 debinds the green part
491 to produce a brown part 492, and the furnace 440 sinters the
brown part 492 to produce the finished part 491. The devices 420,
430, 440 may be communicatively coupled to a process controller 405
and user interface 410 via a network 460 (e.g., a wired, wireless
and/or cloud network). The process controller 405 may be
implemented as a network server, workstation or off-site cloud
service, and may communicate with, and control operations at, one
or more of the printer 420, debinder 430 and furnace 440. The
process controller 405 may also include a distributed processing
architecture, where processing elements at the printer 420,
debinder 430 and/or furnace 440 perform portions of the control
operations. The user interface 410 may comprise one or a plurality
of devices connected to the network 460, such as a laptop,
workstation, mobile device (e.g., smartphone, tablet), and/or or
touchscreens integrated into the printer 420, debinder 430 and/or
furnace 440.
[0078] Via the user interface 410, a user may communicate with the
process controller 405 to indicate one or more parts to be
manufactured. In response, the process controller 405 can manage
the entire manufacturing process, controlling the printer 420,
debinder 430 and furnace 440 to manufacture to produce the green
part 491, brown part 492 and finished part 493, respectively, and
instructing the user via the user interface 410 as necessary to
manipulate the parts during the process.
[0079] The system 400 may incorporate one or more features of the
printer 100 and system 300 described above with reference to FIGS.
1-3. For example, the printer 420 may incorporate features of the
printers 100, 300 and the process controller 405 may include
features of the control system 118 and database 120. Further, the
debinder 430 and furnace 440 may incorporate features of the
post-processing station 306, and the system 400 may carry out the
manufacturing process 200 to fabricate a part.
[0080] FIG. 5 is a flow diagram of a process 500 of fabricating a
part that may be carried out by the system 400 of FIG. 4. With
reference to FIG. 4, upon initial setup or in response to a prompt,
the printer 420, debinder 430 and furnace 440 may communicate with
the controller 405 to convey the features and/or status of each of
the devices (505). For example, the devices 420 can indicate 1)
capacities for accommodating parts of a maximum size and/or
thickness, 2) build materials available and quantities thereof, and
3) errors, alerts or other notifications that may affect or limit
the manufacturing process. Based on this information, the
controller 405 can define part bounds, which can specify maximum
part geometries, quantities and/or constituent materials (510).
[0081] A user may define a part (or parts) to be manufactured via
the user interface 410 (515). To do so, a user may select a part
from a menu at the user interface 410, may import data for the
part, or may design the part directly at the user interface 410.
The part may be defined by geometric parameters (e.g., a CAD file)
and material(s) from which the part is to be fabricated. The user
may make further adjustments to the geometric parameter, such as
scaling up or scaling down the size of the finished part. Based on
the desired properties of the finished part 491 (e.g., part
geometry and material composition), as well as the anticipated
effects on the part exerted by the printer 420, debinder 430 and
furnace 440, the process controller 405 may generate print
instructions for printing the part (520). The print instructions
may include a toolpath (e.g., gcode) and related parameters that
are transmitted to the printer 420, which then prints the green
part 491 in accordance with the instructions (524). The controller
405 may also report a print status to the user via the user
interface 410, and may also instruct the user on operating the
printer 420 before, during and/or after the print (522). For
example, the user interface 522 may display instructions for
initializing or activating the printer 420, performing printer
maintenance (e.g., cleaning the print nozzle or loading build
material), and removing the printed green part 491 from the printer
420 once the printing is completed. The controller 405 may issue
such reports and instructions based on status reports conveyed by
the printer (e.g., 505) as well as the print instructions
[0082] Following the printing of the green part 491, the controller
405 may determine parameters for debinding the green part 491 in
the debinder 430 (525). For example, the controller 405 may
determine a volume of solvent required to debind the part, a length
of time to immerse the part in the solvent, circulation of the
solvent, and whether to exchange solvent during the debind. If more
than one green parts are available, then the controller 405 may
also define a batch of parts that can be debound together. The
controller 405 may determine such debind parameters based on the
properties of the green part 491 (and other green parts, if
available), including the geometry, material, thickness and mass of
the green part 491. For example, the controller 405 may determine
that a part having thicker features or greater mass may require a
longer solvent immersion time. The properties of the green part 491
may be measured directly by the user and entered at the user
interface 410, or may be estimated based on the print parameters
for the part. The controller may also determine the debind
parameters based on the capacity or status of the debinder 430 as
communicated by the debinder 430 (e.g., 505). Features of the
debinder 420, as well as communications between the debinder 420
and controller 405, are described in further detail below with
reference to FIGS. 7-9.
[0083] Based on the debind parameters, the controller 405
determines debind instructions for the user interface 410 and
debinder 430 (530). For the user interface 410, the controller 405
may present a menu of options and instructions to the user (see,
e.g., FIG. 7, described below) (532). For example, the user
interface 410 may 1) allow selection of one or more parts to
debind, 2) instruct the user on how to place and orient the
selected part(s) within a process chamber of the debinder 430, and
3) instruct the user regarding any maintenance required at the
debinder 430 (e.g., removing waste or adding solvent). For the
debinder 430, the controller 405 may initiate and manage the debind
process based on the debind parameters and the aforementioned user
input (534). For example, for the given selection of part(s), the
controller 405 may configure the volume of solvent used, solvent
immersion time, circulation of the solvent, whether to exchange
solvent during the debind, and drying time and temperature. Once
the debind is complete, the controller 405 may then instruct the
user, via the user interface 410, to open the process chamber of
the debinder 430 and remove the brown part(s) 492 (532).
[0084] Following the debinding, the controller 405 may determine
parameters for sintering the brown part 492 in the furnace 440
(535). For example, the controller 405 may determine parameters
including one or more of sintering time, temperature, gas flow rate
and furnace load (i.e. a selection of parts that may be sintered
concurrently). The controller 405 may determine the sinter
parameters based on the properties of the brown part 492 (and other
parts, if sintering concurrently), including the geometry,
material, thickness and mass of the brown part 492. For example,
the controller 405 may determine that a part having thicker
features or greater mass may require a longer solvent immersion
time. The properties of the brown part 492 may be measured directly
by the user and entered at the user interface 410, or may be
estimated based on the print parameters for the part. The
controller 405 may also determine the sinter parameters based on
the capacity or status of the furnace 440 as communicated by the
furnace 440 (e.g., 505).
[0085] In an example illustrating determination of sinter
parameters, the brown part 492 may be printed from 4140 alloy
nominal feedstock steel. The user may select, for example, a
particular material content (e.g., carbon content) of the
constituent 4140 alloy steel to be present in the steel after
sintering. The controller 405 may evaluate the desired carbon
content input from the user and generate therefrom the sinter
parameters to produce a desired carburization/decarburization
effect. For example, the sinter parameters may include a
configuration of the gas flow rate within furnace 440.
[0086] Adjusting the carbon content of the 4140 alloy steel may
produce a wide range of ductility and/or hardness to the user for
alloy steels. The user may enter a given ductility and/or hardness
as a desired property at the user interface 410, and in response,
the controller 405 may determine the required carbon content to
achieve the desired ductility and/or hardness, and then determine
the sinter parameters to produce the determined carbon content of
the finished part 493. The carbon content of the finished part 493
can be altered by furnace load (i.e., the total mass of parts
placed in the furnace 440) as well as gas flow rate. This is due to
the effect of binder amount on carburizing potential of sintering
process. Furnace load and gas flow rate are thus two sinter
parameters that the controller 405 may determine and provide to the
furnace 440 to adjust the final microstructure of the finished part
493, while keeping other sinter parameters (e.g., temperature,
time, etc.) constant.
[0087] The controller 405 may also provide furnace load
recommendations to the user via the user interface 410, allowing
the user to manually adjust the furnace load. Alternatively, the
furnace 440 may automatically adjust the furnace load based on
sinter parameters communicated to it by the controller 405.
Further, the user may enter at the user interface 410 a selection
of multiple parts to be sintered concurrently and/or the total mass
of the parts to be sintered in in a given sintering run, along with
the desired microstructure. The controller 405 may then determine,
based on the total mass of the parts and desired microstructure for
a particular production run, the gas flow needed to achieve that
microstructure in that particular production run.
[0088] The controller 405 may sintering parameters, as a function
of the input materials properties, based on a fixed mapping. In
such cases, the controller 405 may employ a look-up table (LUT),
implemented in local memory, to accomplish the mapping. The
contents of the LUT may be generated empirically, based on actual
production runs. The contents of the LUT may alternatively be
generated analytically according to formulae based on established
materials theory. Alternatively, the controller 405 may produce the
sinter parameters analytically, in real-time or near real-time, by
a processor executing instruction code that evaluates the input
materials properties according to formulae based on established
materials theory.
[0089] The controller may provide further sinter parameters to
accommodate particular materials or produce specific effects in the
finished part 493. For example, the oxygen content in the gas flow
may be varied for processing titanium-based alloys to provide
variations in hardness vs. ductility of the part material, or to
produce hardened oxide layers on a material such as titanium or
aluminum. The controller 405 may also define sinter parameters
specifying a particular cool-down rate. For example, one cool down
rate may be defined for banite, and a slower cool down rate may be
defined for ferrite. The controller 405 may define sinter
parameters that adjust the internal sintering furnace atmosphere,
vacuum level and the furnace loading, to selectively
harden/carburize the parts. Certain parts may only require a
selected region to be hardened (e.g., the teeth of a gear), but
require other regions of the part maintain ductility (e.g., thin
sections that are prone to embrittlement when too hard/carburized).
Accordingly, the controller 405 may direct the printer 420 to print
a thin stop-off layer on selected surfaces to prevent carburization
of those selected surfaces, resulting in selective carburizing at
the furnace 440.
[0090] If the brown part 492 contains substantial amounts of
binding agents (e.g., as a result of incomplete debinding), the
binding agents may affect the carbon content of the final part 493.
In such a case, the sections under the thin stop-off described
above may pick up carbon due to prolonged exposure to carbon from
the binder and become harder selectively. Thus, the controller 405
may configure the sinter parameters to selectively distribute the
stop-off to facilitate the sintering of functionally gradient
steel. Similar techniques of distributing stop-off material may
alternatively be used for oxygen hardening of titanium to
facilitate the sintering of functionally gradient titanium. Similar
techniques may apply to other processes, for example for processing
titanium with oxygen hardening.
[0091] Based on the sinter parameters, the controller 405
determines sinter instructions for the user interface 410 and
debinder 430 (540). For the user interface 410, the controller 405
may present a menu of options and instructions to the user (542).
For example, the user interface 410 may 1) allow selection of one
or more parts to sinter, 2) instruct the user on how to place and
orient the selected part(s) within the furnace 440, and 3) instruct
the user regarding any maintenance required at the furnace 440. For
the furnace 440, the controller 405 may initiate and manage the
sinter process based on the sinter parameters and the
aforementioned user input (544). For example, for the given
selection of part(s), the controller 405 may control the
temperature, time, gas flow, oxygen content, and other parameters
of the furnace 440 as described above. Once the sinter is complete,
the controller 405 may then instruct the user, via the user
interface 410, to open the process chamber of the furnace 440 and
remove the finished part(s) 493 (542).
[0092] In order to increase efficiency of the manufacturing
process, the controller 405 may also manage a plurality of queues.
For example, the controller may maintain 1) a queue of parts to be
printed, 2) a list of parts at each stage of the manufacturing
process (i.e., printed, debound, sintered), and 3) the operational
status of each device. Based on this information, the controller
405 can define a local order of operations (e.g., a part queue) at
each device, prioritizing and grouping parts to manufacture the
parts more quickly and utilize resources (e.g., feedstock, solvent)
most efficiently.
[0093] In configuring the print, debind and sinter parameters and
controlling the devices as described above, the controller 405 may
calculate an anticpated transformation of the part at each stage in
the manufacturing process. For example, the controller may
calculate an anticipated 1) deformation of a part surface during
the printing as a result of the part geometry and mass, 2) a
portion of the part that may retain binder after debinding, or 3)
uniform or uneven shrinkage of the part during sintering.
Similarly, the controller 405 may calculate anticipated properties
of the green part 491, brown part 492 and/or finished part 493
(including any transformations) prior to beginning the print. In
response, the controller 405 may configure the print, debind and/or
sinter parameters to compensate for the anticipated transformation
at the same or different stage of the manufacturing process.
[0094] Thus, the controller 405 can perform a predictive analysis
of the manufacturing process. For example, by analyzing the initial
properties of the part to be manufactured (e.g., geometry and
materials), the effects on the part exerted by each of the printer
420, debinder 430 and furnace 440 (via empirical observation and/or
modeling), and the desired properties of the finished part 491, the
controller 405 may then control the system 400 to ensure that the
finished part 491 is produced within acceptable tolerances. By
tracking operations at each of the devices in the system 400, as
well as the status of each of the unprinted, green and brown parts
within the manufacturing queue, the controller 405 can optimize the
efficiency of the system 400. For example, the controller 405 can
group multiple parts for printing, debinding or sintering, and can
define a part queue at each of the printer 420, debinder 430 and
furnace 440 to efficiently occupy the runtime of each device.
Further, the process controller 405 order a part within the queue
based on the properties of the part relative to properties of other
parts in the queue.
[0095] FIGS. 6A-B illustrate orientation of a printed part on a
build plate. With reference to FIG. 4, in some embodiments, a
finished part 493 may require further processing upon exiting the
furnace 440. For example, some surfaces of the finished part 440
may require grinding, sanding or filing to remove imperfections or
rough portions to produce a consistent or smooth surface. Such a
process may involve finishing the part by hand, which may be
time-consuming and laborious, as well as unfeasible for larger
production volumes.
[0096] Accordingly, the controller 405 may orient the part during
the initial print to minimize the need for further processing. For
example, as shown in FIG. 6A, a part 612 is printed on a build
plate 610 within a build chamber 605 of a printer (e.g., printer
420). A surface 615 requiring post-sinter finishing occupies an
upright side of the part 612. This surface may require the
post-sinter finishing because the printer may deposit material
unevenly across the upright surface. In contrast, a bottom surface
of the part 612, which is aligned with the surface of the build
plate 610 (or an interface layer on the build plate, not shown),
may exhibit a smoother, more consistent surface as a result of the
material distributing against the build plate 610. Thus, a part
surface that is printed against the build plate 610 may not
require, or require less, post-sinter finishing. Likewise, due to
the effects of gravity settling the deposited material during
printing, a part surface oriented parallel to the surface of the
build plate 610 (e.g., an upper surface), or at an angle other than
perpendicular to the build plate 610, may require less finishing
than a surface printed perpendicular to the build plate 610.
[0097] Accordingly, the controller 405 may identify (based on the
part properties and/or user entry) which of the surfaces of the
part 612 may require post-sinter finishing and, based on this
indication, control the printer 420 to print the part 612 in an
orientation to reduce or minimize post-sinter finishing. As shown
in FIG. 6B, for example, the surface to be finished (615 of FIG.
6A) is oriented to align with the surface of a build plate 610. As
a result, the surface 615 may require less or no finishing after
exiting the furnace 440. If the controller 405 identifies more than
one surface requiring post-sinter finishing, it may control the
print orientation of the part 612 to minimize the total surface
area of the part 612 requiring post-sinter finishing.
[0098] FIG. 7 illustrates a display 700 presented by a user
interface and configured to guide the user through a debind
process. With reference to FIGS. 4 and 5, the display 700 may be
presented by the user interface 410 before beginning the debind
process (534), as a portion of the interaction with the user
regarding the debind (532). The display 700 may be preceded by
another menu allowing the user to select the part(s) for debinding.
As shown, the display 700 presents a series of instructions guiding
the user in preparing the green part(s) and debinder for the debind
process. First, the display 700 instructs the user to place the
selected parts (identified by corresponding codes, names or
illustrations) into the basket of the process chamber of the
debinder (705). For parts requiring a particular orientation in the
process chamber, the display may then instruct the user on how to
orient those parts, providing an illustration for each (710, 715).
Once the parts are placed and oriented (and, optionally, the user
verifies the same through the user interface 410), the display 700
instructs the user to close and/or lock the lid of the process
chamber (720). The user may then select a button to begin the
debind (750) or cancel (770).
[0099] FIG. 8 is a schematic of a debinder system 800 for debinding
printed parts. The debinder system 800 may be employed to debind
fabricated green parts that are printed as described above with
reference to FIGS. 1-7, and may be implemented as the debinder 430
of FIG. 4. The system 800 includes a process chamber 810, into
which the fabricated green parts may be inserted for debinding. A
storage chamber 840 stores a volume of solvent for use in the
debinding process. The storage chamber 840 may be filled and
refilled with solvent via a port at the storage chamber 840.
Alternatively, the storage chamber 840 may be configured to be
removable and replaceable to maintain a sufficient amount of
solvent within the system 800. For example, the storage chamber 840
may be removed and replaced by a replacement storage chamber (not
shown) to replenish the solvent in the system 800, or may be
removed, refilled with solvent, and then reconnected within the
system 800.
[0100] The distill chamber 820 collects the post-debinding solution
from the process chamber 810 following the debinding process, and
enables distillation of the solvent. A waste chamber 830 may be
coupled to the distill chamber 820, and collects waste accumulated
in the distill chamber 820 as a result of distillation. The waste
chamber 830 may be configured to be removable and replaceable after
a number of distillation cycles, wherein the waste chamber 830 may
be removed and replaced by a replacement waste chamber (not shown),
or may be removed, emptied of waste, and then reconnected to the
distill chamber 820. A condenser 860 operates to condense vaporized
solvent from the distill chamber 820 and return the liquid solvent
to the storage chamber 840.
[0101] FIG. 9 is a flow diagram of a debinding process 900 that may
be carried out by the debinder system 800 of FIG. 8. The process
900 may be incorporated into the process 500 of FIG. 5 described
above, and particularly the operations of defining the debind
parameters 525, determining the debind instructions 530,
interfacing with the user 532, and debinding the part 534. With
reference to FIGS. 4 and 8, a user may insert one or more
fabricated green parts 491 into a basket within the process chamber
810 (905). The controller 405, communicating with the user via user
interface 410, may maintain information regarding the parts for
debinding (e.g., material, geometry). Based on this information,
the controller 405 may instruct the user on which of the available
parts to place in the process chamber 810 and/or how to position
and orient the parts in the chamber 810. The controller 405 may
also control some or all of the debinding process 900. For example,
the controller 405 may determine debind parameters based on the
properties of the inserted parts, such as solvent volume in the
process chamber, debinding time, and solvent circulation.
[0102] After inserting the parts into the process chamber 810
according to the presented instructions, the user may close a lid
of the process chamber 810, optionally enter a measured weight of
the green parts (which may be used to determine the volume of
solvent used), and initiate the debinding process. Once initiated,
solvent is pumped from the storage chamber 840 into the process
chamber 810 up to a level as determined by the controller 405
(910). The process chamber 810 then raises the temperature of the
solvent to a controlled value (e.g., 46.degree. C.) via one or more
heaters, and, optionally, engages a pump to circulate the solvent
within the process chamber 810 (915). The temperature and
circulation may be maintained for a length of time determined by
the controller 405 (i.e., "debind time"). The controller 405, the
debinder 800, or another device may determine the time to debind
the part to provide sufficient debinding based on the geometry
and/or weight of the green parts (918). Embodiments for determining
the time to debind the part are described in further detail below.
During this time, the solvent dissolves the binder within the green
parts, and the liquid in the process chamber 810 becomes a solution
containing the binder.
[0103] Upon reaching the debind time, the part may be removed from
the solvent. Upon removal, the part may retain a small portion
(e.g., 10% or less) of the binder, which can be subsequently
removed via thermal debinding or a subsequent chemical debinding.
The process chamber 810 drains the solution into the distill
chamber 820, thereby removing the part from the solvent (920). Once
drained, the temperature in the process chamber 810 may be
controlled at a higher temperature (e.g., 50.degree. C.) to
facilitate drying of the brown parts (925). During this time,
solvent vapor may be vented to the storage chamber 830 and/or to
the distill chamber 820. Upon drying the brown parts, the
temperature of the process chamber 810 may be reduced (e.g., by
disabling the corresponding heater(s)), and a fan or other
mechanical means (e.g., a blower, pump, or compressor) may be
engaged to facilitate purging the remaining solvent vapor from the
process chamber 810 and into the storage chamber 830 and/or to the
distill chamber 820 (930). After purging the solvent vapor and,
optionally, manually or automatically locking the process chamber
810 for a time allowing the part to cool sufficiently, the user may
then open the lid and remove the brown parts from the process
chamber 810.
[0104] The system 800 may then undergo a process to distill the
solvent from the solution drained from the process chamber 810 into
the distill chamber 820 (935). The waste chamber 830 may be
positioned below the distill chamber 820 and connected by a
coupling enabling the solution to flow into the waste chamber 830.
The waste chamber 830 (and, optionally, the distill chamber 820)
may be heated to a given temperature (e.g., 50.degree. C.) to cause
the solvent to evaporate from the solution. The condenser 860
collects the solvent vapors, condenses the vapors to a liquid, and
pumps the liquid solvent to the storage tank 840. Concurrently, the
waste remaining from the distilling is collected at the bottom of
the waste chamber 830.
[0105] After the distilling is complete, the waste may be allowed
to cool and dry. Periodically, or upon detecting that the collected
waste reaches a threshold volume, the waste chamber 830 may be
removed and replaced by a replacement waste chamber, or may be
removed, emptied of waste, and then reconnected to the distill
chamber 820.
[0106] Optionally, for parts requiring a larger volume of solvent
or longer debinding times, the solvent may be exchanged in the
process chamber 810 during a debinding. For example, following
draining the process chamber 810 (920), the operations of filling
the process chamber with solvent (910), debinding (915) and
draining (920) may be repeated prior to drying the parts (925). A
distill operation (935) may also be performed for the exchanged
solution concurrently with the debinding using the subsequent
solvent. Exchanging the solvent during a debinding may improve the
effectiveness and debind time particularly for larger or denser
parts, or for parts having thicker geometries.
[0107] As indicated above, the storage chamber 840 may be filled
and refilled with solvent via a port at the storage chamber 840, or
may be removed and refilled or replaced by a replacement storage
chamber. Alternatively, the storage chamber may be filled with
solvent via the process chamber 810. For example, a volume of
solvent may be poured into the process chamber 810, where it is
permitted to flow into the storage chamber 840. The process chamber
810 may then be purged (930) to ensure that no solvent vapors
remain in the process chamber 810. The system 800 may then enable
the user to add green parts to initiate the debinding process
500.
[0108] As a result of the debinding process 900, the system 800
provides several advantages. By controlling the process parameters
(e.g., solvent volume, debind time and circulation) based on the
properties of the green parts (e.g., mass and geometry), the system
800 makes efficient use of the solvent. By distilling the solvent
after a debinding, the system 800 also conserves and recycles the
solvent for future use. The system 800 may be embodied in a
compact, self-contained unit that is suitable for an office or
workshop environment. In particular, the system 800 can contain all
solvent vapor and waste within the unit, thereby maintaining a safe
environment around the system 800. Further, the system 800 can be
implemented with the controller 405 or another control system
(integral to the system 800 or operated by a computer workstation
or cloud network) to control the debind process and guide the user
on operation (e.g., insertion/removal of parts and waste removal),
making the system accessible to a wide range of users.
[0109] In further embodiments, the process chamber 810, distill
chamber 820, waste chamber 830, and storage chamber 840 may be
implemented in alternative configurations. For example, the distill
chamber 820 and waste chamber 830 may be implemented as a single
chamber, which may be removable to be cleaned of waste and
reconnected, or may be replaced by a replacement chamber. Further,
the distill chamber 820 and waste chamber 830 may also serve as the
storage chamber 840, whereby the distill chamber 820 distills the
solvent, via a condenser, into the process chamber 810. In such an
embodiment, the process chamber 810 may include divisions or
sub-chambers to hold the solvent prior to a debinding
operation.
Determination of Time to Debind a Part
[0110] Example embodiment enable the time to debind a part to be
determined based on the geometry of the part, which can be derived
from CAD drawings, print instructions such as toolpaths, or other
information defining the part. From this geometry, example
embodiments can predict the time required for a binding agent of a
part to be substantially or fully removed from the part through
chemical dissolution when the part is immersed in a solvent. As a
result, the debind process can be terminated immediately or shortly
after the part is debound, thereby minimizing the occupation time
of the debinder and improving the speed of the additive
manufacturing process. Further, the debind completion time can be
predicted, and an indication of the completion time, as well as the
current progress of the debind, can be reported to the user.
Although embodiments below describe chemical debinding, in further
embodiments, the time to debind a part via thermal debinding may be
determined alternatively or in addition to a chemical
debinding.
[0111] FIG. 10 is a flow diagram illustrating a process 1000 of
determining a time to debind a part in an example embodiment. With
reference to FIGS. 4 and 8, the process 1000 may be carried out by
one or more of the controller 405, the debinder 800, or another
device before or during a process of debinding the part. For
example, the process 1000 may be carried out before or during the
debinding process 900 described above with reference to FIG. 9. The
geometry of the part may be received, where the geometry may
include one or more of a CAD drawing, print instructions, and other
properties or parameters defining the part (1050). From this
geometry, descriptors may be computed (1055). Descriptors may
include one or more properties of the part that relate to the time
required for diffusion of a solvent through the part. In
applications of thermal debinding, the descriptors may relate to
the time required for the binding agent to be evaporated from the
part. Example descriptors are described in further detail below.
Based on the descriptors, the time required to debind the part may
then be determined (1060).
[0112] Example embodiments may be applied to parts of a range of
different geometries or compositions. For example, a "full-filled"
part may be composed of a solid material occupying a substantial
portion or all of its internal volume. In contrast, an "infilled"
part may comprise a shell encompassing an interior cellular
structure, where the cellular structure contains voids absent of
material. Example embodiments as applied to full-filled and
infilled parts are described, in turn, below.
Determination of Time to Debind a Full-Filled Part
[0113] Many debinding and sintering processes are diffusively
controlled, meaning that the process is a function of the diffusion
of a substance through a part. Solvent debinding of parts, in
particular, is a diffusively-controlled process for many parts.
Thermal debinding is also a diffusively-controlled process for many
binder-powder combinations. For such diffusively-controlled
scaling, the largest diffusion length in the part controls the
kinetics for the process to reach completion. The diffusion length
may be a maximum length to which a substance must be diffused into
or out from the part.
[0114] For small parts, the debinding process may instead be
interface-reaction limited, depending on the solvent and binder
system chosen. However, for large parts, the worst-case complexity
in scaling of debinding times may be given by a quadratic scaling
of debinding times with respect to diffusion length:
t.sub.debind.varies.L.sup.2 (1)
[0115] Thus, if a diffusion length of a 3D-printed geometry (i.e.,
the rate-limiting cross-section for the entire part) can be
determined, this length-scale can be used to determine the time
over which the debinding must take place to guarantee process
completion. That is, an asymptotically optimal bound on the scaling
of time for fully-filled parts in solvent debinding, heat transfer
in sintering, and mass transfer in thermal debinding is with the
square of the diffusion length of the part:
t.sub.debind=.THETA.(L.sup.2) (2)
[0116] For many cases, the diffusion length for an arbitrary
geometry can be calculated by a set of geometric analyses aimed at
defining the "effective thickness" of the part, which may be
determined based on the deepest point from any surface in the
geometry. The deepest point may be a descriptor of the part
identified as the point that is a maximum distance from any surface
of the representation. The effective thickness, in turn, may be a
linear function of the maximum distance. The deepest point and
effective thickness may be determined in a number of different
ways. In one example as described below with reference to FIGS.
11A-B, the largest sphere that fits inside the part may be
calculated. In a second example, described below with reference to
FIGS. 12-13, a set of shelling operations (e.g., uniformly
displacing the exterior of the geometry inward on its local normal
vectors and recalculating a new "shell," and performing the same
operation recursively) may be performed until the shelling can no
longer continue because the shell achieves zero volume. The largest
sphere that can fit inside a geometry may be equal to the deepest
shelled distance in the part in the limit as the shelling distance
at each step approaches zero. Thus, a debinding schedule for a part
may be predicted, wherein the diffusion length is calculated as the
largest sphere which can fit inside the outer envelope of the part,
and the timescale of the schedule can be scaled according to the
computed diffusion length of the part raised to a power. The power
may have an exponent greater than 1. For example, the power may
have an exponent of 2 as shown in equation 2 above, or may have an
exponent within a range approximate to 2, such as a range of
1.6-2.4.
[0117] FIGS. 11A-B illustrates a geometry of an example full-filled
part 1110 that is subject to a calculation of diffusion length in
one embodiment. FIG. 11A illustrates the part 1110 in three
dimensions, while FIG. 11B illustrates a two-dimensional
cross-section of the part 1110. To calculate the diffusion length
of the part 1110, a series of computations may first determine the
largest (or near-largest) sphere that can be entirely encompassed
by the interior volume of the part 1110. A first example sphere
1130 is too large to be encompassed as such. A second sphere 1132,
shown inside the part 1110, is small enough to be contained within
the part 1110, but is not the largest possible sphere that can fit
inside the part 1110. In contrast, the largest sphere 1134 occupies
the largest spherical volume within the part 1110.
[0118] The largest sphere 1134 may be determined in a number of
different ways. For example, a random sampling of points from the
part geometry may be produced. For each of the points, a distance
from the point to a closest surface may be calculated. The radius
of the largest sphere 1134 may then be determined as a maximum of
the calculated distances. Thus, the center of the sphere 1134 may
coincide with a point interior to the part 1110 that is a maximum
distance from any surface of the printed part 1110. As an
alternative to the random sampling of points, a uniform grid
sampling of points may be generated at the part geometry.
[0119] The center of the largest sphere 1134 may coincide with a
point interior to the part 1110 that is a maximum distance from any
surface of the part 1110. Thus, the center of the sphere 1134 may
indicate the deepest point of the part 1110, and the radius of the
sphere 1134 may indicate the diffusion length of the part 1110.
Accordingly, based on the geometry of the sphere 1134, the time to
debind the part 1110 can be determined as described above.
[0120] FIG. 12 is a flow diagram illustrating a process 1200 of
determining an effective thickness of a part in a further
embodiment. The process 1200 comprises a series of shelling
operations, generating a sequence of smaller shell geometries based
on the geometry of the outer surface of the part. The process 1200
is described below with reference to FIGS. 13A-B.
[0121] FIG. 13A illustrates a cross-section of a part 1310 having a
cubic geometry. With reference to FIG. 12, upon receipt of the
geometry of the part 1310 (1205), a representation of the outer
surface of the part 1310 may be normally displaced inward,
producing a first shell 1342 (1210). As shown, the first shell 1342
occupies an internal volume of the representation of the part 1310,
and has a geometry corresponding to a displacement of a surface
inward along its local normal vector relative to a geometry of the
part 1310. Optionally, intersecting or missing portions of a
preliminary shell produced by the above operation may be trimmed
from the shell (1215). If there is internal volume of the part that
remains inside the last-generated shell (1220), then the
last-generated shell may be analyzed to determine its contiguous
geometries (1225), and the shelling operation (1210) may be
repeated, producing a shell (e.g., second shell 1343) that has a
geometry corresponding to a displacement of a surface inward along
its local normal vector relative to a geometry of a preceding
reduced part (e.g., the first shell 1342).
[0122] The shelling operation (1210) may be repeated a number of
times until a last shell 1344, having either no interior volume or
an interior volume below a given threshold, is generated (1220).
From the location of the last shell 1344, an innermost distance
1350 (indicating the distance from the nearest surface of the part
1310 to the last shell 1344) may be measured. Thus, the location of
the last shell 1344 may indicate the deepest point of the part
1310, and the innermost distance 1350 may indicate the diffusion
length of the part 1310. Accordingly, the innermost distance 1350
can be reported (1230), and the time to debind the part 1310 can be
determined based on the innermost distance 1350.
[0123] FIG. 13B illustrates a cross-section of a part 1311 in a
further embodiment. In contrast to the cubic geometry of the part
1310, the part 1311 has a geometry that can create a shell with
discontiguous geometries during the process 1200. As shown, a first
shell 1352 exhibits a single, contiguous geometry. However, a
subsequent shell 1354 exhibits a discontiguous geometry, comprising
two shapes that are not connected. In such a case, the shelling
process (1210) may be repeated for both of the shapes until either
1) only one shape having an internal volume remains, and the
remaining shape is then further reduced until it has no internal
volume; or 2) both shapes are reduced to having no internal volume
in the same cycle. In the case of (2), the innermost distance may
be measured for either of the shapes of the last shell.
Determination of Time to Debind an Infilled Part
[0124] In the case of an infilled part, for a small-to-medium-sized
molecule (e.g., having molecular weights up to approximately
10,000), the diffusivity of the molecule in a solvent may be many
times higher than the effective diffusivity of the same molecule
inside a powdered body filled with high polymer (e.g., at least
40.times., and up to 1000.times.). For higher-molecular weight
molecules, diffusing in a solvent versus a powdered preform having
interstices filled with high-polymer, the difference in diffusivity
is even higher. Therefore, the open parts of the structure can be
considered approximately infinitely diffusive, and the topology of
the connections between the cells (i.e., the connectivity of the
diffusion "superhighways") determines the debinding times for open
cellular structures, and the sum of thicknesses of the walls
arranged in series correctly determines the debinding timescale for
closed-cell cellular structures.
[0125] FIGS. 14A-B illustrate a part 1410 in a further embodiment,
where FIG. 14A is a top-down cross-section, and FIG. 14B is a side
cross-section. The part 1410 includes an outer shell 1420
encompassing an infill having a cellular structure 1430. The shell
1420 includes side walls 1422, a ceiling 1424, and a floor 1426.
The cellular structure 1430 comprises a number of interconnected
cells (e.g., cell 1440), each cell containing a void. The part 1410
exhibits a honeycomb structure, which may comprise a
two-dimensional array of polygons that pack to fill a plane, the
material being axially symmetric in the third axis. A honeycomb
structure may comprise a cellular material wherein the voids extend
from one end of the material to the other along a single axis, and
the voids are largely parallel to one another along their major
axes. In the plane perpendicular to the axis of parallelism of the
voids, the cellular walls of the structure may have a substantially
uniform size and shape. A void of each honeycomb cell may be in
geometric contact with the shell. A honeycomb structure is not
specific to a hexagonal cell shape as exhibited by the part 1410,
and may instead comprise cells of a different shape in the x-y
plane, such as a square or rectangular shape.
[0126] For closed-cell infilled parts such as the part 1410, a time
required to debind the part can be determined by computing a length
of a longest cell along an axis of symmetry of the infill
structure. The time of exposure can then be scaled according to the
length of the longest cell raised to a power. Example embodiments,
described below, provide for such computation and scaling.
[0127] FIGS. 15A-B illustrate representations of a single cell of
an infilled part that may be implemented to model a debinding
process. FIG. 15A illustrates a resistor-capacitor (RC) circuit
1560 that may be referenced as a representation of an infilled part
during a debinding process. FIG. 15B illustrates a single cell 1570
of an infilled part, such as the cell 1440 of FIGS. 14A-B.
[0128] With reference to FIGS. 14A-B, the part 1410 is a
closed-cell infilled part that has interconnected porosity only in
the vertical direction (z-axis). In this type of structure, the
fast diffusion path is in the direction of the z-axis. An upper
bound for debinding and/or sintering times may be approximated by
presuming that no binder diffuses laterally out of the cells (i.e.,
to neighboring cells), and that the binder only diffuses out the of
top and bottom of the cells (i.e., through the floor 1426 and
ceiling 1424). In such a case, the debinding process of the part
1410 may be modeled as the discharging of a capacitor. As shown in
the circuit 1560 of FIG. 15A, a single cell 1440 may be represented
by a capacitor C.sub.cell, and the top and bottom layers of the
cell 1440 may be represented by resistors R.sub.floor,
R.sub.ceiling. The kinetics of the discharge of the capacitor
C.sub.cell scale as the characteristic time of the RC circuit 1560,
which may be expressed by the following relation:
R floor , ceiling .varies. t floor , ceiling area over which binder
flux occurs ( 3 ) ##EQU00001##
[0129] Here, t.sub.floor,ceiling refers to the thickness of the top
and bottom of the infill cell respectively. Depending on the
approximations made, the area over which binder flux occurs could
be considered the area of the cell 1570 or the area of the cell
1570 minus the area covered by toolpathing. Representing the cell
1570 with the dimensions as shown in FIG. 15B, the following
equation may be obtained:
area over which binder flux occurs=LW (4)
Alternatively:
area over which binder flux occurs=LW(1-.PHI.) (5)
Here, .PHI. is the areal fraction of the cell covered by infill.
The capacitance C.sub.cell representing the cell 1570 may be
expressed by the following relation:
C.sub.cell.varies.(volume of material to be discharged)=LWH.PHI.
(6)
[0130] By implementing the scaling analysis and modeling debinding
as discharging of an RC circuit as described above, the scaling of
a debind time for an infilled cell can be approximated. Applying
such a solution to the tallest infill cell of a part may provide a
rigorous upper bound on the time to debind the part.
[0131] FIG. 16 is a flow diagram of a process 1600 for determining
a tallest infill cell height of a part. With reference to FIGS.
15A-B, many of the parameters described above may be computed by
CAD slicing software. To determine the tallest infill cell height
from a received part geometry (1605), a vertical distance field in
the geometry may first be computed (1410). To do so, the process
1600 may compute the distance a ray projected vertically downward
from all upward facing surfaces (e.g., a surface with a component
of its surface normal lying along the infill direction axis, which
is typically the vertical direction) extends before the ray
intersects with another surface in the part. The process 1600 may
then identify the maximum of the vertical distance field over the
domain of the part geometry (1615). This maximum can be determined
by computing this ray projection distance in a sufficiently
tightly-spaced grid across the part geometry, and identifying the
maximum value of this computation. The thickness of the top and
bottom layers may be subtracted from this maximum value, and the
resulting value may be reported as the tallest infill cell height
(1620).
[0132] FIG. 17 is a diagram of an example internal structure of the
process controller 405. As described above, the controller 405 may
be implemented as a network server, workstation or off-site cloud
service. As shown in FIG. 10, the controller 405 is implemented as
a server in an example embodiment, where the printer 420, debinder
430, and furnace 440 are communicatively coupled to the process
controller 405 via a local communications interface 316.
Alternatively, the controller may communicate with the devices 410,
420, 430, 440 via a network 308 (e.g., a wired, wireless and/or
cloud network).
[0133] The controller 405 may contain a system bus 1002, being a
set of hardware lines used for data transfer among the components
of a computer or processing system. Attached to the system bus 1002
is a user I/O device interface 1004 for connecting the user
interface 410 and/or various input and output devices (e.g.,
keyboard, mouse, displays, printers, speakers, etc.) to the
controller 405. A network interface 1006 allows the computer to
connect to various other devices attached to the network 1008.
Memory 1010 provides volatile and non-volatile storage for
information such as computer software instructions used to
implement one or more of the embodiments of the present invention
described herein, for data generated internally and for data
received from sources external to the controller 405. A central
processor unit 1012 may also be attached to the system bus 1002,
and provides for the execution of computer instructions stored in
memory 1010. The controller 405 may also include support
electronics/logic 1014.
[0134] In one embodiment, the information stored in memory 310 may
comprise a computer program product, such that the memory 310 may
comprise a non-transitory computer-readable medium (e.g., a
removable storage medium such as one or more DVD-ROM's, CD-ROM's,
diskettes, tapes, etc.) that provides at least a portion of the
software instructions for the invention system. The computer
program product can be installed by any suitable software
installation procedure, as is well known in the art. In another
embodiment, at least a portion of the software instructions may
also be downloaded over a cable communication and/or wireless
connection.
[0135] The process controller 405 may also include a distributed
processing architecture, where processing elements at the printer
420, debinder 430 and/or furnace 440 perform portions of the
control operations. The user interface 410 may comprise one or a
plurality of devices in communication with the controller 405, such
as a laptop, workstation, mobile device (e.g., smartphone, tablet),
and/or or touchscreens integrated into the printer 420, debinder
430 and/or furnace 440.
[0136] It will be apparent that one or more embodiments described
herein may be implemented in many different forms of software and
hardware. Software code and/or specialized hardware used to
implement embodiments described herein is not limiting of the
embodiments of the invention described herein. Thus, the operation
and behavior of embodiments are described without reference to
specific software code and/or specialized hardware, it being
understood that one would be able to design software and/or
hardware to implement the embodiments based on the description
herein.
[0137] Further, certain embodiments of the example embodiments
described herein may be implemented as logic that performs one or
more functions. This logic may be hardware-based, software-based,
or a combination of hardware-based and software-based. Some or all
of the logic may be stored on one or more tangible, non-transitory,
computer-readable storage media and may include computer-executable
instructions that may be executed by a controller or processor. The
computer-executable instructions may include instructions that
implement one or more embodiments of the invention. The tangible,
non-transitory, computer-readable storage media may be volatile or
non-volatile and may include, for example, flash memories, dynamic
memories, removable disks, and non-removable disks.
[0138] While example embodiments have been particularly shown and
described, it will be understood by those skilled in the art that
various changes in form and details may be made therein without
departing from the scope of the embodiments encompassed by the
appended claims.
* * * * *