U.S. patent application number 17/443597 was filed with the patent office on 2021-11-18 for system and method for 3d printing with metal filament materials.
The applicant listed for this patent is Stratasys, Inc.. Invention is credited to S. Scott Crump, Dominic F. Mannella, Robert L. Zinniel.
Application Number | 20210354368 17/443597 |
Document ID | / |
Family ID | 1000005740400 |
Filed Date | 2021-11-18 |
United States Patent
Application |
20210354368 |
Kind Code |
A1 |
Zinniel; Robert L. ; et
al. |
November 18, 2021 |
SYSTEM AND METHOD FOR 3D PRINTING WITH METAL FILAMENT MATERIALS
Abstract
An additive manufacturing system configured to a 3D print using
a metal wire material includes a drive mechanism configured to feed
the metal feedstock into an inlet tube and a liquefier. The
liquefier has a chamber configured to accept the metal feedstock
from the inlet tube. The metal feed stock is heated in the chamber
such that a melt pool is formed in the chamber. The liquefier has
an extrusion tube in fluid communication with the chamber, the
extrusion tube having a length (L) and a diameter (D) wherein the
ratio of length to diameter (L/D) ranges from about 4:1 to about
20:1. The system has a platen with a surface configured to accept
melted material from the liquefier, wherein the platen and the
liquefier move in at least three dimensions relative to each other.
The system includes a regulated source of pressurized inert gas
flowably coupled to the liquefier and configured to place a
controlled positive pressure onto the melt pool sufficient to
overcome the resistance of the extrusion tube such that a part may
be formed by the extrusion of the liquidus metal along toolpaths
defined by the relative motion of the liquefier and the platen.
Inventors: |
Zinniel; Robert L.;
(Plymouth, MN) ; Crump; S. Scott; (Wayzata,
MN) ; Mannella; Dominic F.; (Minnetonka, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Stratasys, Inc. |
Eden Prairie |
MN |
US |
|
|
Family ID: |
1000005740400 |
Appl. No.: |
17/443597 |
Filed: |
July 27, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15994584 |
May 31, 2018 |
11104058 |
|
|
17443597 |
|
|
|
|
62513152 |
May 31, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2948/92571
20190201; B29C 64/40 20170801; B21C 33/02 20130101; B29C 64/20
20170801; B33Y 30/00 20141201; B29C 64/295 20170801; B29C
2948/92904 20190201; B29C 64/124 20170801; B29C 2948/9258 20190201;
B33Y 10/00 20141201; B29C 64/118 20170801; B29C 48/92 20190201 |
International
Class: |
B29C 64/118 20060101
B29C064/118; B29C 64/124 20060101 B29C064/124; B29C 64/40 20060101
B29C064/40; B33Y 30/00 20060101 B33Y030/00; B29C 64/295 20060101
B29C064/295; B21C 33/02 20060101 B21C033/02; B33Y 10/00 20060101
B33Y010/00; B29C 48/92 20060101 B29C048/92; B29C 64/20 20060101
B29C064/20 |
Claims
1-20. (canceled)
21. An additive manufacturing system configured to 3D print a part
from a metal material, the system comprising: an inlet tube for
conveying a metal feedstock in wire form; a liquefier comprising: a
chamber configured to accept the metal feedstock from the inlet
tube at an upstream end thereof and to accumulate melted metal
feedstock as a melt pool in a downstream end thereof; an extrusion
tube in fluid communication with the chamber, the extrusion tube
having a length (L) and a diameter (D) and terminating in an
extrusion tip, wherein the ratio of length to diameter (L/D) ranges
from about 4:1 to about 20:1, and wherein the L/D ratio is selected
to resist a flow of liquidus metal from the melt pool through the
extrusion tube at atmospheric pressure; and a heater configured to
impart heat into the chamber and the extrusion tube, and wherein
the heat causes the metal feedstock in the chamber to melt and form
the melt pool; a drive mechanism configured to feed the metal
feedstock through the inlet tube and into the liquefier at a
controlled rate; a platen having a surface configured to accept
melted material from the liquefier, wherein the platen and the
liquefier move in at least three dimensions relative to each other;
and a regulated source of pressurized inert gas flowably coupled to
the liquefier and configured to place a controlled positive
pressure onto the melt pool sufficient to overcome the resistance
of the extrusion tube such that liquidus metal will flow from
chamber through the extrusion tip and onto the platen in a
continuous extrusion stream such that a part may be formed by the
extrusion of the liquidus metal along toolpaths defined by the
relative motion of the liquefier and the platen and without use of
further flow control mechanisms.
22. The additive manufacturing system of claim 21, wherein the
inlet tube is a ceramic tube.
23. The additive manufacturing system of claim 21 and further
comprising a cooling unit at least partially positioned about the
inlet tube, wherein the cooling unit is configured to remove heat
from the metal feedstock before it enters the liquefier.
24. The additive manufacturing system of claim 21, and further
comprising a source of cryogenic gas wherein the cryogenic gas
directly contacts the metal wire feedstock upstream of the
liquefier.
25. The additive manufacturing system of claim 23, wherein the
cooling unit comprises a jacket with an internal chamber with an
inlet and an outlet such that a cooling fluid can flow through the
jacket.
26. The additive manufacturing system of claim 21, wherein L/D
ranges from about 4:1 to 10:1
27. The additive manufacturing system of claim 21, wherein the
extrusion tip is replaceable.
28. The additive manufacturing system of claim 21, wherein the
liquefier further comprises a purge port in fluid communication
with the chamber, wherein the purge port is configured to be opened
to remove slag buildup and closed during extrusion.
29. The additive manufacturing system of claim 21 and further
comprising: a first electrode attached to the liquefier; a second
electrode attach to the platen; and an electric source connected to
both the first and second electrode wherein the electric source is
directed through either the first or second electrode and passed to
the other electrode through the liquidus metal between the first
and second electrodes wherein a change in voltage changes a
viscosity of the extruded metal.
30. The additive manufacturing system of claim 21, wherein D ranges
from about 0.012 inches to about 0.020 inches and L ranges from
about 0.048 inches to about 0.4 inches.
31. The additive manufacturing system of claim 21, wherein the
controlled positive pressure ranges from about 2-20 psig.
32. The additive manufacturing system of claim 21, wherein the
controlled positive pressure ranges from about 5-15 psig.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] The present application claims the benefit of U.S.
Provisional Patent Application Ser. No. 62/513,152 entitled SYSTEM
AND METHOD FOR BUILDING THREE-DIMENSIONAL OBJECTS WITH METALS AND
METAL ALLOYS that was filed on May 31, 2017, the contents of which
is incorporated by reference in its entirety.
BACKGROUND
[0002] The present disclosure relates to systems and methods for
building three-dimensional (3D) metal parts in additive
manufacturing systems. In particular, the present disclosure
relates to extrusion-based additive manufacturing systems for
printing 3D parts using metal materials.
[0003] Additive manufacturing, also called 3D printing, is
generally a process in which a three-dimensional (3D) part is built
by adding material to form the part rather than subtracting
material as in traditional machining. Using one or more additive
manufacturing techniques, a three-dimensional solid object of
virtually any shape can be printed from a digital model of the
object by an additive manufacturing system, commonly referred to as
a 3D printer. A typical additive manufacturing work flow includes
slicing a three-dimensional computer model into thin cross sections
defining a series of layers, translating the result into
two-dimensional position data, and feeding the data to a 3D printer
which manufactures a three-dimensional structure in an additive
build style. Additive manufacturing entails many different
approaches to the method of fabrication, including material
extrusion, jetting, laser sintering, powder/binder jetting,
electron-beam melting, electrophotographic imaging, and
stereolithographic processes.
[0004] In a typical extrusion-based additive manufacturing system
(e.g., fused deposition modeling systems developed by Stratasys,
Inc., Eden Prairie, Minn.), a 3D object may be printed from a
digital representation of the printed part by extruding a viscous,
flowable thermoplastic or filled thermoplastic material from a
print head along toolpaths at a controlled extrusion rate. The
extruded continuous flow of material is deposited as a sequence of
roads onto a substrate, where it fuses to previously deposited
material and solidifies upon a drop in temperature. The print head
includes a liquefier which receives a supply of the thermoplastic
material in the form of a flexible filament, and a nozzle tip for
dispensing molten material. A filament drive mechanism engages the
filament such as with a drive wheel and a bearing surface, or pair
of toothed-wheels, and feeds the filament into the liquefier where
the filament is melted. The unmelted portion of the filament
essentially fills the diameter of the liquefier tube, providing a
plug-flow type pumping action to extrude the molten filament
material further downstream in the liquefier, from the tip to print
a part, to form a continuous flow or toolpath of resin material.
The extrusion rate is unthrottled and based only on the feed rate
of filament into the liquefier, and the filament is advanced at a
feed rate calculated to achieve a targeted extrusion rate, such as
is disclosed in Comb U.S. Pat. No. 6,547,995. The printing
operation is thus dependent on a predictable and controlled
advancement of filament into the liquefier at a feed rate that will
extrude material at the targeted rate; because the viscosity of the
melted resin is high enough, it does not drip out of the extruder
tip even though the exit is unrestricted with a valve or other
throttling means.
[0005] Extrusion of metals and metal alloys poses challenges for
traditional extrusion-based additive manufacturing
equipment/techniques. Due to the low viscosity of molten metals as
compared to molten thermoplastics, the flow of metal from a print
head exit is not readily controllable solely by feeding of
filament, as is done in a typical thermoplastic extrusion-based 3D
printer. Furthermore, heating a metal above its liquidus
temperature may cause dendrite formation in the print head,
resulting in clogging of the liquefier and nozzle tip. Prior art
methods of metal extrusion 3D printing include utilizing a freeze
valve to start and stop extrusion, such as is disclosed in Crump et
al. U.S. Pat. Nos. 7,942,987 and 9,027,378; and employing a
pressure oscillator to jet droplets of liquidus metal from a
liquefier, such as is disclosed in US2017/0087632. Thus, there is
an ongoing need for systems and methods for building 3D objects
from metals and metal alloys with extrusion-based additive
manufacturing techniques.
SUMMARY
[0006] The present disclosure is directed to an additive
manufacturing system configured to 3D print a part from a metal
material. The system includes an inlet tube for conveying a metal
feedstock in wire form to a liquefier. The liquefier has a chamber
configured to accept the metal feedstock from the inlet tube at an
upstream end thereof and to accumulate melted metal feedstock as a
melt pool in a downstream end thereof and an extrusion tube in
fluid communication with the chamber. The extrusion tube has a
length (L) and a diameter (D) and terminating in an extrusion tip,
wherein the ratio of length to diameter (L/D) ranges from about 4:1
to about 20:1, and wherein the L/D ratio is selected to resist a
flow of liquidus metal from the melt pool through the extrusion
tube at atmospheric pressure. A heater is configured to impart heat
into the chamber and the extrusion tube, and wherein the heat
causes the metal feedstock in the chamber to melt and form the melt
pool. The system includes a drive mechanism configured to feed the
metal feedstock through the inlet tube and into the liquefier at a
controlled rate and a platen having a surface configured to accept
melted material from the liquefier, wherein the platen and the
liquefier move in at least three dimensions relative to each other.
The system includes a regulated source of pressurized inert gas
flowably coupled to the liquefier and configured to place a
controlled positive pressure onto the melt pool. The positive
pressure is sufficient to overcome the resistance of the extrusion
tube such that liquidus metal will flow from chamber through the
extrusion tip and onto the platen in a continuous extrusion stream
such that a part may be formed by the extrusion of the liquidus
metal along toolpaths defined by the relative motion of the
liquefier and the platen and without use of further flow control
mechanisms.
[0007] Another aspect of the present disclosure includes method of
printing a 3D part from a metal filament material utilizing an
additive manufacturing system. The method includes providing a
build platen and a liquefier having a chamber flowably coupled to
an extrusion tube terminating in an extrusion tip, the extrusion
tube characterized by an L/D ratio ranging from about 4:1 to about
20:1, where L is its land length and D is its diameter. The method
includes feeding a metal wire along a material feed path from a
supply to the liquefier and heating the metal wire in the liquefier
to form a melt pool of molten metal in the chamber. The molten
metal has a viscosity, and wherein a resistance or back pressure
created by the extrusion tube contains the melt pool in the
chamber. The method includes pressurizing the chamber with an inert
gas to a controlled positive pressure sufficient to force the
molten metal material from the melt pool through the extrusion tube
by overcoming the resistance created by the extrusion tube and
moving the build platen and the liquefier relative to each other
along toolpaths generated from a digital model while maintaining
the positive pressure in the chamber and feeding the metal wire to
the liquefier, such that liquidus metal will flow through the
extrusion tip and onto the platen in a continuous extrusion stream
such that a part may be formed by the extrusion of the liquidus
metal along the toolpaths.
Definitions
[0008] Unless otherwise specified, the following terms as used
herein have the meanings provided below:
[0009] The terms "preferred", "preferably", "example" and
"exemplary" refer to embodiments of the invention that may afford
certain benefits, under certain circumstances. However, other
embodiments may also be preferred or exemplary, under the same or
other circumstances. Furthermore, the recitation of one or more
preferred or exemplary embodiments does not imply that other
embodiments are not useful and is not intended to exclude other
embodiments from the scope of the present disclosure.
[0010] Directional orientations such as "above", "below", "top",
"bottom", and the like are made with reference to a layer-printing
direction of a part. In the embodiments shown below, the
layer-printing direction is the upward direction along the vertical
z-axis. In these embodiments, the terms "above", "below", "top",
"bottom", and the like are based on the vertical z-axis. However,
in embodiments in which the layers of parts are printed along a
different axis, such as along a horizontal x-axis or y-axis, the
terms "above", "below", "top", "bottom", and the like are relative
to the given axis.
[0011] The term "providing", such as for "providing a material",
when recited in the claims, is not intended to require any
particular delivery or receipt of the provided item. Rather, the
term "providing" is merely used to recite items that will be
referred to in subsequent elements of the claim(s), for purposes of
clarity and ease of readability.
[0012] The term "metal", "metals" or "metal materials", as used
herein, are intended to include materials that are pure elemental
metals and/or metal alloy blends.
[0013] Unless otherwise specified, temperatures referred to herein
are based on atmospheric pressure (i.e. one atmosphere).
[0014] The terms "about" and "substantially" are used herein with
respect to measurable values and ranges due to expected variations
known to those skilled in the art (e.g., limitations and
variabilities in measurements).
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a front view of an additive manufacturing system
for building 3D objects from metal filament materials.
[0016] FIG. 2 is a diagrammatic illustration of a print head
configured for extruding liquefied low-temperature metal wire, for
example, bismuth-based wire, which may be employed with the
additive manufacturing system of FIG. 1.
[0017] FIG. 3 is a diagrammatic illustration of a print head for
building 3D objects using metal filament materials which may be
employed with the additive manufacturing system of FIG. 1, and
including a cryogenic based wire cooling system for pre-cooling the
metal wire.
[0018] FIG. 4 is a diagrammatic illustration of a pressurized
liquefier assembly of the present invention for use in providing a
controlled extrusion of liquefied metal.
[0019] FIG. 5 is a diagrammatic illustration of a print head having
a ceramic tube and a metal nozzle base and a heat transfer module
for use in melting and pre-cooling the in-coming metal feed wire
which may be employed with the additive manufacturing system of
FIG. 1.
[0020] FIG. 6 is a diagrammatic illustration of a liquefier
assembly including thermo-electric heating material and a
thermo-electric controller for use in controlling the flow and
viscosity of extruded liquefied metal.
[0021] FIGS. 7 and 8 are diagrammatic illustrations of embodiments
of liquefier inductive heat systems for melting metal wire for
extrusion.
[0022] FIG. 9 is a diagrammatic illustration of a ceramic inlet
tube and a metal base with a removable liquefier assembly, with
retaining and sealing mechanisms.
[0023] FIG. 10 is a diagrammatic illustration of a liquefier
assembly and a cartridge of removable extrusion tips.
[0024] FIG. 11 is a diagrammatic illustration of a portion of a
liquefier assembly of the present invention including a titanium
insert.
[0025] FIG. 12 is a diagrammatic illustration of a liquefier
assembly embodiment which includes a purge port for purging
solidified metal from the liquefier assembly.
[0026] FIG. 13 is a diagrammatic illustration of a liquefier
assembly such as shown in FIG. 12, and also including a solids
purge mechanism.
[0027] FIG. 14 is a diagrammatic illustration of a screen-like
metal pre-coated substrate/build platform onto which a metal part
can be printed.
[0028] FIG. 15 is a diagrammatic illustration of another build
platform onto which a metal part can be printed.
[0029] FIG. 16 is a diagrammatic illustration of a liquefier
assembly printing a metal part in accordance with the present
invention and showing an optimization feature.
[0030] FIG. 17 is a diagrammatic illustration of a liquefier
assembly in accordance with an alternate embodiment.
DETAILED DESCRIPTION
[0031] FIG. 1 is a front perspective view of system 10, which is an
exemplary additive manufacturing system for 3D printing of metal
parts from metal filament materials. System 10 is provided for
illustrative purposes, and disclosed embodiments are not limited to
use with system 10. FIG. 1 illustrates a 3D printer 10 that has a
substantially horizontal print plane where the part being printed
is indexed in a substantially vertical direction as the part is
printed by material extrusion in a layer-by-layer manner using at
least one print head. For example, in FIG. 1, 3D printer 10
includes two print heads 18A, 18B and two consumable assemblies 12.
Consumable assembly 12 supplying print head 18A retains a supply of
a consumable metal or metal alloy wire for printing with system 10,
and consumable assembly 12 supplying print head 18B typically
retains a supply of support material but may alternatively retain a
secondary part material. While two consumable assemblies and two
print heads are shown, only one consumable assembly and print head
are necessary.
[0032] Print head 18A is an exemplary print head for melting and
extruding filaments to print metal parts. As shown in FIG. 2, an
exemplary embodiment of print head 18A is an easily loadable,
removable and replaceable device comprising a housing that retains
a liquefier assembly 20 having an extrusion tip 14. Print head 18A
is configured to receive a low-temperature metal consumable
filament material, melt the material in liquefier assembly 20 to
produce a molten material, and deposit the molten material from an
extrusion tip 14 of liquefier assembly 20, in a similar manner as
is done in plastic extrusion. In the shown exemplary embodiment,
the filament material used is bismuth or bismuth-based wire such as
a bismuth-telluride compound, and liquefier assembly 20 melts the
bismuth, bismuth alloy or bismuth-based compound for
extrusion-based metal printing. With metal materials having
relatively low-temperature melting points, aspects of conventional
3D printing equipment can be utilized, with modification. Higher
melting temperature metals can be used as well, with additional
hardware accommodations. In alternate embodiments discussed below,
other metals are utilized, such as, aluminum, aluminum compounds
and/or aluminum alloys.
[0033] Guide tube or feed tube 16 (also shown in FIG. 2)
interconnects each consumable assembly 12 and the respective print
head 18A or 18B, where a drive mechanism 118 (as shown in FIG. 3)
of print head 18A or 18B (or of 3D printer 10) draws consumable
filament from consumable assembly 12, through guide tube or feed
tube 16, to liquefier assembly 20 of print head 18A or 18B. Guide
or feed tube 16 may be a component of 3D printer 10, or a
sub-component of consumable assemblies 12. During a build
operation, the continuous consumable filament is driven into print
head 18A or 18B are heated and melted in the liquefier assembly 20.
The continuous bead of molten material is extruded through
extrusion tip 14 in a layer wise pattern to produce printed
parts.
[0034] In some embodiments, such as using the exemplary print head
of FIG. 2, the wire is typically driven into the liquefier at a
rate equivalent to the desired exit or deposition rate where the
feed rate is directly proportional to the deposition rate. In other
embodiments, a melt pool of liquid or molten metal wire is formed
within the liquefier and using pressure-control techniques as
described below with reference to FIGS. 3 and 4, the liquefied
metal is selectively extruded through the extrusion tip at a rate
independent of the feed rate, but the extrusion is still
coordinated the filament feed rate.
[0035] Exemplary 3D printer 10 is an additive manufacturing system
for 3D printing parts or models using a layer-based, additive
manufacturing technique, similar to fused deposition modeling
systems sold by Stratasys, Inc., Eden Prairie, Minn. under the
trademark "FDM," but with the capability for printing metals
[0036] As shown, 3D printer 10 includes system casing 26, build
chamber 28, platen 30, platen gantry 32, head carriage 34, and head
gantry 36. System casing 26 is a structural component of system 10
and may include multiple structural sub-components such as support
frames, housing walls, and the like. In some embodiments, system
casing 26 may include container bays configured to receive
consumable assemblies 12. In alternative embodiments, the container
bays may be omitted to reduce the overall footprint of 3D printer
10. In these embodiments, consumable assembly 12 may stand
proximate to system casing 26, while providing sufficient ranges of
movement for guide or feed tubes 16 and print heads 18 that are
shown schematically in FIG. 1.
[0037] Build chamber 28 may be an enclosed, inerted environment
that contains platen 30 for 3D printing part 22 and support
structure 24. Build chamber 28 may be heated (e.g., with
circulating heated air) to reduce the rate at which the part and
support materials solidify after being extruded and deposited
(e.g., to reduce distortions and curling). In alternative
embodiments, build chamber 28 may be omitted and/or replaced with
different types of build environments. For example, part 22 and
optional support structure 24 may be built in a build environment
that is open to ambient conditions or may be enclosed with
alternative structures (e.g., flexible curtains). Alternatively,
the liquefier assembly may be locally inerted in an otherwise
ambient build chamber. Platen 30 is a platform on which part 22 and
support structure 24 are printed and is supported by platen gantry
32. In the illustrated embodiment, platen gantry 32 is a gantry
assembly configured to move platen 30 along (or substantially
along) the vertical z-axis.
[0038] In some alternative embodiments, platen 30 can be heated or
otherwise temperature controlled, thus conducting heat up through
the printed part, to influence metal resolidification and crystal
structure. As the metals/alloys (e.g., aluminum) used are heat
conductive, heating platen 30 can be effective at controlling the
solidification rate of the parts and/or support materials. Using a
heated platen, the build environment (e.g., build chamber 28) may
also be heated, but likely to a lesser degree. Heating platen 30
aids in heat conduction of the metal material, without requiring a
build environment furnace to bring the environment to such a high
temperature. For example, in the case of aluminum, aluminum-based
alloys and/or aluminum-based compounds, gasses in the build
envelope environment could be heated and circulated at about
300.degree. C. while the platen is heated to about 600.degree.
C.
[0039] Head carriage 34 is a unit configured to receive and retain
one or both print heads 18A and 18B and is supported by head gantry
36. Head carriage 34 preferably retains each print head 18A and 18B
in a manner that prevents or restricts movement of the print head
18 relative to head carriage 34 so that extrusion tip 14 remains in
the x-y build plane but allows extrusion tip 14 of the print head
18 to be controllably moved out of the x-y build plane through
movement of at least a portion of the head carriage 34 relative the
x-y build plane (e.g., servoed, toggled, or otherwise switched in a
pivoting manner).
[0040] In the shown embodiment, head gantry 36 is a mechanism
configured to move head carriage 34 (and the retained print heads
18A and 18B) in (or substantially in) a horizontal x-y plane above
platen 30. Examples of suitable gantry assemblies for head gantry
36 include those disclosed in Swanson et al., U.S. Pat. No.
6,722,872; and Comb et al., U.S. Pat. No. 9,108,360, where head
gantry 36 may also support deformable baffles (not shown) that
define a ceiling for build chamber 28. Head gantry 36 may utilize
any suitable bridge-type gantry or robotic mechanism for moving
head carriage 34 (and the retained print heads 18), such as with
one or more motors (e.g., stepper motors and encoded DC motors),
gears, pulleys, belts, screws, robotic arms, and the like.
[0041] In an alternative embodiment, platen 30 may be configured to
move in the horizontal x-y plan, and head carriage 34 (and print
heads 18A and 18B) may be configured to move along the z-axis.
Other similar arrangements may also be used such that one or both
of platen 30 and print heads 18A and 18B are moveable relative to
each other.
[0042] 3D printer 10 also includes control system 38, which may
include one or more control circuits (e.g., controller 40) and/or
one or more host computers (e.g., computer 42) configured to
monitor and operate the components of 3D printer 10. For example,
one or more of the control functions performed by control system
38, such as performing move compiler functions, can be implemented
in hardware, software, firmware, and the like, or a combination
thereof; and may include computer-based hardware, such as data
storage devices, processors, memory modules, and the like, which
may be external and/or internal to 3D printer 10.
[0043] Control system 38 may communicate over communication line 44
with print heads 18A and 18B, with environmental controls for
chamber 28, head carriage 34, motors for platen gantry 32 and head
gantry 36, and various sensors, calibration devices, display
devices, and/or user input devices. In some embodiments, control
system 38 may also communicate with one or more of platen 30,
platen gantry 32, head gantry 36, and any other suitable component
of 3D printer 10, some of which are described below in greater
detail. While illustrated as a single signal line, communication
line 44 may include one or more electrical, optical, and/or
wireless signal lines, which may be external and/or internal to 3D
printer 10, allowing control system 38 to communicate with various
components of 3D printer 10.
[0044] During operation, control system 38 may direct platen gantry
32 to move platen 30 to a predetermined height within build chamber
28. Control system 38 may then direct head gantry 36 to move head
carriage 34 (and the retained print heads 18A and 18B) around in
the x-y build plane above build chamber 28. Control system 38 may
also direct print heads 18A and 18B to selectively draw successive
segments of the consumable wire or filament from consumable
assemblies 12 and through guide or feed tubes 16, respectively.
[0045] While FIG. 1 illustrates a 3D printer 10 where a build plane
is in a substantially horizontal x-y plane and the platen 30 is
moved in a z direction substantially normal to the substantially
horizontal x-y build plane, the present disclosure is not limited
to a 3D printer 10 as illustrated in FIG. 1. For instance, the
print head can be stationary and the platen can move in the x, y
and z directions. However, the present disclosure is not limited to
layer-based additive manufacturing. The part can also be printed
using 3D tool paths, such as by replacing head carriage with a
robot arm and connecting the print head to a robot end
effector.
[0046] Referring now to FIG. 3, shown are components of an
exemplary print head 200A metal or metal-alloy wire 124 is shown
being fed, from a consumable spool or other source (not shown), by
a drive mechanism 118 having a drive roller 132 and an idler roller
134. The narrow metal wire 124 is fed into a liquefier assembly 220
having a chamber 235, where it is melted by heaters or heat sources
222 under the control of controller 224 and formed into a melt pool
236 of liquidus metal wire. Melt pool 236 forms within chamber 235
in fluid communication with an extrusion tube 270 of liquefier 220,
so that it can be controllably extruded through extrusion tip 240
of extrusion tube 270. In the shown embodiment, the wire is melted
in chamber 235, but alternative embodiments are contemplated where
the wire could be melted in the liquefier upstream of chamber 235
to form a reservoir of molten metal. An inert gas head pressure is
placed on the chamber 235 using pressure control 290 (discussed
further with respect to FIG. 4), to create a force for deposition
through extrusion tip 240 or extrusion tube 270 onto a build platen
or surface as a continuous bead of molten metal. Using
pressure-control techniques as described further below, the
liquefied metal is selectively extruded through the extrusion tip
at a rate independent of the feed rate, but in coordination with
the feeding of wire filament. Wire 124 can be a variety of metal
types. While the present disclosure references the use of an
aluminum filament material, other materials such as bismuth,
stainless steel or other commercially valuable materials such as
titanium are also contemplated. In one embodiment, the metal wire
124 diameter is smaller than that of typical thermoplastic filament
types, which is commonly 0.07''. In the example of aluminum, a
diameter of 0.032'' was used. In the case of bismuth, 0.051'' was
used. However, these diameters are exemplary in nature and are
non-limiting to the scope of the present disclosure.
[0047] The extrusion tube 270 is defined based on its land length
and an L/D ratio. The land length is nominally the length of the
extrusion tube 270 between a location where the flow channel is
constricted after the melt pool, and an outlet of the extrusion tip
240. The extrusion tube 270 can be characterized by the ratio of
its land length (L) to diameter D, where a higher ratio of L/D
creates a higher back pressure and flow resistance, and therefore a
higher inert gas head pressure is required to force liquidus metal
through the extrusion tube 270 to create a continuous extrusion
flow.
[0048] In order to prevent excessive heat from transferring up from
liquefier assembly 220 and prematurely melting wire before it
enters the liquefier, the wire 124 is fed through a ceramic inlet
tube 230 prior to entering the heated liquefier zone. Optionally,
the wire 124 can also be cryogenically pre-cooled prior to entering
ceramic tube 230. Selecting a narrow diameter of wire will also
minimize and reduce heat buildup in the inlet tube so as not to
melt prior to entering the liquefier zone. As shown, a tank 241 of
liquid nitrogen or other cooling fluid, can be optionally connected
to a cooling chamber 242 by a conduit 244 and a pair of pressure
valves 246 and 248. Controlling pressure valves 246 and 248, liquid
nitrogen is output from tank 240 into conduit 244. Wire 124 passes
through cooling chamber 242 and directly contacts the super cooled
gas to cool the wire 124 prior to entering ceramic tube 230. This
super cooling of wire 124 counteracts heat transfer from the
liquefied metal within chamber 235 in an upward direction to the
wire within ceramic tube 230.
[0049] Referring now to FIG. 4, shown is one example embodiment of
a method of using positive pressure to control the flow of
liquefied metal from chamber 235 of liquefier assembly 220 through
extrusion tube 270 and out of extrusion tip 240. As shown in FIG.
4, a source 280 of regulated inert gas, such as a regulated gas
tank, can be connected by a tube or conduit 285 to liquefier
assembly 220. In exemplary embodiments, the gas provided by
pressure source 280 is an inert gas such as argon or nitrogen.
While pressure source 280 is shown connected to liquefier assembly
220 directly by tube 285, it should be understood that such
connection can also be through ceramic tube 230 and other conduits
or pathways which are not shown in FIG. 4 for simplified
illustrative purposes.
[0050] Wire 124 is shown in FIG. 4 piercing or entering tube or
conduit 285 carrying a pressurized gas from source 280. From the
point of entry into tube or conduit 285, wire 124 is fed interior
to tube 285 and any other conduits or pathways into liquefier
assembly 220 for melting by a heat source (not shown in FIG. 4),
such as described above. In some embodiments, a seal such as an
O-ring 287 can be used to seal the point of entry of wire 124 into
tube or conduit 285. A controller 290 is used to control the
pressure of gas flowing into tube or conduit 285 from source 280
creates pressure within tube 285 and liquefier assembly 220 and
provides an assisting force to push liquid metal within chamber 235
into extrusion tube 270 and out of extrusion tip 240. In typical
thermoplastic extrusion 3D printing, the high viscous fluid does
not require a highly constrained flow path and many suitable
channel dimensions are possible, to provide adequate flow through
the extrusion tip. However, molten metal it is not viscous in
comparison to thermoplastics, and the L/D ratio becomes much more
important to controlling flow. In a typical thermoplastic liquefier
operation, the feeding of filament determines the overall flow rate
through the print head, and there is no pressure assist on the
liquefier to assist with pumping. With molten metals, the overall
printing rate is determined by the filament feed rate, but the melt
reservoir 235 holds a small pool of material. The amount of
material that exits liquefier assembly 220 is controlled by the
rate of drainage of the relatively non-viscous material, but is
also increased by controlling the pressure in the chamber 235. The
extrusion of a liquefied metal from extrusion tip 240 can be
controlled at a desired rate to deposit the liquefied metal
material along toolpaths without the need for a control valve or
other flow restriction at the extrusion tip/exit. Prior art
solutions for non-viscous molten metal flow have required valving,
freeze valves, pressurized droplet creation, or pumping to limit
the flow to a desirable rate. This approach removes the need to
control or restrict the flow rate.
[0051] By selecting or designing the liquefier assembly 220 to
control the land length L of extrusion tube 270 relative to its
diameter D between chamber 235 containing the liquefied metal and
extrusion tip 240, in conjunction with controlling other forces
such as provided by pressure source 280, improved control of the
extrusion of the liquidus metal can be achieved. Overall, the feed
rate of the exiting metal bead is influenced by the height of the
melt pool 236 of liquid metal, the inert gas head pressure on the
molten pool within the liquefier, and the balance of the surface
tension of a particular molten metal, in conjunction with the
selection of the land length L and diameter D of the extrusion tube
270. The longer the length, the more controllable the flow.
[0052] The level of inert gas head pressure (i.e., pressure in the
chamber 235) that is needed to create a constant flow of liquidus
metal out of the extrusion tip 240 can be estimated by calculating
the back pressure exerted from the extrusion tube 270 and the
extrusion tip 240 as a sum of the Laplace pressure at the tip and
the pressure drop through the tube. Laplace pressure is the back
pressure from the suspended droplet below a nozzle tip that tends
to resist flow (until the hemispherical surface is distorted by
contact with the part, or the droplet extends beyond a hemisphere).
For a hemispherical surface of radius r and an alloy with a surface
tension .gamma., the back pressure resisting the alloy is:
2r/.gamma..
For example, for an aluminum droplet having a surface tension of
0.86 newtons/meter and a 30 mil diameter tip face, the back
pressure is 0.65 psi. The pressure rises as the tip size is
reduced.
[0053] The pressure drop P for a flow Q through a cylindrical
channel of radius R and length L (absent contaminants in the alloy)
is from Poiseuille:
P = 32 .times. Q .times. .times. .eta. .times. .times. L .pi.
.times. .times. R 4 ##EQU00001##
[0054] Where .eta. is the alloy viscosity, which for many of the
discussed alloys is roughly 0.5 centipoise. A 10 mil diameter
extrusion tube that is 50 mils long and having a volumetric flow
rate of 500 micro-cubic inches per second (mic/s) will have a
viscous pressure drop of 0.09 psi along its land length.
[0055] In metal extrusion, when the pendant droplet contacts the
part under construction, several things happen at once. First,
surface tension no longer restrains the metal flow; in fact, the
opposite happens. As long as the extrusion has a wetting contact
angle with the part (such as is illustrated in FIG. 16), the
liquidus metal will attempt to wick out over the surface of the
part. Further, the (presumed solid) part build surface will quickly
conduct heat from the molten metal, generally forming a peritectic
slush between the part surface and the extrusion tip that does
constrain the alloy flow. Additionally, the thermal sink of the
part build surface puts a thermal load on the extrusion tip, which
for a thermoelectrically controlled liquefier (e.g., temperature
sensed at tip with a thermocouple or other mechanism and the
heating energy is correspondingly controlled) prompts the
controller to pour more energy into the tip, which in turn starts
melting back the part build surface.
[0056] For a given length and diameter of the liquefier tube, the
amount of flow restriction experienced for each particular
viscosity of molten metal will vary. Likewise, the amount of back
pressure on the liquidus metal melt pool 236 can be controlled by
adjusting the land length of the extrusion tube 270. A typical
range of the L/D ratio is between about 4:1 and about 20:1. Another
typical range of the L/D ratio is between about 4:1 and about 10:1.
For a selected L/D ration in this range, a continuous flow
extrusion of liquidus metal through a print head can be controlled
by applying a gas head pressure, and removing the pressure in
combination with withdrawing the supply of filament to stop the
flow, without employing additional mechanical means of flow
restriction (such as a control valve or freeze valve). In a
preferred embodiment, the extrusion tube diameter D was selected to
be 0.012'', with an extrusion tube length of 4 times that, or
0.048''. In another embodiment, an extrusion tube diameter was
selected at 0.016'', and 0.020'' in another device. As a larger
diameter is selected, melt can begin to leak or drip out of the tip
slightly, referred to as die drool. At L/D of 4:1, more drool will
occur than at L/D of 10:1 or 20:1, but as the ratio increases, the
more pressure must be applied to force the molten metal through the
extrusion tube pathway outlet.
[0057] Example One: An aluminum alloy welding wire Alloy 3043 was
selected for use, suitable for a filament feedstock for 3D
printing, was purchased from AlcoTec Wire Corporation of Traverse
City, Mich. The wire had a diameter of 0.035'' and a melting
temperature of 1065-1170 F. An extrusion tube was selected with a
diameter of 0.012'' and length of 0.048''. The melt chamber was
heated to 1110.degree. F. to bring it to an optimal viscosity for
deposition. Nitrogen at a pressure of 2-5 psig was applied to the
liquefier to create flow, and to vary deposition amount/speed.
[0058] Referring next to FIG. 5, shown are certain exemplary
components of an embodiment in which cooling is provided to limit
heat transfer through metal or metal-alloy wire 124 upstream of
liquefier assembly 220 and chamber 235. As shown in FIG. 5, in some
exemplary embodiments, a heat transfer module or unit 300 is
included and is jacketed about at least a portion of ceramic tube
or conduit 230 through which wire 124 is fed instead of having the
cooling medium directly contact the metal wire. The heat transfer
unit 300 includes an inlet 302 and an outlet 304 coupled to a
coolant pump/reservoir 306. The coolant from pump/reservoir 306 is
pumped into inlet 302, through an interior chamber surrounding
ceramic tube 230, and back out of outlet 304. By circulating the
coolant into heat transfer unit 300, heat energy conducted by wire
124 and by ceramic tube 230 is transferred to the coolant, thereby
preventing the temperature within ceramic tube 230 from increasing
to the point that wire 124 begins to melt prior to entering
liquefier assembly 220. While coolant pump/reservoir 306 is shown
as a single unit, those who are skilled in the art will understand
that coolant pump/reservoir 306 can include a separate reservoir or
tank of coolant, and electric or other type of pump for pumping the
coolant, and other mechanisms for dissipating the heat transferred
to the coolant. The coolant can be any suitable medium including,
but not limited to, liquid nitrogen, dry ice, cooling water,
chilled cooling water, glycol-based liquids and dried or
conditioned chilled air.
[0059] Referring next to FIG. 6, shown are some exemplary
components of a 3D printer, such as discussed above, as well as
thermoelectric components configured to aid in the control of the
extrusion of liquefied metal from extrusion tip 240. Using a
thermoelectric electrode 320 proximate extrusion tip 240 and an
electrode 321 on a build platen 323 a current or a voltage can be
generated by a thermos-electric controller 325 in the liquid metal
flowing from the extrusion tip 240 to the build platen 323 or from
the build platen 323 to the extrusion tip 323 depending upon the
effect desired on the liquid metal exiting the liquefier. For
instance, heat energy can be added or removed from the liquefied
metal flowing from chamber 235 and out of extrusion tip 240
depending on the direction of the flow of the electric current
and/or the change in voltage. For example, using a
bismuth-telluride material for thermoelectric material 320, and
using the thermo-electric controller 325 to control the voltage
differential across the thermoelectric material between the
liquefier and the build platen, the electrodes 320, 321 can be used
to heat or cool the liquid metal material. Using this technique,
cooling or heating of the liquefied metal can be applied to
increase or decrease the viscosity of the metal as it is being
deposited. In exemplary embodiments, thermoelectric controller 325
and electrodes 320, 321 can be used both to aid in the control of
flow of liquefied metal, and in aiding the extruded liquefied metal
in returning to its solid state more quickly to improve the
deposition process and the part being manufactured.
[0060] Referring now to FIGS. 7 and 8, shown are other exemplary
liquefier assemblies 350 and 352, and an inductive heat system 380
which can be used as the heat source in some exemplary embodiments.
Liquefier assemblies 350 and 352 shown respectively in FIGS. 7 and
8 differ only in that in liquefier assembly 352, ceramic tube 230
extends all the way through the liquefier assembly to extrusion tip
360, while in liquefier assembly 350, ceramic tube 230 does not. In
each of liquefier assemblies 350 and 352, portions 370 which
surround an extrusion tube 365 through which the metal wire or
liquefied metal passes, are made from a ferrous metal or
metal-alloy, such as carbon steel. Also, inductive heat system 380
includes an inductive coil 385 surrounding ferrous metal portions
370 of the liquefier assembly. Using an inductive heat controller
390, which includes an electronic oscillator to control an
alternating current through the coil 385, the ferrous portions 370
of liquefiers 350 and 352 are heated by electromagnetic
induction.
[0061] The inductive heat generated within portions 370 of the
liquefier assemblies melts the wire (not shown in FIGS. 7 and 8)
and allows deposition of the liquefied metal or metal-alloy through
extrusion tip 360. Using an inductive heat system, temperatures are
generated that are sufficient to melt high temperature metals, such
as aluminum. As coils 385 of inductive heating system 380 can
themselves become too hot for preferred use in a printer, in some
embodiments, inductive heat control 390 can also include a coil
cooling pump and reservoir 395. The coils 385 can then be in the
form of metal tubes which have water or other coolants circulated
through in order to remove excess heat from the coil.
[0062] Referring now to FIG. 9, shown are features of some example
liquefier assemblies which allow connection and removal of the
liquefier assembly from a ceramic tube. As shown in FIG. 9, a
liquefier assembly 405 includes a metal base 410, which can be, for
example, steel or titanium. The metal base 410 forms an inlet
chamber 415 which is configured to receive ceramic tube 230. Once
inserted into inlet chamber 415, a set screw 420 is used to secure
the ceramic tube within the chamber and prevent its unintended
removal from the chamber 415. In exemplary embodiments, a high
temperature packing material 430 is positioned between ceramic tube
230 and metal base 410 of liquefier assembly 405 to provide a seal
therebetween to prevent liquid metal from entering the seam and
passing therethrough, especially when using a pressurized gas to
control the extrusion of liquid metal from a liquefier as discussed
above.
[0063] When extruding liquefied metals, one difficulty is that the
liquefied metal can re-solidify, or build up dendrites of slag
material, within the liquefier assembly, for example at the
extrusion tip of the liquefier assembly. If the system lacks a heat
source positioned to prevent re-solidification of a metal near the
extrusion tip or in the liquefier tube, the extrusion tip or tube
can clog and prevent further printing. In addition to interrupting
printing, this can require that the entire liquefier assembly be
removed for repair or replacement. To address this difficulty, in
some exemplary embodiments, disclosed liquefier assemblies include
removable or replaceable extrusion tips which can be quickly
changed if the liquefier assembly becomes clogged, or which can be
changed periodically to prevent the liquefier from becoming clogged
or overly worn. For example, as shown in FIG. 10, a liquefier
assembly 450 is configured to utilize removable or replaceable
extrusion tips 470. In one embodiment, a revolving or otherwise
moveable cartridge 460 containing multiple extrusion tips 470 can
be used to replace the extrusion tip on liquefier 450. In an
exemplary embodiment, cartridge 460 rotates or revolves about an
axis member 465 to position different extrusion tips 470 in
position for use by liquefier assembly 450. In such a revolving
cartridge configuration, the extrusion tips 470 would be
concentrically located at equidistant positions from the axis
member 465. In other embodiments, the cartridge 460 can be linearly
moved to change extrusion tips 470. While not shown in FIG. 10,
such a system may include actuators or an actuation system for
rotating or otherwise moving cartridge 460 into place. Further, in
some embodiments, extrusion tips 470 are disposable items that lock
into place on liquefier assembly 450, for example using a cam
locking mechanism. In such embodiments, the disposable liquefier
tips 470 would not need to be disposed on a cartridge 460. They
could, in some embodiments, be individually connected and removed
from the liquefier assembly by an operator.
[0064] Referring now to FIG. 11, shown is a portion of a liquefier
assembly 500 having heat sources 505 such as resistive heater
blocks. Liquefier assembly 500 includes a ceramic tube 510
extending therethrough for carrying the metal or metal-alloy wire
and/or liquefied metal. In order to conduct heat from the heat
sources 505, liquefier assembly 500 includes a titanium insert
through which the ceramic tube 510 extends. When using aluminum or
an aluminum alloy as the molten metal, many materials will dissolve
in the presence of the liquefied aluminum. Carbon, ceramic and
titanium are three materials that do not dissolve with contact to
molten aluminum, and therefore these types of materials can be used
to provide a protective liner sleeve in the flow path, to contain
the melt pool, to transfer heat, and serve as a barrier to protect
the other heater block components.
[0065] Referring now to FIG. 12, shown is an exemplary portion of
another embodiment of a liquefier assembly 550. As shown in FIG.
12, liquefier assembly 550 is in a clogged state in which
solidified metal slag 560 is preventing further extrusion of
liquefied metal from extrusion tip 555. In some embodiments,
increasing the pressure in the liquefier assembly 550 will force
the slag 560 from the extrusion nozzle. However, depending upon the
amount of slag 560 clearing the liquefier assembly 550 with
pressure may not be possible.
[0066] In the illustrated embodiment, liquefier assembly 550
includes a purge port 570 having a controllable valve or sealing
member 575. Under the control of a purge port controller 580, which
can be an electric or hydraulic controller, valve or sealing member
575 can be opened when liquefier assembly 550 is clogged such that
a pressure source 585, for example of pressurized liquid or gas,
can be used to force or blow out the solidified metal 560 through
the purge port 570. Once the solidified metal 560 is purged from
the liquefier assembly 550, purge port control 580 closes valve or
sealing member 575 such that liquefier assembly 550 can again be
used to extrude liquefied metal.
[0067] An alternative approach to clearing a nozzle clog would be
to utilize the revolving cartridge configuration of FIG. 10, with
one of the opening ports being larger than the others, so as to
clear any slag or dendrites from the system.
[0068] Referring now to FIG. 13, the same liquefier assembly 550,
having a purge port 570, can be used with a chemical purge
mechanism 590. The chemical purge mechanism 590 can include a
reservoir of a chemical material and a pump which pumps the
chemical material through liquefier assembly 550 to dissolve the
solidified metal 560. In some embodiments including a purge
chemical mechanism, a purge port 570, a purge port control 580 and
a pressure source 585 may not be necessary.
[0069] Referring next to FIG. 14, shown is a first example of a
build platform onto which a metal part can be printed. When using a
high temperature metal such as aluminum to print a part, providing
a suitable platen or build platform onto which a part can be
printed by extrusion of the liquefied aluminum can be difficult.
Thermoplastics and other common materials used to provide a build
surface typically have a lower melting temperature than aluminum.
Further, if a solid aluminum build surface is utilized, removal of
the printed part from the surface can be extremely difficult,
requiring extensive machining and cutting. It has been discovered
that a steel mesh or screen 605 can be spattered with a thin
pre-coating layer of liquefied aluminum to form a build surface 610
onto which a part can be built using liquefied aluminum extrusion.
As the layer of aluminum which solidifies on screen 605 to form
build surface 610 is thin, removal of an aluminum part from the
build surface 610 is not difficult, and the part will typically
snap off. While aluminum is described, it is understood that any
metal can be spattered and layered onto the platen prior to
printing with a like metal to enhance the bonding of the part to
the platen.
[0070] Referring now to FIG. 15, shown is a build tray or platen
620 made of a thermoplastic material. It has been found that, when
using bismuth to print a part, the part will adhere well to a
pre-applied thin layer of bismuth spattered on a platen. Thus,
build surface 625 includes the thin splattered layer of bismuth on
a thermoplastic or other platen 620. As bismuth has a melting
temperature which is lower than a melting temperature of many
thermoplastic materials, a well-adhering build surface 625 can be
created, and a part printed on that surface, without melting the
thermoplastic platen. While a plastic substrate spattered with
bismuth is disclosed as an example, other disclosed embodiments are
not limited to plastic substrates or to bismuth for spattering. For
instance, in another example embodiment, the build surface can be
formed by spraying aluminum onto a ceramic build platform.
Disclosed embodiments include build surfaces and methods which
incorporate the discovery that putting a small (thin) layer of the
build alloy onto a substrate improves adhesion of the part during
the build.
[0071] Referring now to FIG. 16, shown is a portion of a liquefier
assembly 650 printing a part by extruding layers 665 of liquefied
metal or metal-alloy from extrusion tip 655. The layers of the part
are being deposited upon a build platen or surface 660. In 3D
printers and printing systems, either the print heat (including
liquefier assembly 650) is moved relative to the build platen 660,
the build platen 660 is moved relative to the print head, or both
are moved relative to each other. It has been found that the
extrusion of liquefied metal for printing a part produces improved
or optimized deposition results when the relative speed between the
print head and the build platen is controlled such that the leading
edge of contact between the molten bead of the currently extruding
toolpath, and the underlying layer, is substantially aligned with a
rear edge of the flow from extrusion tip 655. In FIG. 16, this is
shown where the extruded metal 670 exiting extrusion tip 655 has a
wetting contact angle V with the underlying layer and has a leading
point of contact with the underlying layer at point 672.
Controlling the location of this "V" spot by controlling the
relative takeaway speed between the print head and the build platen
produced optimized results when the speed of the print head
relative to the build platen was such that point 672 is
substantially aligned with rear extrusion edge 675 of extrusion tip
655. This observation was noted to be consistent with different
metals used, regardless of molten metal viscosity. Utilizing this
movement approach, a continuous and consistent bead of molten
material was successfully deposited upon the platen, enabling the
fabrication of a metal FDM part.
[0072] With some lower melt temperature metals, such as bismuth,
the melt temperature is in a range such that thermoplastic support
materials such as ULTEM 1010, available from Stratasys Inc., could
be used in conjunction with the molten metal part, to enable the
building of otherwise unprintable geometries.
[0073] Referring now to FIG. 17, shown is a portion of an extruder
720 which can be used with control methods in an alternate
embodiment. Extruder 720 appears for illustrative purposes to be
similar to liquefier assembly 220. However, in extruder 720,
instead of melting the metal wire in a melt reservoir (e.g.,
chamber 235 discussed above) above the extrusion tip 725, contact
heater elements 730 are included and are configured to heat a
center-fed spool of wire at the tip 725. The wire (not shown) is
fed to extruder 720 using techniques described above, and travels
to tip 725 through a feed tube 740. Heater elements 730 can be
resistive or other types of heating devices, and can include a
temperature sensing means, to allow control of the temperature by
the heater control 735.
[0074] Using extruder 720 or a similar device configured to melt
the metal or metal-alloy wire at extrusion tip 725, a deposition
procedure can be implemented as follows. In a quiescent state,
heater control 735 maintains the tip ring 725 thermoelectrically
above liquidus for the alloy used to print a part. The feed
mechanisms are controlled to maintain the alloy feed wire
substantially retracted from the tip 725, and the ring is
maintained such that it is not in contact with the part build
surface.
[0075] To start a "road" (to begin extrusion), the tip 725 is moved
to the desired start position and positioned onto the part build
surface. The local region of the part build surface is then
pre-heated to a temperature above melting. At this point, the wire
begins feeding through the center of the tip 725 into a forming
melt pool. The tip is then lifted and moved as wire is fed.
Movement of the tip includes movement of the tip relative to the
build surface, movement of the build surface relative to the tip,
or a combination of movement of both of the tip and the build
surface.
[0076] Movement of the tip relative to the build surface/part
continues at a fixed distance from the part, feeding wire through
the center of tip 725, to maintain a molten continuous bead between
the part surface and the tip. To stop extrusion at the end of a
"road", the wire is retracted away from tip 725, and the tip is
lifted further off of the surface of the part or build surface.
This technique uses a local region of the part build surface as the
liquefier to prevent or reduce clogging within the extruder.
[0077] In the present disclosure, "3D printer", "additive
manufacturing system" and the like are inclusive of both discrete
3D printers and/or toolhead accessories to manufacturing machinery
which carry out an additive manufacturing sub-process within a
larger process.
[0078] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *