U.S. patent application number 14/697157 was filed with the patent office on 2015-08-13 for multiple-zone liquefier assembly for extrusion-based additive manufacturing systems.
The applicant listed for this patent is Stratasys, Inc.. Invention is credited to J. Samuel Batchelder, William J. Swanson.
Application Number | 20150224714 14/697157 |
Document ID | / |
Family ID | 45492951 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150224714 |
Kind Code |
A1 |
Swanson; William J. ; et
al. |
August 13, 2015 |
MULTIPLE-ZONE LIQUEFIER ASSEMBLY FOR EXTRUSION-BASED ADDITIVE
MANUFACTURING SYSTEMS
Abstract
A liquefier assembly for use in an extrusion-based additive
manufacturing system, and a method for building a three-dimensional
model with the extrusion-based additive manufacturing system, where
the liquefier assembly includes a liquefier tube having multiple,
independently heatable zones along a longitudinal length of the
liquefier tube.
Inventors: |
Swanson; William J.; (St.
Paul, MN) ; Batchelder; J. Samuel; (Somers,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Stratasys, Inc. |
Eden Prairie |
MN |
US |
|
|
Family ID: |
45492951 |
Appl. No.: |
14/697157 |
Filed: |
April 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12841341 |
Jul 22, 2010 |
9022769 |
|
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14697157 |
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Current U.S.
Class: |
264/308 ;
425/378.1 |
Current CPC
Class: |
B33Y 30/00 20141201;
B29C 64/112 20170801; B29C 64/209 20170801; B29C 67/0085 20130101;
B29K 2101/12 20130101; B29C 64/106 20170801; B33Y 10/00 20141201;
B29C 48/05 20190201; B29C 64/118 20170801; B29C 48/266
20190201 |
International
Class: |
B29C 67/00 20060101
B29C067/00 |
Claims
1. A liquefier assembly for use in an extrusion-based additive
manufacturing system, the liquefier assembly comprising: a
liquefier tube having a first end and a second end offset along
longitudinal length; an extrusion tip secured to the first end of
the liquefier tube; a first thermal unit operably secured to the
liquefier tube adjacent the first end of the liquefier tube; and a
second thermal unit operably secured to the liquefier tube between
the first thermal unit and the second end of the liquefier tube,
wherein the first thermal unit and the second thermal unit are
configured to be operated independently of each other.
2. The liquefier assembly of claim 1, wherein the first thermal
unit comprises: a first thermally-conductive component in thermal
contact with an outer surface of the liquefier tube; and a first
electrically-conductive component configured to heat the first
thermally-conductive component;
3. The liquefier assembly of claim 2, wherein the first thermal
unit further comprises a first temperature sensor configured to
detect a temperature of at least one of the first
thermally-conductive component, the liquefier tube at a location
adjacent to the first thermally-conductive component, and a
combination thereof.
4. The liquefier assembly of claim 2, wherein the second thermal
unit comprises: a second thermally-conductive component in thermal
contact with the outer surface of the liquefier tube; and a second
electrically-conductive component configured to heat the second
thermally-conductive component.
5. The liquefier assembly of claim 4, wherein the second thermal
unit further comprises a second temperature sensor configured to
detect a temperature of at least one of the second
thermally-conductive component, the liquefier tube at a location
adjacent to the second thermally-conductive component, and a
combination thereof.
6. The liquefier assembly of claim 1, and further comprising a
drive mechanism configured to feed successive portions of a
filament to the second end of the liquefier tube.
7. The liquefier assembly of claim 1, and further comprising at
least one electrically-insulative sleeve.
8. The liquefier assembly of claim 1, and further comprising a
third thermal unit operably secured to the liquefier tube between
the second thermal unit and the second end of the liquefier
tube.
9. A liquefier assembly for use in an extrusion-based additive
manufacturing system, the liquefier assembly comprising: a
liquefier tube having a first end and a second end offset along
longitudinal length; an extrusion tip secured to the first end of
the liquefier tube; and a plurality of thermal units operably
secured to the liquefier tube at different locations along the
longitudinal length of the liquefier tube, wherein each of the
plurality of thermal units is configured to be operated
independently of each other.
10. The liquefier assembly of claim 9, wherein each of the
plurality of thermal units comprises: a thermally-conductive
component in thermal contact with an outer surface of the liquefier
tube; an electrically-conductive component configured to heat the
thermally-conductive component; and a temperature sensor configured
to detect a temperature of at least one of the thermally-conductive
component, the liquefier tube at a location adjacent to the
thermally-conductive component, and a combination thereof.
11. The liquefier assembly of claim 10, wherein the
electrically-conductive component comprises a wire wrapped around
at least a portion of the thermally-conductive component.
12. The liquefier assembly of claim 9, and further comprising at
least one electrically-insulative sleeve.
13. The liquefier assembly of claim 9, wherein the plurality of
thermal units range from two thermal units to ten thermal
units.
14. The liquefier assembly of claim 13, wherein the plurality of
thermal units range from two thermal units to five thermal
units.
15. A method for building a three-dimensional model with an
extrusion-based additive manufacturing system having an extrusion
head, the method comprising: providing a liquefier tube of the
extrusion head having multiple heatable zones along a longitudinal
length of the liquefier tube; heating a first zone of the multiple
heatable zones; at least partially melting a portion of a filament
of a thermoplastic material within the first zone of the liquefier
tube; and extruding the molten thermoplastic material from an
extrusion tip mounted to a bottom end of the liquefier tube.
16. The method of claim 15, and further comprising, while only the
first zone is heated, moving the extrusion head along a toolpath
that defines an outer perimeter surface of the three-dimensional
model.
17. The method of claim 15, and further comprising heating a second
zone of the multiple heatable zones, the second zone being located
between the first zone and a top end of the liquefier assembly.
18. The method of claim 17, and further comprising moving the
extrusion head along a toolpath that defines an inner region of the
three-dimensional model.
19. The method of claim 17, and further comprising stopping the
heating of the second zone while maintaining the heating of the
first zone.
20. The method of claim 15, wherein heating the first zone of the
multiple heatable zones comprises applying an electrical current
through a conducive wire in contact with a thermally-conductive
component in thermal contact with the liquefier tube at the first
zone.
Description
BACKGROUND
[0001] The present disclosure relates to additive manufacturing
systems for building three-dimensional (3D) models with layer-based
additive manufacturing techniques. In particular, the present
disclosure relates to liquefier assemblies for use in
extrusion-based additive manufacturing systems.
[0002] An extrusion-based additive manufacturing system (e.g.,
fused deposition modeling systems developed by Stratasys, Inc.,
Eden Prairie, Minn.) is used to build a 3D model from a digital
representation of the 3D model in a layer-by-layer manner by
extruding a flowable consumable modeling material. The modeling
material is extruded through an extrusion tip carried by an
extrusion head, and is deposited as a sequence of roads on a
substrate in an x-y plane. The extruded modeling material fuses to
previously deposited modeling material, and solidifies upon a drop
in temperature. The position of the extrusion head relative to the
substrate is then incremented along a z-axis (perpendicular to the
x-y plane), and the process is then repeated to form a 3D model
resembling the digital representation.
[0003] Movement of the extrusion head with respect to the substrate
is performed under computer control, in accordance with build data
that represents the 3D model. The build data is obtained by
initially slicing the digital representation of the 3D model into
multiple horizontally sliced layers. Then, for each sliced layer,
the host computer generates a build path for depositing roads of
modeling material to form the 3D model.
[0004] In fabricating 3D models by depositing layers of a modeling
material, supporting layers or structures are typically built
underneath overhanging portions or in cavities of objects under
construction, which are not supported by the modeling material
itself. A support structure may be built utilizing the same
deposition techniques by which the modeling material is deposited.
The host computer generates additional geometry acting as a support
structure for the overhanging or free-space segments of the 3D
model being formed. Consumable support material is then deposited
from a second nozzle pursuant to the generated geometry during the
build process. The support material adheres to the modeling
material during fabrication, and is removable from the completed 3D
model when the build process is complete.
SUMMARY
[0005] A first aspect of the present disclosure is directed to a
liquefier assembly for use in an extrusion-based additive
manufacturing system. The liquefier assembly includes a liquefier
tube having a first end and a second end offset along longitudinal
length, and an extrusion tip secured to the first end of the
liquefier tube. The liquefier assembly also includes a first
thermal unit operably secured to the liquefier tube adjacent the
first end of the liquefier tube, and a second thermal unit operably
secured to the liquefier tube between the first thermal unit and
the second end of the liquefier tube.
[0006] Another aspect of the present disclosure is directed to a
liquefier assembly for use in an extrusion-based additive
manufacturing system, where the liquefier assembly includes a
liquefier tube having a first end and a second end offset along
longitudinal length, and an extrusion tip secured to the first end
of the liquefier tube. The liquefier assembly also includes a
plurality of thermal units operably secured to the liquefier tube
at different locations along the longitudinal length of the
liquefier tube, where each of the plurality of thermal units is
configured to be operated independently of each other.
[0007] Another aspect of the present disclosure is directed to a
method for building a three-dimensional model with an
extrusion-based additive manufacturing system having an extrusion
head. The method includes providing a liquefier tube of the
extrusion head having multiple heatable zones along a longitudinal
length of the liquefier tube, and heating a first zone of the
multiple heatable zones. The method also includes at least
partially melting a portion of a filament of a thermoplastic
material within the first segment of the liquefier tube, and
extruding the molten thermoplastic material from an extrusion tip
mounted to a bottom end of the liquefier tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a front view of an extrusion-based additive
manufacturing system that includes a liquefier assembly of the
present disclosure.
[0009] FIG. 2 is a schematic illustration of the liquefier
assembly.
[0010] FIG. 3 is a schematic illustration of a first alterative
liquefier assembly, which includes heatable zones with different
lengths.
[0011] FIG. 4 is a schematic illustration of a second alternative
liquefier assembly, which includes modified thermal units.
[0012] FIG. 5 is a sectional view of section 5-5 taken in FIG.
4.
DETAILED DESCRIPTION
[0013] While operating at steady state, a conventional liquefier
has its maximum flow rate dictated by its heated length and the
thermal diffusivity of the material being extruded. Thus, the
longer liquefier is, the faster the system can build a 3D model or
support structure. Additionally, a conventional liquefier, which
typically includes an extrusion tip with a flow resistance that is
large compared to the rest of the liquefier, has a response time
that increases with the square of the heated length of the
liquefier. Therefore, the longer the liquefier, the harder it is to
change the flow rate quickly (i.e., a slower response time). This
slower response time accordingly slows down the build speed when
building 3D model and support structures.
[0014] Stated another way, when an extrusion head carrying a
liquefier moves quickly through interior fill patterns of a 3D
model or support structure, a longer liquefier is preferred.
Alternatively, when the extrusion head traces surface details with
numerous stops and starts, a shorter liquefier is preferred.
Accordingly, a long heated portion of the liquefier provides a high
flow rate and a slow time response, while a short heated portion of
the liquefier provides a low flow rate and a fast time
response.
[0015] For a given slice thickness and tip manufacturing technique,
the tip inner diameter and tip axial length are typically fixed.
Thus, the basic difference between a short and a long liquefier is
the length of the heated section of a liquefier. Accordingly, as
discussed below, the liquefier assembly of the present disclosure
is capable of adjusting its heatable length to function as a
variable-length liquefier. In particular, the liquefier assembly of
the present disclosure includes multiple, independently heatable
zones that adjust its overall heatable length. As such, the
liquefier assembly may have a short heatable length when fast
response times are desired (e.g., when tracing surface details with
numerous stops and starts), and may have a long heatable length
when fast flow rates are desired (e.g., through interior fill
patterns).
[0016] As shown in FIG. 1, system 10 is an extrusion-based additive
manufacturing system for building 3D models with the use of support
structures, and includes build chamber 12, platen 14, gantry 16,
extrusion head 18, and supply sources 20 and 22. Examples of
suitable systems for system 10 include extrusion-based additive
manufacturing systems, such as fused deposition modeling systems
developed by Stratasys, Inc., Eden Prairie, Minn. As discussed
below, extrusion head 18 may include one or more multiple-zone
liquefier assemblies (not shown in FIG. 1) for melting successive
portions of filaments (not shown in FIG. 1) during a build
operation with system 10.
[0017] Build chamber 12 is an enclosed, heatable environment that
contains platen 14, gantry 16, and extrusion head 18 for building a
3D model (referred to as 3D model 24) and a corresponding support
structure (referred to as support structure 26). Platen 14 is a
platform on which 3D model 24 and support structure 26 are built,
and desirably moves along a vertical z-axis based on signals
provided from computer-operated controller 28. Gantry 16 is a guide
rail system that is desirably configured to move extrusion head 18
in a horizontal x-y plane within build chamber 12 based on signals
provided from controller 28. The horizontal x-y plane is a plane
defined by an x-axis and a y-axis (not shown in FIG. 1), where the
x-axis, the y-axis, and the z-axis are orthogonal to each other. In
an alternative embodiment, platen 14 may be configured to move in
the horizontal x-y plane within build chamber 12, and extrusion
head 18 may be configured to move along the z-axis. Other similar
arrangements may also be used such that one or both of platen 14
and extrusion head 18 are moveable relative to each other.
[0018] Extrusion head 18 is supported by gantry 16 for building 3D
model 24 and support structure 26 on platen 14 in a layer-by-layer
manner, based on signals provided from controller 28. In the
embodiment shown in FIG. 1, extrusion head 18 is a dual-tip
extrusion head configured to deposit modeling and support materials
from supply source 20 and supply source 22, respectively. Examples
of suitable extrusion heads for extrusion head 18 include those
disclosed in LaBossiere, et al., U.S. Patent Application
Publication Nos. 2007/0003656 and 2007/00228590; and Leavitt, U.S.
Patent Application Publication No. 2009/0035405. Furthermore,
system 10 may include a plurality of extrusion heads 18 for
depositing modeling and/or support materials.
[0019] The modeling material is supplied to extrusion head 18 from
supply source 20 via feed line 30, thereby allowing extrusion head
18 to deposit the modeling material to build 3D model 24.
Correspondingly, the soluble support material is supplied to
extrusion head 18 from supply source 22 via feed line 32, thereby
allowing extrusion head 18 to deposit the support material to build
support structure 26. During a build operation, gantry 16 moves
extrusion head 18 around in the horizontal x-y plane within build
chamber 12, and one or more drive mechanisms (e.g., drive
mechanisms 33a and 33b) are directed to intermittently feed the
modeling and support materials through extrusion head 18 from
supply sources 20 and 22.
[0020] The received modeling and support materials are then
deposited onto platen 14 to build 3D model 24 and support structure
26 using a layer-based additive manufacturing technique. Support
structure 22 is desirably deposited to provide vertical support
along the z-axis for overhanging regions of the layers of 3D model
24. This allows 3D object 24 to be built with a variety of
geometries. After the build operation is complete, the resulting 3D
model 24/support structure 26 may be removed from build chamber 12,
and placed in a bath containing an aqueous solution (e.g., an
aqueous alkaline solution) to remove support structure 26 from 3D
model 24.
[0021] The modeling and support materials may be provided to system
10 in a variety of different media. For example, the modeling and
support materials may be provided as continuous filament strands
fed respectively from supply sources 20 and 22, as disclosed in
Swanson et al., U.S. Pat. No. 6,923,634; Comb et al., U.S. Pat. No.
7,122,246; and Taatjes et al, U.S. patent application Ser. Nos.
12/255,808 and 12/255,811. Examples of suitable average diameters
for the filament strands of the modeling and support materials
range from about 1.27 millimeters (about 0.050 inches) to about 3.0
millimeters (about 0.120 inches). The term "about" is used herein
with respect to measurable values and ranges of temperatures due to
expected variations known to those skilled in the art (e.g.,
limitations and variabilities in measurements).
[0022] FIG. 2 shows liquefier assembly 34 in use with filament 36,
where liquefier assembly 34 is a liquefier assembly of extrusion
head 18 (shown in FIG. 1) for extruding a material from filament
36. As such, liquefier assembly 34 may be used to deposit the
modeling material and/or the support material. Extrusion head 18
desirably includes a separate liquefier assembly 34 for depositing
the modeling material and for depositing the support material.
[0023] Filament 36 may be fed to liquefier tube 38 from supply
source 20 or supply source 22 (shown in FIG. 1) with one or more
drive mechanisms (e.g., drive mechanisms 33a and 33b, shown in FIG.
1). Examples of suitable drive mechanisms for use with liquefier
assembly 34 include those disclosed in Batchelder et al., U.S.
Application Publication No. 2009/0274540; and LaBossiere et al.,
U.S. Pat. Nos. 7,384,255 and 7,604,470; the disclosures of which
are incorporated by reference in their entireties.
[0024] As shown in FIG. 2, liquefier assembly 34 includes liquefier
tube 38, thermal units 40a and 40b, and extrusion tip 42. Liquefier
tube 38 is a thin-walled, thermally-conductive tube, which is
desirably electrically grounded. Examples of suitable materials for
liquefier tube 38 include stainless steel. Examples of suitable
designs for liquefier tube 38 and extrusion tip 42 include those
disclosed in Batchelder et al., U.S. patent application Ser. No.
12/612,329; Batchelder et al., U.S. Application Publication No.
2009/0273122; Swanson et al., U.S. Pat. No. 6,004,124; Comb, U.S.
Pat. No. 6,547,995; and LaBossiere et al., U.S. Pat. Nos. 7,384,255
and 7,604,470; the disclosures of which are incorporated by
reference in their entireties.
[0025] Thermal units 40a and 40b are a pair of thermally-conductive
units configured to transfer thermal energy to liquefier tube 38 in
separate heatable zones (referred to as zones 44a and 44b). While
liquefier assembly 34 is shown having two thermal units configured
to provide two heatable zones, liquefier assemblies of the present
disclosure may alternative include additional numbers of thermal
units. Examples of suitable numbers of thermal units and thermal
zones range from two to ten. In one embodiment, suitable numbers of
thermal units and thermal zones range from two to five. In another
embodiment, suitable numbers of thermal units and thermal zones
range from two to four. In yet another embodiment, suitable numbers
of thermal units and thermal zones range from two to three.
[0026] As shown, liquefier tube 38 desirably includes a length
(referred to as length 45) between the top end of liquefier tube 38
and the top-most thermal unit (i.e., thermal unit 40a in the shown
embodiment). Length 45 desirably prevents filament 36 from melting
at the top end of liquefier tube 38. In one embodiment, cooling air
may be supplied to the top end of liquefier tube 38 to further
reduce the risk of filament 36 from melting at the top end of
liquefier tube 38.
[0027] In the shown embodiment, thermal unit 40a includes thermal
spreader 46, conductive wire 48, and thermistor 50. Thermal
spreader 46 is a thermally-conductive sleeve that encases liquefier
tube 38 at zone 44a for spreading thermal energy (i.e., heat) from
conductive wire 48 to liquefier tube 38. Thermal spreader 46 may be
fabricated from one or more thermally-conductive materials, such as
aluminum (e.g., anodized aluminum). Conductive wire 48 is wrapped
around thermal spreader 46 and receives electrical energy from
electrical connection 52 to generate the thermal energy. A portion
of conductive wire 48 may also be secured to liquefier tube 38
(e.g., welded to liquefier tube 38), as shown in FIG. 2. Thermistor
50 is a resistor that measures the temperature of zone 44a. As
shown, thermistor 50 includes a lead secured to liquefier tube 38
(e.g., welded to liquefier tube 38) and electrical connection 54
for relaying the detected resistance to control 28 (shown in FIG.
1).
[0028] Correspondingly, thermal unit 40b includes thermal spreader
56, conductive wire 58 (having electrical connection 60), and
thermistor 62 (having electrical connection 64), which function in
the same manner as the components of thermal unit 40a for heating
and monitoring the temperature of zone 44b. In alternative
embodiments, thermistor 50 and/or thermistor 62 may be replaced
with one or more thermocouple units for monitoring the temperature
of zones 44a and 44b.
[0029] Liquefier assembly 34 may also include insulation sleeve 66,
which is an electrically-insulative sleeve that desirably wraps
around thermal units 40a and 40b. This arrangement allows liquefier
tube 38 to be heated in multiple zones (e.g., zones 44a and 44b)
based on the independent operation of thermal unit 40a and thermal
unit 40b.
[0030] During operation, zone 44b (i.e., the lowest zone, closest
to extrusion tip 42) is desirably always heated when liquefier
assembly 34 is extruding a material. Additional heatable zones
above the lowest zone (e.g., zone 44a) may be turned on when
extended high flow rate, nearly steady velocity toolpaths are
planned for a future time corresponding to the several second
thermal diffusion time for heating filament 36 in those upper
zone(s).
[0031] When preparing to shut off a one or more zones of liquefier
assembly 34, the zones away from extrusion tip 42 are desirably
shut off first, allowing the meniscus of molten material (referred
to as meniscus 68) to move downward towards extrusion tip 42,
thereby drying out the upper zone(s). In the shown example, thermal
unit 40a is shut off, thereby positioning meniscus 68 at a location
at or above thermal zone 44b due to heat being provided solely by
thermal unit 40b.
[0032] In embodiments in which liquefier assembly 34 includes three
or more heatable zones, the thermal units of the top-most zone is
desirably shut off first, followed by the adjacent lower thermal
unit, in a downward serial manner. Despite this action, it is often
the case (particularly with support materials) that filament 36
will adhere to the inner wall of liquefier tube 38 above the lowest
zone on start-up. With conventional, single zone liquefiers, this
is addressed by over-heating the single zone and shutting off the
cooling air to the liquefier. In comparison, with the multiple-zone
liquefier assembly 34, start-up may be accomplished by briefly
heating all the zones simultaneously (e.g., operating both thermal
unit 40a and thermal unit 40b).
[0033] During start-up, thermal units 40a and 40b may each be
heated to at least partially melt filament 36 within liquefier tube
38. During operation, thermal unit 40a may be turned on and off
independently of thermal unit 40b. Accordingly, when controller 28
directs extrusion head 18 to deposit extrudate 70 of a modeling or
support material along a toolpath that has numerous stops and start
(e.g., when tracing surface details), a fast response time is
desired. As such, controller 28 may direct thermal unit 40a to shut
off to reduce the heatable length of liquefier assembly 34
generally to the length of liquefier tube 38 at and below zone
44b.
[0034] Alternatively, when controller 28 directs extrusion head 18
to deposit extrudate 70 of the modeling or support material along a
toolpath that is desirably filled quickly (e.g., through interior
fill patterns), fast flow rates of the given material are desired.
As such, controller 28 may direct thermal unit 40a to heat zone 44a
to increase the heatable length of liquefier assembly 34 generally
to the length of liquefier tube 38 at and below zone 44a. This
combination allows both fast response times when tracing surface
details of 3D model 24 and support structure 26, along with fast
deposition rates when filling interior regions of 3D model 24 and
support structure 26.
[0035] In some embodiments, the one or more upper zones may cover
longer segments of liquefier tube 38 compared to lower zones. For
example, as shown in FIG. 3, thermal unit 40a covers a longer
length of liquefier tube 38 compared to the length covered by
thermal unit 40b. As such, zone 44a is longer than zone 44b.
Examples of suitable lengths for zone 40a range from about 100% of
the length of zone 40b to about 500% of the length of zone 40b. In
some embodiments, suitable lengths for zone 40a range from about
100% of the length of zone 40b to about 300% of the length of zone
40b. In additional embodiments, suitable lengths for zone 40a range
from about 150% of the length of zone 40b to about 250% of the
length of zone 40b. In further additional embodiments, the length
for zone 40a range is about 200% of the length of zone 40b.
[0036] FIGS. 4 and 5 show an alternative design to the liquefier
assemblies shown in FIGS. 2 and 3, which operates under
substantially the same mechanics for providing multiple,
independently-heatable zones. As shown in FIG. 4, liquefier
assembly 134 includes liquefier tube 138 (e.g., a stainless-steel
tube), thermal units 140a and 140b, and extrusion tip 142, where
thermal units 140a and 140b respectively define heatable zones 144a
and 144b. In this embodiment, thermal unit 140a includes thermal
block 172, electrode 174, and thermocouple 176. Correspondingly,
thermal unit 140b includes thermal block 178, electrode 180, and
thermocouple 182. Liquefier assembly 134 also include ground
contact 184 disposed longitudinally between thermal blocks 172 and
178.
[0037] Thermal blocks 172 and 178 may each be fabricated from one
or more thermally-conductive materials. In one embodiment, thermal
blocks 172 and 178 are each fabricated from graphite. The use of
graphite for thermal blocks 172 and 178 is beneficial due it low
material costs, capabilities of handling elevated temperatures,
capabilities of being substantially uniform heat generators, and
providing good thermal conductivity.
[0038] During operation, a first electrical current may be supplied
to electrode 180, where the electrical current then flows axially
upward through thermal block 178 to ground contact 184, thereby
heating thermal block 178. The heat from thermal block 178 is then
transferred to liquefier tube 138 at zone 144b. Correspondingly, a
second electrical current may be supplied to electrode 174, where
the electrical current then flows axially downward through thermal
block 172 to ground contact 184, thereby heating thermal block 172.
This heats zone 144a in a manner that is independent from the
heating of zone 144b.
[0039] Thermocouples 176 and 182 independently sample the
temperatures of thermal blocks 172 and 178. The outputs from
thermocouples 176 and 182 may be used by controller 28 (shown in
FIG. 1) to control the current flow through electrodes 174 and 180
based on target temperatures for zones 144a and 144b,
respectively.
[0040] Liquefier assembly 134 may also include insulation sleeve
184 disposed between liquefier tube 138 and thermal units 140a and
140b. Examples of suitable materials for insulation sleeve 184
include one or more electrically-insulative materials, such as
ceramic materials and/or aluminum oxide. Above insulation sleeve
184, liquefier assembly 134 may also include cold block 186, which
contains an embedded heat pipe 188. This causes the top end of
liquefier tube 138 to be well below the softening point of the
modeling or support material being fed to liquefier assembly
134.
[0041] During a fast interior fill of either 3D model 24 or support
structure 26, zones 144a and 144b may be heated in parallel, as
discussed above for liquefier assemblies 34 (shown in FIGS. 2 and
3). This provides a relatively long heated length for liquefier
assembly 134, which provides larger peak flows and slower time
responses. Since this is for interior fill, some degradation in
seam quality is tolerable for higher deposition rates.
[0042] Alternatively, when extrusion head 18 is building surface
roads with feature details, zone 144a is desirably unheated and
zone 144b is desirably heated. As discussed above, this provides
faster response times, with reduced peak flow rates. These
parameters are acceptable when building detailed features, such as
surface features.
[0043] As shown in FIG. 5, liquefier assembly 134 may also include
outer insulation sleeve 190 and clip 192. Outer insulation sleeve
190 desirably extends around thermal units 140a and 140b, and may
also be fabricated from one or more electrically-insulative
materials, such as ceramic materials and/or aluminum oxide. Clip
192 is a biasing clip configured to securely retain thermal units
140a and 140b, and insulation sleeves 184 and 190 against liquefier
tube 138.
[0044] The above-discussed liquefier assemblies of the present
disclosure provide multiple heatable zones, where the temperature
within a given zone is substantially uniform while temperatures of
adjacent zones may vary. The liquefier assemblies allow controller
28 to regulate the temperature of each zone, along with
capabilities of preventing filaments of the modeling and support
materials from melting at the top ends of the liquefier tubes.
Furthermore, controller 28 is desirably configured to direct how
many zones should be operating for a given toolpath, based on the
type of toolpath being followed.
[0045] Suitable modeling materials for use with the liquefier
assemblies of the present disclosure include polymeric and metallic
materials. In some embodiments, suitable modeling materials include
materials having amorphous properties, such as thermoplastic
materials, amorphous metallic materials, and combinations thereof.
Examples of suitable thermoplastic materials for ribbon filament 34
include acrylonitrile-butadiene-styrene (ABS) copolymers,
polycarbonates, polysulfones, polyethersulfones,
polyphenylsulfones, polyetherimides, amorphous polyamides, modified
variations thereof (e.g., ABS-M30 copolymers), polystyrene, and
blends thereof. Examples of suitable amorphous metallic materials
include those disclosed in U.S. patent application Ser. No.
12/417,740.
[0046] Suitable support materials for use with the liquefier
assemblies of the present disclosure include materials having
amorphous properties (e.g., thermoplastic materials) and that are
desirably removable from the corresponding modeling materials after
3D model 24 and support structure 26 are built. Examples of
suitable support materials include water-soluble support materials
commercially available under the trade designations "WATERWORKS"
and "SOLUBLE SUPPORTS" from Stratasys, Inc., Eden Prairie, Minn.;
break-away support materials commercially available under the trade
designation "BASS" from Stratasys, Inc., Eden Prairie, Minn., and
those disclosed in Crump et al., U.S. Pat. No. 5,503,785; Lombardi
et al., U.S. Pat. Nos. 6,070,107 and 6,228,923; Priedeman et al.,
U.S. Pat. No. 6,790,403; and Hopkins et al., U.S. patent
application Ser. No. 12/508,725.
[0047] Although the present disclosure 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 disclosure.
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