122A]
`
`
`
`43
`
`US 2009027
`
`as) United States
`a2) Patent Application Publication co) Pub. No.: US 2009/0273122 Al
`(43) Pub. Date: Nov. 5, 2009
`
`Batchelderetal.
`
`(54) LIQUEFIER ASSEMBLYFOR USE IN
`EXTRUSION-BASED DIGITAL
`MANUFACTURING SYSTEMS
`
`(75)
`
`Inventors:
`
`J. Samuel Batchelder, Somers, NY
`(US); William J. Swanson, St.
`Paul, MN (US)
`
`Correspondence Address:
`WESTMAN CHAMPLIN & KELLY, P.A.
`SUITE 1400, 900 SECOND AVENUE SOUTH
`MINNEAPOLIS, MN 55402 (US)
`
`(73) Assignee:
`
`Stratasys, Inc., Eden Prairie, MN
`(US)
`
`(21)
`
`Appl.No.:
`
`12/150,669
`
`(22)
`
`Filed:
`
`Apr. 30, 2008
`
`Publication Classification
`
`(51)
`
`Int.Cl.
`B29C 47/78
`
`(2006.01)
`
`(52) US. CD. ceecccsscccssssesessssssccsseseeeee 264/401; 425/144
`
`(57)
`
`ABSTRACT
`
`A liquefier assembly comprising a liquefier tube, where the
`liquefier tube comprises a sidewall having an inlet opening
`configuredto receivea filament strand, an outlet opening, and
`a port disposed through the sidewall at a location between the
`inlet opening and the outlet opening, the port being config-
`ured to provide access for a filament drive mechanism to
`engage with the receivedfilament strand. The liquefier assem-
`blyfurther comprises a heat transfer component configured to
`generate a thermalgradient along a longitudinal length ofthe
`sidewall between the port and the outlet opening.
`
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`Patent Application Publication
`
`§Nov.5,2009 Sheet 1 of 6
`
`US 2009/0273122 Al
`
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`FIG. 1
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`

`

`Patent Application Publication
`
`§Nov.5,2009 Sheet 2 of 6
`
`US 2009/0273122 Al
`
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`Patent Application Publication
`
`§Nov.5,2009 Sheet 3 of 6
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`US 2009/0273122 Al
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`

`Patent Application Publication
`
`Nov.5,2009 Sheet 4 of 6
`
`US 2009/0273122 Al
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`5
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`Patent Application Publication
`
`Nov.5,2009 Sheet 5 of 6
`
`US 2009/0273122 Al
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`Patent Application Publication
`
`§Nov.5,2009 Sheet 6 of 6
`
`US 2009/0273122 Al
`
` Load filamentinto liquefier
`
`tube
`
` 404|Engage loaded filament strand Drive engaged filament strand
` 400
`strand
`
`Melt material of filament
`
`FIG. 9
`
`
`
`Extrude molten material
`
`
`7
`
`

`

`US 2009/0273122 Al
`
`Nov. 5, 2009
`
`FIG. 1 is a front viewof an extrusion-baseddigital
`[0007]
`manufacturing system that includes a liquefier assemblyfor
`melting received filament strands.
`TI
`[0008]
`FIG. 2 is a top perspective view of the liquefier
`assembly in use with a filament drive mechanism having a
`rotatable pulley.
`[0009]
`FIG. 3 is an exploded perspective viewofthe lique-
`fier assembly.
`Tr
`[0010]
`FIG. 4 is a side view ofa liquefier tube in use with
`the filament drive mechanism for melting and extruding a
`filament strand.
`
`FIG. 5isa side view ofthe liquefier tube in use with
`[0011]
`a first alternative filament drive mechanism having threaded
`rotatable shaft.
`
`FIG. 6 isa side view of an alternative liquefier ube
`[0012]
`in use with a secondalternative filament drive mechanism
`
`
`
`[0003] An extrusion-based digital manufacturing system
`e.g.,
`fused deposition modeling systems developed by
`Stratasys, Inc., Eden Prairie, Minn.) is used to build a 3D
`object from a computer-aided design (CAD) model in a layer-
`by-layer mannerby extruding a flowable build material. The
`build materialis extruded through an extrusion tip carried by
`havingrotatableroller.
`an extrusion head, and is deposited as a sequence of roads on
`
`[0013] FIG.7is a top perspective view of a secondalterna-
`a substrate in an x-y plane. The extruded build material fuses
`tive liquefier tube, which includesa strain gauge.
`0 previously deposited build material, and solidifies upon a
`TI
`[0014]
`FIG. 8 is a top perspective view of an alternative
`drop in temperature. The position ofthe extrusion head rela-
`liquefier assembly in use with a filament drive mechanism
`ive to the substrate is then incremented along a z-axis (per-
`having a rotatable pulley, where the alternative liquefier
`pendicularto the x-y plane), and the process is then repeated
`assembly includes a curved liquefier tube.
`0 form a 3D object resembling the CAD model.
`[0015] FIG. 91saflow diagram of a method for building a
`
`[0004] Movementofthe extrusion head with respectto the
`3D object with the extrusion-based digital manufacturing
`substrate is performed under computercontrol, in accordance
`system.
`with build data that represents the 3D object. The build datais
`obtainedby initially slicing the CAD model of the 3D object
`into multiple horizontallysliced layers. Then, for each sliced
`layer, the host computer generates a build path for depositing
`roadsof build material to form the 3D object.
`[0005]
`In fabricating 3D objects by depositing layers of
`build material, supporting layers or structures are typically
`built underneath overhanging portions or in cavities of
`objects under construction, which are not supported by the
`build materialitself. A support structure maybe built utilizing
`the same deposition techniques by whichthebuild materialis
`deposited. The host computer generates additional geometry
`acting as a support structure for the overhangingorfree-space
`segmentsof the 3D object being formed. Support material is
`then deposited from a second nozzle pursuant to the gener-
`ated geometryduring the build process. The support material
`adheresto the build material during fabrication, and is remov-
`able from the completed 3D object whenthe build processis
`complete.
`
`LIQUEFIER ASSEMBLY FOR USE IN
`EXTRUSION-BASED DIGITAL
`MANUFACTURING SYSTEMS
`
`
`
`CROSS-REFERENCE TO RELATED
`
`APPLICATION(S)
`[0001] Reference is hereby made to co-pending U.S. patent
`application Ser. No.
`filed on even date, and entitled
`
`“Filament Drive Mechanism For Use In Extrusion-Based
`
`Digital Manufacturing Systems”(attorney docket no. $697.
`12-0118).
`
`BACKGROUND
`
`[0002] The present invention relates to digital manufactur-
`ing systems for building three-dimensional (3D) objects. In
`particular, the present inventionrelates to extrusion-headliq-
`efiers for use in extrusion-based digital manufacturing sys-
`ems.
`
`
`
`figured to provide access for a filament drive mechanism to
`engage with the receivedfilamentstrand. The liquefier assem-
`bly also includes a heat transfer component configured to
`generate a thermal gradient along at least a portion of a
`longitudinal length of the sidewall between the port and the
`outlet opening.
`
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`
`
`
`
`DETAILED DESCRIPTION
`
`FIG. 1 is a front view of system 10, which is an
`[0016]
`extrusion-based digital manufacturing system that includes
`build chamber 12, substrate 14, gantry 16, extrusion head 18,
`and filament supply source 20, where extrusion head 18
`includes liquefier assembly 22. As discussed below,liquefier
`assembly 22 is a ported liquefier for melting successivepor-
`tionsoffilament 24 during a build operation with system 10.
`Suitable digital manufacturing systems for system 10 include
`fused deposition modeling systems developed byStratasys,
`Inc., Eden Prairie, Minn. Build chamber 12 is an enclosed
`environmentthat contains substrate 14, gantry 16, and extru-
`sion head 18 for building a 3D object (referred to as 3D object
`26) and a corresponding support structure (referred to as
`support structure 28).
`[0017]
`Substrate 14 is a platform on which 3D object 26 and
`support structure 28 are built, and moves along a vertical
`z-axis based on signals provided from a computer-operated
`controller (not shown). Gantry 16 is a guide rail system con-
`figured to move extrusion head 18 in a horizontal x-y plane
`within build chamber 12 based on signals provided from the
`computer-operated controller. The horizontal x-y plane is a
`plane defined by an x-axis and a y-axis (not shownin FIG.1),
`wherethe x-axis, the y-axis, and the z-axis are orthogonal to
`each other. In an alternative embodiment, substrate 14 maybe
`configured to movein the horizontal x-y plane within build
`chamber 12, and extrusion head 18 maybe configured to
`movealong the z-axis. Other similar arrangements may also
`
`SUMMARY
`
`[0006] The presentinventionrelatesto a liquefier assembly
`for use in an extrusion-based digital manufacturing system,
`an extrusion head containing the liquefier assembly, and a
`method of building a 3D object with the extrusion-based
`digital manufacturing system. The liquefier assembly
`includesa liquefier tube having a sidewall, an inlet opening
`configured to receive a filament strand, an outlet opening, and
`a port disposed throughthe sidewallat a location between the
`inlet opening and the outlet opening, where theport is con-
`
`8
`
`

`

`US 2009/0273122 Al
`
`Nov. 5, 2009
`
`be used suchthat one or both of substrate 14 and extrusion
`ead 18 are moveable relative to each other.
`
`
`
`[0018] Extrusion head 18 is supported by gantry 16 for
`building 3D object 26 and support structure 28 on substrate 14
`in a layer-by-layer manner, based on signals provided from
`he computer-operated controller. In addition to liquetier
`assembly 22, extrusion head 18 also includes drive mecha-
`ism 30 engaged with liquefier assembly 22, where drive
`nechanism 30 feeds successive portions of filament 24
`hroughliquefier assembly 22 from filament supply source
`20. Liquefier assembly 22 thermally melts the successive
`portionsof filament 24, thereby allowing the molten material
`0 be extruded to build 3D object 26 or support structure 28.
`For ease of discussion, extrusion head 18 is shown in FIG. 1
`with a single liquefier(1.e., liquefier assembly 22) anda single
`filament drive mechanism (1.e., drive mechanism 30). How-
`ever, extrusion head 18 mayinclude multiple filamentdrive
`mechanismsandliquefiers for extruding multiple build and/
`or support materials.
`[0019]
`Filament supply source 20 is a supply source(e.g., a
`spooled container)
`for filament 24, which is desirably
`retained at a remote location from build chamber 12. Filament
`
`
`
`cylindrical geometries, elliptical geometries, polygonal
`geometries(e.g., rectangular and square geometries), axially-
`tapered geometries, andthe like. Liquefier tube 32 includes
`sidewall 38, inlet opening 40, and an outlet opening (not
`shown in FIG. 2) that is opposite from inlet opening 40.
`Sidewall 38 is the circumferential, thin-wall portion oflique-
`fier tube 32 that has a longitudinal length along axis 42, andis
`desirably formed from a metallic material (e.g., stainless
`steel). Inlet opening 40 is an openingata first end of sidewall
`38 along axis 42, which is configured to receive filament 24
`from filament supply source 20 (shownin FIG. 1). Theoutlet
`openingof liquefier tube 32 is an opening at a second end of
`sidewall 38 along axis 42 that allows the molten material of
`filament 24to exit liquefier tube 32 through extrusiontip 36.
`[0022] Thermal block 34 is a heat transfer componentthat
`extends arounda portion ofliquefier tube 32, andis config-
`ured to generate a thermal gradient along axis 42. Examples
`of suitable heat transfer components for thermal block 34
`includethose disclosed in Swansonet al., U.S. Pat. No. 6,004.
`124; Comb, U.S. Pat. No. 6,547.995; and LaBossiereet al..
`USS. Publication No. 2007/0228590. In alternative embodi-
`
`ments, thermal block 34 maybe replaced with a variety of
`different heat transfer components that generate thermal gra-
`24 is a filament strand of a build or support material for
`dients along axis 42 (e.g., conductive, convective, and induc-
`building 3D object 26 or support structure 28, respectively.
`tive heat transfer components). The thermal gradient gener-
`The dimensions of filament 24 may vary depending on the
`ated by thermal block 34 creates a temperature profile in
`material of filament 24, and on the dimensionsofliquefier
`filament 24 along axis 42, which melts successive portions of
`assembly 22 and drive mechanism 30. Examples of suitable
`filament 24 as filament24 is driven through liquefier tube 32.
`average diameters for filament 24 range from about 1.143
`The properties of the generated thermal gradient may vary
`millimeters (about 0.045 inches) to about 2.54 millimeters
`depending on the material and feedrate of filament 24, and
`(about 0.100 inches). Suitable assembliesfor filament supply
`source 20 and suitable filament strands for filament 24 are
`desirablyallow the unmelted portion offilament 24 to func-
`tion as a piston with a viscosity-pump action to extrude the
`disclosed in Swanson et al., U.S. Pat. No. 6,923,634 and
`molten portionout of extrusiontip 36.
`Combet al., U.S. Pat. No. 7,122,246. While the materials of
`[0023] Extrusion tip 36 is a small-diametertip that is desir-
`filament 24 are discussed herein as being build materials and
`ably secured to sidewall 38 at the outlet opening of sidewall
`support materials, suitable materials for use with extrusion
`36, and is configured to extrude the molten material offila-
`ead 18 include any type of extrudable material (e.g., ther-
`ment 24 witha desired road width.In one embodiment, extru-
`moplastic materials).
`sion tip 36 is removably securable to sidewall 38, thereby
`[0020] Duringabuild operation,gantry 16 moves extrusion
`allowing multiple extrusion tips 36 to be interchangeably
`ead 18 around in the horizontal x-yplane within build cham-
`used. Examples of suitable inner tip diameters for extrusion
`ber 12, and drive mechanism 30 is directed to feed successive
`tip 36 range from about 125 micrometers (about 0.005 inches)
`portions offilament 24 through liquefier assembly 22 from
`to about 510 micrometers (about 0.020 inches).
`filament supply source 20. As shown, the feed pathway of
`filament 24 between filament supply source 20 and extrusion
`[0024] Drive mechanism 30 includes support plate 44, base
`ead 18 is desirably curved. Assuch, filament 24 desirably
`block 46, and pulley 48, where pulley 48 is rotatably secured
`ters liquefier assembly 22 in a curved orientation. As dis-
`between support plate 44 and base block 46. Support plate 44
`ussed below, the curved orientation reduces the axial rota-
`and base block 46 are support components of drive mecha-
`tion offilament 24 as drive mechanism 30 feeds the succes-
`nism 30, and oneor bothof support plate 44 and base block 46
`sive portions offilament 24 through liquefier assembly 22.
`are desirably secured to extrusion head 18 (shownin FIG.1).
`Thereceived portions offilament 24 are melted within lique-
`Pulley 48 is a rotatable component that drives successive
`fier assembly 22, and the upstream, unmelted portions of
`portionsoffilament 24 throughliquefier tube 32 with the use
`filament 24 functionas a piston with a viscosity-pumpaction
`of an internally-threaded surface (not shown in FIG. 2).
`to extrude the molten material out of extrusion head 18.
`Examples of suitable filament drive mechanismsfor drive
`Examples ofsuitable extrusion rates from extrusion head 18
`mechanism 30 include those disclosed in U.S. patent appli-
`based onthe driverate offilament 24 from drive mechanism
`cation Ser. No.
`. entitled “Filament Drive Mechanism
`
`30 include rates up to about 6,000 micro-cubic-inches/second
`ForUseIn Extrusion-Based Digital Manufacturing Systems”
`(mics).
`(attorney docket no. $697.12-118), where liquefier tube 32
`functions as the ported filaments tube of the filament drive
`FIG. 2 is a top perspective view ofliquefier assem-
`[0021]
`mechanisms. As such, liquefier assembly 22 is engaged with
`bly 22 in use with drive mechanism 30. As shown,liquefier
`drive mechanism 30, and thermal block 34 maybe securedto
`assembly 22 includes liquefier tube 32, thermal block 34, and
`base block 46.
`extrusiontip 36, where liquefier tube 32 is a hollowtube that
`extends through drive mechanism 30 and thermal block 34,
`and is configuredto receivefilament 24 (shown in FIG. 1). As
`used herein, the term “tube” includes a variety of hollow
`geometries that allow filament 24 to pass through, such as
`
`
`
`
`
`
`
`c
`
`e C
`
`In alternative embodiments, pulley 48 may be
`[0025]
`replaced with a variety ofdifferent rotatable components that
`have internally-threaded surfaces, thereby allowing alterna-
`tive rotatable componentsto drivefilament 24. For example,
`
`9
`
`

`

`US 2009/0273122 Al
`
`Nov. 5, 2009
`
`pulley 48 may be replaced with a rotatable gearthat operably
`engages with one or more additional motor-driven gears (not
`shown) to drive filament 24. Examples ofsuitable rotatable
`gear configurations include spur, herringbone, bevel, sector,
`and combinations thereof. Alternatively, pulley 48 may be
`replaced with a friction-drive roller that operably engages
`with one or more additional motor-drivenrollers (not shown)
`to drive filament 24. Furthermore, pulley 48 may be replaced
`with a rotatable componentthatis axially connectedto a drive
`motor (not shown),
`thereby allowing the drive motor to
`directly rotate the rotatable component. For example, the
`rotatable component may bea threaded hollow shaft ofa drive
`motor, where filament 24 is driven by the rotation of the
`threaded hollow shaft.
`
`
`
`
`[0026] During a build operation in system 10 (shown in
`FIG. 1), filament 24 is loaded into liquefier tube 32 at inlet
`opening 40 to engage with the internally-threaded surface of
`pulley 48. Pulley 48 is then rotated (represented by arrow 50)
`based on signals provided from the computer-operated con-
`roller (not shown). Therotation ofpulley 48 correspondingly
`rotates the internally-threaded surface of pulley 48, which
`drives successive portionsof filament 24 through liquefier
`tube 32. As filament 24 passes through liquefier tube 32, the
`hermal gradient generated by thermal block 34 melts the
`naterial of filament 24 within liquefier tube 32. The
`pstream, unmelted portion of filament 24 being driven by
`drive mechanism 30 functions as a piston with a viscosity
`pump acting on the molten material between the unmelted
`portion and sidewall 38, thereby extruding the molten mate-
`rial out of liquefier tube 32 and extrusiontip 36. The extruded
`naterial is then deposited as roads to form 3D object 26
`shown in FIG. 1) or support structure 28 (shown in FIG. 1) in
`a layer-by-layer manner.
`[0027] As shown in FIG. 2, inlet opening 40 of liquefier
`tube 32 is located at an upstream position along axis 42
`relative to drive mechanism 30. As such, filament 24 enters
`liquefier tube 32 prior to engaging with drive mechanism 30,
`and is continuously supportedby filament tube 32 during and
`after the engagement with drive mechanism 30. This is in
`contrast to an extrusion head having a filament drive mecha-
`ism that is separate from the liquefier tube, wherethefila-
`nent drive mechanism engages anddrivesthe filamentstrand
`into the liquefier tube. In such an extrusion head, to ensure
`proper entry into the liquefier tube, the filament strand exiting
`he filament drive mechanismis typically required to be prop-
`erly aligned with the inlet openingofthe liquefier tube. Addi-
`ionally, the filament strand may potentially buckle underthe
`compression between thefilament drive mechanism and the
`inlet openingof the liquefier tube. Each of these issues may
`reduce the efficiency and accuracy of the extrusion head
`during a build operation. In contrast, as shown in FIG.2, the
`location of inlet opening 40(i.e., upstream from drive mecha-
`ism 30 along axis 42) effectively prevents these issues from
`occurring. This reducesthe risk of interrupting a build opera-
`ion with extrusion head 18, and may allow higher driving
`forces to be attained because filament 24 is supported from
`buckling.
`FIG. 3 is an exploded perspective view of liquefier
`[0028]
`assembly 22, whichillustrates the engagements betweenliq-
`efier tube 32, thermal block 34, and extrusion tip 36. As
`shown, liquefier tube 32 further includes outlet opening 52,
`interior surface 54, port 56, and thermal gradient region 58.
`Outlet opening 52 is the openingat the secondend of sidewall
`
`38 along axis 42 that allows the molten material offilament 24
`(shownin FIG.1)to exit liquefier tube 32 through extrusion
`tip 36.
`Interior surface 54 of sidewall 38 is the surface of
`[0029]
`sidewall 38 that laterally supports filament 24 whilefilament
`24 extends through liquefier tube 32. Interior surface 54 may
`include a low-surface energy coating to further reducefric-
`tion with filament 24. Suitable coating materials for interior
`surface 54 include fluorinated polymers(e.g., polytetrafluo-
`roethenes, fluorinated ethylene propylenes, and perfluoro-
`alkoxypolymers), diamond-like carbon materials, and com-
`binations thereof. As discussed below, due to the thermal
`gradient that is generated along the longitudinal length of
`sidewall 38 (1.c., along axis 42), the low-surface energy coat-
`ing is desirablyplaced along interior surface 54 at a location
`outside of thermal gradient region 58 (e.g., adjacent to port
`56) to reduce the risk of melting the low-surface energy
`coating. In one embodiment, interior surface 54 is smoothed
`and/or polished adjacentto port 56 to reduceslidingfriction,
`and mayalso include axial scoring along axis 42 adjacent to
`port 56 to further reduce axialrotation of filament 24.
`[0030] The outer diameter of sidewall 38 (referred to as
`outer diameter 60) desirably allows liquefier tube 32 to be
`inserted through support plate 44 (shown in FIG.2), pulley 48
`(shownin FIG. 2), and base block 46 (shownin FIG. 2), and
`to be retained by one or both of support plate 44 and base
`block 46. The inner diameter of sidewall 38 (referred to as
`inner diameter 62) is defined by interior surface 54 and may
`vary depending on the average diameteroffilament 24. Inner
`diameter 62 desirably allows filament 24 to pass through
`liquefier tube 32 without excessive frictional resistance(e.g.,
`about 5%to about 30%greater than the average diameter of
`filament 24). For example, for filament 24 having an average
`filament diameter of about 1.78 millimeters (about 0.070
`inches), suitable average inner diameters 62 for sidewall 38
`range from greater than about 1.78 millimeters (about 0.070
`inches) to about 2.54 millimeters (about 0.100 inches), with
`particularly suitable average inner diameters ranges from
`about 2.03 millimeters (about 0.080 inches) to about 2.29
`millimeters (about 0.090 inches). Examples of suitable aver-
`age wall
`thicknesses for sidewall 38 (i.e.,
`the difference
`between outer diameter60 and inner diameter62) range from
`about 0.127 millimeters (about 0.005 inches) to about 1.02
`millimeters (about 0.040 inches), with particularly suitable
`average wall thicknesses ranging from about 0.254 millime-
`ters (about 0.010 inches) to about 0.508 millimeters (about
`0.020 inches).
`[0031]
`Port 56 is an opening in sidewall 38 at a location
`between inlet opening 40 and outlet opening 52, andis desir-
`ably located adjacentto inlet opening 40 to provide a suitable
`length along sidewall 38 for thermal gradient region 58. As
`discussed below,port 56 allows pulley 48 (shownin FIG.2)
`to engage with filament 24 after filament 24 is loaded into
`liquefier tube 32. This allowsthe internally-threaded surface
`(not shown)ofpulley 48 to drive filament 24 through liquefier
`tube 32 toward thermal gradient region 58.
`[0032] The dimensionsof port 56 may vary depending on
`the dimensions of filament 24 and on the filament drive
`
`mechanism used (e.g., drive mechanism 30). For example, the
`length ofport 56 along the longitudinal length of sidewall 38
`(referred to as length 64) may vary depending on the dimen-
`sions of the internally-threaded surface of pulley 48.
`Examples of suitable lengths 64 for port 56 along axis 42
`range from about 1.25 millimeters (about 0.05 inches) to
`
`10
`
`10
`
`

`

`US 2009/0273122 Al
`
`Nov. 5, 2009
`
`about 25.0 millimeters (about 1.0 inch), with particularly
`suitable lengths 64 ranging fromabout 5.1 millimeters (about
`0.2 inches) to about 12.7 millimeters (about 0.5 inches). Fur-
`thermore, the angle ofthe radial openingof port 56, as taken
`from a cross section of sidewall 38 that is normalto axis 42,
`mayalso vary depending on the engagement between the
`internally-threaded surface of the pulley 48 and filament 24.
`Examples of suitable angles for the radial opening of port 56
`range from about 90 degrees to about 180 degrees, with
`particularly suitable angles ranging from about 130 degrees
`to about 160 degrees.
`[0033] Thermal gradient region 58 is a region along the
`longitudinal length of sidewall 38 in which the thermal gra-
`dient generated by thermal block 34 (shownin FIG.2)exists.
`Thermal gradient region 58 desirably extends along thelon-
`gitudinal length of sidewall 38 belowport 56, thereby pre-
`venting filament 24 from melting while engaged with pulley
`48. Accordingly,
`thermal gradient
`region 58 desirably
`extends along the longitudinal length of sidewall 38 between
`port 54 and outlet opening 52. The desired length ofsidewall
`38 along axis 42 for thermal gradient region 58 to exist,
`between port 56 and outlet opening 52 (referred to as length
`66), may vary depending on the heat transfer properties of
`thermal block 34, the wall thickness and material of sidewall
`38, and the thickness, material, and drive rate offilament 24.
`Examples of suitable lengths 66 along axis 42 range from
`about 25 millimeters (about 1.0 inch) to about 250 millime-
`ers (about 10 inches), with particularly suitable lengths 66
`ranging from about 50 millimeters (about 2.0 inches) to about
`130 millimeters (about 5.0 inches). In one embodiment,
`extrusion head 18 (shown in FIG.1) also includes an airflow
`nanifold (not shown) configured to direct cooling air toward
`inlet opening 40 and/orport 56 to furtherreducethe risk ofthe
`hermalgradient affecting filament 24 at port 56.
`[0034] As further shown in FIG. 3,
`thermal block 34
`includes channel 68, whichis an openingthat extends through
`hermalblock 34 for receiving andretainingliquefier tube 32.
`During the assemblyof liquefier assembly 22, liquefier tube
`32 is secured within channel 64 of thermal block 34 suchthat
`port 56 extends above thermal block 34. As discussed above,
`his desirablyrestricts thermal gradient region 58 to a location
`below port 56. Liquefier tube 32 may be secured within chan-
`el 64 of thermal block 34 in a variety of manners. In one
`embodiment, thermal block 34 is separated (or otherwise
`opened) to allow direct access to channel 68. Liquefier tube
`32 maythenbe inserted within channel 68, and thermal block
`maybe reassembled (or otherwise closed) to provide good
`thermally-conductive contact between liquefier tube 32 and
`
`thermal block 34. Extrusiontip 36 is also secured to sidewall
`38 at outlet opening 52. Liquetier assembly 22 may then be
`secured to drive mechanism 22 for use in extrusion head 18.
`
`
`
`FIG. 41s a side view of liquefier tube 32 in use with
`[0035]
`pulley 48 of drive mechanism 30 (shown in FIG.2) for melt-
`ing and extruding material of filament 24 to build 3D object
`26. Thermal block 34 of liquefier assembly 22, and support
`plate 44 and base block 46 ofdrive mechanism 30 are omitted
`in FIG.4 for ease ofdiscussion. As shown,pulley 48 includes
`inner surface 70, which is the internally-threaded surface of
`pulley 48 and is engaged with filament 24 at port 56.
`Examples of suitable internally-threaded surfaces for inner
`surface 70, and suitable engagements betweenfilament 24
`and inner surface 70 at port 56 are disclosed in U.S. patent
`
`application Ser. No.
`, entitled “Filament Drive
`
`Mechanism For Use In Extrusion-Based Digital Manufactur-
`ing Systems”(attorney docket no. $697.12-118).
`[0036] During the build operation to form 3D object 26,
`filament24 is loaded into liquefier tube 32 at inlet opening 40.
`Asdiscussed above, filament 24 desirably entersinlet open-
`ing 40 in a curved orientation due the curved feed pathway
`between filament supply source 20 (shownin FIG. 1) and
`liquefier tube 32. Examples of suitable average angles “a”for
`the curved orientation of filament 24 range from about 5
`degrees to about 60 degrees, with particularlysuitable aver-
`age angles @ ranging from about 10 degrees to about 30
`degrees, where the average angle a is measured between the
`longitudinal length of liquefier tube 32 (.e., along axis 42)
`and a line thatis tangent to the curvatureoffilament 24, and
`where the tangentialline is taken at a point along filament 24
`that is adjacentto liquefier tube 32 andprior to entering inlet
`opening 40. As discussed below, the curved orientation of
`filament 24 reduces the axial rotation of filament 24 while
`passing through liquefier tube 32.
`[0037]
`Therotation of pulley 48 allows inner surface 70 to
`drive successive portionsoffilament 24 downward along axis
`42 through liquefier tube 32 toward thermal gradient region
`58. While passing throughliquefier tube 32 at thermal gradi-
`ent region 58, the thermal gradient generated by thermal
`block 34 (shown in FIGS. 2 and 3) melts the material of
`filament 24 to an extrudable state. The unmelted, successive
`portion offilament 24, located upstream from thermal gradi-
`ent region 58, is driven by pulley 48 andinner surface 70, and
`functions as a piston with a viscosity pump acting on the
`molten material between the unmelted portion and sidewall
`38, thereby extruding the molten material of filament 24
`through extrusion tip 36. The extruded materialis then depos-
`ited as roads to build 3D object 26 ina layer-by-layer manner.
`[0038] As discussed above, inlet opening 40 of liquefier
`tube 32 is located at an upstream position along axis 42
`relative to pulley 48. As such,filament 24 entersliquefier tube
`32 prior to engaging with inner surface 70, and is continu-
`ously supported by liquefier tube 32 during and after the
`engagement with inner surface 70. This effectively eliminates
`the potential issues that may occur with extrusion heads hav-
`ing separate filament drive mechanismsandliquefiers(e.g.,
`filament alignment andfilament buckling), thereby reducing
`the risk of interrupting a build operation with extrusion head
`18 (shown in FIG.1).
`[0039]
`FIG. 5isa side viewof liquefier tube 32 in use with
`rotatable shaft 72 of an alternative filament drive mechanism
`
`for melting and extruding material offilament 24 to build 3D
`object 26. Thermalblock 34 ofliquefier assembly22 1s omit-
`ted in FIG. 5 for ease of discussion. In this embodiment.
`rotatable shaft 72 includes threaded surface 74, whichis an
`externally-threaded surface engaged with filament 24 at port
`56. The rotation of rotatable shaft 72 allows threaded surface
`74 to drive successive portions of filament 24 downward
`along axis 42 through liquefier tube 32 toward thermalgra-
`dient region 58. The material of filament 24 is then melted in
`liquefier tube 32 at thermalgradientregion 58, thereby allow-
`ing the molten materialto be extrudedfrom extrusion tip 36 to
`build 3D object 26 in a layer-by-layer manner.
`[0040]
`In this embodiment, inlet opening 40 of liquefier
`tube 32 is located at an upstream position along axis 42
`relative to threaded surface 74. As such, filament 24 enters
`liquefier tube 32 prior to engaging with threaded surface 74,
`and is continuously supported byliquefier tube 32 during and
`after the engagement with threaded surface 74. This effec-
`
`11
`
`11
`
`

`

`US 2009/0273122 Al
`
`Nov. 5, 2009
`
`tively eliminates the potential issues that may occur with
`extrusion heads having separate drive mechanismsandlique-
`fiers
`(e.g.,
`filament alignment and filament b ckling).
`Accordingly, liquefier assembly 22 is suitable for use with a
`variety of different filament drive mechanisms, where the
`filament drive mechanisms engagefilament 24 after filament
`24 is supported by liquefier tube 32 (e.g., at port 56).
`se with
`[0041]
`FIG.6 is a side view ofliquefier tube 132 in
`roller 176 of an additional alternative filament drive mecha-
`
`nism for melting and extruding material of filament 24 to
`be of an
`build 3D object 26. Liquefier tube 132 is a liquefier t
`alternative liquefier assembly
`to liquefier assembly 22
`(shown in FIGS. 1-5), where respective reference labels are
`increased by “100”, and the thermal block corresponding to
`thermal block 34 (shown in FIGS. 2 and 3) is omitted in FIG.
`6 for ease ofdiscussion.
`
`[0042]
`In the embodiment shownin FIG.6, liquefier tube
`132 includes port 156 in lieu of
`port 56 (shown in FIGS. 3-5),
`whereport 156 has dimensions that accommodate the cylin-
`Roller 176 is rotatable roller
`drical geometry ofroller 176.
`configured to engage filament
`24 at port 156, and to drive
`filament 24 downward along axis 142 through liquefier tube
`132 toward thermalgradient region 158. In one embodiment,
`roller 176 includes one or more topographical features to
`assist in gripping anddriving filament 24. For example,roller
`176 may be a knurledroller as disclosed