WO2016090164A1

WO2016090164A1 - Improved filament for fused deposit modeling

Info

Publication number: WO2016090164A1
Application number: PCT/US2015/063788
Authority: WO
Inventors: Stephen F. HESTON; Anna TOTARO; Sunil Ramachandra
Original assignee: Fenner U.S., Inc.
Priority date: 2014-12-03
Filing date: 2015-12-03
Publication date: 2016-06-09

Abstract

An apparatus for forming an object by an additive process, commonly referred to as 3-D printing, is provided. The apparatus includes a composite filament comprising a soft core surrounded by a harder jacket that provides columnar support to increase the axial rigidity of the filament, a nozzle depositing a layer of melted material onto a surface and a feeder feeding the filament to the nozzle. A heating element melts the filament and a controller controls the position of the nozzle in a plane to control the configuration of the layer of melted material deposited by the nozzle. Additionally, a method for forming polymer filament used in 3-D printing devices is also provided. The method includes the steps melting a first material, wherein the first material comprises a polymer, extruding the first material to produce an elongated core and forming a layer of second material onto the core to form a coated filament, wherein the second material is harder than the first material.

Description

Improved Filament for Fused Deposit Modeling

Field of the invention

[001 ] This application claims priority to U.S. Provisional Patent Application No.

62/087,195, filed on December 3, 3014. The entire disclosure of the foregoing application is hereby incorporated herein by reference.

[002] The present invention relates to the field of additive manufacturing

technology commonly referred to as fused deposition modeling or fused filament fabrication. More specifically, the present invention relates to an additive manufacturing technology using low durometer materials having improved characteristics for feeding the materials.

Background

[003] The use of fused deposition modeling or fused filament fabrication, which are collectively referred to as FFF herein, have grown rapidly in the 21 ^st century and show promise in a variety of fields. Commonly referred to as 3-D printing, these additive manufacturing techniques build 3-dimensional components layer by layer. A variety of materials can be used in the field of FFF, but acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) are the predominant materials used. ABS and PLA have properties that work well in the FFF process, but the materials tend to be rigid, resulting in products that are brittle at room temperature.

[004] On the other hand, materials such as polyurethanes, silicones, and certain nylon compositions generally provide a broader range of mechanical properties, such as reduced modulus, higher elasticity, and reduced brittleness. However, in many cases the elasticity and reduced stiffness of these materials cause difficulties in many FFF machines. For this reason, despite the advantages for the resulting product, these materials are not yet widely used in FFF machines.

Summary of the Invention

[005] In light of the foregoing, the present invention provides low durometer elastomer materials that work efficiently with known additive manufacturing machines, such as FFF machines. In one aspect, the present invention provides a filament for use with an additive manufacturing machine. The filament may be formed of multiple materials. For instance, the filament may comprise an outer jacket formed around an inner core. The inner core may be a more flexible material, while the outer jacket may be more rigid.

Alternatively, or additionally, the outer surface of the filament may have a reduced tackiness to improve the ability to feed the filament through the FFF machine. For instance, the filament may have a core of low durometer thermoplastic material within a coating formed of a higher durometer material. Additionally, the outer jacket and the inner core may be formed from materials having similar glass transition temperatures.

[006] In yet another aspect, the present invention comprises a method of using a thermoplastic filament having a core formed of a first material and a jacket surrounding the core formed of a second material. The second material may be harder than the first material. Alternatively, or additionally, the second material may be more rigid than the first material. Alternatively or additionally, the first and second materials may have similar glass transition temperatures. The method comprises the steps of feeding the filament into a nozzle, melting the core and jacket of the filament, and selectively controlling the position of the nozzle relative to a platform to deposit a plurality of layers of melted materials to produce a three-dimensional item.

[007] In yet another aspect, the present invention provides a system for

producing an object by an additive process. The system includes an elongated filament comprising a central core of a first material and an outer coating formed of a second material. The second material may be harder than the first material. Alternatively, or additionally, the second material may be more rigid than the first material. Alternatively or additionally, the first and second materials may have similar glass transition temperatures. The system may include a nozzle, a feeder for feeding the filament to the nozzle and a heating element for melting the filament into a melted material. A controller controls the position of the nozzle to control the configuration of the layer of melted material deposited by the nozzle. Specifically, the controller may control the operation of the feeder and the position of the nozzle to build a series of layers of melted material to form a three-dimensional object.

Description of the Drawings

[008] The foregoing summary and the following detailed description of the

preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which:

[009] Fig. 1 is a side view of a system for creating three-dimensional objects; and

[010] Fig. 2 is an enlarged fragmentary view of an extrusion head of the system illustrated in Fig. 1 ;

[01 1 ] Fig. 3 is a diagram illustrating stress/strain curves of various filament

materials; and

[012] Fig. 4 is an enlarged cross-section view of a filament illustrated in the

system of Fig. 1 .

Detailed Description of the Invention

[013] Referring now to the figures in general, a system for creating three- dimensional objects by depositing multiple layers of material is designated generally 10. The system includes a head 20 for selectively depositing melted material 85 onto a support element, such as a planar platform or other stage (not shown). A length of feedstock 80 is fed to the head 20, which melts the feedstock. The melted material 85 is then deposited in a series of layers to build the object as discussed further below.

[014] The system 10 can be any of a variety of additive manufacturing systems.

The system 10 may include a controller for controlling the operation of the head 20 to form an object based on an electronic model of the object. For instance, the electronic model may break the object down into a series of layers. The controller controls the operation of the head to selectively deposit material in accordance with the series of layers that form the electronic model. For instance, the controller may comprise a computer or other microprocessor controlled device that controls the operation of actuators, such as one or more motors that drive the head 20 along two axes in a plane. In this way, the controller controls the position of the head 20 to control where each layer of material is deposited onto a platform or table. By depositing sequential layers of material the system progressively builds the object from numerous layers of deposited material. Alternatively, rather than controlling the position of the head, the system can be configured to move the platform relative to the head 20. In either instance, the system controls the position of the head relative to the platform.

[015] Although the system 10 may be one of a variety of additive manufacturing systems, in the present instance the system is one that includes an extrusion head for extruding the material that forms the object. For instance, the system may be a fused deposition modeling device or fused filament fabrication device, such as one or several systems commonly referred to as a 3-D printing device that extrude thermoplastics and other materials.

[016] Referring to Fig. 2, the details of the head 20 will be described in greater detail. In the present instance, the head is an extrusion head 20 having an input for receiving feedstock 80 that is extruded through a nozzle 30. A feeder 50 positively engages the feedstock to drive the feedstock toward the nozzle 30 in response to signals received from the controller to control the discharge of extruded material from the extrusion head 20.

[017] The feeder 50 includes a drive wheel 52 and an opposing idler wheel 54.

The idler wheel 54 is mounted on a pivot arm 55 that pivots around a pivot axis 56. A biasing element 58 biases the arm 55 to bias the idler wheel 54 toward the drive wheel 52. In this way, the drive wheel 52 and idler wheel 54 form a nip to positively engage the feedstock 80. The drive and idler wheels 52, 54 are rotatable wheels so that the wheels rotate as the feedstock is driven through the nip. In the present instance, the drive wheel 52 positively engages the feedstock to drive the feedstock forwardly. For example, the drive wheel may include a plurality of engagement teeth spaced around the circumference of the drive wheel as shown in Fig. 2. The engagement teeth have edges that dig into or bite the feedstock so that rotating the drive wheel drives the material forwardly toward the nozzle 30. Alternatively, the drive wheel 52 may have a different mechanism for engaging the feedstock. For instance, the drive wheel may have a high-friction surface to frictionally engage the feedstock.

[018] Operation of the drive wheel 52 is controlled by a positional controller. For instance, in the present instance a motor 60 such as a stepper motor selectively drives the drive wheel 52. The motor 60 receives signals from a controller, such as the central controller controlling operation of the system. In this way, the motor 60 selectively drives the drive wheel 52 to control the feeding of the feedstock to thereby control the flow of melted material exiting the nozzle 30.

[019] The feeder 50 drives the feedstock 80 through a barrel that extends to the nozzle 30. The nozzle 30 includes a discharge orifice 32 through which the extruded material 85 exits the extrusion head 20. A heating element 35 at the nozzle is operable to heat the feedstock 80 to an elevated temperature above ambient temperature so the material can be extruded through the nozzle. A heat sink 40 is operable to limit the transfer of heat to the feedstock before the feedstock enters the nozzle 30 so that the feedstock does not start to melt before entering the nozzle. The heatsink also limits of transfer of heat from the nozzle to other components of the extrusion head 20.

[020] Referring again to Fig. 1 , in the present instance the feedstock 80

comprises an elongated element, such as a filament. The filament 80 may be formed into a variety of shapes, however in the present instance the filament is a substantially cylindrical solid filament. A variety of diameters may be used depending on various factors such as the material from which the filament is formed. In the present instance, the filament 80 is approximately 2 mm in diameter.

[021 ] The filament 80 may be wound onto a spool 90 to provide a substantially constant supply of material to the extrusion head 20. The spool may be any of a variety of configurations. For instance, the spool may include a central hub or axle around which the material is wound. The hub may be cylindrically shaped or it may comprise a shaped having a non-circular cross-section. Additionally, the spool may include flanges that project radially outwardly away from the hub. For instance, the flanges may be circular as shown in Fig. 1 . The flanges may be spaced apart from one another so that the flanges form sidewalls. In this way, the filament may be wound around the central hub between the flanges. The flanges may form end walls to protect the filament wound around the hub. As the feeder 50 drives the filament forwardly toward the nozzle 30, the feeder pulls the filament from the spool. The filament extends through a hollow feed tube 70 that guides the filament as the filament extends from the spool 90 to the extrusion head 20.

[022] Referring to Fig. 4, the filament may be formed of a variety of materials, however, in the present instance, the filament 80 comprises a core 84 of a first material surrounded by a coating or jacket 82 of a second. For instance, in the present instance the core 84 may be formed of a low durometer material, having one or more of the following materials: silicone, rubber, nylon and/or thermoplastic, such as polyurethane. For instance, the core material may be primarily formed from a material having a durometer of less than approximately 50 Shore D and greater than approximately 60 Shore A. In particular, the durometer of the core material may be less than 90 on the Shore A scale and in the present instance is 85 on the Shore A scale. Such low durometer materials tend to have tacky surfaces so that the materials have a generally high coefficient of friction relative to materials such as ABS and PLA.

Additionally, such low durometer materials tend to be much less rigid.

[023] The filament 80 is coated or jacketed by a layer of second material 82 that may have one or more characteristics that are different than the first material from which the core is formed. For instance, the second material may be more rigid than the first material. Alternatively, or additionally, the second material may be harder than the first material. Alternatively or additionally, the second material may have greater tensile strength. Alternatively or additionally, the second material may have greater tensile strength. Alternatively or

additionally, the second material may have a lower coefficient of friction than the core material. Additionally, the second material may have a glass transition temperature that is similar to the glass transition temperature of the first material.

[024] For example, the jacket may be formed of a more rigid material so that the jacket 82 increases the axial rigidity of the filament to reduce the likelihood that the filament will buckle during feeding of the filament to the extrusion head 50. Additionally, the jacket may have a lower coefficient of friction than the core material to limit the pull force necessary to draw the filament from the spool. Preferably, the thickness of the jacket is substantially uniform along the length of the filament so that the cross-section of the filament is substantially uniform along the length of the filament. ] The jacket 82 may be formed of a variety of thermoplastic polymers, including, but not limited to acrylonitrile butadiene styrene ("ABS"), polylactic acid ("PLA"), polyvinyl alcohol ("PVA"), nylon, polystyrene, and polycarbonate. The jacket material is selected to provide a columnar support element, increasing the rigidity of the filament. The jacket thickness may vary depending on the thickness of the filament and the materials used. In the present instance, the jacket thickness is minimized to reduce the percentage that the jacket forms of the overall filament material, while still providing the desired axial rigidity. For instance, for a 1 .75 mm diameter filament, the thickness of the jacket may vary from 0.025 mm to 0.25 mm, so that the coating is between approximately 5% and 50% of the overall composition of the filament. In the present instance, the thickness of the jacket is between 0.05 mm and 0.2 mm, so that the coating is between approximately 1 1 % and 40% of the overall composition of the filament. More specifically, the thickness of the jacket may be between 0.1 0 mm and 0.15 mm. In particular, the thickness of the jacket may be approximately 0.130 mm. [026] In the present instance, the filament 80 is a composite filament formed of more than one layer. For instance, as described above, the inner core 84 may be formed of a relatively soft material, such as a polyurethane having a durometer of less than approximately 50 Shore D. In particular, the durometer of the core material may be greater than approximately 60 and less than 90 on the Shore A scale and in the present instance is between 80 and 90 on the Shore A scale. The inner core is surrounded by a jacket formed of a material that is harder that the core material. For instance, the jacket 82 may be formed of PLA or ABS having a hardness of over 40 Shore D/90 Shore A. In particular, the jacket material 82 may be formed of material having a hardness of over 50 Shore D/100 Shore A.

[027] Additionally, the jacket 82 may be formed of a material having a different solubility than the material forming the core. For instance, the jacket 82 may be formed from polyvinyl alcohol (PVA) that is a water-soluble synthetic polymer and the core may be formed of thermoplastic polyurethane, which is not soluble in water. When the jacket is formed of a material having a different solubility than the core material, preferably the jacket material is soluble in water and the core material is insoluble in water. However, it should be understood that solvents other than water may be used. In such applications, the jacket material is soluble in the in the solvent, while the core material is not soluble in the solvent in which the jacket material is soluble.

[028] As discussed above, the filament may comprise an inner core formed of a first material and an outer jacket formed of a first material. The first material may be a generally flexible and/or resilient material, while the second material may be a more rigid material to provide increased columnar strength. For instance, the first material may have a Young's modulus that is significantly lower than the Young's modulus of the second material. In particular, the Young's modulus of the second material may more than twice the Young's modulus of the first material. More specifically, the Young's modulus of the second material may be more than five times the Young's modulus of the first material. Further still, the Young's modulus of the second material may be more than ten times the Young's modulus of the first material. The resulting filament has a rigidity that is stiffer than the first material, but not as stiff as the second material. For instance, the composite filament may have a Young's modulus that is at least twice as great as the Young's modulus of the first material, but is less than the Young's modulus of the second material. More specifically, the Young's modulus of the composite filament may have a Young's modulus that is more than five times the Young's modulus of the first material, but is less than the Young's modulus of the second material.

Preferably, the Young's modulus of the composite filament is at least approximately 40% less than the Young's modulus of the second material. In fact, the Young's modulus of the composite filament may be 50% less than the Young's modulus of the second material. Further still, the Young's modulus of the composite filament may be less than 50% of the Young's modulus of the second material. [029] The first material may have an ultimate tensile strength (i.e. the maximum stress the material can withstand before breaking) that is less than the ultimate tensile strength of the second material. More specifically, the ultimate tensile strength of the second material may be at least twice the ultimate tensile strength of the first material. Further still, the ultimate tensile strength of the second material may be at least five times the ultimate tensile strength of the first material. In particular, the ultimate tensile strength of the second material may be ten times the ultimate tensile strength of the first material. In this way, the ultimate tensile strength of the second material may be between two and ten times the ultimate tensile strength of the first material. In particular, the ultimate tensile strength of the second material may be between five and ten times the ultimate tensile strength of the first material. In this way, the ultimate tensile strength of the composite material is greater than the ultimate tensile strength of the first material and less than the ultimate tensile strength of the second material. For instance, the ultimate tensile strength of the composite filament may be at least twice the ultimate tensile strength of the first material and less than the ultimate tensile strength of the second material. In particular, the ultimate tensile strength of the composite filament may be three times the ultimate tensile strength of the first material. In fact, the ultimate tensile strength of the composite filament may be more than five times the ultimate tensile strength of the first material.

[030] The first material may have an ultimate elongation that is greater than the ultimate elongation of the second material. Ultimate elongation is the maximum increase in length a material can withstand before breaking. For instance, the first material may have an ultimate elongation that is at least 25% greater than the second material. In particular, the first material may have an ultimate elongation that is at least 50% greater than the second material.

Specifically, the first material may have an ultimate elongation that is 75% greater than the second material, and may be twice the ultimate elongation of the second material. In this way, the first material may have an ultimate elongation that is between 25% and 100% greater than the second material. More specifically, the first material may have an ultimate elongation that is between 25% and 75% greater than the second material. 1 ] Although the first material may have different characteristics than the second material, as described above, it may be desirable that the first and second materials have certain characteristics that are similar. For instance, it is desirable for the first and second materials to be thermoplastic materials. It is desirable that the first and second materials have similar glass transition temperatures, which is the temperature at which a material transitions between a hard state to a relatively rubbery or molten state, and is commonly referred to as the T_g temperature of a material. For instance, the glass transition temperature of the first material is within about 50 degrees C of the second material. Specifically, the glass transition temperature of the first material may be within 30 degrees C of the second material and may be within 20 degrees C. [032] As described above, the first and second material may have various characteristics. It should be understood that these characteristics may be chosen independently or they may be combined. For instance, the first material may have a hardness (e.g. durometer) and a stiffness (i.e. Young's modulus) that are both significantly less than the second material. Similarly, the first material may have a greater ultimate elongation than the second material, but a lower Young's modulus than the second material.

[033] Referring now to Fig. 3, a stress strain diagram is illustrated for filaments formed of a variety of materials. For instance, a composite filament having an overall diameter of 1 .75 mm may be formed of a core of a first material and a jacket of a second material. The jacket may be approximately 0.1 30 mm. The first material may have a Young's modulus of 3,500-4,000 PSI and a flexural modulus of 7,500-1 0,000 PSI. The first material may have a hardness of approximately 85 on the Shore A scale. The first material may have an ultimate elongation of approximately 550%. The first material may have an ultimate tensile strength of approximately 500-600 PSI. The first material may have a glass transition temperature of approximately -30 degrees C. For the jacket, the second material may have a Young's modulus of 50,000-60,000 PSI and a flexural modulus of 180,000-200,000 PSI. The second material may have a hardness of approximately 75 on the Shore D scale. The second material may have an ultimate elongation of approximately 330%. The second material may have an ultimate tensile strength of approximately 4,500-5,000 PSI. The second material may have a glass transition temperature of approximately -1 0 degrees C. In this way, the composite filament may have a Young's modulus of 20,000-30,000 PSI. The composite filament may have a hardness of 50-60 on the Shore D scale. The composite filament may have an ultimate tensile strength of 2,000 - 2700 PSI. It should be understood that the foregoing first and second material characteristics are meant by way of illustration and are not necessarily limits on the variety of characteristics which the first and second materials or the composite filament may have. 4] The stress strain curves in Fig. 3 show the stress strain curve of the composite filament formed of an inner core material and an outer shell or jacket material. The stress strain curves are also provided for a filament formed entirely of the first material and a filament formed entirely of the second material. These three curves are also compared against the stress strain curve for a filament formed of ABS. In particular, the stress strain curve in Fig. 3 shows the results for an exemplary filament formed from two thermoplastic polyurethane resins. The inner core is formed of an ester based thermoplastic polyurethane. The outer shell or jacket is formed of an aromatic polyether based thermoplastic polyurethane. The materials are co-extruded to form a composite filament in which the outer shell is bonded to the inner core. The filament has a diameter of 1 .75 mm and a jacket thickness of 0.130 mm.

However, it should be noted that these are exemplary materials and sizes and are not intended to limit the variety of materials that can be used to form the inner and outer elements of the composite filament. [035] As can be seen in Fig. 3, the core material generally remains in the elastic range throughout the entire curve, whereas, the jacket material and composite filament both have distinct elastic regions and plastic regions. The yield stress and ultimate tensile strength are both higher for the jacket material than for the composite filament.

[036] Configured as discussed above, the system 10 may be used to create a three-dimensional object as follows. A length of filament 80 is selected having a diameter of between 1 mm and 10 mm. More specifically, the diameter may be less than 5 mm. In particular, the diameter may be between 1 .5 mm and 3 mm and in the present instance, the diameter is either 1 .75 mm or 3.0 mm.

[037] The length of filament 80 is wound onto a spool 90 and the free end of the filament is fed into the feeder 50 of a deposition machine 10, such as an FFF. The FFF 10 is controlled by a controller having digital instructions to produce a three-dimensional object based on a digital model of the object to be produced The controller controls the feeder 50 to pull the filament from the spool. In the present instance, the filament is formed of a relatively low durometer material so that the teeth of the drive wheel 52 can dig into or deform the filament radially inwardly to positively engage the filament to feed the filament forwardly. In addition, the jacket material of the filament provides axial rigidity to prevent the filament from buckling as the drive wheel 52 urges the filament downwardly toward the extrusion head 20. [038] The feeder 50 feeds the filament through the extrusion head 20 to form a flow of melted material discharging from the nozzle 30 from melting the filament. The filament 80 melts in the extrusion head 20 so that both the jacket material and the core material of the filament melt together. The position of the nozzle 30 is controlled by the controller to move the nozzle within a plane to deposit a layer of melted filament 85 to form a layer of the three-dimensional object on a build platform. After depositing the first layer of material, the system then deposits a subsequent layer of melted filament to build-up a layer on the first layer. The process continues by building up successive layers on top of one another, with the pattern of material being deposited during each layer being controlled by the controller by moving the nozzle along two axes to control the position of the nozzle within a plane. When a layer is complete, the controller may then move the nozzle or the build platform along a third axes transverse the first two axes to raise or lower the nozzle relative to the build platform.

[039] After the three-dimensional object is completed, the object may be exposed to a solvent to alter the object. For instance, as described above, the filament may be formed of two materials each having different solubilities. For example, as described above, the filament jacket may be formed of PVA, which is water soluble, while the filament core may be formed of polyurethane, which is not water soluble. By exposing the object to a solvent the harder material (such as the jacket material) may be dissolved, thereby altering the rigidity of the object. More specifically, by dissolving the more rigid material, the flexibility of the object will be increased. In this way, the overall flexibility of the object can be increased after the object is formed using the FFF process.

[040] A method for producing the filament 80 used in a deposition machine 10, such as an FFF machine is also provided. The method provides a low- durometer extruded filament core having a jacket formed from a material that is harder than the core material.

[041 ] The method of producing the filament comprises the step of melting a

polymer to form the core. In particular, the polymer used to make the core is selected to be a low durometer material having less than Shore 50D or between Shore 60A and 90A. For instance, the polymer may be thermoplastic urethane or silicone. Additionally, the polymer may be a mixture of polymeric materials. In the present instance, the filament may be substantially formed of thermoplastic elastomers, such as urethane, meaning that the filament is at least 50% thermoplastic elastomer, and more preferably is at least 70% thermoplastic elastomer, and most preferably is at least 90% thermoplastic elastomer.

[042] The melted material is fed to an extrusion die according to any of a variety of known processes for feeding material to an extrusion die. In the present instance, the extrusion die comprises a capillary die having a round die opening. The feeder feeds the melted polymer to the die head so that the polymer is extruded from the die to form a cylindrical filament. A puller pulls the extrusion to maintain tension on the filament as it emerges from the extrusion die. For instance, the puller may comprise a pair of opposing belts forming a nip that engages the filament to pull the filament.

[043] The jacket may be applied to the core using a variety of processes. For instance, the jacket may be coextruded with the core. Alternatively, the jacket material may be spray coated onto the core. However, in the present instance, a coating head is used to apply the jacket to the core. Specifically, the core is fed through an inlet die of the coating head into a coating chamber that is filled with melted jacket material. The melted jacket material covers the core and the coated core then passes through an exit die having a round orifice that is larger than the core diameter.

[044] When the filament core emerges from the extrusion die, the core is at an elevated temperature. Similarly, when the filament emerges from the coating head, the core and jacket are at an elevated temperature (i.e. a temperature significantly above ambient air temperature). Accordingly, the core or core/jacket combination may be cooled by any of a variety of means, such as by pulling the core or core/jacket combination through a bath of cooling fluid, such as water. The core may be cooled before the jacket or the core and jacket combination may be cooled after the jacket is applied. After the core is cooled, the filament is wound onto a spool.

[045] Additionally, it is desirable to maintain a consistent profile for the filament. Accordingly, the process may include a mechanism for measuring a characteristic of the filament, such as the diameter of the filament. Any of a variety of mechanisms can be incorporated to measure the filament between the point that the filament emerges from the coating head and the filament is wound onto the spool. In the present instance, a non-contact gauge is used for measuring the diameter of the filament. For instance, the gauge may comprise a plurality of laser elements to measure the filament diameter.

[046] The gauge may automatically detect the diameter of the filament while the filament is moving through the processing line. For instance, it may be desirable to maintain the filament diameter within a tolerance of +/- 0.05 mm of the desired diameter, such as 1 .75 mm +/- 0.05 mm. Similarly, the gauge may be used to measure the roundness of the filament to monitor whether the cross section of the filament is round or oval. For instance, it may be desirable to maintain the filament roundness within a tolerance of +/- 0.07 mm.

[047] The gauge may provide a signal indicating that the filament diameter is above or below a pre-determined diameter. In response, the system may alter the speed of either the feeder feeding the melted material to the extrusion die or the system may alter the speed of the puller. Specifically, a central controller, such as a microprocessor may control either the feeder or the puller in response to signals from the gauge indicative of the filament diameter being above or below the pre-determined diameter. ] It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims.

Claims

1 . A filament for use in an apparatus for producing an object by an additive process having a heater for melting the filament, a feeder for feeding the filament to the heater, a nozzle for depositing the melted filament and a controller for controlling the position of the nozzle, wherein the filament comprises:

an elongated core formed of a first thermoplastic material; and

a jacket around the elongated core, wherein the jacket is formed of a

second thermoplastic material that is different from the first material, wherein the core and jacket are formed of materials having a melting point below 200 degrees centigrade.

2. The filament of claim 1 wherein the second material has a Young's modulus that is greater than 1 0,000 PSI and is greater than the Young's modulus of the first material.

3. The filament of claim 2 wherein the second material has a Young's modulus that is greater than 20,000 PSI.

4. The filament of claim 3 wherein the second material has a Young's modulus that is greater than 30,000 PSI.

5. The filament of claim 2 wherein the second material has a Young's modulus that is greater than 40,000 PSI.

6. The filament of claim 2 wherein the second material has a Young's modulus that is greater than 50,000 PSI.

7. The filament of any of claims 1 -6 wherein the second material has a

Young's modulus that is at least five times the Young's modulus of the first material.

8. The filament of any of claims 1 -6 wherein the second material has a Young's modulus that is at least ten times the Young's modulus of the first material.

9. The filament of any of claims 1 -8 wherein the first material has a glass

transition temperature that is within 30 degrees C of the glass transition temperature of the second material.

10. The filament of any of claims 1 -9 wherein the first material has a glass

transition that is within 20 degrees C of the glass transition temperature of the second material.

1 1 . The filament of any of claims 1 -10 wherein the first material has a glass transition temperature that is below 20 degrees C.

12. The filament of claim 10 wherein the first material has a glass transition temperature that is below 0 degrees C.

13. The filament of any of claims 1 -12 wherein the second material has a

flexural modulus that is at least twice as great as the flexural modulus of the first material.

14. The filament of claim 13 wherein the second material has a flexural

modulus that is at least three times as great as the first material.

15. The filament of any of claims 1 -14 wherein the filament is wound onto a spool having a core to form a coil of filament.

16. The filament of claim 15 wherein the spool comprises a pair of spaced apart radially extending flanges forming end walls and the filament is wound around the core between the flanges.

17. The filament of any of claims 1 -16 wherein the filament has a hardness that is greater than the first material but less than the second material.

18. The filament of claim 17 wherein the filament has a hardness of

approximately 50-60 Shore D.

19. The filament of any of claims 1 -18 wherein the filament has a diameter of approximately 1 .75 mm or approximately 3.0 mm.

20. The filament of claim 19 having a diameter of 1 .75 mm plus or minus 0.05 mm or a diameter of 3.0 mm plus or minus 0.05 mm.

21 . The filament of any of claims 1 -20 wherein the jacket has a thickness of 0.100 - 0.250 mm.

22. The filament of any of claims 1 -21 wherein the jacket has a thickness of approximately 0.1 30 mm.

23. The filament of any of claims 1 -22 wherein the core comprises

polyurethane.

24. The filament of any of claims 1 -23 wherein the second material comprises less than 50% of the composition of the filament.

25. The filament of any of claims 41 -24 wherein the second material comprises less than 30% of the composition of the filament.

26. The filament of any of claims 1 -65 wherein the second material comprises less than 15% of the composition of the filament.

27. The filament of any of claims 1 -26 wherein the second material comprises more than 5% of the composition of the filament.

28. The filament of any of claims 1 -27 wherein the first material comprises a thermoplastic polymeric elastomeric material having a hardness of 60-90 on the Shore A scale.

29. The filament of any of claims 1 -28 wherein the second material comprises a thermoplastic material having a hardness of 65-85 on the Shore D scale.

30. The filament of claim 29 wherein the second material comprises a

thermoplastic material having a hardness of 70-80 on the Shore D scale.

31 . The filament of any of claims 1 -30 wherein the first material has an ultimate tensile strength that is substantially less than the ultimate tensile strength of the second material.

32. The filament of any of claims 1 -31 wherein the second material has an

ultimate tensile strength that is at least twice as great as the ultimate tensile strength of the first material.

33. The filament of any of claims 1 -32 wherein the second material has an

ultimate tensile strength that is at least five times as great as the ultimate tensile strength of the first material.

34. The filament of any of claims 1 -33 wherein the second material has an

ultimate tensile strength that is at least ten times as great as the ultimate tensile strength of the first material.

35. The filament of any of claims 1 -34 wherein the jacket provides columnar support for the core to increase the axial rigidity of the filament.

36. The filament of claim 35 wherein the jacket is soluble in a solvent and the core is not soluble in the solvent.

37. The filament of claim 36 wherein the second material is polyvinyl alcohol.

38. A method for forming a polymer filament for use in an apparatus for

producing an object by an additive process, wherein the method for forming the polymer filament comprises the steps of:

melting a first material, wherein the first material comprises a polymer; extruding the first material melted polymer to produce an elongated core; forming a layer of second material onto the core to form a coated filament, wherein the second material is harder than the first material.

39. The method of claim 38 comprising the step of winding the filament on a spool.

40. The method of claim 38 or 39 wherein the step of extruding comprises extruding a polyurethane thermoplastic elastomer.

41 . The method of any of claims 38-40 wherein the step of forming a layer of second material comprises co-extruding the second material with the first material to produce a coated filament having a core formed of the first material and a jacket formed of the second material.

42. The method of claim 38 wherein the step of forming a layer of second

material comprises melting the second material and applying a layer of the melted second material to the elongated core.

43. The method of any of claims 38-42 comprising the steps of:

selecting the second material so that the second material is soluble in a solvent; and

selecting the first material so that the first material is insoluble in the

solvent.

44. The method of claim 43 comprising the step of cooling the extrusion to form a filament having a core having a durometer between 60-90 on the Shore A scale and a jacket that is harder than the core.

45. The method of claim 43 or 44 comprising selecting the second material so that the second material is soluble in water.

46. The method of claim 45 comprising wherein the step of selecting the

second material comprises selecting a material comprising polyvinylalcohol.

47. The method of any of claims 38-42 comprising the step of selecting the second material so that the second material has a Young's modulus that is greater than Young's modulus of the first material.

48. The method of claim 47 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is greater than 10,000 PSI.

49. The method of claim 47 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is greater than 20,000 PSI.

50. The method of claim 47 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is greater than 30,000 PSI.

51 . The method of claim 47 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is greater than 40,000 PSI.

52. The method of claim 47 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is greater than 50,000 PSI.

53. The method of any of claims 47-52 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is at least twice the Young's modulus of the first material.

54. The method of any of claims 47-53 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is at least five times the Young's modulus of the first material.

55. The method of any of claims 47-54 wherein the step of selecting the second material comprises selecting the second material so that the second material has a Young's modulus that is at least ten times the Young's modulus of the first material.

56. The method of any of claims 47-55 wherein the step of selecting the second material comprises selecting the second material so that the second material has a glass transition temperature that is within 30 degrees C of the glass transition temperature of the first material.

57. The method of any of claims 47-56 wherein the step of selecting the second material comprises selecting the second material so that the second material has a glass transition temperature that is within 20 degrees C of the glass transition temperature of the first material.

58. The method of any of claims 47-57 comprising the step of selecting the first material so that the first material has a glass transition temperature that is below 20 degrees C.

59. The method of claim 58 wherein the step of selecting the first material comprises selecting the first material so that the first material has a glass transition temperature that is below 0 degrees C.

60. The method of any of claims 47-59 wherein the step of selecting the second material comprises selecting the second material so that the second material has a flexural modulus that is at least twice as great as the flexural modulus of the first material.

61 . The method of any of claims 47-59 wherein the step of selecting the second material comprises selecting the second material so that the second material has a flexural modulus that is at least three times as great as the first material.

62. The method of any of claims 47-61 wherein the step of selecting the second material comprises selecting the second material so that the filament has a hardness that is greater than the first material but less than the second material.

63. The method of any of claims 47-62 wherein the step of selecting the second material comprises selecting the second material so that the filament has a hardness of approximately 50-60 Shore D.

64. The method of any of claims 38-63 wherein the step of forming the second layer comprises the step of co-extruding the second material with the first material to form a filament having a diameter of approximately 1 .75 mm or approximately 3.0 mm.

65. The method of claim 64 wherein the step of co-extruding comprises forming a filament having a diameter of 1 .75 mm plus or minus 0.05 mm or a diameter of 3.0 mm plus or minus 0.05 mm.

66. The method of claim 64 or 65 wherein the step of co-extruding comprises co-extruding the first and second materials so that the second material forms a layer having a thickness of 0.100 - 0.250 mm.

67. The method of any of claims 64-66 wherein the step of co-extruding

comprises co-extruding the first and second materials so that the second material forms a layer having a thickness of approximately 0.130 mm.

68. The method of any of claims 38-67 comprising the step of selecting the first material so that the first material is a thermoplastic polyurethane.

69. The method of any of claims 38-68 wherein the step of forming the layer of second material comprises for the layer so that the second material comprises less than 50% of the composition of the filament.

70. The method of any of claims 38-68 wherein the step of forming the layer of second material comprises for the layer so that the second material comprises less than 30% of the composition of the filament.

71 . The method of any of claims 38-68 wherein the step of forming the layer of second material comprises for the layer so that the second material comprises less than 15% of the composition of the filament.

72. The method of any of claims 38-68 wherein the step of forming the layer of second material comprises for the layer so that the second material comprises less than 5% of the composition of the filament.

73. The method of any of claims 38-72 comprising the step of selecting the first material so that the first material comprises a thermoplastic polymeric elastomeric material having a hardness of 60-90 on the Shore A scale.

74. The method of any of claims 38-73 comprising the step of selecting the second material so that the second material comprises a thermoplastic material having a hardness of 65-85 on the Shore D scale.

75. The method of claim 74 wherein the step of selecting the second material comprises selecting a thermoplastic material having a hardness of 70-80 on the Shore D scale.

76. The method of any of claims 38-75 comprising the step of selecting the first material so that the first material has an ultimate tensile strength that is substantially less than the ultimate tensile strength of the second material.

77. The method of any of claims 38-76 wherein the step of selecting the second material comprises selecting the second material so that that the second material has an ultimate tensile strength that is at least twice as great as the ultimate tensile strength of the first material.

78. The method of claim 77 wherein the step of selecting the second material comprises selecting the second material so that that the second material has an ultimate tensile strength that is at least five times as great as the ultimate tensile strength of the first material.

79. The method of claim 77 wherein the step of selecting the second material comprises selecting the second material so that that the second material has an ultimate tensile strength that is at least ten times as great as the ultimate tensile strength of the first material.

80. The method of any of claims 38-79 comprising the step of measuring the outer diameter of the filament while the layer of second material is being formed on the core to ensure that the diameter of the filament is within a range of plus or minus 0.010 mm of a desired diameter.

81 . The method of claim 80 comprising the step of providing an alert in response to the step of measuring indicating that the diameter of the filament is outside the range of plus or minus 0.010 mm of the desired diameter.

82. A method for producing an object by an additive process, comprising the steps of :

selecting a feedstock comprising an composite filament comprising a core material surrounded by a jacket material, wherein the jacket material is harder than the core material;

feeding the feedstock to a device operable to melt the filament to form a stream of melted material; and

controlling the stream of melted material to build a series of layers to form an object by an additive process.

83. The method of claim 82 wherein the step of selecting a feedstock

comprises selecting a filament wound onto a spool and wherein the step of feeding comprises pulling the filament to unwind the filament from the spool.

84. The method of claim 83 wherein the step of selecting a feedstock

comprises selecting the feedstock so that the jacket material comprises less than 50% of the overall composition of the filament.

85. The method of claim 84 wherein the step of selecting a feedstock

comprises selecting the feedstock so that the jacket material comprises less than 30% of the overall composition of the filament.

86. The method of claim 85 wherein the step of selecting a feedstock

comprises selecting the feedstock so that the jacket material comprises less than 15% of the overall composition of the filament.

87. The method of any of claims 84-86 wherein the step of selecting a feedstock comprises selecting the feedstock so that the jacket material comprises more than 5% of the overall composition of the filament.

88. The method of any of claims 82-87 wherein the step of selecting a

feedstock comprises selecting the feedstock so that the jacket material is soluble in a solvent and the core material in insoluble in the solvent.

89. The method of claim 88 comprising the step of exposing the object to the solvent to dissolve at least a portion of the jacket material.

90. The method of claim 86 wherein the step of selecting a feedstock

comprises selecting the filament so that the core material has a durometer of 60-90 on the Shore A scale.

91 . The method of claim 90 wherein the step of selecting a feedstock

comprises the selecting the filament so that the core material comprises a thermoplastic elastomer.

92. A method for producing an object by an additive process, comprising the steps of:

feeding a feedstock toward a heating element, wherein the feedstock

comprises a core formed of a first material and a coating surrounding the core formed of a second material that is harder than the first material;

melting the feedstock using the heating element so that the first and second materials melt to form a stream of melted material; and controlling the stream of melted material to build a series of layers to form an object by an additive process.

93. The method of claim 92 wherein the first material has a durometer of

between 60-90 on the Shore A scale.

94. The method of claim 93 wherein the first material is a thermoplastic elastomer.

95. The method of claim 93 wherein the first material comprises thermoplastic urethane or silicone.

96. The method of claim 92 wherein the second material is soluble in a solvent and the first material is insoluble in the solvent, wherein the method comprises the step of exposing the object to the solvent to dissolve at least a portion of the second material.

97. The method of claim 96 wherein the step of exposing the object to the solvent increases the flexibility of the object.