Patent Publication Number: US-2015084222-A1

Title: Filament for fused deposit modeling

Description:
PRIORITY CLAIM 
     This application claims priority under 35 U.S.C.§119 to U.S. Provisional Application No. 61/881,690 filed Sep. 24, 2013. The entire disclosure of the foregoing application is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     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 
     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. 
     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 
     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 an additive manufacturing machine with a spool of low durometer elastomer filament. The outer surface of the filament has reduced tackiness to improve the ability to feed the filament through the FFF machine. For instance, the filament may comprise a plurality of melt fractures that reduce the coefficient of friction of the filament. 
     According to another aspect, a low durometer filament for an FFF machine is provided. The filament has an elongated axis extending the length of the filament and an outer surface. The outer surface comprises a plurality of melt fractures extending transverse the elongated axis. For example, the plurality of melt fractures may comprise a plurality of ridges running transverse the elongated axis. 
     In yet another aspect, the present invention comprises a method of using a thermoplastic filament having an elongated axis extending the length of the filament and having a plurality of distortions along the length of the filament. The method comprises the steps of feeding the filament into a nozzle, melting the filament, and selectively controlling the position of the nozzle relative to a platform to deposit a plurality of layers of material to produce a three-dimensional item. 
     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 series of irregularities along the length of the filament, 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 
       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: 
         FIG. 1  is a side view of a system for creating three-dimensional objects; 
         FIG. 2  is an enlarged fragmentary view of an extrusion head of the system illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged fragmentary view of a filament used in the system of  FIG. 1 ; 
         FIG. 4  is a series of enlarged fragmentary views of filaments for the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures in general and to  FIGS. 1-2  specifically, 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. 
     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. 
     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. 
     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 . 
     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. 
     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 . 
     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 . 
     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. 
     The filament  80  may be wound onto a spool  90  to provide a substantially constant supply of material to the extrusion head  20 . 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 . 
     As noted above, the filament may be formed of any of a variety of materials. However, in the present instance the filament is 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 filament material may be 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 filament 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. 
     The filament  80  is configured to limit the pull force necessary to draw the filament from the spool and to improve the feeding of low-durometer filaments. Referring to  FIG. 3 , the filament  80  is an elongated element having a central axis  82  extending along the length of the filament. The filament  80  includes a plurality of distortions or irregularities  84  formed along the length of the filament. 
     In the present instance, the filament is an extruded element and extrudate irregularities are formed by inducing die flow instabilities during the extrusion process. The extrudate irregularities may comprise surface melt fractures or gross melt fractures. For example, surface melt fractures in the form of surface distortions may be formed on the outer surface of the filament by extruding the filament at a temperature and rate that causes small amplitude periodic surface distortions on the filament. As shown in  FIGS. 3 and 4(   a ), in the present instance, the extrudate irregularities  84  are surface distortions that comprise a series of ridges that extend transverse the axis of the filament  82 . Additionally, as shown in  FIG. 3 , the extrudate irregularities extend over substantially the entire length and substantially the entire surface of the filament. The ridges may be periodic ridges, such as the extrudate irregularity commonly referred to as sharkskin. Although the sharkskin irregularity may extend over only a portion of the filament, as noted above, in the present instance, the sharkskin extends over substantially the entire surface of the filament as shown in  FIG. 3 . 
     Surface distortions  84  such as those illustrated in  FIGS. 3 and 4(   a ) may be formed during the process of extruding the filament  80 . Specifically, the flow rate of the extrusion material and/or the temperature of the extrusion die and the filament material may be controlled so that the center of the extruded material flows faster than the outer edges of the extrusion where the die walls hinder the flow of the extruded material. 
     Alternatively, as shown in  FIGS. 4(   b ) &amp;  4 ( c ), gross melt fractures can be induced that more significantly affect the filament extrusion, such as melt fractures that alter the cross-section of the extrusion. Such melt fractures may include, but are not limited to: spiraling, bambooing, regular ripple, random ripple and other melt fractures that create distortions so that the surface of the filament is variable in a radial direction along the length of the filament. In this way, the gross melt fractures may create a series of ridges transverse the axis along which the filament is extruded, which in the present instance, in the filament axis  82 . 
     Configured as discussed above, the system  10  operates as follows. A length of filament  80  having a series of irregularities  84  is provided. The irregularities may be extrudate irregularities forming a plurality of ridges extending transverse the filament axis  82 . In the present instance, the irregularities  84  are a plurality of ridges extending generally perpendicular to the filament axis  82 . The ridges may be periodic ridges having a small amplitude. Specifically, the amplitude of the ridges may be substantially smaller than the diameter of the filament. The diameter of the filament  80  may vary, for instance, the diameter of the filament may be between 1 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. In the present instance, the diameter is either 1.75 mm or 3.0 mm. 
     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 product 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, as discussed above, the filament may have surface irregularities, such as ridges protruding radially outwardly along the surface of the filament. Such surface irregularities extend transverse the longitudinal axis of the filament. Therefore, the surface irregularities also extend transverse the direction of travel as the filament is fed toward the feeder  50 . As a result, the surface irregularities are generally parallel to surfaces of the teeth of the drive wheel  52  so that the surface irregularities can also form engagement surfaces or ridges to engage the teeth of the drive wheel  52  to facilitate feeding of the material. 
     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 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. 
     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 having a plurality of irregularities along the length of the filament. 
     The method of producing the filament comprises the step of melting a polymer. In particular, the polymer 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. 
     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. 
     When the filament emerges from the extrusion die, the filament is at an elevated temperature. Accordingly, the filament may be cooled by any of a variety of means, such as by pulling the filament through a bath of cooling fluid, such as water. After the filament is cooled, the filament is wound onto a spool. 
     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 die and the filament is wound onto the spool. In the present instance, a non-contact gauge for measuring the diameter of the filament. For instance, the gauge may comprise a plurality of laser elements to measure the filament diameter. 
     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. 
     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. 
     Several characteristics of the extrusion process affect the profile of the extruded filament. For instance, elements that affect the extrusion profile include, but are not limited to: the temperature of the die, the temperature of the thermoplastic material, the temperature of the cooling bath and the flow rate of the material through the die. In order to induce polymer flow instabilities during the extrusion process, one of the characteristics is selected so as to provide the desired melt fracture in the filament. Specifically, the filament may be extruded using the selected extrusion characteristic to provide a filament having extrusion irregularities along the length of the filament. For instance, the extrusion characteristic, such as the flow rate through the die, may be controlled to provide a filament having a melt fracture, such as a plurality of small amplitude ridges around the filament. Specifically, the ridges may have an amplitude that is substantially smaller than the diameter of the filament. 
     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.