Abstract:
A method of fabricating (printing) parts utilizing flexible filaments includes anchoring a portion of a flexible filament to a substrate. A length of flexible filament is extended over the substrate while the flexible filament is in tension to thereby avoid buckling of the flexible filament. The flexible filament may comprise a thermoplastic material and fibers or other reinforcing materials whereby composite 3D parts can be fabricated.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/294,499, filed on Feb. 12, 2016, titled “DEVICES AND METHODS FOR ADDITIVE MANUFACTURING USING FLEXIBLE FILAMENTS,” and U.S. Provisional Patent Application No. 62/252,825, filed on Nov. 9, 2015, titled “DEVICES AND METHODS FOR ADDITIVE MANUFACTURING USING FLEXIBLE FILAMENTS,” the entire contents of each application is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    The invention described herein was made in the performance of work under NASA contracts and by employees of the United States Government and is subject to the provisions of the National Aeronautics and Space Act, Public Law 111-314, §3 (124 Stat. 3330, 51 U.S.C. Chapter 201) and 35 U.S.C. §202, and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefore. In accordance with 35 U.S.C. §202, the contractor elected not to retain title. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to the use of an additive manufacturing process to build parts using flexible filaments. More particularly, it relates to a method for printing filaments having material properties that do not permit effective extrusion using compressive force. 
       BACKGROUND OF THE INVENTION 
       [0004]    Various processes for fabricating polymer components have been developed. For example, Fused Deposition Modeling (FDM), generically called Fused Filament Fabrication (FFF), is a fabrication method (“3D printing”) that may involve heating and extruding polymeric filaments (e.g. thermoplastics) to produce 3D components. 
         [0005]    Various methods for processing continuous and discontinuous wires and fibers as well as fiber reinforced filaments have also been disclosed. Wicker et. al. (US 20140268604) discloses methods for embedding wires and mesh into a 3D printed structure. Mark et. al. (US 20150108677) discloses methods for 3D printing continuous and semi-continuous reinforced fiber filaments. Jang et. al. (U.S. Pat. No. 6,934,600 B2) discloses methods for manufacturing and printing continuous nanomaterial reinforced filaments. Batchelder et. al. (U.S. Pat. No. 8,221,669 B2) discloses the use of asymmetrical filaments for 3D printing. Kappesser et. al. (US 20130233471) discloses a fiber placement system for small flat laminates. Tyler et. al. (US 20140061974) discloses 3D printing using continuous fiber filaments. Hoagland, Abraham (US 17835) which describes a device for holding proper tension on thread in a sewing machine. However, known processes may suffer from various drawbacks. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    As noted above, additive manufacturing methods such as Fused Filament Fabrication (FFF) involve extruding, a feedstock material from a nozzle via a compressive force applied to the feedstock. However, the compressive forces may cause buckling of the filament. Thus, in known FFF processes the feedstock material must be of sufficient size and stiffness to undergo the required compression without buckling. 
         [0007]    However, filaments having small filament diameters and/or filaments comprising highly conformable (flexible) materials (e.g. CNT yarns), may not have sufficient size and stiffness to permit extrusion in FFF processes. Processes for printing small diameter/flexible filaments/materials have been developed. For example, Jang et. al U.S. Pat. No. 6,934,600 presents a method for printing CNT materials within a matrix. However the total CNT content (&lt;50% wt.) of the materials utilized in the Jang &#39;600 process is significantly lower than required for some applications, especially those requiring high performance components (e.g. aerospace applications). Kappesser et. al. U.S. 20130233471 also demonstrates a method for placing small diameter/flexible materials. However, the method of Kappesser does not provide for printing of small features, especially features that are on the order of 100 microns. 
         [0008]    In some cases, constraining the sides of a flexible filament may be sufficient to prevent buckling. This is not always practical given the design requirements of a 3D printing system such as filament size, print temperature, and machining constraints. In particular, constraining the sides of a flexible filament may not be viable for highly flexible, continuous thin nanotube yarn based filaments. 
         [0009]    One aspect of the present disclosure is a process that reduces or eliminates buckling by printing filament without applying a compressive force on the material. A process and system according to one aspect of the present disclosure allows a feedstock material to be printed while maintaining a tension force of greater than or equal to zero in the feedstock throughout the extrusion system. The present disclosure also provides a method for printing continuous filaments which are capable of carrying very little or no axial compressive load. The present disclosure enables enhanced filament-substrate adhesion in specific areas along the printed part to facilitate printing. Another aspect of the present disclosure is a method for printing flexible continuous filaments in which an additional compaction force can be applied on the filament after printing. Yet another aspect of the present disclosure is a method for printing flexible continuous filaments in which enhanced filament-substrate adhesion can be achieved throughout the entire printed element. The present disclosure further includes a method for creating a machine tool path which identifies areas where additional movements are needed for filament printing. 
         [0010]    These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a partially fragmentary schematic cross-sectional view of a flexible filament printing device; 
           [0012]      FIG. 2  is a partially fragmentary schematic cross-sectional view showing a flexible filament printing on pre-deposited filament; 
           [0013]      FIG. 3  is a partially fragmentary schematic cross-sectional view of a flexible filament prior to being attached to a substrate; 
           [0014]      FIG. 4  is a partially fragmentary schematic cross-sectional view showing a filament being held at a substrate surface; 
           [0015]      FIG. 5  is a partially fragmentary schematic cross-sectional view showing a nozzle that has been retracted away from a substrate surface; 
           [0016]      FIG. 6  is a partially fragmentary schematic cross-sectional view showing the nozzle moved back towards the substrate surface; 
           [0017]      FIG. 7  is a partially fragmentary schematic cross-sectional view of a filament being held between a nozzle and a substrate surface; 
           [0018]      FIG. 8  is a partially fragmentary schematic cross-sectional view showing a nozzle and a compaction foot; 
           [0019]      FIG. 9  is a partially fragmentary schematic cross-sectional view of the compaction foot and a linear actuator; 
           [0020]      FIG. 10  is a schematic representation of a tool path used for adhesion enhancement of filament in select areas; 
           [0021]      FIG. 11  is a schematic representation of a tool path used for adhesion enhancement over the entire length of a filament; and 
           [0022]      FIG. 12  is a block diagram of an automated tool for modifying tool path commands. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
         [0024]    With reference to  FIGS. 1 and 2 , a 3D printing device  1  according to one aspect of the present disclosure includes a nozzle  2  have an outlet opening  4 . Outlet opening  4  preferably has a diameter “D 1 ” that is greater than or equal to a diameter “D 2 ” of a thin/flexible filament  6 . Filament  6  may comprise a thermoplastic polymer material that softens/melts upon heating nozzle  2  or a thermoset polymer material that cures upon heating nozzle  2 . Filament  6  may comprise CNTs and/or other materials in combination with thermoplastic or thermoset polymer materials. As used herein, the term “filament” generally refers to a filament that comprises at least some thermoplastic and/or thermoset polymer material, and may include but is not limited to filaments comprising thermoplastic or thermosetting materials and other materials such as CNTs, CNT yarn, boron nitride nanotubes (BNNTs) and BNNT yarn, silicon carbide (SiC) nanotubes and SiC yarn. An electrical heating element  8  is attached to the nozzle  2  to control the temperature of the nozzle  2  during operation. Heating element  8  is operably connected to controller  12  of 3D printing device  1 . 
         [0025]    A metering device  10  is located upstream from the heating element  8 . Metering device  10  may include electrically-powered rollers  10 A and  10 B that are selectively actuated by controller  12  to control the direction, speed and length of the filament  6  between the nozzle  2  and metering device  10 . The metering device  10  is also used to pull the filament  6  off a filament dispensing unit  14  which holds the filament  6  prior to printing. 
         [0026]    Printing can be performed onto a substrate  20  and/or onto previously deposited material  16  ( FIG. 2 ). Filament  6  is loaded into the 3D printing device  1  by threading the filament  6  through the metering device  10 , passageway  18 A, heating element  8 , and nozzle  2  so that a short end portion  22  ( FIG. 3 ) of filament  6  having a length “L” extends from the nozzle outlet  4 . Controller  12  then actuates heating element  8  to heat the nozzle  2  to a temperature above the melting point of the feedstock material, the substrate material, or both. Once the nozzle  2  is at the desired temperature, the end portion  22  of filament  6  is anchored to the substrate  20  as shown in  FIG. 4 . During anchoring, the nozzle  2  is moved towards the substrate  20  in a negative Z-direction while simultaneously tracking along the substrate surface  20  in the X-direction until the end portion  22  of filament material  6  is sandwiched/clamped between lower end  26  of the nozzle  22  and substrate material  20  at a starting point  24 . Lower end  26  of nozzle  2  and substrate  20  may be in contact. The end portion  22  of filament  6  is held in the clamped position ( FIG. 4 ) for a predetermined duration greater than or equal to zero seconds to allow for adhesion of the end portion  22  of filament  6  to the substrate  20 . Nozzle  2  may heat filament  6  to a molten or partially molten state, such that filament  6  adheres to substrate  20  as filament  6  cools and solidifies. 
         [0027]    To begin printing additional filament, the nozzle  2  is moved upwardly away from the substrate  20  for a short distance Z 1  ( FIG. 5 ). Distance Z 1  may vary as required for a particular application. During movement of nozzle  2  from the position of  FIG. 4  to the position of  FIG. 5 , the metering device  10  extrudes a material length equal to the tool path length (distance Z 1 ) to ensure that tension in the filament  6  between the metering device  10  and the nozzle  2  remains at or near zero. 
         [0028]    With further reference to  FIGS. 6 and 7 , a linear movement of the nozzle  2  in an angled direction (arrow B) is then performed to bring adjacent end portion  22 A the filament material  6  in contact with the substrate  20  at a predetermined location  24 A at a distance X 1  from the last contact point  24 . The direction of movement (arrow B) is between 0° and 90° relative to the X axis, and more preferably between about 30° and 60° (e.g. 45°). During movement of nozzle  2  from the position of  FIG. 6  to the position of  FIG. 7 , the metering device  10  extrudes or retracts filament material as required to ensure that the total length of filament material  6  extruded between the first and second contact points  24  and  24 A, respectively is equal to the linear distance X 1  between these two points. The filament is then held in the position of  FIG. 7  for a predetermined duration of time greater than or equal to zero seconds to allow for adhesion of the end portion  22 A of filament  6  to the substrate material. Once a single trace of filament  6  has finished printing, it is cut so that a small length L ( FIG. 3 ) of filament  6  extends from the outlet  4  of the nozzle  2  for the next print run. Filament printing continues by repeating this process as many times as necessary to build up the required number of layers  28 A,  28 B, etc. ( FIG. 2 ). It will be understood that the matrix material of layers  28 A,  28 B, etc. of a final component preferably bond and/or flow (melt) together to form a substantially continuous matrix that does not include seams or boundaries between the layers  28 A,  28 B, etc. 
         [0029]    With further reference to  FIG. 8 , a 3D printing device  1 A according to another aspect of the present disclosure includes a nozzle  2 A having an outlet opening  4 A having a diameter D 3  that is preferably greater than or equal to a diameter D 1  of filament  6 A. Device  1 A includes a compaction foot  30  in the form of a flat plate that may include a countersunk (conical) aperture or hole  32 . Hole  32  has a minimum diameter D 5  and a maximum diameter D 6 . The minimum diameter D 5  is preferably at least somewhat greater than the diameter D 1  of the filament  6 A. The hole  32  preferably includes a beveled or rounded edge  34  at the bottom of the plate  30 . Device  1 A may be configured such that nozzle outlet  4 A and hole  32  in the flat plate  32  are concentric, with the larger diameter D 6  of the hole  32  in the flat plate  30  facing the nozzle outlet  4 A. Alternatively, diameter D 6  of hole  32  may be offset in the X-direction slightly relative to outlet  4 A of nozzle  2 A. As discussed below in connection with  FIG. 9 , plate  30  may be shifted downwardly to clamp an end portion  36  of filament  6 A against substrate  20 A. The configuration of hole  32  allows for clamping compaction to take place regardless of the printing direction (i.e. regardless of the direction of movement of nozzle  2 A in the X-Y plane relative to substrate  20 A). 
         [0030]    With further reference to  FIG. 9 , the configuration of nozzle  2 A and the plate  30  permits these components to move linearly relative to each other along the Z axis perpendicular to the flat plate  30 . Nozzle  2 A and plate  32  can be moved relative to one another in the Z-direction utilizing either passive or active linear devices such as powered actuators  38 A and  38 B. Nozzle  2 A may be mounted to an upper plate  40 , and plate  30  may be mounted to lower plate  42 . The powered actuators  38 A and  38 B may be operably connected to upper and lower plates  40  and  42 , respectively. Device  1 A may include a controller  12 A that selectively actuates powered actuators  38 A and  38 B to clamp an end portion  44  of filament  6 A against substrate  20 A in a manner that is similar to the process described above in connection with  FIGS. 1-7 . Although actuators  38 A and  38 B are preferably powered actuators (e.g. electrically-powered linear actuators), actuators  38 A and  38 B may alternatively comprise passive devices (e.g. spring-biased cylinders). The compaction/clamping force on the substrate  20 A is adjustable and controllable for both passive or active linear devices. 
         [0031]      FIG. 10  shows a tool path  50  for a process/method according to the present disclosure wherein the adhesion between the filament  6  and substrate  20  is enhanced in selected areas. In this method, once the filament  6  has been anchored to the substrate  20  at a first point  54 , the nozzle  2  is then retracted perpendicular to the substrate  20  for a short distance  56  in the Z direction. During this movement, the metering device  10  extrudes a material length equal to the tool path length Z 10  along path segment  56  to ensure that tension in the filament  6  between the metering device  10  and the nozzle  2  remains zero or approximately zero. A linear movement  58  of nozzle  2  is then performed to again bring the filament material  6  into contact with the substrate  20  at a predetermined location  60  that is a horizontal distance X 10  from the prior contact point  54 . The metering device  10  extrudes and/or retracts the filament material  6  to ensure that the total length of material extruded between the first and second contact points  54  and  60  is substantially equal to the linear distance (i.e. the sum of path segments  56  and  58 ) between points  54  and  60 . The filament  6  is then held in position at point  60  for a predetermined duration greater than or equal to zero seconds to allow for adhesion of the filament  6  to the substrate  20  at point  60 . This process is repeated as many times as necessary as shown by path segments  62 ,  64 ,  68 ,  70  and contact points  66 ,  72 , etc. to ensure that the bond between filament  6  and substrate  20  is consistent with design or printing requirements. After the final contact point  72 , the nozzle  2  is moved across the surface of the substrate  20  at the same height (e.g. in the X direction). As nozzle  2  moves relative to substrate  20 , the filament material  6  is pulled out of the nozzle  2  under tension. Tension on filament  6  is created due to friction between the nozzle  2  and filament  6  and the reinforced filament substrate bond  74 . Once a single trace of filament  6  has finished printing, the trace of filament  6  may be cut so that a small length of filament (e.g. end portion  22 ,  FIG. 3 ) extends from the outlet  4  of the nozzle  2 . This process can be used in corners and other areas where sharp runs with a small radius (e.g. &gt;&gt;1 inch) are required. 
         [0032]    In the process of  FIG. 10 , the line segments  56 ,  62 ,  68  of the tool path  50  are substantially perpendicular to substrate  20 , and the angled line segments  58 ,  64 ,  70  extend at an angle of about 45° relative to substrate  20 . Also, the vertical distance Z 10  may be about 0.0625 to about 0.25 inches, and the horizontal distance X 10  may be about 0.0625 to about 0.25 inches. However, it will be understood that the angles and lengths of the path segments may vary as required for a particular material and/or application. 
         [0033]    With further reference to  FIG. 11 , a tool path  80  for a method/process according to another aspect of the present disclosure provides for improved adhesion between filament  6  and substrate  20  along substantially the entire length of a printed filament  6 . In this method, after moving from a START location (e.g. point  78 ) along an angled path segment  82 , the filament  6  is then anchored to the substrate  20  at a point  84 . The nozzle  2  is then retracted perpendicular to the substrate in a Z direction for a short distance Z 12  along path segment  86 . During this movement, the metering device  10  extrudes a length of filament  6  that is substantially equal to the length of path segment  86  to ensure that the tension in the filament  6  between the metering device  10  and the nozzle  2  remains at or near zero. A linear move along an angled path segment  88  is then performed to again bring the filament material  6  into contact with the substrate  20  at a predetermined location  90  at a horizontal distance X 12  from the prior contact point  84 . The metering device  10  extrudes or retracts filament material  6  to ensure that the total length of filament material  6  extruded between the first and second contact points  84  and  90  is substantially equal to the linear distance between these two points (i.e. the sum of the lengths of path segments  86  and  88 ). The filament  6  is then held in this position (point  90 ) for a predetermined duration greater than or equal to zero seconds to allow for adhesion of the filament  6  to the substrate material  20 . This process is repeated at a series of points along the printed filament tool path  80  to enhance adhesion between the filament  6  and substrate material  20 . Once a single trace of filament  6  has finished printing, it may be cut so that a small length of filament extends from the outlet  4  of the nozzle  2 . 
         [0034]    Distance Z 12  may be about 0.0625 to about 0.25 inches, and distance X 12  may be about 0.0625 to about 0.25 inches. Line segments  88  are preferably about 45° relative to substrate  20 . However, the length and angles of line segments  86  and/or  88  may be varied as required for a particular application. 
         [0035]    With further reference to  FIG. 12 , the embodiments of the present disclosure may be implemented utilizing an automated process (tool) for determining locations in a printed filament where bonding reinforcement is necessary and adding the required movements to the tool path to affect the reinforcement. An initial filament printing tool path  106  is produced utilizing 3D CAD data  102  for a part to be fabricated. CAD data  102  is supplied to a slicing engine  104  that outputs the initial tool path  106 . Initial tool path data  106  comprising at least two points (e.g. points  54 ,  72 ,  FIG. 10 ) and a printing direction is supplied to the bond reinforcement program  100 . Additionally, a user also supplies specifications  116  for areas of the print that will require additional compactions. These specifications include (but are not limited to) the length of filament  6  to be printed between two turns, the radius of the turn, and the speed of the print (e.g. speed of nozzle  2  relative to substrate  20 ). The user may also supply information  114  on how bond reinforcement is to be performed, including nozzle temperature, duration on compaction at a point, compaction force applied, etc. The bond reinforcement program  100  then analyzes the filament printing tool path to identify areas (e.g. points in X, Y, Z coordinates) where bond reinforcement is needed as shown at  108  based on the user-supplied data  114  and  116 . At these points, addition commands are automatically inserted into the tool path to perform the bonding reinforcement process according to modified tool path  112 . Additional moves or commands may be added to enable printing with a compaction foot  30  ( FIGS. 8 and 9 ). The automated tool inserts additional commands such as cutting commands in required areas, and commands to ensure that a length of material (e.g. end  22 ,  FIG. 3 ) is left extending from the nozzle  2  after cutting to allow printing to resume. If desired, the user can manually adjust the tool path to correct any issues. 
         [0036]    It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise. \ 
         [0037]    The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein. 
         [0038]    All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference. 
         [0039]    All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. Each range disclosed herein constitutes a disclosure of any point or sub-range lying within the disclosed range. 
         [0040]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As also used herein, the term “combinations thereof” includes combinations having at least one of the associated listed items, wherein the combination can further include additional, like non-listed items. Further, the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). 
         [0041]    Reference throughout the specification to “another embodiment”, “an embodiment”, “exemplary embodiments”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and can or cannot be present in other embodiments. In addition, it is to be understood that the described elements can be combined in any suitable manner in the various embodiments and are not limited to the specific combination in which they are discussed.