Abstract:
A method of fabricating composite articles includes supplying electrical current to an electrically conductive filament. The electrically conductive filament may include a first material that is electrically conductive and a polymer second material. The polymer second material comprises at least one of a thermoplastic polymer and a partially cured thermosetting polymer. The heated filament is deposited according to a predefined pattern in successive layers to adhere the polymer material of the layers together and build up a three dimensional article. The article includes strands of the first material embedded in a substantially continuous polymer matrix of the second material.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/251,969, filed on Nov. 6, 2015 and titled “METHOD FOR THE FREE FORM FABRICATION OF ARTICLES OUT OF ELECTRICALLY CONDUCTIVE FILAMENTS USING LOCALIZED HEATING,” the entire contents of which 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 a NASA contract and by employees of the United States Government and is subject to the provisions of Public Law 96-517 (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. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    Multifunctional composites such as mechanically reinforced, electrically and thermally conductive parts are of interest in a range of areas including aerospace, automotive, high performance sporting goods and other applications. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The present disclosure generally relates to the use of electrically conductive filaments, especially polymer coated carbon nanotube yarn filaments, for producing additively manufactured items and, more particularly, to an improved apparatus and process for fabricating components (3D printing) from electrically conductive filaments that are heated via resistive heating. 
         [0005]    Free form fabrication of articles (“3D printing”) may involve heating the fabrication material feedstock to melt it. Controlled cooling may be utilized to ensure that the fabricated structure does not suffer from excessive distortion after the material is put into place. The present disclosure includes a method of applying localized heat using an electrically conductive nozzle and a conductive plate as the electrodes to supply electrical current through electrically conductive filaments during the free form fabrication process. The method may be used for laying down electrically conductive filaments in a fast, accurate and controlled manner with localized heat. 
         [0006]    The present disclosure includes a method for fabricating articles out of electrically conductive filaments that generates localized heat through resistive heating of the filament. Another aspect of the present disclosure is a method for manufacturing articles of electrically conductive filament without use of a heating mechanism such as an environmental chamber, heating bed, or other auxiliary heat sources. Another aspect of the present disclosure is a method for fabricating articles that includes a way to cut electrically conductive filaments depending on the level of electrical current (or voltage). The electrically conductive filaments can be cut as needed at a point in very close proximity to where deposition occurs. Another aspect of the present disclosure is a method for fabricating articles wherein the heat is localized at or near the point where filament placement and cutting occur. Distortion of the fabricated part is substantially reduced or avoided altogether because a large heat gradient is not generated during the fabrication process. Yet another aspect of the present disclosure is a method for fabricating articles that is both fast and accurate due, at least in part, to the restriction of heat to the zone that needs to be heated. 
         [0007]    The method may include fabricating composite articles by supplying electrical current to an electrically conductive filament. The electrically conductive filament may include a first material that is electrically conductive and a polymer second material. The electrically conductive first material may comprise at least one of a continuous carbon assemblage and a polymer doped with an electrically conductive filler (e.g. carbon) having a concentration in the polymer matrix that is above the electrical percolation threshold. The continuous carbon assemblage may comprise one or more of carbon fiber, carbon nanotube, graphite, activated carbon, and/or graphene. The electrically conductive carbon filler to be used as a polymer dopant may comprise one or more of chopped carbon fiber, carbon nanotubes, graphite, activated carbon, and/or graphene powders. Alternatively, the electrically conductive first material may comprise at least one of a conductive polymer, metal wire, metal alloy, metal/carbon hybrid or combination thereof. The polymer second material may comprise at least one of a thermoplastic polymer and a partially cured thermosetting polymer. The polymer second material may contain thermally and electrically conductive fillers to enhance the heating and printability as well as the properties of the completed part. These fillers may include one or more of dispersed chopped carbon fibers, chopped carbon fiber, carbon nanotubes, graphite, activated carbon, and/or graphene powders. The heated filament is deposited on a substrate in successive layers to adhere the polymer material of the layers together and build up a three dimensional article having strands of the first material embedded in a substantially continuous polymer matrix of the second material. 
         [0008]    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 SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. 
           [0010]      FIG. 1  is a schematic cross-sectional view of a device for free form fabrication of components using localized heating of electrically conductive filaments; 
           [0011]      FIGS. 2A-2F  are photo images of polymer coated CNT yarn filaments and IR thermographs at various applied voltages; 
           [0012]      FIG. 3  shows a filament having a polymer core and conductive outer mesh; 
           [0013]      FIG. 4  is an isometric view of a filament including conductive reinforcement fibers and polymer fibers; 
           [0014]      FIG. 5  is an isometric view of a printed article fabricated utilizing the filament of  FIG. 3 ; 
           [0015]      FIG. 6  is an isometric view of a printed article fabricated from the filament of  FIG. 4 ; 
           [0016]      FIG. 6A  is a schematic cross-sectional view of a filament having a conductive core and a polymer matrix that is doped with electrically conductive filler material; 
           [0017]      FIG. 6B  is a schematic cross-sectional view of a filament comprising a polymer matrix that is doped with electrically conductive filler material; 
           [0018]      FIG. 7  is a perspective view of a test set-up utilized for the preparation of engineered filaments such as those shown in  FIG. 4 ; 
           [0019]      FIG. 8  is a fragmentary enlarged view of a portion of the test set-up of  FIG. 7 ; 
           [0020]      FIG. 9  is a graph showing voltage-current-temperature profiles for engineered filament preparation showing data from the test set-up of  FIGS. 7 and 8 ; 
           [0021]      FIGS. 10A-10F  are images (IR thermographs) corresponding to the steps in the engineered filament processing voltage-current-temperature profiles of  FIG. 9 . 
           [0022]      FIG. 11  is a partially fragmentary perspective view of a portion of an engineered CNT/PEI resistive heating printer filament prepared utilizing the setup of  FIG. 7 ; 
           [0023]      FIG. 12  is a partially fragmentary perspective view of a test set-up of a resistive heating 3D printer; 
           [0024]      FIG. 13  is a bottom perspective view of a heating foot for the resistive heating printer of  FIG. 12 ; 
           [0025]      FIG. 14  is a top perspective view of a heating foot for the resistive heating printer of  FIG. 13 ; 
           [0026]      FIG. 15  is a partially fragmentary perspective view showing a lower portion of the 3D printer of  FIG. 13 ; and 
           [0027]      FIG. 16  is a partially fragmentary perspective view showing a lower portion of the 3D printer of  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    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. 
         [0029]    The ability to fabricate multifunctional composite components may be important where tailorability of function is achieved by strategic placement of materials with unique functionality in locations that may not be accessible by conventional manufacturing techniques. Some examples include embedded conductive paths interspersed in components to act as sensing elements, or as heaters, or to carry electrical current to power electrical components. The processing of these materials typically requires adhesion of filaments to each other, as well as to a substrate. In particular, additive manufacturing processes of electrically conductive and continuous fiber reinforced composites typically require specific placement and cutting technologies for the filaments. 
         [0030]    Various methods of heating composites to promote polymer resin or filaments infusion and cure have been reported in the literature. Microwave, infrared, ultrasonic, inductive, resistive heating, and electromechanical and electrothermal heating methods have been reported. Resistive heating and electromechanical and electrothermal heating methods allow for targeted heating to specific zones, potentially minimizing the overall energy requirements for large part fabrication. 
         [0031]    With reference to  FIG. 1 , a free form fabrication device such as 3D printing apparatus  1  includes an electrically conductive nozzle  2  that is movably disposed above a substrate or plate  4 . 3D printing apparatus  1  includes a controller  6  and an electrically-powered actuating system/mechanism  8  that moves the nozzle  2  relative to the substrate  4 . 3D printing apparatus  1  also includes a controller  6  and an actuating system/mechanism  8  that move the nozzle  2  relative to the substrate  4  in a known manner. Various computer programs for controlling movement of nozzle  2  to fabricate 3D components utilizing 3D CAD data or the like are known in the art. 3D printing apparatus  1  also includes a filament supply  10  that feeds an electrically conductive filament  12  to head  2 . As discussed in more detail below in connection with  FIGS. 3 and 4 , filament  12  may include one or more strands of conductive material (including but not limited to carbon fiber and carbon nanotube) forming a conductive core  13 , and polymer material  13 A forming an outer layer. During the fabrication process, filaments  12  are successively layered onto substrate  4  to fabricate a component  25 . In  FIG. 1 , the individual layers  26 A- 26 D are shown as distinct layers. However, it will be understood that the polymer material of adjacent layers flows together and/or joins together to form a substantially continuous polymer matrix  28  in which the fibers of core  13  of filament  12  are embedded. 
         [0032]    Nozzle  2  is made of an electrically conductive material (e.g. metal) and forms a first electrode. Nozzle  2  has an outlet opening  14  having a diameter that may be equal to a diameter “D” of the filament  12 . Alternatively, opening  14  may be larger or smaller than diameter “D.” A plate  16  forms a second electrode. Plate  16  is also made of an electrically conductive material (e.g. metal), and includes a tapered/countersunk hole  18  with a minimum diameter “D 1 ” that is greater than the diameter D of the filament  12 , and a larger upper diameter “D 2 .” The hole  18  extends through the thickness of the plate  16  and creates a sharp edge  20  at the bottom of the plate  16 . 
         [0033]    The nozzle outlet opening  14  and the hole  18  in plate  16  are preferably concentric with the larger diameter D 2  of the hole  18  in plate  16  facing the nozzle outlet  14 . A power supply  22  provides a current (AC or DC) or voltage between the two electrodes (nozzle  2  and plate  16 ) and thereby causes an electrical current to flow and heat up the filament  12  in the section  12 A between the exit opening  14  of nozzle  2  and the plate  16  to a desired temperature. The current provided by power supply  22  may range from a few micro amperes to a few hundred amperes as required to provide proper/required heating of filament  12 . Power supply  22  may be operably connected to controller  6 , and controller  6  may be configured to adjust the current (or voltage) of power supply  22  during the fabrication process. A vertical distance “Z” between the nozzle  2  and the plate  16  is also preferably adjustable upon actuation of mechanism  8  by controller  6 . 
         [0034]    To perform the filament placement operation, the filament  12  is first anchored by positioning a portion of filament  8  between plate  16  and substrate  4 . Plate  16  and substrate  4  are then moved together to apply a force on filament  8  and clamp an end portion of filament  8  between plate  16  and substrate  4 . Anchoring of filament  12  can be conducted with or without resistive heating. Next, the vertical distance Z between the nozzle  2  and plate  16  is adjusted so that nozzle  2  and plate  16  are not touching each other (or any other surface) to thereby avoid creating a short in the circuit. The filament  12  is then pulled taut by a tensioning mechanism (e.g. clamps/rollers  10 A and  10 B) that is a standard component of known 3D printing devices. Tensioning filament  12  causes secure electrical contact to be made between the filament  12  and the nozzle  2  and between the filament  12  and edge  20  of plate  16 . Greater tension on the filament  12  typically provides a better electrical connection between filament  12  and nozzle  2  and plate  16 , thereby reducing the overall resistance of the circuit and providing for faster heating of filament  12 . Filament  12  may have a conductive core  13 A. In general, heating of filament  12  causes coating  13 A to at least partially melt such that nozzle  2  and plate  16  contact core  13  to thereby transmit electrical current through core  13 . Also, core  13  may comprise one or more strands of conductive material that are at least partially exposed at an outer surface of filament  12  prior to melting of polymer material  13 A such that the conductive material of core  13  contacts nozzle  2  and plate  16  to complete the current such that electrical current flows through filament  12 . 
         [0035]    The electrical current applied to the filament  12  creates a heated zone or portion  24  of filament  12  between the nozzle  2  and the plate  16 . To effect the fabrication of articles (e.g. article  25 ) the temperature of the heated portion  24  should be high enough to cause softening or partial melting of the polymer material  13 A of conductive filament  12  and/or a coating surrounding filament  12 . The partially molten segment  24  of the filament  12  is then laid onto substrate  4  or onto an already deposited/solidified portion  25 A of article  25 . A filament feed mechanism (e.g. pinch wheels  10 A and  10 B) feeds filament  12  at a rate that is substantially equal to a nozzle speed “V” across the substrate  4  to ensure that the electrical connection between the electrodes (nozzle  2  and plate  16 ) and the filament  12  remains optimal. A rapidly cooling and tacky molten zone  30  enabled by the localized heating of filament  12  allows this placement of the material. A compaction force to push the partially molten zone into the substrate or existing portion  25 A of article  25  parts may be applied as required. For example, a powered press plate  32  may be brought into contact with molten zone  30  to press the molten or partially molten material of zone  30  into existing (solidified) portion  25 A of article  25 . The process described above is repeated to build up layers  26 A,  26 B,  26 C, etc. as required to create a finished structure/article  25 . 
         [0036]    Infrared (IR) images of test samples of filaments  12  ( FIG. 2A ) are shown in  FIGS. 2B-2F . The IR images show temperature profiles of a polymer coated carbon nanotube (CNT) yarn filament  12  during testing in which the electrically conductive CNT filament was heated by applying an electrical current that caused partial melting and fusing of the polymer coating and eventually cutting the filament  12 . In  FIG. 2A , electrical clips  34 A and  34 B are applied to a filament  12 ,  FIGS. 2B-2F  are IR thermographs showing the temperatures of the test filament  12 . In  FIG. 2B , the maximum temperature of fiber  12  is 107.8° C. In  FIG. 2C , the maximum temperature of fiber  12  is 199.3° C. In  FIG. 2D  the maximum temperature of test fiber  12  is 417.8° C. In  FIG. 2E , the maximum temperature of test filament  12  is 645.7° C. In  FIG. 2F , the maximum temperature of test filament  12  is 59.4° C. after filament failure. The IR thermographs of  FIGS. 2A-2F  demonstrate that passing electrical current through a filament  12  results in significant heating of the filament  12 . The temperatures attainable are high enough to enable bonding (typically ranging between glass transition temperature and inciting temperature) or cure of state-of-the-art high performance; engineering thermoplastics or thermosetting resins. 
         [0037]    Filament  12  may comprise a CNT core  13  that is coated by a polymer material  13 A as discussed above. Alternatively, electrically conductive filament  12  may comprise a conductive core  13  that is coated by a partially cured (B-stage) thermosetting resin. If thermosetting resin is utilized for the polymer, the application of electrical current causes resistive heating of the filament  12 , and the heating causes final curing of the thermosetting resin. Localized heating permits the material to be laid down so as to enable crosslinking of the thermosetting resin between layers  26 A,  26 B, etc, and fabrication of an article  25  having a substantially continuous polymer matrix  28 . 
         [0038]    With reference to  FIG. 3 , a filament  12 A may be utilized in a process according to the present disclosure. Filament  12 A includes a polymer core  36  and conductive reinforcement fiber  38  disposed around the polymer core  36 . The conductive reinforcement fiber  38  may comprise carbon nanotube yarn or other conductive material. As shown in  FIG. 3 , the outer conductive reinforcement  38  may comprise a mesh including a plurality of first strands  40 A that spiral around polymer  36  in a first direction, and a plurality of second strands  40 B that spiral around polymer  36  in a second direction to thereby form a grid  42  defining a plurality of generally square or rectangular openings  44 , The strands  40 A and/or  40 B may comprise carbon fibers, carbon nanotube yarn, or other suitable conductive material. The conductive material  38  provides for electrical conduction in a free form fabrication process according to the present disclosure. 
         [0039]    With further reference to  FIG. 4 , a filament  12 B according to another aspect of the present disclosure includes at least one polymer strand  46  and one or more conductive reinforcing strands  47 ,  48 ,  49 . The reinforcing strands  47 ,  48 ,  49  may comprise carbon fibers, carbon nanotube yarn, or other suitable conductive material. The individual loops  46 A- 46 H of polymer strand  46  are disposed between the individual loops  47 A,  48 A,  49 A, etc. of the reinforcing strands  47 ,  48 ,  49 . 
         [0040]    It will be understood that the number and configuration of the conductive and noon-conductive strands may vary and the present disclosure is not limited to any specific filament configuration. In general, virtually any filament that includes conductive material may be utilized in connection with the present disclosure. The filament preferably includes conductive material on an outside of the filament as shown in  FIGS. 3 and 4  to ensure that the filament conducts electricity to heat the filament during additive fabrication of components. 
         [0041]    With reference to  FIG. 5 , a printed article or component  50  may be fabricated utilizing a plurality of filaments  12 A ( FIG. 3 ). In  FIG. 5 , the individual filaments  12 A are designated  12 A 1 - 12 A 6 . In  FIG. 5 , vertically adjacent filaments (e.g.  12 A 1  and  12 A 4 ) are vertically aligned. However, it will be understood that the individual filaments  12 A may be offset to form a “close packed” configuration. Also, it will be understood that  FIG. 5  is partially schematic in nature, and shows nominal positioning and shapes of the filaments  12 A 1 - 12 A 6 . During the fabrication process, the polymer material  36  (not shown in  FIG. 5 ) melts and flows through the reinforcing material  38  to fill the spaces  52 A,  52 B,  52 C, etc. shown in  FIG. 5  to form a substantially continuous polymer matrix. Also, during fabrication the reinforcing mesh  38  may deform somewhat into a shape that is at least somewhat non-cylindrical. 
         [0042]    With reference to  FIG. 6 , a printed article or component  60  may be fabricated utilizing a plurality of filaments  12 B ( FIG. 4 ).  FIG. 6  is partially schematic, and shows nominal shape and positioning of the individual filaments  12 B 1 - 12 B 6 . It will be understood that during the free form fabrication process the polymer strands  47 ,  48 ,  49  ( FIG. 4 ) at least partially melt and form a substantially continuous polymer matrix that is preferably free of voids. 
         [0043]    With reference to  FIG. 6A , an engineered filament  212  comprises a polymer matrix material  136  that is doped with a dispersed electrically conductive filler  136 B (e.g. carbon or metal particles, flakes, etc.) surrounding a continuous conductive core  138 . Core  138  may comprise carbon fiber CNT yarn, or other suitable electrically conductive material. The loading (e.g. weight %) of the dispersed electrically conductive filler  136 B is preferably above the electrical percolation threshold in order to enable current flow. Electrical current passing through the filament of  FIG. 6A  causes resistive heating of both the conductive core  138  and the percolating network of dispersed electrically conductive filler  136 B. During fabrication, the heat causes fusion of the polymer matrix material  136  of adjacent filaments  212  to form a part. The polymer matrix material  136  may fuse to form a substantially continuous matrix in the part. The dispersed electrically conductive filler  136 B may comprise a thermally conductive material that enhances heat transport between the resistively heated core  138  and the polymer matrix  136 . If a thermally conductive dispersed filler material  136  is used, the filler loaded matrix material serves to ensure that there is always an electrical bridge between the printer electrodes and the conductive core. A thermally conductive filler material  136  also provides for additional resistive heating of the matrix polymer as well as enhanced heat transport. 
         [0044]    With further reference to  FIG. 6B , an engineered filament  214  according to another aspect of the present disclosure comprises a polymer matrix  146  that is doped with an electrically conductive filler  146 B whose loading (e.g. weight %) is above the electrical percolation threshold in order to enable electrical current flow through polymer matrix  146 . Electrical current passing through the filament  214  of  FIG. 6B  causes resistive heating of the percolating network of dispersed electrically conductive filler  146 B. During fabrication of parts, the heat causes fusion of the polymer matrix material  146  of adjacent filaments  214  to form the part. The dispersed electrically conductive filler  146 B may comprise a thermally conductive material that enhances heat transport to the polymer matrix material  146 . The presence of the percolating network of electrically conductive filler  146 B throughout the filament also ensures that there is good electrical contact between the printer electrodes and the filament  214 . In other embodiments of the invention, an intrinsically electrically conductive polymer matrix material may be used in place of the finer loaded polymer matrix described above. However, an intrinsically electrically conductive polymer matrix material may also be doped with electrically conductive filler. 
         [0045]    With further reference to  FIG. 7 , a test setup  62  was utilized for the preparation of an engineered filament  12 . In the test, a DC power source  64  was operably connected to carbon nanotube (CNT) yarn wound helically around a polyetherimide (PEI) filament by electrodes  66 A and  66 B (see also  FIG. 8 ), and a controller/laptop computer  68  was operably connected to the DC power source  64 . The filament preparation material was positioned on ceramic material  70 , and a voltage was applied to electrodes  66 A and  66 B, thereby causing DC electrical current to flow through the CNT and fuse it to the PEI to form filament  12  (see also  FIG. 11 ). 
         [0046]      FIG. 9  is a graph showing test results from the setup  62  of  FIGS. 7 and 8 . Line  72  represents measured temperature, dashed line  74  represents the electrical current, and the stepped line  76  represents the applied voltage. The horizontal line segment  72 A is due to detector saturation, and the temperature results for this applied voltage (12V) shown in the graph of  FIG. 9  is therefore not believed to be accurate. 
         [0047]      FIGS. 10A-10F  are IR thermographs showing temperature at various stages during the filament preparation process, and the times and voltages correspond to the same in  FIG. 9 . The thermographs are snapshots taken at T=0, 1, 238, 257, 305 and 350 s. The test shows that the temperature during the filament preparation process can be carefully controlled (by control of the applied current) to enable the partial melting of the polymer and fusing to the conductive fiber that allows the resulting composite filament to be used in the additive manufacturing process. 
         [0048]    With reference to  FIG. 11 , an engineered carbon nanotube (CNT) and polyetherimide (PEI) filament  12 C according to another aspect of the present disclosure includes a polymer core strand  78  and a continuous conductive strand  80 . Strand  80  comprises CNT yarn that is spiraled around the PEI core  78 . The CNT strand  80  provides for conduction of electrical current when the filament  12 C is utilized in an additive manufacturing process according to the present disclosure. 
         [0049]    A test setup  90  ( FIGS. 12-16 ) was utilized to further test a 3D additive process according to the present disclosure. Test setup  90  includes a controller such as a laptop computer  92  and a DC power supply  94 . A 3D printer  96  comprises a modified open source 3D printer and includes a head assembly  100  that is movable via a known support/actuation assembly  102 . A power supply control unit  104  controls the electrical power provided by power source  94 . The electrical power is supplied to the head assembly  1  by electrical lines  106 . An IR camera  108  may be utilized to determine the temperature of the components during the fabrication process. The 3D printer  96  also includes a platform or support  110  upon which the filaments are deposited by the head assembly  100 . The head assembly  100  includes a heating foot  112  that operates in a manner that is somewhat similar to the plate  16  ( FIG. 1 ) described in more detail above. 
         [0050]    With further reference to  FIGS. 13 and 15 , heating foot  112  includes an outer support  114  that may be formed from a polymer or other suitable material. The heating foot  112  is movably connected to structure  118  of head assembly  100  by one or more springs  116 A,  1160  and one or more shafts  120 A,  120 B. Shafts  120 A,  120 B, etc. linearly guide heated foot  112  relative to structure  118 . A conductive metal foot component  122  includes an opening  124 . Foot component  122  is operably connected to a first pole or terminal of electrical power supply  94  to form a first electrode. In use, filament is fed through opening  124  such that the filament contacts conductive metal foot component  122  of heating foot  112 . Heating foot  112  also includes a second electrode  126  ( FIG. 14 ) that is connected to a second pole or terminal of an electrical power supply. Second electrode  126  is positioned above the foot component  122 . In use, the filament  12  contacts the electrodes  122  and  126  to heat the filament. 
         [0051]    With further reference to  FIGS. 15 and 16 , a suitable substrate such as polymer part  128  may be positioned on the platform  110 . During the test, a continuous CNT yarn filament  12  (ABS/CNT yarn) was placed on the substrate  128  in a desired location. A voltage (or current) was applied to the filament  12  by electrodes  122  and  126 . The nozzle  2  moves relative to the plate  110  and substrate  128  to print continuous CNT yarn filament under controlled voltage (or current). As shown in  FIG. 16 , filament  12  may be cut to form a gap  130  between the filament segments. The filament  12  can be cut by applying a cutting voltage to the filament  12  utilizing electrodes  122  and  126 , thereby melting and/or ablating a portion of the filament  12 . In the example shown in  FIG. 16 , the cutting voltage is 25V. 
         [0052]    The process and devices described herein provide a unique way to build continuously reinforced components using a simple and energy efficient heating process. In particular, the design and fabrication of a filament is specially engineered to enable free form fabrication using Joule heating, (i.e. a process in which there is a continuous conductivity path). The electrodes are specifically configured to utilize the engineered filament to provide continuous flow of electrical current through a portion of the filament disposed between the first and second electrodes. 
         [0053]    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. 
         [0054]    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. 
         [0055]    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. 
         [0056]    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. 
         [0057]    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). 
         [0058]    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.