Patent Publication Number: US-11383407-B2

Title: Layup and fabrication of tows of braided fiber for hybrid composite parts

Description:
FIELD 
     The disclosure relates to the field of fabrication, and in particular, to fabrication of fiber reinforced composite parts via the layup of tows. 
     BACKGROUND 
     Multi-layer laminates of constituent material (e.g., Carbon Fiber Reinforced Polymer (CFRP)) may be formed into any of a variety of shapes for hardening into a composite part. A laminate may be laid-up in layers that each comprise a tow of unidirectional fiber-reinforced material. Laminates may be laid-up by hand, by an Automated Tape Layup Machine (ATLM), or by an Automated Fiber Placement (AFP) machine. 
     While laminates provide desired levels of performance when hardened into composite parts, layup processes for laminates remain complicated and time-consuming. Furthermore, techniques for affixing laminates together, such as induction welding, may be difficult to perform upon laminates made from such materials. For example, heating a laminate made from these materials via induction may require more current to be run through an induction coil than is desirable. 
     Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. 
     SUMMARY 
     Embodiments described herein provide for tows that comprise braided fibers for a laminate. The tows are pre-impregnated with thermoplastic, and may be laid-up by an ATLM or AFP machine. Furthermore, because the fibers are conductive, intersections between the fibers generate heat in response to applied magnetic fields. This increases the amount of heating at the tows during induction welding, as compared to tows of unidirectional fiber. 
     One embodiment is a method for fabricating tows of braided thermoplastic fiber-reinforced material. The method includes braiding pre-impregnated fibers of unidirectional material to form a weave having a circumference that forms a closed cross-sectional shape around a mandrel, tacking the pre-impregnated fibers at tacking positions along the circumference, and cutting the weave at a cut position between the tacking positions, with a knife that proceeds in the process direction along the length of the weave and is disposed behind the rollers. 
     A further embodiment is a non-transitory computer readable medium embodying programmed instructions which, when executed by a processor, are operable for performing a method. The method includes braiding pre-impregnated fibers of unidirectional material to form a weave having a circumference that forms a closed cross-sectional shape around a mandrel, tacking the pre-impregnated fibers at tacking positions along the circumference, and cutting the weave at a cut position between the tacking positions, with a knife that proceeds in the process direction along the length of the weave and is disposed behind the rollers. 
     A further embodiment is an apparatus for fabricating tows of braided thermoplastic fiber-reinforced material. The apparatus includes rollers that apply heat and pressure at tacking positions along a circumference of a weave of braided pre-impregnated fibers of unidirectional material that is laid-up at a cylindrical mandrel, and that proceed in a process direction along a length of the weave, and a knife that cuts the weave at a cut position between the tacking positions, proceeds in the process direction along the length of the weave, and is disposed behind the rollers. 
     Other illustrative embodiments (e.g., methods and computer-readable media relating to the foregoing embodiments) may be described below. The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present disclosure are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1  is a block diagram of a fabrication environment in an illustrative embodiment. 
         FIG. 2  is a flowchart illustrating a method for operating a hybrid layup system in an illustrative embodiment. 
         FIG. 3A  is a side view of an end effector laying up tows of braided fibers onto a laminate consisting of tows of unidirectional fibers in an illustrative embodiment. 
         FIG. 3B  is a top view of an end effector laying up tows of braided fibers onto a laminate consisting of tows of unidirectional fibers in an illustrative embodiment. 
         FIGS. 4-6  are side views of laminates that include tows of braided fibers along a location at which induction welding will occur in an illustrative embodiment. 
         FIG. 7  is a block diagram of a fabrication system for creating tows of braided fibers in an illustrative embodiment. 
         FIG. 8  is a flowchart illustrating a method for operating a fabrication system to create tows of braided fibers in an illustrative embodiment. 
         FIG. 9  is side view of the fabrication system of  FIG. 7  cutting a closed-weave of braided fibers to form a tow of material in an illustrative embodiment. 
         FIG. 10  is a perspective view of a weave that has been cut and removed from a mandrel in an illustrative embodiment. 
         FIG. 11  is a flow diagram of aircraft production and service methodology in an illustrative embodiment. 
         FIG. 12  is a block diagram of an aircraft in an illustrative embodiment. 
     
    
    
     DESCRIPTION 
     The figures and the following description provide specific illustrative embodiments of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within the scope of the disclosure. Furthermore, any examples described herein are intended to aid in understanding the principles of the disclosure, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the disclosure is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
     Composite parts, such as Carbon Fiber Reinforced Polymer (CFRP) parts, are initially laid-up in multiple layers that together are referred to as a preform. Individual fibers within each layer of the preform are aligned parallel with each other, but different layers may exhibit different fiber orientations in order to increase the strength of the resulting composite part along different dimensions. The preform may include a viscous resin that solidifies in order to harden the preform into a composite part (e.g., for use in an aircraft). Carbon fiber that has been impregnated with an uncured thermoset resin or a thermoplastic resin is referred to as “prepreg.” Other types of carbon fiber include “dry fiber” which has not been impregnated with thermoset resin but may include a tackifier or binder. Dry fiber may be infused with resin prior to curing. For thermoset resins, the hardening is a one-way process referred to as curing, while for thermoplastic resins, the resin may reach a viscous form if it is re-heated. 
       FIG. 1  is a block diagram of a fabrication environment  100  that includes a hybrid layup system  110  in an illustrative embodiment. Hybrid layup system  110  comprises any system or device that is capable of laying up unidirectional tows  126  (i.e., tows of unidirectional fiber) and braided tows  128  (i.e., tows of braided fibers) to form a laminate  160  having both unidirectional fiber layers and braided fiber layers. The braided tows  128  may be biasedly braided, in order to exhibit any desired combination of fiber orientations that are not parallel or perpendicular to the length of the tow. For example, the fiber orientations may be +22°/−22°, +45°/−45°, +10°/−10°, +80°/−80°, etc. Furthermore, the fibers in each of the tows of braided thermoplastic fiber-reinforced material may form an open weave, a closed weave, or any desired pattern. 
     According to  FIG. 1 , hybrid layup system  110  includes controller  112  and memory  114 . Controller  112  directs the operations of hybrid layup system  110 , and memory  114  stores instructions (e.g., a Numerical Control (NC) program) for operating the hybrid layup system  110 . Controller  112  may be implemented, for example, as custom circuitry, as a hardware processor executing programmed instructions, or some combination thereof. 
     Hybrid layup system  110  also includes a spool  116 , which stores unidirectional tows  126  (e.g., tows of unidirectional fiber pre-impregnated with thermoplastic), and a spool  118  which stores braided tows  128  (e.g., tows of braided fiber pre-impregnated with thermoplastic). Each other tows described herein may comprise a linear, integral tape that extends for tens or hundreds of feet. End effector  136  lays up unidirectional tows  126 , and end effector  138  lays up braided tows  128 . Heaters  142  and  144  (e.g., radiant heaters, lasers, etc.) and cooling systems  144  and  148  (e.g., fans, cold mandrels, etc.) facilitate the layup process as described below with regard to  FIG. 3 . The tows described herein may comprise “dry fiber” tows secured with a binder or tackifier, or tows that are pre-impregnated with thermoplastic. 
     Laminate  160  is laid-up by hybrid layup system  110  onto mandrel  150 , and includes both unidirectional tow layers  162  and braided tow layers  164 . Unidirectional tow layers  162  include thermoplastic  163  (e.g., polyetheretherketone (PEEK), polyetherketoneketone (PEKK)) and unidirectional fibers  165 , while braided tow layers  164  include thermoplastic  163  and woven fibers  167 . As used herein, braided/woven fibers are fibers which are interwoven with each other to form a pattern. These patterns may include open weaves, closed weaves, triaxial weaves, etc. In one embodiment, a size (e.g., a diameter) of fibers in a first set of layers (i.e., unidirectional tow layers  162 ) is equal to a size of fibers in a second set of layers (i.e., braided tow layers  164 ). 
     Illustrative details of the operation of hybrid layup system  110  will be discussed with regard to  FIG. 2 . Assume, for this embodiment, that hybrid layup system  110  is disposed above the mandrel  150 , and is about to perform layup of a laminate. 
       FIG. 2  is a flowchart illustrating a method  200  for operating a hybrid layup system in an illustrative embodiment. The steps of method  200  are described with reference to hybrid layup system  110  of  FIG. 1 , but those skilled in the art will appreciate that method  200  may be performed in other systems. The steps of the flowcharts described herein are not all inclusive and may include other steps not shown. The steps described herein may also be performed in an alternative order. 
     In step  202 , controller  112  operates the end effector  136  to retrieve tows of unidirectional fiber-reinforced material from a first spool. In one embodiment, this comprises drawing the tows via pinch rollers (not shown) at the end effector  136 . The feed rate may be any desired rate, such as several feet per minute or more. 
     In step  204 , controller  112  lays up a first set of layers comprising the tows of unidirectional thermoplastic fiber-reinforced material for the laminate  160 . In one embodiment, this comprises operating the end effector  136  according to instructions in an NC program stored in memory  114 . This comprises dispensing and cutting segments from the tows at directions and orientations indicated by the NC program. In further embodiments, the tows may occupy each of multiple lanes which are separately dispensed and cut. 
     In step  206 , controller  112  operates the end effector  138  to retrieve tows of braided thermoplastic fiber-reinforced material from a second spool. In one embodiment, this comprises drawing the tows via pinch rollers (not shown) at the end effector  138 . The feed rate may be any desired rate, such as several feet per minute or more. In one embodiment, step  206  is performed synchronously with step  202 , while in further embodiments, step  206  is performed independently of step  202 . 
     In step  208 , controller  112 , lays up a second set of layers comprising the tows of braided thermoplastic fiber-reinforced material for the laminate  160 . In one embodiment, this comprises operating the end effector  138  according to instructions in an NC program stored in memory  114 . This comprises dispensing and cutting segments from the tows at a direction and orientation indicated by the NC program. In further embodiments, the tows may occupy each of multiple lanes which are separately dispensed and cut. In some embodiments, laying up the second set of layers is performed at a location where the laminate will be induction welded to another laminate. 
     Laying up the second set of layers may further comprise steering the tows of braided thermoplastic fiber-reinforced material. For example, controller  112  may operate the end effector  136  and the end effector  138  during layup, and may steer the second set of layers while the end effector  138  is laying up of the second set of layers. Steering a braided tow is beneficial in comparison to steering a unidirectional tow, because fibers within the braided tow shift more easily with respect to each other and are easier to place into shear than an entire sheet of fabric. 
     Method  200  provides an advantage over prior systems and techniques because it enables the crafting of composites having both woven layers and unidirectional layers. Furthermore, because the braided layers are formed from tows (and not from a single continuous prefabricated sheet), the tows may be laid-up to form a braided layer of any desired size. Method  200  also provides a substantial advantage in facilitating induction welding, which is discussed below. 
       FIG. 3A  is a side view of an end effector  138  laying up braided tows  128  of braided fibers onto a laminate consisting of unidirectional tows  126  (made of unidirectional fibers) in an illustrative embodiment. According to  FIG. 3 , braided tows  128 , which are arranged into one or more lanes for layup at end effector  138 , are heated by heater  146 . This increases the temperature of the braided tows  128  to a tacking temperature (e.g., a temperature within thirty degrees Fahrenheit of a melting temperature of thermoplastic in the braided tows  128 ). In a further embodiment, heaters heat the layers of a laminate to a melting temperature of the thermoplastic while laying up the layers. Compaction roller  300  presses the braided tows  128  onto the laminate, and cooling system  148  applies a cooling fluid (e.g., room temperature air at a high volumetric flow rate, water, etc.) to the surface of the braided tows  128  after compaction by compaction roller  300 . 
       FIG. 3B  is a top view of an end effector  138  laying up tows of braided fibers onto a laminate consisting of tows of unidirectional fibers in an illustrative embodiment. According to  FIG. 3B , the end effector  138  moves along a curve  370  while placing tows  360 , performing what is known as “steering” of the tows  360 . This enables the tows  360  to match complex contours, and to vary from tows  350  in underlying layers. 
       FIGS. 4-6  are side views of laminates that include tows of braided fibers along a location at which induction welding will occur in an illustrative embodiment. Specifically,  FIG. 4  illustrates laminate  410  and laminate  420  arranged for an induction weld along a line L in an illustrative embodiment. As shown in  FIG. 4 , layers  414  of laminate  410  and laminate  420  are disposed proximate to the line L. These layers  414  comprise tows of braided fiber. In embodiments where the fiber is made from an electrically conductive material such as carbon fiber, intersections between the fibers experience inductive heating when exposed to a magnetic field. This in turn increases a temperature of the laminates  410  and  420  proximate to the line L to a temperature above a melting temperature of thermoplastic in the laminates, which facilitates induction welding. Hence, a benefit in induction welding is achieved even though layers  412  comprise tows of unidirectional fiber. 
       FIG. 5  illustrates a variation of  FIG. 4 , wherein a laminate  510  and a laminate  520  are arranged for an induction weld to be formed along a line L. As shown in  FIG. 5 , layer  514  of braided fibers is disposed at the line L, and is adjacent to layers  512  of unidirectional fiber to the left and right. This arrangement localizes the region which experiences the most inductive heating during an induction weld. 
     In  FIG. 6 , a layer  630  of braided fibers is provided, in order to facilitate an induction weld that forms an elbow joint  640 . As shown in  FIG. 6 , an elbow-shaped laminate  610  is induction welded along line L to a flat laminate  620 . Layer  630  is disposed between the two laminates along the line L. When exposed to a magnetic field, such as during an induction weld, intersections between fibers in layer  630  act as susceptors and generate heat. This heat melts thermoplastic in the neighboring laminates, which commingles thermoplastic between the laminates. Upon solidification of the thermoplastic, the laminates are united into a single composite part. 
       FIG. 7  is a block diagram of a fabrication system  700  for creating tows of braided fibers in an illustrative embodiment. Fabrication system  700  comprises any system or device that is capable of cutting a woven/braided preform having a closed cross-sectional shape, and winding the preform onto a spool for later layup onto a laminate. 
     In this embodiment, fabrication system  700  includes controller  720 , which operates fabrication system  700  in accordance with a Numerical Control (NC) program. Controller  720  may be implemented, for example, as custom circuitry, as a hardware processor executing programmed instructions, or some combination thereof. 
     Braiding machine  710  comprises a three-dimensional braiding machine that braids unidirectional tows of material into a three-dimensional braid. For example, braiding machine  710  may include spools which each provide unidirectional fibers, and that orbit each other in predefined patterns in order to braid those fibers into a weave  740  that is formed about a mandrel  730  and that has a desired pattern. Upon completion of the weave  740 , the weave  740  is wrapped around mandrel  730 , has a circumference  780 , and may extend for tens or hundreds of feet (in a direction proceeding into the page). 
     After braiding, weave  740  is cut (e.g., as explained with regard to  FIG. 9  below) and removed from the mandrel  730 . To facilitate this process, rollers  750  are heated by heaters  752 , and increase a temperature of the weave  740  to a tacking temperature of a thermoplastic within the weave  740 . The rollers also apply force F pushing the weave  740  into the mandrel  730  at tacking locations T. After rollers  750  proceed (e.g., in a direction proceeding into the page), the thermoplastic cools and adheres the thermoplastic to the mandrel. This prevents the weave  740  from sliding when the weave  740  is cut. Knife  760  cuts the weave  740  along a cut location C. The weave  740  is then released from the mandrel  730 , and is wound about the spool  770 . When it is wound about the spool  770 , the circumference of the weave  740  is uncurled and pressed flat. 
       FIG. 8  is a flowchart illustrating a method  800  for operating a fabrication system to create tows of braided fibers in an illustrative embodiment. According to  FIG. 8 , step  802  includes braiding pre-impregnated fibers of unidirectional material to form a weave having a circumference that forms a closed cross-sectional shape (e.g., a circle, an ellipse, a square) around a mandrel. In one embodiment, this step is performed by an industrial three-dimensional braiding machine operating in accordance with an NC program. 
     In step  804 , the pre-impregnated fibers are tacked at tacking positions along the circumference of the weave  740 , by heating and compacting the pre-impregnated fibers with rollers  750  that proceed in a process direction along a length of the weave (e.g., by heating and compacting surface layers, or all layers at the weave). The tacking process adheres the weave  740  at the tacking positions. This means that the weave  740  is secured, and resists sliding along the mandrel  730  when the weave  740  is cut. 
     Step  806  includes cutting the weave  740  at the cut position between the tacking positions, with a knife  760  that proceeds along the weave  740  and is disposed behind the rollers  750 . This cut opens the weave  740 , enabling the weave to be flattened and rolled/taken up onto a spool. 
       FIG. 9  is side view of the fabrication system of  FIG. 7  cutting a weave  740  of braided fibers to form a tow of material in an illustrative embodiment. As shown in  FIG. 9 , roller  750  is heated by heater  752  and compacts the weave  740  onto the mandrel  730 . As the roller  750  proceeds in a process direction, a knife  760  follows and cuts the weave  740 . The weave  740  is then pulled off of the mandrel  730  (e.g., forward, downward, etc., breaking any tacking that secures the weave  740  to the mandrel  730 ). A circumference  780  of the weave  740  is flattened into a planar shape, and the weave  740  is rolled onto a spool such that each turn of the spool acquires more of the length of the weave  740  (i.e., its longitudinal length is rolled onto the spool). 
       FIG. 10  is a perspective view of a weave  1000  that has been cut and removed from a mandrel in an illustrative embodiment. In this embodiment, the weave  1000  includes side  1010  and side  1012 , as well as cut edge  1020  and cut edge  1022 . The weave  1000  has been flattened into a planar shape (e.g., by a press), although some curvature remains in the illustration to distinguish the sides of the weave from the cut edges. 
     In one embodiment, the weave  1000  is rolled onto a spool by placing a first cut edge (e.g., cut edge  1020 ) of the weave in contact with the spool, rolling the spool to take up the sides (e.g., side  1010  and side  1012 ) of the weave, and finishing by placing a second cut edge (e.g., cut edge  1022 ) of the weave at the spool. In a further embodiment, the weave  1000  is rolled onto a spool by placing a first side (e.g., side  1010 ) of the weave in contact with the spool, rolling the spool to take up the cut edges (e.g., cut edge  1020  and cut edge  1022 ) of the weave, and finishing by placing a second side (e.g., side  1012 ) of the weave at the spool. 
     EXAMPLES 
     In the following examples, additional processes, systems, and methods are described in the context of a fabrication and layup system for hybrid composite parts. 
     Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of aircraft manufacturing and service in method  1100  as shown in  FIG. 11  and an aircraft  1102  as shown in  FIG. 12 . During pre-production, method  1100  may include specification and design  1104  of the aircraft  1102  and material procurement  1106 . During production, component and subassembly manufacturing  1108  and system integration  1110  of the aircraft  1102  takes place. Thereafter, the aircraft  1102  may go through certification and delivery  1112  in order to be placed in service  1114 . While in service by a customer, the aircraft  1102  is scheduled for routine work in maintenance and service  1116  (which may also include modification, reconfiguration, refurbishment, and so on). Apparatus and methods embodied herein may be employed during any one or more suitable stages of the production and service described in method  1100  (e.g., specification and design  1104 , material procurement  1106 , component and subassembly manufacturing  1108 , system integration  1110 , certification and delivery  1112 , service  1114 , maintenance and service  1116 ) and/or any suitable component of aircraft  1102  (e.g., airframe  1118 , systems  1120 , interior  1122 , propulsion system  1124 , electrical system  1126 , hydraulic system  1128 , environmental system  1130 ). 
     Each of the processes of method  1100  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 12 , the aircraft  1102  produced by method  1100  may include an airframe  1118  with a plurality of systems  1120  and an interior  1122 . Examples of systems  1120  include one or more of a propulsion system  1124 , an electrical system  1126 , a hydraulic system  1128 , and an environmental system  1130 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
     As already mentioned above, apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service described in method  1100 . For example, components or subassemblies corresponding to component and subassembly manufacturing  1108  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  1102  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the subassembly manufacturing  1108  and system integration  1110 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  1102 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  1102  is in service, for example and without limitation during the maintenance and service  1116 . For example, the techniques and systems described herein may be used for material procurement  1106 , component and subassembly manufacturing  1108 , system integration  1110 , service  1114 , and/or maintenance and service  1116 , and/or may be used for airframe  1118  and/or interior  1122 . These techniques and systems may even be utilized for systems  1120 , including, for example, propulsion system  1124 , electrical system  1126 , hydraulic system  1128 , and/or environmental system  1130 . 
     In one embodiment, a part comprises a portion of airframe  1118 , and is manufactured during component and subassembly manufacturing  1108 . The part may then be assembled into an aircraft in system integration  1110 , and then be utilized in service  1114  until wear renders the part unusable. Then, in maintenance and service  1116 , the part may be discarded and replaced with a newly manufactured part. Inventive components and methods may be utilized throughout component and subassembly manufacturing  1108  in order to manufacture new parts. 
     Any of the various control elements (e.g., electrical or electronic components) shown in the figures or described herein may be implemented as hardware, a processor implementing software, a processor implementing firmware, or some combination of these. For example, an element may be implemented as dedicated hardware. Dedicated hardware elements may be referred to as “processors”, “controllers”, or some similar terminology. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, a network processor, application specific integrated circuit (ASIC) or other circuitry, field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), non-volatile storage, logic, or some other physical hardware component or module. 
     Also, a control element may be implemented as instructions executable by a processor or a computer to perform the functions of the element. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to perform the functions of the element. The instructions may be stored on storage devices that are readable by the processor. Some examples of the storage devices are digital or solid-state memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. 
     Although specific embodiments are described herein, the scope of the disclosure is not limited to those specific embodiments. The scope of the disclosure is defined by the following claims and any equivalents thereof.