Abstract:
A tape laminating machine having a compaction roller lays up composite tape over a substrate having a convex radius. The compaction roller folds the tape as it moves over the convex radius, while simultaneously pivoting about a trailing edge of the tape to prevent the compaction roller from lifting off the tape laid just before the convex radius.

Description:
BACKGROUND INFORMATION 
       [0001]    1. Field 
         [0002]    The present disclosure broadly relates to fabrication of fiber reinforced composite laminates, and deals more particularly with a method of laminating composite tape over edges having convex radii. 
         [0003]    2. Background 
         [0004]    Composite laminate structures such as those used in the automotive, marine and aerospace industries may be fabricated using automated composite material application machines, commonly referred to as automated fiber placement (AFP) machines. AFP machines may be used in the aircraft industry, for example, to fabricate structural members and skin assemblies by wrapping relatively narrow strips of slit prepreg tape known as “tows”, collimated into a wider band around a manufacturing tool or other substrate. AFP machines have a material application head that includes a plurality of tape control modules which align, cut and place the tape strips, typically six or more, “on-the-fly” under numeric control. The tape strips are aligned in continuous, edge-to-edge contact forming a single wide conformal bandwidth which is compacted against the tool using a compaction device such as a compaction roller or a shoe. 
         [0005]    The plies forming the laminate structure may be made up of plies have differing fiber orientations, such as 0°, 45° and 90° plies, with each ply being formed by multiple courses of a conformal bandwidth of tape strips placed by the AFP machine. In some cases, depending upon the shape of the part, the substrate (e.g. the tool) may have one or more radius edges over which the tape strips must be applied and compacted. However, a problem sometimes exists where it is necessary to apply the tape strips at an angle, such as a 45° angle, over an edge having a relatively sharp, convex radius, such as a 90° convex radius. As the compaction device moves over the radius edge at an angle, the trailing edge of the conformal bandwidth of tape strips just laid before the radius edge may be lifted away from the substrate by continued movement of the compaction device over the radius edge, resulting in voids or wrinkles in the plies which can adversely affect the quality of the completed structure. 
         [0006]    Accordingly, there is a need for a method of laminating composite tape over convex radius edges that reduces or eliminates voids or wrinkles in plies caused by lifting of the tape after it has been placed and compacted. 
       SUMMARY 
       [0007]    The disclosed embodiments provide a method of laminating composite tape over a relatively sharp convex radius edge, where the tape is applied with a fiber orientation that forms an angle, such as a 45° angle relative to the convex radius edge. The method reduces or eliminates lifting of just-laid tape away from the substrate is the radius edge, as a compaction roller traverses over the radius edge. 
         [0008]    According to one disclosed embodiment, a method is provided of laminating composite tape over a convex radius edge on a substrate. The method comprises moving a material placement head over the substrate toward and around the convex radius edge, and laying down a bandwidth of the composite tape strips on the substrate is a material placement head moves over the substrate and around the convex radius edge, including using a compaction device to compact the tape strips against the substrate. The method further includes for preventing the compaction device from lifting off tape strips laid near the convex radius edge by pivoting the compaction device around a trailing edge of the bandwidth in contact with the convex radius edge. The method also includes folding in the bandwidth of the tape strips as the material placement head moves around the convex radius edge. The compaction device has a longitudinal axis and a tool center point lying along the longitudinal axis at one end of the compaction device, and pivoting the compaction device around the trailing edge of the bandwidth of tape strips includes pivoting the compaction device about the tool center point. Laying down the bandwidth of tape strips includes laying down a plurality of tape strips side-by-side on the substrate, and pivoting the compaction device includes pivoting the compaction device at a point lying along one of the tape strips near an edge of the bandwidth. Pivoting the compaction device is performed as the material placement head moves around the convex radius edge. The compaction device may be a compaction roller having an axis of rotation that is angularly offset from the convex radius edge. In one embodiment, the axis of rotation of the compaction roller is angularly offset from the convex radius edge by approximately 45°. Contact between the compaction device and the substrate is maintained throughout the movement of the material placement head around the convex radius edge. 
         [0009]    According to another disclosed embodiment, a method is provided of laying down prepreg fibers on a substrate having two surfaces connected by a radius edge. The method comprises moving a composite material placement head across a first substrate surface at an angle to the radius edge, and laying down a bandwidth of prepreg fibers on the first substrate surface. The method further comprises moving the material placement head around the radius edge from the first substrate surface to a second substrate surface, and pivoting the material placement head about a point near one edge of the bandwidth of the prepreg fibers as the material placement head moves around the radius edge. The method may further comprise moving the material fiber placement head from a radius edge across the second substrate surface and an angle to the radius edge, and laying down a bandwidth of the prepreg fibers on the second substrate surface. Laying down a bandwidth of the prepreg fibers on the first substrate surface includes laying down strips of fiber tows in side-by-side, edge to edge contact with each other, and compacting the strips of fiber tows. The point about which the material placement head is pivoted is located within one of the strips of fiber tows near one edge of the bandwidth of prepreg fibers. Compacting the strips of fiber tows is performed using a compaction roller, and pivoting the material placement head includes pivoting the compaction roller about a tool center point lying near one end of the compaction roller. The method further comprises folding the bandwidth of prepreg fibers as the material placement head is moved around the radius edge from the first substrate surface to the second substrate surface. The angle of movement of the material placement head to the radius edge may be approximately 45°. 
         [0010]    According to still another embodiment, a method is provided of laminating composite tows over a convex radius using a material placement head having a compaction roller. The method comprises moving the material placement head around the convex radius as composite tows are being laminated in a bandwidth over the convex radius. The method further comprises pivoting the compaction roller at a location across the bandwidth that prevents a compaction roller from lifting off the tows laid just before the material placement head begins moving around the convex radius. The method also includes folding the bandwidth of prepreg tows as the compaction roller moves around the convex radius. The location across the bandwidth about which the compaction roller is pivoted is between a center tow and a last tow along the trailing edge of the bandwidth. 
         [0011]    According to a further embodiment, a method is provided of laminating composite tape over a convex radius using a tape laminating machine having a compaction roller. The method comprises programming the tape laminating machine to move along a path over a substrate, and directing the compaction roller to move along the path and pivot around a trailing edge of the tape that contacts the convex radius to prevent the compaction roller from lifting off the tape played just before the convex radius. The method also includes folding the tape as the compaction roller moves over the convex radius. The method may further comprise digitally defining a composite layup having a convex radius, and using the tape laminating machine to layout plies of the digitally defined layup. The tape laminating machine may be programmed such that the tape laminating machine moves along a modified path for laying up plies respectively having 0°, 45° and 90° fiber orientations. Directing the compaction roller to move along the path and pivot around a trailing edge of the tape is performed while folding the tape as the compaction roller moves over the convex radius. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is an illustration of a perspective view of a tape laminating machine laying down composite tape over a substrate having a convex radius edge. 
           [0014]      FIG. 2  is an illustration of a front view of a conformal bandwidth of tape being placed over a convex radius edge using a prior art method. 
           [0015]      FIG. 3  is an illustration of the substrate shown in  FIG. 1 , showing an area of the bandwidth that is pulled away from the substrate when using the prior art method. 
           [0016]      FIG. 4  is an illustration similar to  FIG. 3 , but showing the compaction or roller having folded the bandwidth of tape around the radius edge using the prior art method. 
           [0017]      FIG. 5  is an illustration of a flow diagram of a method of laminating composite tape over a convex radius edge. 
           [0018]      FIG. 6  is an illustration of a front view similar to  FIG. 2 , but showing a modified tool center point about which the compaction roller is pivoted as the radius edge is traversed by the compaction roller. 
           [0019]      FIG. 7  is an illustration of a perspective view of a compaction roller beginning to traverse over the radius edge, according to the disclosed method. 
           [0020]      FIG. 8  is an illustration similar to  FIG. 7 , but showing the compaction roller having pivoted about the modified tool center point at the trailing edge of the conformal bandwidth. 
           [0021]      FIG. 9  is an illustration of an overall flow diagram of a method of laying up a composite part which employs the disclosed technique of rotating the compaction roller as it traverses a radius edge at an angle. 
           [0022]      FIG. 10  is an illustration of a flow diagram of aircraft production and service methodology. 
           [0023]      FIG. 11  is an illustration of a block diagram of an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring first to  FIG. 1 , an automatic fiber placement (AFP) machine  12  includes a material placement head  20  whose movements may be controlled by a robot  14  suitable for the application. The robot  14 , as well as the functions of the material placement head  20  are controlled by a controller  16  which may comprise, without limitation, a CNC (computer numerically controlled) controller or a computer employing one or more NC programs  18 . The material placement head  20  may be similar to those described in U.S. Pat. No. 7,213,629, U.S. patent application Ser. No. 12/038,155 filed Feb. 27, 2008, and US Patent Publication No. 20070029030 published Feb. 8, 2007, the entire contents of which are incorporated by reference herein. The material placement head  20  may include a material supply system (not shown) and a plurality of tape control modules (not shown) which may include rethread mechanisms, material guides, and material cutting mechanisms, all not shown but well known in the art. 
         [0025]    The material placement head  20  feeds  25  a conformal bandwidth  24 , sometimes also referred to herein as a tape bandwidth  24 , of composite tape strips  26  in the form of tape strips, prepreg tows or other rovings to a nip  45  between a compaction device such as a compaction roller  22 , and a substrate  34  which may comprise a tool or a previously laid ply of composite material. As used herein, “tape strips” is intended to include reinforced and reinforced plastic strips, prepreg tapes, tows and other rovings, and “bandwidth” and “conformal bandwidth” are intended to include a plurality of tape strips arranged in continuous side-by-side, substantially edge-to-edge contact with each other. Other compaction devices, such as a shoe may be used to place the conformal bandwidth  24  onto the substrate  34 . The compaction roller  22  is cylindrical in shape and has an axis of rotation  32  as well as a tool center point  30 . The material placement head  20  moves the compaction roller  22  over the substrate  34 , compacting the conformal bandwidth  24  onto the substrate  34 . Each pass of the material placement head  20  over the substrate  34  results in the placement of a course of tape strips  26  forming conformal bandwidth  24 , and multiple passes of the material placement head  20  result in the formation of plies (not shown) of composite material being laid down on and compacted against the substrate  34 . 
         [0026]    The substrate  34  may have non-parallel substrate surfaces  36 ,  38  that are connected together along a convex radius edge  40 . The material placement head  20  may place courses of the conformal bandwidths  24  of tape strips  26  at various angles of fiber orientation including, but not limited to 0°, 45° and 90° orientations relative to a reference axis  35  which corresponds to a horizontal or Z axis in the XYZ coordinate system  43 . In  FIG. 1 , the material placement head  20  has partially placed a bandwidth  24  of tape strips twenty-six over one substrate surface  36  and is moving in a direction  27  toward the radius edge  40  at an angle θ, which may be, for example and without limitation, a 45° angle. As will be discussed below in more detail, the compaction roller  22  moves from the substrate surface  36  up around the radius edge  40 , and then across substrate surface  38  during placement of a tape course. 
         [0027]    Attention is now directed to  FIGS. 2-4  which illustrate a prior art method of placing composite tape strips  26  in a conformal bandwidth  24  over a convex radius edge  40 . As shown in  FIGS. 2 and 3 , the tool center point  30  of the compaction roller  22  lies substantially midway between the two ends of the compaction roller  22 , and along the centerline  42  of the center tape strip  26   a  in the conformal bandwidth  24 . Because the compaction roller  22  moves toward the radius edge  40  at an angle θ, when the tool center point  30  reaches the beginning of the radius edge  40 , the leading edge  44  of the conformal bandwidth  24  has moved up above and begins to move over the radius edge  40  while the just-laid trailing edge  53  of the conformal bandwidth  24  remains beneath the radius edge  40 . 
         [0028]    When the tool center point  30  reaches the radius edge  40 , it begins moving up over the radius edge  40  onto the substrate surface  38 . During this movement of the compaction roller  22  over the radius edge  40 , the pressure applied by the compaction roller  22  to the trailing edge of the tape bandwidth  24  is reduced, while compaction pressure continues to be applied to the leading edge  44  of the tape band  24 . This differential in compaction pressure being applied to the tape bandwidth  24  causes an area of the tape bandwidth  24  along the trailing edge  31  represented by the crosshatching  46  to pull away from the substrate surface  36 , resulting in potential voids or wrinkling of the laminate structure.  FIG. 4  shows compaction roller  22  having traversed around the radius edge  40 , and beginning to compact the tape bandwidth  24  onto the substrate surface  38 . As can be seen in  FIG. 4 , although the tape bandwidth  24  is applied around the radius edge  40 , an area  46  of the tape bandwidth  24  is not tightly compacted against the substrate surface  36 . 
         [0029]    Attention is now directed to  FIGS. 5-8  which broadly illustrate a method of laminating composite tape over a convex radius edge  40 , that avoids pulling the tape bandwidth  24  away from the substrate surface  36  to which it has been compacted, described previously in connection with  FIGS. 2-4 . Referring particularly to  FIG. 5 , the method begins at step  50  in which a compaction roller  22  or similar compaction device, is moved over a substrate surface  36  at an angle θ to a convex radius edge  40 , such as when 45° tape courses are being placed to form a 45° ply. In  FIGS. 6-8 , the radius edge  40  is shown as a 90° radius, however it should be noted here that the disclosed method may be employed to laminate composite tape over convex radius edges of other relatively sharp angles. At step  52 , composite prepreg tape is fed to the compaction roller  22  which compacts the tape against the substrate surface  36 . At step  54 , the compaction roller  22  moves over the convex radius edge  40 . In step  56 , the compaction roller  22  is rotated about the trailing edge  31  of the tape to prevent the just-laid tape below the radius edge  40  from being pulled away from the substrate surface  36 . 
         [0030]      FIGS. 7 and 8  illustrate further details of the method outlined in  FIG. 6 . In this example, modifications to the NC program  18  ( FIG. 1 ) used to control the movements of the compaction roller  22  result in the relocation of the tool center point  30  along the axis of rotation  32  to the location designated as  30   a,  near the trailing edge  31  of the tape bandwidth  24 . For example, the tool center point  30  may be aligned with the centerline  39  ( FIG. 6 ) of the second-to-last tape strip  26   b,  or at other points along the trailing edge  31 . When the modified tool center point  30   a  of the compaction roller  22  passes around the radius edge  40  in a sweep-like bending or wiping motion, the compaction roller  22  also pivots in the XZ plane about the Y axis through an angle □ ( FIG. 8 ). Because the pivot point, i.e. the tool center point  30   a  is located near the trailing edge  31  of the tape bandwidth  24  as the compaction roller  22  continues around the radius edge  40 , minimal or no force applied to the tape strips  26  at the trailing edge  31  which would tend to pull the just laid tape strips  26  away from the substrate surface  36 . Instead. The coordinated movements of the compaction roller  22  about both the X and Y axes as it translates over the radius edge  40  results in compaction pressure being maintained across the entire tape bandwidth  24  until the compaction roller  22  has completely traversed the radius edge  40 . 
         [0031]      FIG. 9  illustrates an overall diagram of a method of laying up composite laminate parts using the method previously described in connection with  FIGS. 5-8 . Beginning at step  58 , the desired of part layup is digitally defined, using for example and without limitation, a CAD system (not shown). At step  60 , NC programming is initiated to produce a program suitable for controlling the operation and movements of the AFP machine. At  62 , the NC programming is modified to shift the compaction roller rotation point (i.e. the tool center point  30 ) on 45° plies, such that the tool center point  30   a  is near the trailing edge  31  of the tape bandwidth  24  as the compaction roller  22  moves over the radius edge  40 . At  64 , the necessary and NC paths are generated which control the movement of the material placement head  20 . At  66 , the part program is post-processed, readying it for use for NC control of an AFP machine  12  used to layup the part. At step  68 , the program is loaded into a controller  16  used to control the AFP machine  12 , following which the part may be laid up at step  70 . 
         [0032]    Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where composite parts may be used. Thus, referring now to  FIGS. 10 and 11 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  72  as shown in  FIG. 10  and an aircraft  74  as shown in  FIG. 11 . Aircraft applications of the disclosed embodiments may include, for example, without limitation, fabrication of stiffener members such as, without limitation beams, spars and stringers, to name only a few. During pre-production, exemplary method  72  may include specification and design of the aircraft  74  and material procurement  78 . During production, component and subassembly manufacturing  80  and system integration into of the aircraft  74  takes place. Thereafter, the aircraft  74  may go through certification and delivery  84  in order to be placed in service  86 . While in service by a customer, the aircraft  74  is scheduled for routine maintenance and service  88 , which may also include modification, reconfiguration, refurbishment, and so on. 
         [0033]    Each of the processes of method  72  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. 
         [0034]    As shown in  FIG. 11 , the aircraft  74  produced by exemplary method  72  may include an airframe  90  with a plurality of systems  92  and an interior  94 . Examples of high-level systems  92  include one or more of a propulsion system  96 , an electrical system  98 , a hydraulic system  100 , and an environmental system  102 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries. 
         [0035]    Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method  72 . For example, components or subassemblies corresponding to production process  80  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  74  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  80  and  82 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  74 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  96  is in service, for example and without limitation, to maintenance and service  88 . 
         [0036]    The description of the different illustrative embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different advantages as compared to other illustrative embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.