Patent Publication Number: US-2005115046-A1

Title: Methods and systems for fastening components, including composite aircraft panels

Description:
TECHNICAL FIELD  
      The present invention is directed generally toward methods and systems for fastening components, including composite aircraft panels.  
     BACKGROUND  
      The aircraft industry has developed a multitude of fasteners and fastening systems for quickly and reliably fastening aircraft components. One arrangement, provided by the Hi-Shear Corporation of Torrance, Calif., and referred to as a Hi-Lok® system, includes a pin that is typically forced (with a rivet gun or other power tool) into coaxially aligned holes of the two components to be fastened. Accordingly, the pin has an interference fit with the holes in the two components. The pin includes a head at one end that engages one of the components, and helical threads at the opposite end that project outwardly from the other component. In one specific arrangement, a nut or collar is threadably attached to the pin threads. The nut includes a shear section which fractures at a predetermined torque, leaving the rest of the nut tightened onto the pin with the predetermined torque. Alternatively, the pin can have axially spaced apart swage grooves, and the nut can be swaged rather than threaded onto the pin. In another arrangement, the end of the pin opposite the head can include a hexagonal broach which can receive a hex key to prevent the pin from rotating while the threaded collar is installed on the pin. However, a drawback with this approach is the broach may tend to strip, particularly when the pin is installed in a clearance hole (rather than an interference fit hole), which provides no gripping action on the pin. Further aspects of these arrangements are disclosed in U.S. Pat. Nos. 4,326,825; 4,485,510; and 4,957,401.  
      Another drawback with the foregoing arrangements is that the collar may inadvertently be cross-threaded onto the pin, reducing the security of the resulting bond. Accordingly, an alternate arrangement, (referred to in the industry as a lockbolt arrangement and available from Huck International, Inc. of Kingston, N.Y.), includes a pin having swage grooves for receiving a swaged collar, and a removable extension or pintail projecting outwardly from the swage grooves to receive an installation tool. In operation, the installation tool grips pintail grooves on the removable extension, pneumatically swages the collar onto the swage grooves, and simultaneously pulls the extension off in an axial direction. An advantage of this arrangement is that it may be relatively simple and reliable, and eliminates the possibility for cross-threading the collar on the pin. Another advantage is that it can be used in clearance holes without requiring the pin to be restrained against rotational motion.  
      Still another arrangement, available from the Hi-Shear Corporation, combines aspects of the two foregoing arrangements. This arrangement includes a pin having helical threads in the manner of a Hi-Lok® pin, together with a grooved, removable extension in the manner of a lockbolt. During installation, a tool grips the extension to pull the pin axially through the holes in the components. The extension is then broken off with an off-axis (e.g., lateral) force, and a threaded collar is installed on the threaded portion of the pin. One feature of this installation is that it is typically used when the pin has an interference fit with the holes into which it is inserted. Accordingly, the pin will not rotate when the threaded collar is installed.  
      While lockbolts may be easier to install in components having clearance holes (rather than interference fit holes), lockbolts also suffer from drawbacks.  
      For example, it may be desirable to coat the clearance holes with a sealant to make the joint between the attached components liquid-tight. The sealant can become trapped in the swage grooves of the lockbolt, reducing the gripping effectiveness of the swaged collar. One approach to addressing this drawback has been to add an axial sealant escape groove to the swage grooves, which allows the sealant to escape during the swaging operation. However, even this approach suffers from drawbacks. For example, the joint is generally not considered fluid-tight. Another approach to eliminating the sealing fluid from the swage grooves has been to wipe each pin before swaging on the collar. A disadvantage with this approach is that it is time consuming, which increases the cost of fabricating the associated aircraft components.  
      Still another approach has been to swage collars directly onto the threaded portion of a Hi-Lok®-type pin. However, this arrangement requires a complex and/or noisy C-shaped riveter to drive the pins through the components to be attached. Accordingly, the arrangement may be cumbersome to implement.  
     SUMMARY  
      The present invention is directed generally toward methods and systems for fastening components, including composite aircraft components. A method in accordance with one aspect of the invention includes inserting an elongated member through at least one component (e.g., a first hole in a first component and a second hole in a second component), with a head of the elongated member positioned at least proximate to the first component. A collar is then swaged to a helical groove of the elongated member, with the first and second components positioned between the head and the collar, and with the collar positioned between the second component and a removable portion of the elongated member. The removable portion of the elongated member is then removed to complete the installation.  
      In one aspect of the invention, swaging the collar and removing the removable portion of the elongated member can include engaging the removable portion of the elongated member with a first portion of an installation tool, engaging the collar with a second portion of the installation tool, and moving at least one of the first portion and the second portion axially relative to the other. The elongated member can be inserted with an interference fit or a clearance fit, and can have a fluid applied to it (e.g., a sealing fluid) without obstructing the swaging operation. In another aspect of the invention, the elongated member and collar can be attached to a single component, for example, to fill a hole in the component.  
      A fastener system in accordance with another aspect of the invention includes a collar having an aperture, and an elongated member having a head portion and a shaft portion. The shaft portion is configured to be received in the aperture of the collar and includes at least one helical thread, a tool engagement portion, and a frangible portion between the at least one helical thread and the tool engagement portion. The frangible portion is configured to break under an axial tension when a tool engages the tool engagement portion and swages the collar onto the at least one helical thread.  
      In a further aspect of the invention, the fastener system can include an installation tool having a first portion positioned to engage the tool engagement portion of the elongated member, and a second portion positioned to contact the collar. At least one of the first and second portions is movable relative to the other, for example, to swage the collar onto the at least one helical thread and break the frangible portion of the elongated member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a partially schematic, side elevation view of components of a fastener system configured in accordance with an embodiment of the invention.  
       FIG. 2  is a partially schematic, side elevation view of a portion of an elongated member configured in accordance with an embodiment of the invention.  
       FIG. 3  is a partially schematic, partially broken side elevation view of an elongated member configured in accordance with another embodiment of the invention.  
       FIG. 4  is a partially schematic, cross-sectional view of a tool for installing fastener system components in accordance with an embodiment of the invention.  
       FIGS. 5A-5C  are flow diagrams illustrating methods for installing fastener system components in accordance with embodiments of the invention.  
       FIG. 6  is a partially schematic, partial cross-sectional side view of a tool positioned to install fastener components in accordance with an embodiment of the invention.  
       FIG. 7  is a partially schematic, side elevation view of fastener components and fastened components after completion of an installation procedure in accordance with an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
      The present invention is directed generally toward methods and systems for fastening components, for example, aircraft components that include composite materials. Several embodiments of systems and methods for fastening such components are described below. A person skilled in the relevant art will understand, however, that the invention may have additional embodiments, and that the invention may be practiced without several of the details of the embodiments described below with reference to  FIGS. 1-7 .  
       FIG. 1  is a partially schematic, side elevation view of a fastener system  100  that includes an elongated member  110  and a collar  140  configured in accordance with an embodiment of the invention. In one aspect of this embodiment, the elongated member  110  includes a head  111  and a shaft  118 . The shaft  1   18  can include a first portion  1   12  and an adjacent second portion  113 . The first portion  112  is configured to pass through a hole in a first component, and the second portion  113  is configured to pass through a hole in a second component prior to fastening the first and second components together, as described in greater detail below with reference to  FIG. 6 .  
      The elongated member  110  can further include a third portion  114  (e.g., an engagement portion) having engagement features  115 , some of which are indicated schematically by phantom lines in  FIG. 1 . The engagement features  115  can be engaged by a tool (a) to support the elongated member  110  as the collar  140  is attached to the elongated member  110 , and/or (b) to allow the tool to pull the elongated member  110  through the holes of the components to which it is fastened. In one aspect of this embodiment, the engagement features  115  include axially spaced apart, ring-shaped ridges. In other embodiments, the engagement features  115  include other elements, for example, helical grooves and/or knurled surfaces. A frangible region  116  is positioned between the third portion  114  and the first and second portions  112 ,  113 , which allows the third portion  114  to be removed from the elongated member  110  during installation. A threaded portion  117  (having threads indicated schematically by dashed lines in  FIG. 1 ) can be positioned between the frangible region  116  and the second portion  113 . The threaded portion  117  is sized to securely engage the collar  140 .  
      The collar  140  can include a barrel  143  having an aperture  141  and, optionally, a flange  142  disposed around the aperture  141 . In a particular aspect of an embodiment shown in  FIG. 1 , the aperture  141  is large enough to slip over the engagement features  115  of the elongated member  110 . In a further aspect of this embodiment, the aperture  141  is also large enough to slip over the threaded portion  117 . Accordingly, the collar  140  securely engages the threaded portion  117  only after the collar  140  is swaged onto the threaded portion  117 .  
      The material compositions of the elongated member  110  and the collar  140  can be selected based on criteria that include weight, strength and cost. In a particular embodiment, the elongated member  110  can include titanium and/or a titanium alloy. In other embodiments, the elongated member  110  can include Inconel®, steel and/or other materials. The collar  140  can include titanium, a titanium alloy, aluminum and/or other materials.  
       FIG. 2  is a cross-sectional illustration of part of the elongated member  110  described above with reference to  FIG. 1 . As shown in  FIG. 2 , the threaded portion  117  of the elongated member  110  can include a generally continuous, helical groove  119  extending at least approximately from the frangible portion  116  to the second portion  113  of the shaft  118 . Although the helical groove  119  may be sized and manufactured in the manner of standard threads (e.g., threads that receive standard nuts), the helical groove  119  receives the collar  140  ( FIG. 1 ) in a swaging operation, rather than a rotary torquing operation, as described in greater detail below with reference to  FIG. 6 .  
       FIG. 3  is a partially schematic, partially broken side elevation view of an elongated member  210  configured in accordance with another embodiment of the invention. The elongated member  210  includes a shaft  118  having features generally similar to the shaft  118  described above with reference to  FIG. 1 . The elongated member  210  can further include a head  211  configured to be flush-mounted in a countersunk hole. Conversely, the head  111  described above with reference to  FIG. 1  is configured to protrude from the hole after installation. The particular elongated member chosen for a specific application can depend upon whether the installation requires a flush-mount or protruding head. In other embodiments, the head or other parts of the elongated member can have other arrangements, again, depending upon the specific application(s) for which the elongated member is to be used.  
       FIG. 4  is a partially schematic, cross-sectional illustration of a tool  430  configured to install elongated members (e.g., the elongated members  110 ,  210  described above with reference to  FIGS. 1-3 ) in accordance with an embodiment of the invention. In one aspect of this embodiment, the tool  430  includes a driver  438  and an interchangeable nose portion  437 . Suitable drivers  438  are available from Huck International, Inc. of Kingston, N.Y., under the trade name Pneudraulic Installation Tool. Suitable nose portions  437  are also available from Huck International, Inc.  
      In one embodiment, the nose portion  437  includes a housing  431  carrying a collet  432  which in turn carries a chuck  433 . The chuck  433  includes chuck aperture  434  (sized to receive the elongated member  110 ,  210  described above with reference to  FIG. 1-3 ), and a grip portion  435  which is configured to be tightened by the collet  432  around the elongated member  110 ,  210  described above. An anvil  436  is positioned around the collet  432  and is movable relative to the collet  432 . In one aspect of this embodiment, the anvil  436  has an anvil aperture  438  with a diameter smaller than an outer diameter of the collar  140 . Accordingly, the anvil  436  can swage the collar  140  onto the elongated member  110 ,  210 . Further details of this operation are described below with reference to  FIGS. 5A-7 .  
       FIG. 5A  is a flow diagram illustrating a process  500  for fastening components in accordance with an embodiment of the invention. In one aspect of this embodiment, the process  500  can include inserting an elongated member through a first hole in a first component and a second hole in a second component, with a head of the elongated member positioned at least proximate to the first component (process portion  502 ). In process portion  504 , a collar is swaged onto a helical groove of the elongated member, with the first and second components positioned between the head and the collar, and with the collar positioned between the second component and a removable portion of the elongated member. In process portion  506 , the removable portion of the elongated member is removed, completing the installation process.  
       FIGS. 5B and 5C  are flow diagrams illustrating details associated with specific embodiments of the process  500  described above with reference to  FIG. 5A . Referring first to  FIG. 5B , process portion  502  (inserting an elongated member through holes in the first and second components), can include inserting the elongated member with a clearance fit (process portion  510 ) or with an interference fit (process portion  512 ). If the elongated member is inserted with a clearance fit, it is loosely positioned in the holes and can accordingly be inserted into the holes relatively easily without the use of power tools and without the need for mechanically driving the elongated member through the holes. If the elongated member is inserted with an interference fit, it may be driven through the holes manually or with a power tool.  
      When the elongated member is installed with a clearance fit, the process  500  can optionally include applying a sealant (process portion  514 ) to seal the space between the walls of the hole and the exterior surface of the elongated member. In one aspect of this embodiment, the sealant can provide a liquid-tight connection between the elongated member and the first and second components that it fastens. Alternatively, the sealant can provide a less than liquid-tight seal, while still providing other functions, for example, corrosion resistance at the interface between the elongated member and the walls of the first and second holes into which it is inserted. Whether the elongated member is inserted with a clearance fit (with or without a sealant) or an interference fit, it can be inserted far enough so that the head of the elongated member bears against the first component (process portion  516 ).  
      Referring next to  FIG. 5C , process portion  504  (swaging the collar onto a helical groove of the elongated member) can include engaging a first portion of an installation tool with a removable portion of the elongated member (process portion  520 ). For example, the installation tool can include a collet and chuck that apply a radial clamping force to the removable portion of the elongated member. In another embodiment, the installation tool can threadably engage the removable portion. In either embodiment, a second portion of the installation tool can then be contacted with the collar (process portion  522 ). At least one of the first and second portions is moved axially relative to the other (process portion  524 ) so as to swage the collar onto the helical groove of the elongated member (process portion  526 ). In process portion  528 , the connection between the removable portion and the remainder of the elongated member is broken. In one aspect of this embodiment, the connection can be broken as the collar is swaged onto the elongated member. In another embodiment, the connection can be broken after the swaging process is completed. In either embodiment, the connection can be broken by applying an axial force to the connection. The removable portion can be removed after the connection is broken (process portion  506 ).  
       FIG. 6  is a partially schematic, cross-sectional illustration of the tool  430  positioned to install the collar  140  and the elongated member  110  described above, in accordance with an embodiment of the invention. For purposes of illustration, only the nose portion  437  of the tool  430  is shown in  FIG. 6 . In one aspect of this embodiment, a first component  650   a  having a first hole  651   a  is positioned adjacent to a second component  650   b  having a second hole  651   b , so that the first hole  651   a  is axially aligned with the second hole  651   b . In a further aspect of this embodiment, the first and second components  650   a ,  650   b  can include composite aircraft panels, for example, wing panels, fuselage panels, empennage panels or other external surface panels and/or structural panels. These panels can have a graphite/epoxy composite composition. In other embodiments, the first and second components  650   a ,  650   b  can include other elements having the same and/or other compositions. For example, the first component  650   a  and/or the second component  650   b  can include aluminum, titanium or associated alloys.  
      In a particular aspect of an embodiment shown in  FIG. 6 , the elongated member  110  has a clearance fit within the first hole  651   a  and the second hole  651   b . Accordingly, the first portion  112  of the elongated member  110  has a diameter smaller than a diameter of the first hole  651   a , and the second portion  113  of the elongated member  110  has a second diameter smaller than a diameter of the second hole  651   b . If the resulting gap  620  between the elongated member  110  and the inner surfaces of the first and second holes  651   a ,  651   b  is to be sealed, a flowable sealant  652  can optionally be disposed in the gap  620 . In a particular embodiment, the sealant  652  can include polysulfide. In other embodiments, the sealant  652  can be eliminated, and/or the first and second holes  651   a ,  651   b  can provide an interference fit with the elongated member  110 .  
      When the elongated member  110  is installed through the first component  650   a  and the second component  650   b , the head  111  of the elongated member  110  abuts against the first component  650   a . The collar  140  is then passed along the elongated member  110  until it abuts against the second component  650   b  (as shown in dashed lines in  FIG. 6 ). In other embodiments, other elements (e.g., washers) may be inserted between the head  111  and the first component  650   a  and/or between the collar  140  and the second component  650   b . In any of these embodiments, the collar  140  can pass over the threaded portion  117  axially and without rotating either the collar  140  or the elongated member  110 .  
      An operator (not shown) can then clamp the chuck  433  of the tool  430  around the engagement features  115  at the third portion  114  of the elongated member  110 . The operator can then drive the anvil  436  away from the chuck  433  and against the collar  140  to swage the collar  140  onto the threaded portion  117  of the elongated member  110 . In one aspect of this embodiment, the anvil  436  engages the barrel  143  of the collar  140  and, as it slides along the barrel  143 , deforms collar  140  radially inwardly to mesh with the threaded portion  117 . The anvil  436  also forces the collar  143  axially into tight engagement with the second component  650   b . Accordingly, the anvil  436  provides an axial force in a first direction (as indicated by arrow A) on the collar  140 , while the chuck  433  provides a reaction force on the elongated member  110  in an opposite axial direction (as indicated by arrow B).  
      As the axial force applied to the elongated member  110  increases beyond a threshold level, the frangible portion  116  of the elongated member  110  breaks, releasing the third portion  114  from the rest of the elongated member  110 . At this point, the swaging operation ceases. The tool  430  can then be withdrawn and the removed third portion  114  discarded. In one embodiment, the frangible portion  116  is configured to break after at least part of the collar  140  is swaged to the elongated member  110 , but before the progress of the anvil  436  is halted by the second component  650   b . Accordingly, the anvil  436  will not apply a potentially damaging force directly on the second component  650   b.    
       FIG. 7  illustrates the elongated member  110  and the collar  140  after the third portion  114  has been removed. As shown in  FIG. 7 , the elongated member  110  and the collar  140  provide a low profile, secure and (optionally) liquid-tight joint between the first component  650   a  and the second component  650   b.    
      In other embodiments, the fastening system  100  described above can be used in other contexts. For example, the system  100  can be used to bond more than two components together by extending the elongated member through corresponding axially aligned holes of the components. In other embodiments, the system  100  can be used with a single component, for example, to seal a hole in a single panel. In one aspect of this embodiment, the head of the elongated member can bear on one surface of the component and the collar can bear on the opposite facing surface of the same component. Accordingly, the fastening operation described above can include fastening the elongated member and the collar to each other and to a single component, as well fastening multiple components to each other.  
      One aspect of an embodiment of the arrangement described above with reference to  FIGS. 1-7  is that the elongated member  110  and the collar  140  can provide a secure, sealable attachment between the first component  650   a  and the second component  650   b , even though the elongated member  110  may have a clearance fit in the first and second holes  651   a ,  651   b . This feature is advantageous because it allows the arrangement to be used for a variety of applications (e.g., with composite materials) where it is more desirable to use clearance holes than interference fit holes. In particular, the clearance holes may allow the elongated member to be installed more quickly, more quietly and with less stress to the attached components  650   a ,  650   b  than is possible with conventional techniques, while still permitting a sealable connection.  
      Another feature of an embodiment of an arrangement described above with reference to  FIGS. 1-7  is that the elongated member need not be secured against rotation while the collar is installed, because the collar is installed in a swaging operation. An advantage of this feature is that when the elongated member is installed in clearance holes, the operator need not use additional tools (e.g., a hex key) to prevent the elongated member from rotating as the collar is attached.  
      Still another feature of an embodiment of the arrangement described above with reference to  FIGS. 1-7  is that the helical threads provide an avenue by which excess sealant on the elongated member can escape as the collar is swaged on. An advantage of this arrangement is that it can eliminate the need to manually remove excess sealant from the elongated member (e.g., by wiping), thereby reducing the time required to complete the assembly process.  
      Yet feature of an embodiment of the elongated member  110  described above and shown in  FIG. 6  is that it can have an overall length L that is less than that of corresponding, existing pins. This is so because the elongated member  110  can slip through the first and second holes  651   a ,  651   b  with a clearance fit. Accordingly, the third portion  114  need not project so far outwardly from the second hole  651   a  as to allow the tool  430  to engage the third portion  114  and pull the elongated member through the holes  651   a ,  651   b .) As a result, the elongated member  110  can include less material than an existing elongated member  110  sized for the same application and can accordingly be cheaper to manufacture.  
      From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.