Abstract:
An apparatus and its method of use enables a thermoplastically deformable fastener assembly to be deformed to hold an installation preload torque after the fastener has been torqued to a predetermined value.

Description:
FIELD 
       [0001]    This disclosure pertains to an apparatus and method that enables a thermoplastically deformable fastener assembly to be deformed to hold an installation preload and maintain or increase the breakaway torque after the fastener has been torqued to a predetermined value. 
       BACKGROUND 
       [0002]    In the construction of aircraft and other vehicles having combustion engines and fuel tanks, it is desirable to reduce the presence of electrical conductors in the environment of the fuel tank to reduce the potential of an electrical spark in the area of the fuel tank. Non-conductive plastic nut and bolt fastener assemblies have been used in these environments in place of conductive metal nut and bolt fastener assemblies. Additionally, replacing thousands of metal fastener assemblies used in constructing an aircraft or other vehicle with plastic fastener assemblies reduces the weight of the aircraft or vehicle, making the aircraft or vehicle more fuel efficient. However, existing plastic fastener assemblies are known to lose preload torque. A plastic fastener assembly comprising a threaded bolt and nut can lose preload torque or have the fastener assembly preload torque decrease due to the unthreading of the nut from the bolt over time. 
       SUMMARY 
       [0003]    The apparatus of this disclosure that torques a threaded nut and bolt fastener assembly to a preload, and then deforms the fastener assembly to hold the preload resolves the issue of existing plastic fastener assemblies that are known to lose preload torque. The apparatus is ideally used with thermoplastic nut and bolt fastener assemblies. The apparatus is basically comprised of a wrench device that rotates the nut on the bolt and torques the nut to a predetermined torque, and a piercing tip that pierces into the fastener assembly to hold the fastener assembly at the preload torque. 
         [0004]    The wrench device has a socket with a plurality of engagement surfaces inside the socket. The socket engagement surfaces are dimensioned to engage around the nut of the nut and bolt fastener assembly. The wrench device is operable to rotate the socket around the bolt, whereby the socket engaging around the nut rotates the nut on the bolt and torques the nut to a predetermined torque and preload. 
         [0005]    The piercing tip of the apparatus is positioned adjacent the wrench device socket. The piercing tip is moveable between first and second positions of the piercing tip relative to the socket. In the first position the piercing tip is displaced from the socket. In the second position the piercing tip extends into the socket and into the fastener assembly inside the socket, deforming the fastener assembly. 
         [0006]    A heat source of the apparatus communicates with the piercing tip. The heat source heats the piercing tip when the piercing tip is moved to its second position. The heated piercing tip extending into the fastener assembly thermally deforms the fastener assembly. The deformation of the fastener assembly holds the fastener assembly at the preload torque. 
         [0007]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a representation of a side view of a thermoplastic nut and bolt fastener assembly and a first embodiment of the apparatus of this disclosure. 
           [0009]      FIG. 2  is a representation of a left end view of the apparatus shown in  FIG. 1 . 
           [0010]      FIG. 3  is a representation of the thermoplastic fastener assembly engaged by the apparatus of  FIG. 1 . 
           [0011]      FIG. 4  is a representation of a side view of the thermoplastic nut and bolt fastener assembly and a further embodiment of the apparatus of this disclosure. 
           [0012]      FIG. 5  is a representation of a top plan view of the fastener assembly and apparatus of  FIG. 4 . 
           [0013]      FIG. 6  is a representation of a left end view of the apparatus shown in  FIG. 4 . 
           [0014]      FIG. 7  is a representation of the left end view of the apparatus similar to that of  FIG. 6 , but representing the apparatus when engaging the fastener assembly. 
           [0015]      FIG. 8  is a representation of a side view of the apparatus of  FIG. 4  shown engaging the fastener assembly. 
       
    
    
     DESCRIPTION 
       [0016]    The apparatus of this disclosure torques a threaded nut and bolt fastener assembly to a preload torque and then deforms the fastener assembly to hold the preload torque. In the description to follow the fastener assembly is a plastic nut and bolt fastener assembly. The plastic is a thermoplastic, although other types of plastic nut and bolt fastener assemblies could be used with the apparatus. Furthermore, the apparatus could be adapted to be used to torque and then deform fastener assemblies other than plastic nut and bolt fastener assemblies, for example metal nut and bolt fastener assemblies. 
         [0017]      FIG. 1  is a representation of a side view of a threaded nut and bolt fastener assembly  10  and a first embodiment of the apparatus  12  of this disclosure. 
         [0018]    The fastener assembly  10  is a nut  14  and bolt  16  thermoplastic fastener assembly. As stated earlier, other materials could be used in producing the fastener assembly  10 . The bolt  16  has a bolt head  18  at one end of the bolt and screw threading  20  adjacent an opposite end of the bolt. The nut  14  is a hex nut or a nut having six side surfaces  22 . The nut  14  could have other, equivalent configurations. The nut  14  has internal screw threading (not shown) that is screw threaded on the bolt screw threading  20 . The nut  14  and bolt  16  fastener assembly  10  has a center axis  24  that defines mutually perpendicular axial and radial directions relative to the fastener assembly  10 . In use of the fastener assembly  10  in joining two or more structural pieces together, the nut  14  is to be rotated on the bolt  16  to a predetermined preload torque in securing the structural features together. 
         [0019]    The apparatus  12  is basically comprised of a wrench device  26  and a piercing tip  28 . The wrench device  26  and piercing tip  28  are each constructed of a metal or other equivalent material that gives the wrench device  26  and the piercing tip  28  sufficient strength for their intended functions. 
         [0020]    The wrench device  26  is represented schematically in the drawing figures. The device  26  has a cylindrical exterior surface  30  with a center axis  32 . The wrench device center axis  32  defines mutually perpendicular axial and radial directions relative to the wrench device  26 . The device has an axial length that extends between a proximal end  34  and a distal end  36  of the device. A cylindrical interior surface  38  surrounds a center bore of the device that is coaxial with the center axis  32 . The cylindrical surface  38  extends axially through the device from the device proximal end  34  to a socket  42  recessed axially in the device distal end  36 . Referring to  FIG. 2 , the socket  42  is a hexagonal socket having six engagement surfaces  44 . The engagement surfaces  44  are dimensioned to be positioned around the nut  14  of the fastener assembly with at least two of the engagement surfaces  44  engaging with opposite side surfaces  22  of the nut. The wrench device  26  can be a hand held tool that is manually rotated about the device center axis  32 . Alternatively, the wrench device  26  could be an automated tool that is controlled to automatically rotate about the device center axis  32 . The device being a manual tool or an automated tool is represented schematically by the dashed lines  46  in  FIG. 1 . 
         [0021]    The piercing tip  28  is positioned at a distal end of an elongate cylindrical rod  48 . The rod  48  is positioned in the interior bore surrounded by the wrench device interior surface  38  and has a center axis that is coaxial with the wrench device center axis  32 . The rod proximal end  52  is operatively connected with an actuator and heat source  54 . The actuator and heat source  54  is operable to move the rod and the piercing tip  28  axially between a first position represented in  FIG. 1  to a second position where the piercing tip  28  of the rod  48  is moved into the socket  42 . The actuator and heat source  54  also heats the piercing tip  28  when the piercing tip is in the second position. The actuator and heat source  54  communicates with a torque sensing device  56  in the wrench device tool  46  and is controlled to move the piercing tip  28  from the first position to the second position in response to the torque sensing device  56  sensing the nut  14  being turned on the bolt  16  to the predetermined preload torque. 
         [0022]      FIG. 3  is a representation of the method of using the apparatus  12  to torque the nut  14  on the bolt  16  of the fastener assembly  10  to a preload torque and then deforming the fastener assembly  10  to hold the preload torque. As represented in  FIG. 3 , the wrench device  26  and the wrench device socket  42  are moved axially toward the nut  14  and bolt  16  fastener assembly  10  until the nut  14  is received in the socket  42 . The socket engagement surfaces  44  are positioned around the nut  14  with at least two of the engagement surfaces  44  engaging with opposite side surfaces  22  of the nut  14 . The wrench device socket  42  is then rotated to tighten the nut  14  on the bolt  16 . The wrench device socket  42  is rotated and torques the nut  14  to a preload torque on the bolt  16 . When the preload torque is reached, the torque sensing device  56  senses the torque and communicates with the actuator and heat source  54  to initiate the axial movement of the piercing tip  28 . The actuator and heat source  54  moves the piercing tip  28  from its first position represented in  FIG. 1 , to its second position represented in  FIG. 3 . In the second position of the piercing tip  28  the tip pierces into the fastener assembly  10 , and more specifically pierces into the end of the bolt  16  with the screw threading  20 . The heat source of the actuator  54  then heats the piercing tip  28 . The heated piercing tip  28  thermally deforms the fastener assembly  10  and more specifically the fastener assembly bolt  16 . The deformation of the fastener assembly  10  holds the fastener assembly at the preload torque. Thus, the deformed fastener assembly  10  overcomes the problem of the torqued bolt  16  and nut  14  of the fastener assembly losing their preload torque. 
         [0023]      FIG. 4  is a representation of a side view of the fastener assembly  10  with a second embodiment of the apparatus  62 . As in the first embodiment  12 , the second embodiment of the apparatus  62  is also comprised of a wrench device  64  and a piercing tip  66 . The second embodiment of the apparatus  62  also torques the nut  14  on the bolt  16  of the fastener assembly  10  to a preload torque and then deforms the fastener assembly  10  to hold the preload torque. However, there are structural differences in the second embodiment of the apparatus  62 . 
         [0024]    The wrench device  64  is schematically represented in the drawing figures. As shown in  FIG. 4 , the wrench device  64  has a cylindrical exterior surface  68  with a center axis  72  that defines mutually perpendicular axial and radial directions relative to the wrench device  64 . The wrench device  64  has an axial length that extends from a proximal end  74  of the device to a distal end  76  of the device. As in the first described embodiment, the wrench device  64  has a socket  78  recessed axially in the device distal end  76 . Referring to  FIG. 6 , the socket  78  has six engagement surfaces  82  that are dimensioned to be positioned around the nut  14  of the fastener assembly  10  with at least two of the engagement surfaces  82  engaging against opposite sides  22  of the nut. The socket  78  also has a pair of openings  84 ,  84 ′ that extend radially through opposite sides of the socket  78 . As represented in  FIG. 6 , the pair of openings  84 ,  84 ′ extend through the socket  78  and between at least two engagement surfaces  82  of the socket. As in the first described embodiment, the wrench device  64  and the socket  78  can be part of a hand held tool  86  that is manually rotated about the device center axis  72 . Alternatively, the wrench device  64  and the socket  78  could be an automated tool that is controlled to automatically rotate about the center axis  72 . The device  64  being a manual tool or an automated tool is represented schematically by the dashed lines  86  in  FIG. 4 . 
         [0025]    As represented in  FIG. 4 , the second embodiment of the apparatus  62  comprises a pair of piercing tips  66 ,  66 ′. Each of the piercing tips  66 ,  66 ′ is positioned at a distal end of an elongate rod  88 ,  88 ′. The opposite proximal ends of the rods  88 ,  88 ′ are operatively connected with an actuator and heat source represented by the dashed lines  92  in  FIG. 4 . The actuator and heat source  92  is operable to control movement of the piercing tips  66 ,  66 ′ radially between first positions of the tips represented in  FIG. 4 , to second positions of the tips represented in  FIGS. 7 and 8 . In this embodiment of the apparatus  62  the piercing tips  66 ,  66 ′ are moved from the first positions radially inwardly through the socket openings  84 ,  84 ′ into the socket  78  as represented in  FIG. 7 . 
         [0026]    As with the first embodiment of the apparatus  12 , a torque sensing device  94  communicates with the actuator and heat source  92 . The torque sensing device  94  senses the torque exerted by the wrench device socket  78  on the nut  14  as the wrench device  64  and socket  78  torque the nut  14  on the bolt  16  of the fastener assembly  10 . 
         [0027]    The second embodiment of the apparatus  62  operates in a similar manner to that of the first embodiment of the apparatus  12 .  FIG. 8  is a representation of the method of using the apparatus  62  to torque the nut  14  on the bolt  16  of the fastener assembly  10  to a preload torque and then deforming the fastener assembly  10  to hold the preload torque. As represented in  FIG. 8 , the wrench device  64  and the wrench device socket  78  are moved axially toward the nut  14  and bolt  16  fastener assembly  10  until the nut  14  is received in the socket  78 . The socket engagement surfaces  82  are positioned around the nut  14  with at least two of the engagement surfaces  82  engaging with opposite side surfaces  22  of the nut  14 . The wrench device socket  78  is then rotated to tighten the nut  14  on the bolt  16 . The wrench device socket  78  is rotated and torques the nut  14  to a preload torque on the bolt  16 . When the preload torque is reached, the torque sensing device  94  senses the torque and communicates with the actuator and heat source  92  to initiate the radial movement of the piercing tips  66 ,  66 ′. The actuator and heat source  92  moves the piercing tips  66 ,  66 ′ from their first positions represented in  FIGS. 4 and 6 , to their second positions represented in  FIGS. 7 and 8 . In the second positions of the piercing tips  66 ,  66 ′ the tips pierce into the fastener assembly  10 , and more specifically pierce into the opposite sides of the nut  14 . The heat source of the actuator and heat source  92  then heats the piercing tips  66 ,  66 ′. The heated piercing tips  66 ,  66 ′ thermally deform the fastener assembly  10  and more specifically the fastener assembly nut  14 . The deformation of the fastener assembly  10  holds the fastener assembly at the preload torque. Thus, the deformed fastener assembly  10  overcomes the problem of the torqued bolt  16  and nut  14  of the fastener assembly losing their preload torque. 
         [0028]    As various modifications could be made in the construction of the apparatus and its method of operation herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.