Abstract:
A tube form assembly includes an inner member and an outer member. Each of the inner and outer members has an offset which creates a cavity therebetween. During assembly of the tube form assembly, an adhesive is located in the cavity and squeezed out and through the adjacent bond lines between the inner member and outer member. The pressurization and flow of adhesive outward from the cavity facilitates removal of air bubbles, as well as prevents the introduction of air bubbles into the bond line.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/471,232, filed 4 Apr. 2011, titled “Self Pumping and Priming Adhesive Joint System,” which is hereby incorporated by reference for all purposes as if fully set forth herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present application relates to a method and apparatus for an adhesive joint that controls the adhesive bond during assembly. 
     2. Description of Related Art 
     Tube form assemblies are particularly useful in many aerospace structures. A typical tube form assembly includes an outer cylindrical member bonded to an inner cylindrical member. The structural integrity of the tube form assembly relies in part on the quality of the adhesive bond between the outer cylindrical member and the inner cylindrical member. Conventional assembly methods allow for the introduction of air bubbles in the adhesive. Air bubbles in the adhesive result in voids in the adhesive bond line, thereby decreasing the bond strength. Voids in the adhesive bond line may lead to failure to the tube form assembly. If the tube form assembly is a flight critical part on an aircraft, failure of the bond can lead to catastrophic results. 
     Hence, there is a need for an improved adhesive joint in a tube form assembly. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the system and method of the present application are set forth in the appended claims. However, the system and method themselves, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of a rotorcraft, according to an embodiment of the present application; 
         FIG. 2  is a perspective view of a tilt rotor aircraft, according to an embodiment of the present application; 
         FIG. 3  is a cross-section view of a tube form assembly, according to the preferred embodiment of the present application; 
         FIG. 4  is a cross-section view of a tube form assembly, according to the preferred embodiment of the present application; 
         FIG. 5  is a cross-section view of a tube form assembly, according to the preferred embodiment of the present application; 
         FIG. 6  is partial sectional view of a tube form assembly, according to the preferred embodiment of the present application; 
         FIG. 7  is partial sectional view of a tube form assembly, according to the preferred embodiment of the present application; 
         FIG. 8  is partial sectional view of a tube form assembly, according to the preferred embodiment of the present application; 
         FIG. 9  is partial sectional view of a tube form assembly, according to an alternative embodiment of the present application; 
         FIG. 10  is partial sectional view of a tube form assembly, according to an alternative embodiment of the present application; and 
         FIG. 11  is a schematic view of a method for manufacturing a tube form assembly, according to an illustrative embodiment of the present application. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the system and method of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. 
     Referring to  FIG. 1  in the drawings, a rotorcraft  101  is illustrated. Rotorcraft  101  has a rotor system  103  with a plurality of rotor blades  111 . The pitch of each rotor blade  111  can be selectively controlled by a pitch link  113  in order to selectively control direction, thrust, and lift of rotorcraft  101 . Rotorcraft  101  further includes a fuselage  105 , landing gear  107 , and an empennage  109 . 
     Referring to  FIG. 2  in the drawings, a tiltrotor aircraft  201  is illustrated. Tiltrotor aircraft  201  includes a fuselage  207 , a landing gear  209 , a wing  209 , and rotatable nacelles  203   a  and  203   b . Each nacelle  203   a  and  203   b  includes a plurality of rotor blades  211 . The position of nacelles  203   a  and  203   b , as well as the pitch of rotor blades  211 , can be selectively controlled in order to selectively control direction, thrust, and lift of tiltrotor aircraft  201 . 
     It can be especially desirable for components of rotorcraft  101  and tiltrotor aircraft  201  to be manufactured as a tube form assembly. Illustrative tube form assemblies can include: a pitch link, a vibration isolator, control link, a pitch restraint link, a lead/lag damper, to name a few. As such, the system and method of the present application may be utilized to manufacture tube form assemblies for rotorcraft  101  and tiltrotor aircraft  201 . It should be appreciated that the system and method of the present application may be utilized to manufacture tube form assemblies on other types of aircraft, as well as non-aircraft applications. For example, the system and method of the present application may be utilized to manufacture a tube form assembly on a space vehicle, ground vehicle, surface marine vehicle, amphibious marine vehicle, and submersible marine vehicle, to name a few examples. 
     The system of the present application includes a tube form assembly  101  with components that are configured to self pump adhesive to the bond line during the assembly process. The self pumping of adhesive expels air bubbles, thereby minimizing voids in the adhesive bond line. The aforementioned features of tube form assembly  101  are described further herein. The method of the present application includes steps for assembling a tube for assembly so as to expel any air bubbles in the adhesive, thereby minimizing voids in the adhesive bond line. 
     Referring to  FIGS. 3-5 , tube form assembly  301  is illustrated in progressive assembly views. Tube form assembly  301  includes an outer member  303  and an inner member  305 . Inner member  305  and outer member  303  are bonded together with adhesive  313  (shown in  FIGS. 6-8 ). Adhesive  313  is preferably a paste adhesive, or other adhesive that exhibits pre-cure fluid properties during assembly of components of tube form assembly  301 . In one embodiment, adhesive  313  is EA  9346  paste adhesive manufactured by Henkel and Hysol Corporations. It should be appreciated that exact type of adhesive  313  is implementation specific. In the illustrated embodiment, each of the outer member  303  and inner member  305  are cylindrically shaped. However, alternative embodiments can include any variety of shapes, including but not limited to: prismatic, triangular, and hexagonal, to name a few. Further, outer member  303  and inner member  305  may also have interlocking and/or mating features, such as splined, keyed, and/or threaded portions. 
     In the illustrative embodiment, tube form assembly  301  is a spring structure configured to treat dynamic loading generated by rotor system  103  in rotorcraft  101 . An elastomer member  311  provides the spring constant to treat forces in the load path between inner member  305  and outer member  303 . In the illustrated embodiment, a first attachment member  321  and a second attachment member  323  are configured for attaching tube form assembly  301  to structures that exhibit relative oscillatory motion or forces therebetween. Elastomer member  311  is attached between an inner surface of inner member  305  and an outer surface of first attachment member  321 . For example, tube form assembly can be a gearbox pylori mounting link that provides structural support and vibration attenuation between the gearbox pylori and the aircraft structure. It should be appreciated that tube form assembly  301  is merely exemplary of a wide variety of tube form assembly structures. For example, tube form assembly  301  can include fluid reservoirs with one or more fluid passages that are configured for provide fluid damping and/or isolation as the fluid is forces back and forth between the fluid reservoirs. 
     The inner member  305  has an inner offset  307 . Similarly, outer member  303  has an outer offset  309 . Inner offset  307  is a physical change in the size of the outer periphery or outer surface of inner member  305 . In the illustrated embodiment, inner offset  307  represents a step change in the outer diameter of inner member  305 . Outer offset  309  is a physical change in the size of the inner periphery or inner surface of outer member  303 . In the illustrated embodiment, outer offset  309  represents a step change in the inner diameter of outer member  303 . As discussed further herein, inner offset  307  and outer offset  309  form a cavity  315  therebetween when inner member  305  and outer member  303  are mated together. In the illustrated embodiment, each offset  307  and  309  includes an arcuate or radius surface in the step change transition. The volume of cavity  315  decreases during assembly of inner member  305  and outer member  303 . Cavity  315  acts as an integral adhesive pump that pumps adhesive  313  outward as inner member  305  and outer member  303  are assembled together, as discussed further herein. 
     Referring now to  FIGS. 6-8 , a partial sectional view of tube form assembly  301  is illustrated.  FIGS. 6-8  progressively illustrate the process for assembling tube form assembly  301 . Referring specifically to  FIG. 6 , adhesive  313  is deposited in the cavity  315 , as well as portions of bonding surfaces  317   a ,  317   b ,  319   a , and  319   b . Referring also to  FIG. 7 , inner member  305  and outer member  303  are translated together along lengthwise centerline axis. In the illustrated embodiment, the volume of cavity  315  is defined by the width W 3  and length L 1 . As inner member  305  and outer member  303  are compressed together, a volume of high pressure is created in cavity  315 . As the volume of cavity  315  decreases, the increase in pressure causes adhesive  313  to flow toward the extremities. As such, cavity  315  acts an integral pump by pumping adhesive  313  outward as inner member  305  and outer member  303  are squeezed together. During this assembly procedure, air bubbles are also squeezed out along with excess adhesive. Further, as the volume of cavity  315  decreases, the resulting increase in pressure causes compressible air bubbles in adhesive  313  to migrate toward zones of lower pressure outward from cavity  315 . Furthermore, the flow of adhesive outward acts to prevent air bubbles from being suctioned from the exterior into the bondlines between bond surfaces  317   a  and  319   a , as well as the bondlines between bond surfaces  317   b  and  319   b.    
     Referring now also to  FIG. 8 , inner member  305  and outer member  303  are illustrated in a final assembly position. Excess adhesive  313   a  and  313   b  has been squeezed out, along with air bubbles. The dimensions W 1  and W 2  (shown in  FIG. 7 ) are the thickness between bond surfaces  317   a  and  319   a , as well as between bond surfaces  317   b  and  319   b . In the illustrative embodiment, W 1  and W 2  are approximately 0.005 inch. However, the exact dimensions W 1  and W 2  are implementation specific. Moreover, specific paste adhesives have specific optimal bond thickness or ranges of thickness. As such, it is preferred that thickness W 1  and W 2  are selectively tailored in accordance with the specific adhesive  313  being used. 
     After inner member  305  and outer member  303  are located in a final position, excess adhesive  313   a  and  313   b  can be removed. Further, adhesive  313  can be cured in accordance with the implementation specific requirements of the adhesive  313 . 
     Referring to  FIG. 9 , an alternative embodiment tube form assembly  901  is illustrated. Tube form assembly  901  is substantially similar to tube form assembly  301 , except for including a seal  903 . Seal  903  acts to cause adhesive  313  to be squeezed out only one direction. Seal  903  is particularly useful in embodiments have a closed end which would prevent a manufacturer from having access to clean and remove adhesive that would otherwise squeeze out in the area of seal  903 . 
     Referring to  FIG. 10 , an alternative embodiment tube form assembly  1001  is illustrated. Tube form assembly  1001  is substantially similar to tube form assembly  301  except inner offset  107  and outer offset  109  are replaced with an inner tapered surface  1003  and an outer tapered surface  1005 , respectively. As such, a cavity, similar to cavity  315 , is formed between the tapered surfaces  1003  and  1005 . During assembly, adhesive  313  is squeezed out as inner member  305  and outer member  303  are squeezed together. Tube form assembly  1001  is exemplary of a wide variety of volume shapes that cavity  315  can form. 
     Referring now also to  FIG. 11 , a method  1101  for manufacturing a tube form assembly, such as tube form assembly  301 , is schematically illustrated. A step  1103  includes providing an inner member and an outer member that form a cavity therebetween. An exemplary inner member and outer member are illustrated in  FIGS. 3-10 , and further described herein. A step  1105  includes locating an uncured adhesive in the cavity and on the bonding surfaces. Step  1105  is illustrated in  FIG. 6 , and further described herein. A step  1107  includes pressing the inner member and the outer member together so as to force a portion of the adhesive out of the cavity. Step  1107  is illustrated in  FIGS. 7 and 8 , and further described herein. In one embodiment, the inner member and outer member are each attached to tooling so that the translation of inner member and outer member is maintained along an axial centerline of the tube form assembly. A step  1109  is an optional step that includes removing the excess adhesive from the tube form assembly. The excess assembly is illustrated at least in  FIG. 8 . A step  1111  includes curing the adhesive so that inner member and outer member are securedly bonded together. The exact curing process is implementation specific, as different adhesives require different curing processes, as one of ordinary skill in the art will fully appreciate with benefit of this disclosure. For example, step  1111  can include subjecting the adhesive to an elevated temperature for a duration of time. 
     The disclosed tube form assembly, and method of making the same, provide significant advantages, including: 1) providing a self pumping adhesive joint which prevents drawing air bubbles into the bond line during assembly; and 2) providing a self pumping adhesive joint which expels air bubbles during assembly. 
     It is apparent that a system and method with significant advantages has been described and illustrated. The particular embodiments disclosed above are illustrative only, as the application may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the application. Although the system of the present application is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof. Accordingly, the protection sought herein is as set forth in the claims below.