Abstract:
A method and fastener for distributing an anchoring material and securing abutting honeycombed panels in a generally perpendicular alignment. The fastener is provided with a pointed tip to penetrate into undrilled portion of the inner cellular structure of one of the panels. The hollow fastener allows for the injection and distribution of an anchoring material into the ruptured cell core and into predrilled bores in the first panel.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a novel method and fastener for joining composite honeycomb panels. More particularly, a pointed fastener is provided to penetrate the internal cell structure of honeycomb construction panels without destroying the internal integrity of the honeycomb and without requiring drilling of bores through selected panels prior to insertion of the fasteners. 
   Existing fasteners utilized in the assembly of the T or L joints with honeycomb panels have been blunt-nosed and have required drilling bores through the first panel and the perpendicularly abutting panel before the insertion of the blunt-nosed, hollow, tubular fastener. After the fastener is in place through the predrilled bores, an adhesive or anchoring material is injected through the center of the hollow fastener and into the internal cell structure. U.S. Pat. No. 4,370,372 teaches currently utilized technologies. 
   With the introduction of computer numerically controlled (CNC) technology, there has arisen a need to modify the joining processes with existing honeycomb panels. CNC machines precut composite honeycomb panels and pre-drill holes or bores in the flat panel according to design standards. However, abutting panels are not predrilled. Thus, in order to join a first, flat panel with a perpendicularly abutting panel, the panels are first secured in a jig to properly align the panels for drilling (through the predrilled bore into the undrilled abutting panel) and for the insertion of the blunt-nosed fastener. 
   One embodiment of the present invention eliminates the necessity to pre-drill the abutting panel. A small, pointed fastener of one embodiment of the present invention provides the capability for penetrating the outer sheet member of an abutting composite honeycomb panel, passing through the internal cell structure of the abutting panel without collapsing or destroying the cell integrity in the abutting panel, and joining the predrilled flat panel with the abutting panel. It further allows for the elimination of clumsy and expensive jigs or frames for holding the panel cabinetry during fabrication. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a prior art fastener. 
       FIG. 2  shows abutting panels of the present invention in a partial top view. 
       FIG. 3  illustrates a side elevation view of one embodiment of the fastener of the present invention. 
       FIG. 3A  shows the fastener of  FIG. 3  in cross section. 
       FIG. 4  shows a cross sectional view of an alternative embodiment of the present invention. 
       FIG. 5  illustrates a partial side elevation view of abutting panels and fasteners of the present invention. 
       FIG. 6  depicts a prior art fastener pressed into an undrilled abutting panel thereby collapsing and destroying the cell integrity. 
       FIG. 7  is a partial cross sectional view of the present invention with anchoring material injected through the fastener and into the cell structures. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a prior art fastener  10  having a generally hollow cylindrical body portion  12 . On a first end is provided a flared head  14  with an opening  16  into the hollow inner section of the body  12 . At an opposite end is a blunt nose  18  with an anchoring material discharge opening  20 . Along the length of the fastener  10  are provided a plurality of anchoring material discharge openings  22  which allow anchoring material or adhesive injected through the opening  16  flared head  14  to pass from the inside of the body  12  into the cell structure of joined honeycomb panels as will be described below. 
     FIG. 2  is a partial top view of abutting honeycomb panels joined by a fastener of the present invention shown in broken lines. A first flat panel  30  of well known honeycomb panel construction has a cellular core  32  formed from a multiplicity of side-by-side similar parallel cells  34  (normally {fraction (3/16)} inch in diameter) sandwiched between stiff parallel outer cover sheet members  36  and  38  made of moisture impervious composition. The panel is normally ⅛ to 1 inch in thickness. The core  32  may be of a thin paper-like, cellulose fiber material covered with shellac and defining thin hexagonal cell walls. The outer cover sheet members  36  and  38  may be quite thin, hard sheets of woven or non-woven fiberglass bonded in a suitable stiffening resin or similar inert fibrous material secured by adhesive (or equivalent) across the opposite ends of all of the core cells to effectively close the cells. Each of the cells have a longitudinal axis A 1 . 
   A second panel  40  of similar construction is shown in  FIG. 2  in generally perpendicular abutment with the first panel  30 . Each of the cells  34   1  of the cellular core  32   1  of the second panel  40  has a longitudinal axis A 2 . When the panels are joined, axes A 1  are generally perpendicular to axes A 2 . 
   The first step in securing panels  30  and  40  in an abutting arrangement is to form all fastener bores  31  at right angles to the plane of panel  30  according to specifications of the design standard. This is most effectively accomplished by the use of computer numerically controlled (CNC) machines, but may be accomplished by other drilling or punching technologies. The predrilled bores  31  are the same diameter as the fastener  11  to allow for ready slidable insertion of the fastener  11  through the bore  31 . 
     FIG. 3  illustrates one embodiment of the present fastener  11 . The fastener has a flared head  14   1  to limit insertion of the fastener and to terminate the fastener flush with the outer shell member  36  of panel  30  (see FIGS.  2  and  3 ). An insertion end  18   1  of the fastener  11  is pointed, allowing for easy penetration of the inner fiber cell structure  32   1  of the second panel without crushing the cell walls and destroying the overall integrity of the honeycomb core. The second panel is not predrilled; and, therefore, there is no need to align bore holes or place the panels in an alignment jig or frame. 
   Typically, the fastener  11  is a relatively rigid aluminum tube one-and-a-half (1½) to five (5) inches long with a uniform body diameter of {fraction (3/16)} inch to ½ inch. The discharge openings  22   1  are a serial of {fraction (3/32)} inch (diameter) longitudinally and peripherally spaced circular apertures. The pointed end  18   1  has a plurality of slotted openings  19   1  ⅜ inch to one inch in length peripherally disposed. While the fastener is generally metal, other stiff or rigid substitute material compositions may be used. 
   It should be understood that the diameter of the fastener  11  is greater than the diameter of the cells  34  and  34   1  so that as the pointed end  19   1  of the fastener penetrates the abutting panel  40 , it creates its own bore. Surrounding cells are ruptured in the same direction as the inserted fastener. This rupturing action creates disjoined cell wall sections  35   1  which urge against the fastener  11  to cause a frictional force to keep the fastener from disengaging from the penetrated core section. Further, the outer surface of the fastener  11  may be provided with one or more knurled sections  60  which cooperate with the disjoined cell walls  35   1  to enhance the retention of the fastener in the penetrated bore until the anchoring material is injected and hardens. 
     FIG. 4  illustrates another embodiment of the present invention. A prior art fastener  10  has been adapted to receive in the blunt nose  18  a pointed insert  100 . Insert  100  has an appropriately sized collar  102  and shoulder  104  to fit within and abut against the opening  20 . The insert  100  has a discharge opening  20   1  and a plurality of discharge slots  19   1  to allow anchoring material to be injected into the cell core as previously described. Thus, in the embodiment of  FIG. 4 , a prior art fastener may be modified or retrofitted to function as an improved fastener of the present invention. 
     FIG. 5  shows a partial side elevation view of abutting panels  30  and  40  and fastener  11  of the present invention. It may be seen that the fastener  11  has been passed through predrill bore  31  and pointed end  18   1  has penetrated the core  32   1  rupturing some cells  34   1  creating disjoined fiber cell walls  35   1  urged in the direction of penetration (arrow) and against the outer surface of the fastener. 
   It should be noted that the cell core  32   1  has not collapsed and the overall integrity of the core is maintained except where the pointed end  18   1  has punctured a cell  34   1 . A clamp or jig would normally be used to hold the panels  30  and  40  in an assembled/joined relation. However, with the present fasteners  11  and  11   1  this is not necessary as the joint end  18   1  penetrates the cell structure and creates its own bore. 
     FIG. 6  illustrates the problem of attempting to use a prior art fastener  10  without predrilling bores in the second abutting panel  40 . The blunt nose  18  crushes and collapses the cell core  32 , tearing the cell walls far from the outer surface of the body  12 . Not only is the honeycomb structure&#39;s integrity destroyed, but excessive anchoring material would be injected to fill the huge void  110  created by the tearing action of the blunt nose  18 . 
   One purpose of the pointed end  18   1  of the present invention is to allow for a controlled penetration and rupturing of only the necessary cells.  FIG. 7  shows how anchoring material  66  fills only the most adjacent opened cells thereby minimizing the amount of material  66  which must be injected through the fastener  11   1  out of the discharge openings  19   1 ,  20   1 , and  22   1 , and into the cores  32  and  32   1  out the discharge openings  19   1  and  22   1 . 
   Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. On the contrary, various modifications of the disclosed embodiments will become apparent to those skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications, alternatives, and equivalents that fall within the true spirit and scope of the invention.