Joints and connections – Member deformed in situ – Deformation occurs simultaneously with assembly
Reexamination Certificate
1999-10-20
2001-12-04
Kim, Harry C. (Department: 3629)
Joints and connections
Member deformed in situ
Deformation occurs simultaneously with assembly
C403S375000, C403S361000
Reexamination Certificate
active
06325568
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of building construction using mortise and tenon joints to connect structural members, such as in aerospace commodities, and more particularly, to the use of minimum edge margin mortise and tenon joints which implement self tooling characteristics to produce overhead stowage bins for aircraft from a single folded composite sandwich panel.
BACKGROUND OF THE INVENTION
The practice of the aerospace industry has been to adapt long established carpentry methods of joinery into aerospace commodities in an attempt to capture the advantages of reduced weight and assembly complexity. Substantial difficulties have sometimes been encountered however, because tolerances achievable with fine carpentry in wood-working are far superior than that which can be achieved using many aerospace materials, such as composite honeycomb sandwich panel type structures, and their related assembly methods. Thus, time proven joinery techniques that have been effectively implemented in wood-working applications, have proved ineffectual in the aerospace industry.
One such problem area for aerospace applications, which has been encountered in the prior art, has been how to maximize the volume of a defined envelope using extended tab and pocket cutout joinery methods, while also maintaining maximum joint strength. The rabbet joint has become the standard design for the majority of aerospace commodities that utilize extended tab and pocket cutout joinery. In a rabbet joint, the pocket cutouts are at the very edge of the panel, with the pocket sidewalls actually incorporated into the outer edge of the panel. This type of joint permits joint location to occur at the edge of a panel, thus providing the benefit of a non-interfering edge profile The disadvantage of the rabbet joint, is that the joint must be adhesive bonded to secure the panel connection, and the primary load path is through the relatively weak adhesive bondline at the rabbet joint.
The standard alternate to the rabbet joint is commonly referred to as a mortise and tenon joint Although, the term mortise and tenon has become somewhat generic in fine carpentry uses, aerospace usage has defined a mortise and tenon joint as a term of art, describing a joint utilizing sandwich panel construction with square cut tabs (tenons) and blind (joint not visible after joining has occurred) slotted pocket cutouts (mortises), without dovetailing.
The bonding process of a mortise and tenon joint also involves applying adhesive into the mortise pocket, however, since the pocket is fully enclosed in the mortise panel (not incorporated into the panel edge as in the rabbet joint), the primary load path is through the mortise panel itself and not the adhesive bondline. The disadvantage of the mortise and tenon joint is the existence of an edge margin of the mortise panel that extends from the mortise pocket to the actual edge of the panel. This interfering edge margin reduces the volume which can be achieved inside a defined envelope It is desirable to have a joint that would provide the combined benefits of both a rabbet joint and a mortise and tenon joint.
Another unresolved problem in the prior art is that although tight tolerance control of the standard square cut mortise (panel hole) can be achieved through the use of NC panel and profile routers, large clearances are still usually required between the tenon tabs and mortise cutout sidewalls, in order to allow for variation in tenon panel thickness. The current state of the art in composite honeycomb sandwich panel production utilizes a multi-opening press (MOP) process, that does not presently afford a high degree of control of panel thickness variation.
Thus, relatively large clearances must be designed into mortise and tenon joint interfaces so that costly interference conditions do not occur, preventing the tenon tabs from fitting into the mortise pockets, and resulting in the scrapping of parts or expensive rework. These large clearances between the mortise pocket sidewalls and the tenon tab surfaces, increase the need for elaborate and expensive tooling to accurately locate and secure the panels. While the panels are held in place, an adhesive, which is used to bond the joint, is allowed the necessary time to cure. A joint structure with inherent self-tooling features that could eliminate the need for expensive additional tooling is highly desirable.
Still an additional unresolved problem in the prior art involves the efficient production of lightweight overhead stowage bins for aircraft Currently, overhead stowage bins for aircraft are produced by joining together four (typically) composite sandwich panels using structural adhesives and either aluminum brackets fastened to potted inserts or modified box joints (typically rabbet joints). Both of these methods depend on the strength of the adhesives to carry the required structural loads.
This reliance on adhesives presents two major disadvantages. First, the loads that adhesives are typically capable of carrying are inferior to the loads that can be carried through the composite panels themselves. Second, adhesives present substantial manufacturing problems, in that parts must be jigged in the proper configuration while the adhesive cures, a time period generally of around eight hours. It is desirable to have a aircraft stowage bin that can be produced without structural adhesives.
SUMMARY OF THE INVENTION
The present invention discloses a one-piece aircraft stowage bin constructed from a single piece of folded, thermoplastic-composite-skinned, honeycomb-cored sandwich panel. The aircraft stowage bin is formed by folding the composite material into a locking open box type structure The composite sandwich panel contains interlocking joints which can be characterized as minimum edge margin mortise and tenon joints (described below).
A minimum edge-margin mortise and tenon joint corner structure is formed from a tenon panel, having tenon tabs, engaging mortise pockets formed in an angularly disposed tenon panel In the minimum edge margin joint, the mortise pockets are located along the edge of the mortise panel, as in a rabbet joint, but with the mortise panel edge containing outwardly extended bulges in the regions of the mortise pockets, such that a minimum edge margin is maintained around each mortise pocket (instead of the pockets being incorporated into the panel edge as in a rabbet joint).
In a preferred embodiment of the present invention, the single piece thermoplastic composite honeycomb sheet is cut so that sections of the sheet can be folded, using a thermoplastic folding method, to form the stowage bin. Side portions of the sheet are designed such that their shape facilitates being folded upwards to form end panels of the stowage bin. Another portion of the sheet is designed such that its shape facilitates being folded upwards and then over, to form the top panel of the stowage bin.
The minimum edge margin mortise and tenon joints are used at the connection between the top edge of the end panels and the top panel of the stowage bin. The mortise pockets in the mortise portion of the panel joint, are located along the edge of the top panel of the stowage bin. The tenon tabs in the tenon portion of the panel joint are located along the top edge of the end panels. This allows the minimum edge margin mortise and tenon joints to engage during the folding process of the stowage bin panel.
Finally, two formed angle brackets are through-bolted to the top panel of the stowage bin and the end panels. This provides a load path for downloading forces and securely locks the bin together. This locking method, which utilizes the formed angle brackets, allows the folded composite panel to form joints that connect such that no adhesive is required, either to carry loading forces or to hold the bin together. The only direction in which the minimum edge margin mortise and tenon joint is subject to detachment during loaded conditions, is secured by the formed angle brackets.
Another aspect of the invention disclo
Burnham Richard C.
Button Scott D.
Dewar Paul S.
Druckman Ralph D.
Griffing James S.
Christensen O'Connor Johnson & Kindness PLLC
Kim Harry C.
The Boeing Company
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