Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-12-21
2001-03-06
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S285000, C156S382000, C156S500000, C249S134000, C264S257000, C264S258000, C264S511000, C425S403000, C425S500000, C425S504000
Reexamination Certificate
active
06197146
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method and apparatus for forming an airfoil assembly such as a helicopter rotor blade. More particularly, this invention relates to a method and apparatus for bonding the airfoil assembly skin to the airfoil assembly core. This invention is particularly useful for bonding the airfoil skin to the airfoil core when the airfoil core, and thus the airfoil assembly, is provided with complex and pronounced surface contour changes.
BACKGROUND ART
Modern day airfoil assemblies such as helicopter rotor blades, flaps, ailerons, and the like, such as those shown in U.S. Pat. No. 5,320,494, include internal components which are structural support components, such as rotor blade spars; airfoil-shaping honeycomb components; and the like. These airfoil assemblies include an external skin which forms an envelope for the airfoil, and is typically made of a varying number of plies of fiberglass, or graphite impregnated with a resin matrix, generally epoxy, which is referred to in the industry as “prepreg”. The internal airfoil components are preassembled and then are positioned in a bonding assembly which serves to locate and bond the external skin to the internal components of the airfoil. The bonding assembly includes cooperating mold parts including a steel base member having an internal cavity that conforms to the desired configuration of the upper or lower surface of the airfoil; and a caul plate member which forms the upper closure of the bonding cavity. The caul plate member can take the form of a steel or aluminum cover for the bonding cavity during the bonding operation.
The use of rigid upper and lower components of the mold is acceptable in most cases; however, when an air foil having complex and pronounced surface contour changes is being formed, the rigid caul plates may not be useful since such airfoils must be formed at higher pressures so as to ensure that the skin follows the machined contours of the core without leaving voids between the airfoil skin and the airfoil core. We have experimented with a compound caul for high pressure molding of airfoils, which compound caul included a central flexible component and peripheral rigid elements. The flexible component was formed from silicone rubber, and the peripheral rigid elements were formed from aluminum spars or beams. We found that the rigid aluminum caul elements resulted in the formation of undesirable peripheral areas in the molded airfoil which contained voids wherein the skin was not bonded to the core. We believe that these voids are the result of the inability of the rigid caul elements to adapt to areas of the core wherein pronounced surface contour changes occur.
We have also experimented with a caul which was made solely from the silicone rubber material. When such a flexible caul was used, there were no voids between the skin and core, but the edges of the core were undesirably deformed, i.e., crushed, by the molding pressure, and the inability of the flexible material to protect the edges of the core against crushing. What is needed is a caul component which can conform to the contours of the core, while at the same time protecting the edges of the core against crushing. We have discovered that a wire mesh which is commonly used as a conveyer belt has the necessary properties to be used as an airfoil caul component in combination with a wholly flexible component of silicone rubber, or some similar elastomer.
DISCLOSURE OF THE INVENTION
This invention relates to a compound caul assembly for use in pressure bonding the skin of an airfoil to the airfoil core, and to a mold assemblage including such a compound caul assembly. The compound caul assembly includes a central elastomeric component which is preferably formed from silicone rubber, and also includes peripheral components which are formed from mesh belts which are flexible in one direction, and are rigid in a transverse direction. We have chosen to categorize such mesh belt caul components as “semi-rigid” for purposes of linguistic economy.
The structure of such belts will be more clearly set forth hereinafter.
The skin-to-core bonding assemblage includes a basal contoured support plate, which is preferably formed from steel, and the composite caul plate assembly. The support plate is pre-machined so as to provide a negative mold of one of the contoured surfaces of the airfoil. The composite skin is placed on the support plate, and a pre-machined contoured core is placed on the skin. The surface of the core facing away from the skin is then covered with an elastomeric covering which will evenly transmit the bonding pressure exerted on the assembly in a pressurized autoclave. The edges of the assembly are covered with the semi-rigid elongated caul plates which are flexible in the direction of elongation, but rigid in the transverse direction. The caul plates are preferably formed from a wire mesh. The elongated-direction flexibility of the caul plates allows them to closely follow the changes in the surface contours of the core, and the transverse rigidity of the caul plates enables them to protect the edges of the core from crushing during the bonding process. All peripheral edges of the core are overlain by the semi-rigid caul plates, and the caul plates are then overlain by silicone rubber. When the aforesaid bonding assembly is employed, the result is a void-free bond between the core and skin, with the edges of the core being free of any crushing.
It is therefore an object of this invention to provide an improved bonding assembly for evenly bonding a composite material skin to a contoured surface of a honeycomb core in an airfoil assembly.
It is a further object of this invention to provide an improved bonding assembly of the character described which produces a complete bond between the skin and the core that is free of skin-core voids.
It is yet another object of this invention to provide an improved bonding assembly of the character described including a compound bonding assembly caul that includes a medial elastomeric member and peripheral semi-rigid elongated members.
It is an additional object of this invention to provide an improved bonding assembly of the character described wherein the peripheral semi-rigid caul members are flexible in their elongated direction, and are rigid in a direction which is transverse to their elongated direction.
It is yet another object of this invention to provide an improved bonding assembly of the character described wherein the peripheral caul members are operative to closely conform to core contours in the elongated direction and are operative to protect edges of the core from crushing during the bonding operation.
REFERENCES:
patent: 5354195 (1994-10-01), Dublinski et al.
patent: 5484277 (1996-01-01), Lindsay
patent: 1049198 (1966-11-01), None
Sucic Lori Ann M.
Sucic Steve
Aftergut Jeff H.
Jones William W.
Sikorsky Aircraft Corporation
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