The present invention pertains generally to components needed for the production of airplane fuselages. More particularly, the present invention pertains to caul sheets used to form composite material into airplane fuselage skins. The present invention is particularly, but not exclusively, useful as a device and method for manufacturing a unitary caul sheet for use in creating unitary fuselage skins.
Aircraft manufacturers continually strive to find ways that will improve aircraft efficiency and reduce the costs that are associated with the manufacture and maintenance of aircraft. One consideration that is frequently taken to improve aircraft efficiency is to reduce the weight of the craft. In many fields, composite materials have been used in place of heavier traditional materials for this purpose. Accordingly, the use of composite materials for the manufacture of structural components has expanded considerably over the past years. In particular, composite materials that are made of carbon fibers and epoxy resins have been successfully used for the manufacture of various types of vehicles (e.g. cars, boats and airplanes). In part, this has happened because these materials are relatively light-weight, and they exhibit high strength in both tension and compression. They are also quite damage tolerant and resistant to puncture. Further, they inhibit water migration. However, conventional methods for manufacturing aircraft components with composite materials typically require relatively expensive tooling and labor-intensive assembly procedures. Frequently, an aircraft component is assembled from composite segments cured on separate caul sheets.
In light of the above, it is an object of the present invention to provide a method and device for manufacturing a caul sheet for use in creating a unitary airplane fuselage that is to be made from composite materials. Another object of the present invention is to provide a method for manufacturing a substantially tubular caul sheet. Another object of the present invention is to provide a method for manufacturing a caul sheet that is relatively simple and easy to implement and that is comparatively cost effective.
When creating a composite component for an airplane, a caul sheet may be required. Importantly, when used, the caul sheet needs to be formed as an inner mold line (IML) with a surface that is a mirror-image (i.e. a negative) of a desired surface of the component. The present invention involves a method for manufacturing such a caul sheet as a unitary structure. This requires the use of a generally tubular tool. Structurally, the tool has a hollow interior cavity that defines the inner mold line (IML) surface for the caul sheet. More specifically, the tool is formed from three tool portions that are juxtaposed to establish the hollow interior cavity and IML surface.
In order to manufacture the caul sheet, a caul sheet material such as a self-curing, two-component polyurea is sprayed onto the interior cavity's IML surface. Thereafter, an armature is inserted into the interior cavity of the tool. Then, a filler material such as polystyrene is introduced into the interior cavity between the armature and the caul sheet material.
After the caul sheet material, filler material and armature are established in the interior cavity of the tool, steam is injected into the filler material to cause the filler material to form into infrastructure. Further, due to its self-curing nature, the caul sheet material cures on the IML surface. After the curing process is finished, the three tool portions are removed from the caul sheet material to expose the finished caul sheet. Thereafter, composite material may be applied to the caul sheet for formation of a fuselage skin.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Referring initially to
Referring now to
With
Turning now to
In order to manufacture a unitary caul sheet 18, the three tool portions 28a-c are juxtaposed as shown in
After the caul sheet 18 is formed, it may be used to create the fuselage skin 10 for an aircraft. During the manufacture of a fuselage skin 10, composite material is initially applied to the outer surface 20 of the caul sheet 18 while the caul sheet 18 is still supported on the armature 44 by the filler infrastructure 56. Specifically, composite material is wound onto the caul sheet 18 as the armature 44 rotates the caul sheet 18 about the axis 36. After the composite material is positioned on the caul sheet 18, the armature 44 is inserted into a hollow mold cavity (not shown). In order to form the desired fuselage skin 10, the hollow mold cavity has an inner surface that is a negative or mirror image of the fuselage skin's desired OML. After the armature 44 is inserted into the mold cavity, heat is applied to cause the filler infrastructure 56 to shrink and collapse. Then the armature 44 is removed from the mold cavity, leaving the semi-rigid caul sheet 18 in position with the composite material adjacent to the mold cavity's inner surface. Thereafter, the caul sheet 18 is pressurized to between about 40 and 90 psi and slightly inflated to push the composite material against the inner surface of the mold cavity. During this step, the composite material is cured with an IML imposed by the caul sheet 18 and an OML imposed by the cavity mold. Specifically, the composite material is cured by a heat regimen of 2 hours at a temperature of at least 275° F., and preferably between 275° and 350° F. Typically, this heating process involves a ramp up period of approximately 2 hours to reach 275° F., as well as a 2 hour cool down period. After the curing process is finished, the pressurization of the caul sheet 18 is ended and the caul sheet 18 contracts away from the cured composite material forming the fuselage skin 10. Then, the caul sheet 18 is removed from the fuselage skin 10 and the fuselage skin 10 is extracted from the cavity mold.
While the particular Method and Device for Manufacturing a Unitary Caul Sheet as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
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Number | Date | Country | |
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20080224360 A1 | Sep 2008 | US |