Moldable Fly-Away Tool Structure System
A composite structure includes a first face sheet, a second face sheet, and a foam member located between the first face sheet and the second face sheet. The foam member has a molded contour, the mold contour being configured to provide tooling surface for at least one of the first face sheet and the second face sheet prior to curing of the composite structure. A method of making the foam member includes creating a mold tool having an interior surface which resembles the desired outer contour of the foam member. A mixture is poured into a pour opening in the mold tool. The mixture is allowed to polymerize into a foam as the foam expands and distributes within the mold tool. Vent openings in the mold tool are selectively tailored to control the density of the foam member. The foam member is cured in the mold tool.
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The system of the present application relates composite structure. In particular, the system of the present application relates to an efficient method for generating stiffness in a composite structure.
2. Description of Related ArtComposite structures are often used in aerospace, in part due to the high strength to weight ratio, and desirable fatigue qualities. Structural characteristics of the composite structure, such as stiffness and area moment of inertia, can be tailored through a variety of methods. One common method is use a cellular core material, such as honeycomb core, between an upper and lower face sheet. Another common method is to bond two separately cured composite parts together, thus forming a composite structure assembly.
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Although the developments in composite structures have produced significant improvements, considerable shortcomings remain.
The novel features believed characteristic of the embodiments of the present application are set forth in the appended claims. However, the embodiments 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:
While the system and method of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTIllustrative embodiments of the system 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'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.
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The molded foam member 307 is preferably formed with a pourable and expandable structural foam in a mold, as discussed further herein. The molded foam member 307 is preferably cured prior to assembly with the first face sheet 303 and second face sheet 305. The molded foam member 307 is configured to provide the structural integrity to composite structure 301 in a wide variety of geometries and contours. Molded foam member 307 is particular useful in providing structural stiffness in portions of composite structure 301 where narrow and slender stiffener geometry is required. Curing of composite structure 301 may require pressure, such as autoclave curing pressure, in order to properly cure the first face sheet 303 and second face sheet 305. As such, molded foam member 307 is configured to provide structural resistance to the pressure so as to preserve the desired geometry around molded foam member 307. In contrast, tall and narrow portions of honeycomb core are very susceptible to collapsing when subjected to autoclave pressure and temperature. For example, a honeycomb core portion hypothetically having a height of H1 and width of W1 of foam member 307, would likely crush inward along directions A1, A2, and A3, when subjected to autoclave pressure and temperature. However, foam member 307 is configured to be isotropic, unlike honeycomb core. As such, the isotropic properties of foam member 307 allow it to retain structural integrity in a wide variety of geometries and contours.
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The total weight amount of mixture 807 is at least partially dependent upon the desired density and the volume of foam member 307. For example, because density is the relationship is mass per unit volume, the desired density of foam member 307 at least partially dictates the weight amount of mixture 807. However, a small portion of the mixture 807 may escape through openings 711, 713a, and 713b, which affects the final density of foam member 307.
In the preferred embodiment, a “captive process” uses openings 711, 713a, and 713b to allow volatiles to escape during the polymerization of mixture 807, while also creating a desired pressure within mold 703. Pressure within mold 703 inhibits expansion of foam mixture 807 during the polymerization process, thereby increasing the density of the foam member 307. As such, the size and number of openings 711, 713a, and 713b are configured so as to selectively tailor the density of foam member 807. For example, the openings 711, 713a, and 713b in mold tool 703 create a foam member 307 having a density of approximately 12-16 pounds/ft3. However, this size and quantity of openings 711, 713a, and 713b can be increased to produce a foam member 307 of lower density.
In an alternative embodiment, mold 703 may be void of lid member 707 so that the foam mixture 807 is allowed to “free rise” within the base member 705. In the “free-rise” embodiment, a density of approximately 8.0 pounds/ft3 and less can be achieved. The “free rise” embodiment of foam member 307 may be particularly desirable when the geometry and contours of foam member 307 are relatively simple. This is because the exposed surface would require a cutting or shaving operation to trim the exposed surface of foam member 307 to the desired contour.
The density of foam member 307 is preferably customized in accordance with the specific implementation of a foam member 307 in composite structure 301. For example, one type of composite structure 301 may require a higher curing pressure as compared to another composite structure 301; therefore, a foam member 307 used in the composite structure that requires a higher curing pressure may be manufactured having a high density so as to withstand the higher curing pressure of composite structure 101. In one embodiment, composite structure 301 is configured such that the foam member 307 minimally performs the function of physical supporting of first face sheet 303 and second face sheet 305 before and during the curing cycle. In such an embodiment, foam member 307 acts as a “fly-away tool” such that it acts as a tool during the assembly and curing of composite structure 301, but also remains with the composite structure 301 during operation of the aircraft. It should be appreciated that composite structure 301 may also be used in vehicles and structures other than aircraft. Further, when foam member 307 acts simply as a “fly-away tool”, a release member may be applied during the assembly of composite structure 301 to prevent bonding contact between first face sheet 303, second face sheet 305, and foam member 307.
The expected operational loading of composite structure 101 is another factor that may contribute to the customization of the density of foam member 307. The density of foam member 307 can be customized in accordance with the desired structural strength of foam member 307. For example, in one embodiment of composite structure 101, foam member 307 may be configured to provide a structural load path between first face sheet 303 and second face sheet 305. In such an embodiment, first face sheet 303 and second face sheet 305 are preferably each in bonding contact with foam member 307. The bonding contact can be created with the resin from each first face sheet 303 and second face sheet 305. The bonding contact can also be created or supplemented with an adhesive layer located between each of the first face sheet 303, second face sheet 305 and foam member 307. The bonding contact facilitates the structural load transfer between first face sheet 303, second face sheet 305, and foam member 307, in a variety of load path directions.
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The system of the present application provides significant advantages, including: (1) providing a stiffness producing foam member in a composite structure that can be molded in a variety of geometries and contours; (2) providing a stiffness producing foam member in a composite structure that can withstand autoclave curing pressure; (3) providing a stiffness producing foam member in a composite structure, the density of the foam member selectively tailored; (4) providing a stiffness producing foam member in a composite structure that provides continuous support for an upper face sheet such that the foam member prevents sagging of the upper face sheet; and (5) providing a stiffness producing foam member in a composite structure that provides continuous support for an upper face sheet such that the foam member prevents sagging of the upper face sheet.
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. Accordingly, the protection sought herein is as set forth in the claims below. It is apparent that a system with significant advantages has been described and illustrated. 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.
Claims
1. A method of making a foam member for a rigid composite structure, comprising:
- creating a mold tool having an interior surface which resembles the desired outer contour of the foam member;
- pouring a liquid mixture into a pour opening in the mold tool;
- allowing the liquid mixture to polymerize into a foam so as to expand and distribute within the mold tool;
- selectively configuring one or more vent openings in the mold tool so as to selectively dictate the density of the foam member so as to tailor a strength of the foam member so that the foam member is able to rigidly support a skin member during a subsequent curing cycle of the skin member; and
- curing the foam member in the mold tool.
2. The method according to claim 1, wherein the one or more vent openings are located near the extremities of the mold tool.
3. The method according to claim 1, wherein the one or more vent openings are located in a lid member of the mold tool.
4. The method according to claim 1, further comprising:
- applying a release agent in the mold tool prior to pouring the liquid mixture into the pour opening.
5. The method according to claim 1, wherein the selectively configuring the one or more vent openings allow volatiles to escape during expansion of the liquid mixture into the foam.
6. The method according to claim 1, wherein the selectively configuring the one or more vent openings includes selectively sizing a diameter of the vent openings.
7. The method according to claim 1, wherein the selectively configuring the one or more vent openings includes selectively generating a quantity of the one or more vent openings.
8. A method of making a composite structure, comprising:
- providing an uncured composite lower face sheet;
- providing an uncured composite upper face sheet;
- providing an at least partially cured foam member, the foam member being rigid by having a foam body of uninterrupted foam, an outer molded surface of the foam member being an outer surface of the foam body;
- laying up the uncured composite lower face sheet onto a surface;
- positioning the foam member at a desired location on the lower face sheet;
- laying up the uncured composite upper face sheet onto the lower face sheet and the foam member so that the outer molded surface of the foam member supports a portion of the upper face sheet at a desired geometry; and
- curing the composite lower face sheet and the composite upper face sheet while the foam member supports the portion of the upper face sheet.
9. The method according to claim 8, wherein the step of providing the at least partially cured foam member comprises:
- creating a mold tool having an interior surface which resembles the desired outer molded surface of the foam member;
- pouring a mixture into a pour opening in the mold tool;
- allowing the mixture to polymerize into a foam as the foam expands and distributes within the mold tool;
- selectively configuring one or more vent openings in the mold tool so as to selectively control the density of the foam member; and
- curing the foam member in the mold tool.
10. The method according to claim 8, further comprising:
- selectively tailoring a volume of the mixture to correspond with the density of the foam member.
11. The method according to claim 8, further comprising:
- applying an adhesive between the lower face sheet and the foam member, as well as between the upper face sheet and the foam member.
12. The method according to claim 8, wherein the selectively configuring one or more vent openings in the mold tool includes locating the one or more vent openings near an extremity of the mold tool.
Type: Application
Filed: Jan 16, 2018
Publication Date: May 24, 2018
Applicant: BELL HELICOPTER TEXTRON INC. (FORT WORTH, TX)
Inventors: Suvankar Mishra (Carrollton, TX), John R. McCullough (Weatherford, TX), Mark Chris (Dallas, TX), Stanley B. Woychesin (McKinney, TX)
Application Number: 15/872,706