Patent Description:
Resin film infusion is a known process for manufacturing laminate composite structures which uses, as its basic feedstock material, sheets of resin film and dry fabric. The resin film and the dry fabric sheets are laid up in alternating layers onto or into a forming tool, and then heated for consolidation and then curing. During heating, the resin film first melts, or undergoes a significant viscosity reduction, and wets the adjoining fibers substantially completely coating or encapsulating them. The resin and now-wetted fibers then cure into a single solid structure. <CIT> discloses a method for creating a fan cowl with a hollow hat stiffener comprising draping at least a first prepreg over a tool to create an outer layer of the fan cowl, setting a mandrel over the outer layer; and draping the second prepreg over at least a portion of the mandrel and at least a portion of the first prepreg to form the hollow hat stiffener having a geometry similar to a shape of the mandrel.

Resin film infusion is selected as an effective and efficient process for forming many large composite structures. But, when a laminate structure requires internal laminate edges (where the resin and dry fabric sheets have an edge that is overlaid on a prior layer, and will not form part of a perimeter of the part) resin film infusion can result in a part with degraded material properties because of the propensity of the dry fabric sheet edges to fray, and the difficulty in precisely aligning edges of the resin film sheet with edges of the dry fabric sheet.

Methods of creating composite structures are provided.

A method for creating a fan cowl with a hollow hat stiffener comprises: pressing a resin film between a non-crimp fabric (NCF) and a release poly-film to tack the resin film to the NCF and the release poly-film and to create a resin-fabric sheet comprising at least a resin film layer and an NCF layer; cutting the resin-fabric sheet to a pre-determined shape to create at least one of a first resin-fabric preform, a second resin-fabric preform, and a third resin-fabric preform; draping at least the first resin-fabric preform over a tool to create an outer layer of the fan cowl; setting a mandrel over the outer layer; and draping the second resin-fabric preform over at least a portion of the mandrel and at least a portion of the first resin-fabric preform to form the hollow hat stiffener having a geometry similar to a shape of the mandrel.

In various embodiments, the method may further comprise, draping the third resin-fabric preform over at least a portion of the second resin-fabric preform to create a desired thickness of the hollow hat stiffener. The method may further comprise, heating the first resin-fabric preform, the second resin-fabric preform, and the third resin-fabric preform to cure the first resin-fabric preform, the second resin-fabric preform, and the third resin-fabric preform to create the fan cowl. The method may further comprise, removing the mandrel from the fan cowl. In response to the first resin-fabric preform being draped over the tool with the resin film layer contacting the tool, the resin film layer of the second resin-fabric preform may be adjacent to the NCF layer of the first resin-fabric preform. In response to the first resin-fabric preform being draped over the tool with the NCF layer contacting the tool, the NCF layer of the second resin-fabric preform may be adjacent to the resin film layer of the first resin-fabric preform. The pressing may be performed at a room temperature.

The features, elements, steps, or methods as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration.

As used herein the term "prepreg" may refer to fibrous structures, with glass fibers, carbon fibers, aramid fibers, and/or the like, pre-impregnated with an uncured or at least partially uncured matrix material, such as a resin, where the substantial majority of fibers are generally completely encased in the matrix material.

As used herein the term "dry fabric" may refer to a fabric sheet made up of dry fibers (e.g., carbon fibers, glass fibers, and/or the like) that have not been impregnated with resin or matrix material.

As used herein the term "non-crimp fabric" or "NCF" may refer to a type of dry fabric made of uni-directional, non-woven, generally straight fibers (e.g., carbon fibers, glass fibers and/or the like).

As used herein the term "resin film" or "RF" may refer to a film or sheet of semi-solid, uncured or at least partially uncured resin. The RF may generally be supplied on a release paper and configured to be interleaved with layers of dry fabric during a film infusion process.

As used herein the term "drapability" may refer to the ability to smoothly drape a continuous sheet, or the like, over a contoured surface, especially a surface contoured in multiple directions. Stated another way, "drapability" may refer to how closely such structure takes on the shape of the surface over which it is being draped or placed without wrinkling or other defects.

Manufacturing laminated composite structures, such as those now commonly used in aerospace structures, can be time consuming and expensive. For example, a layup process for creating a laminated composite structure may comprise forming and cutting many thin composite layers and then laying them by hand onto or into a forming tool before curing. The layup process typically constitutes a large portion of the total labor hours needed to form a part, and is also a potential source of many quality problems due to its manual nature and its reliance on individual technician skill and performance.

Certain materials used in creating laminated composite structures are relatively expensive. Prepreg material is one example of a relatively expensive material. It constitutes a fiber fabric (woven or nonwoven) that has been pre-impregnated with an uncured or partially cured resin. Typically, the highest quality prepreg materials must be stored at low temperatures to prevent the resin from curing before a part is laid-up. The low temperature storage equipment adds costs, and even at low temperatures a high-quality prepreg typically has a limited shelf life before it must be cured, otherwise the performance of the end structure is compromised. Thus, even when stored at low temperatures, some prepreg is typically scrapped and wasted because it is not used within its shelf-life, adding to the operational cost of producing parts with prepregs.

Another disadvantage of prepregs is their lack of drapability. Because the individual fibers are fairly tightly bound together by the uncured, but viscous and very tacky resin, the fibers cannot easily slide relative to one another, and therefore the prepreg sheet does not stretch or compress easily. This can make draping large prepreg sheets over tool surfaces curved in multiple directions very difficult.

To address these difficulties, some laminate composite parts are made using a resin film infusion process which typically constitutes sheets of dry fabric (woven or nonwoven) layered alternately with separately laid up sheets of resin film, which are then heated for consolidation and then curing. During heating, the resin film first melts, or undergoes a significant viscosity reduction, and wets the adjoining fibers substantially completely coating or encapsulating them. The resin and now-wetted fibers then cure into a single solid structure. Such a resin film infusion process utilizes a dry fiber fabric feedstock (which is typically much more expensive than the resin film) that has a practically unlimited shelf life because it is kept separate from the resin film which has a limited shelf life, resulting in less waste of the fiber fabric and improved operational costs. Also, the dry fiber fabric and thin resin film sheets generally have better drapability properties than prepregs. As already known to those of ordinary skill in this art, these advantages make resin film infusion processes attractive for making many different parts.

A disadvantage of resin film infusion is that the dry fabric can be difficult to handle. Especially in the case of the nonwoven non-crimp fabrics (NCF), the dry fibers in the fabric can fray easily at the sheet edges, resulting in uneven fiber distribution and degraded material properties after curing. This risk is addressed by making the layup larger than the final part, and then after curing by trimming the perimeter of the part where fraying may have occurred. Any frayed edges are trimmed off, leaving an edge where the fiber distribution is more consistent. While this method effectively addresses fraying of the dry fabric on external edges of the part, it does not work for internal edges. Some layups are designed with detail pieces of fabric laid up inside of a larger field, where some or all of the edges of the detail sheet of fabric are not external edges, but rather are overlaid onto the larger sheets of fabric and resin film underneath. Such an internal edge cannot be trimmed after curing, and without trimming the edge of the sheet laid up on the tool becomes the "net edge" after curing.

In addition to the risk of fraying, there is also a related risk of the dry fabric and the resin film sheet edges not being perfectly aligned when laid up by the technician. Any misalignment of the two sheets or layers on an external edge can be trimmed away as described above, but internal edges cannot be trimmed after curing to solve this problem.

As a solution to the above problems previously inherent with resin film infusion processes, the inventors have developed a method of tacking together dry fiber fabric and resin film feedstocks to one another, before trimming into sheets and lay up on the forming tool. The two layers are merely loosely tacked together, and remain separate and distinct layers. The combined material thus maintains most of the advantageous drapability properties of the dry fabric and resin film used in a resin film infusion process. The combined material also advantageously controls fiber fraying at the edges, as the tackiness of the resin film tends to hold the fibers in place during handling and lay up. Also, if trimming into a desired sheet shape for lay up is performed after the resin film and dry fiber fabric are tacked together, then the two layers stay tacked together and the edges of each layer remain perfectly aligned during handling and after lay up on the forming tool. Use of this tacked-together, pre-combined resin film and dry fiber feedstock has been found to significantly increase the quality of a resin film infusion production process, and to significantly reduce the labor hours and resultant costs of the process.

With reference to <FIG>, an aerostructure article, illustrated as fan cowl <NUM> is provided, in accordance with various embodiments. Although illustrated as a fan cowl <NUM>, it is contemplated herein that the method of creating a composite structure, as described herein, may be used on any composite structure. Fan cowl <NUM> may be a cocured composite structure having a unitary skin <NUM> and reinforcing hat sections (also referred to herein as hollow hat stiffeners) <NUM>, <NUM>, and <NUM>. Reinforcing hat sections <NUM>, <NUM>, and <NUM> may be circumferentially extending and axially spaced apart sections. Reinforcing hat sections <NUM>, <NUM>, and <NUM> may comprise hollow hat stiffeners. The fan cowl <NUM> is shown as generally arcuate in shape, as illustrated in <FIG>, but the use of the disclosed methods may extend to other shapes and applications. In various embodiments, longeron members <NUM> may be attached to the ends of fan cowl <NUM>. Longeron members <NUM> may be used for hinging the fan cowl to another structure or for latching two such fan cowls together or for other desired purposes.

With reference to <FIG>, a method <NUM> is provided, in accordance with various embodiments. Method <NUM> may be used in preparation for and during a composite layup process. With reference to <FIG>, a method <NUM> for creating a fan cowl is provided, in accordance with various embodiments. Method <NUM> may be used for creating fan cowls with hollow hat stiffeners. With reference to <FIG>, a method <NUM> for creating a fan cowl with hollow hat stiffeners is provided, in accordance with various embodiments. Method <NUM> may allow for on-demand combination of resin-film and non-crimp fabric in preparation for forming a fan cowl or other composite structures. With reference to <FIG>, <FIG>, and <FIG>, the steps to method <NUM>, method <NUM> and method <NUM>, respectively, are provided herein.

With reference to <FIG>, a combiner <NUM> is illustrated, in accordance with various embodiments. Combiner <NUM> may be for combining resin film (RF) <NUM> to a dry fabric, such as non-crimp fabric (NCF) <NUM>. Combiner <NUM> may include a body <NUM> attached to one or more rolls for supplying or catching material. Roll <NUM> may supply NCF <NUM>. Roll <NUM> may supply RF <NUM>. Roll <NUM> may supply a release poly-film <NUM>. Roll <NUM> may catch release paper (also referred to herein as a first release paper) <NUM>. Roll <NUM> may catch release paper (also referred to herein as a second release paper) <NUM>. Release poly-film <NUM> may comprise a drapable material. In various embodiments, release poly-film <NUM> may comprise a polyurethane film, a polyethylene film, a polypropylene film, or any other suitable poly material which is drapable. In various embodiments, first release paper <NUM> and second release paper <NUM> may comprise a poly material, a paper material, or any other suitable material. First release paper <NUM> may be removed from RF <NUM>. Second release paper <NUM> may be removed from RF <NUM>.

With momentary reference to <FIG>, NCF <NUM> may be tacked to RF <NUM> by first roller <NUM> and second roller <NUM> to combine NCF <NUM> and RF <NUM> into a single resin-fabric sheet <NUM> (see step <NUM>). With momentary reference to <FIG>, NCF <NUM> and RF <NUM> may be compressed or pressed between first roller <NUM> and second roller <NUM> to combine NCF <NUM> and RF <NUM> into the single sheet (see step <NUM>). Such combination may be performed at room temperature. However, in various embodiments, such combination may be performed with additional heat applied to increase the tackiness of RF <NUM>. Then, with momentary reference to <FIG>) release poly-film <NUM> may be rolled or otherwise applied over RF <NUM> (see step <NUM>) to protect and cover RF <NUM> until it is ready for use. Release poly-film <NUM> may be compressed or pressed between third roller <NUM> and table <NUM> for tacking release poly-film <NUM> to RF <NUM>. Stated another way, with momentary reference to <FIG>, RF <NUM> may be pressed between NCF <NUM> and release poly-film <NUM> (see step <NUM>).

In response to RF <NUM> being tacked onto NCF <NUM>, as described herein, RF <NUM> may hold the fibers of NCF <NUM> in place to prevent NCF <NUM> from fraying during a cutting process. Furthermore, the tackiness of RF <NUM> may prevent fibers from fraying at the edges of NCF <NUM> during handling and lay up.

In various embodiments, resin-fabric sheet <NUM> may be immediately cut into preforms after being formed. However, resin-fabric sheet <NUM> may be rolled over itself or onto a roller for storage or transport before being cut into preforms.

With reference to <FIG>, a resin-fabric sheet <NUM> is illustrated having a release poly-film <NUM>, in accordance with various embodiments. Resin-fabric sheet <NUM> may comprise NCF <NUM> (also referred to herein as an NCF layer), RF <NUM> (also referred to herein as a resin film layer), and, in various embodiments, release poly-film <NUM> (also referred to herein as a release poly-film layer). NCF <NUM> and RF <NUM> may comprise two distinct layers tacked together, without any (or minimal) wetting or coating of the fibers of NCF <NUM>. Thus, the fibers of NCF <NUM> may remain substantially dry without resin.

With reference now to <FIG> and <FIG>, in various embodiments, it may be desirable to store resin film (RF) <NUM> in a refrigerator or freezer (i.e., a cold storage environment) to extend the shelf-life of the RF <NUM> (see step <NUM>). Non-crimp fabric (NCF) <NUM> may be stored at room temperature (see step <NUM>). Thus, NCF <NUM> may be stored separately from RF <NUM> until time of use. Thus, at time of use, RF <NUM> may be removed from the cold storage environment (see step <NUM>) to increase the temperature of the resin film to the room temperature. Accordingly, storing NCF <NUM> and RF <NUM> separately until time of use may free up storage space in the cold storage environment, decreasing the required volume of storage space in the cold storage environment.

With reference to <FIG>, resin-fabric preforms <NUM>, <NUM>, and <NUM> cut from resin-fabric sheet <NUM> are illustrated, in accordance with various embodiments. With momentary reference to <FIG> and <FIG>, resin-fabric preform (also referred to herein as a first resin-fabric preform) <NUM>, resin-fabric preform (also referred to herein as a second resin-fabric preform) <NUM>, and resin-fabric preform (also referred to herein as a third resin-fabric preform) <NUM> may be cut from resin-fabric sheet <NUM> (see step <NUM> and step <NUM>) via any suitable method such as via a knife or the like, for example. First resin-fabric preform <NUM>, second resin-fabric preform <NUM>, and third resin-fabric preform <NUM> may be cut from resin-fabric sheet <NUM> before draping over a tool for forming into a composite structure. First resin-fabric preform <NUM>, second resin-fabric preform <NUM>, and third resin-fabric preform <NUM> may comprise pre-determined geometries or shapes. In various embodiments, any one of resin-fabric preform <NUM>, <NUM>, and/or <NUM> may be draped over a contoured surface (see step <NUM>) as described herein.

With reference to <FIG> and <FIG> a process of creating a composite structure <NUM> is illustrated, in accordance with various embodiments. In various embodiments, first resin-fabric preform <NUM> may be draped or placed over tool <NUM> (see step <NUM>). In various embodiments, tool <NUM> may have a shape complementary to the shape of a fan cowl. First resin-fabric preform <NUM> may create an outer layer of a composite structure. Although illustrated as a single layer, it is well known to a person having ordinary skill in the art that the outer layer of the composite structure may comprise multiple layers (i.e., multiple layers of resin-fabric preform <NUM>) in order to create a desired thickness. <FIG> illustrates a single layer comprising the outer layer but it is contemplated that the outer layer may comprise multiple layers. In this regard, first resin-fabric preform <NUM> may, in fact, comprise multiple resin-fabric preforms. Furthermore, multiple resin-fabric preforms may be used to create a desired width of the outer layer. For example, a roll of resin-fabric preform may not be as wide as a desired width of a fan cowl. Thus, first resin-fabric preform <NUM> may comprise multiple resin-fabric preforms overlapped to create a desired width, in addition to the desired thickness. With momentary reference to <FIG>, first resin-fabric preform <NUM> may form outer layer <NUM> of fan cowl <NUM>. Mandrel <NUM> may be placed over first resin-fabric preform <NUM> (see step <NUM>). In various embodiments, with further reference to <FIG>, second resin-fabric preform <NUM> may be draped over mandrel <NUM> and over a portion of first resin-fabric preform <NUM> to create a feature of the composite structure (see step <NUM> and step <NUM>) having a geometry similar to a shape of mandrel <NUM>. In various embodiments, second resin-fabric preform <NUM> may comprise an internal edge <NUM>. In various embodiments, internal edge <NUM> may be an edge of a dry fabric sheet located inward of the external or outside edges of a part. For example, internal edge <NUM> is located inward of external edge <NUM>. Mandrel <NUM> may comprise a contoured surface <NUM>. Next, third resin-fabric preform <NUM> may be draped over at least a portion of second resin-fabric preform <NUM> to create a desired thickness <NUM> (see step <NUM>) of the feature. In various embodiments, third resin-fabric preform <NUM> may overlap internal edge <NUM>. In various embodiments, the feature may comprise a hollow hat stiffener.

In various embodiments, after a layup process is completed, a curing process may be performed on the preforms to consolidate the preforms into a unitary composite structure. The curing process may be performed by encapsulating the preforms between a vacuum bag and the tool and sucking air out of the bag. Thus, vacuum may be applied to the preforms. The curing process may further include heating the layup in an autoclave in a resin film infusion process as previously mentioned herein. In various embodiments, method <NUM>, <NUM>, and/or <NUM> (see <FIG>, <FIG> and/or <NUM>, respectively) may include the curing process. The baking may be performed at baking temperatures of between one hundred degrees Celsius (<NUM>° F) and three hundred degrees Celsius (<NUM>° F), for example. The baking may be performed for any suitable duration such as between <NUM> minutes and <NUM> hours, for example. In various embodiments, baking may be performed using ramped temperatures or in cycles.

Next, with continuing reference to <FIG>, mandrel <NUM> may be removed from between first resin-fabric preform <NUM> and second resin-fabric preform <NUM>. With momentary reference to <FIG>, the resulting composite structure <NUM> may comprise a fan cowl <NUM> having one or more reinforcing hat sections <NUM>, <NUM>, and/or <NUM> as illustrated in <FIG>.

With reference to <FIG>, in response to the first resin-fabric preform <NUM> being draped over tool <NUM> with the resin film layer <NUM> contacting tool <NUM>, as illustrated in <FIG>, the resin film layer <NUM> of the second resin-fabric preform <NUM> is placed adjacent to the NCF layer <NUM> of the first resin-fabric preform <NUM>. However, in various embodiments, in response to the first resin-fabric preform <NUM> being draped over tool <NUM> with the NCF layer <NUM> contacting tool <NUM>, the NCF layer <NUM> of the second resin-fabric preform <NUM> is adjacent to the resin film layer <NUM> of the first resin-fabric preform <NUM>.

Claim 1:
A method for creating a fan cowl (<NUM>) with a hollow hat stiffener (<NUM>, <NUM>, <NUM>) comprising
pressing a resin film (<NUM>) between a non-crimp fabric (<NUM>) and a release poly-film (<NUM>) to tack the resin film to the non-crimp fabric and the release poly-film and to create a resin-fabric sheet (<NUM>) comprising at least a resin film layer and an non-crimp fabric layer;
cutting the resin-fabric sheet to a pre-determined shape to create at least one of a first resin-fabric preform (<NUM>), a second resin-fabric preform (<NUM>), and a third resin-fabric preform (<NUM>);
draping at least the first resin-fabric preform over a tool to create an outer layer of the fan cowl;
setting a mandrel over the outer layer; and
draping the second resin-fabric preform over at least a portion of the mandrel (<NUM>) and at least a portion of the first resin-fabric preform to form the hollow hat stiffener having a geometry similar to a shape of the mandrel.