BACKGROUND OF THE INVENTION

Composite parts of aircrafts or other vehicles are made from several layers, or plies, of fibers and resin, which are hardened or cured to maintain rigidity. These composite parts are relatively lightweight as compared to traditional metallic parts, while exhibiting similar or even improved strength and longevity properties. Thus, many aircraft components such as fuselages, wings, and other parts that traditionally were made of steel, aluminum, or other metal are now produced as composite parts. These composite parts may be formed using a thermoplastic polymer, which turns to liquid when heated and turns solid when cooled, or else using a thermoset polymer, which is a polymer that is pliable at room temperatures and thereafter cures when heated to elevated temperatures.

Unlike metal components, however, composite parts are not electrically conductive, and thus do not inherently provide adequate lighting strike protection. When fuselages or wings are made from aluminum, steel, or other metallic substances, the outer surface provides a highly conductive path such that, if the part is subject to a lightning strike during flight, the current passes from the entry point across the surface to an exit point without structurally damaging the aircraft. On the other hand, the materials used to form composite aircraft components such as, for example, carbon or graphite fibers combined with a thermoplastic or thermoset resin, are not electrically conductive and thus cannot, on their own, sufficiently pass current across the outer skin of the component.

Composite parts of aircraft in lightning strike zones are therefore provided with a lightning strike protection layer, which increases the conductivity of the outer surface of the composite part and enables the composite part to sufficiently absorb and pass current from a lightning strike across the outer surface of the part without structural damage to the part similar to the more traditional aluminum, steel, or other metallic components. The lightning strike protection layer may be a conductive metallic mesh or foil that is affixed to the outer surface of the composite part. If the part is thereafter subjected to a lightning strike, the current passes from the entry point to an exit point via the conductive mesh or foil eliminating structural damage to the aircraft part.

Often, composite parts are created using a thermoset resin, which is relatively pliable at normal manufacturing temperatures and which cures and hardens when heated to elevated temperatures. For such thermoset parts, adding lightning strike protection may include adding an outermost layer comprised of a thermoset resin and wire mesh or foil, and then heating the part to cure the thermoset resin thus bonding the wire mesh or foil to the component part and holding the mesh or foil in place. Because the thermoset resin is pliable at normal manufacturing temperatures, the lightning strike protection layer can relatively easily conform to the outer contour of the wing, fuselage, or other aircraft part being produced.

Recently, however, there has been a push to produce aircraft components from thermoplastic polymers because thermoplastic components exhibit certain advantages over thermoset components. For example, thermoplastic components may be more easily recycled than thermoset components, may exhibit increased strength as compared to thermoset components, and are less expensive and easier to produce because the parts can be heated and cooled repeatedly and produced rapidly without the need for autoclaves or other expensive equipment.

Thermoplastic component parts have certain drawbacks, however. For one, semi-crystalline thermoplastic composites have a very low surface energy and thus can be difficult to bond with primer or paint. Thus, in order to achieve sufficient paint adhesion for thermoplastic component parts, the outermost layer must be subjected to slow and expensive surface treatment such as plasma or corona etching to achieve a sufficient surface roughness or surface energy increase for paint adhesion. Similarly, to repair surface defects in thermoplastic parts, additional surface treatment (such as etching or similar) is necessary so that the filler may adequately bond to the defect.

Moreover, the low surface energy of the semi-crystalline thermoplastic parts makes it difficult for the secondary application of lightning strike protection to a thermoplastic skin in a durable fashion. That is, thermoplastic processing resins that are compatible for simultaneous melt processing with the composite parts are in the form of a film, which at ordinary manufacturing temperatures are not pliable and thus not drapable. In this regard, the film must be applied to the compound contours of the part being formed (fuselage, wing, etc.) in narrow strips. When applying a lightning strike protection in the form of a metallic mesh or foil or the like, each strip must form sufficient contact with the neighboring strip in order to ensure sufficient conductivity across the outer surface of the composite part. Any because such films do not have any tack at normal manufacturing temperatures, it is challenging to keep the narrow strips in place during application and processing.

Still more, the high processing (melt) temperature and crystalline content of advanced thermoplastic resins results in substantial shrinkage when they cool, especially for a resin rich area. This results in substantial residual tensile stress in the resin when processed with a low coefficient of thermal expansion (CTE) carbon fiber laminate that shrinks very little during cool-down. These stresses can result in cracking of the resin, especially when exposed to low temperatures. Furthermore, when complex thermoplastics structures are processed in production surface porosity and pitting often occur. Repairing these defects can be expensive, especially when they occur in lightning strike protected areas.

Thus, although it would be desirable to form certain composite parts from thermoplastic polymers, the difficulty in applying a sufficient surfacer, particularly in lightning strike protected areas, has limited the use of thermoplastic component parts in practice. Thus, there exists a need exists for an improved surfacer to be implemented on thermoplastic composite parts.

BRIEF SUMMARY OF THE INVENTION

At a high level, the present invention is directed to an improved surfacer to be used with thermoplastic component parts, and methods of producing the same. More particularly, embodiments of the invention are directed to a paintable surfacer for thermoplastic composite laminates with integral lightning strike protection mesh or foil that has drape and reinforced surface healing capability, and methods of producing the same.

For example, some embodiments of the invention are directed to a thermoplastic surfacer for providing lightning strike protection to a composite component of an aircraft. The thermoplastic surfacer includes a broadgood having an amorphous thermoplastic resin, one or more fillers embedded into the broadgood, and a lightning strike protection mesh or foil embedded into the broadgood.

Other embodiments of the invention are directed to a method of manufacturing a thermoplastic surfacer for providing lightning strike protection to a composite component of an aircraft. The method includes conveying a matrix resin fleece along one or more conveyor tables, with the matrix resin fleece including a broadgood having an amorphous thermoplastic resin embedded therein. The method also includes embedding one or more fillers into the matrix resin fleece and heating the matrix resin fleece until at least a portion of the amorphous thermoplastic resin reaches a melt temperature of the amorphous thermoplastic resin. Finally, the method includes embedding a lightning strike protection mesh or foil into the matrix resin fleece.

Still other embodiments of the invention are directed to a method of applying a thermoplastic surfacer to a composite part of an aircraft. The method includes draping a thermoplastic surfacer on an at least partially unconsolidated composite part, such as the thermoplastic surfacer discussed above or the thermoplastic surfacer produced by the method discussed above. The method further includes consolidating the at least partially unconsolidated composite part thereby forming a consolidated composite part by heating the at least partially unconsolidated composite part to a temperature at or above a melt temperature of a resin used in the at least partially unconsolidated composite part and at or above a melt temperature of the amorphous thermoplastic polymer resin of the thermoplastic surfacer. Finally, the method includes filling at least one surface defect in the consolidated part using the amorphous thermoplastic polymer resin and milled fibers provided in the thermoplastic surfacer.

These and other features will be discussed in more detail below in connection with the accompanying drawings.

