Induction Welding of Composite Structures

A composite structure and methods of forming composite structures are provided. A composite structure comprises a first composite part; a second composite part welded to the first composite part at a joint; and the joint between the first composite part and the second composite part comprising doped fibers.

BACKGROUND INFORMATION

The present disclosure relates generally to composite manufacturing and more specifically to induction welding of composite structures.

Thermoplastic polymer composites are suitable for structural aircraft applications due to their mechanical performance capabilities. Thermoplastic polymer composites are able to be processed quickly and to be re-melted and re-formed. The ability to re-melt and re-form enables induction welding. induction welding is a process through which composite structures can be joined together without the use of chemical adhesive bonding or mechanical fasteners. induction welding can be performed without external heaters making direct contact with the structure.

In induction welding, alternating current is induced in the carbon fibers, which melts the surrounding polymer. Two thermoplastic structures can be joined together by melting and re-crystallizing them together.

Induction welding can be difficult to control due to a need for specific fiber contacts in order to induce currents in the structures. Induction welding can be difficult to control because induced currents can melt the whole structure, leading to deconsolidation and poor surface quality without precise tooling.

Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.

SUMMARY

An embodiment of the present disclosure provides a composite structure. The composite structure comprises a first composite part, a second composite part welded to the first composite part at a joint, and the joint between the first composite part and the second composite part comprising doped fibers.

Another embodiment of the present disclosure provides a method of welding two composite parts to form a composite structure. A first composite part is formed with a doped prepreg ply comprising doped fibers at a first surface of the first composite part. A second composite part is positioned in contact with the first surface such that the doped prepreg ply is positioned at a joint between the first composite part and the second composite part. The first composite part and the second composite part are welded at the joint using heat generated by the doped fibers in response to an electromagnetic field.

Yet another embodiment of the present disclosure provides a method. Fibers are doped to form doped fibers with increased conductivity. A doped prepreg ply is formed comprising the doped fibers. The doped prepreg ply is applied to a first composite part. A second composite part is positioned relative to the composite part such that the doped prepreg ply is positioned between the second composite part and the first composite part.

DETAILED DESCRIPTION

The illustrative examples recognize and take into account several considerations. The illustrative examples recognize and take into account that some challenges of induction welding could be overcome by isolating the current generation to only the surface of the structures to be joined, at the joint interface.

The illustrative examples isolate the current generation at the joint interface by using at least one surface ply with functionalized fibers and increased conductivity.

The fibers can be functionalized using Plasma Enhanced Chemical Vapor Deposition (PECVD) which causes vertical graphene to grow from the existing fibers, increasing the conductivity of the fibers. The increased conductivity increases the current which can be induced in the fibers at the joint interface, which increases the heat energy that can be generated there by a theoretical power of two.

Turning now toFIG.1, an illustration of an aircraft is depicted in accordance with an illustrative embodiment. Aircraft100has wing102and wing104attached to body106. Aircraft100includes engine108attached to wing102and engine110attached to wing104.

Aircraft100is an example of an aircraft that can have a composite structure induction welded using the illustrative examples. In some illustrative examples, an induction welded composite structure can be present in at least one of wing102, wing104, or body106of aircraft100.

Turning now toFIG.2, an illustration of a block diagram of a manufacturing environment is depicted in accordance with an illustrative embodiment. Composite structure202can be induction welded in manufacturing environment200. Composite structure202can be a composite component of aircraft100.

Composite structure202comprises first composite part204, second composite part206welded to first composite part204at joint208, and joint208between first composite part204and second composite part206comprising doped fibers210.

In some illustrative examples, doped fibers210comprise fibers211doped with vertical graphene212. In some illustrative examples, fibers211comprise carbon-based fibers. Vertical graphene212can be deposited on fibers211using plasma enhanced chemical vapor deposition214.

In some illustrative examples, doped fibers210comprise unidirectional fibers216. In some illustrative examples, doped fibers210comprise woven fabric218. After forming vertical graphene212on fibers211, resin220is applied to fibers211to form doped prepreg ply224. In some illustrative examples, resin220present in joint208is the same as resin222present in first composite part204. In some illustrative examples, resin220present in doped prepreg ply224does not include conductive metal additives.

After applying resin220to doped fibers210, doped prepreg ply224can be applied to one of first composite part204or second composite part206. As depicted, doped prepreg ply224is a part of first composite part204. In other illustrative examples, doped prepreg ply224is not present in first composite part204. In some illustrative example, doped prepreg ply224is present in second composite part206.

When present in first composite part204, doped prepreg ply224forms first surface226. First surface226of first composite part204is in contact with second surface228of second composite part206in joint208.

First composite part204is formed of plurality of composite plies230. Plurality of composite plies230are formed of fibers and resin222. Plurality of composite plies230comprises structural composite plies232. Structural composite plies232are present in first composite part204to contribute to material and structural characteristics of first composite part204. Structural composite plies232are part of a design for first composite part204.

Plurality of composite plies230comprises surface composite plies234forming first surface226. Surface composite plies234are not present to meet design specifications for strength or other characteristics of first composite part204.

In some illustrative examples, doped prepreg ply224is one of surface composite plies234. In some illustrative examples, doped prepreg ply224is applied after structural composite plies232sufficient to meet structural characteristics for first composite part204.

In some illustrative examples, doped prepreg ply224is one of structural composite plies232. In these illustrative examples, doped prepreg ply224is manufactured according to a manufacturing method for the respective structural ply after doping using plasma enhanced chemical vapor deposition214.

As depicted, doped fibers236are also present at joint208. In some illustrative examples, doped fibers236comprise fibers238doped with vertical graphene240. Vertical graphene240can be deposited on fibers238using plasma enhanced chemical vapor deposition214.

In some illustrative examples, doped fibers236comprise unidirectional fibers242. In some illustrative examples, doped fibers236comprise woven fabric244. After forming vertical graphene240on fibers238, resin246is applied to fibers238to form doped prepreg ply248. In some illustrative examples, resin246present in joint208is the same as resin251present in second composite part206. In some illustrative examples, resin246present in doped prepreg ply248does not include conductive metal additives.

Second composite part206is formed of second plurality of composite plies250. Second plurality of composite plies250is formed of fibers and resin251. Second plurality of composite plies250comprises second structural composite plies252. Second structural composite plies252are present in second composite part206to contribute to material and structural characteristics of second composite part206. Second structural composite plies252are part of a design for second composite part206.

Second plurality of composite plies250comprises second surface composite plies254forming second surface228. Second surface composite plies254are not present to meet design specifications for strength or other characteristics of second composite part206.

In some illustrative examples, doped prepreg ply248is one of second surface composite plies254. In some illustrative examples, doped prepreg ply248is applied after second structural composite plies252sufficient to meet structural characteristics for second composite part206.

In some illustrative examples, doped prepreg ply248is one of second structural composite plies252. In these illustrative examples, doped prepreg ply248is manufactured according to a manufacturing method for the respective structural ply after doping using plasma enhanced chemical vapor deposition214.

In some illustrative examples, doped fibers210are isolated within joint208.

In some illustrative examples, doped fibers210are part of a structural ply of one of first composite part204or second composite part206. In some illustrative examples, doped fibers210are part of an additional ply present for joining first composite part204and second composite part206independently of a structural design for first composite part204and a second structural design for second composite part206.

Doped fibers210in doped prepreg ply224are more conductive than conventional prepreg plies. The increase in conductivity can increase heat generation in doped prepreg ply224. By locating doped prepreg ply224in joint208, heat during induction welding can be located within joint208.

Doped fibers in joint208, such as doped fibers210or doped fibers236, enable induction welding without undesirable effects to resulting composite structure202. Doped fibers in joint208enable induction welding without component deconsolidation and without reduced surface quality, without the need for high precision tooling.

Doped fibers210isolate welding heat262to plies within set distance256from doped fibers210by increased heat generation of doped fibers210. Doped fibers236isolate welding heat262to plies within set distance256from doped fibers236by increased heat generation of doped fibers236. By applying doped fibers210and doped fibers236only within joint208, welding heat262is isolated at or near joint208.

Increased heat generation of doped fibers210and doped fibers236enables induction welding coil258to operate at current260. Current260is a lower operating current than conventional induction welding. By utilizing a reduced current, current260, induction welding coil258reduces or eliminates heat generation in the remainder of first composite part204and second composite part206.

Joint208is formed between first composite part204and second composite part206by welding heat262generated in response to electromagnetic field261generated by induction welding coil258. Induction welding coil258generates electromagnetic field261having current260. At least one of doped fibers210or doped fibers236are present in joint208and generate welding heat262in response to electromagnetic field261.

By using at least one of doped prepreg ply224with doped fibers210or doped prepreg ply248with doped fibers236to heat joint208, first composite part204and second composite part206can be processed in a conventional way, and then joined together without additional materials or joining assistance. Plasma enhanced chemical vapor deposition214process to dope fibers211and the pre-impregnation of doped fibers210results in doped prepreg ply224with increased conductivity without any changes to the part design, joint208interface, or processing methods.

For example, more than one doped ply can be present in at least one of first composite part204or second composite part206. As another example, only one of doped prepreg ply224or doped prepreg ply248can be present in composite structure202. Although resin222and resin251are discussed separately, resin222can be the same as resin251. In some illustrative examples, resin222, resin251, resin220, and resin246can be the same.

Turning now toFIG.3, an illustration of an isometric view of induction welding a composite structure with a doped ply at the joint is depicted in accordance with an illustrative embodiment. Composite structure302in view300is a physical implementation of composite structure202ofFIG.2.

Doped prepreg ply312is in contact with second composite part306. In some illustrative examples, second composite part306comprises a doped composite ply in place of or in addition to doped prepreg ply312of first composite part304.

To inductively weld first composite part304to second composite part306, inductive welding coil314is positioned relative to first composite part304and second composite part306. Inductive welding coil314can have a reduced current in welding first composite part304and second composite part306due to doped fibers in doped prepreg ply312.

Due to a reduced current of inductive welding coil314, heat affected zone316of first composite part304and second composite part306is reduced. Doped prepreg ply312isolates welding heat to plies within set distance318from the doped fibers by increased heat generation of the doped fibers.

Turning now toFIG.4, a flowchart of a method of welding two composite parts to form a composite structure is depicted in accordance with an illustrative embodiment. Method400can be used to weld together first composite part204and second composite part206ofFIG.2. Method400can be used to weld together first composite part304and second composite part306ofFIG.3.

A first composite part is formed with a doped prepreg ply comprising doped fibers at a first surface of the first composite part (operation402). A second composite part is positioned in contact with the first surface such that the doped prepreg ply is positioned at a joint between the first composite part and the second composite part (operation404). The first composite part and the second composite part are welded at the joint using heat generated by the doped fibers in response to an electromagnetic field (operation406). Afterwards, method400terminates.

In some illustrative examples, method400applies an electromagnetic field having a reduced current to the joint (operation414). The reduced current induces heat generation in the doped fibers. The reduced current does not generate undesirable amounts of heat in non-doped fibers.

In some illustrative examples, forming the first composite part with the doped prepreg ply comprises forming the first composite part with the doped prepreg ply replacing a structural ply (operation408). In some illustrative examples, when the doped prepreg ply replaces the structural ply, the doped prepreg ply has the same fiber orientation as the structural ply.

In some illustrative examples, method400forms the second composite part with a second doped prepreg ply comprising doped fibers at a second surface of the second composite part (operation410). In some illustrative examples, positioning the second composite part in contact with the first surface comprises positioning the second surface in contact with the first surface (operation412).

In some illustrative examples, method400isolates welding heat to plies within a set distance from the doped fibers by increased heat generation of the doped fibers (operation416). Isolating heat to plies within the set distance of the doped fibers limits the heat applied to the first composite part and the second composite part outside of the joint. Isolating heat to plies within the set distance of the doped fibers can result in a higher quality composite structure than conventional induction welding.

Turning now toFIG.5, a flowchart of a method of placing doped fibers between a first composite part and a second composite part is depicted in accordance with an illustrative embodiment. Method500can be used to weld together first composite part204and second composite part206ofFIG.2. Method500can be used to weld together first composite part304and second composite part306ofFIG.3.

Method500dopes fibers to form doped fibers with increased conductivity (operation502). Method500forms a doped prepreg ply comprising the doped fibers (operation504). Method500applies the doped prepreg ply to a first composite part (operation506). Method500positions a second composite part relative to the composite part such that the doped prepreg ply is positioned between the second composite part and the first composite part (operation508). Afterwards, method500terminates.

In some illustrative examples, doping the fibers comprises forming vertical graphene on the fibers to form doped fibers (operation510). In some illustrative examples, forming vertical graphene on the fibers comprises applying plasma enhanced chemical vapor deposition to the fibers (operation512).

In some illustrative examples, forming the doped prepreg ply comprises infusing resin into a woven fabric comprising the doped fibers (operation514). In some illustrative examples, forming the doped prepreg ply comprises mixing unidirectional fibers comprising the doped fibers with a resin (operation516). In some illustrative examples, forming the doped prepreg ply comprises applying a same resin to the doped fibers as is contained in the first composite part (operation518). In some illustrative examples, the resin present in the doped prepreg ply does not include conductive metal additives (operation520).

In some illustrative examples, method500welds the first composite part and the second composite part while isolating welding heat to plies within a set distance from the doped prepreg ply by increased heat generation of the doped prepreg ply (operation522). The increased heat generation of the doped fibers in the doped prepreg ply can allow for the induction welding coil to operate at a reduced current.

As used herein, the phrase “at least one of,” when used with a list of items, means different combinations of one or more of the listed items may be used and only one of each item in the list may be needed. For example, “at least one of item A, item B, or item C” may include, without limitation, item A, item A and item B, or item B. This example also may include item A, item B, and item C or item B and item C. Of course, any combinations of these items may be present. In other examples, “at least one of” may be, for example, without limitation, two of item A; one of item B; and ten of item C; four of item B and seven of item C; or other suitable combinations. The item may be a particular object, thing, or a category. In other words, at least one of means any combination items and number of items may be used from the list but not all of the items in the list are required.

As used herein, “a number of,” when used with reference to items means one or more items.

Illustrative embodiments of the present disclosure may be described in the context of aircraft manufacturing and service method600as shown inFIG.6and aircraft700as shown inFIG.7. Turning first toFIG.6, an illustration of an aircraft manufacturing and service method in a form of a block diagram is depicted in accordance with an illustrative embodiment. During pre-production, aircraft manufacturing and service method600may include specification and design602of aircraft700inFIG.7and material procurement604.

During production, component and subassembly manufacturing606and system integration608of aircraft700takes place. Thereafter, aircraft700may go through certification and delivery610in order to be placed in service612. While in service612by a customer, aircraft700is scheduled for routine maintenance and service614, which may include modification, reconfiguration, refurbishment, or other maintenance and service.

With reference now toFIG.7, an illustration of an aircraft in a form of a block diagram is depicted in which an illustrative embodiment may be implemented. In this example, aircraft700is produced by aircraft manufacturing and service method600ofFIG.6and may include airframe702with plurality of systems704and interior706. Examples of systems704include one or more of propulsion system708, electrical system710, hydraulic system712, and environmental system714. Any number of other systems may be included.

Apparatuses and methods embodied herein may be employed during at least one of the stages of aircraft manufacturing and service method600. One or more illustrative embodiments may be manufactured or used during at least one of component and subassembly manufacturing606, system integration608, in service612, or maintenance and service614ofFIG.6.

The illustrative examples enable induction welding without undesirable effects to component quality or surface quality, and without the use of high precision tooling. The illustrative examples provide improved induction welding using doped fibers to increase heat generation locally in the joint between two composite parts.

The illustrative examples comprise fibers doped with vertical graphene. In some illustrative examples, the fibers can take the form of unidirectional carbon fibers. In other illustrative examples, the fibers take the form of woven fibers. The fibers are doped with vertical graphene and pre-impregnated with materials using pre-pregging methods. The doped prepreg ply is then laid up at the faying surface of component laminates. In the illustrative examples, composite parts can be processed in the same way, then joined together without additional materials or joining assistance.

The illustrative examples provide the targeted application of doped fiber pre-pregs at the faying surface of the component laminate. By isolating the doped fiber pre-pregs at the joint the heat generation during induction heating is isolated at the joint interface.

The illustrative examples enable the use of low-melt polymer composite materials with fewer impacts to structure quality. The illustrative examples increase the efficiency of the joining process in terms of energy consumption, processing rate, and requirements for tooling and equipment.