Patent Description:
Composite reinforcing substructures such as stringers, one example of which is referred to as blade stiffeners, are frequently used in various vehicles in the marine and aircraft industries. The stringers may be constructed from a single flat laminate. Existing forming methods for forming blade stringers from a single flat laminate include positioning the single flat laminate over a die cavity. A central section of the laminate extends over the die cavity with outer edges being positioned away from the die cavity. A punch die moves downward and forces the laminate into the die cavity. The section of the laminate that is moved into the die cavity forms a first section of the stringer. The sections at the ends of the laminate that remain out of the die cavity form a second section of the stringer.

This existing punching process has several limitations. The single laminate design does not allow for the different, facing sides of the stringer to move independently during formation. This can result in anomalies to be created in the blade stiffener during certain punch forming configurations. Using a single laminate charge can also restrict the ability to create localized geometrical features on each of the different sides of the stringer within that one charge. Further, the first section of the laminate that is forced into the die cavity is in tension. However, the second sections of the laminate that remain out of the die cavity are not in tension.

Document <CIT> is relative to a device for the manufacture of three-dimensional beam type elements in composite material with reinforcing fibres preimpregnated with polymeric resins, starting with laminates layed and precut without polymerization, said device comprising a head that comprises in its turn a roller train, it being possible for said head to move longitudinally along a fixed bedplate, in such a way that, as said head moves, the roller train acts on the laminates without polymerization, compacting and forming them, thus forming laminates with their final geometry in one go, in such a way that said laminates are ready for their subsequent integration. Document <CIT> also relates to a method of manufacture of three-dimensional beam type elements in composite material.

Document <CIT> relates to a mould for producing fibre stringers for aerospace structures, and to a method for producing fibre stringers with said mould, comprising a female tool and a male tool, by means of which a fibre laminate is formed, which is cut through the middle region in order to form two L-shaped profiles with which a T-shaped profile is formed, the female tool being formed by two facing side assemblies provided with inflatable membranes, while the male tool is formed by a central block and two side blocks, between which intermediate blocks are inserted, said intermediate blocks being, in turn, provided with inflatable membranes, in order to fold and join the two halves of the fibre laminate by means of a combined set of both tools and inflating the membranes.

Document <CIT> relates to a method of manufacturing T-shaped stringers made of composite material, comprising a second shaping step for shaping laminates into L-shaped preforms, which comprises providing a set of tools formed by a fixed tool comprising a lower portion and an upper portion, and a moveable tool comprising a lower element and an upper element. It also comprises the segment of the laminate intended for the foot of the preform being located between the lower portion and the upper portion of the fixed tool, and the segment of the laminate intended for the web of the preform being located between the lower element and the upper element of the moveable tool. It further comprises vertically moving the moveable tool to progressively bend the web of the preform supporting it on a vertical wall of the fixed tool. The end of its web adopts a rounded shape.

Document <CIT> relates to an installation for manufacturing fiber stringers for aerospace structures formed by at least one swivel-mounted cylindrical carousel, peripherally incorporating a distribution of male configured tools and in relation to said carousel a bed capable of lateral movement, incorporating a distribution of female configured tools, a fiber strip applicator head for making fiber laminates on the male configured tools also being arranged in relation to the carousel, which allows making omega-shaped or T-shaped stringers by means of the interaction of each male configured tool of the carousel with a respective female configured tool of the bed. <CIT> discloses in particular a method comprising the following features: positioning first and second charges at a die cavity with first ends of each of the first and second charges extending over the die cavity; said first charge including a blade and a flange and said second charge including a blade and a flange; securing second ends of each of the first and second charges away from the die cavity; driving the first ends of each of the first and second charges into the die cavity while the second ends remain secured away from the die cavity; moving together first and second form blocks that form the die cavity and applying lateral force to blades of the first and second charges.

Document <CIT> relates to a composite part, such as a stiffener is formed in place. A composite charge is placed on a tool spanning a mold cavity, with the centerline of the charge offset from the centerline of the mold cavity. Opposite sides of the charge are held against the tool as the charge is formed into the mold cavity. One side of the charge is held against movement on the tool while the other side of the charge is allowed to slip over the tool toward the mold cavity.

The invention provides a method according to the features of independent claim <NUM>. Particular embodiments of the invention are defined in the dependent claims.

The present disclosure includes methods and devices of fabricating a stringer for a vehicle. The stringer is constructed from two charges that are formed together into the stringer. During fabrication, the separate charges are each positioned with a first section placed over a die cavity and a second section positioned away from the die cavity. The second sections of the charges are secured. A punch die forces the first sections into the die cavity forming a first section of the stringer. The second sections are secured away from the die cavity during the punching process thus tensioning the charges along their lengths.

<FIG> illustrates a stringer <NUM> that is formed by a first charge 9a and a second charge 9b that are positioned in a back-to-back orientation. The first charge 9a includes a blade 11a and a flange 12a. Likewise, the second charge 9b includes a blade 11b and a flange 12b. Each of the charges 9a, 9b includes a first end <NUM> and an opposing second end <NUM>. The charges 9a, 9b can include the same or different geometries such as shapes and sizes. The charges 9a, 9b can be constructed from the same or different materials. One stringer <NUM> includes each of the charges 9a, 9b formed from one or more plies of composite material, such as but not limited to carbon fiber reinforced plastic (CFRP), carbon fiber reinforced polymer, carbon fiber reinforced thermoplastic, and fiberglass reinforced plastic (FRP), and other fiber reinforced thermoset or thermoplastic material.

The stringer <NUM> includes a blade section <NUM> formed by the blades 11a, 11b and a flange section <NUM> formed by the flanges 12a, 12b. The flanges 12a, 12b can be aligned at different angles relative to the blades 11a, 11b. In one design as illustrated in <FIG>, the flanges 12a, 12b are perpendicular to the blades <NUM>1a, 11b. A height H measured between an outer side of the flange section <NUM> and an end of the blade section 11can vary. A width W measured along the flange section <NUM> can also vary. The stringer <NUM> can include different lengths and the thicknesses of the blade sections <NUM> and flange sections <NUM> can also vary.

The stringer <NUM> can be used in a variety of contexts. <FIG> includes the stringer <NUM> connected to a panel <NUM>, such as the wing skin or fuselage of a vehicle. Filler material <NUM> can be placed in a groove formed between the charges 9a, 9b and the panel <NUM>.

<FIG> illustrates a tooling assembly <NUM> employed to form the stringers <NUM>. The tooling assembly <NUM> generally includes a die assembly <NUM> and a punch assembly <NUM>.

The die assembly <NUM> includes a pair of form blocks <NUM>, <NUM> that are spaced apart to form a die cavity <NUM>. The form blocks <NUM>, <NUM> can be constructed from relatively rigid material, such as but not limited to wood, metal, ceramic or a composite. The first form block <NUM> includes an inner surface <NUM> and an upper surface <NUM>. Likewise, the second form block <NUM> includes an inner surface <NUM> and an upper surface <NUM>. The form blocks <NUM>, <NUM> can include inside radii between the inner surfaces <NUM>, <NUM> and the upper surfaces <NUM>, <NUM> that provides for a smooth transition of the charges 9a, 9b between the blade section <NUM> and the flange section <NUM>.

A pair of L-shape, elongated brackets <NUM>, <NUM> is mounted on a plate <NUM> on opposite sides of form blocks <NUM>, <NUM>. The brackets <NUM>, <NUM> retain the form blocks <NUM>, <NUM> on the plate <NUM> as well as react lateral forming forces generated by the form blocks <NUM>, <NUM>. One or more actuators <NUM> can move the form blocks <NUM>, <NUM> to adjust a width of the die cavity <NUM>. Inflatable bladders <NUM> can be positioned between the form blocks <NUM>, <NUM> and the brackets <NUM>, <NUM>. The bladders <NUM> can be adjusted in size by the actuators <NUM> to control the position of the form blocks <NUM>, <NUM>. The bladders <NUM> can also provide for adjustable pressure to control the movement and forces on the form blocks <NUM>, <NUM>. The forms blocks <NUM>, <NUM> can also be connected to one or more mechanical devices that move and apply adjustable pressure on the forms blocks <NUM>, <NUM>.

The punch assembly <NUM> includes a punch die <NUM>. The punch die <NUM> includes a first section <NUM> sized to fit within the die cavity <NUM> and a second section <NUM> providing the punch die <NUM> with a sectional shape that resembles the letter T. The transitions between the first section <NUM> and second section <NUM> can include various curvatures to form smooth transitions on the stringer <NUM> between the blade section <NUM> and the flange section <NUM>. One or more actuators <NUM> are configured to power the punch die <NUM> into and out of the die cavity <NUM>.

As will be shown in the following illustrative figures, the charges 9a, 9b are tensioned along their length during the punching process. The amount of tensioning in the different charges 9a, 9b can be the same or different. This allows independent fiber movement within the different charges 9a, 9b and different sections of the stringer <NUM>. This can reduce wrinkles in the charges 9a, 9b during the forming process which could result in disposing of the stringer <NUM> and/or requiring repair.

<FIG> illustrate a method of forming a stringer <NUM> with separately tensioned charges 9a, 9b. <FIG> illustrates the charges 9a, 9b placed over the form blocks <NUM>, <NUM>. A first section of the charges 9a, 9b including the first ends <NUM> extend over the die cavity <NUM>. A second section of the charges 9a, 9b are positioned over support members <NUM> that are located in proximity to the form blocks <NUM>, <NUM>.

Holding members <NUM> secure the charges 9a, 9b to the support members <NUM>.

According to the invention, as shown in <FIG>, the holding members <NUM> are plates <NUM> sized and shaped to contact and apply a force to secure the charges 9a, 9b against the support member <NUM>. As illustrated in <FIG>, the holding member <NUM> can include a clamp <NUM> that applies an additional force to secure the plate <NUM> to the charges 9a, 9b. Mechanical fasteners can also extend between the plate <NUM> and support member <NUM> to secure the charges 9a, 9b.

The holding members <NUM> can also include a grip surface <NUM> to control movement of the charges 9a, 9b. The grip surface <NUM> can include surface configurations including but not limited to knurling, etching, and bossing.

Each of the holding members <NUM> can also include an inflatable bladder <NUM> as illustrated in <FIG>. The bladders <NUM> are disposed at the support member <NUM> and can be formed of various suitable materials capable of being pressurized and inflated to the required degree using, for example, pneumatic pressure. The positioning can include being over the support <NUM> and a second end <NUM> of the charges 9a, 9b. An actuator <NUM> can control fluid that is moved to and from a reservoir to inflate and deflate the bladders <NUM> as necessary to control the pinch force.

The holding members <NUM> secure the charges 9a, 9b to the support members <NUM> to allow tensioning of the charges 9a, 9b during the punching process. The holding members <NUM> contact the charges 9a, 9b at the second ends <NUM>. This provides for the charges 9a, 9b to be tensioned along their lengths measured between the first and second ends <NUM>, <NUM>.

As illustrated in <FIG>, the charges 9a, 9b extend outward from the form blocks <NUM>, <NUM> with the first ends <NUM> positioned over the die cavity <NUM>. The first ends <NUM> can be spaced apart as illustrated in <FIG>, in abutting contact with one another, or can overlap. At the start of the process, the punch die <NUM> can be raised upward away from the charges 9a, 9b.

As illustrated in <FIG>, the holding members <NUM> apply a force B that secures the charges 9a, 9b against the support members <NUM>. The punch die <NUM> begins the punching process and is brought downward in the direction of arrow A.

The punching process continues with the punch die <NUM> moving farther in the direction of arrow A and into the die cavity <NUM> as illustrated in <FIG>. This movement forces the first ends <NUM> and adjacent sections of the charges 9a, 9b into the die cavity <NUM>. The charges 9a, 9b are tensioned during the punching process because the holding members <NUM> maintain the position of the charges 9a, 9b on the support members <NUM> as the first ends <NUM> and adjacent sections are forced into the die cavity <NUM>. As illustrated in <FIG>, the first sections that are driven into the die cavity <NUM> form the blades 11a, 11b of each of the charges 9a, 9b. The second sections that remain out of the die cavity <NUM> form the flanges 12a, 12b.

The punch die <NUM> can include a surface configured to provide friction to create a tension state within the charges 9a, 9b as the punch <NUM> is being moved into the die cavity <NUM>. To provide for the tensioning forces on the charges 9a, 9b, the punch die <NUM> can be constructed from a material or be coated with a material that provides for the tensioning. This can also include surface configurations including but not limited to knurling, etching, and embossing.

To further facilitate the tensioning of the charges 9a, 9b, release film <NUM> can be positioned between the punch die <NUM> and the charges 9a, 9b as illustrated in <FIG>. The release film <NUM> can be constructed from material that provides for contact and tensioning with the charges 9a, 9b and prevents adherence of the first and second charges 9a, 9b to the punch die <NUM>. The release film <NUM> can be constructed from a variety of materials, including but not limited to Teflon. The release film <NUM> can be sized to extend over the entirety or limited sections of the punch die <NUM>.

During the forming process, the punch die <NUM> can be inserted various depths into the die cavity <NUM>. This can include the second section <NUM> contacting against the sections of the charges 9a, 9b that remain out of the die cavity <NUM>. This contact can provide a forming force to shape the flanges 12a, 12b. Other methods can include a lesser amount of insertion into the die cavity <NUM> with the second section <NUM> remaining spaced away from the flanges 12a, 12b.

The charges 9a, 9b are independently tensioned during the forming process. This tensioning minimizes wrinkling of the charges 9a, 9b as the charges 9a, 9b can move independently of one another during formation. The individual movement facilitates formation of stringers <NUM> that are not geometrically symmetric and/or constructed from different materials. The charges 9a, 9b can be individually tensioned to obtain the desired contour of the stringer <NUM>.

Once the charges 9a, 9b have been formed, the punch die <NUM> is removed from the die cavity <NUM>. As illustrated in <FIG>, the punch die <NUM> is moved in the direction of arrow C away from the die cavity <NUM> and out of contact with the charges 9a, 9b.

Once the punch die <NUM> is removed from the die cavity <NUM>, the form blocks <NUM>, <NUM> are moved inward towards one another in the direction of arrows D. This movement of the form blocks <NUM>, <NUM> can apply a lateral force and join the blades 11a, 11b together. The holding members <NUM> can remain in contact with the charges 9a, 9b as the form blocks <NUM>, <NUM> move towards one another. In one design, the movement of the form blocks <NUM>, <NUM> pulls the charges 9a, 9b out of contact with the holding members <NUM>. In another design, the holding members <NUM> remain in contact after the form blocks <NUM>, <NUM> have completed their inward movement. The holding members <NUM> can also be removed from the charges 9a, 9b prior to movement of the form blocks <NUM>, <NUM>.

The formed stringer <NUM> that includes the first and second charges 9a, 9b can then be cured. This can include moving the formed stringer <NUM> into a cure tool. As illustrated in <FIG>, the stringer <NUM> can remain between the form blocks <NUM>, <NUM> which acts as the cure tool. A composite filler material <NUM> can be placed into the groove formed between the charges 9a, 9b as illustrated in <FIG>. The stringer <NUM> can be installed in a vacuum bag assembly and cured.

The stringer <NUM> disclosed above is referred to as a blade stringer <NUM>. The process of tensioning charges 9a, 9b can also be used stringer geometry including but not limited to trapezoidal, hemispherical, and rounded shapes. <FIG> and <FIG> illustrate fabrication of a hat stringer <NUM>. As illustrated in <FIG>, the die cavity <NUM> is formed within a die block <NUM>. The die block <NUM> includes top surfaces that form support members <NUM> for the first and second charges 9a, 9b. Holding members <NUM> are positioned at each of the support members <NUM> to secure the second ends <NUM> of the charges 9a, 9b.

The charges 9a, 9b are each positioned on the support members <NUM> with a first section that extends outward and over the die cavity <NUM>. The charges 9a, 9b are positioned in an overlapping orientation over the die cavity <NUM> with one of the charges 9a, 9b extending over the other. The overlap prior to forming allows for sufficient length of charge 9a and 9b to completely form the hat stringer. As will be described in detail below, the overlap will be eliminated and form a joint between the charges 9a, 9b when forming is complete. <FIG> includes the specific orientation of the first charge 9a positioned over the second charge 9b.

The punch die <NUM> is shaped to conform to the shape of the die cavity <NUM>. As illustrated in <FIG>, the punch die <NUM> is lowered into the die cavity <NUM> with the first section <NUM> of the punch die <NUM> contacting against and driving the charges 9a, 9b into the die cavity <NUM>. While the charges 9a, 9b are being formed into the die cavity <NUM>, the holding members <NUM> secure the second sections of the charges 9a, 9b to the support members <NUM>. This results in the charges 9a, 9b being tensioned along their lengths. The punch die <NUM> can extend into the die cavity <NUM> an amount for the second section <NUM> to contact against and charges 9a, 9b over to be spaced away from the charges 9a, 9b as illustrated in <FIG>.

Once the forming is complete, the punch die <NUM> is moved away from the die cavity <NUM>. The holding members <NUM> are released from the flanges 12a, 12b and the formed stringer <NUM> can be removed from the die body <NUM>.

A scarf joint <NUM> can be formed between the charges 9a, 9b as illustrated in <FIG>. Each of the charges 9a, 9b is a laminate with multiple plies and having ply drops with offsetting tapers at the first ends <NUM>. These first ends <NUM> are mated together during the forming process. Various other joints can also be formed with the overlapping configuration, including but not limited to an overlap joint and a butt joint. The charges 9a, 9b can then be cured either while within the die cavity <NUM> or after removal from the die cavity <NUM>.

<FIG> includes a flowchart of the steps of fabricating a stringer <NUM>. The process includes positioning first and second charges 9a, 9b with first ends <NUM> extending over the die cavity <NUM> (block <NUM>). This can include positioning the charges over a die cavity <NUM> formed between first and second form blocks <NUM>, <NUM>, or over a die cavity formed in a die body <NUM>. The second ends <NUM> of the first and second charges 9a, 9b are secured (block <NUM>). The second ends <NUM> are positioned away from the die cavity <NUM>. A punch die <NUM> is inserted into the die cavity <NUM> (block <NUM>). The punch die <NUM> drives the first ends <NUM> of the first and second charges 9a, 9b into the die cavity <NUM> while the second ends <NUM> remain secured away from the die cavity <NUM>. Moving the punch die <NUM> and securing of the second ends <NUM> tensions the charges 9a, 9b along their length between the first and second ends <NUM>, <NUM>. The punch die <NUM> can then be removed from the die cavity <NUM> (block <NUM>).

The charges 9a, 9b are tensioned along their lengths. The amount of tensioning of each of the charges 9a, 9b can be the same or can be different. With similar charges 9a, 9b having the same construction and geometry, the tensioning can be equal. Differences in tensioning can be caused by charges 9a, 9b with different constructions and/or different geometries such as thickness. Different tensioning can also be caused by the contour of the stringer <NUM>.

Prior to inserting the punch die <NUM>, the charges 9a, 9b can be heated. This can include positioning a heating blanket <NUM> loaded onto the charges 9a, 9b as illustrated in <FIG>. The heating blanket <NUM> heats the charges 9a, 9b which can soften the charge thermoset or the thermoplastic resin which can facilitate forming the charges 9a, 9b. Other heating methods include exposure to radiant or inductive type heaters. Heating can increase the tensioning state with the punch die <NUM>.

The stringers <NUM> and fabrication methodologies can being used in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where automated layup equipment can be used. The stringers <NUM> and methodologies can be used in the context of an aircraft manufacturing and service method <NUM> as illustrated in <FIG> and a vehicle <NUM> such as an aircraft as illustrated in <FIG>. During pre-production, exemplary methods <NUM> can include specification and design <NUM> of the vehicle <NUM> and material procurement <NUM>. During production, component and subassembly manufacturing <NUM> and system integration <NUM> of the vehicle <NUM> takes place. Thereafter, the vehicle <NUM> can go through certification and delivery <NUM> in order to be placed in service <NUM>. While in service by a customer, the vehicle <NUM> is scheduled for routine maintenance and service <NUM>, which can also include modification, reconfiguration, refurbishment, and so on.

The processes of method <NUM> can be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator can include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party can include without limitation any number of vendors, subcontractors, and suppliers; and an operator can be an airline, leasing company, military entity, service organization, and so on.

As shown in <FIG>, the vehicle <NUM> such as an aircraft produced by exemplary method <NUM> can include an airframe <NUM> with a plurality of systems <NUM> and an interior <NUM>. Examples of high-level systems <NUM> include one or more of a propulsion system <NUM>, an electrical system <NUM>, a hydraulic system <NUM>, and an environmental system <NUM>. Any number of other systems can be included. Although an aerospace example is shown, the principles of the disclosure can be applied to other industries, such as the marine and automotive industries.

Systems and methods embodied herein can be employed during any one or more of the stages of the production and service method <NUM>. For example, components or subassemblies corresponding to production process <NUM> can be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft <NUM> is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof can be utilized during the production stages <NUM> and <NUM>, for example, by substantially expediting assembly of or reducing the cost of an aircraft <NUM>. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof can be utilized while the aircraft <NUM> is in service, for example and without limitation, to maintenance and service <NUM>.

Claim 1:
A method of fabricating a composite stringer (<NUM>) for a vehicle (<NUM>), the method comprising:
positioning first and second charges (9a, 9b) at a die cavity (<NUM>) with first ends (<NUM>) of each of the first and second charges (9a, 9b) extending over the die cavity (<NUM>), said first charge (9a) including a blade (11a) and a flange (12a) and said second charge (9b) including a blade (11b) and a flange (12b);
securing second ends (<NUM>) of each of the first and second charges (9a, 9b) away from the die cavity (<NUM>);
inserting a punch die (<NUM>) into the die cavity (<NUM>) and driving the first ends (<NUM>) of each of the first and second charges (9a, 9b) into the die cavity (<NUM>) while the second ends (<NUM>) remain secured away from the die cavity (<NUM>), said punch die (<NUM>) including a first section (<NUM>) sized to fit within the die cavity (<NUM>) and a second section (<NUM>) providing the punch die (<NUM>) with a sectional shape that resembles the letter T, the punch die (<NUM>) being shaped to conform to the shape of the die cavity (<NUM>) and being lowered into the die cavity (<NUM>) with the first section (<NUM>) of the punch die (<NUM>) contacting against and driving the charges (9a, 9b) into the die cavity (<NUM>); and
moving the punch die (<NUM>) out of the die cavity (<NUM>);
moving together first and second form blocks (<NUM>, <NUM>) that form the die cavity (<NUM>) and applying lateral force to blades (11a, 11b) of the first and second charges (9a, 9b),
wherein securing the second ends (<NUM>) of each of the first and second charges (9a, 9b) away from the die cavity (<NUM>) comprises compressing each second end (<NUM>) between a support member (<NUM>) that is located in proximity to the form block (<NUM>, <NUM>) and a holding member (<NUM>) that is a plate (<NUM>) sized and shaped to contact and apply a force to secure the charge (9a, 9b) against the support member (<NUM>),
during the forming process the punch die (<NUM>) being inserted various depths into the cavity (<NUM>) with the second section (<NUM>) of the punch die (<NUM>) contacting against sections of the charges (9a, 9b) that remain out of the die cavity (<NUM>) or less amount of insertion into the die cavity (<NUM>) with the second section (<NUM>) of the punch die (<NUM>) remaining spaced away from the flanges (12a, 12b).