Patent Description:
Composite stringers are used in aircraft and other applications as to stiffen and transfer loads on outer skins. In some cases, a stringer must be contoured along its length and/or contain out-of-plane features such as joggles. These features make the production of composite stringers more challenging due to stress concentrations that are generated when forming these features.

One technique for producing composite stringers having out-of-plane features such as joggles involves the use of a punch to form a flat composite charge into a die. After the stringer is formed to the desired cross-sectional shape by the punch, it is transferred to a forming die in a kitting tray where out-of-plane features such as joggles are formed in the stringer. Forming the joggles in this manner tends to produce stress concentrations that can cause undesired ply wrinkling and/or resin pooling which may affect stringer performance. Consequently stringers containing these nonconformities must be reworked and sometimes must be discarded.

Accordingly it would be desirable to provide a stringer production method and equipment that reduces stringer wrinkling and resin pooling by forming the stringer to net shape.

<CIT>, according to its abstract, concerns a method and tooling apparatus for forming a composite charge into a contoured composite blade stringer including an elongate punch and an elongate die flexible along their lengths. The charge is press formed by using the punch to drive the charge into the die. The punch and the die are mounted between a pair of flexible plates. A press coupled with the plates contours the charge by bending the plates into a desired contour. The stringer is allowed to cool down to room temperature while being constrained, before withdrawing the stringer from the tooling apparatus in order to reduce wrinkling.

<CIT>, according to its abstract, states an uncured composite member is formed over a mandrel having a contour using a flexible compactor. Forming is performed outwardly from the apex of the contour.

<CIT>, according to its abstract, states provided are end effectors and methods of using such end effectors for handling various composite structures. An end effector includes a support structure bendable relative the principal axis of the end effector. The support structure is disposed within a cavity partially formed by an engaging portion of the end effector. The engaging portion is formed from a flexible material and includes multiple openings in fluid communication with the cavity. When the engaging portion contacts a composite structure and when the pressure inside the cavity is reduced below the ambient level, the composite structure is forced against the engaging portion due to this pressure differential. The flexibility of the support structure and of the engaging portion allows the end.

effector to conform to the shape of the composite structure. At the same time, the support structure maintains the shape of the cavity in the directions normal to the principal axis.

<CIT>, according to its abstract, states a method of forming a flat composite charge into a contoured composite part reduces wrinkles in the part as the charge is being formed. Dies are used to form a portion of charge to the steepest contour of the part, while tension is maintained on the charge as the remaining portions of the charge are formed.

<CIT>, according to its abstract, states a contoured composite laminate stiffener is fabricated by assembling a substantially flat composite laminate charge and forming the charge into a substantially straight stiffener having a desired cross sectional shape. A contour is formed in the stiffener which has an inside radius and an outside radius. Ply wrinkling is substantially eliminated by reducing compression strain on the inside radius as the stiffener as being contoured.

The disclosure relates in general to the production of composite stringers, and more specifically to production processes and equipment for making composite stringers having out-of-plane features.

According to one aspect, apparatus according to claim <NUM> is provided.

According to another aspect, which goes beyond the scope of the appended claims, apparatus is provided for making a composite stringer. The apparatus includes a punch, a die into which a composite charge may be formed by the punch, and a family of shims. The shims are respectively configured to form differing features in the composite charge. Each of the shims is releasably attached to the punch, allowing a single punch to be configured to produce stringers having differing features.

According to a further feature, a method according to claim <NUM> is provided.

One of the advantages of the disclosed embodiments is that composite stringers having one or more out-of-plane features such as joggles can be formed to net shape in a single forming operation. Another advantage is that composite stringers can be formed to net shape with reduced wrinkling and resin pooling. Another advantage is that secondary forming operations previously needed to produce out-of-plane features in the stringers can be eliminated. A further advantage is that composite stringers can be produced with various out-of-plane features using a family of shims that adapt a single forming tool to form these features. Another advantage is that the number of tools required to produce composite stringers with differing features is reduced, thereby reducing flow times and saving material and labor costs. A still further advantage is that stringers with out-of-plane features can be produced that exhibit higher quality, and the need for stringer rework is reduced.

The features, functions, and advantages can be achieved independently in various examples of the present disclosure or may be combined in yet other examples in which further details can be seen with reference to the following description and drawings.

The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative examples of the present disclosure when read in conjunction with the accompanying drawings, wherein:.

Referring first to <FIG>, a composite stringer <NUM> comprises a composite laminate of fiber reinforced plies of a polymer such as a thermoset or thermoplastic. In the illustrated example, the composite stringer <NUM> is a hat stringer comprising a hat section <NUM> and a pair of outwardly extending flanges <NUM>. The hat section <NUM> comprises a cap <NUM> connected to the flanges <NUM> by a pair of inclined sides <NUM>, sometimes referred to as webs. Although the disclosed embodiments will be described in connection with a hat shaped stringer, principles of the disclosed embodiments may be employed to produce composite stringers having any of a wide variety of cross-sectional shapes.

Referring particularly to <FIG>, <FIG>, the composite stringer <NUM> includes one or more out-of-plane features <NUM> along its length. In the illustrated example, the out-of-plane feature <NUM> is a joggle <NUM> comprising a ramp-up/ramp-down <NUM> in the cross-sectional shape of the composite stringer <NUM> along its length. However, the joggle <NUM> is merely illustrative of a wide range of possible out-of-plane features <NUM> in the composite stringer <NUM> that may be required in a particular application. In the illustrated example, the composite stringer <NUM> is attached to a skin <NUM> by any suitable technique such as co-curing, bonding or fasteners. The skin <NUM> includes a pad-up <NUM> of composite plies <NUM> that may be required to locally strengthen an area of the skin <NUM>, or for other reasons. The joggle <NUM> bridges over the pad-up <NUM> and has a length and contour that closely matches the cross-sectional shape of the pad-up <NUM>. Although the composite stringer <NUM> is shown with only one joggle <NUM> therein, depending on the application, it may have any number of joggles <NUM> of the same or differing profiles in order to accommodate a variety of features present on the skin <NUM>, or other conditions.

<FIG> illustrate a toolset <NUM> for forming a composite charge <NUM> into a composite stringer <NUM> having a joggle <NUM> therein. The toolset <NUM> comprises a tool <NUM>, which in this example is a punch <NUM>, and a die <NUM> comprising a pair of die sections <NUM> that are spaced apart to form a die cavity <NUM>. The punch <NUM> may be formed of a flexible material, such as an elastomer, nylon or PTFE (polytetrafluoroethylene) to name only a few, allowing it to flex as required. In the illustrated example, the punch <NUM> is mounted on the bottom of a top plate <NUM> that is flexible and may comprise, for example and without limitation, sheet aluminum. In other examples, however, the top plate <NUM> may also be an elastomer or other polymer that is integrally formed with the punch <NUM>. The cross sectional shape of the punch <NUM> substantially matches the IML (inner mold line) of the hat section <NUM> (<FIG>) of the composite stringer <NUM>.

The die sections <NUM> are mounted for lateral movement <NUM> on a bottom plate <NUM>. In one example, the die sections <NUM> comprise a series of interconnected die blocks that permit the die sections <NUM> to flex out-of-plane. A pair of side plates <NUM> are secured to the bottom plate <NUM>, outboard of the dies <NUM>. Inflatable side bladders <NUM> are respectively located between the dies <NUM> and the side plates <NUM>. The side bladders <NUM> may be inflated with a fluid such as air, and function to control the outward lateral movement of the dies <NUM> during the forming process. The toolset <NUM> may be installed in a press (not shown) which move the top and bottom plates <NUM>, <NUM> relative to each other, causing displacement of the punch <NUM> into the die cavity <NUM> at a desired rate and with a desired amount of force.

In the illustrated example, the punch <NUM> is substantially straight along its length. However, in other examples discussed below, the punch <NUM> may have one or more curvatures along its length. In order to form the joggle <NUM> or other out-of-plane feature <NUM> in the composite stringer <NUM>, a shim <NUM> is installed over the punch <NUM> which has a surface profile substantially matching the joggle <NUM>. The shim <NUM> may be releasably attached to the punch <NUM> and/or the top plate <NUM> by any suitable means, such as by double-sided tape, a mechanical latch (not shown) or a later discussed magnetic latch. Thus differently shaped shims <NUM> may be interchangeably installed on the same punch <NUM> to form different out-of-plane features. Depending on the application it may be necessary to also install shims <NUM> on top of the die sections <NUM>.

The shim <NUM> includes a cap <NUM>, sides <NUM> and flanges <NUM> which form a profile substantially matching the IML of the joggle <NUM>. The thickness T, as well as other dimensions or features of the shim <NUM> will depend on the application, and the geometry/dimensions of the joggle <NUM>. The shim <NUM> includes ramp-up/ramp-downs <NUM> at its outer ends which form smooth transitions between the shim <NUM> and the body of the punch <NUM>. The shim <NUM> may be formed of any suitable material by any of various manufacturing processes. For example, the shim <NUM> may comprise laser sintered nylon or photo-cured epoxy produced by <NUM>-D printing. Although only a single shim <NUM> is illustrated in the drawings, any number of shims <NUM> may be installed at any location along the length of the punch <NUM> to form corresponding out-of-plane features in the composite stringer <NUM>.

A stringer forming operation begins with the toolset <NUM> arranged as shown in <FIG>, and the punch <NUM> in a raised position. A composite charge <NUM>, which in this example is flat, is placed on top of the die sections <NUM>, spanning the die cavity <NUM>. To form the composite charge <NUM> into the desired cross sectional shape of the composite stringer <NUM>, the top plate <NUM> moves down, causing the punch <NUM> to form the composite charge <NUM> into the die cavity <NUM>. As the punch <NUM> forms the composite charge <NUM> into the cross-sectional shape of the composite stringer <NUM>, the shim <NUM> also forms the joggle <NUM> or other out-of-plane feature in the composite stringer <NUM>. Thus, the out-of-plane feature <NUM> is formed in the stringer <NUM> at the same time the stringer <NUM> is formed to the desired cross sectional shape. Simultaneous forming of the stringer <NUM> and the out-of-plane features <NUM> reduces strain in the stringer <NUM> during the forming process which can cause wrinkling and resin pooling.

In some examples, the composite stringer <NUM> may be formed to a desired contour along its length in a secondary forming operation, in which the punch <NUM>, as well as the die <NUM>, are contoured by a suitable contour changing mechanism (not shown). In order to allow the shim <NUM> to flex as the punch <NUM> is being contoured, the shim <NUM> is provided with a set of first openings <NUM> in the form of slots that extend completely across the cap <NUM> and sides <NUM> of the shim <NUM>. Optionally, the shim <NUM> may further include a set of second openings <NUM> therein which may also be in the form of slots that extend fully across the cap <NUM>, but only partially through the sides <NUM> of the shim <NUM>. The second openings <NUM> reduce wrinkling or buckling of the composite stringer <NUM> as it is being formed the contour.

Referring also to <FIG>, as the composite stringer <NUM> is being contoured, the first openings <NUM> may partially or fully close <NUM>, thereby allowing the shim <NUM> to flex along with the punch <NUM>. However, during this contouring, the second openings <NUM> remain open, allowing the composite charge <NUM> to strain into the second openings <NUM>, wherein they form wrinkles <NUM> that that are relatively small in size and therefore do not materially affect stringer performance.

As previously mentioned, the shim <NUM> is releasably attached to the tool <NUM>. The shims <NUM> may be releasably attached to the tool <NUM> using magnets <NUM>, allowing easy installation and removal of the shims <NUM> to provide for various joggle locations and conditions. The use of magnets <NUM> also facilitates interchangeability of multiple differently configured shims <NUM> with a single tool. <FIG> illustrates one technique for shim attachment, comprising one or more magnetic latches <NUM>, each including magnets <NUM> embedded in the flanges <NUM> of the shim <NUM>. In this example, the top plate <NUM> is formed of a magnetic material, or a flexible binder material containing magnetic material. The top plate <NUM> is attracted to the magnets <NUM>, thereby releasably latching the shim <NUM> to the tool <NUM>.

<FIG> illustrates another example of a magnetic latch <NUM> in which magnetic material inserts <NUM> are embedded in the top plate <NUM>, aligned with magnets <NUM> that are embedded in the flanges <NUM> of the shim <NUM>.

<FIG> illustrates a further example of a magnetic latch <NUM> in which magnetic material inserts <NUM> are embedded in the flanges <NUM> of the shim <NUM>. Electromagnets <NUM> mounted on or embedded in the top plate <NUM> are electrically energized to attract the magnetic material inserts <NUM>, thereby releasably holding the shim <NUM> on the tool <NUM>. Other combinations of magnets and magnetic materials may be used to magnetically attach the shim <NUM> to the tool <NUM>.

Attention is now directed to <FIG>, which illustrate families 102a, 102b, 102c of shims <NUM> that may be used to form any of a variety of out-of-plane features such as joggles <NUM> in composite stringers <NUM>. By providing one or more families 102a, 102b, 102c of shims <NUM> having different characteristics commonly used to form out-of-plane features, the need for custom fabrication of shims to meet the requirements of a particular application may be avoided. Shims <NUM> may be designed to achieve various joggle conditions used in multiple stringers <NUM>. For example, stringers <NUM> with joggles <NUM> having ramps or heights within a certain specified range could all use the same shim <NUM>. Thus, it may be desirable to provide a family of shims <NUM>, each having unique characteristics, allowing a particular one of the shims <NUM> in a family to be selected for use in forming joggles <NUM> in any of number of stringers <NUM>.

Any desired characteristic of a shim <NUM> may be designed to vary within a family 102a, 102b, 102c. For example, <FIG> illustrates a family 102a of shims <NUM> in which the ramp angle RA may vary either linearly or non-linearly from RA<NUM> to RAn. <FIG> illustrates a family 102b of shims <NUM> in which the length of the shim <NUM> may vary either linearly or non-linearly from L<NUM> to Ln. <FIG> illustrates a family 102c of shims <NUM> in which the height of the shim <NUM> may vary either linearly or non-linearly from H<NUM> to Hn. Although not shown the Figures, families <NUM> of the shims <NUM> may also be provided that contain variations in multiple shim characteristics, for example ramp angle, length and/or height, to name only a few.

<FIG> broadly illustrates the steps of a method of making a composite stringer <NUM> having one or more out-of-plane features <NUM>. Beginning at <NUM>, a shim <NUM> is installed on a tool <NUM>. At <NUM>, a composite charge <NUM> is formed into a composite stringer <NUM> using the tool <NUM>, including using the shim <NUM> to form an out-of-plane feature <NUM> in the composite charge <NUM> as a composite charge <NUM> is formed by the tool <NUM>. The use of the shim <NUM> permits the out-of-plane feature <NUM> to be formed in the stringer <NUM> at the same time the stringer <NUM> is being formed, rather than later in a secondary forming operation. Simultaneous forming of the out-of-plane feature <NUM> and the shape of the stringer <NUM> reduces strain in the stringer <NUM>, particularly in the regions of the cap <NUM> and sides <NUM> which can lead to ply wrinkling and/or resin pooling.

Attention is now directed to <FIG> which illustrate a tool <NUM> in the form of a compactor <NUM> that may be used to form, transport, and/or compact a composite stringer <NUM>, which in this example is a hat stringer. The compactor <NUM> comprises a one-piece, hat shaped body <NUM> and integral flanges <NUM> formed of a flexible material such as an elastomer. The hat shaped body <NUM> includes an interior chamber <NUM>, and a series of openings <NUM> which may comprise slots arranged along the length of the compactor <NUM>. In some examples, the openings <NUM> may be configured to redirect stresses created in the composite charge <NUM> during contouring of the composite stringer <NUM>, and thereby reduce stringer wrinkling. The compactor <NUM> includes an end wall <NUM> provided with a tube fitting <NUM> that is adapted to couple the interior chamber <NUM> with a vacuum source (not shown). A vacuum applied to the interior chamber <NUM> results in air being drawn in through the openings <NUM>, producing a suction effect.

When the compactor <NUM> is placed inside a correspondingly shaped composite stringer <NUM> and a vacuum is drawn within the compactor <NUM>, the composite stringer <NUM> is drawn against the compactor <NUM>, allowing the compactor <NUM> to pick up and transport the composite stringer <NUM> to a desired location, such as to a forming station or kitting tray (both not shown). One or more shims <NUM> may be attached at any location along the length of the compactor <NUM> in order to form and/or compact one or more out-of-plane features <NUM> in the composite stringer <NUM>, similar in function to the shims <NUM> attached to the punch <NUM> previously described. The shim <NUM> includes openings <NUM> such as slots which allow air to pass through the shim <NUM> and be drawn into interior chamber <NUM> of the compactor <NUM>.

<FIG> broadly illustrates the steps of a method of forming and transporting a composite stringer <NUM> using the compactor <NUM> of <FIG>. Beginning at <NUM>, one or more shims <NUM> are installed on the compactor <NUM>. At <NUM>, a composite charge <NUM> is formed into a composite stringer <NUM> using the compactor <NUM> as a forming tool. At <NUM>, local out-of-plane features are formed in the composite stringer <NUM> as the composite charge <NUM> is being formed, using the shim <NUM> that has been attached to the compactor <NUM>. Optionally, at <NUM>, the shim <NUM> may be removed from the compactor <NUM> after the composite charge <NUM> has been formed into a composite stringer <NUM>. At <NUM>, the compactor <NUM> may be used to pick up and transport the composite stringer <NUM> to a desired location, such to a kitting tray, a compaction tool or to a storage location.

<FIG> shows the compactor <NUM> having picked up a composite stringer <NUM> using suction drawn through the openings <NUM> (<FIG>) and about to lower <NUM> the composite stringer <NUM> into a die cavity <NUM> in a forming die <NUM>. The forming die <NUM> includes a die surface <NUM> that is contoured along its length. After placing the composite stringer <NUM> in the die cavity <NUM>, forming pressure is applied to the compactor <NUM>, causing the composite stringer <NUM> to be formed to the contour of the die cavity <NUM>. Additionally, the shim <NUM> forms-out-of plane features in the composite stringer <NUM> during this contour forming process. Additional pressure applied to the compactor <NUM> by any suitable means such as a vacuum bag (not shown) results in compaction of the composite stringer on the forming die <NUM>.

<FIG> broadly illustrates the steps of a method of compacting and/or forming a composite stringer <NUM> to a desired contour which includes one or more out-of-plane features <NUM>. Beginning at <NUM>, a composite charge <NUM> is punch formed into a composite stringer <NUM> having a desired cross-sectional shape. Next, at <NUM> one or more shims <NUM> are installed on a compactor <NUM>. At <NUM>, the compactor <NUM> is used to pick up and transfer the composite stringer <NUM> a forming die <NUM> or kitting tray. At <NUM>, the compactor <NUM> having the shim <NUM> installed thereon is used to form and/or compact the composite stringer <NUM>. At <NUM>, local out-of-plane features are formed in the composite stringer <NUM> during the forming/compaction using the shim <NUM>.

Examples of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where composite stiffeners, such as composite stringers in aircraft, may be used. Thus, referring now to <FIG>, examples of the disclosure may be used in the context of an aircraft manufacturing and service method <NUM> as shown in <FIG> and an aircraft when <NUM> as shown in <FIG>. Aircraft applications of the disclosed examples may include a variety of composite stringers that have contours, curvatures, varying thicknesses and/or one or more out-of-the plane features along their lengths. During pre-production, exemplary method <NUM> may include specification and design <NUM> of the aircraft <NUM> and material procurement <NUM>. During production, component and subassembly manufacturing <NUM> and system integration <NUM> of the aircraft <NUM> takes place. Thereafter, the aircraft <NUM> may go through certification and delivery <NUM> in order to be placed in service <NUM>. While in service by a customer, the aircraft <NUM> is scheduled for routine maintenance and service <NUM>, which may also include modification, reconfiguration, refurbishment, and so on.

As shown in <FIG>, the aircraft <NUM> produced by exemplary method <NUM> may 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 may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries.

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

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, and item C" may include, without limitation, item A, item A and item B, or item B. 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.

Claim 1:
Apparatus for making a composite stringer (<NUM>) having at least one out-of-plane feature (<NUM>), comprising:
a die (<NUM>) including a die cavity (<NUM>);
a tool (<NUM>) configured to form a composite charge (<NUM>) into the die cavity (<NUM>); and
a shim (<NUM>) attached to the tool (<NUM>) and configured to form an out-of-plane feature (<NUM>) in the composite stringer (<NUM>) as tool (<NUM>) forms the composite charge (<NUM>) into the die cavity (<NUM>), wherein the shim (<NUM>) includes:
a set of first openings (<NUM>) therein allowing the shim (<NUM>) to flex, and
a set of second openings (<NUM>) therein into which the composite charge (<NUM>) may strain as the composite charge (<NUM>) is formed by the tool (<NUM>),
wherein the set of first openings (<NUM>) is in the form of slots that extend completely across a cap (<NUM>) and sides (<NUM>) of the shim (<NUM>), and
characterised in that the set of second openings (<NUM>) is in the form of slots that extend fully across the cap (<NUM>), but only partially through the sides (<NUM>) of the shim (<NUM>).