Patent Description:
Composite stringers such as those used in the aircraft and marine industries can be made by compression forming a flat stack of composite plies between a pair of tool dies placed in a press or similar device that compresses the dies together. Each of the dies has unique tool surfaces that are configured to produce a particular cross-sectional stringer shape. Each stringer shape therefore requires the use of dies that are unique to that shape, and cannot be used to make stringers having other shapes. The dies can be costly to manufacture, consequently, considerable expense is incurred where different sets of dies are required to produce different stringer shapes.

Producing stringers having different shapes can also be costly due to the time and labor required to change out the dies in a press. In some types of stringers, it is necessary to change parts of a die that are unique to a certain processing stage, such as compaction of parts of the stringer after it has been formed to shape. The need for changing out parts of a die further adds to the expense of the stringer manufacturing process.

Accordingly, it would be desirable to provide a stringer forming apparatus and related method that reduces the need for uniquely configured dies and die parts needed to make different stringer shapes. It would also be desirable to reduce the time and labor required to modify a forming apparatus to produce different forms of stringers.

Document <CIT>, with its abstract, discloses a method and associated apparatus for forming a composite structural member from a charge. The charge can be disposed on a first die of the apparatus and formed to a desired configuration defined by a recess of the die by inserting a second die or a tool into the recess. In some cases, the first die can include two portions that are adjustable in a transverse direction so that the recess can be opened by the insertion of the second die or tool. The second die or tool can be a substantially rigid member or an inflatable bladder. In either case, the charge can be disposed on the first die, formed, and then further processed on the first die, thereby facilitating indexing of the charge for each operation.

The disclosure relates in general to equipment and processes for making composite laminate parts, and more specifically to an apparatus and method of making composite laminate stringers having various shapes.

According to one aspect, an apparatus is provided for punch forming a composite charge into a stringer having the features disclosed in claim <NUM>. The dependent claims outline advantageous forms of embodiment of the apparatus.

According to another aspect, a method is provided of forming a composite stringer comprising the steps defined at claim <NUM>. The dependent claims outline advantageous ways of carrying out the method.

One of the advantages of the disclosed apparatus method is that the time and labor needed to compression form composite stringers can be reduced. Another advantage is that universal dies are provided that can easily and quickly reconfigured to produce stringers having different cross sectional shapes. A further advantage is that the die changing process is partially automated, thereby reducing labor costs and increasing throughput.

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:.

The disclosed embodiments relate to a method and apparatus for making composite stiffeners such as stringers used in the aircraft, marine and other industries. For example, referring to <FIG>, an airplane <NUM> includes a fuselage <NUM>, wings <NUM> and an empennage comprising a vertical stabilizer <NUM> and horizontal stabilizers <NUM>. Each of these airframe components includes a composite outer skin <NUM> that is reinforced and stabilized by stringers <NUM> beneath the skin <NUM>. The stringers <NUM> are joined to the IML (inner mold line) of the skin <NUM>, typically by co-curing or by co-bonding. The stringers <NUM> may have any of a variety of cross-sectional shapes depending on the application. One example of a stringer <NUM>, sometimes referred to as a blade stringer, is shown in <FIG>. The blade stringer <NUM> includes a base <NUM> formed by outwardly extending flanges, and a blade <NUM>, sometimes referred to as a web. Another example of a stringer 44a is shown in <FIG>, commonly known as a rounded hat stringer 44a. The hat stringer 44a includes a rounded hat section <NUM> and a pair of outwardly extending flanges <NUM>. The disclosed method and apparatus can be used to make the stringers <NUM>, 44a and any of a variety of other types of stringers, such as, without limitation, I, J, Y, Z stringers as well as other forms of hat stringers.

Depending upon the application, the stringers <NUM> may have various out-of-plane features such as contours, pad ups and/or joggles (not shown) at one or more locations along their lengths. Contouring of the stringers <NUM> is sometimes necessary in order to match the contour of a skin <NUM> to which the stringers <NUM> are attached. For example, as shown in <FIG>, the stringer <NUM> has a contour <NUM> along its entire length in the XZ plane within coordinate system shown at <NUM>, however in other examples the stringer <NUM> may have straight sections as well as local contours along its length. The stringer <NUM> may also have one or more contours along its length in the XY plane. Each of the base <NUM> and the blade <NUM> may have a variable thickness at one or more locations along their lengths in order to conform the stringer <NUM> to localized features of the structure to which it is attached.

Attention is now directed to <FIG> which diagrammatically illustrate a process for forming a flat, multi-ply composite charge <NUM> into a stringer <NUM> or similar stiffener of the type previously described. In this example, the stringer <NUM> being formed is a blade stringer <NUM>, however the principles described below can be used to form any of a variety of other type of stringers. Referring to <FIG>, a tool set <NUM> for compression forming the charge <NUM> into a stringer shape, broadly comprises an upper die <NUM> and a lower die <NUM>. The upper die <NUM> comprises a punch <NUM> attached to a top plate <NUM>, while the lower die <NUM> comprises a pair of die blocks <NUM> that are slideable <NUM> toward and away from each other on a bottom plate <NUM>, and form a die cavity <NUM>. Both the top plate <NUM> and the bottom plate <NUM> are formed of a flexible material, such as a flexible metal or a composite, while the die blocks <NUM> as well as the punch <NUM> are segmented along their lengths to allow them to flex.

In use, with the upper die <NUM> in a raised position above the lower die <NUM>, a flat, multiply ply composite charge <NUM> is placed between the upper die <NUM> and upper surfaces of the die blocks <NUM>. The top plate <NUM> is then displaced downwardly with a force F, causing the punch <NUM> to compression form or "punch" the charge <NUM> into the die cavity <NUM>, thereby forming a pair of web portions <NUM>. As web portions <NUM> of the stringer <NUM> are being formed by the punch <NUM>, flange portions <NUM> of the stringer <NUM> are constrained but are allowed to slide between the top plate <NUM> and the die blocks <NUM>.

Next, as shown in <FIG>, the top plate <NUM> is removed and replaced by a flat plate 56a. Then, as shown in <FIG>, a force F is applied to the flat plate 56a which constraints the flange portions <NUM>, while the die blocks <NUM> are forced toward each other, causing the web portions <NUM> to collapse toward each other into a blade <NUM>, while the flange portions <NUM> are drawn together to form the base <NUM> of the stringer <NUM>. Finally, the flat plate 56a is removed and the die blocks <NUM> are drawn apart, allowing the stringer <NUM> to be removed from the tool set <NUM>. The stringer <NUM> may be contoured along its length in the XY and/or XZ planes (<FIG>) by contouring the tool set <NUM> using appropriate apparatus (not shown).

Attention is now directed to <FIG> which illustrate a forming apparatus <NUM> for forming a flat composite charge <NUM> into a stringer <NUM> using a punch forming process similar to that described above in connection with <FIG>. As will be discussed below in more detail, the forming apparatus <NUM> is a reconfigurable pallet and end effector employing universal dies that can be readily adapted to form any of a wide variety of stringer shapes with simple modifications that can be easily and quickly performed. The forming apparatus <NUM> broadly comprises upper and lower supports 82a, 82b that respectively include an upper arm <NUM> and a lower arm <NUM>. The supports 82a, 82b are coupled with one or more drive mechanisms (not shown) that move the arms 82a, 82b along the Z axis toward and away from each other.

The forming apparatus <NUM> further comprises an upper tray <NUM> having an upper die <NUM>, and a lower tray <NUM> having a lower die <NUM>. The upper tray <NUM> is connected to the upper arm <NUM> by a plurality of upper pivots <NUM> which allow the upper tray <NUM> to bend as required in the XZ plane (<FIG>). Each of the upper pivots <NUM> includes removable pivot pins <NUM> (<FIG>) which releasably mount the upper tray <NUM> on the upper arms <NUM>. The upper tray <NUM> includes a flexible top plate <NUM> and a punch <NUM> which functions similar to punch described earlier in connection with <FIG>. Although not shown in the Figures, the punch <NUM> may be segmented along its length to allow it to flex.

The upper tray <NUM> further includes inflatable clamping hoses <NUM> that apply pressure to the composite charge <NUM> through a pair of laterally spaced caul plates <NUM> positioned on opposite sides of the punch <NUM>. The caul plates <NUM> function to evenly apply clamping pressure to the composite charge <NUM>, and also act as a heat sink to evenly distribute heat applied to the composite charge <NUM> by heating blankets <NUM> interposed between the caul plates and the hoses <NUM>. Referring to <FIG>, a vertically aligned pair of the hoses <NUM>, a caul plate <NUM> and a heating blanket <NUM> may be arranged as a stacked subassembly <NUM> on opposite sides of the punch <NUM>. The subassemblies <NUM> may be attached to the top plate <NUM> by any suitable means.

The lower tray <NUM> is pivotally connected to the lower arms <NUM> by a plurality of lower pivots <NUM>. The lower tray <NUM> is releasably connected to adapter arms <NUM> by removable pivot pins <NUM>. The lower tray <NUM> comprises die block assemblies <NUM> that are reconfigurable to allow different stringer shapes to be formed. The die block assemblies <NUM> include a plurality of die blocks <NUM> slidably mounted on a flexible bottom plate <NUM>. The die block assemblies <NUM> further comprise a cap assembly <NUM> which includes die block adapters <NUM> that cover and are removably mounted on the die blocks <NUM>. The die block adapters <NUM> have tool surfaces that determine in part, the cross-sectional shape of the stringer <NUM> being formed. In some applications, depending on the shape of the stringer being formed, it may be desirable to clamp portions of the composite charge, such as the flanges, to the die block adapters <NUM>. Accordingly, the lower die <NUM> may optionally include a vacuum clamping capability in which the top of each of the die block adapters <NUM> is provided with one or more air inlet openings <NUM> that are connected with vacuum ports <NUM> on the side. The vacuum ports <NUM> are connected through hoses (not shown) to a vacuum source <NUM> (<FIG>) which draws a vacuum at the air inlet openings <NUM>, causing the composite charge <NUM> to be drawn down and clamped against the tops of the die block adapters <NUM>.

The die blocks <NUM> include oval shaped cooling passageways <NUM> which allowing cooling of the die block assemblies <NUM> either by convection or forced air. The die blocks <NUM> may be constrained together using rods or cables (both not shown) which pass through circular holes <NUM> in the die blocks. The circular holes <NUM> may function to dissipate heat from the die blocks <NUM>. An inflatable block separation hose <NUM> is positioned between the die blocks <NUM> and acts as a barrier or stop that maintains a minimum separation distance between the die blocks <NUM>, thus preventing the punch <NUM> from unintentionally coming into contact with the tops of the die block adapters <NUM> when upper die <NUM> is lowered toward the lower die <NUM> during a forming operation.

Referring to <FIG> and <FIG>, the top plate <NUM> is formed from a flexible material, such as flexible metal or a flexible composite. An upper pivot plate <NUM> is secured to the top plate <NUM> and is pivotally connected to the upper arms <NUM> through the upper pivots <NUM>. The upper pivot plates <NUM> are also guided by roller assemblies <NUM> that allow the upper pivot plates <NUM> and top plate <NUM> to move along the X axis relative to the upper arms <NUM>, thus permitting the top plate <NUM> to flex in the XZ plane as required in order to form the stringer <NUM> to a desired contour. As will be discussed below, the slideable connection formed between the upper pivot plates <NUM> and the rollers <NUM> slideably mounts the top plate <NUM> on the upper arms <NUM>, thereby allowing the assembly of top plate <NUM> and the punch <NUM> to be removed from the forming apparatus <NUM> by sliding the top plate <NUM> along the X axis until the upper pivot plate <NUM> is clear of the rollers <NUM>. Thus, the upper die <NUM> can be removed and replaced with a differently configured upper die <NUM> either by removing the pivot pins <NUM> or by sliding the top plate <NUM> along the rollers <NUM>.

Attention is now directed to <FIG>, <FIG> and <FIG>, which illustrate further details of the lower tray <NUM>. Each of the bottom guides <NUM> and core blocks <NUM> is secured to a bottom plate <NUM>. The die block adapters <NUM> are releasably mounted by fasteners such as screws on the die blocks <NUM> and are spaced apart from each other to form a die cavity <NUM> into which the composite charge <NUM> (<FIG>) is formed by the punch <NUM>. As best seen in <FIG>, a lower pivot plate <NUM> is secured to the bottom of the bottom plate <NUM>. Lower pivots <NUM> pivotally connect the lower pivot plate <NUM> to the top of adapter arms <NUM> which are secured to bottom adapter bases <NUM>. The adapter arms <NUM> are mounted on the bottom adapter base <NUM>. The lower pivot plate <NUM> is supported on rollers <NUM>, which allow the bottom plate <NUM> to move along the X direction during contouring of the stringer <NUM>.

The bottom adapter bases <NUM> are mounted on linear guides <NUM> that slide along tray rails <NUM> on the lower arms <NUM>. The linear guides <NUM> and tray rails <NUM> form a slide assembly that allow the lower tray <NUM> to move along the Y axis between two operating positions discussed below. Referring also to <FIG>, the lower tray <NUM> is shifted laterally between these two operating positions by motor drives <NUM>. Each of the motor drives <NUM> comprises a suitable pneumatic, hydraulic or electric motor <NUM> driving a pinion gear <NUM> that engages a toothed rack <NUM> on one of the lower arms <NUM>. Each of the motors <NUM> includes a motor housing <NUM> that is secured to one of the bottom adapter bases <NUM> by screws (not shown) or other means.

As discussed above, the lower tray <NUM> can be shifted by the motor drives <NUM> linearly along the lower arms <NUM>. <FIG> shows the lower tray in a punch position <NUM> at the outer end of the lower arms <NUM>, in which the upper die <NUM> is aligned above the lower die <NUM>, and more particularly the punch <NUM> is vertically aligned above the die cavity <NUM>. In this example, the punch <NUM> is a blade which punches a flat composite charge into the die cavity <NUM> in a process step similar to that previously described in connection with <FIG>, in which the upper and lower dies <NUM>, <NUM> are closed to form a pair of flange portions <NUM> and web portions <NUM>. After this initial forming step, the upper arms <NUM> are shifted upwardly, thereby raising the upper tray <NUM> and withdrawing the punch <NUM> from the die cavity <NUM>.

Referring to <FIG>, with the upper tray <NUM> shifted upwardly to withdraw the punch <NUM> from the die cavity <NUM>, the motor drives <NUM> are activated, causing the entire lower tray <NUM> to shift to the left as viewed in <FIG>, to a compaction position <NUM> in which the top plate <NUM> is positioned directly above the die block adapters <NUM>. In the compaction position <NUM>, the upper arms <NUM> can be lowered to bring the top plate <NUM> into contact with the flange portions <NUM> of the composite charge <NUM>, similar to the process previously described in connection with <FIG>, thereby compacting the flange portions <NUM>.

Various control systems can be used to control operation of the forming apparatus <NUM>. For example, referring to <FIG>, one suitable control system comprises a controller <NUM>, such as a PC or programmable controller which controls the operation of the motor drives <NUM>, a vacuum source <NUM>, a compressed air supply <NUM>, and a die block heating/cooling system <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, in use, the process of forming a flat composite charge <NUM> into a stringer <NUM> begins with installing an upper tray <NUM> having a punch <NUM> of a desired tool shape, and installing die block adapters <NUM> of a desired shape on the die blocks <NUM>. The shapes of the punch <NUM> and the die block adapters <NUM> determine the cross-sectional shape of the stringer <NUM> to be formed. Next, with the lower tray <NUM> in the punch position <NUM> shown in <FIG>, the upper arms <NUM> are raised enough to allow a flat composite charge <NUM> to be placed on the upper surfaces of the die block adapters <NUM>. Hoses <NUM> are pressurized, causing the die blocks <NUM> to move apart and form a die cavity <NUM> of the desired width. Hoses <NUM> are then depressurized while both hoses <NUM> and <NUM> are pressurized at a controlled rate. The upper arms <NUM> move down, bringing caul plates <NUM> into contact with and apply a desired amount of pressure to composite charge <NUM>.

Continued downward movement of the upper arms <NUM> causes the punch <NUM> to form the composite charge <NUM> into the die cavity <NUM>, while the flange portions <NUM> of the charge <NUM>, although restrained, are allowed to slip between the caul plates <NUM> and the top of the die block adapters <NUM>. The pressure in the hoses <NUM> is gradually reduced as the punch <NUM> moves down, permitting the die blocks <NUM> to move apart as the punch <NUM> forms the composite charge <NUM> into the die cavity <NUM>.

Next, the upper arms <NUM> are displaced upwardly, causing the punch <NUM> to be withdrawn from the die cavity <NUM>. Then, the motor drives <NUM> are activated, causing the entire lower tray <NUM> to move along the Y axis from the punch position <NUM> shown in <FIG> to the compaction position <NUM> shown in <FIG>. In the compaction position <NUM>, the lower tray <NUM> is no longer vertically aligned with the punch <NUM> but and instead is vertically aligned with the top plate <NUM>. The upper arms 78a are again displaced downwardly until the top plate <NUM> comes in contact with the flange portions <NUM> of the partially formed charge <NUM>. While the top plate <NUM> applies compaction pressure to the flange portions <NUM>, the pressure in the hoses <NUM> is increased, causing the die blocks <NUM> and cap assemblies <NUM> to move toward each other which squeeze and collapse the web portions <NUM> of the composite charge <NUM>, similar to the process step described earlier in connection with <FIG>. In those examples where the stringer <NUM> is to be contoured along its length (see <FIG>), a die changing mechanism (not shown) bends the punch <NUM> as well as the die blocks <NUM> and cap assembly <NUM>, thereby forming the stringer <NUM> to the desired contour. The stringer <NUM> having been fully formed and compacted, hoses <NUM> are deflated, upper arms <NUM> raise the upper tray <NUM>, and hoses <NUM> are inflated which cause the die blocks <NUM> and cap assemblies <NUM> to move away from each other and allow the stringer <NUM> to be removed from the forming apparatus <NUM>.

Attention is now directed to <FIG> which broadly illustrates the steps of a method of making a composite stringer <NUM> which can be carried out using the forming apparatus <NUM> previously described. Beginning at <NUM>, a flat composite charge <NUM> is placed between first and second dies <NUM>, <NUM>. At <NUM>, the second die <NUM> is moved to a punch forming position <NUM> aligned with the first die <NUM>. At <NUM>, the composite charge <NUM> is punch formed into the shape of a stringer <NUM> while the second die <NUM> is in the punch forming position <NUM>. The composite charge <NUM> is formed into a die cavity <NUM> in the second die <NUM> using a punch <NUM> on the first die. At <NUM>, the second die <NUM> is shifted from the punch forming position <NUM> to a compaction position <NUM>. At <NUM>, at least a portion <NUM> of the stringer <NUM> is compacted using the first die <NUM> while the second die <NUM> is in the compaction position <NUM>.

Examples of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, and other application where composite stiffeners such as composite laminate stringers for 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 <NUM> as shown in <FIG>. Aircraft applications of the disclosed examples may include a variety of composite stringers of various cross-sectional shapes, including those that are that have contours, curvatures, varying thicknesses or other non-uniformities 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 punch forming a composite charge (<NUM>) into a stringer (<NUM>), comprising:
a set of upper arms (<NUM>);
an upper tray (<NUM>) coupled with the upper arms (<NUM>), the upper tray (<NUM>) including a top plate (<NUM>) and a punch (<NUM>) ;
a set of lower arms (<NUM>);
a lower tray (<NUM>) including a die (<NUM>) having a die cavity (<NUM>) into which the punch (<NUM>) may form the composite charge (<NUM>) into a stringer shape;
a slide assembly (<NUM>) mounting the lower tray (<NUM>) on the lower arms (<NUM>) for sliding movement between a first position (<NUM>) in which the punch (<NUM>) forms the composite charge (<NUM>) into the die cavity (<NUM>) and second position (<NUM>) in which the top plate (<NUM>) compacts the composite charge (<NUM>);
wherein the slide assembly (<NUM>) includes:
rails (<NUM>) respectively extending along the lower arms (<NUM>), and linear guides (<NUM>) respectively mounted for movement along the rails (<NUM>) and coupled with the lower tray (<NUM>).