Patent Description:
Fiber reinforced, composite laminate stiffeners such as stringers are frequently used in the marine, aircraft and other industries to transfer loads. In some applications, the stiffeners must be contoured along their lengths in order to conform them to a structure to which they are to be attached, such as a contoured aircraft skin. Difficulty can be encountered in producing highly contoured composite laminate stiffeners because of the tendency of the plies to wrinkle as they are being formed to a desired contour. As a stiffener is being contoured, the reinforcing fibers on the inside radius of the stiffener are compressed, which may cause the plies to buckle and form wrinkles. Ply wrinkling is undesired because it may undesirably affect stiffener performance and/or may limit the degree to which the stiffener can be contoured without unacceptable wrinkling.

Accordingly, it would be desirable to provide a method and equipment for producing contoured composite laminate stiffeners that reduce or eliminate ply wrinkling.

<CIT>, in accordance with its abstract, states a tool for making contoured composite hat stringers allows control of stringer wrinkling. The tool includes a set of first openings that allow the tool to flex during contouring of the stringer, and a set of second openings into which portions of the composite charge may strain during the contouring.

<CIT>, in accordance with 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.

The disclosure relates in general to methods and equipment for producing composite structures, and more particularly to compression mold tooling employing diffusers that reduce wrinkling of a composite laminate stiffener as it is being contoured along its length.

According to one aspect, apparatus is provided for forming a contoured composite laminate stiffener. The apparatus comprises first and second dies between which a multi-ply ply composite charge may be formed into a stiffener. The dies are configured to form a contour in the stiffener. The apparatus further includes at least a first diffuser positioned between the first die and the second die which is configured to diffuse wrinkles in the stiffener is being formed to the contour.

According to another aspect, apparatus is provided for making a contoured composite laminate stringer having a flange and a web. The apparatus includes a first die and a second die between which a multi-ply ply composite charge may be formed into a stringer shape having a flange and a web, and contoured along its length. A first wrinkle diffuser is mounted on the first die and a second wrinkle diffuser is mounted on the second die opposing the first wrinkle diffuser. The first and second wrinkle diffusers are configured to diffuse wrinkles in the flange and the web as the charges is being formed to the contour.

According to a further aspect, a method is provided of making a contoured composite laminate stiffener. A multi-ply ply composite charge along with at least one wrinkle diffuser are placed between first and second dies. The composite charge is formed into a stiffener having a desired cross-sectional shape by compressing the charge between the dies. The stiffener is formed to a desired contour having in inside radius. Wrinkling of the stiffener along the inside radius is controlled using the wrinkle diffuser.

One of the advantages of the disclosed method and apparatus is that ply wrinkling of composite laminate stiffeners during contouring is controlled, so that undesired ply wrinkling is reduced. Another advantage is that the size and/or other physical characteristics such as frequency and spacing of ply wrinkles is controlled to a level that does not materially affect stiffener performance. Still another advantage of the disclosed method and apparatus is that scrap and rework of stiffeners caused by unacceptable ply wrinkling is reduced or eliminated. A further advantage is that diffusers used to reduce ply wrinkling are readily adapted for use with existing tooling employed to form the stiffeners. Additionally, the diffusers are easily interchanged and/or replaced, thus allowing the diffusers to be used with different tools employed to form various configurations of stiffeners.

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>, 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 an outer skin <NUM> that is reinforced and stabilized by stiffeners <NUM> such as stringers <NUM>. For example, as shown in <FIG>, each of the wings <NUM> includes a wing box <NUM> formed by spars <NUM>, ribs <NUM> and stringers <NUM> that are covered by a composite laminate skin <NUM> such as a carbon fiber reinforced polymer (CFRP) laminate. The wing box <NUM> includes an upper wing panel <NUM> and a lower wing panel <NUM>. In the illustrated example, the stiffeners <NUM> are blade-type stringers <NUM>, however, the principals disclosed herein are applicable to a wide range of other types of stringers such as, without limitation, I, J, Y , Z and hat stringers. Each of the stringers <NUM> is joined to the IML (inner mold line) of the skin <NUM>, typically by co-curing or by co-bonding.

Depending upon the application, the stringers <NUM> may have various out of plane features such as contours, pad ups and/or joggles at one or more locations along their length. 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, referring to <FIG>, a blade type stringer <NUM> such as that used in the wing of <FIG> comprises a blade <NUM>, sometimes also referred to herein as a web <NUM>, and a flange <NUM> extending perpendicular to the blade <NUM>. In this example, 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 shown in in <FIG> is concave downwardly however it may be concave upwardly, depending on the application. Further, the stringer <NUM> may have one or more contours along its length in the XY plane, and in some examples, the stringer <NUM> may have compound contours comprising contours in both the XZ and XY planes. Each of the web <NUM> and the flange <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 illustrates one form of tooling <NUM> using compression dies that form the blade type stringer <NUM> or a similar stiffener <NUM> using a fiber-reinforced composite charge <NUM> (hereinafter referred to as a "charge"), which in the illustrated example is generally flat and comprises multiple plies <NUM> of a fiber reinforced composite material. The charge <NUM> may also include pad-up plies <NUM>. The plies <NUM> may comprise a fiber-reinforced polymer such as, for example and without limitation, a thermoset or thermoplastic reinforced with continuous fibers such as carbon fibers. The tooling <NUM> broadly comprises an upper die <NUM> mounted on an upper flexible plate <NUM>, and a lower die <NUM> mounted on a lower flexible plate <NUM>. The upper die <NUM> includes a punch <NUM> having a blade-like shape that is provided with slits <NUM> along its length. The slits <NUM> segment the punch <NUM> into a plurality of punch portions <NUM> that allow the punch <NUM> to flex along its length.

The lower die <NUM> comprises a pair of die blocks <NUM> that are segmented <NUM> along their lengths. The die blocks <NUM> are spaced apart from each other to form a die cavity <NUM> into which the charge <NUM> can be formed by the punch <NUM> as the upper die <NUM> is closed against the lower die <NUM>. The die blocks <NUM> are laterally slideable <NUM> toward and away from each other on the lower flexible plate <NUM>. Segmentation <NUM> of the die blocks <NUM> allows them to flex along their lengths.

A pair of L-shape brackets <NUM> are mounted on and extend along the length of the lower flexible plate <NUM>, on opposite sides of lower die <NUM>. The L-shape brackets <NUM> function to both retain the die blocks <NUM> on the lower flexible plate <NUM>, and react lateral forming forces generated by the die blocks <NUM> during a forming operation. A pair of inflatable hoses <NUM>, sometimes referred to as bags or bladders, are sandwiched between the L-shape brackets <NUM> and the die blocks <NUM>, and are adapted to be coupled with a suitable source of pressurized air (not shown). The inflatable hoses <NUM> may be selectively pressurized in order to apply a lateral force on the die blocks <NUM> during forming and/or contouring operations. Other mechanisms, however, may be provided to apply the lateral force to the die blocks <NUM>.

As mentioned earlier, the flange <NUM> of the stringer <NUM> may have a variable thickness in localized areas along its length in order to conform the stringer <NUM> to local contours of the structure to which it is attached, such as a skin <NUM>. In order to accommodate these thickness variations so that a constant pressure is evenly applied to the composite charge <NUM> in these localized areas, shims (not shown) may be placed on or beneath the die blocks <NUM>, as necessary along their length so as to conform to the local contours caused by these thickness variations. As the charge <NUM> is formed to a desired contour, both of the die blocks <NUM> flex as necessary to maintain a constant forming pressure on the charge <NUM>. As will be discussed below, during a forming operation, a charge <NUM> is place on the top <NUM> of the die blocks <NUM>, and the upper and lower dies are closed against each other at a controlled rate, effectively punch forming the charge <NUM> to the desire stringer cross sectional shape. In the illustrated stringer example, the flange <NUM> of the stringer <NUM> is formed between the top <NUM> of the die blocks <NUM> and the upper plate <NUM>, while the blade or web <NUM> of the stringer <NUM> is formed between the punch <NUM> and the sides <NUM> of the die blocks <NUM>.

<FIG> illustrates a former <NUM> which incorporates the tooling <NUM> shown in <FIG>, along with a die changing mechanism <NUM>. The die changing mechanism <NUM> may comprise, for example and without limitation, a press <NUM> and a plurality of individual, spaced apart actuators <NUM>. The actuators <NUM> are respectively mounted on opposing press plates <NUM> of the press <NUM> that are adapted for movement toward and away from each other, indicated by the arrows <NUM>. The tooling <NUM> is installed between the press plates <NUM>. The press plates <NUM> may be coupled with any suitable power operated mechanisms such as cylinder actuators (not shown) which displace the press plates <NUM> to open/close the tooling <NUM> during a charge forming operation.

The die changing mechanism <NUM> changes the shape of the dies <NUM>, <NUM>, thereby contouring the partially formed charge <NUM>. This contouring process causes portions of the charge <NUM> to be placed in tension while other portions are placed in compression. Compression of the charge <NUM> in this manner results in the formation of wrinkles in the plies <NUM> of the charge <NUM>, typically along the inside radius <NUM> of the contour <NUM>. According to one aspect of this disclosure however, wrinkle diffusers, discussed in more detail below (but not shown in <FIG>) are installed between the charge <NUM> and the upper and lower dies <NUM>, <NUM> and function to control wrinkling and/or buckling of the charge <NUM> during a contouring operation. Each of the actuators <NUM> includes a plunger <NUM> coupled with one of the upper and lower flexible plates <NUM>, <NUM> that applies a bending force to these two plates in order to bend them to a desired stringer contour. Bending the upper and lower flexible plates <NUM>, <NUM> in turn bends the die blocks <NUM>, thereby contouring the stringer <NUM> along its length. Other mechanisms however, may be employed to contour the tooling <NUM> along its length. In some examples, the charge <NUM> is first punch formed to the desired stringer cross sectional shape, and is subsequently contoured along its length by the die changing mechanism <NUM>. In other examples however, the dies <NUM>, <NUM> are first contoured by the die changing mechanism <NUM>, following which the charge <NUM> is punch formed to the desired cross sectional shape.

The sequential steps for forming a charge <NUM> into a desired stringer cross sectional shape are shown in <FIG>. Referring first to <FIG>, a pair of first wrinkle diffusers 114a, 114b, also referred to herein as upper diffusers 114a, 114b, are installed on the upper die <NUM>, on opposite sides of the punch <NUM>. A pair of second wrinkle diffusers 116a, 116b, also referred to herein as lower diffusers 116a, 116b are installed on the die blocks <NUM> of the lower die <NUM>. The upper diffusers 114a, 114b and lower diffusers 116a, 116b function to control wrinkling of the charge <NUM> as it is being formed into a desired stringer contour <NUM> (<FIG>) by diffusing the wrinkles into a series of smaller wrinkles having a predetermined length-to-depth ratio.

With the upper die <NUM> in a raised position (<FIG>) and the die blocks <NUM> in their open, spaced apart position, a flat, multi-ply ply composite charge <NUM> is placed on the lower die <NUM>, overlying flange sections <NUM> of the lower diffusers 116a, 116b. Next, as shown in <FIG>, a downward force F is applied to the upper die <NUM>, causing the punch <NUM> to form the charge <NUM> into the die cavity <NUM> while the upper plate <NUM> compresses the flanges <NUM> of the charge <NUM> against the die blocks <NUM>. With the partially formed charge <NUM> restrained between the upper and lower dies <NUM>, <NUM>, the charge <NUM> is contoured along its length using the die changing mechanism <NUM> as described earlier in connection with <FIG>. During this contouring operation, the inside radius <NUM> of portions of both the web <NUM> and the flange <NUM> are placed in compression, which may cause them to wrinkle or buckle along the contour <NUM>. As will be discussed later, the wrinkle diffusers <NUM>, <NUM> are configured to diffuse the wrinkles in a manner that reduces any undesired effect on the performance of the stiffener <NUM>.

Referring to <FIG>, following the contouring operation, the upper die <NUM> is displaced upwardly, causing the punch <NUM> to be withdrawn from the die cavity <NUM>. Next, as shown in <FIG>, the upper die <NUM> is replaced by a flat plate <NUM>, which is placed on top of the flange <NUM> of the partially formed charge <NUM>. A downward force F is applied to the flat plate <NUM> which causes it to force the left and right portions of the flange <NUM> against the die blocks <NUM>, thereby restraining the flange <NUM>. With the flange <NUM> restrained by the flat plate <NUM>, the die blocks <NUM> are forced <NUM> toward each other, causing the open web <NUM> to close and form a blade <NUM>. In the example described above in connection with <FIG>, the charge <NUM> is punch formed to a desired cross-sectional shape before it is contoured along its length. However, in other examples, the dies <NUM>, <NUM> are first changed to the desired contour by the die changing mechanism <NUM>, following which the charge <NUM> is punch formed into the contoured dies <NUM>, <NUM>, thereby simultaneously forming and contouring the stiffener <NUM>.

The type and placement of the diffusers <NUM>, <NUM> on the dies <NUM>, <NUM> will vary with the application. Depending on the geometry of the stiffener <NUM>, the number and severity of the contours and other factors, the diffusers <NUM>, <NUM> may be installed on some tool surfaces of the dies <NUM>, <NUM> but not on others. For example, referring to <FIG>, an upper diffuser 114a is installed on the upper die <NUM> on only the left side of the punch <NUM>. In order to assure that equal pressure is applied to both the left and right portions of the flange <NUM> of the charge <NUM> during the forming process, an inflatable bladder <NUM> is placed on the right portion of the flange <NUM>. When inflated (<FIG>), the inflatable bladder <NUM> applies pressure to the right portion of the flange <NUM>, substantially equal to the pressure applied to left portion by the upper diffuser 114a. During the forming process, the inflatable bladder <NUM> is deflated at a controlled rate in order to reduce the applied pressure enough to allow the right portion of the flange <NUM> to slip between the upper die <NUM> and the die block <NUM>, similar to slippage of the left portion as the punch <NUM> forms the charge <NUM> into the die cavity <NUM>.

As will be discussed below, the diffusers <NUM>, <NUM> function to control the dimensions and geometry of the wrinkles that are formed in the charge <NUM> in those areas of the stiffener <NUM> that are placed under compression during the forming/contouring process, such as along the inside radius <NUM> of contours <NUM> or other out-of-plane features in the stiffener <NUM>. Rather than allowing wrinkles of uncontrolled size, shape, and spacing to form, which may have an undesirable effect on stiffener performance, the wrinkling is diffused by forcing the formation of wrinkles that are a desired size, shape, and/or spacing, and thereby are configured to have minimal or no effect on stiffener performance. This controlled wrinkling is achieved by providing depressions in the diffusers <NUM>, <NUM> into which the portions of the charge <NUM> may strain as a result of the compressive stresses in the charge <NUM> caused by the forming/contouring process.

<FIG> illustrates one example of diffused wrinkles <NUM> formed by the diffusers <NUM>, <NUM> in a charge <NUM> along an inside radius <NUM> of the contour <NUM> (<FIG>) in the stiffener <NUM>. In this example, the wrinkles <NUM> form a sine wave pattern in which each of the wrinkles <NUM> has a preselected length L (wavelength) and depth D, resulting in a desired length-to-depth (L/D) ratio. Although a sine wave pattern of wrinkles is shown in <FIG>, the diffusers <NUM>, <NUM> may be configured to produce various other patterns of wrinkles <NUM> having a desired L/D. Depending upon the geometry of the stiffener <NUM>, the wavelength L and/or the depth D of the wrinkles <NUM> may vary along the length of the stiffener <NUM> in order to address local stiffener conditions such as changes in the geometry of the stiffener <NUM>. Another example of diffused wrinkles <NUM> that can be formed by the wrinkle diffusers <NUM>, <NUM> is shown in <FIG>, wherein individual wrinkles <NUM> are formed that have length L and a depth D. In this example, the wrinkles <NUM> are formed only on one side of the charge <NUM>, for example on the inside radius <NUM> of the stiffener <NUM>. However, depending upon the geometry of the stiffener <NUM>, the wrinkles <NUM> may be formed on both sides of the charge <NUM>. In the example shown in <FIG>, the length L is constant, however in other examples, the length L of the wrinkles <NUM> may vary to address local stiffener conditions, such as where there is variation in the contour <NUM> of the stiffener <NUM>. As will become apparent below, a variety of other controlled wrinkle configurations can be achieved using the wrinkle diffusers <NUM>, <NUM>.

Attention is now directed to <FIG> illustrating one example of the diffusers <NUM>, <NUM>, which respectively may be sometimes referred to herein as first and second diffusers <NUM>, <NUM>, or upper and lower diffusers <NUM>, <NUM>. Each of the upper diffusers <NUM> comprises a plurality of interconnected plates <NUM>, each formed of a flexible material such as a metal or a composite may be removably attached to the upper die <NUM> by any suitable means, such as magnets or fasteners (not shown). Each of the plates <NUM> includes a plurality of spaced apart depressions <NUM> therein along its length, each of which is configured to form a wrinkle having a desired length L and depth D. In the illustrated example, the depressions <NUM> comprise first depressions 122a and second depressions 122b in the form of slots or gaps that are arranged in alternating relationship to each other. As used herein, the term "depressions" includes, without limitation gaps, slots, cavities, voids, pockets and similar out-of-plane features in the surface of the plate <NUM> that form spaces into which portions of the charge <NUM> may strain as a result of compressive stresses in the charge <NUM>.

In the example shown in <FIG>, the plates <NUM> are interconnected by interlocks <NUM> comprising tabs <NUM> in one end of the plate <NUM> that are received within matching notches <NUM> in the end of an adjoining plate <NUM>. Other techniques for interconnecting the plates <NUM> are possible. Also, depending on the length of the stiffener <NUM> being formed, each of the plates <NUM> may comprise a single piece, rather than multiple, interconnected pieces. As previously mentioned, the upper diffusers <NUM> can be removably attached to the upper die <NUM> using any of several techniques, including fasteners or magnets. In one example, magnets (not shown) installed on the upper die <NUM>, are received within recesses <NUM> in the backside of the plates <NUM>, thus providing a means of removably holding the plates <NUM> in proper registration on the upper dies <NUM>. In other examples, the plates <NUM> can be permanently attached to, embedded or otherwise incorporated into the upper dies <NUM>.

Referring particularly to <FIG>, the dimensions of the depressions 122a, 122b will vary depending on the application, as well as the length L and depth D of the wrinkles <NUM> that are to be formed. In the illustrated example, the depressions 122a, 122b are in the shape of slots, however other shapes are possible. The depressions 122a each have a length L1 that is greater than the length L2 of the depressions 122b. The widths W1, W2 of the depressions 122a, 122b may be the same or different from each other, and will depend upon the dimensions of the wrinkles <NUM> to be formed. Finally, the pitch P1 between the depressions 122a, the pitch P2 between depressions 122b, and the pitch P3 between depressions 122a, 122b will also vary depending on the dimensions of the wrinkles <NUM> to be formed. Additionally, although not shown in <FIG>, the depths of the depressions 122a, 122b are selected to achieve a desired depth D of the wrinkles <NUM>.

<FIG> illustrates another example of an upper diffuser <NUM> in which depressions <NUM> in the form of slots are equally spaced, and have the same lengths L, width W and depth D. As previously mentioned, the size, shape and frequency of the depressions <NUM> may vary along the length of the upper diffuser <NUM>. For example, <FIG> illustrates an upper diffuser <NUM> having various forms of depressions <NUM> in different sections <NUM>-<NUM> of the plate <NUM>. The depressions <NUM> in section <NUM> have the same widths and lengths as those in an adjoining section <NUM> but have different pitches P1, P2. The depressions <NUM> in another section <NUM> have a width W greater than those in sections <NUM> and <NUM>. Section <NUM> is devoid of any depressions <NUM>, while an adjoining section <NUM> includes depressions 122a, 122b of two different lengths. Depending on local stiffener geometry, one or more sections <NUM> of the upper diffuser <NUM> may include depressions <NUM> that are oriented at an angle relative to the longitudinal axis <NUM> of the diffuser <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, each of the lower diffusers <NUM> comprises multiple diffuser segments <NUM> mounted on the die blocks <NUM> and interconnected using interlocks <NUM>, similar to the interlocks <NUM> described above in connection with the upper diffusers <NUM>. The diffuser segments <NUM> are formed of a suitable flexible material such as a metal or a composite similar to the upper diffusers <NUM>. Each of the diffuser segments <NUM> has an L-shaped cross section formed by a flange section <NUM> overlying the top of the die block <NUM>, and a web section <NUM> covering a side of the die block <NUM> within the die cavity <NUM>. As best seen in <FIG> and <FIG>, the flange sections <NUM> include hooked ends <NUM> that extend down over the backside <NUM> (<FIG>) of the die blocks <NUM>, and function to retain the lower diffusers <NUM> in proper registration on the die blocks <NUM>. The lower diffusers <NUM> can be removably or permanently attached to, embedded or otherwise incorporated into the lower die blocks <NUM>. Removable attachment of the upper and lower diffusers <NUM>, <NUM> to the upper and lower dies <NUM>, <NUM> allows the diffusers to be interchanged so that differently configured diffusers can be used the same set of dies.

Each of the lower diffusers <NUM> includes first and second sets of depressions 124a, 124b in the form of slots having two different lengths that are arranged in an alternating configuration similar to the slots in the upper diffusers <NUM>. However, other forms of depressions 124a, 124b in the lower diffusers <NUM> are possible. The depressions 124a, 124b extend transverse to the longitudinal axis of the lower die <NUM>, across the flange section <NUM>, and down through the web section <NUM>. In the illustrated example, the depressions 124a, 124b in the flange section <NUM> are aligned with the depressions 122a, 122b, however in other examples these two sets of depressions may be offset from each other. Similarly, the depressions 124a, 124b in the facing web sections <NUM> of the lower diffusers <NUM> are aligned with each other in the illustrated example, but in other examples they may be offset from each other.

It should be noted here that in the illustrated examples described above, the depressions <NUM> are formed in plates or similar members that are attached to the upper and lower dies <NUM>, <NUM>. However, in other examples, the diffusers <NUM>, <NUM> may comprise depressions <NUM> that are formed in the tool surfaces of the upper and lower dies <NUM>, <NUM>, as by machining or other techniques.

Attention is now directed to <FIG>, which illustrates how the upper and lower diffusers <NUM>, <NUM> diffuse wrinkles in the flange <NUM> as the stiffener <NUM> is being contoured along its length. Upon completion of the final step of forming the charge <NUM> into the desired cross-sectional shape of the stiffener <NUM> (<FIG>), the stiffener <NUM> is formed to the desired contour using the die changing mechanism <NUM> discussed above in connection with <FIG>. In the illustrated example, the stiffener <NUM> is contoured downwardly as shown in <FIG>. Contouring the stiffener <NUM> in this manner causes the plies <NUM> in upper regions <NUM> of the flange section <NUM> to be placed in tension T, while those plies <NUM> in the lower regions <NUM> are placed in compression C. The depressions <NUM> in the lower diffuser <NUM> adjacent the lower regions <NUM> provide a space into which the fibers and resin of the plies <NUM> may strain and form diffused wrinkles <NUM> that have predetermined lengths and depths. Because the depressions <NUM> in the lower diffuser <NUM> have a uniform depth and pitch, a series of substantially identical wrinkles <NUM> are formed within the depressions <NUM>. Effectively, the wrinkling caused by the compressive forces C is diffused, and uncontrolled formation of potentially undesirable wrinkles is avoided.

Referring to both <FIG> and <FIG>, although not shown in the Figures, if the stiffener <NUM> shown in <FIG> is contoured upwardly rather than downwardly, compressive stresses would be generated in the upper region <NUM>, causing the plies <NUM> in this region to strain into the depressions <NUM> in the upper diffuser <NUM>. The exact location in the stiffener where compressive stresses may be generated will depend upon the location and direction of the contouring. Ply wrinkling in stiffeners <NUM> having compound curvatures or contours (those occurring in both the XY and XZ planes) can be mitigated using wrinkle diffusers that are specifically configured to address the localized stresses caused by these types of contours.

<FIG> illustrates how the lower diffusers <NUM> diffuse wrinkles in the web <NUM> of the charge <NUM> as the stiffener <NUM> is being contoured along its length. During contouring of the stiffener <NUM> into the downwardly concave shape shown in <FIG>, the upper region <NUM> of the web <NUM> is in tension while the lower region <NUM> is in compression. The sectional view shown in <FIG> is taken through the lower region <NUM>. The compressive forces present in the lower region <NUM> create compressive stresses in the plies <NUM>, which causes the plies <NUM> on each side of the web <NUM> strain into the depressions <NUM>, thereby forming wrinkles <NUM> having predetermined and uniform length-to-depth ratios. Similar to the wrinkle diffusion that occurs in the flange <NUM>, wrinkling caused by the compressive stresses in the lower region <NUM> of the web <NUM> is diffused, and formation of larger undesirable wrinkles is avoided. In the event that the stiffener <NUM> shown in <FIG> is contoured upwardly rather than downwardly, the compressive forces would be generated in the upper region <NUM>, causing the outer plies <NUM> in this region to strain into the depressions <NUM> in the upper region <NUM> of the lower diffusers <NUM>.

Attention is now directed to <FIG>, which illustrate another example of diffusers installed on the tooling <NUM>. A pair of first diffusers <NUM>, sometimes referred to herein as upper diffusers <NUM> are installed on the upper plate <NUM>, on opposite sides of the punch <NUM>. A pair of second diffusers <NUM>, also referred to as lower diffusers <NUM>, are respectively installed on the die blocks <NUM> of the lower die <NUM>. Each of the upper diffusers <NUM> comprises a diffuser plate <NUM> removably attached to the upper plate <NUM> by any suitable means, such as by magnets or fasteners (both not shown), similar to the upper diffusers <NUM> described in connection with <FIG>. As will be described below in more detail, each of the upper and lower diffusers <NUM>, <NUM> have features that diffuse wrinkles formed in the stiffener <NUM> as it is being contoured.

Referring to <FIG>, <FIG>, each of the upper diffusers <NUM> includes a plurality of groove-like depressions <NUM> therein which, in the illustrated example, extend parallel to each other and transverse to the longitudinal axis of the upper die <NUM>. In other examples, however, the depressions <NUM> may extend at an angle upper die <NUM>, and may not be parallel to each other, depending upon local out-of-plane conditions in the stiffener <NUM>. Each of the depressions <NUM> comprises alternating peaks <NUM> and troughs <NUM> forming a serpentine pattern when viewed in cross section. As best seen in <FIG>, the depressions <NUM> are formed by flat surfaces in the plate <NUM>, however, in other examples these surfaces may be curved to form a smooth wave having a preselected length L (wavelength) and depth D, similar to the depressions <NUM> previously discussed in connection with the example shown in <FIG>. The length L, depth D, and frequency may very along the length of the upper diffuser <NUM>.

<FIG> illustrate additional details of the lower diffusers <NUM>. Each of the lower diffusers <NUM> is L-shaped in cross-section, and includes a flange section <NUM> and a web section <NUM>. The flange section <NUM> includes a second set of depressions <NUM> that are substantially identical to the first depressions <NUM> in the upper diffuser <NUM>. The web section <NUM> of the lower diffuser <NUM> includes groove-like second depressions <NUM> substantially identical in cross-sectional shape to the depressions <NUM> in the flange section <NUM>. In the illustrated embodiment the depressions <NUM> in the flange section <NUM> and web section <NUM> are aligned with each other, however, in other examples, they may be offset from each other. Optionally, the web section <NUM> may include slots <NUM> or similar openings that are located at the peaks and troughs <NUM> of the depressions <NUM>. The depressions <NUM>, <NUM> as well as the slots <NUM> can be formed directly in the tool surfaces of the die blocks <NUM>, rather than in members that are attached to the die blocks <NUM>.

<FIG> illustrates the web portion of the charge <NUM> being compressed between the opposing, wave shaped surfaces <NUM> of the upper and lower diffusers <NUM>, <NUM>, resulting in a sine wave pattern having a desired length L and depth D. <FIG> shows how the opposing wave shaped surfaces <NUM> of the opposing web sections <NUM> form the web section of the charge <NUM> into a sine wave pattern having a desired length L and depth D. Additionally, the slots <NUM> provide additional space in the diffusers <NUM> into which the charge <NUM> may strain, while providing the diffusers <NUM> with additional flexibility to better allow them to be contoured by the die changing mechanism <NUM>.

<FIG> broadly illustrates the steps of a method of making a contoured composite laminate stiffener. Beginning at <NUM>, a multi-ply composite charge <NUM> is placed between first and second dies <NUM>, <NUM>. At <NUM>, at least one wrinkle diffuser <NUM> is placed between the first and second dies <NUM>, <NUM>. At <NUM>, the multi-ply composite charge <NUM> is formed into a stiffener <NUM> having a desired cross-sectional shape by compressing the composite charge <NUM> between the first and second dies <NUM>, <NUM>. At <NUM>, the stiffener <NUM> is contoured to a desired contour <NUM> having an inside radius <NUM>. At <NUM>, wrinkling of the stiffener <NUM> is controlled during the contouring using the wrinkle diffusers <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 contoured stiffeners such as 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 <NUM> as shown in <FIG>. Aircraft applications of the disclosed examples may include a variety of the elongate stiffeners such as stringers that have contours, curvatures, varying thicknesses or other out-of-plane features along their lengths. During preproduction, 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>.

Claim 1:
Apparatus for making a contoured composite laminate stringer (<NUM>) having a flange (<NUM>) and a web (<NUM>), comprising:
a first die (<NUM>) and a second die (<NUM>) between which a multi-ply composite charge (<NUM>) may be formed into a flange (<NUM>) and a web (<NUM>) having a contour (<NUM>); and
a first wrinkle diffuser (<NUM>, <NUM>) on the first die (<NUM>); and
a second wrinkle diffuser (<NUM>, <NUM>) on the second die (<NUM>) and opposing the first wrinkle diffuser (<NUM>, <NUM>), wherein the first and second wrinkle diffusers (<NUM>, <NUM>, <NUM>, <NUM>) are configured to diffuse wrinkles (<NUM>) in the contour (<NUM>) of the flange (<NUM>) and the web (<NUM>) as the multi-ply composite charge (<NUM>) is being formed wherein each of the first wrinkle diffuser (<NUM>, <NUM>) and the second wrinkle diffuser (<NUM>, <NUM>) includes a plurality of depressions therein (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) into which the multi-ply composite charge (<NUM>) may strain within the contour (<NUM>) as the multi-ply composite charge (<NUM>) is being formed to the contour (<NUM>).