Method for high rate production of composite laminate structures

Multi-ply composite charges are laid up by a multi-head laminator in a single pass, enabling high rate production of composite laminate structures such as stringers.

BACKGROUND INFORMATION

The present disclosure generally relates to processes and equipment used to form composite structures, and deals more particularly with a method and apparatus for high rate production of charges used to form composite laminate structures.

Composite laminate structures such as stiffeners are used throughout the aircraft, marine and other industries. For example, composite laminate stringers having any of various cross sectional shapes are used in the fuselage and wings of airplanes. These stringers often have one or more contours or other out-of-plane features along their lengths.

Composite laminate stiffeners can be made by compression forming a flat stack of composite plies, sometime referred to as a charge, between a pair of dies matching the desired stringer shape. This technique, sometimes referred to as “punch forming”, is problematic when producing contoured stringers because of the tendency of the plies in contoured areas to wrinkle or buckle during the forming process. The flat charge is produced either by hand layup or using automated equipment, both of which build the charge ply-by-ply. These techniques are both costly and relatively slow, and therefore not well-suited high volume production.

Accordingly, there is a need for a method and apparatus for producing charges used to form composite laminate structures that are highly efficient and therefore well suited for high rate production environments.

SUMMARY

The disclosure relates in general to composite structures, and more specifically to a method and apparatus for high rate production of charges used to form composite laminate stringers.

According to one aspect, an apparatus is provided for laying up a flat composite charge. The apparatus comprises a laminator including a plurality of tape heads arranged in series and mounted on supporting frame.

According to another aspect, a method is provided of making charges used to form composite structures. The method comprises laying up a stack of fiber prepreg plies by laying down strips of fiber prepreg tape on top of each other simultaneously in a row over a substrate using a plurality of tape heads.

According to a further aspect, a method is provided of making composite charge used to form composite laminate structures. The method comprises laying up at least first and second stacks of fiber prepreg plies simultaneously. The method includes laying down strips of fiber prepreg tape on top of each other in a row by moving a group of tape heads over first and second substrates, wherein the group of tape heads begin to lay up the second stack of plies while simultaneously completing laying up the first stack of plies.

According to another aspect, a method is provided of making a contoured composite laminate structure. The method comprises predicting loads on the composite structure along its length, and generating a ply schedule based on the predicted loads. The ply schedule includes plies having differing fiber orientations, including determining the contribution of each of the plies in the ply schedule required to meet the loads. The method also includes determining an amount of stretching of each of the plies in the ply schedule required for forming the plies into the desired structure shape without ply wrinkling. The method further includes selecting a length of the fibers in each of the plies representing an optimized combination of structure strength and formability. The method also includes laying up the flat stack of the plies in accordance with the ply schedule, and forming the flat stack of plies into the desired structure shape.

According to a further aspect, a method is provided of making a composite charge used to form a composite structure. The method comprises laying up a stack of fiber prepreg plies by laying down strips of fiber prepreg tape on top of each other on substrate, and compacting the strips of fiber prepreg tape in series as the strips of fiber prepreg tape are being laid down.

One of the advantages of the disclosed method and apparatus is that multi-ply composite charges can be laid up more quickly. Another advantage is that labor costs of laying up flat composite charges can be reduced. A further advantage is that flat composite charges can be produced that are well suited for forming highly contoured composite laminate stiffeners that are tailored along their length to meet local load demands or other requirements. A further advantage is that flat composite charges can be produced that can be formed into contoured laminate stringers with minimal or no ply wrinkling. Still another advantage is that flat composite charges can be produced in sections that are later joined together.

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.

DETAILED DESCRIPTION

Referring first toFIG.1, an airplane40has airframe components38including a fuselage42, wings44and an empennage48comprising a vertical stabilizer50and horizontal stabilizers52. Engines46are suspended from the wings44by pylons56. Each of the airframe components38includes an outer skin53that is reinforced and stabilized by stiffeners such as stringers54, comprising a composite laminate such as a carbon fiber reinforced polymer (CFRP). Each of the stringers54may have any of a variety of cross sectional shapes, such as, without limitation, I, J, Y, Z, and hat shapes. The stringers54are joined to the IML (inner mold line) of the outer skin53, typically by co-curing or by co-bonding.

The nature of the loads carried by the stringers54is different than those carried by the outer skin53and other components such floor beams and control surfaces (both not shown), making stringers54unique in their design and production. The design and production of stringers54used in airplanes can be particularly challenging because they are seldom straight, but rather comprise differing sections that are contoured and tailored to suit local conditions and/or structural geometries. For example, referring toFIG.2, an inboard section74of a wing44possesses a curvature that requires the stringers54in this section to be similarly curved. An intermediate section76of the wing44that supports the weight of a pylon56and engine46may require ramps, pad ups or other out-of-plane features in the stringers54in order to carry added loads. An outboard section78of the wing44may include internal components (not shown) that require that the stringers54in this section have joggles or unique features. The loads that a stringer54may be required to react in the inboard section74, as well as the intermediate section76, and also the outboard section78of the wing44can be quite different, consequently it is often necessary to tailor the stringer54along its length to meet local load conditions in the inboard section74, the intermediate section76, and the outboard section78.

As indicated above, a stringer54may have any of a variety of out-of-plane features at differing sections along its length. As used herein, “contoured” and “contoured stringer” refer to a stringer having one or more out-of-plane features or sections, including but not limited to ramps, pad-ups, curvatures and/or joggles.FIGS.3and4illustrate stringers54that are contoured and have typical out-of-plane features. For example, referring toFIG.3, a stringer54such as that used in the wings44of the airplane40shown inFIGS.1and2comprises a blade58, sometimes referred to as a web, and a flange or cap60that is configured to match contours of the outer skin53to which the cap60is to be attached. In this example, the stringer54has a curvature70along its entire length in the XZ plane within coordinate system shown at61, however in other examples the stringer54may have straight sections as well as other local contours or out-of-plane features along its length.

Referring now toFIGS.5-9, composite laminate structures such as the stringers54described above can be produced by forming a charge80, sometimes referred to herein as a ply stack, to the desired shape. The charge80is formed of a composite and may be flat. The tendency of a composite charge to wrinkle or buckle during the forming process due to the presence of out-of-plane features can be reduced or eliminated by optimizing the plies of the charge in the manner described below. Highly formable flat charges comprising optimized plies can be laid up quickly and efficiently using the method and apparatus described later in this description. During layup of the charge, the plies can be tailored along the length of the charge to meet local load demands and other requirements in the inboard section74, the intermediate section76, and the outboard section78of a wing other area of the airplane40.

The charge80comprises an optimized stack of plies82, each of which comprises fibers92held in a polymer matrix that provide unidirectional reinforcement. The fibers92may comprise carbon, fiberglass, Kevlar® or other suitable fibers, while the polymer matrix may comprise a suitable thermoset or thermoplastic, or a hybrid material system containing both a thermoset and a thermoplastic, depending on the application. The plies82may have various fiber orientations relative to a reference direction86, such as the longitudinal axis84(FIG.4) of the stringer54to be formed using the charge80. In some examples, each of the plies82comprises fiber prepreg tape having a width that is equal to the width W of the charge80(FIG.5), and a thickness T that is suitable for the application. The plies82of the charge80are laid up using a later discussed automated tape laying laminator that lays up all of the plies82of the charge80on top of each other substantially simultaneously, thereby contributing to production efficiency. The charge80can be formed to the desired shape by any of several techniques, including compression “punch” forming, LASH forming or stretch forming, to name only a few.

The plies82of the charge80are laid up as a flat stack according to a predetermined ply schedule which determines the number of plies82and the fiber orientation of each of the plies82. For example, as shown inFIG.7, a charge80may be formed of any number of 0°, +45°, −45°, and 90° plies (only 4 plies of the charge are shown). Each of the 0°, +45° and −45° plies82is provided with a pattern of angled cuts94therein, which sever the fibers92in those plies82and form ply segments96(FIG.9) each having a length L1. The spacing between the angled cuts94determines the length of the fibers92in the ply segment96. As will discussed below in more detail, the length of the fibers92and the angle of the angled cuts94relative to the fiber direction88are selected in a manner that optimizes the formability of the charge80without materially reducing the performance of the stringer54, including its strength. In the illustrated example, the 90° plies do not contain angled cuts94because they can readily stretch longitudinally in the reference direction86during forming of the charge80. However, in some examples, the 90° plies may contain cuts angled94for other reasons. It should be noted here that fiber angles (0°, ±45°, 90°) of the charge80used in this description are merely exemplary. A range of other fiber angles may be used, depending upon the application. For example, a different set of fiber angles may be required in applications where there is an emphasis on weight reduction.

FIGS.8and9, illustrate a 0° ply having one suitable pattern of angled cuts94. The angled cuts94are arranged in columns90that are staggered relative to each other a suitable distance95(FIG.8). The fibers92of the 0° plies are aligned with the reference direction86, and the angled cuts94in each column90are spaced apart from each to form groups of fibers92that will be referred to as ply segments96. Each ply segment96contains fibers92having a length L1that is determined by the longitudinal spacing between the angled cuts94. Generally, it is desirable that the length L1is as long as possible, providing that the desired formability can be achieved, because loads are transferred through the stringer54primarily along the X-axis (FIGS.3and4), i.e. in the reference direction86. However, in sections of the stringer54having tighter contours, such as along curvatures within the XZ plane, the fiber lengths L1may need to be shorter in order to allow the ° plies to stretch to a greater degree, and thereby allow them to better conform to contours.

As best seen inFIG.9, each of the angled cuts94forms an angle θ with respect to the direction of the fiber92. The length L1is determined by the spacing between the angled cuts94, and the angle θ Will depend upon the application, and more particularly on the load conditions, geometry and out-of-plane features at differing locations along the length of the stringer54. In one stringer example, L1is between approximately 10 inches and approximately 20 inches, while angle θ is in the range of approximately 10° to approximately 30°. In another example, L1is approximately 20 inches, and angle θ is approximately 15°. Generally, it has been found that cuts at an angle θ Of 15°, although severing the reinforcing fibers, minimizes any reductions in the strength of the stringer64, sometimes referred to as strength “knockdown”, in those areas where the fibers92are cut. Moreover, the use of angled cuts94at a 15° angle in combination with the pattern of angled cuts94disclosed herein, reduces any potential problems with removing the backing paper (not shown) on the fiber prepreg tape, particularly along the edges98of the plies82, as the plies82are being laid up by the automated laminator.

Referring toFIG.10, the fibers92in the +45° plies are oriented at a 45° angle relative to the reference direction86, and the fibers92in the ply segments96formed by the angled cuts94have a length L2. The angled cuts94form an angle θ relative to the fiber directions88in the +45° plies. Both the length L and the angle θ depend on the application and more particularly on the load conditions, geometry and out-of-plane features at differing locations along the length of the stringer54. In one example, L2is between approximately 2 inches and approximately 4 inches, and el is in the range of approximately 10° to approximately °. In another example, L2is approximately 2 inches, and el is approximately 15°. The length L2and angle θ for the −45° plies are substantially the same as those for the +45° plies. Generally, L2may need to be at the lower end of the range mentioned above in those areas where the stringer54is highly contoured within the YZ plane since the 45° plies need to stretch transversely a greater amount in this areas. In the case of a stringer54having ramps, the +45° and −45° fibers need to be shorter, typically in the range of 2 to 4 inches long, because there is a need for a greater amount of ply stretching in the ramps but a reduced need for strength compared to the 0° plies which primarily carry the loads along the X-axis.

The fiber lengths L1, L2and the cut angle θ are optimized for each stringer configuration to allow forming of the charge80to a desired contour at various sections along the length of the stringer54with minimal or no ply wrinkling. The need for providing the charge80with the ability to stretch during forming is particularly important in those sections of the stringer54, such as ramps, that have compound curvatures. Optimization of the fiber lengths L1and L2involves a selection process representing a balance between strength and formability in each ply direction (0°, +45°, −45°).

It should be noted here that while some sections of the charge80have angled cuts94to provide the necessary formability due to stringer contours, angled cuts94in other sections of the stringer54, such as straight sections, may not be required because those sections can be formed to shape without wrinkling. During the forming process, the angled cuts94in the 0° plies permit the fibers in those plies to separate slightly and move apart longitudinally in the reference direction86, allowing the ply to stretch and bend within the XZ plane (FIGS.3and4) without wrinkling. However, the fiber length L1is sufficient to maintain the strength necessary to carry loads on the stringer54at each section along its length. In a similar manner, the angled cuts94in the +45° and −45° plies allow the fibers92in those plies to move apart slightly in the transverse direction, allowing the +45° and −45° plies to stretch and bend as necessary in the YZ plane without wrinkling during the forming process.

The pattern of angled cuts94in the example shown inFIG.8is merely illustrative of a wide range of cut patterns that are possible. The particular pattern of angled cuts94chosen will depend upon the application, including the loading and other requirements of various sections of the stringer54along its length. In some examples, the angled cuts94may be randomly distributed over the area of each of the plies82.FIG.11illustrates a 0° ply having another example of a pattern of angled cuts94. In this example, the angled cuts94in alternate columns100are arranged at two opposite angles, +θ, −θ relative to the fiber direction88. In other words, the angles of the angled cuts94are reversed in alternate columns100and are staggered relative to each other. Staggering the angled cuts94disperses them, thereby reducing strength knockdown. This alternating arrangement of the angled cuts94minimizes the reduction in load carrying capacity of the 0° plies caused by the cuts. The angles of the angled cuts94, as well as the length L1of the cut fibers92are similar to those described earlier in connection with the example shown inFIGS.8and9. A similar arrangement of alternating cut angles can be used in the 45° plies (not shown) where the cut angles +θ, −θ as well as the cut fiber lengths L2will be similar to those described above in connection with the example shown inFIG.10.

As previously noted, the description above illustrates the use of a charge80suitable for forming stringers54, however similar design principals, which will be described in greater detail below, can be used to produce any of a wide variety of composite laminate components such as those used in the airframe of the airplane40. Each application requires optimization of a series of parameters, including but not limited to fiber angles, fiber length in each fiber direction, cutting patterns, manufacturability considerations of the chosen cutting pattern and the strains encountered when forming the charge80to a desired shape. The angled cuts94determine the fiber lengths in each fiber direction. Shorter ply segments96(fiber lengths) are more easily formed, but may have reduced strength, while longer ply segments96may be less formable but result in higher strength.

The cutting pattern selected determines the fiber length as well as the distribution of the angled cuts94. Also, appropriate consideration is given to the distribution of the cuts. For example, if all of the angled cuts94are located in a single, unique location in the charge80, the strength of the structure will be lower than if the cuts are fully disbursed through the volume of the charge80and/or disbursed through the area of each of the plies82. Thus, a cut pattern should be selected that disburses the angled cuts94over the area of each of the plies82.

As noted above, consideration must be given to the manufacturability of the chosen cutting pattern. The exit angle of the angled cut94relative to the direction in which the backing paper is removed significantly affects whether the backing paper is drawn away without snagging or leaving bits of paper on the prepreg. Any bits of backing paper left on the prepreg constitute FOD (foreign objects and debris) which will require removal, which not only adds to production costs, but may result in rejection of the part because it fails inspection. Furthermore, the chosen cutting pattern may also determine the type and design of the equipment used to produce the angled cuts. Some types of equipment designs may not be feasible to produce or may be prohibitively expensive for a particular application or production environment. Other equipment choices, while effective, may not be sufficiently efficient for high rate production.

As indicated earlier, designing a charge for a particular application requires careful consideration be given to the strains that result from forming the charge to particular shapes for a given application. Each application, such as skins, stringers, floor beans, floor panels and control surfaces for airplanes require different amounts of forming which produce different amounts of strains that require consideration when designing the charge. For example, some components such as floor panels are relatively flat, and may not require that any of the fibers in the plies of the charge be cut. Other components such as stringers, may be only slightly contoured but are required to possess a high degree of strength, thus giving rise to unique design considerations. In the case of wing stringers, the curvature of the stringers follows that of the curvature of the wing, which typically is on the order of a radius of 1000 inches. Thus, in the case of a wing stringer, it has been found that in order to maintain the necessary stringer strength while allowing forming of the charge to the necessary wing curvature, the fibers in the 0° plies of the charge should be cut to lengths in the range of approximately 10 to 20 inches. Fiber lengths that are longer than the high end of this range reduce the formability of the charge and increase the possibility of ply wrinkling which results in strength knockdown. However, fiber lengths that shorter than the low end of this range reduce the strength of the stringer below an acceptable level.

As described above, the fibers in the 0° plies82are cut to lengths between 10 and 20 inches to allow the 0° fibers92to stretch and allow the charge80to be formed to the curvature of the wing44along its length. In those locations where the stringer54must conform to out-of-plane features such as ramps on the outer skin53where the outer skin53thickens, forming the charge80into the shape of the ramps is dominated by shearing of the 45° fibers92, rather than their extension as in the case of the 0° fibers92. Consequently, the fibers92in the 45° plies82must stretch transversely considerably more than the 0° plies82must stretch to accommodate wing curvature. In order to achieve the necessary transverse stretch, the 45° fibers are cut to a shorter length, within the range of 2 to 4 inches, but only in those particular areas of the stringer54, e.g. the ramps, were a high degree of transverse stretching (shearing) is necessary during forming without ply wrinkling. Although the ° fibers92are cut to a length that is much less than the ° fibers92, any knockdown in strength of the stringer54is minimal and therefore acceptable because the primary loads on the stringer54are carried by the 0° plies82, rather than the 45° plies82. As discussed earlier, in areas of the stringer54that are not curved or have out of plane features, the fibers92in the plies82of the charge80in those areas need not be cut since those plies82are not required to stretch as the charge80is being formed to the desired stringers shape.

Attention is now directed toFIGS.12-16, which illustrate apparatus101for high rate of production of charges80, optimized as previously described connection withFIGS.5-11. The apparatus101comprises a laminator102, and a translator108, both of which are operated by a controller106. The controller106may comprise a suitable PC, PLC (programmable logic controller), or one or more digital processors. The translator108may comprise any suitable mechanism for moving the laminator102and a substrate114relative to each other. In one example, the substrate114comprises a stationary table or work platform, and the translator108comprises a mechanism that moves the laminator102on a supporting frame132along a linear path or common axis130(FIG.16) over the substrate114. In another example, the laminator102can be an end effector mounted on an articulated arm or gantry type robot (not shown). Other arrangements are possible that would allow the supporting frame132to be moveable relative to the substrate114along a common axis130.

The laminator102comprises a plurality of tape laying heads (hereafter “tape heads”)104that are mounted as a group on a supporting frame132. The tape heads104are arranged in series with each other, aligned along a common axis130(FIG.16). Each of the tape heads104is operable to lay down a strip of fiber prepreg tape110(hereinafter “tape”) on the substrate114, or on an underlying layer of the tape110. The width of each of the strips of tape110may be equal to the width of the plies. Consequently, each strip of the fiber prepreg tape110can form a single one of the plies82of the charge80. As a result, in one example, the number of tape heads104used is equal to the number of the plies82specified in the particular ply schedule for the stringer or other structure that will be formed using the charge80. The tape heads104are arranged in series (87) and are spaced from each other along a common axis130(FIG.16) such that each of the tape heads104lays down a strip of the tape110immediately ahead of a strip of the tape110being laid down by adjacent tape head104. Each of strip of the tape110is a unidirectional fiber prepreg forming one of the plies82of the charge80, some of which may have angled cuts94therein forming a series of ply segments96(FIG.9) of predetermined lengths. As previously discussed, the angled cuts94allow the charge80to stretch longitudinally and/or transversely as needed, as the charge80is being formed to a desired stringer contour, thereby reducing or eliminating ply wrinkling due to contours.

The tape heads104are mounted on a common, supporting frame132and therefore move together as group over the substrate114in a linear direction of travel128, and simultaneously lay down and compact strips of tape110on top of each other, in succession, one after another in a row115, thereby laying up all of the plies82of the charge80simultaneously. In other words, all of the tape heads104are laying down strips of the tape110at the same time in a row115as the laminator102moves over the substrate114. As a result, all of the plies82of the charge80can be laid up in a single pass or “stroke” of the laminator102.

As will be explained below, each of the tape heads104lays down strips of the tape110by removing a backing paper122from the strips of tape110, feeding strips of the tape to a compactor126, compacting the strips, and cutting the strips to a desired length. Each of the tape heads104includes a supply of the tape110carried on a supply reel112. Each tape head104is load with tape having a particular fiber orientation, e.g. 0°, ±45°, 90°. The tape110includes a layer of removable backing paper122, which prevents the tape110from sticking together on the reel112because of the prepreg's tack. The tape110, along with the backing paper122is fed through one or more guides116to a compactor126such as a compaction roller or similar compaction device. The compactors126of the tape heads104are aligned with each other along the common axis130. A suitable cutter118cuts the tape110to the desired length. The backing paper122is drawn off of the tape110by a take-off roller120and fed to a take-up reel124where it is accumulated and can be periodically discarded. The arrangement described above results in the backing paper122being removed from the tape110before the tape110is fed to the compactor126and compacted over the substrate114or an underlying one of the plies82. Consequently, the backing paper122is not compacted against the tape110by the compactor126which could increase adhesion of the backing paper122to the tape110and lead to bits of the backing paper122remaining on the ply segments96as FOD, particularly along the edges98(FIG.8) of the tape110.

Referring particularly toFIG.14-16, as previously explained, the laminator102can lay up all of the plies82of the charge80in a single pass of the laminator102over the substrate114. However, depending on the ply schedule and the degree of production efficiency that is required for a particular application, the charge80can be laid up by 2 or more passes of the laminator102over the substrate114. For example, if a ply schedule calls for 32 plies82, and the laminator102comprises 8 tape heads104, then all of the plies82of the charge80can be laid up in 4 passes of the laminator102over the substrate114. Alternatively, if the laminator102comprises 32 tape heads104, then all of the plies of the charge80can be laid up by the laminator102in a single pass. Referring toFIG.15, the tape heads104can be nested together to form a more compact laminator envelop. As shown inFIG.16, the tape heads104are arranged in a row115, one after another, aligned in series87along a common axis130so that the layers of tape110are likewise aligned with each other as they are being laid down to form the charge80.

Attention is now directed toFIG.17which shows a laminator102having ten tape heads104in the process of simultaneously laying up portions of two charges80a,80bon two different substrates114a,114b. On the right side ofFIG.17, six of the tape heads104are completing layup plies of the charge80a, while at the same time, on the left side of the Figure, two of the tape heads104are beginning down to lay down plies of charge80b. In this example, two of the tape heads104are inactive (not laying tape). As the laminator102continues its movement from right to left, laminator102completes laying up charge80a, and the tape heads104that were either inactive or laying up charge80a, begin laying down the plies82of charge80buntil it is completed.

The laminator102can continue laying up any number of different charges80simultaneously in this manner. The charges80may be identical or different from each other in terms of their ply schedules. Moreover, the charges80a,80bshown inFIG.17may comprise charge segments (discussed below) that are later joined together to form a single charge Actuation of the tape heads104is individually controlled by the controller106shown inFIG.12. Since the tape heads104may be loaded with tape having differing fiber orientations, any of the tape heads104can be activated or the deactivated to begin or stop laying tape at any point in the travel of the laminator102over the substrate114.

Referring now toFIGS.18-20, stringers54that are contoured and comprise a composite laminate may be produced using a plurality of overlapping charges segments134that are joined together to form a charge80that is complete. Each of the charge segments134comprises stack of plies82laid up according to a predetermined ply schedule that may include, for example, any number of 0°, +45°, −45° and 90° plies, although many other ply orientations are possible. The plies82in each of the charge segments134has a pattern of angled cuts94therein corresponding to the description of the examples previously described in connection withFIGS.7-11.

In some examples, all of the charge segments134may have plies arranged according to the same ply schedule. In other words, all of the charge segments134may be substantially identical. In one example, the charge80may comprise two or more charge segments134in order to produce longer stringers54that can be accommodated by production equipment that is limited to forming charges80that are shorter. In other examples, however, the charge segments134may be different in terms of their ply schedules, fiber lengths, cut angles and/or cut patterns, in order to tailor the charge80along its length to meet local load demands and/or other conditions. For example, the charge segments134can be tailored and optimized to respectively meet local load demands and geometries of stringers54used in the inboard section74, as well as the intermediate section76and also the outboard section78section74,76,78(FIG.2) of the wing44. Shorter charge segments134enhance the formability of a charge80in those areas of the stringer54that are highly contoured. The charge segments134may have the same or different lengths.

The charge segments134may be laid up with ply drop-offs138(FIG.20) at one or both ends. Following layup, the charge segments134can be joined together as by co-curing at the joints136. In the illustrated example, the charge segments134are connected by step lap joints, however any of a variety of other types of joints136may be used, depending upon the application. In some examples, each of the charge segments134comprises prepreg tape having a width that is equal to the width of the charge segments134however, in other examples, each one of the plies82may comprise multiple tape widths. The plies82of the charge segment134may be laid up either individually or all together substantially simultaneously by the laminator102previously described.

The charge80can be formed to a desired shape using any of various techniques. For example, referring toFIGS.21and22, the charge80can be compression formed in a die set139, comprising upper and lower dies141,143, respectively. As the charge80is being compressed between the upper and lower dies141,143, the die set139along with the charge80may be stretched using an applied force F. Stretching of the charge80as it is being formed assists in reducing wrinkling of the plies82in any contoured areas of the structure being formed. Similarly, the charge80may be LASH performed over one or more forming blocks in order to reduce ply wrinkling.

FIG.23broadly illustrates the overall steps of a method of making a charge80used to form a composite laminate structure such as a stringer54. As shown at140, the method comprises laying up a stack of plies82of fiber prepreg by laying down strips of fiber prepreg tape110on top of each other over a substrate114using a plurality of tape heads104, such that all of the plies82of the stack are laid up simultaneously.

FIG.24illustrates another method for laying up a charge80used to form a composite laminate structure. As shown at141, the method includes laying up at least first and second stacks of plies82of fiber prepreg simultaneously, including laying down strips of the tape110on top of each other in a row115by moving a group of tape heads104over first and second substrates114, wherein the group of tape heads104begins laying up the second stack of plies while completing laying up the first stack of plies.

Attention is now directed toFIG.25which illustrates a method of making a composite laminate structure. Beginning at142, loads on the composite structure are predicted along its length. At144, a ply schedule is generated for a fat charge based on the predicted loads. The ply schedule includes plies having different fiber orientations. A determination is made of the contribution of each of the plies required to meet the predicted loads. At146, a determination is made of the amount each ply in the flat charge is required to stretch in order to form the plies into a desired shape without substantial ply wrinkling. At148, the length of the fibers in each of the plies is selected that is required to stretch which represent an optimize combination of structural strength and formability. At150, the flat charge is assembled by laying up a flat stack of the plies in accordance with the ply schedule. Finally, at152the flat charge is formed to the desired shape.

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 laminate structures such as stiffeners used in aircraft may be used. Thus, referring now toFIGS.26and27, examples of the disclosure may be used in the context of an aircraft manufacturing and service method154as shown inFIG.26and an aircraft156as shown inFIG.27. Aircraft applications of the disclosed examples may include a variety of composite stringers and similar stiffeners which may have contours, curvatures, varying thicknesses or other out of plane features along their lengths. During pre-production, exemplary method154may include specification and design158of the aircraft156and material procurement160. During production, component and subassembly manufacturing162and system integration164of the aircraft156takes place. Thereafter, the aircraft156may go through certification and delivery166in order to be placed in service168. While in service by a customer, the aircraft156is scheduled for routine maintenance and service170, which may also include modification, reconfiguration, refurbishment, and so on.

As shown inFIG.27, the aircraft156produced by exemplary method154may include an airframe172with a plurality of systems174and an interior176. The airframe172may include stringers178having one or more contours, curvatures or other out of plane features along their lengths. Examples of high-level systems174include one or more of a propulsion system180, an electrical system182, a hydraulic system184and an environmental system186. 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 method154. For example, components or subassemblies used during component and subassembly manufacturing162may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft156is in service. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during component and subassembly manufacturing162and system integration164, for example, by substantially expediting assembly of or reducing the cost of an aircraft156. Similarly, one or more of apparatus examples, method examples, or a combination thereof may be utilized while the aircraft156is in service, for example and without limitation, to maintenance and service170.

The description of the different illustrative examples has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the examples in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative examples may provide different advantages as compared to other illustrative examples. The example or examples selected are chosen and described in order to best explain the principles of the examples, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various examples with various modifications as are suited to the particular use contemplated.