Field of the Invention

The invention relates to the field of composites manufacture and in particular to achieving consistent structural properties around female radiused regions of composite articles.

Background to the Invention

Composite materials are widely used in a number of industries, such as aerospace, automotive, civil engineering and sports goods, due to their high strength-to-weight ratio.

Composite materials such as carbon fibre composite and fibreglass composite are formed from a multiple plies or layers of fabric impregnated with and reinforcing a polymer matrix. For example, a carbon fibre fabric is formed by carbonizing a synthetic polymer fabric material and may be provided in the form of woven fabric, non-woven fabric or may consist of unidirectional fibres. Similar composites may be formed using alternative fibrous materials, such as glasses or synthetic polymers (e.g. aramid), or combinations of such materials.

A conventional approach to composite manufacture, and to carbon fibre composite manufacture in particular, is to "lay-up" fabric layers on a mould or tool, impregnate with uncured resin and transfer the article into an autoclave to be cured under high temperature (ca. 100-300°C) and pressure (up to 7 Bar) conditions. Whilst this method of curing is effective at compressing the layers and eliminating voids, it is associated with high capital expenditure, and high operating costs.

In the aerospace industry in particular, there has been increasing adoption of so called "out of autoclave" (OOA) curing methods, in which a composite article is held at a reduced pressure (in a vacuum bag) and cured on a heated tool, or between heated tools. The initial and operating costs for OOA curing are significantly reduced.

Since pressure differentials applied during OOA curing are far lower than conventional autoclave methods, it is of increased importance to "de-bulk" the article periodically during lay-up to assist in eliminating voids and ensuring a uniform structure. During de-bulking, sheets of uncured fabric are compressed together, typically under vacuum, and the regions of an article are compressed from a first thickness down to a smaller second thickness. In female radii, such as concavities, tight radius corners and edges, undesirable "bridging" may occur.

This is illustrated in Figure 1 (a), which shows a region of a pre-forming tool 1 having a female radiused surface 3. A composite lay-up 5 comprising multiple plies 7 is placed upon the tool. When compressed under vacuum from a first thickness Ti down to a second thickness T2, as shown in Figure 1 (b), insufficient material exists on outer-most plies to follow the increased radius, causing bridging or gaps between the plies. In addition, due to the bridging, the overall thickness T2 of the resulting composite article in the female radiused region may be greater than in adjacent more planar regions. These effects can result in undesirable or inconsistent physical properties in the affected region of the composite article.

Bridging is particularly problematic where there is high inter-layer friction, for example due to a binder (e.g. of dry carbon fibre fabric) or from the resin or a pre-impregnated fabric.

Conventional techniques to address bridging include introducing additional de-bulking steps or modifying lay-up in affected areas; both of which require additional time and increase manufacturing costs. Accordingly, there remains a need to improve composite

manufacturing in order to address bridging associated with female radiused corners, edges or concavities. Summary of the Invention

According to a first aspect of the invention there is provided a method of manufacture of a composite article, the method comprising:

providing a composite lay-up having a female radiused portion;

compressing the composite lay-up so as to reduce its thickness; and

applying additional compression to the female radiused portion.

The additional compression applied to the female radiused portion reduces or substantially eliminates the bridging that might otherwise occur. This may be manifested for example in a more consistent material thickness around the female radiused portion, and/or more consistent and greater fibre volume ratio. The additional compression may locally deform the fabric layers in the female radiused portion so as to provide the required additional area once compressed. Alternatively, or in addition, some lateral movement between adjacent fabric layers may be caused. The force(s) applied by compressing the composite lay-up and also the additional compression applied to the female radiused portion are preferably applied locally

transversely to the fabric layers. It will be appreciated that some variation in the direction of these applied forces is possible, for example as might result when manufacturing a complex composite article, due to physical constraints and the like.

By lateral, we refer to a direction or orientation generally parallel or tangential to the fabric layers. By transverse, we refer to a direction or orientation generally perpendicular to the fabric layers. The additional compression may be applied to the female radiused portion before, during and/or after compression of the composite lay-up as a whole.

The periods for which the composite lay-up is compressed (compression period), and for which the additional compression is applied to the female radiused portion (application period) will depend on a number of factors, such as the type of fabric, resin, the number of layers being compressed, the technical function of the resulting composite article and other manufacturing steps etc. The compression period may typically be of the order of minutes or tens of minutes, for example between around 5-30 minutes, or 5-20 minutes, or 10-15 minutes.

The compression period and the application period may be of the same or different lengths.

It is however preferred that the additional compression be applied to the female radiused portion during at least a part of the compression period. For example, the composite lay-up may be compressed by applying a vacuum and the additional compression may be applied before or at the start of an evacuation process; i.e. as the vacuum builds up.

The compression and the applied additional compression may, independently, be constant or may vary over time. In some embodiments, the compressing the composite lay-up comprises more than one stage. For example, the method may comprise compressing the composite lay-up at a first compression pressure for a first compression period and compressing the composite lay-up at a second compression pressure for a second compression period. This may be achieved for example by varying the level of vacuum applied during vacuum bagging.

In some embodiments, the additional compression is applied to the female radiused portion during the second compression period (e.g. only during the second compression period and/or for some or all of the second compression period).

The female radiused portion may be an internal edge or a corner; for example, respectively, between two or three adjacent respective generally planar regions. The female radiused portion may be a concavity or form part of a recess. The additional compression may be applied to the female radiused portion evenly along a line or across a region thereof.

The additional compression may vary across the female radiused portion. The additional compression may be at a maximum at a point or along a line and may decrease with distance therefrom. For example the additional compression may be applied by a tapered member or a rounded member more tightly radiused than the female radiused portion of the composite lay-up. Suitable pressure members are described in further detail below.

The method may comprise applying additional compression to portions of the composite lay- up adjacent to the female radiused portion. For example additional compression may in some embodiments be applied to the female radiused portion and to regions of adjacent planar regions extending therefrom. It will be understood that the additional compression is not typically applied across the entire of said adjacent regions. Measures such as varying the applied additional compression away from a focal point/line and/or applying additional compression to regions adjacent to the female radiused portion may be required for example to avoid undesirable "steps" on a surface or in density or volume fraction of the resulting composite article. Additional compression may be applied at a single location, or at multiple locations. The composite lay-up may for example comprise more than one female radiused portion, to which additional compression is applied.

Additional compression may be applied at more than one location of a female radiused portion. It may for example be desirable in some embodiments to apply differing amounts of additional compression to different locations of a female radiused portion (more compression might be required in a corner than along adjacent edges, for example).

The method may comprise compressing the composite lay-up by applying a vacuum.

Accordingly, the method may comprise vacuum bagging the composite lay-up and evacuating the vacuum bag so as to apply the vacuum.

Typically, a composite lay-up or a composite article is vacuum bagged by covering with an air impermeable sheet material, referred to as a vacuum bag (for example formed from a pliable material such as a silicone), and sealing the vacuum bag against a tool or mould surface around a periphery of the composite lay-up/article.

The method may comprise draping the vacuum bag over the composite lay-up, e.g. by unrolling or unfurling the vacuum bag. The vacuum bag may be lowered onto the composite lay-up.

The vacuum bag may be draped over the composite lay-up from a first side to a second side (or from the middle working out), to avoid trapping air pockets, or forming wrinkles in the material of the vacuum bag.

The method may comprise applying additional compression to the/each female radiused portion during or after vacuum bagging. Thus, the additional compression may be applied to an outside of the vacuum bag.

In some embodiments, a pressure member by which the additional compression is applied may be used to assist with draping the vacuum bag over the composite lay-up.

The method may comprise sweeping a pressure member across a surface of the composite lay-up towards a said female radiused portion, so as to expel trapped air from under the vacuum bag and/or to eliminate wrinkles in the vacuum bag. This may be conducted whilst the vacuum bag is being draped over the composite lay-up.

The method may comprise applying the additional pressure during sweeping or at the end of sweeping. The additional pressure may be progressively increased during sweeping.

The method may comprise laying-up fabric, for example on a mould surface of a lay-up or pre-forming tool. The method may comprise impregnating the laid-up fabric with resin. Alternatively, the fabric may be pre-impregnated with resin, or coated one/both sides with resin. The method may comprise adding additional resin to laid-up pre-impregnated fabric.

The method may comprise consolidating two or more impregnated fabric layers.

The method may comprise consolidating the composite lay-up.

By "consolidating", we refer to a process in which the composite lay-up is changed from a state in which it comprises separable fabric layers to a state in which the fabric layers are no longer separable.

Consolidating the composite lay-up may be achieved by the step of compressing.

For example, a binder (such as a thermoplastic binder) may adhere fabric plies of the composite layers together, during consolidation. Where the composite lay-up comprises a resin, consolidation may cause resin of adjacent layers to flow or comingle. An initial stage of curing, or "gelation" of the resin may occur during consolidation.

Consolidation may alternatively or additionally comprise heating. In embodiments in which the composite lay-up comprises a resin, consolidation may be conducted at a temperature significantly below the normal curing temperature for the resin. For example, where a resin is to be cured at 300-400°C, consolidation may be conducted at a temperature in the range of 50-200°C, or 60-180°C or 70-170°C, or indeed at ambient temperature. Even where elevated temperature is normally used for curing, a resin may cure slowly at a lower temperature (e.g. ambient). Consolidation may be conducted at a temperature at which a resin curing reaction proceeds, but for a significantly shorter period of time.

Thus, the method may comprise compressing the composite lay-up, and optionally also heating during at least a part of the compression period, so as to reduce its thickness and consolidate two or more fabric layers thereof.

Methods in which a composite lay-up is consolidated may be referred to in the art as "preforming" of a composite article. A pre-formed composite article requires subsequent curing, but has sufficient structural integrity to be moved as a single item, yet some degree of reshaping is also possible if required.

The method may comprise more than one step of laying-up, compressing the composite lay- up and/or applying additional compression to the/each female radiused portion.

The method may comprise alternate steps of laying-up and compressing. The method may comprise compressing the composite article after every 2, 3, 4, 6, 10, 20 or indeed any predetermined number of fabric layers have been laid-up. The number of layers applied between successive compressions may vary during the course of the manufacture of the composite article. A composite article may comprise different numbers of layers in different regions thereof, and so laying up may comprise adding different numbers of layers to different regions of the composite lay-up. The method may comprise applying additional compression to the/each female radiused portion every time the composite lay-up is compressed. The method may comprise applying the additional compression less frequently; for example after alternate steps of laying-up, or after all the layers of the composite article have be laid up. The method may comprise consolidating two or more fabric layers each time the composite lay-up is compressed (e.g. where consolidation occurs as a result of compression), or consolidation may be less frequent; for example after alternate steps of laying-up and compressing or after all the layers of the composite article have be laid up. Indeed the method may comprise one or more steps of consolidating by compressing, and one or more steps of consolidating by compressing and heating (e.g. after alternate steps of laying-up, or less frequently). The method may comprise consolidating two or more impregnated fabric layers each time the additional compression is applied, or consolidation may be more, or less frequent. The method may further comprise curing the composite lay-up, to form a composite article.

The composite lay-up may be cured in an autoclave, or by out-of-autoclave (OOA) methods.

The method may comprise placing a composite lay-up (for example a "pre-formed" article) on a curing tool and/or removing it therefrom after curing. The method may comprise placing a composite lay-up (for example a "pre-formed" article) in an autoclave, for curing.

In some embodiments, however, the curing is performed on the same tool or mould as the compressing and applying the additional compression. For example the curing may be conducted on a lay-up or pre-forming tool.

The method may comprise curing the composite lay-up under a vacuum. The method may comprise vacuum-bagging the composite lay-up and then curing. Curing may be conducted using a heated tool or mould, on one or both sides thereof.

The method may comprise bagging, or vacuum bagging the composite lay-up, and applying an external pressure of gas (for example in some embodiments in the region of 2-10 Bar pressure) at an elevated temperature (e.g. in the region of 100-300°C). The method may comprise applying the external pressure of gas and the elevated temperature in an autoclave.

The method may comprise changing the radius of a radiused portion prior to curing.

Additional tension and/or slack is thereby introduced into outer-most plies of the composite material, which further contributes to avoiding wrinkling and/or bridging.

The method may comprise tightening the radius of a said female radiused portion and/or increasing the radius of a male radiused portion of a composite lay-up prior to curing.

For example, where a said female radiused portion is an internal edge, between adjacent generally planar regions of the composite lay-up, the method may comprise reducing the angle therebetween. The angle may be reduced from a first angle to a second angle. The relationship between the first and second angle will depend on factor such as the tightness of the radius, the second angle (i.e. the nominal angle of the final cured composite article) and the thickness of the composite lay-up.

Figure 2 schematically illustrates a composite lay-up before compressing to reduce its thickness, and after compressing. The composite lay-up 50 has a female radiused portion 52, extending to adjacent planar regions 54. The difference between the first and second angles (between the adjacent planar regions) ΔΘ may be given by Equation 1 , as follows:

(1 ) ΔΘ = AD (1 - R _E /(RE + ΔΤ)) Where;

AD is the angle between the normal to each of the adjacent planar regions, at the second angle θ ₂ ; i.e. A _D = 180 - θ ₂ ;

RE is the desired (i.e. nominal) exterior surface radius of the composite article; and

ΔΤ is the change in thickness as a result of compressing the composite lay-up.

In embodiments wherein the method comprises more than one step of compressing the composite lay-up, ΔΤ may be the sum of the changes of thickness.

ΔΘ may be in the range of around 1 -20°, or around 5-20°, or 5-15°, or 10-15°, or around 12°, 13°, 14° or 15°

ΔΤ may be in the range of around 1 mm to 15 mm, or 3-10 mm or around 5 mm. Typically, compression of a carbon fibre fabric results in a ΔΤ of between around 20-70% (i.e. where lay-up thickness before compression is Ti and the nominal thickness after compression is T2, (Ti-T2) T2 is between around 1 .2-1 .7). ΔΤ may be between around 30-60%, or between around 45-55%. In some embodiments, ΔΤ is around 50%.

ΔΤ may vary in different parts of a composite lay-up, and may for example be greater (by around 2-5%) in generally planar regions than in radiused portions, in particular female radiused portions (e.g. around 50% in a planar region corresponding to around 47% in a female radiused portion). In some embodiments of the invention, the angle AP, where AP = 180 - Θ2 may be in a range of around 45 to 120 degrees, 60 to 100 degrees, or 80 to 90 degrees. The angle AD may be in a range of 60 to 120 degrees, 80 to 100 degrees, or 89 to 91 degrees.

The desired exterior surface radius (RE) may be in a range of around 5 mm to 100 mm, or 6 mm to 70 mm, or 20 mm to 60 mm, or 30 mm to 45 mm.

In some embodiments of the invention, the thickness prior to compression is in a range of around 5 mm to 40 mm, 10 mm to 30 mm, or 20 to 25 mm. The thickness after compression may be in a range of around 3 mm to 35 mm, 10 mm to 30 mm, or 15 mm to 20 mm.

The method may comprise tightening the radius of a said female radiused portion before, or more preferably during or after applying additional compression to the female radiused portion. In some embodiments, the method comprises using a pressure member to tighten the radius of a said female radiused portion, for example by pressing the composite lay-up into a mould/tool.

Conveniently, the radius of the female radiused portion may be tightened by transferring the composite lay-up from a first tool, to a second tool, each tool having a female radiused formation between adjacent generally planar regions, wherein the angle between the planar regions on the first tool is greater than the angle between the corresponding planar regions on the second tool. Accordingly, when the composite lay-up conforms to the shape of the second tool, the radius of the female radiused portion is tightened as it conforms to the female radiused formation of the second tool.

The first tool may be a lay-up tool and the second tool may be a curing tool. Accordingly, the various steps of laying-up, compressing and applying additional compression, and consolidation, may be performed before the composite lay-up is transferred to a curing tool, on which the radius of the female radiused portion is tightened.

The method may comprise, changing the conformation of a tool, the tool having a female radiused formation between adjacent generally planar regions, from a first conformation to a second conformation, wherein the angle between the generally planar regions in the first conformation is greater than the angle between the generally planar regions in the second conformation.

The tool may be changed from the first conformation to the second conformation by inserting a wedge or wedges between the composite lay-up and a said generally planar portion.

Other means for adjusting an angle between the generally planar regions are envisaged. For example, the tool may alternatively be provided with a flexible mould surface and a wedge may alternatively be inserted between a flexible or compliant mould surface and a support, or the generally planar regions of the tool may be in hinged relationship to one another, e.g. by an active hinge.

In embodiments using a reconfigurable tool, the radius of the female radiused portion may be tightened before, during or after consolidation.

The composite lay-up may comprise layers of a fabric for a composite material, for example on a lay-up tool or a mould surface. The fabric may be already impregnated with, or coated on one or both sides with, an uncured resin. The fabric may be woven, non-woven or unidirectional. The fabric may be a "non-crimp" fabric, comprising unidirectional layers of differing orientations coupled by binding fibres extending between the layers. As discussed further below, the composite lay-up may comprise consolidated layers, which have been already been compressed, which are underlying the layers of the fabric to be compressed as well as uncompressed and/or unconsolidated layers. A composite article formed therefrom thus comprises the fabric reinforcing a matrix material formed by curing the resin. Any suitable fabric, or combination of fabrics, may be used, including carbon fibre, glass fibre, aramid, or basalt fabrics. A composite lay-up or article may comprise any suitable curable resin, including epoxy resins, polyester resins, vinylester resins, alkyd resins, for example. Other components may be embedded or encapsulated within or attached to the reinforcing material/curable matrix material, such as honeycomb structures or metallic couplings or reinforcements.

The method is of particular utility in the manufacture of carbon fibre composite articles.

Where we refer herein to reducing the thickness of a composite lay-up, we include reducing the number of layers per unit thickness (i.e. the average inter-layer distance) generally perpendicular to the fabric layers, through at least a part of the thickness of the composite lay-up. Reducing the thickness of a composite lay-up may also be expressed in terms of increasing the fibre-volume ratio of the composite lay-up.

According to a second aspect of the invention there is provided an apparatus for use in the manufacture of a composite article, the apparatus comprising;

a tool having a mould surface;

a pressure member for selectively applying pressure to a female radiused portion of a composite lay-up placed on the mould surface. The tool may be a lay-up tool, on which a layers of fabric of a composite material may be laid-up, to form a composite lay-up in use.

The tool may be a pre-forming tool, on which adjacent layers of a composite lay-up may be consolidated.

A given tool may be used both as a lay-up and a pre-forming tool, on which laying-up, compression and optionally consolidation (by heating and/or compression), as described in relation to the first aspect, may be performed. The mould surface may have a female radiused mould portion, such as an internal edge or a corner; for example, respectively, between two or three adjacent respective generally planar regions. The female radiused mould portion may be a concavity or recess.

The mould surface will in use define the shape of a composite lay-up. Accordingly, each female radiused mould portion will correspond to a male radiused portion of a carbon lay-up thereon and also typically correspond to a female radiused portion of said composite lay-up. However, there may be exceptions when, for example, a composite lay-up comprises a sandwiched structure such as a honeycomb or metallic reinforcement. Thus, the pressure member is typically configured to selectively apply pressure in a direction locally transversely to the mould surface at the female radiused mould portion. It will be appreciated that some variation in the direction of the applied pressure is possible, for example as might result when manufacturing a complex composite article, due to physical constraints, sandwiched components and the like. The pressure member may be provided with a shape to apply additional pressure to a particular shape of female radiused portion.

The said pressure member may be tapered to a point or an edge.

The pressure member may have a rounded face for applying pressure to a composite lay- up. The pressure member may have a part cylindrical surface, or a part spherical or ovoid surface. The pressure member may comprise one or more rollers, which may be cylindrical.

The pressure member may comprise a rotatable pressure applying surface, such as a roller, wheel or ball. A rotatable surface may assist in sweeping the pressure member, as disclosed herein, or otherwise changing its configuration without "dragging" a vacuum bag or fabric layer with it as it moves.

In some embodiments the pressure member has a variable curvature. A variable curvature pressure member may be adjusted as the curvature of a female radiused portion changes during the course of laying-up.

Variable curvature of a rounded or part cylindrical surface may be accomplished for example by flexing a sheet material by a greater or lesser degree.

The pressure member may be adapted for variable curvature by being conformable.

The pressure member may comprise a resilient member; e.g. formed from or coated with a resilient material such as an elastomer. The resilient member may be conformable.

The pressure member may comprise an inflatable member, such as an inflatable bladder, for applying pressure to the composite lay-up. The inflatable member may be inflatable with a gas or a liquid, and the apparatus may comprise such additional apparatus as required to regulate inflation and deflation of the inflatable member. The inflatable member may be conformable. An inflatable member may also provide means for regulating the amount of pressure applied, in use, by adjusting the pressure within the inflatable member. The pressure member may be shaped and sized so as to contact a composite lay-up at the female radiused portion and also in regions adjacent to the female radiused portion. The pressure member may be provided with a curvature that is more tightly radiused than the nominal female radiused portion of the composite lay-up or article. Thus, the pressure member may be adapted to apply pressure that decreases away from a focal point or line.

In use, a biasing arrangement may urge the pressure member against the female radiused portion. A biasing force may be applied by the biasing arrangement by any suitable means, such as a hydraulic or pneumatic actuator or actuators, electromechanically, and/or by a resilient member such as a spring. The biasing arrangement may form a part of apparatus for selectively moving the pressure member, as discussed in further detail below. The pressure member may be selectively movable from a first configuration, spaced apart from the mould surface (to allow sufficient space for a carbon lay-up to be placed thereon, or for composite fabric to be laid-up), to a second configuration in which pressure is applied to a female radiused portion of a composite lay-up placed on the mould surface, in use. The pressure member may be selectively movable between the first and second

configurations.

The selective movement of the pressure member may be effected at least in part by the biasing arrangement.

The pressure member may be moveable by inflating or deflating a said inflatable member.

The pressure member may be moveable by way of one or more actuators, such as a hydraulic or pneumatic ram or the like. At least a part of the movement between the first and second configurations may be achieved by way of the biasing arrangement.

The pressure member may be pivotally moveable. Pivoting movement of the pressure member may be resiliently biased.

The movement may be effected by a combination of such measures. The pressure member may be configured to move from the first configuration to the second configuration in a sweeping motion, in some embodiments following a part of the mould surface. The sweeping motion may be used to assist in deploying a vacuum bag over a composite lay-up, by expelling trapped air from between the composite lay-up and the vacuum bag.

The apparatus may comprise vacuum bagging apparatus, such as a vacuum bag and a spool or frame for deploying a vacuum bag. The spool may be moveable, for example across a portion of the mould surface, or vertically so as to lower the vacuum bag over the tool. The pressure member may be configured to follow the movement of the spool over at least a part of its path.

The apparatus may comprise a single pressure member, or more than one pressure member (or the same or different types). For example, where the female radiused portion is an edge, the apparatus may comprise two or more pressure members in a line, or a single elongate pressure member.

The apparatus may be configured to selectively apply pressure to more than one female radiused portion. The apparatus may comprise one pressure member, or more than one pressure member, corresponding to each female radiused portion.

In some embodiments the mould surface may comprise more than one female radiused mould portion. It is to be appreciated that in practice, where a female radiused mould portion corresponds to a female radiused portion of a composite lay-up, the composite lay-up may be of a thickness such that in the second configuration a said pressure member is capable of applying pressure directly to the mould surface. The apparatus may comprise additional equipment for manufacturing a composite, such as a vacuum pump for evacuating a vacuum bag, one or more heat sources for heating the mould surface of the tool or a composite lay-up on a tool, control equipment for such heating, and the like. The or each pressure member may be attached to of form a part of a lay-up tool or a preforming tool. The or each pressure member may be adapted for use with a lay-up or pre- forming tool. For example, the/each pressure member may form part of a frame, which can be placed over, next to or around a tool when it is desired to apply additional pressure to a female radiused portion of a composite lay-up on the tool. Indeed movement of the frame may effect, at least in part, movement between the first and second configurations of said pressure member(s).

Accordingly, the invention extends in a third aspect to a frame, comprising one or more pressure members as disclosed herein. The frame may comprise apparatus, such as mechanical linkages, hydraulic or pneumatic actuators, or electromechanical arrangements, for moving the pressure member(s) and/or regulating the pressure applied by the pressure member(s) as disclosed herein.

In a further aspect, the invention relates to the use of the apparatus of the second aspect, or the frame of the first aspect, in the manufacture of a composite article. The apparatus or frame may be used in the method of the first aspect. Moreover, it is to be understood that preferred and optional feature of each aspect of the invention correspond to preferred and optional features of each other aspect of the invention.

Description of the Drawings

Example embodiments of the invention will now be described with reference to the following figures in which:

Figure 1 shows a schematic cross section of a female radiused portion of a pre-forming tool showing a composite lay-up (a) before and (b) after compression using a prior art composite manufacturing method.

Figure 2 schematically illustrates a composite lay-up before compressing and after compressing to reduce its thickness and tightening the angle to reduce its thickness, showing the parameters relevant to Equation (1).

Figure 3 shows an apparatus for use in manufacturing a composite article, in accordance with the invention. Figure 4 shows a close-up view of the apparatus of Figure 4 with a vacuum bag secured to a support frame, above a composite lay-up on a pre-forming tool. Figure 5 shows the apparatus following application of the vacuum bag and movement of the pressure members into position to apply additional compression to the female radiused portions of the composite lay-up.

Figure 6 shows schematic side views of the apparatus of Figure 3, with a pressure member in (a) a first configuration (b) in position to sweep down a surface of the composite article and (c) a second configuration in which it is positioned to apply additional compression to the female radiused portions of the composite lay-up. Figure 6(d) shows a close up view of the female radiused portion of the composite lay-up when the pressure member is in the second configuration.

Figure 7 shows schematic cross sectional views of a preforming tool and a curing tool for an omega section.

Figure 8 shows a portion of an angle-adjustable preforming tool for an omega section.

Figure 9 shows an alternative embodiment of pressure members of apparatus for manufacturing a composite article in accordance with the invention.

Figure 10 shows a further embodiment of pressure members of apparatus for manufacturing a composite article in accordance with the invention.

Figure 11 shows a still further embodiment of pressure members of apparatus for manufacturing a composite article in accordance with the invention.

Figure 12 is a photograph of a carbon fibre composite test article having a region "A" manufactured in accordance with the invention and a region B manufactured conventionally. Figure 13 shows a perspective view of an Omega section pre-formed composite lay-up.

Figure 14 shows results of experiments in which the radius of a female radiused portion of a Z-section preforming tool was varied. Detailed Description of Example Embodiments

An apparatus 100 in accordance with an embodiment of the invention is shown in Figure 3. The apparatus includes a tool 102 having a mould surface 104. In this instance, the mould surface defines an "omega section" (a structural member forming in use three sides of a box- section).

The mould surface has a female radiused portion 106 on one side of the tool, and another female radiused portion 108 on the other side of the tool. Each of the female radiused portions are edges that extend between generally planar sections 110, 112, 114 and 116 of the mould surface 104.

A composite lay-up 118 on the mould surface is shown in Figure 4. The composite lay-up in this example has female radiused portions 106a, 108a extending to adjacent generally planar sections 1 10a, 112a, 114a and 116a; each of which correspond to those of the mould surface 104.

The tool 102 is supported on a lower platform 119, within a frame 120. At an upper part of the frame the apparatus includes a pressure member 122, for applying pressure to the female radiused portion 106a of a composite lay-up 118 placed on the mould surface. On the opposite side of the frame, there is a corresponding pressure member 124, for applying pressure to the female radiused portion 108a of the composite lay-up 118.

The apparatus 100 further comprises a vacuum bag support frame 140. The support frame is vertically moveable within the frame 120, electrically driven by a belt drive 142 (which can be seen in Figure 4). In use, a vacuum bag 144 is clamped to the support frame 140 over the tool 102, so as to be lowered onto the tool when required.

The pressure members 122, 124 are moveable from the first configuration shown in

Figure 3, to a second configuration shown in Figure 5 in which pressure is applied by the pressure members 122, 124 to the female radiused portions 106a, 108a of the composite lay-up 1 18.

As best seen in the simplified side view of Figures 6(a)-(c), each pressure member 122 is at the distal end of a pneumatic actuator 126, oriented so as to apply additional compression transversely to the mid-point of the female radiused portions. The pressure member actuator 126 is slideably moveable within the side frame 128 (in the direction indicated by arrow "a"), under the action of a further pneumatic actuator 130;

coupled at each end at pivots 132 and 134, to the pressure member actuator 126 and the side frame 128, respectively. The compressed air supply for the actuators, and associated apparatus, are omitted for clarity.

The pressure member 122 is moved towards the composite lay-up 118 by the actuator 126. The actuator 126 further acts as a biasing arrangement to apply pressure to the pressure member and thus the female radiused portion 106a of the composite lay-up, when it is in the second configuration shown in Figure 6(c).

Although Figures 6(a)-(c) show only one actuator 126 and 130, the apparatus 100 comprises two of each, coupled to an elongate pressure member 122 and it will be understood that the pairs of actuators function in concert with one another.

As shown in Figure 6(d), the pressure members in cross section are tapered and provided with radiused ends 123, having a tighter radius than the female radiused portion 106a of the composite lay-up 118.

Alternative shapes and configurations of pressure members are also possible. In an alternative embodiment (not shown) the pressure members are covered with an elastomeric coating so as to conform to the shape of the female radiused portions, and in other embodiments, they are inflatable.

The apparatus 100 may be used in the manufacture of a composite article as follows.

A composite lay-up 118 is provided on the mould surface 104, by laying up multiple layers between 2-6 layers of a pre-preg carbon fibre on the mould, in a conventional manner.

The vacuum bag is then lowered over the tool 102, by lowering the support frame 140 and smoothed down manually where required.

Release layers 146 may be used between the mould surface and the fabric and between the fabric and the vacuum bag, and sealed around the periphery of the lay-up 118. The vacuum pump (not shown) is activated to pump air from the vacuum bag and thereby compress the composite lay-up to reduce its thickness.

While the vacuum builds up, the pressure members 122, 124 are moved from the first configuration (Figure 6(a)) to the second configuration (Figure 6(c)) the actuators 126 pressurized so that the pressure members 122, 124 apply an additional compression to the female radiused portions 106a, 108a.

IR heater banks (not shown) are moved to adjacent each side of the tool 102 and used to warm the composite lay-up 118, typically for approximately 10-15 minutes to a temperature of below around 175°C (although these parameters will vary depending on the resin system and composite lay-up in question). The compression and heating acts to consolidate the layers that have been laid-up. In alternative embodiments, for example where dry fabric is used, consolidation may be performed at ambient temperature.

Once the apparatus has cooled following consolidation, the pressure members 122, 124 are returned to their first configuration and the vacuum pump deactivated; to allow for the support frame 140 to be raised to remove the vacuum bag 144. Additional layers of carbon fibre pre-preg fabric is then applied to the composite lay-up and the process repeated.

Once the pre-formed carbon lay-up is complete it is then removed from the tool 102 and transferred to a curing tool 150 for curing to form the final composite article, in a

conventional manner (whether in an autoclave or on an OOA tool).

In alternative embodiments, the sequences of these steps may be varied. For example, the steps of laying up and then compressing may be repeated until the all of the layers of the composite lay-up have been applied, with the additional pressure being applied by the pressure members and the lay-up being consolidated only during the final vacuum compression step. It will also be understood that a greater number, or fewer, layers of fabric may be laid-up between compressions.

Optionally, the sequence of actuation of the actuators 126, 130 may be controlled so that the path of the pressure member 122 runs parallel to the composite lay-up 118 along at least a part of its surface (in this case the planar surface 112a); i.e. between the positions shown in Figures 6(b) and 6(c), respectively.

This may assist in smoothing the vacuum bag 144 over the composite lay-up 118, so as to wash (i.e. excess) material and reduce wrinkling. Figure 5 shows an embodiment in which the vacuum bag has been smoothed over the surfaces 1 12a, 1 14a by this sweeping action of the pressure members 122, 124. In this embodiment, the pressure members 122, 124 have been moved and the additional compression applied, before the vacuum pump has been activated to compress the composite lay-up as a whole.

In an optional further step, the female radiused portions 106a, 108a are tightened prior to curing.

This is achieved in one embodiment by use of a preforming/lay-up tool 202 (see Figure 7) in place of tool 102, and transferring the pre-formed composite lay-up to a curing tool 150 for curing. The tool 202 has female radiused portions that are less tightly radiused than the curing tool 150. That is to say, the angle between the planar regions 210 and 212, and the angle between regions 214 and 216 (and thus of the corresponding regions of the composite lay-up on the tool) is larger than the nominal angle, i.e. of the curing tool 150.

The difference between the cross sectional profiles of the tools 202, 150 is illustrated in Figure 7. For a nominal angle of 84°, a pre-formed angle of around 100° was found to be optimal (see "results" below). In another embodiment, the female radiused portions are tightened during pre-forming.

Figure 8 shows a tool 302 for which the angle between the planar portions 310 and 312 can be tightened by the insertion of wedges 313 between the lay-up and the tool 302. In this embodiment, the wedges are added before the final consolidation step. In a further embodiment, the wedges are added at each consolidation step and subsequently removed for lay-up of further layers of fabric.

In another embodiment, the lay-up/preforming tool is also used for curing. The platform 1 19 and the frame 120 may be movable in relation to one another in such embodiments, to enable the tool to be moved away for curing (e.g. placed in an autoclave or within an insulated cover for OOA curing). An alternative embodiment of pressure members is shown in Figure 9. Only the mould surface 404, the pressure members 422 and 424 and the vacuum bag 444 are illustrated. The pressure members 422 and 424 take the form of an array of rollers 425, which rotate around axes 427. The structure by which the rollers are supported is shown for illustrative purposes only and it is to be understood that the rollers may be used with any mechanical arrangement for applying pressure to a composite lay-up on the mould surface 402. The radius of the rollers is selected according to the required tightness of the female radiused portions 406, 408.

The rollers are of particular benefit when used to deploy a vacuum bag 444 from a reel 420. As illustrated by the arrows in the figure, the rollers can be moved into their second configuration whilst the bag 444 is being lowered, so that the required amount of vacuum bag material is unrolled.

In the analogous embodiment of Figure 10, the pressure members 522, 524 take the form of wedges 525, with angles corresponding to the angles between the respective planar regions 510, 512 and 514, 516 of the mould surface 502. In this way, the pressure members apply additional compression to the female radiused portions 506a, 508a and also to part of the respective planar regions extending therefrom.

Figure 11 shows an alternative arrangement for applying the additional compression. A pressure member 622 is pivotally mounted to the tool 602, and spring biased towards the second configuration shown in Figure 11 a (by a coil spring, now shown). Either the pressure member can be manually movable using the handle 626 and, for example, latched in its first position, or the movement may be automated. A single pressure member is illustrated, but it is understood that an array may be provided. Alternatively, the pressure member may be mounted on a rail (not shown) so as to be sliceable along the tool to apply additional compression to each female radiused portion in turn. In this way, and optionally by varying the angle between the pressure member 622 and the armature 623, a single pressure member may be used to apply additional pressure to more than one female radiused portion of a composite lay-up on a tool. Results

Exemplary tests were conducted using an Omega-section" pre-forming tool. One half of the female radiused section was laid-up with a dry, non-crimp, bindered carbon fibre fabric and compressed under vacuum (to around 900 mBar) in a conventional fashion, and the other half additionally compressed using a pressure member. The pressure member was provided with a rounded end having a 12 mm radius. The target radius of the female radiused section of the preform was 24 mm.

Equivalents of between around 10-30 atm pressure was applied through the pressure member, on lay-ups of between 6-12 ply thickness.

During vacuum compression, IR heaters were applied until all parts of the composite lay-up reached a minimum of 100°C for 20 minutes.

Qualitatively similar results were obtained, indicating that bridging is reduced by applying the additional pressure to the female radiused portion of the carbon fibre composite lay-up. An example of the pre-formed composite, made from 6 plies of the NCF is shown in Figure 12. The step in the female radiused portion of the preform between the region A that has been additionally compressed (ca. 1200 N additional pressure being applied to region A) and the region B that has been compressed by the vacuum bag only, is clearly visible (see arrow C).

In further tests, an Omega-section was laid-up and pre-formed as described above, with additional compression being applied along the entirety of the female radius.

The thickness of the pre-form was generated by sectioning and measurements using microscopy and Image-J software ("Image-J" is a Trade Mark). Measurements were made at selected locations across the planar sections 700 and along each male radius 702 and each female radius 704. The measurement points are marked p1-p24 in Figure 13. Fibre volume fraction (Vf) was calculated from the measured thicknesses and data are shown in Table 1.

These data show that the average FVf of the planar sections 700 are at the nominal value of 60%. The average FVf of the male radii 702 was 58%, and of the female radii 704, 55%. These values are considered acceptable for aerospace applications. Table 1

In comparison, Omega section pre-forms prepared conventionally (i.e. using compression and consolidation under vacuum only) are found to have significantly lower average FVf in the female radii, in the range 50-55%.

Further testing was conducted to assess the effect of tightening the radius of the female radiused portion of the preform. A "Z-section" carbon fibre preform was laid-up on a tool having a set of modular wedges securable to the base of the tool, to vary the female angle of the preform (as illustrated in Figure 8). A 20 ply preform was constructed, in 4 ply stages separated by vacuum bagging and IR heating as described above.

Each preform was then transferred to a curing tool with a nominal angle of 84° for OOA curing, using a room temperature infusion that had a resin pot life of 75 minutes. Curing was completed within this period. The average thickness of the cured composite Z-section was then measured at 3 points along the midpoint of the female radius. Tests were conducted using preform angles of 110°, 105°, 100°, 95° and 84°. That is to say, the angle was tightened by between 9 and 26 degrees between preforming and curing. Results are shown in Figure 13, and indicate that parts manufactured at a preform angle of 105° and 110° have essentially the same female radius part thickness. The benefit of tightening the radius therefore levels off above an angle change of around 20°. Additionally, substantially all of the benefit is conveyed at a preform angle of 100° (tightening of 16° of the angle). This is regarded as optimal for manufacture, to avoid any internal damage to the structure of the preform resulting from changing the angle prior to curing.

Whilst exemplary embodiments have been described herein, these should not be construed as limiting to the modifications and variations possible within the scope of the invention as disclosed herein and recited in the appended claims.