GB2486230A

GB2486230A - Placement head for composite structure

Info

Publication number: GB2486230A
Application number: GB201020741A
Authority: GB
Inventors: Giovanni Marengo; David Maclean; Jonathan Moram; Ben Ralfs; Marcus Gawn
Original assignee: GKN Aerospace Services Ltd
Current assignee: GKN Aerospace Services Ltd
Priority date: 2010-12-07
Filing date: 2010-12-07
Publication date: 2012-06-13
Anticipated expiration: 2030-12-07
Also published as: GB201020741D0; GB2486230B

Abstract

A placement head 9 for laying-up a strip of ply material 21 of a composite structure (2 figure 2) comprises a body 72, 82 supporting a main roller 71 and a secondary tool 81 and defines a placement path for delivering strip 21 to a placement position (715 figure 6), (716 figure 8), (811 figure 7). Tool 81 has a curved portion with a radius R2 (figure 6) which is less than radius R1 (figure 6) of roller 71. Roller 71 and tool 81 have a first configuration (figure 6) in which roller 71 projects beyond tool 81 and the placement path ends at roller 71; and there is a second configuration (figure 7) in which tool 81 projects beyond roller 71 and the placement path ends at tool 81. The second configuration is used when laying-up the material in the internal corner (64 figure 6) of a concave bend (63 figure 6) of a mould (6 figure 6). There is also a method using such a head and it is particularly suited to forming a fan containment case (2 figure 1) for a gas turbine engine (1 figure 1).

Description

Placement head

Field of the Invention

The present invention relates to a placement head for laying-up a strip of ply material of a composite structure such as a containment case for a gas turbine engine, although the present invention is broadly applicable to any composite structure which includes an elongate concave recess such as a concave bend between two portions of the composite structure.

Background

Characteristics of composite materials have meant that composite components are employed in an increasing range of applications from aerospace to automotive parts.

In the aerospace industry, for example, composite materials have been used for a number of years owing to their strength to weight ratio. The term "composite materials" (known also as "composites") is used to describe materials comprising for example glass fibre or carbon fibres and an epoxy resin (or similar). These are also known as glass reinforced plastic or carbon fibre reinforced composites. The carbon fibre reinforced composite material offers improved properties such as lower weight, improved fatigue/damage resistance, corrosion resistance and negligible thennal expansion.

The use of these materials has increased throughout the aerospace industry predominantly because of the fuel savings which can be achieved over the life of an aircraft by reducing the overall sum weight of the components making up the aircraft. Aerodynamic as well as structural components are formed of composite materials and particularly carbon fibre materials.

A composite component may be laid-up using a cloth, tape or the like pre-impregnated with resin to form a stack corresponding to the desired shape of the part to be formed. The stack is then cured either at ambient temperature and pressure or at elevated temperature and pressure in an autoclave to create a hardened component.

A gas turbine engine such as a turbofan may be provided with a containment case for preventing a broken blade of the engine from exiting the engine and damaging the rest of the aircraft. For example, a containment case may be provided around the fan at the front of the S turbofan engine. The containment case may be made of composite material such as carbon fibre reinforced composite material and/or Kevlar reinforced composite material. The containment case is in the shape of a generally cylindrical barrel or housing. The containment case needs to be attached to adjacent structural components of the engine and it is therefore desirable for the containment case to include a flange at one or both of the ends of the barrel or housing.

Fig. I is a diagrammatic side view of a typical known turbofan engine 1 having a fan case 11 defining a fan duct 12 which contains a rotating disc of fan blades 13. The fan blades 13 rotate around a central longitudinal axis 14 of the engine 1.

The fan case 11 is annular and is centred on the longitudinal axis 14. The fan case 11 is shown partly cut away in Fig. 1 in order to diagrammatically illustrate the fact that the fan case 11 includes an annular containment case 2 positioned around the periphery of the disc of fan blades 13 in order to contain any broken fan blade 13. The containment case 2 comprises a generally-cylindrical barrel or housing 3 at the front end of which is an outwardly-extending annular flange 41 and at the rear end of which is an outwardly-extending annular flange 42.

The containment case 2 is centred on the longitudinal axis 14 of the engine 1 and is held in position by being fastened to other components of the fan case 11 such as an annular front leading edge 51 and an annular rear edge 52. The flanges 41 and 42 may be provided with holes for fasteners which are used to attach the containment case 2 to the structure of the leading and rear edges 51, 52.

Fig. 2 is a diagrammatic perspective view of the containment case 2 shown in Fig. 1.

It is convenient to use a machine, such as an automated tape laying (ATL) machine or an automated fiber placement (APP) machine, to lay-up the plies of composite material of the housing of the containment case on a mould or mandrel. It can prove difficult to use a machine to lay-up the plies of the composite material of the flange and to integrate the composite material of the flange with the composite material of the housing, before the housing and the flange are cured. Thus, it has sometimes proved necessary to manually lay-up the plies of the flange, ply by ply, against an outwardly-projecting annular wall of the mould which extends outward from the main cylindrical mould surface on which the plies of the housing have been machine-laid up. The plies of the flange are hand laid and must be intermeshed with the machine-laid plies of the housing. This tends to produce a flange of inconsistent quality and, in order to compensate for this, a flange which is heavier than it needs to be because it is using an excess of composite material.

Machine lay-up is clearly preferable to hand lay-up, but machine lay-up is only possible if the placement head of the machine can achieve good access to the corner between the wall of the mould and the main mould surface. The placement head has a main roller which lays-up the tape (in the case of an ATL machine) or the fiber tow (in the case of an AFP machine) onto the surface of the mould, and the main roller has a diameter which is relatively large in order to avoid damaging the tape or tow during high-speed lay-up on the main mould surface. The main roller is not well suited to the intricate matter of laying-up in the tight corner between the wall of the mould and the main mould surface.

Figs. 3 to 5 are diagrammatic depictions of art attempt to use a cunent ATL machine to lay-up the part of the front flange 41 circled in dashed lines 410 in Fig. 2.

Figs. 3 to 5 are diagrammatic cross-sections of a portion of a mould 6 onto which a ply 21 of pre-impregnated uni-directional tape of composite material is being laid-up by a main roller 71 of a placement head of an ATL machine. The tape 21 may, for example, be carbon fibre tape which is pre-impregnated with a suitable resin such as epoxy resin.

The mould 6 has a generally-cylindrical main mould surface 61 and an annular mould surface 62 which is in the form of a wall which is perpendicular to the main mould surface 61. The plies which are to form the front flange 41 are laid-up on the annular mould surface 62, and the plies which are to form the housing 3 are laid-up on the main mould surface 61. In Figs. 3 to 5, only one ply (the first ply) is shown for reasons of clarity. In practice, the placement head would lay-up a sufficient ply depth to form the required thickness of composite material for the containment case 2.

In Fig. 3, the main roller 71 is travelling towards the concave bend 63 between the main surface 61 and the annular surface or wall 62. The main roller 71 is unwinding the tape 21 along a placement path which runs from a spool of tape (not shown) inside the placement head to a placement position 711 at which the tape 21 is placed on (laid-up on) the main mould surface 61.

In Fig. 4, the main roller 71 has reached the annular wall 62. The internal corner 64 of the concave bend 63 has a radius of curvature which is considerably less than the radius of curvature (the radius Ri) of the main roller 71. Thus, the tape 21 that is laid-up bridges the corner 64 by extending from a placement position 712 on the main surface 61 to a placement position 713 on the annular wall 62, and a gap or void 65 is left between the corner 64 and the laid-uptape2l.

In Fig. 5, the main roller 71 has moved up the annular wall 62, and the placement position for the tape 21 is now at position 714. The main roller 71 exerts a tugging or pulling force Fl as the main roller carries on moving away from the corner 64. This force Fl can drag the tape 21 that has already been laid-up in the area 210 and such dragging will increase the size of the void 65 that is bridging the corner 64. Thus, a first undesirable characteristic (the initial formation of the void 65) can be worsened by a second undesirable characteristic (the increase in size of the void 65).

It would be desirable to improve the placement head to obtain a better machine lay-up so that it is not necessary to have to revert to hand lay-up.

Summary of the Invention

According to a first aspect of the present invention, there is provided a placement head for laying-up a strip of ply material of a composite structure, comprising: a body supporting a main roller and a secondary tool and defining a placement path for delivering the strip of ply material to a placement position; wherein: the secondary tool has a curved portion with a radius of curvature which is less than the radius of the main roller; the main roller and the secondary tool have a first configuration in which the main roller projects beyond the curved portion of the secondary tool and the placement path ends at the main roller; and the main roller and the secondary tool have a second configuration in which the curved portion of the secondary tool projects beyond the main roller and the placement path ends at the curved portion of the secondary tool.

Thus, the secondary tool may be used when laying-up the strip of ply material in the internal corner of a concave bend of a mould. The radius of curvature of the secondary tool may be matched to the radius of curvature of the internal corner of the concave bend so that the laid-up ply material does not have an unwanted void between the internal corner and the ply material.

For example, the ply material may be uni-directional tape or a strip of fabric (in the context of a placement head for an ATL machine) or one or more side-by-side fiber tows (in the context of a placement head for an AFP machine). It is preferred to use ply material that is pre-impregnated with resin, although the ply material could be "dry" and the resin could be added after lay-up.

In a preferred embodiment, the secondary tool is a secondary roller and the curved portion of the secondary tool is a roller surface of the secondary roller. An alternative secondary tool might be a round bar covered with a low-friction material.

In a preferred embodiment, in the first configuration, the secondary tool is at a refracted position adjacent the placement path. Thus, the secondary tool is positioned ready for the transition from the first to the second configuration.

In a preferred embodiment, in the first configuration, the curved portion of the secondary tool is positioned adjacent the placement path. Thus, the secondary tool might be used by a control unit of the placement head to help with tensioning the strip of ply material as it passes along the placement path before it reaches the main roller.

In a preferred embodiment, the placement head is arranged to change from the first configuration to the second configuration by advancing the curved portion of the secondary tool beyond the main roller by passing the curved portion of the secondary tool circumferentially around the main roller.

In a preferred embodiment, the secondary tool advances from its retracted position and passes around the main roller and, in so doing, distorts the placement path until the placement path separates from the roller surface of the main roller, at which point the placement position for the strip of ply material is on the curved portion of the secondary tool.

In a preferred embodiment, the main roller and the secondary tool have a third configuration in which the curved portion of the secondary tool projects beyond the main roller and the placement path ends at the main roller. This may be achieved, in use, by positioning the main roller ahead of the curved portion of the secondary tool in the direction of travel of the placement head.

In a preferred embodiment, in the third configuration, the placement head is arranged to increase the separation between the curved portion of the secondary tool and the main roller.

In use, in the third configuration, the curved portion of the secondary tool may be held at a previous position that the secondary tool defmed in the second configuration (at which the laid-up ply material is at the inside of a bend), until sufficient further ply material has been laid-up that the ply material at the inside of the bend is unlikely to be pulled out of (lifted out of) the inside of the bend.

In a preferred embodiment, the placement head is arranged to change from the second configuration to the third configuration by rotating the main roller around the curved portion of the secondary tool.

In use, this may be achieved by rotating in a forward direction relative to the direction of motion of the placement head over the mould surface.

In a preferred embodiment, the placement head is arranged to change from the third configuration to the first configuration by passing the curved portion of the secondary tool cireumferentially around the rear side of the main roller.

In a cycle of going from the first configuration to the second configuration, from the second configuration to the third configuration, and from the third configuration to the first configuration, the curved portion of the secondary tool (e.g. the secondary roller) may perform a full revolution around the main roller.

In a preferred embodiment, in the second configuration, the curved portion of the secondary tool has an adjustable yaw angle and/or roll angle relative to an axis of rotation of the main roller.

Thus, for example, the axis of rotation of the secondary roller is adjustable (can be "gimballed") relative to the rotational axis of the main roller so that, if the direction of approach of the main roller to a concave bend of the mould is not perpendicular to the line of the bend, then the secondary roller can accommodate the difference.

According to a second aspect of the present invention, there is provided a placement head according to the first aspect of the present invention and means for moving the placement head relative to a mould surface. The movement means may, for example, be a robot arm or a gantry system.

According to a third aspect of the present invention, there is provided a method of manufacturing a composite structure comprising a first portion and a second portion which is connected to the first portion through a bend, the method comprising the steps of: providing a mould having first and second mould surfaces which meet along a concave bend; providing a placement head which has a main roller with a first radius of curvature and a secondary tool with a curved portion with a second radius of curvature which is smaller than the first radius of curvature; feeding a strip of ply material along a placement path of the placement head to the main roller, when the main roller and the secondary tool are in a first configuration in which the main roller projects beyond the curved portion of the secondary tool, and to the curved portion of the secondary tool, when the main roller and the secondary tool are in a second configuration in which the curved portion of the secondary tool projects beyond the main roller; moving the placement head relative to the mould and laying-up the ply material on the first mould surface to form the first portion of the composite structure and on the second mould surface to form the second portion of the composite structure; wherein the laying-up includes the placement head crossing the concave bend of the mould and, when the placement head approaches the concave bend of the mould, the placement head changes from the first configuration to the second configuration; and curing resin in the laid-up composite structure.

In a preferred embodiment, the main roller and the secondary tool have a third configuration in which the curved portion of the secondary tool projects beyond the main roller, the placement path ends at the main roller, and the main roller is ahead of the curved portion of the secondary tool in the direction of travel of the placement head relative to the mould; and, when the placement head is crossing the concave bend of the mould and is moving away from the concave bend of the mould, the placement head changes from the second configuration to the third configuration.

Preferably, in the third configuration, the placement head is arranged to keep the curved portion of the secondary tool at the concave bend of the mould as the main roller moves further ahead of the curved portion of the secondary tool. Thus, the secondary tool may continue to hold the ply material in the concave bend to prevent the ply material from being dragged out of the bend by the forward motion of the main roller and the placement head.

In a preferred embodiment, when the placement head has moved a predetermined distance away from the concave bend of the mould, the placement head changes from the third configuration to the first configuration. The predetermined distance may be chosen by a control unit of the placement head to be such that the danger has passed of the ply material being dragged out of the bend. The predetermined distance may be influenced by parameters such as the speed of movement of the placement head, the shape of the mould-surface contour that the placement head is following and the characteristics of the ply material.

In a preferred embodiment, the composite structure is a fan containment case for a gas turbine engine, the first portion is an annular housing of the containment case and the second portion is an annular flange of the containment case.

Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic side view of a turbofan engine, partly cut away to show a containment case and a fan blade.

Fig. 2 is a diagrammatic perspective view of the containment case shown in Fig. 1.

Figs. 3 to 5 are diagrammatic depictions of an attempt to use a current ATL machine to lay-up part of the front flange circled in dashed lines in Fig. 2.

Figs. 6 to 8 are diagrammatic depictions of three stages of a method of manufacturing a fan containment case of a gas turbine engine in accordance with the present invention.

Fig. 9 is a diagrammatic perspective view of a placement head in accordance with the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail.

It should be understood, however, that the drawings and detailed description of the specific embodiments are not intended to limit the invention to the particular forms disclosed. On the contrary, the invention covers all modifications, equivalents and alternatives falling within the spirit and the scope of the present invention as defined by the appended claims.

Description of Embodiments

Embodiments of the present invention will be described with reference to Figs. 6 to 9 which illustrate how the present invention builds on the existing technology already described above with reference to Figs. 1 to 5.

As shown in Figs. 6 to 9, the embodiment of the placement head of the present invention adds a secondary roller 81 to the main roller 71 of the placement head. The secondary roller 81 has a radius R2 which is less than the radius Rl of the main roller 71.

In a first configuration shown in Fig. 6, the main roller 71 projects in front of the secondary S roller 81, and the placement path of the strip of ply material 21 ends at the main roller 71, which at a placement position 715 is laying-up the ply material 21 on the main mould surface 61. The secondary roller 81 is positioned behind the main roller 71 and is touching the tape 21 and is positioned ready to be rotated from the first configuration to the second configuration in which the secondary roller is moved forwards from its retracted position of Fig. 6 to an advanced position.

The radius R2 of the secondary roller 81 has been chosen to be substantially the same as the radius of curvature of the internal corner 64 of the concave bend 63. The particular roller that is used as the secondary roller may be chosen from a set of secondary rollers having different radiuses so that the one that is used substantially matches the radius of curvature of the internal corner 64.

In a second configuration shown in Fig. 7, the secondary roller 81 has been rotated anti-clockwise around the main roller 71 from its retracted position of Fig. 6 to an advanced position in which it projects beyond the main roller 71. This deployment of the secondary roller 81 as the first configuration changes to the second configuration happens as the placement head approaches the concave bend 63. By the time the placement head reaches the concave bend 63, the placement path of the tape 21 has been switched to ending at the secondary roller 81, which at a placement position 811 is laying-up the tape 21 into the internal corner 64 of the concave bend 63 and is pushing the tape 21 into the internal corner 64 to ensure that substantially no gap or void is left between the tape 21 and the internal corner 64.

The software that is controlling the ATL machine and the placement head now changes the direction of travel of the placement head so that, instead of laying-up tape on the main mould surface 61, the placement head starts to lay-up the tape 21 on the annular mould surface 62 used to form the flange 41 of the containment case 2.

In order to transition from the second configuration (Fig. 7) to a third configuration (Fig. 8), the secondary roller 81 holds its position in the internal corner 64 whilst the main roller 71 rotates anti-clockwise around the secondary roller 81 until the main roller is pressing against the mould surface 62. The secondary roller 81 still projects beyond the main roller 71 but the main roller 71 is now ahead of the secondary roller 81 in the direction of travel of the placement head (the upward direction in Fig. 8) and the placement path of the tape 21 now ends at the main roller 71, which at a placement position 716 is laying-up the tape 21 onto the wall of the mould surface 62.

if the mould 6 is stationary during the lay-up of the containment case 2, the secondary roller 81 will also be stationary when the placement head is in the third configuration. If the mould 6 moves (e.g. rotates around the longitudinal axis 14), the secondary roller 81 will track the movement of the mould 6 so that, in the third configuration, the secondary roller 81 is stationary relative to the internal corner 64.

When the main roller 71 has moved a sufficient distance up the wall of the mould surface 62, such that the dragging effect on the laid-up tape 21 of the forward movement of the main roller 71 is no longer in danger of pulling the laid-up tape 21 out of the internal corner 64, the placement head may transition from the third configuration (Fig. 8) back to the first configuration (Fig. 6) by rotating the secondary roller 81 anti-clockwise around the rear side of the main roller 71.

The main roller 71 is used for the bulk laying-up of the tape 21 on the main surface of the mould because it can travel over the mould surface more quickly than the secondary roller 81 because of its greater radius of curvature than that of the secondary roller. The tight radius of curvature of the secondary roller, whilst suited to the special task of laying-up in the concave bend 63, might damage the composite material of the tape 21 if the secondary roller were to be used all of the time.

After the required ply depth of tape 21 of the containment case 2 has been laid-up on the mould 6, the resin in the prepreg tape 21 is cured.

Fig. 9 is a diagrammatic perspective view showing a placement head 9 in accordance with the present invention. For reasons of clarity, Fig. 9 does not show standard components of the placement head such as a spool for carrying the tape 21, tape winder guides, a compaction shoe, a position sensor and a tape cutter or slitter.

The placement head 9 incorporates the secondary roller 81 in addition to the main roller 71.

The main roller 71 is carried on main arms 72 (only one of which is visible in Fig. 9) so as to be rotatable around a main axis 73.

The secondary roller 81 is carried on second arms 82 so as to be rotatable around a second axis 83 and is carried at its ends on bearings 84 in the form of universal joints so as to allow the second axis 83 to articulate or gimbal relative to the main axis 73. This enables the second axis 83 to undergo yawing motion (arrows Y) relative to the main axis 73 and also to undergo rolling motion (arrows RM) relative to the main axis 73. This is useful if the direction of approach of the placement head 9 to the concave bend 63 is not perpendicular to the line of the concave bend. The secondary roller 81 may be yawed and/or rolled relative to the main roller 71 so that, in the transition from the first configuration to the second configuration, the secondary roller is positioned to have its axis 83 generally aligned along the direction of the concave bend 63 in order to fit accurately in the internal corner 64.

The placement head 9 is shown as being used to form a flange which is generally perpendicular to the main surface of a main body of a composite structure. The included angle between the wall surface of the flange (the surface of a second portion of the composite structure) and the main surface of the main body (the surface of a first portion of the composite structure) could be other than 90° and could, for example, be 40° to 140°, or 50° to 130°, or 60° to 120°, or 70° to 110°, or 800 to 1000.

The surface of the second portion of the composite structure might be generally planar and the surface of the first portion of the composite structure might also be generally planar, at least adjacent the bend which connects the first portion to the second portion, such that the bend would be generally straight along its length rather than being annular as for the containment case 2.

There have been described embodiments of a placement head 9 for laying-up a strip of ply material 21 of a composite structure 2, comprising: a body 72, 82 supporting a main roller 71 and a secondary tool 81 and defming a placement path for delivering the strip of ply material 21 to a placement position 715, 716, 811; wherein: the secondary tool 81 has a curved portion with a radius of curvature R2 which is less than the radius Ri of the main roller 71; the main roller 71 and the secondary tool 81 have a first configuration in which the main roller 71 projects beyond the curved portion of the secondary tool 81 and the placement path ends at the main roller 71; and the main roller 71 and the secondary tool 81 have a second configuration in which the curved portion of the secondary tool 81 projects beyond the main roller 71 and the placement path ends at the curved portion of the secondary tool 81.

There have also been described embodiments of method of manufacturing a composite structure 2 comprising a first portion 3 and a second portion 41 which is connected to the first portion 3 through a bend, the method comprising the steps of: providing a mould 6 having first and second mould surfaces 61, 62 which meet along a concave bend 63; providing a placement head 9 which has a main roller 71 with a first radius of curvature Ri and a secondary tool 81 with a curved portion with a second radius of curvature R2 which is smaller than the first radius of curvature Ri; feeding a strip of ply material 21 along a placement path of the placement head 9 to the main roller 71, when the main roller 71 and the secondary tool 81 are itt a first configuration in which the main roller 71 projects beyond the curved portion of the secondary tool 81, and to the curved portion of the secondary tool 81, when the main roller 71 and the secondary tool 81 are in a second configuration in which the curved portion of the secondary tool 81 projects beyond the main roller 71; moving the placement head 9 relative to the mould 6 and laying-up the ply material 21 on the first mould surface 61 to form the first portion 3 of the composite structure 2 and on the second mould surface 62 to form the second portion 41 of the composite structure 2; wherein the laying-up includes the placement head 9 crossing the concave bend 63 of the mould 6 and, when the placement head 9 approaches the concave bend 63 of the mould 6, the placement head 9 changes from the first configuration to the second configuration; and curing resin in the laid-up composite structure 2. p

Claims

CLAIMS1. A placement head for laying-up a strip of ply material of a composite structure, comprising: a body supporting a main roller and a secondary tool and defining a placement path for delivering the strip of ply material to a placement position; wherein: the secondary tool has a curved portion with a radius of curvature which is less than the radius of the main roller; the main roller and the secondary tool have a first configuration in which the main roller projects beyond the curved portion of the secondary tool and the placement path ends at the main roller; and the main roller and the secondary tool have a second configuration in which the curved portion of the secondary tool projects beyond the main roller and the placement path ends at the curved portion of the secondary tool.
2. A placement head according to claim 1, wherein the secondary tool is a secondary roller and the curved portion of the secondary tool is a roller surface of the secondary roller.
3. A placement head according to claim 1 or 2, wherein, in the first configuration, the secondary tool is at a retracted position adjacent the placement path.
4. A placement head according to claim 3, wherein, in the first configuration, the curved portion of the secondary tool is positioned adjacent the placement path.
5. A placement head according to any preceding claim, wherein the placement head is arranged to change from the first configuration to the second configuration by advancing the curved portion of the secondary tool beyond the main roller by passing the curved portion of the secondary tool circumferentially around the main roller.
6. A placement head according to any preceding claim, wherein the main roller and the secondary tool have a third configuration in which the curved portion of the secondary tool projects beyond the main roller and the placement path ends at the main roller.
7. A placement head according to claim 6, wherein, in the third configuration, the placement head is arranged to increase the separation between the curved portion of the secondary tool and the main roller.
8. A placement head according to claim 6 or 7, wherein the placement head is arranged to change from the second configuration to the third configuration by rotating the main roller around the curved portion of the secondary tool.
9. A placement head according to any one of claims 6 to 8, wherein the placement head is arranged to change from the third configuration to the first configuration by passing the curved portion of the secondary tool circumlerentially around the rear side of the main roller.
10. A placement head according to any preceding claim, wherein, in the second configuration, the curved portion of the secondary tool has an adjustable yaw angle relative to an axis of rotation of the main roller.
11. A placement head according to any preceding claim, wherein, in the second configuration, the curved portion of the secondary tool has an adjustable roll angle relative to an axis of rotation of the main roller.
12. A placement machine comprising a placement head according to any preceding claim and means for moving the placement head relative to a mould surface.
13. A method of manufacturing a composite structure comprising a first portion and a second portion which is connected to the first portion through a bend, the method comprising the steps of: providing a mould having first and second mould surfaces which meet along a concave bend; providing a placement head which has a main roller with a first radius of curvature and a secondary tool with a curved portion with a second radius of curvature which is smaller than the first radius of curvature; feeding a strip of ply material along a placement path of the placement head to the main roller, when the main roller and the secondary tool are in a first configuration in which the main roller projects beyond the curved portion of the secondary tool, and to the curved portion of the secondary tool, when the main roller and the secondary tool are in a second configuration in which the curved portion of the secondary tool projects beyond the main roller; moving the placement head relative to the mould and laying-up the ply material on the first mould surface to form the first portion of the composite structure and on the second mould surface to form the second portion of the composite structure; wherein the laying-up includes the placement head crossing the concave bend of the mould and, when the placement head approaches the concave bend of the mould, the placement head changes from the first configuration to the second configuration; and curing resin in the laid-up composite structure.
14. A method according to claim 13, wherein the secondary tool is a secondary roller and the curved portion of the secondary tool is a roller surface of the secondary roller.
15. A method according to claim 13 or 14, wherein the placement head changes from the first configuration to the second configuration by advancing the curved portion of the secondary tool beyond the main roller by passing the curved portion of the secondary tool circamferentially around the main roller.
16. A method according to any one of claims 13 to 15, wherein: the main roller and the secondary tool have a third configuration in which the curved portion of the secondary tool projects beyond the main roller, the placement path ends at the main roller, and the main roller is ahead of the curved portion of the secondary tool in the direction of travel of the placement head relative to the mould; and when the placement head is crossing the concave bend of the mould and is moving away from the concave bend of the mould, the placement head changes from the second configuration to the third configuration.
17. A method according to claim 16, wherein the placement head changes from the second configuration to the third configuration by rotating the main roller around the curved portion of the secondary tool.
18. A method according to claim 16 or 17, wherein, in the third configuration, the placement head is arranged to keep the curved portion of the secondary tool at the concave bend of the mould as the main roller moves further ahead of the curved portion of the secondary tool.
19. A method according to claim 18, wherein, when the placement head has moved a predetermined distance away from the concave bend of the mould, the placement head changes from the third configuration to the first configuration.
20. A method according to any one of claims 16 to 19, wherein the placement head changes from the third configuration to the first configuration by passing the curved portion of the secondary tool circumferentially around the rear side of the main roller.
21. A method according to any one of claims 13 to 20, wherein, in the second configuration, the placement head adjusts the yaw angle of the curved portion of the secondary tool relative to an axis of rotation of the main roller in order to improve the alignment of the curved portion of the secondary tool with the concave bend of the mould.
22. A method according to any one of claims 13 to 21, wherein, in the second configuration, the placement head adjusts the roll angle of the curved portion of the secondary tool relative to an axis of rotation of the main roller in order to improve the alignment of the curved portion of the secondary tool with the concave bend of the mould.
23. A method according to any one of claims 13 to 22, wherein the second portion of the composite structure is a flange.
24. A method according to any one of claims 13 to 22, wherein the composite structure is a fan containment case for a gas turbine engine, the first portion is an annular housing of the containment case and the second portion is an annular flange of the containment case.
25. A method according to any one of claims 13 to 24, wherein the strip of ply material is pre-impregnated composite material tape.
26. A placement head substantially as herein described with reference to, or with reference to and as illustrated in, Figs. 6 to 9 of the accompanying drawings.
27. A method of manufacturing a composite structure substantially as herein described with reference to Figs. 6 to 9 of the accompanying drawings.