WO2015025166A1

WO2015025166A1 - Microwave curing of composite materials

Info

Publication number: WO2015025166A1
Application number: PCT/GB2014/052562
Authority: WO
Inventors: Stephen OLLIER
Original assignee: Pentaxia Ltd
Priority date: 2013-08-23
Filing date: 2014-08-21
Publication date: 2015-02-26
Also published as: GB2519636A; GB201315084D0; GB201414863D0

Abstract

A tool (10, 110, 210, 310, 410, 510, 610) for moulding curable composite materials CM, the tool (10, 210, 310, 410, 510, 610) comprising a tool body (12, 112, 212, 312, 412, 512, 612) having a mould cavity (14, 114, 214, 314, 414, 514, 614) defined at least by a mould surface (16, 116, 216, 316, 416, 16, 616) on which composite material CM can be moulded, a microwave source (18, 118, 218, 318, 418, 518, 618) located in or on the tool body to emit microwaves into the cavity (14, 114, 214, 314, 414, 514, 614) to at least partially cure composite material CM on the mould surface (16, 116, 216, 316, 416, 516, 616) and pressurisation means (20, 120, 220, 320, 420, 520, 620) arranged to facilitate consolidation of the composite material CM during cure. A method of moulding curable composite materials using such a tool is also provided.

Description

MICROWAVE CURING OF COMPOSITE MATERIALS

The present invention relates to the microwave curing of composite materials, particularly but not exclusively to tools for and methodologies of curing curable resinous composite materials including fibre-reinforced curable resinous composite materials using microwaves.

Curable resinous composite materials, particularly fibre-reinforced curable resinous composite materials, are used in the manufacture of components and structures in many situations and industries including the aerospace, space, automotive, energy, marine and infrastructure industries amongst many others, due in the main to their relatively high strength, low weight and corrosion resistance. Fibre-reinforced resinous composite materials typically comprise reinforcing fibres, such as glass, carbon, aramid, boron, ceramic and/or natural fibres such as basalt, flax, hemp, jute and sisal in a curable resin matrix which often consists of one or a blend of thermosetting resins such as epoxies, phenolics, polyesters, bismaleimides, polyimides, benzoxazines and cyanate esters.

The reinforcing fibres are generally insoluble in the resin matrix, acting to strengthen and reinforce the resinous matrix, particularly once the resin is fully cured.

Such composite materials are typically moulded on a tool to form the desired components and structures. In the present specification, the term "tool" should be considered interchangeable with the term "mould". According to conventional techniques such curable composite material is placed, usually in multiple layers, on a surface of a tool and then subjected to cure conditions. Often, the layers of material are of fibres already impregnated with the matrix resin. The extent of impregnation or the amount of the resin impregnated can either be total (in this case the layers are typically called "prepregs") or the level of resin impregnation provided is partial (such layers are typically called "semi-pregs"). In further moulding techniques, layers of dry fibres (with no resin pre-impregnated in them) are layered up (on occasion with prepregs and/or semi-pregs) and the resin is provided either as separate films or layers and/or infused as a liquid. These are conventional techniques and the details will be well known to those skilled in the art.

Typically, the cure conditions involve the application of radiant heat and pressure (typically up to 7 bar) and autoclaves are used to provide these conditions.

Such techniques can produce moulded articles with very satisfactory performance levels, and indeed high levels of laminate quality and good dimensional accuracy. However, there are a number of significant drawbacks to such techniques.

Autoclave techniques are characterised by temperatures up to or exceeding 450°C and pressures up to 20 bar. The cure times are considered lengthy (typically up to 6 hours)) and very energy inefficient, because the techniques involve not only heating the composite material being moulded, but the moulds or tools themselves. Often the tools are metallic and represent large heat sinks. In an effort to address these inefficiencies, techniques have been devised that are so-called "out-of-autoclave" processes using low pressures (maximum 1 bar). However, whilst obviating the need to purchase expensive autoclaves, these techniques typically involve very long cure times (potentially up to 2 hours longer than autoclave cycles) and the quality of the product can be inferior in respect of void content and part surface quality. Indeed, it is often found that little, if any, reduction in energy consumption over autoclave processes is realised. Laminating layers of prepregs or semi-pregs, particularly bearing relatively heavy resin loads, can result in the entrapment of air between the layers. Trapped pockets of air can result in the formation of voids in the moulded article which for many applications can render the article inferior or potentially unusable.

In addition, some matrix resins used in prepreg materials (eg phenolics) can produce volatiles during the heated cure cycle, which volatiles can again, if not removed, produce voids in the finished article. It is therefore generally desirable to strive to remove such entrapped air and volatiles during the cure process.

According to aspects of the present invention there is provided a tool for moulding curable composite materials, the tool comprising a tool body having a mould cavity defined at least in part by a mould surface on which composite material can be moulded, a microwave source located in or on the tool body to emit microwaves into the cavity to at least partially cure composite material on the mould surface and pressurisation means arranged to facilitate consolidation of the composite material during cure.

The microwave source may be located, at least in part, within the mould cavity. The microwave source may comprise one or more magnetrons, the or one or more of which may be located in or on the tool body.

The or one or more of the magnetrons may be remote from the tool body, but connected thereto by connection means, such as a conduit along which microwaves generated by the magnetron(s) can travel to one or more antenna(e) from which microwaves are emitted. The or at least one of the antenna(e) may be located within the cavity and/or in close proximity to the cavity, such that microwaves emitted therefrom are emitted directly into the cavity. The microwave source or the or at least one antenna(e) may be embedded in or behind a surface defining in part the cavity, which surface may comprise the mould surface.

The microwave source and the antenna(e) located within the cavity are pressure sealed to enable the pressurisation means to establish pressurisation of moulding material on the mould surface and/or to prevent or limit damage to the source/antenna(e) and antenna(e) by the pressurisation means.

The microwave source used may produce microwave frequencies in the range 900 MHz to 100 GHz, more ideally in the range 2 GHz to 30 GHz. The antenna(e) is/are sited to emit microwaves at predetermined locations within the cavity to provide the exposure of the composite material on the mould surface to appropriate microwave radiation to provide suitable cure thereof, particularly substantially uniform cure thereof. A plurality of magnetrons may be provided and control means may be provided to control the generation of microwaves. The control means may control magnetrons within the plurality and/or antennae individually to control and may be pulse the emission of microwaves into the cavity. One or more deflectors and/or microwave intensifiers may be provided within the cavity to deflect microwaves to predetermined locations within the cavity, preferably to help ensure suitable and preferably even cure. The microwave source may provide a homogenous electromagnetic heating field.

Reflector means may be located within the cavity to reflect microwaves away from the tool body to help prevent heating of the tool body by the microwaves. The reflector means may be metallic, including one or more of gold, silver, aluminium, alloys thereof and other metals and their alloys. The reflector means may comprise one or more surfaces which are highly polished. Alternatively or in addition, the reflector means may comprise non-metallic material. The reflector means may comprise a coating or layer on one or more surfaces of the tool body defining the cavity. The mould cavity may be lined with such reflector means. Reflector means may be provided over some or all of the mould surface, and may provide some or all of the mould surface on which composite material can be moulded. Reflector means may be provided on selected areas of one or more other surfaces defining the cavity. Alternatively or in addition the reflector means may be located behind the mould surface, maybe a short distance or immediately behind the mould surface, to prevent microwaves from penetrating into the tool body and thus reducing unwanted heating of the tool body. The tool may comprise heating means arranged to heat some or all of the mould surface. The heating means may comprise a radiant heat source, such as heated liquid or vapour.

The heating means may be comprised on or in the reflector means. Alternatively or in addition the heating means may be comprised in or in close proximity to, and maybe beneath the mould surface, and may comprise one or more of an electric heating element and/or a heated liquid source such as heated water, oil or other liquid, and/or a heated gas or vapour source such as steam. The heating means may comprise one or more conduits and may comprise a network of conduits which may be formed in the tool body, through which heated fluid can be pumped. The mould surface may be defined on a composite layer or other structure eatable in the cavity, such as a slipper skin.

The material of the mould surface may comprise the same material or otherwise have a similar coefficient of thermal expansion (CTE) as composite material being moulded thereon.

The composite layer or structure may be integrally formed in the tool, adhered within the tool and/or locatably removable within the tool.

The tool body may comprise a plurality of sections which between them define the cavity.

One or more of said sections may comprise or carry the microwave source. One or more of said sections may define the mould surface.

The sections may be selectively separable and preferably sealingly selectively separable from each other to enable access to the tool cavity for placement and removal of composite material on and from the mould surface, whilst enabling the pressurisation means to establish non-atmospheric pressure conditions within the cavity.

One or more seals may be provided between or eatable between the sections, to provide such sealing.

The pressurisation means may comprise a vacuum arrangement arranged to selectively draw air from within the cavity and maybe from beneath a sealed membrane such as vacuum bag located over composite material being moulded, to urge the material against the mould surface and draw air from within the composite material. The membrane may be transparent to microwaves so as not to be directly heated to any significant extent by the microwaves passing therethrough to the material on the mould surface. Alternatively, the membrane may be translucent to microwaves, allowing a degree of heating of the membrane by the microwaves passing therethrough.

Membranes of predetermined and selective thickness, chemistry and/or structure may be selectively used.

Alternatively or in addition, the pressurisation means may comprise an arrangement to increase the pressure generally within the cavity to cause the composite material being moulded to be pressed against the mould surface. The pressurisation means may comprise a source of compressed gas, such as air, and means to enable selective delivery of compressed gas into the mould cavity. The pressurisation means may comprise a compressor or similar means arranged to enable selective delivery of compressed gas, including air, into the mould cavity.

Alternatively or in addition, the pressurisation means may comprise a formation or other body eatable in the cavity to locate against and compress material being moulded against the mould surface. The formation may comprise an integral part of a section of the tool body.

The formation or other body may be transparent or translucent to microwaves. The or at least one of the microwave source(s) and/or antenna(e) may be located on or in the formation or other body. The tool body may be formed at least primarily of metallic material such as Invar, aluminium, steel, any other suitable materials and/or alloys thereof. The tool body may be formed at least primarily of non-metallic material, such as one or more of composite material, plastics materials, ceramics, non-metallic foams and the like. One or more thermal insulators may be located within the tool body, and preferably within the tool cavity to help insulate the tool against heating by heat radiating from materials heated by the microwaves.

According to further aspects of the present invention there is provided a method of moulding curable composite materials using a tool as described in any of the preceding thirty one paragraphs, the method comprising placing mouldable material on the mould surface, applying pressure to the material using pressurisation means to facilitate consolidation of the curable composite material and activating the microwave source to cause microwaves to be emitted into the cavity and to irradiate the curable composite material to at least partially cure the curable composite material.

The cavity may be airtight or substantially airtight to enable non-atmospheric pressure, typically elevated pressure, to be established within the cavity.

The pressurisation means may be activated prior to or during the activation of the microwave source. Microwave conductive material, which may be in the form of particles, may be provided in the composite material, and may be in the matrix resin of resinous composite materials, to increase the heating effect of the microwaves on the material. The microwave conductive material may comprise metallic particles, such as one or more of steel powder, aluminium powder, magnetic minerals (eg Magnetite) and conductive carbon-based materials, such as graphite powder, graphite flakes, graphite particles, carbon nanotubes and Graphenes. Curable composite materials may be located directly on the mould surface or may be located on a pre-formed body or slipper skin and then transferred to the mould surface. Pressure conditions, such as vacuum and/or elevated pressure (above 1 bar) conditions, may be applied during cure and also during placement of the mouldable composite material on the pre-forming tool and/or mould surface, potentially prior to cure.

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 cross section of a tool according to the present invention;

Fig 2 is a diagrammatic cross section of a tool according to further embodiments of the present invention;

Fig 3 is a diagrammatic cross section of a tool according to still further embodiments of the present invention; Fig 4 is a diagrammatic cross section of a tool according to yet further embodiments of the present invention;

Fig 5 is a diagrammatic cross section of a tool according to further embodiments of the present invention;

Fig 6 is a diagrammatic cross section of a tool according to further embodiments of the present invention; and

Fig 7 is a diagrammatic cross section of a tool according to further embodiments of the present invention. Referring to the drawings, there is provided a tool 10, 1 10, 210, 310, 410, 510, 610 for moulding curable composite materials CM, the tool 10, 210, 310, 410, 510, 610 comprising a tool body 12, 1 12, 212, 312, 412, 512, 612 having a mould cavity 14, 1 14, 214, 314, 414, 514, 614 defined at least by a mould surface 16, 1 16, 216, 316, 416, 516, 616 on which composite material CM can be moulded, a microwave source 18, 1 18, 218, 318, 418, 518, 618 located in or on the tool body to emit microwaves into the cavity 14, 1 14, 214, 314, 414, 514, 614 to at least partially cure composite material CM on the mould surface 16, 1 16, 216, 316, 416, 516, 616 and pressurisation means 20, 120, 220, 320, 420, 520, 620 arranged to facilitate consolidation of the composite material CM during cure.

In more detail, the tool illustrated in Fig 1 comprises a tool body 12 having two main sections 22, 24.

Section 22 defines the mould surface 16, which is illustrated as a very simple rounded, hemispherical surface, for simplicity of illustration. It will of course be appreciated that surface profiles ranging from simple to complex can be provided as the mould surface within tools of the present invention.

Section 24 provides a closure that locates over the section 22 to sealingly close the tool and in particular to ensure that the cavity is selectively sealable during cure of material therein, as will be described. One or more seals 26 are provided to seal the location of the sections together, in generally conventional manner. An inlet 25 is provided through the section 24 connecting the cavity 14 to the pressurisation means 20, which comprises a source of compressed air (or other gas).

The tool section 22 can be formed of any suitable material. Metallic materials, such as nickel-iron alloys (Invar), aluminium, steel, alloys of these and of other metals can be used. Alternatively, non-metallic materials such as composite material, plastics, ceramics, non-metallic foams and the like can be used. The section 24 can again be made of any suitable material, but typically it would be envisaged that all sections would be made of the same material. It is however possible that different materials could be used, known to those skilled in the art.

It will be appreciated that the tool 10 illustrated is a very simple construction, comprising just two sections. However, it is within the scope of the present invention for the tool to be made up of any number of sections, with appropriate seals and suchlike provided to enable the requisite degree of closure and sealing of the cavity, not least for adequate operation of the pressurisation means.

The microwave source 18 which includes a magnetron generating the microwaves is located on the section 24. It is arranged so that it emits microwaves directly therefrom, directly into the cavity and in the direction of the curable composite material CM on the mould surface 16. The propagation of microwaves emitted from the microwave source 18 is illustrated diagrammatically by the arrows M. In alternative embodiments the microwave source 18 may comprise a magnetron located within the tool body 12 but outside of the cavity and in other embodiments the magnetron may be located outside of the tool body 12 and connected to one or more antennae from which microwaves generated by the magnetron are emitted directly within the cavity 14. Further details of such additional embodiments follow.

The microwave source 18 is illustrated as extending from the inside surface 17 of section 24 of the tool 1 0, but it could be embedded, wholly or in part, in or just behind the inside surface of the tool section 24, again as will be discussed in more detail later. The microwave source 18 may be located behind a protective shield 19 to protect it from damage during use of the tool, which shield is transparent or invisible to the microwaves and as such does not appreciably affect the microwaves radiating into the cavity. The source 18 is also sealed against the inside of the cavity, preferably with an airtight seal, to facilitate establishment of pressure within the cavity by the pressurisation means, as will be described. The shield 19 typically provides the seal against the surface 17.

The microwave source 18 is strategically located to ensure that the microwaves emitted therefrom provide efficient and desirably uniform cure of material CM on the mould surface 16. Preferably, the microwave source 18 generates a homogenous electromagnetic heating field.

One or more deflectors and/or microwave intensifiers 28 may be provided within the cavity 14 to deflect or redirect microwaves to predetermined locations within the cavity, again preferably to help ensure suitable and preferably even cure of material CM on the mould surface. The very simple construction of the tool 10 as illustrated in Fig 1 is not considered to require any such deflectors and/or intensifiers, but such features are illustrated and discussed in more detail in relation to the embodiment illustrated in Fig 3.

In use, the tools of the present invention can be used to mould curable composite materials to manufacture components and structures in particular fibre-reinforced composite materials comprising a curable resinous matrix, such as one or more of epoxies, phenolics, polyesters, bismaleimides, polyimides, benzoxazines, cyanate esters, vinyl esters and others known to those skilled in the art (generally thermosetting resins) reinforced with fibres such as of glass, carbon, aramid, boron, ceramic, and natural fibres such as basalt, flax, hemp, jute, sisal and other reinforcing fibres known to those skilled in the art. Such materials are located on the mould surface 16 according to generally conventional techniques. Prepregs or semi-pregs can be laid to form a laminate structure directly on the mould surface, or they can be laid on as a pre-formed body and then transferred in pre-laminated form to the mould surface. The prepregs can be interleaved with other materials such as dry fibres, resin sheets, etc. Such techniques are known to those skilled in the art, with pre-forming off the mould surface typically being employed when the geometry of the component or structure being formed is complex or intricate. The materials CM illustrated in Fig 1 are in the form of prepregs or semi-pregs (although the laminate nature of the material has not been illustrated), where no additional external source of resin is required to be introduced to the cavity during the cure process. However, it will be appreciated that the present invention is suitable for use in moulding techniques where liquid resin is introduced to the fibrous material (whether dry fibre and/or semi-pregs) within the tool 10. Features required for so-called liquid resin infusion/injection techniques are not illustrated, but are well known to those skilled in the art who would readily appreciate how to modify the tools illustrated for use in such techniques.

Once the appropriate amounts and types of curable composite material CM is/are located on the mould surface 16, a generally conventional vacuum bag arrangement is located over the material CM. The vacuum bag arrangement illustrated comprises a breather layer 28 that extends over the material CM and parts of the surface of the cavity 14 and over the breather layer is located an air-impermeable membrane or vacuum bag 30, again sealed appropriately against the tool 10.

As indicated, these can be of generally known type and construction, although in the present invention the selection of such components that are transparent or invisible to microwaves and as such do not inhibit the transmission of microwaves to the material CM are preferred. Indeed, it is preferable that such components are almost entirely unaffected, whether by an increase in temperature or otherwise, as a result of the microwaves passing therethrough. That said, in other embodiments of the present invention the membrane may be only partially transparent or translucent to microwaves, thus experiencing a degree of heating when exposed to the microwave radiation. This selective control of the transparency/translucency enables a degree of control of the heating effect of the microwaves on the material being moulded. The thickness and/or chemistry and/or physical structure of the membrane may be chosen to provide the desired degree of transparency/translucency.

The breather layer 28 and vacuum bag 30 are configured to provide the requisite seal in conjunction with the seals 26 to the cavity, whilst the breather layer 28 is in communication beneath the vacuum bag 30 with a vacuum source, which in this embodiment comprises part of the pressurisation means 20. Once the breather layer 28 and vacuum bag 30 are suitably located, they are, as indicated previously, sealed beneath the seals 26 and the section 24, so that the cavity 14 is closed with an airtight or substantially airtight seal. The material CM is sealed beneath the vacuum bag 30, against the mould surface 16. The seal of the microwave source 18 against the inside of the cavity means that the cavity is effectively airtight. Compressed air (or other suitable gas) is admitted into the cavity 14 through the inlet 25 to increase the pressure in the cavity and urge the material CM against the mould surface 16 to drive consolidation thereof. Pressures are chosen according to the materials being moulded and the articles being formed, but can be up to 20 bar or even higher, the relative confinement and strength of the tool and the seals enabling such high pressures to be achieved and sustained. The combined effects of the vacuum and pressurisation presented by the pressurisation means not only consolidate the material, but simultaneously drive out trapped air and volatiles.

Activation of the microwave source 18 to emit microwaves directly within the cavity radiates the material CM causing rapid heating of the material CM. The speed and efficiency of the heating and thus curing of material CM by the microwaves is such that typically the microwaves would be emitted following appropriate pressurisation of the cavity. However, it will be appreciated that pressurisation and heating can be activated simultaneously and in certain embodiments the heating may precede pressurisation, particularly for more mechanical pressurisation, as will be described later.

In certain embodiments, microwave conductive material, such as conductive particles, may be incorporated into the material CM, and in particular the matrix resin, to enhance the inherent microwave conductibility of the material, particularly the matrix resin, and thus increase the efficiency of heating and thus cure of the material by the microwaves. The conductive material may comprise metallic particles such as one or more of steel and aluminium powder, magnetic minerals (eg Magnetite) and/or conductive carbon-based materials, such as graphite powder, graphite particles, graphite flakes, carbon nanotubes and Graphenes.

Locating the microwave source 18 on or in the tool body so that the microwaves are emitted inside the mould cavity 14 offers a key advantage of the present invention in helping to eliminate unnecessary external heating of the tool 10, whilst providing very efficient and effective heating of the composite material CM. This provides for relatively energy efficient cure of suitable composite materials, compared particularly to conventional autoclave processes that have been used for producing similar articles by moulding similar composite materials, not least because such autoclave processes necessarily involve heating of the tool as well as the material being moulded.

Also, pressurising just the mould cavity in accordance with the present invention again offers considerable efficiencies compared to conventional autoclave processes where the entire autoclave chamber has to be pressurised, which is very energy intensive. It also enables the strength of the tools and seals to be engineered such that very high pressures (over 20 bar) can be established and sustained within the cavity where required, which can help produce improved articles and components in certain applications.

The volumetric heating of the composite materials by the microwaves, which instantaneously penetrate the curable composite material to cause heating thereof, also enables dramatic reductions in cure cycle times to be realised, enabling more efficient production of structures and articles and overall more efficient manufacturing processes.

The externals of the tool 10 generally remain unheated. Particularly in embodiments where the tool body 12, or at least those parts thereof that define the cavity 14 are not conductive to microwaves and are thus not heated directly by them, there is little or no heating of the tool directly by the microwaves.

In certain embodiments one or more thermal insulators can be strategically placed on and in the tool, particularly the tool cavity, to help control the degree of any radiant heating of the tool body from the heated material being moulded or other parts of the tool heated by the microwaves.

Not only does this add energy efficiencies, but it also enables a rapid turnaround or reutilisation of the tool 10, because compared with conventional tools using autoclave processes, there is no need to allow time for the tool to cool down between uses. Fig 2 is a diagrammatic cross sectional view of a tool 1 1 0 according to further embodiments of the present invention. The tool 1 10 shares many of the features of the tool 10 of Fig 1 and corresponding features have been referenced with corresponding reference numerals, prefixed with the numeral

In these particular embodiments, a reflective coating or layer 32 is provided over the mould surface 1 16. Such a reflective coating or layer 32 is reflective to the microwaves, and shields the tool body section 122 from the microwaves, and thus shields it from being heated thereby.

The provision of such a reflective coating/layer is particularly useful for tool bodies made of materials that would otherwise be susceptible to direct heating by the microwaves, such as composite, plastics materials and other generally non-metallics. The reflective coating/layer 32 may be formed of a suitable metallic material such as one or more of gold, silver, aluminium, alloys of one or more of these, and other metals and their alloys. The reflective coating/layer 32 would typically have one or more highly polished surface(s). In certain embodiments, the reflective coating/layer 32 is formed of suitable non-metallic reflective material.

A reflective coating or layer can also be provided on one or more other surfaces of the tool, particularly within the cavity. The inside of the mould cavity can be lined with such reflective material in certain embodiments.

The reflective coating or layer 32 can comprise means to enable it to be selectively heated by means other than microwaves. Suitable heating means comprise an electrical heater such as one or more resistive electric elements located in or on the coating or layer 32. Heated liquids such as heated water and/or oil, heated gases, heated vapours such as steam may be used, pumped through a passage or network of passages formed in the coating or layer 32 from a source of such heated fluids (not shown).

This facility to heat the reflective coating or layer 32 and thus the mould surface 1 16 which the reflective coating/layer as illustrated in Fig 2 presents is desirable to avoid moulding curable moulding materials CM against a cold surface, as a cold surface can impair the surface quality and characteristics of the moulded article formed thereon. Where the tool sections 122, 124, or at least section 122 that define the mould surface 1 16, is itself metallic, a reflective coating or layer 32 is generally not considered necessary, but in such embodiments it has been found desirable to provide a composite layer or coating on the surface thereof, which composite layer defines at least in part the mould surface 1 16. This layer helps to absorb microwaves to be heated thereby. This is found to result in improved surface quality of the material and articles being formed thereof.

This composite layer or coating can also help minimise component distortion by providing adjacent to the material being formed a layer with a coefficient of thermal expansion that is the same or closely matches that of the material of the component being cured.

Such a composite layer or coating would typically be formed of the same or similar material as that being moulded, although it would typically be in pre-cured condition. Such a composite layer or coating can be formed directly into the surface of the mould section, or it can be adhered or otherwise fixed, permanently or removably, onto the section. The composite layer can be in the form of a slipper skin.

Fig 3 is a diagrammatic cross sectional illustration of a mould 210 according to further embodiments of the present invention. Again, the mould 210 shares many features with the tool of Fig 1 and generally corresponding features are referenced with the same numerals, prefixed with the numeral "2".

In this embodiment, the internal profile of the cavity 214 is more complex and is relatively larger in comparison to the microwave source, and as such two microwave sources 218 are provided. The locations of the microwave sources 218 are selected such that they provide a good degree of heating of the majority of the material CM located on the mould surface 216. However, to facilitate uniform heating and thus curing, a microwave deflector or intensifier 34 is located between the microwave sources 218, at a strategically appropriate location to deflect or redirect microwaves impinging thereon onto the material CM. In the embodiment illustrated the deflector or intensifier 34 is sited on the section 124, generally mid-way between the microwave sources 218. The deflector 34 is typically metallic and is profiled to deflect microwaves falling thereon onto the material CM. The deflection of the microwaves is illustrated very diagrammatically with arrows MB to help illustrate the function of the deflectors 34.

Such deflectors 34 will typically be strategically located at one or more locations within a mould cavity 214 to help direct microwaves particularly to areas or parts of the surface of the material being moulded that would otherwise experience little or no effect from the microwaves, such as material in or around corners or other angled or otherwise relatively complex geometries of the mould surface 216.

In this or further embodiments the two microwave sources 218 are controlled by control means (not shown) that controls emission of microwaves into the cavity. The control means can control the magnetron(s) generating the microwaves and/or the antennae emitting the microwaves, so that the microwaves emitted from the sources 218 can be individually controlled, including emitting the microwaves in controlled pulses.

The control of the emission of microwaves provides for further control of heating and cure within the cavity.

Fig 4 is a diagrammatic cross section of a tool 310 according to still further embodiments of the present invention. Again, the tool 310 shares many general features with the tool 10 of

Fig 1 , and shared features are referenced with the same reference numerals, prefixed with the number "3".

In this embodiment, heating means 36 is provided within the tool section 324 which provides for the selective heating of the mould surface 316. The heating means 36 is illustrated diagrammatically as an electrical resistance coil, matrix or similar arrangement, but any suitable heating means can be provided within the scope of the present invention. For example, a liquid based heating system that utilises heated water, oil or other liquid pumped through a chamber or network of capillaries or other passages a short distance beneath the mould surface 316 can be used. Alternatively or in addition, heated gases or vapours, such as steam, could be used, again generally through capillary networks or passages within the tool section 324 at a location close to and just beneath the mould surface 316.

The heating means 36 should not adversely affect the profile of the mould surface 16, so as not to adversely interfere with the surface quality of the material CM moulded on the surface 316. The provision of the heating means 36 helps to ensure good quality surface finishes of structures moulded on the tool 310. Generally it has been found that it is preferable not to mould curable composite materials on relatively cold surfaces. Typically, the mould surface 316 can be cool when the tool is constructed from metallic material. Therefore, providing the facility of being able to heat the mould surface 316 is considered to provide advantage to the tools of at least some embodiments of the present invention.

As has already been indicated, the heating means 36 may be incorporated into the reflective surface 32, as discussed in relation to the tools of Fig 2. Fig 5 is a diagrammatic cross section of a tool 410 according to other embodiments of the present invention. The tool 410 shares many general features with the tool 10 of Fig 1 , and shared features are referenced with the same reference numerals, prefixed with the number "4"). In this embodiment the pressurisation means 420 comprises a formation or body 420a on the underside of the section 424, which is profiled to locate within the corresponding recess in the section 422 so that when the sections 422 and 424 are sealed together as shown in Fig 5, the formation 420a presses against the vacuum bag 430 to urge and press the material CM in the cavity 414 against the mould surface 416. The formation 420a may be integrally formed with the section 424 or may be attached thereto.

In this embodiment the pressurisation means also comprises the vacuum arrangement 420b as described above, but it is within the scope of the present invention that the vacuum arrangement may not be provided, and the pressurisation means consists of the mechanical compression of the material CM within the mould cavity 414 as provided by the formation/body 420a. The microwave source 418 is embedded within the formation 420. The formation 420a is therefore formed of a material that is transparent to microwaves, so as not to impinge or unsatisfactorily affect the progression of the microwaves emitted therefrom to the material CM. Suitable materials for the formation 420a include polytetrafluoroethylene (PTFE).

Embedding the microwave source 18 within the formation 420a helps to protect the microwave source 418 from damage during use of the tool 410, and in embodiments where a vacuum seal is required, can help to establish suitable seals.

It will be appreciated that one or more microwave sources may be located within the formation 420a, and the microwave source could be located closer to the surface 21 thereof in certain embodiments.

Fig 6 is a diagrammatic cross section of a tool 510 according to still further embodiments of the present invention.

Again, the tool 510 shares many general features with the tool 10 of Fig 1 , and shared features are referenced with the same reference numerals, prefixed with the numeral "5"). In this embodiment the microwave source 518 comprises a magnetron

518a which generates the microwaves and an antenna 518b which emits the microwaves. The antenna 518b is located on the underside of the section 524 in generally central location to provide uniform distribution of microwaves within the mould cavity 514. As with other embodiments, the precise location and number of antenna(e) can be engineered as desired.

The magnetron 518a, which generates the microwaves, is connected to the antenna 518b by a conduit 518c along which the generated microwaves are channelled to be emitted from the antenna 518b. It will be appreciated that a plurality of antennae 518b can be connected to a single magnetron 518a, or indeed if necessary, a plurality of magnetrons 518a can be connected to one or more antennae 518b. Fig 7 is a diagrammatic cross section of a tool 610 according to still further embodiments of the present invention.

The tool 610 shares many general features with the tool 10 of Fig 1 , and shared features are referenced with the same reference numbers, prefixed with the number "6".

In this embodiment a plurality of microwave sources 618 are provided within the tool 610. One is located on the underside of the upper section 624 and a further two are embedded in the section 622 at spaced positions just beneath the mould surface 616. The embedded microwave sources 618 are located behind a sealed window 19, which whilst being transparent to microwaves emitted from the sources 618, seals the microwave sources 618 behind the surface 616. It is generally important that the windows 19 are flush with the surface

616 to ensure continuity and no disruption to the mould surface 616.

Locating one or more microwave sources within or behind the mould surface 616 can help provide very targeted and focussed emission of microwaves, and thus heating of material CM being moulded on the mould surface 616.

It will be appreciated that such embodiments are suitable in tools where the material CM is located directly on the tool surface, or any intermediate layers between the source 618 embedded in the tool body and the material CM are transparent or translucent to microwaves. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions can be described with reference to certain features, those functions may be performable by other features, whether described or not. Although features have been described with reference to certain embodiments, those embodiments may also be present in other embodiments, whether described or not.

Various modifications may be made without departing from the spirit or scope of the present invention. For example, the pressurisation means may be operable to increase the pressure within the cavity, to urge the material being formed against the mould surface, to facilitate consolidation thereof. A reflective layer or coating may be located behind the mould surface, maybe a short distance or immediately beneath the mould surface, to prevent microwaves from penetrating too far into the tool body, and thus help reduce unwanted heating thereof. The mould surface may be defined over a plurality of tool sections.

A tool may comprise a plurality of microwave sources, such as two or more magnetrons. The microwave sources may be independently controllable. Alternatively, a single microwave source or magnetron may be connected to two or more antennae or similar devices to emit microwaves into a mould cavity or mould cavities at a plurality of locations. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1 . A tool for moulding curable composite materials, the tool comprising a tool body having a mould cavity defined at least in part by a mould surface on which composite material can be moulded, a microwave source located in or on the tool body to emit microwaves into the cavity to at least partially cure composite material on the mould surface and pressurisation means arranged to facilitate consolidation of the composite material during cure.

2. A tool for moulding curable composite material as claimed in claim 1 , in which the microwave source is located, at least in part, within the mould cavity.

3. A tool for moulding curable composite material as claimed in any preceding claim, in which the microwave source comprises one or more magnetrons.

4. A tool for moulding curable composite material as claimed in claim 3, in which one or more of the magnetrons is located in or on the tool body.

5. A tool for moulding curable composite material as claimed in claim 3 or claim 4, in which the or one or more of the magnetrons is/are remote from the tool body, but connected thereto by connection means along which microwaves generated by the magnetron(s) can travel to one or more antenna(e) from which microwaves are emitted.

6. A tool for moulding curable composite material as claimed in claim 5, in which the connection means is a conduit.

7. A tool for moulding curable composite material as claimed in claim 5 or claim 6, in which the or at least one of the antenna(e) is/are located within the cavity, such that microwaves emitted therefrom are emitted directly into the cavity.

8. A tool for moulding curable composite material as claimed in any of claims 5 to 7, in which the or at least one of the antenna(e) is/are located within the cavity such that microwaves emitted therefrom are emitted directly into the cavity.

9. A tool for moulding curable composite material as claimed in any of claims 2 to 8, in which the microwave source or the or at least one antenna(e) is/are embedded in or behind a surface defining in part the cavity.

10. A tool for moulding curable composite material as claimed in any of claims 2 to 9, in which the microwave source or the or at least one of the antenna(e) is/are embedded in or behind the mould surface.

1 1 . A tool for moulding curable composite material as claimed in any of claims 2 to 10, in which the microwave source and the antenna(e) located within the cavity is/are pressure sealed to enable the pressurisation means to establish pressurisation of moulding material on the mould surface.

12. A tool for moulding curable composite material as claimed in any of claims 2 to 1 1 , in which the microwave source and/or the antenna(e) located within the cavity is/are pressure sealed to prevent or limit damage to the source/antenna(e) and antenna(e) by the pressurisation means.

13. A tool for moulding curable composite material as claimed in any preceding claim, in which the microwave source used produces microwave frequencies in the range 900 MHz to 100 GHz.

14. A tool for moulding curable composite material as claimed in any preceding claim, in which the microwave source produces microwave frequencies in the range 2 GHz to 30 GHz.

15. A tool for moulding curable composite material as claimed in any of claims 5 to 14, in which the antenna(e) is/are sited to emit microwaves at predetermined locations within the cavity to provide the exposure of the composite material on the mould surface to appropriate microwave radiation to provide suitable cure thereof, particularly substantially uniform cure thereof.

16. A tool for moulding curable composite material as claimed in any of claims 3 to 15, in which a plurality of magnetrons is provided along with control means to individually control magnetrons within the plurality.

17. A tool for moulding curable composite material as claimed in claim 16, in which the control means controls the emission of microwaves from the antennae.

18. A tool for moulding curable composite material as claimed in claim 16 or claim 17, in which the control means controls the pulsed emission of microwaves into the cavity.

19. A tool for moulding curable composite material as claimed in any preceding claim, in which one or more deflectors and/or microwave intensifiers is/are provided within the cavity to deflect microwaves to predetermined locations within the cavity.

20. A tool for moulding curable composite material as claimed in claim 19, in which one or more deflectors and/or microwave intensifiers is/are provided within the cavity to deflect microwaves to predetermined locations within the cavity to ensure even cure.

21 . A tool for moulding curable composite material as claimed in any preceding claim, in which the microwave source provides a homogenous electromagnetic heating field.

22. A tool for moulding curable composite material as claimed in any preceding claim, in which reflector means is located within the cavity to reflect microwaves away from the tool body to help prevent heating of the tool body by the microwaves.

23. A tool for moulding curable composite material as claimed in claim 22, in which the reflector means is metallic, including one or more of gold, silver, aluminium, alloys thereof and other metals and their alloys.

24. A tool for moulding curable composite material as claimed in claim 22 or claim 23, in which the reflector means comprises one or more surfaces which are highly polished.

25. A tool for moulding curable composite material as claimed in any of claims 22 to 24, in which the reflector means comprises non-metallic material.

26. A tool for moulding curable composite material as claimed in any of claims 22 to 25, in which the reflector means comprises a coating or layer on one or more surfaces of the tool body defining the cavity.

27. A tool for moulding curable composite material as claimed in any of claims 22 to 26, in which the mould cavity is lined with such reflector means.

28. A tool for moulding curable composite material as claimed in any of claims 22 to 27, in which reflector means is provided over some or all of the mould surface.

29. A tool for moulding curable composite material as claimed in any of claims 22 to 28, in which reflector means is provided over some or all of the mould surface on which composite material can be moulded.

30. A tool for moulding curable composite material as claimed in any of claims 22 to 29, in which reflector means is provided on selected areas of one or more other surfaces defining the cavity.

31 . A tool for moulding curable composite material as claimed in any of claims 22 to 30, in which reflector means is located behind the mould surface to prevent microwaves from penetrating into the tool body and thus reducing unwanted heating of the tool body.

32. A tool for moulding curable composite material as claimed in claim 31 , in which reflector means is located a short distance or immediately behind the mould surface.

33. A tool for moulding curable composite material as claimed in any preceding claim, in which the tool comprises heating means arranged to heat some or all of the mould surface.

34. A tool for moulding curable composite material as claimed in claim 33, in which the heating means comprises a radiant heat source.

35. A tool for moulding curable composite material as claimed in claim 33 or claim 34, in which the heating means comprises heated liquid or vapour.

36. A tool for moulding curable composite material as claimed in any of claims 33 to 35, in which the heating means is comprised on or in the reflector means.

37. A tool for moulding curable composite material as claimed in any of claims 33 to 36, in which the heating means is comprised in or in close proximity to the mould surface.

38. A tool for moulding curable composite material as claimed in claim 37, in which the heating means is beneath the mould surface.

39. A tool for moulding curable composite material as claimed in any of claims 33 to 38, in which the heating means comprises one or more of an electric heating element and/or a heated liquid source such as heated water, oil or other liquid, and/or a heated gas or vapour source such as steam.

40. A tool for moulding curable composite material as claimed in any of claims 33 to 39, in which the heating means comprises one or more conduits formed in the tool body, through which heated fluid can be pumped.

41 . A tool for moulding curable composite material as claimed in claim 40, in which a network of conduits is provided.

42. A tool for moulding curable composite material as claimed in any preceding claim, in which the mould surface is defined on a composite layer.

43. A tool for moulding curable composite material as claimed in any preceding claim, in which the mould surface is defined on a slipper skin in the cavity.

44. A tool for moulding curable composite material as claimed in any preceding claim, in which the material of the mould surface comprises the same material as composite material being moulded thereon.

45. A tool for moulding curable composite material as claimed in any preceding claim, in which the mould surface has a similar coefficient of thermal expansion (CTE) as the composite material being moulded thereon.

46. A tool for moulding curable composite material as claimed in any of claims 42 to 45, in which the composite layer is integrally formed in the tool.

47. A tool for moulding curable composite material as claimed in any of claims 42 to 45, in which the composite layer is adhered within the tool.

48. A tool for moulding curable composite material as claimed in any of claims 42 to 45, in which the composite layer is locatably removable within the tool.

49. A tool for moulding curable composite material as claimed in any preceding claim, in which the tool body comprises a plurality of sections which between them define the cavity.

50. A tool for moulding curable composite material as claimed in claim 49, in which one or more of said sections comprises or carries the microwave source.

51 . A tool for moulding curable composite material as claimed in claim 49 or claim 50, in which one or more of said sections defines the mould surface.

52. A tool for moulding curable composite material as claimed in any of claims 49 to 51 , in which the sections are selectively separable from each other to enable access to the tool cavity for placement and removal of composite material on and from the mould surface.

53. A tool for moulding curable composite material as claimed in claim 52, in which the sections are sealingly selectively separable to enable the pressurisation means to establish non-atmospheric pressure conditions within the cavity.

54. A tool for moulding curable composite material as claimed in claim 53, in which one or more seals is/are provided between or locatable between the sections, to provide such sealing.

55. A tool for moulding curable composite material as claimed in any preceding claim, in which the pressurisation means comprises a vacuum arrangement arranged to selectively draw air from within the cavity.

56. A tool for moulding curable composite material as claimed in claim 55, in which the pressurisation means comprises a vacuum arrangement arranged to selectively draw air from beneath a sealed membrane located over composite material being moulded, to urge the material against the mould surface and draw air from within the composite material.

57. A tool for moulding curable composite material as claimed in claim 56, in which the membrane is transparent to microwaves so as not to be directly heated to any significant extent by the microwaves passing therethrough to the material on the mould surface.

58. A tool for moulding curable composite material as claimed in claim 56, in which the membrane is translucent to microwaves, allowing a degree of heating of the membrane by the microwaves passing therethrough.

59. A tool for moulding curable composite material as claimed in any of claims 56 to 58, in which membranes of predetermined and selective thickness, chemistry and/or structure may be selectively used.

60. A tool for moulding curable composite material as claimed in any preceding claim, in which the pressurisation means comprises an arrangement to increase the pressure generally within the cavity to cause the composite material being moulded to be pressed against the mould surface.

61 . A tool for moulding curable composite material as claimed in claim 60, in which the pressurisation means comprises a source of compressed gas and means to enable selective delivery of compressed gas into the mould cavity.

62. A tool for moulding curable composite material as claimed in claim 60 or claim 61 , in which the pressurisation means comprises a compressor or similar means arranged to enable selective delivery of compressed gas into the mould cavity.

63. A tool for moulding curable composite material as claimed in any preceding claim, in which the pressurisation means comprises a formation or other body eatable in the cavity to locate against and compress material being moulded against the mould surface.

64. A tool for moulding curable composite material as claimed in claim 63, in which the formation comprises an integral part of a section of the tool body.

65. A tool for moulding curable composite material as claimed in claim 63 or claim 64, in which the formation or other body is transparent or translucent to microwaves.

66. A tool for moulding curable composite material as claimed in any of claims 63 to 65, in which the or at least one of the microwave source(s) and/or antenna(e) is/are located on or in the formation or other body.

67. A tool for moulding curable composite material as claimed in any preceding claim, in which the tool body is formed at least primarily of metallic material such as Invar, aluminium, steel, any other suitable materials and/or alloys thereof.

68. A tool for moulding curable composite material as claimed in any of claims 1 to 66, in which the tool body is formed at least primarily of non-metallic material, such as one or more of composite material, plastics materials, ceramics, non-metallic foams and the like.

69. A tool for moulding curable composite material as claimed in any preceding claim, in which one or more thermal insulators is/are located within the tool body, to help insulate the tool against heating by heat radiating from materials heated by the microwaves.

70. A tool for moulding curable composite material as claimed in claim 69, in which one or more thermal insulators are located within the tool cavity.

71 . A method of moulding curable composite materials using a tool as described in any of the preceding claims, the method comprising placing mouldable material on the mould surface, applying pressure to the material using pressurisation means to facilitate consolidation of the curable composite material and activating the microwave source to cause microwaves to be emitted into the cavity and to irradiate the curable composite material to at least partially cure the curable composite material.

72. A method as claimed in claim 71 , in which the cavity is airtight or substantially airtight to enable non-atmospheric pressure, typically elevated pressure, to be established within the cavity.

73. A method as claimed in claim 71 or claim 72, in which the pressurisation means is activated prior to or during the activation of the microwave source.

74. A method as claimed in any of claims 71 to 73, in which microwave conductive material is provided in the composite material, to increase the heating effect of the microwaves on the material.

75. A method as claimed in claim 74, in which the microwave conductive material is in the form of particles.

76. A method as claimed in either of claims 74 or 75, in which the microwave conductive material is in the matrix resin of resinous composite materials.

77. A method as claimed in any of claims 74 to 76, in which the microwave conductive material comprises metallic particles.

78. A method as claimed in claim 77, in which the microwave conductive material comprises one or more of steel powder, aluminium powder, magnetic minerals (eg Magnetite).

79. A method as claimed in claim 77 or claim 78, in which the microwave conductive material comprises conductive carbon-based materials, such as graphite power, graphite flakes, graphite particles, carbon nanotubes and Graphenes.

80. A method as claimed in any of claims 71 to 79, in which curable composite materials are located directly on the mould surface.

81 . A method as claimed in any of claims 71 to 79, in which curable composite materials are located on a pre-formed body or slipper skin and then transferred to the mould surface.

82. A method as claimed in any of claims 71 to 81 , in which pressure conditions, such as vacuum and/or elevated pressure (above 1 bar) conditions, are applied during cure and also during placement of the mouldable composite material on the pre-forming tool and/or mould surface.

83. A method as claimed in claim 82, in which pressure conditions are applied prior to cure.

84. A tool for moulding curable composite material hereinbefore described with reference to the accompanying drawings.

85. A method of moulding curable composite materials substantially as hereinbefore described with reference to the accompanying drawings.

86. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.