METHOD FOR FORMING COMPONENTS FROM FIBRE-REINFORCED THERMOPLASTIC MATERIALS

Abstract: A single stage method for forming and joining pre-consolidated sheets (15, 16, 19) of fibre-reinforced thermoplastics material each having an adherent polymer layer (23, 24) in those areas that are to be joined comprises locating one of the sheets (15, 16) in a female mould tool cavity (18) which is heated to the fusion bonding temperature of the adherent layers (23, 24). A second sheet (19), located in register with the cavity is heated to its melt temperature and formed to shape by a male mould tool part (20) while simultaneously applying pressure to the areas of the sheets to be joined together to form the component.

Description: This invention relates to a method for forming components from fibre-reinforced thermoplastic materials and is particularly concerned with forming such components from at least two pre-consolidated constituent sheet-like parts at least one of which has to be formed to shape before uniting with the other part(s), and at least one of which parts provides a reinforcing function. The aircraft industry makes wide use of fibre-reinforced thermoplastic materials and many components of the above construction exist in that field. For example, conventional stiffening ribs have a web portion and a peripheral reinforced flange portion and a bulkhead may well include internal web stiffeners in addition to peripheral reinforced flange portions. Traditionally such components are made by a three-stage process in which the first stage is pre-consolidation of sheets of material of sizes and thicknesses appropriate to the required shape of the parts of the component; for instance the web portion and flanges of a rib or bulkhead, and one or more reinforcing sheets of a desired thickness. In a second stage, those pre-consolidated sheets requiring to be shaped, eg. the web portion sheet and possibly the reinforcing sheet(s) is/are formed to shape in a mould tool. Finally the sheets, shaped as required, are transferred to and assembled in an assembly tool in which they are held under appropriate heat and pressure for a desired period of time to fusion bond the sheets one to the other. During the pre-consolidation stage, the sheets may be provided with a co-moulded adherent polymer layer in those areas that are eventually to be attached together to assist fusion bonding, as disclosed in EP-A-0 320 155 published on 14.06.89. This three-stage process is time consuming and costly in that separate mould and assembly tools are required. An object of the invention is to mitigate these disadvantages of the current procedures. Accordingly this invention provides a method for forming a component from fibre-reinforced thermoplastic materials, comprising pre-consolidating individual sheet-like parts of fibre-reinforced thermoplastic material each incorporating a co-moulded adherent polymer layer in a junction area, thereby to provide at least one part to be shaped and at least one reinforcing part. locating the reinforcing part in a female mould tool part, locating the part to be shaped in register with the female mould tool part, locating a male mould tool part in register with the female tool part and adjacent the surface of the part to be shaped remote from the female mould tool part, heating the part to be shaped to its melt temperature and the mould tool parts to the fusion bonding temperature of the adherent polymer layers, bringing the mould tool parts together to form to shape the said part to be shaped and simultaneously applying pressure to said junction areas incorporating said adherent polymer layer, maintaining the temperature of the mould tool parts for a predetermined time to ensure fusion bonding of the junction areas to unite the parts one with another, and cooling the mould tool parts and removing the thus-formed component. The male mould tool part may be resilient so that pressure applied in one plane to form to shape said part to be shaped automatically results in simultaneous application of pressure in another plane to assist said fusion bonding in the junction areas. The resilient male mould tool part may be rubber. The adherent polymer layer may comprise either a crystalline polymer having a melting point below that of the thermoplastic material, or an amorphous polymer having a glass transition temperature below that of the melting point of the thermoplastic material. Preferably the melting point of the crystalline polymer or the glass transition temperature of the amorphous polymer is at least 10°C below the melting point of the thermoplastic material. The invention will now be described by way of example only and with reference to the accompanying drawings in which, Figure 1 is a perspective view of a simple channel section component constructed according to the method of this invention, Figure 2 is a cross section illustrating one stage in the method, and Figure 3 is a cross section similar to Figure 2 and illustrating a further stage. Figure 1 illustrates an elongated channel section 11 constructed from fibre reinforced thermoplastic materials in accordance with the method of this invention. The simple channel section has been chosen for explanatory purposes since it will be understood that the invention is by no means limited to use in the manufacture of such simple components and can be used in the manufacture of more complex components having a greater number of constituent parts as will become evident hereinafter. Channel section 11 comprises a web portion 12 and two upstanding flange portions 13 and 14 extending throughout its length. Flange portions 13 and 14 are generally perpendicular to the plane of the web portion 12 and are provided with reinforcing sheets 15 and 16 of fibre reinforced thermoplastic material. Sheets 15 and 16 are first pre-consolidated by hot press forming from a required number of laminae of fibre-reinforced thermoplastic material to build up the desired thickness and a co-moulded adherent polymer layer 24 is incorporated on the surfaces that are to be attached to flange portions 13 and 14. A further flat sheet of material comprising the developed shape of the web portion 12 and flange portions 13 and 14 of channel 11 is similarly pre-consolidated from a required number of laminae of fibre-reinforced thermoplastic material with a co-moulded adherent polymer layer 23 incorporated on the surfaces that are to be attached to reinforcing sheets 15 and 16. The adherent polymer layers 23 and 24 may comprise either a crystalline polymer having a melting point below that of the sheets of thermoplastic material or an amorphous polymer having a glass transition temperature lower than the melting point of the sheets. Preferably the respective melting point or glass transition temperatures are at least 10°C lower than the melting point of the sheets. Referring now to Figure 2, reinforcing sheets 15 and 16 are located along respective edges of a cavity 17 of a female mould tool part 18 with the adherent layers 23 located inwardly. The sheet to be formed to shape comprising the developed shape of web and flange portions 12, 13 and 14 (Figure 1) and identified by numeral 19 in Figure 2 is located in appropriate register with the cavity 17 of female mould tool part 18, and a resilient rubber male mould tool part 20 is located above the sheet 19. The edge regions of sheet 19 carrying the adherent layers 24 are lowermost. Sheet 19 is heated to a temperature sufficient to melt the thermoplastic material. The temperature will vary depending on the material being used and is, for example, about 400°C for Poly Ether Ether Ketone (PEEK) matrix materials. The male and female mould tool parts 18 and 20 are heated to a temperature above the respective melt or glass transition temperatures at which fusion bonding of the adherent polymer layers 23 and 24 can occur, typically about 280°C. The actual temperature will again depend on the material of the adherent layer, examples of suitable materials being amorphous polyethersulphone (PES) having a glass transition temperature of 220°C, and amorphous polyetherimide (PEI) having a glass transition temperature of 213°C. Heating of sheet 19 is accomplished conveniently using electric heating elements which are located on one or both sides of the sheet for movement away from the sheet just prior to forming. The mould tool parts can be heated by location in the heated platens of a platen press. Male mould tool part 20 is moved into cavity 17 of female mould tool part 18 to form sheet 19 into the channel section 11 with web portion 12 and upstanding flange portions 13 and 14 (Figure 3). The temperature of the sheet 19 falls rapidly as heat dissipates into the larger bulk of the mould tool parts 18 and 20 which are maintained at the appropriate fusion bonding temperature and pressure for a predetermined time to ensure fusion bonding of the flange portions 13 and 14 to the respective reinforcing sheets 15 and 16. In the illustrated embodiment bonding pressure is automatically achieved by the use of rubber for the male mould tool part 20 because downward pressure as indicated by arrows 21 results in outward horizontal pressure indicated by arrows 22 being applied to the mated perpendicularly oriented parts 13, 15 and 14, 16. The mould tool parts 18 and 20 are allowed to cool and the finished component is removed. Thus the method of the present invention provides a single stage process for final forming to shape of a component including the application of reinforcing material in desired areas, and is accomplished in a single tool. It will be understood that the reinforcing material may comprise material to be used in the form of stiffeners, flanges, localised reinforcement around holes etc. or any combination of same in a particular component. Whilst described with reference to a simple channel section it is envisaged that the invention will be of particular benefit in the manufacture of more complex components. In the aircraft industry such components may include a typical rib component having corrugated reinforced flange portions and a bulkhead component having a peripheral reinforced flange and web plate reinforcing stiffeners. In the latter case the pre-consolidated stiffeners appropriately provided with an adherent polymer layer could be located in recesses in the surface of cavity 17 of female mould tool part 18 so as to be fusion bonded to the surface of the web portion 12 after forming of the channel section 11 and during the hereinbefore described fusion bonding stage. Consequently whilst one embodiment has been described and illustrated it will be understood that many modifications may be made without departing from the scope of the invention as defined in the appended claims. For example, any known method of forming and pre-consolidating the sheets may be used instead of hot press forming method such as autoclave or conventional mould tool forming. Any alternative means such as infra-red heaters or hot gas may be used to heat sheet 19, and the mould tool parts may contain individual heating means such as electrical elements or hot gas or liquid ducts to maintain the parts at the desired fusion bonding temperatures.

Claims: A method for forming a component (11) from fibre-reinforced thermoplastic materials, comprising pre-consolidating individual sheet-like parts (15, 16, 19) of fibre-reinforced thermoplastic material each incorporating a co-moulded adherent polymer layer (23, 24) in a junction area, thereby to provide at least one part (19) to be shaped and at least one reinforcing part (15, 16), locating the reinforcing part (15, 16) in a female mould tool part (18), locating the part (19) to be shaped in register with the female mould tool part, locating a male mould tool part (20) in register with the female tool part (18) and adjacent the surface of the part (19) to be shaped remote from the female mould tool part, heating the part (19) to be shaped to its melt temperature and the mould tool parts (18, 20) to the fusion bonding temperature of the adherent polymer layers (23, 24), bringing the mould tool parts (18, 20) together to form to shape the said part (19) to be shaped and simultaneously applying pressure to said junction areas incorporating said adherent polymer layers (23, 24), maintaining the temperature of the mould tool parts (18, 20) for a predetermined time to ensure fusion bonding of the junction areas to unite the parts (15, 16, 19) one with another, and cooling the mould tool parts and removing the thus-formed component. A method according to claim 1, wherein said male mould tool part (20) is resilient so that applied pressure in one plane to form to shape said part (19) to be shaped results automatically in said simultaneous application of pressure in another plane to assist said fusion bonding in said junction areas. A method according to claim 2, wherein said resilient male mould tool part is rubber. A method according to any preceding claim, wherein said adherent polymer layer (23, 24) comprises either a crystalline polymer having a melting point below that of the thermoplastic material or an amorphous polymer having a glass transition temperature below that of the melting point of the thermoplastic material. A method according to claim 4, wherein the melting point of the crystalline polymer or the glass transition temperature of the amorphous polymer is at least 10°C below the melting point of the thermoplastic material.

Inventors: DUTHIE, ANTONY CRAIG
Applicants: WESTLAND HELICOPTERS LIMITED
Application year: 1989
Main classification: B29C43
IPC codes: B29C70, B29C53, B29C63, B29C51