GB2141660A

GB2141660A - Fibre-reinforced plastics article

Info

Publication number: GB2141660A
Application number: GB08301430A
Authority: GB
Inventors: Peter James Mobbs
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1982-01-28
Filing date: 1983-01-19
Publication date: 1985-01-03
Also published as: GB8301430D0; GB2141660B

Abstract

A method of making the above involves forming a female mould (10); building up a layer of wax (13) within the mould; positioning formers; pouring a molten elastomer into the mould and allowing it to solidify (18); removing the solidified elastomer, the layer of wax and the formers; placing layers of plastics impregnated fibrous material in the mould (19) and in the former positions (19a) and replacing the elastomer (18), sealing the top of the mould and heating. The process is used in the making of accurate models for wind tunnel testing. <IMAGE>

Description

SPECIFICATION Fibre reinforced plastics forming methods The present invention relates to the forming of articles from composite materials such as fibre reinforced plastics (FRP).

FRP such as carbon fibre reinforced plastics (CFRP) is increasingly being used in a number of fields where its high strength to weight ratio is important. One such field is in the construction of models for aerodynamic test ing in wind tunnels. Such models must be made to a high degree of accuracy, and consequently their construction can prove to be inordinately time consuming and expensive. For example the construction of a model of an aerofoil such as a wing involves the formation of two skins in female moulds, with the simultaneous application of heat and pressure.

The heat and pressure are usually applied in an autoclave, which is an expensive piece of equipment. The two skins must then be joined together. For the finished article to have the required stiffness it must usually have one or more spars, ribs or both, each attached to both skins. It must also, in most cases, internally carry apparatus such as, for example, pressure transducers which are essential for the future use of the model. Assembly of these items with the required accuracy is an arduous process.

According to the present invention a method of forming an article from a composite material includes the steps of: forming a female mould; building up a layer of material within the mould to the required thickness of the article; positioning formers at required sections; pouring molten elastomeric material into the mould and allowing it to solidify; removing the solidified elastomeric material, the layer of material and formers; placing plastics impregnated fibrous material in the mould, and in the former positions and replacing the elastomeric material, sealing the top of the mould, and heating the mould.

The elastomeric material may be any elastomer which is capable of withstanding a moulding temperature of about 1 75 C ie the temperature to which the mould is heated in order to form the plastics impregnated fibrous material into the desired article eg a silicone rubber or neoprene. The layer of material built up on the mould prior to pouring molten elastomeric material into the mould, may be formed with wax, preferably a heat stable wax capable of withstanding the temperature of the molten elastomer.

The plastic impregnated fibrous material may suitably be a pre-preg of uncured or partially cured thermosetting resin impregnated in a carbon or glass fibre fabric which may woven or non-woven. The fibrous material may include any known fibre or combination of known fibres and the plastics material may be thermoplastics or thermosetting.

Articles according to the invention will usually have two skins, each formed as above, joined. along edges formed level with the tops of the moulds. The edges can be machined to a high degree of accuracy whilst the skins are still in the moulds, ensuring that the final article is accurately finished. Using the method of the present invention articles can be made much more cheaply than with conventional techniques, eg about f1500 compared with about 30,000.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is a plain view of a mould, Figure 2 is an elevation, in section, along line Il-Il of Fig. 1, Figure 3 is an elevation, in section, corresponding to Fig. 2, with pre-preg in position, and Figure 4 is an elevation, in section, (at the same section as in Fig. 3) of a moulded article.

A mould 10 (Figs. 1 and 2) for one skin of a model of an aerofoil has a cavity 11 with a surface 12 contoured to the desired contours of the outer surface of the skin. A layer 13 of wax is built up on the surface 12 to the desired thickness of the skin.

A former 14 is positioned spanwise in the cavity 11 at a desired spar position, and formers 1 spa, 1 6a and 1 sub, 1 6b are positioned respectively forward and aft of former 14 at desired rib positions. The mould 10 is thereby divided into six compartments 17 (Fig. 1). Molten silicone rubber is poured into the compartments 17 and allowed to solidify into blocks 18 (Fig 2).

The blocks 18 and formers 14, 15, 16, are then removed from the cavity 11 and the layer 13 stripped from surface 12.

Layers of plastics impregnated carbon fibre pre-preg 19 (Fig. 3) are then positioned against the surface 12. Some layers extend the full chord and span of surface 12 whilst others extend partway from, for example, the leading or trailing edge of surface 12 to the spar position previously occupied by the spanwise former 14. Then, as illustrated at 1 9a in Fig. 3 these layers are angled outwardly relative to surface 12. Similar arrangements are made at rib positions previously occupied by formers 15, 16. Blocks 18 are repositioned over the laminate layers 19 and the layers at spar and rib positions where they extend above blocks 18 are angled substantially parallel to surface 12, as shown at 1 9b in Fig. 3, to form a T shape (as illustrated), or an inverted L shape, relative to the surface 12.

A plate 20 is then positioned over the mould 10 and held in position by clamps (not shown). The mould is heated to about 1 75 C by, for example, being placed in a hot oven.

Heat serves a double purpose both in causing the blocks 18 to exert pressure on the laminate layers 19 (due to the resistance to expansion) and in curing the laminate. After an appropriate time the mould is removed from the heat source.

The required moulding of a model of an aerofoil skin 24 (Fig. 4) with spar 21 and flange 22, and ribs such as 23a, 23b, is then ready for removal from the mould 12. It may in some cases be desirable to machine the surfaces which will be joined to a matching mould. This can conveniently be done before the model is removed from the mould 12.

It will be realised that the invention is applicable to materials other than carbon fibre reinforced plastics and to shapes other than aerofoils.

Claims

1. A method of forming an article from a composite material including the steps of forming a female mould; building up a layer of material within the mould to the required thickness of the article; positioning formers at required sections; pouring molten elastomeric material into the mould and allowing it to solidify; removing the solidified elastomeric material, the layer of material and formers; placing plastics impregnated fibrous material in the mould and in the former positions and replacing the elastomeric material, sealing the top of the mould and heating the mould.

2. A method as claimed in claim 1 and wherein the elastomeric material is a silicone rubber.

3. A method as claimed in claim 1 or claim 2 and wherein the plastics impregnated fibrous material includes thermosetting plastics impregnated carbon fibres or glass fibres.

4. A method as claimed in any one preceding claim, substantially as hereinbefore described and with reference to the drawings.

5. An article made by the method as claimed in any one preceding claim.