GB2243107A

GB2243107A - Moulding a mould and mould liner skin of composite material for moulding an article of composite material

Info

Publication number: GB2243107A
Application number: GB9107051A
Authority: GB
Inventors: Derek Booth; James Blinkhorn
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1990-04-20
Filing date: 1991-04-04
Publication date: 1991-10-23
Anticipated expiration: 2011-04-04
Also published as: GB9107051D0; GB2243107B; GB9008951D0

Abstract

The composite material, such as resin impregnated carbon fibre, is laid up to make the article (7) on a composite mould liner skin (5) which is only located in a composite mould base (6) for curing of the article in an autoclave, post cure stages also being carried out with the skin (5) removed from the base (6). The skin (5) e.g. of 1 or 2 mm. thickness, may be flexible to facilitate article release. To form the skin and base, a simulated skin (2) e.g. of wax, is laid up on a master pattern (1), a female mould (3) of the composite material is laid up upon the simulated skin (2), and after removal of the simulated skin (2) the mould skin (5) is formed between the master (1) and the mould (3) by laying up, or injection onto the fibre, and the mould base (6) is then removably laid up upon the skin (5). A p.t.f.e. release layer may be integrally moulded into the skin. <IMAGE>

Description

COMPOSITE MATERIAL MANUFACTURE This invention relates to a method and tooling for the manufacture of articles from composite materials such as, for example, carbon fibre composites.

A conventional method of manufacturing articles from composite material involves laying up layers of composite material, such as carbon cloth impregnated with resin, in a metal mould tool to a desired thickness. The article is then cured under pressure in an autoclave and the finished article removed from the mould. One problem with this method, however, results from the difference in coefficient of thermal expansion (CTE) between the metal mould tool and the composite material. This difference results in a relative movement between the mould tool and the composite article being formed during the heating and cooling cycle which spoils the surface of the article.

One solution to this problem is to place an intermediate skin of composite material between the metal mould and the article to be formed. Another solution is to use a composite mould tool, that is to say a mould made of the same (or at least similar) material as the article to be formed. This latter method avoids any problems resulting from a CTE differential, and also has further advantages.

For example, a composite mould tool is lighter than a metal equivalent and can be heated more quickly, during the curing step, to the required temperature.

However, composite mould tools are disadvantageous in that they are more susceptible to damage than comparable metal moulds. This applies particularly to the surface which may suffer degradation from various causes. These include shop damage from knife cutting, resin loss due to heat shock, and possibly solvent damage from the use of release agents. The mould surface is also often damaged by the use of inappropriate tools, for example screwdrivers, to release an article from the mould.

According to the present invention there is provided a method of forming composite tooling including a composite mould base and a composite intermediate skin adapted to be received therein, comprising the steps of: forming a simulated skin on a male master, forming a female mould member by laying-up composite material on said simulated skin and then curing, removing said simulated skin, laying-up composite material in the space defined between said male master and said female mould member, and curing, removing the thus formed intermediate skin and locating said skin in a male master, laying-up composite material on said skin and curing to form said mould base.

This method has a number of significant advantages.

Firstly, the skin prevents damage from occurring to the mould tool. Although the skin itself may be damaged this is less important since the skin is a much less expensive item than the mould tool. Secondly, the use of an intermediate skin permits more effective use of a mould tool, which enables a saving in costs in comparison with known conventional techniques. For example, if three skins are provided for each mould tool, three stages of the production cycle can be carried out simultaneously.That is to say, in a first skin, without the mould tool, the laying-up and other pre-cure operations (such as vacuum bagging) can be carried out; in a second skin, located in the mould base, the curing of a previous laid-up article is performed; and in the third skin, removed from the mould base, the post-cure operations such as release and cleaning are carried out on a previously cured article.

The skin sets several important requirements. Firstly, both principal surfaces of the skin must be accurately defined by the manufacturing process. One surface must correspond to the surface of the article to be formed, while the other must, if the manufacturing method is to be effective, correspond closely to the surface of the tool.

Secondly, it must be possible to manufacture repeatedly a number of identical skins if maximum advantage is to be obtained from the present invention. For example, it should be possible to easily replace a damaged skin with an identical new skin. In addition, in the above-described method using a number of skins with one mould tool, all the skins must be identical.

In one method according to the invention, the skin is formed from resin pre-impregnated carbon-fibre cloth.

An alternative, preferred method of manufacturing the skin, which meets all the above requirements, is resin injection or resin transfer moulding. In such a technique resin is injected into the defined space in which is located dry composite material such as dry carbon cloth. A further advantage of this technique is that it allows the skin to be formed with an integral release layer, for example of polytetraflouroethyline (PTFE).

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figures l(a)-(d) illustrate the manufacture of the intermediate skin; Figure 2 illustrates the manufacture of the mould base; and Figure 3 illustrates the use of the skin and mould base to manufacture a desired article; Figures l(a)-(d) illustrate a preferred method of forming the intermediate skin as a first step in the manufacture of the composite tooling. Initially there is provided a male master 1 made of temperature resistant material. Upon this master 1 a simulated skin 2 is laid up in wax. The resin transfer mould 3, including plumbing for the resin injection, is then laid up upon the wax simulated skin. The mould 3 is then removed and the wax is removed from the master 1.Thus formed the mould 3 is able to define in conjunction with the master 1 a cavity 4 corresponding exactly to the shape of the desired skin (Figure l(c)). To construct the skin, dry carbon cloth 5 is located in the cavity 4, resin is injected into the cavity and the whole is cured. Once formed the male master 1 and the mould 3 may be used to repeatedly make identical intermediate skins the surfaces of which are accurately defined by the surfaces of the master 1 and the mould 3.

This method may also be used to incorporate an integral release layer, for example of PTFE, in the skin. This may be achieved by including a layer of PTFE with the carbon cloth in the cavity.

Once made the composite skin 5 can be used to manufacture the mould base. This, as is shown in Figure 2, may be simply achieved by fitting the skin 5 over a male master 1, coating the skin with a release agent and then forming the female mould base 6 by laying up composite material on the skin 5 and then curing. After curing and releasing the mould base, the mould base 6 and skin 5 are ready for use.

To manufacture an article using the mould base 6 and skin 5 attention is drawn to Figure 3. Composite material 7, such as pre-preg carbon cloth, is laid up in the skin 5 while the latter is supported by a wooden saddle. Any other pre-cure steps, such as vacuum bagging may also be carried out at this stage. The skin 5 is then located in the mould base 6 and the whole is cured in an autoclave for the necessary time. After curing the skin is removed from the mould base 6 and the finished article is released from the skin 5 which is then cleared as necessary before the cycle recommences.

Preferably the skin 5 is made to have a thickness of lmm or 2mm so that it is flexible. Hence the walls of the skin 5 may be easily flexed apart thus facilitating release of the finished article.

It will be appreciated that in this production cycle the mould base 6 is only required for the curing step.

Thus, while the mould base is supporting a skin in the autoclave, a further skin may have the next article laid-up and otherwise prepared for cure, while a further skin may be in the post-cure stage of having the finished article released and the skin cleaned in preparation for the next cycle. This provides a far more efficient utilisation of the tooling than is the case of known techniques.

Claims

1. A method of forming composite tooling including a composite mould base and a composite intermediate skin adapted to be received therein, comprising the steps of: forming a simulated skin on a male master, forming a female mould member by laying-up composite material on said simulated skin and then curing, removing said simulated skin, laying-up composite material in the space defined between said male master and said female mould member, and curing, removing the thus formed intermediate skin and locating said skin on a male master, laying-up composite material on said skin and curing to form said mould base.

2. A method according to claim 1 in which the composite material laid in the space defined between said male master and said female mould member is a resin-preimpregnated composite material.

3. A method according to claim 1 in which the composite material laid in the space defined between said male master and said female mould member is a dry composite material and in which resin is injected into said space prior to curing.

4. A method according to Claim 3 wherein a layer of release material is included in said space defined between said female mould member and said master with said dry composite material so as to be included integrally with said skin.

5. A method according to Claim 4, wherein said layer of release material comprises polytetraflouroethylene.

6. A method of forming composite tooling substantially as hereinbefore described with reference to the accompanying drawings.