GB2345877A

GB2345877A - Composite moulding method

Info

Publication number: GB2345877A
Application number: GB9901394A
Authority: GB
Inventors: Geoffrey Michael Suter; Ronald John Dawson
Original assignee: GKN Technology Ltd
Current assignee: GKN Technology Ltd
Priority date: 1999-01-23
Filing date: 1999-01-23
Publication date: 2000-07-26
Anticipated expiration: 2019-01-23
Also published as: GB2345877B; GB9901394D0

Abstract

A cured component is made from laminated pre-preg by hot compression moulding in which a pre-form of the component 16 is separated from the mould surface by a film (17, 18) of polyamide or other thermoplastic material. The polyamide is incorporated into the component as the outer surface thereof.

Description

Composite Moulding Method This invention relates to a method of hot compression moulding. In such a method a preform of uncured polymeric material, e. g. of pre-preg laminates, is introduced into a heated mould in a press, the mould is closed and the material cured. The mould is typically heated to a temperature greater than 120 C. After curing the mould is opened and the cured article removed.

The polymeric material may be, for example, laminates of epoxy-impregnated glass fibre"pre- preg". Conventionally a release agent coating is applied to the mould tool before use so that the moulded article can be separated from the tool when the resin has cured sufficiently.

It is often necessary to clean the mould after each moulding cycle and periodically to re-coat the mould with release agent.

It is an object of the present invention to provide a method of compression moulding a component which reduces the moulding cycle time by enabling a partially cured blank to be removed from the mould after a shorter cure time than heretofore.

According to the invention we provide a method of making a cured component by hot compression moulding in which the external surface of a preform of laminated pre-preg is separated from the mould surface by a film of a polyamide or of another thermoplastic material which retains sufficient strength at the moulding temperature not to rupture and which adheres directly to the external surface of the preform, there being no release agent between said surface and the film, placing the preform in the mould so that said external surface is separated from the mould surface by said film, closing the mould and heating the latter to cure the prepreg and to incorporate the polyamide or other thermoplastic film into the cured article so that the film forms the external surface thereof.

It has heretofore been proposed to provide a shaped article by curing a pre-preg laminate by vacuum-bagging a blank in a polyamide film then autoclaving the bagged blank to cure it. The blank is wrapped in a release film before being bagged in the polyamide film and the air between the release film and the bag evacuated before the bag is autoclaved. After curing of the blank, the polyamide film is removed from the cured article. The release film ensures that the polyamide bag can be removed from the cured blank.

The present invention differs from the prior art in that the polyamide or other thermoplastic film is integrally incorporated into the preform or blank and forms the external surface thereof.

The method has various advantages. Since the polyamide or other thermoplastic film does not stick to the mould surface the partially cured preform can be removed from the mould sooner than heretofore because it is not necessary that the preform be cured to the stage at which the resin loses its adhesive properties.

Another feature of the method is that the preform may be wrapped in e. g. polyamide film and heated in an oven, e. g. a microwave oven, before being placed in the mould thus further reducing the mould cycle time.

Another feature is that the polyamide or other thermoplastic film can serve to bridge over clearances in complex tools with moving surfaces or ejection devices. This can prevent liquid resin from running down such clearances, curing and causing seizure.

The preform may be wrapped in thermoplastic film before being placed in the mould or a sheet of the film may be placed over the lower mould surface, the preform placed in the mould, another sheet of the film place over the preform and the mould closed. The essential point is that the preform is separated from the mould surface by the film.

It would be possible to include an adhesion promoter between the outer surface of the preform and the polyamide or other film.

The polyamide film may e. g. be nylon 6 or nylon 66 such as that known as Capran (TM) made by Allied Signal Inc. It may have a thickness of between 10 and 80ym, e. g. 50, um.

While in carrying out the method it may still be necessary to apply a release agent to the mould from time to time but this may not be necessary after every moulding cycle nor will it be necessary to clean the mould so frequently as heretofore.

The invention will now be described in detail by way of example with reference to the accompanying drawings in which: Figure 1 is a diagram illustrating the principle of the invention; Figure 2 is a diagram illustrating an embodiment in which the preform is wrapped in a film before being placed in the mould; Figure 3 is a diagram illustrating how the film may be applied to the mould rather than to the preform.

Referring first to Figure 1, a mould of a hot compression moulding machine is indicated at 10 and has an upper part 11 and a lower part 12. The upper part 11 has a shaped moulding surface 13 and the lower part 12 has a shaped moulding surface 14. There are ejectors 15 in the lower mould part 12.

A preform 16 is shown which is made of epoxy impregnated glass fibre pre-preg. A nylon film 17 is shown as separating the upper surface of the pre-preg from the mould surface 13 and a second sheet of nylon 18 is shown separating the lower surfaces of the preform from the mould surface 14. The nylon films 17 and 18 separate the faces of the preform from the mould surfaces.

To mould the required article, the mould parts are closed and heated to a temperature greater than 120 C. After moulding the mould parts are opened and the finished article removed, the nylon films 17 and 18 having been incorporated into and forming the surfaces of the article.

No release agent is used between the preform 16 and the films 17 and 18. Indeed an adhesion promoter may be used between the facing surfaces of the preform and the nylon film to improve the adhesion between the surface of the preform and the nylon film.

Since the nylon film does not adhere to the mould surfaces 13 and 14 it has been found that it is possible to remove the moulded article from the mould after a shorter time than would be the case if no nylon film 17 and 18 were used. The film 18 also prevents resin from the preform from leaking down into the ejectors 15, curing and causing the ejectors to stick.

Figure 2 shows a variation in which the preform 16 is wrapped in the sheets 17 and 18 of nylon film before it is put into the mould. In this case it is possible to heat the wrapped preform, e. g. in a microwave, before it is placed in the mould thus reducing the mould cycle time.

Figure 3 shows another variation where the nylon film 18 is placed on the surface 14 of the lower mould part 12, the preform 16 is then placed on the film 18, the film 17 is then placed over the preform and the mould then closed.

It will be noticed in all cases that the nylon films 17 and 18 isolate the faces of the preform 16 from the mould surfaces 13 and 14.

While it may still be necessary to use a mould release agent as conventionally used, this will not be needed as frequently as heretofore. Moreover the use of the nylon film means that the mould surfaces 13 and 14 will require less cleaning.

It will be seen that the invention provides a method of making a cured component which has advantages over those heretofore used and which provides the component with a protective coating of nylon. As has been described above, the nylon film may be replaced by another thermoplastic material which retains sufficient strength at moulding temperature not to rupture and which adheres directly to the external surface of the preform.

Claims

Claims 1. A method of making a cured component by hot compression moulding in which the external surface of a preform of laminated pre-preg is separated from the mould surface by a film of polyamide or of other thermoplastic material which retains sufficient strength at the moulding temperature not to rupture and which adheres directly to the external surface of the preform, there being no release agent between said surface and the film, placing the preform in the mould so that said external surface is separated from the mould surface by said film, closing the mould and heating the latter to cure the pre-preg and to incorporate the polyamide or other thermoplastic film into the cured article so that the film forms the external surface thereof.
2. A method according to Claim 1 wherein the preform is wrapped in said film before being placed in the mould.
3. A method according to Claim 2 wherein the preform is wrapped in said film and then heated before being placed in the mould.
4. A method according to Claim 1 in which the mould has upper and lower mould parts and wherein a sheet of said film is placed over the surface of the lower mould part, the preform is placed over said sheet, a second sheet of said film is placed over the preform and the mould parts are closed.
5. A method according to any preceding claim wherein an adhesion promoter is used between the outer surface of the preform and the film.
6. A method according to any preceding claim in which the film is nylon 6 or nylon 66.
7. A method substantially as herebefore described with reference to the accompanying drawings.

7. A method according to any preceding claim wherein the film has a thickness of between 10 and 80ym.

8. A method substantially as herebefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A method of making a cured component by hot compression moulding in which the external surface of a preform of laminated pre-preg is separated from the mould surface by a film of a polyamide which retains sufficient strength at the moulding temperature not to rupture and which adheres directly to the external surface of the preform, there being no release agent or adhesion promoter between said surface and the film, placing the preform in the mould so that said external surface is separated from the mould surface by said film, closing the mould and heating the latter to cure the pre-preg and to incorporate the polyamide film into the cured article so that the film forms the external surface thereof.

2. A method according to Claim 1 wherein the preform is wrapped in said film before being placed in the mould.

3. A method according to Claim 2 wherein the preform is wrapped in said film and then heated before being placed in the mould.

4. A method according to Claim 1 in which the mould has upper and lower mould parts and wherein a sheet of said film is placed over the surface of the lower mould part, the preform is placed over said sheet, a second sheet of said film is placed over the preform and the mould parts are closed.

5. A method according to any preceding claim in which the film is nylon 6 or nylon 66.

6. A method according to any preceding claim wherein the film has a thickness of between 10 and 80ym.