GB2168647A

GB2168647A - Fibre reinforced polymer articles

Info

Publication number: GB2168647A
Application number: GB08530125A
Authority: GB
Inventors: John William Ashton
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-12-07
Filing date: 1985-12-06
Publication date: 1986-06-25
Also published as: AU5235586A; GB8430948D0; GB8530125D0; WO1986003453A1; EP0204794A1

Abstract

Method of making fibres reinforced polymer article comprising the steps of:- forming a plurality of sheets of fibres reinforced polymer material, laying up the sheets on top of one another in a moulding press such that the fibres reinforcement within certain sheets extended in directions different to those of others of the sheets, and applying pressure to the mould and heating it such that the polymer material in the different sheets coalesces. The porcesses described include the additional steps of forming one or more holes in each of said sheets prior to laying them up in the mould, and providing the mould with one or more finger members in register with the holes in the sheets, the finger members extending through the holes in the sheets in the mould. With advantage the or each hole is formed by index piercing. By appropriately positioning and shaping the holes in adjacent sheets as they are laid up in the mould, and by providing that the finger members are of appropriate shapes, it is possible to produce a laminate article having one or more apertures formed therein of irregular but precisely defined configuration.

Description

SPECIFICATION Fibre reinforced polymer articles The invention concerns fibre reinforced polymer articles, more particularly but not exclusively, fibres reinforced structures made from aromatic polymer materials such as polyethersulphone, polysulphone, polyetheretherketone, and polyamides.

Throughout this specification and in the claims annexed hereto the term fibres reinforcement is to be taken as encompassing filaments, fibres or tows of filaments or fibres mats of filaments or fibres or tows of filaments or fibres and cloths formed by knitting, weaving or laying up such filaments, fibres and tows for use as reinforcement in polymer matrix material.

The invention is related particularly to the production of fibres reinforcement polymer articles which, until now, it has not been possible to make satisfactorily.

The advantages of using fibres reinforced polymer materials for forming articles are known. Such articles are generally be lighter, stiffer, stronger and cheaper, when made from such materials than when made from other more traditional materials (e.g. metal). Carbon fibre reinforcing materials can have a Youngs Modulus approximately 50% greater than that of steel whilst being lighter.

Other fibre reinforcing materials can have even greater strengths, for example Boron fibres reinforcement (in which a coating of Boron is deposited on a small diameter Tungsten filament) can have a Youngs Modulus approximately 33% greater than that of Carbon fibre-twice that of steel.

A disadvantage found when making articles from fibres reinforced polymer materials arises from the directional strength characteristics of the material. Thus a plate made of fibre reinforced thermoplastics material may be significantly more strong in one direction than in another, (e.g. orthogonal to the first direction).

This is due to the orientation of ones of the fibres in the fibres reinforcement within the polymer matrix material.

Attempts have been made to overcome this problem by providing that individual fibres of the fibres reinforcement within the polymer material extend in different directions, for example that the fibres reinforcement be in the form of a woven cloth. However, when using carbon or boron fibres reinforcement weaving is difficult due to the high stiffness of the fibres. Furthermore, even when weaving is possible it is not easy to ensure the uniformity of the strength of the finished article-weak- nesses arise at the points the individual fibres forming a woven cloth cross.

Again, difficulty has been met in making fibres reinforced polymer structures including one or more shaped apertures particularly if the or each aperture needs to be accurately positioned and sized.

It is with the object of overcoming and/or alleviating the difficulties noted above that we propose the present invention.

A first aspect of the invention provides method of making a fibres reinforced thermoplastics material article comprising the steps of; forming a plurality of sheets of fibres reinforced thermoplastics material, laying up the sheets on top of one another in a moulding press such that the fibres reinforcement within certain sheets extend in directions different to those of others of the sheets, and applying pressure to the mould and heating it such that the thermoplastics material in the different sheets coalesces.

Additional sheets of the same or a different thermoplastics material may be interposed between adjacent ones of the sheets of fibres reinforced thermoplastics materials if desired to alter the fibres reinforcement/resin ratio in the finished article.

The method may further include the steps of forming one or more holes in each of said sheets prior to laying them up in the mould, and providing the mould with one or more finger members in register with the holes in the sheets, the finger members extending through the holes in the sheets in the mould.

The or each said hole in the sheet of fibres reinforced material is preferably formed by index piercing.

As they are laid up in the mould the sheets may be selected such that the apertures in apertures in adjacent ones of them are of different sizes and the finger members used may be of differing cross-section along their length such that the apertures formed in the finished article are of non-uniform cross-section along their length. The finger members may be in two parts, a first part being of uniform crosssection and a second part mounted on the first part of non-uniform cross-section, the method providing that the first said part of each finger member is removed from the mould leaving the second parts therein and that the second parts are then removed from the mould.

A second aspect of the invention provides a laminated article made in accordance with the method noted above.

The article may be formed with a plurality of apertures passing therethrough, and those apertures may with advantage be of differing cross-section along their lengths. The invention provides that the forms of the apertures in the the article may differ from place to place across the sheet.

Once a laminate article has been formed in the way noted above it is possible to coat it with any desired material, deposition process.

It has been found that such processes adequately cover the whole of the article-includ- ing the walls of the apertures therein.

A process embodying the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic sectional side view of part of mould usable in the present invention, Fig. 2 is a plan view of part of the arrangement of Fig. 1 drawn on the line Il-Il thereof, Fig. 3 is a schematic plan view of an article made by the process of the invention, Fig. 4 shows at A a side view and at B a face view of a tool usable in the method of the invention, Fig. 5 illustrates different forms of apertures which may be formed in articles embodying the invention, and Fig. 6 illustrates a modified form of finger member usable in the invention.

As can be seen from the drawings, in parti cular Fig. 1 and 2, a mould for use in the process of the invention comprises a solid base plate 10 on which are fixed-e.g. by bolts not shown plurality of castellated strips 12 arranged so as to provide a flat bed pierced by a number of apertures 14. Within each aperture 14 is placed the lower end of a finger member 16 which extends upwardly as shown. Each finger member 16 is apertured at its upper end as shown at 17. A plurality of sheets 18 of fibres reinforced polymer material, e.g.Boron fibres reinforced polyetheretherketone, having apertures therein formed by index blanking are placed on the flat bed formed by the strips 12 such that the finger members 16 extend through the pierced apertures in the sheets to a position slightly above the upppermost sheet 18 in the mould.

On the stack of sheets 18 is placed a top assembly 20 which comprises a first layer 22 formed of castellated strips fixed in juxtaposed relationship similar to the strips 12 on the base plate 10 to provide apertures 23 accurately sized to fit onto the upper ends of the finger members 16. The first layer 22 is fixed (bolted) to a plate 24 apertured as shown at 25. The apertures 25 in plate 24 are slightly larger than the finger members 16. A further plate 26 is located above the top plate 20.

Plate 26 includes an array of large circular holes 28 in register with the finger members 16 and into which the members 16 extend.

At 30 is shown a cover plate which may be located above the plate 26 and upon which a platen of a press will bear; alternatively reference 30 may denote the press platen acting directly on plate 26. Side plates for the mould are provided as shown at 32.

To load the mould first the finger members 16 are located in the apertures 14 formed by the strips 12. Thereafter the sheets 18 are placed on top of strips surrounding the members 16. The top assembly 20, plate 26 and the cover 30 are then located on the stack of sheets 18 (the apertures in the plates 20 and 26 receiving the upper ends of the members 16) and the side plates 32 are located in the position shown.

The mould is positioned on the base plate of a heated press and the platen of the press bought to bear on the top assembly of the mould. Heat and pressure is applied to the mould for a time sufficient for the polymer material in the different sheets 18 to coalesce.

As heat and pressure is applied to the stack of sheets 18 in the mould the thermoplastics material surrounding the fibres flows into and completely surrounds the finger members 16.

After sufficient time to close the mould and completely melt the polymer material, the mould is cooled (whilst pressure on it is maintained) and it is then removed from the press.

The cover plate 30 (if provided) is removed and the finger members 16 pulled out-for example using a tool such as is described with reference to Figure 4. The mould is then dismantled and the laminate article removed from it.

It is possible, by varying the orientation of the fibres in successive strips as they are laid up to provide that the strength and/or other characteristics of the finished article vary.

A typical apertured article made as noted above (e.g. as shown in Fig. 3) may have several thousand apertures 40 of length L and spacing W. The stiffness of it along any axis is proportional to the fourth power of the length and the spacing between adjacent holes in that direction. If it is required to have an article with non-uniform holes (as shown) but which is equally stiff in both directions (A) and (B) it is possible to achieve this by laying up the sheets 18 such that more of them have their fibres or nted in direction (B) than in direction (A). The precise number of sheets oriented in directions (A) and (B) will, of course, vary in dependence upon the dimensions of the apertures and their spacing one from another, the dimensions, and the strength and stiffness requirements of the finished article. A typical article as shown in Fig.

3 may have approximate dimensions 1.3m X 0.7m X 1.5cm, and have approximately 7000 apertures (each of length 0.8cm and width 0.13cm) formed at a spacing of 1.1cm. With a lay-up of the sheets 18 such that the 60% of the fibres in the fibres reinforcement extends along the length of the sheet and 40% extend across its width the stiffness of the sheet along its longitudinal and laterial axes are the same.

By appropriately modifying the proportions of the fibre in the reinforcement running in different directions it is possible to select the desired characteristics the finished article; e.g.

it is possible to impart to the finished article desired stiffness characteristics which are the same or different in different axes of the sheet.

Fig. 4 schematically illustrates one form of tool which may be used to withdraw the fin ger members 16 from the laminated article formed by the method noted above. As can be seen from the Figure the tool comprises an hydraulic ram 50 mounted on a base plate 52 the leading edge of which is slotted and which in use is positioned on the upper surface of a laminate article 54 which has been formed in the mould. The front of the hydraulic ram supports a hook rail 56 comprising a plurality of members 58 the lower ends of which are slotted or formed with apertures 60 as shown. The hook rail overlies the slotted part of the base plate 52 and is rigidly attached to a pull rod 62 coupled at 64 to the hydraulic ram 50 as shown.The hook rail 56 is also coupled to two slides 68 mounted on the base 52 of the tool which act to constrain the movement of the hook rail as it moves when the ram 50 is operated. The tool is provided with a handle which for the sake of clarity has not been shown.

The tool is used after the top assembly has been lifted off the article. The tool is positioned on the top of the of the laminate with the slots in the base plate 52 passing over the upper ends of the fingers 16 and bringing the holes 60 in the members 58 of the hook rail 56 into register with apertures 17 in the upper ends of the finger members 16. An appropriately sized rod 70 is then passed through the holes 60 and the apertures 17 in the finger members 16 and the hydraulic ram operated to lift the hook rail together with the finger members out of the laminated article which has been made.

The number of finger members 16 which may be removed at one time with this tool will depend upon the dimensions (in particular the thickness) and the polymer material used to form the laminate article made which directly effect the power required to pull each finger member out of the laminate article.

With the sheet described above with reference to Figure 3 eleven finger members could be extracted at one time making use of a hydraulic ram having a 2000/3000psi working pressure.

By using the modifications of the described process it is possible for the shape of the apertures to be varied, as desired.

Fig. 5 illustrates various cross-sectional shapes of apertures which can be achieved.

As shown at 51 apertures may run at an angle through the laminated article. This is achieved simply by varying the positions of the holes in the different sheets 18 as they are cut and by providing that the finger members 16 extend at the desired angle from the base of the mould. Alternatively, the holes may be of varying cross-section along their lengths (Fig. 511) by using appropriately shaped finger members 16. Combinations of the above may be provided as shown (Fig. 5111).

The shape and configuration of the different apertures in a single article may vary across the article as required (Fig. 51V).

By making use of the particular shape of finger member shown in Fig. 6 it is possible to form apertures in the laminate article having the non-uniform cross-sections shown (Fig.

5V), that is to say apertures wider in their middle portions than at either surface of the article.

Fig. 6 shows and arrangement in which the finger member is in two parts. A first part 80 being in substance similar to that already described with reference to Fig. 1 and a second part 82 in the form of a slotted bead locatable on the first part 80. The laying up process for a laminate article making use of such composite finger members provides that the parts 80 are located on the base and the first sheets 18 (appropriately cut) are positioned on them; other further sheets are positioned in the mould, the apertures in adjacent sheets increasing in size to a maximum. At this time the second part 82 of the finger member is located on the first part 80 thereof. The part 82 fits into the "cup" formed by the increasingly wide apertures in the sheets 18.Thereafter. ffurther sheets 18 (the apertures in which are of gradually decreasing size) are laid up until the uppermost sheet 18 is in position.

The moulding process is carried out as before and the finger member first parts 80 removed from the laminate structure. The finger member second parts 82 which remain within the article are removed by mechanical crushing, chemical treatment or in any other suitable way.

The described arrangements provide many advantages over the known processes, e.g. in normal cutting methods (e.g. after formation of the article) the fibres reinforcing materials extend to the aperture face, often with ragged material protruding from the cut face; the precut apertures in the sheets of the present invention are with advantage slightly larger than the finished requirement, allowing the polymer material to flow beyond the cut fibre ends in the final moulding process. The surface finish of the face of the apertures is therefore dependent only upon the the accuracy and finish of the tooling.

Thus with the present invention it is possible to provide a laminate article, in the case described of Boron fibre reinforced polyethersulphone material, which includes a number of accurately positioned and shaped holes. The accuracy of the sizing and shaping of the holes in the finished article being significantly better than has until now been possible in a moulding process and only achievable in costly and complex machining processes.

Such products are of particular advantage in various industries (e.g. the Aircraft industry) where there is a requirement for strong, lightweight articles.

Another advantage that the described arrangements have over known processes is that it permits the characteristics of the finished article to be varied as desired e.g. by varying the proportion of fibres extending in a given direction within the article as it is made the strength and/or stiffness of the article in given directions may be selected to meet design requirements.

A further advantage of the described process is that it also enables the desired fibre/resin ratio to be maintained throughout the article-even to those areas adjacent the apertures which may be formed in the article as it is made.

Finally, the described processes enable articles to be made which are stronger, stiffer and lighter than steel equivalents, have controllable directional characteristics, may be significantly cheaper than could be obtained using alternative materials and retain the inherent qualities of the component materials e.g. dielectric, insulating, low toxicity, solvent resistance etc.

Articles made in accordance with the methods described above may be further treated, e.g. they may be metallised by an ion deposition process. By appropriate masking it is possible to ion deposit metal onto only the walls of the apertures formed in the article producing an array of metallised apertures electrically isolated from one another. Such an article is of use for example in wave guide arrays and phased antenna arrays usable for radar and/or radio transmission and reception.

Although the manufacture of a flat sheet has been described it will be seen that with appropriate modification to the apparatus described non-flat articles may be made. Again, it will be seen that other modifications may be made to the described methods without departing from the scope of the invention, for example any thermoplastics material with any desired fibres reinforcement may be used to carry out the described invention.

Claims

1. A method of making a fibres reinforced polymer article comprising the steps of; forming a plurality of sheets of fibres reinforced thermoplastics material, laying up the sheets on top of one another in a moulding press such that the fibres reinforcement within certain sheets extend in directions different to those of others of the sheets, and applying pressure to the mould and heating it such that the thermoplastics material in the different sheets coalesces.

2. A method as claimed in claim 1, wherein additional sheets of the same or a different thermoplastics material are interposed between adjacent ones of the sheets of fibres reinforced thermoplastics materials.

3. A method as claimed in claim 1 or claim 2, further including the steps of forming one or more holes in each of said sheets prior to laying them up in the mould, and providing the mould with one or more finger members in register with the holes in the sheets, the finger members extending through the holes in the sheets in the mould.

4. A method as claimed in claim 4, wherein the or each said hole in each said sheet of fibres reinforced material is formed by index piercing.

5. A method as claimed in claim 3 or claim 4, wherein the finger members are removed from the mould before the finished article is removed therefrom.

6. A method as claimed in any one of claims 3 to 5, wherein the the apertures in adjacent sheets as they are laid up in the mould are of different sizes and the finger members are of differing cross-section along their length such that the apertures formed in the finished product are of nonuniform crosssection along their length.

7. A method as claimed in any one of claims 3 to 6, wherein the the finger members are in two parts, a first part being of uniform cross-section and a second part mounted on the first part of non-uniform cross-section, the method providing that the first said part of each finger member is removed from the mould leaving the second parts therein and that the second parts are then removed from the mould.

8. A laminated sheet article made by the method of any one of the preceeding claims.

9. An article as claimed in claim 8 formed with a plurality of apertures passing therethrough.

10. An article as claimed in claim 9, wherein the apertures passing therethrough are of differing cross-section along their lengths.

11. An article as claimed in claim 10, wherein the forms of the apertures in the the article differ across the sheet.

12. A method of making a fibres reinforced thermoplastics laminate article as claimed in claim 1 or claim 2 and as described herein.

13. Apparatus for use in the method of any preceeding claim substantially as herein described with reference to figures 1, 2 , 4 or 6 of the accompanying drawings.

14. A laminated sheet article as claimed in claim 8 and substantially as herein described.