EP0204793A1

EP0204793A1 - A method of making complex shapes from flat fibre reinforced thermoplastics material composites

Info

Publication number: EP0204793A1
Application number: EP86900180A
Authority: EP
Inventors: Thomas Glenville Doe
Original assignee: HR Smith Technical Developments Ltd
Current assignee: HR Smith Technical Developments Ltd
Priority date: 1984-12-10
Filing date: 1985-12-06
Publication date: 1986-12-17
Also published as: WO1986003451A1; GB2168643B; AU5234286A; GB8530088D0; GB2168643A; GB8431086D0

Abstract

Procédé de fabrication d'une structure de forme complexe en matériau thermoplastique armé de fibres dans lequel: une feuille plate de matériau thermoplastique (16) armé de fibres est chauffée localement à une température à laquelle le matériau polymère qu'elle contient est plastifié, la feuille étant ensuite manipulée de manière à la cintrer ou à la plier au niveau de la zone de chauffage. Après cintrage, certaines desdites fibres d'armature s'étendant autour de l'axe de ladite courbure à l'intérieur de la couche le plus à l'extérieur de ladite armature demeurent intactes et forment, avec ledit matériau polymère, un bourrelet (24) s'étendant sur toute la longueur de ladite courbure ou du pli: sont décrits divers modes de jonctionnement des feuilles ainsi formées avec des feuilles de forme similaire ou des feuilles plates de matériaux thermoplastiques armés de fibres.A method of manufacturing a complex shaped structure of fiber-reinforced thermoplastic material in which: a flat sheet of fiber-reinforced thermoplastic material (16) is locally heated to a temperature at which the polymeric material it contains is plasticized, the sheet then being manipulated so as to bend or fold it at the level of the heating zone. After bending, some of said reinforcing fibers extending around the axis of said curvature inside the outermost layer of said reinforcement remain intact and form, with said polymeric material, a bead (24 ) extending over the entire length of said curvature or of the fold: various modes of joining the sheets thus formed are described with sheets of similar shape or flat sheets of thermoplastic materials reinforced with fibers.

Description

A METHOD OF MAKING COMPLEX SHAPES FROM FLAT FIBRE REINFORCED THERMOPLASTICS MATERIAL COMPOSITES.

DESCRIPTION

The invention concerns the manufacture of complex shaped structures in fibres reinforced high or low tempe¬ rature thermoplastics material.

Throughout this specification and in the claims annexed hereto the term fibres reinforcement encompasses fibres in the form of filaments or tows of filaments, mats of filaments or tows of filaments and cloths made,e.g. by laying up, knitting or weaving, filaments or tows of filaments.

The use of thermoplastics materials (with or without fibres reinforcement) to make articles _.is well known, and_. various methods of making them have been proposed. Genera- lly, the methods involve matching tools with high temperature and pressure to consolidate the materials in, for example film stacking processes; in which layers of fibres reinforce¬ ments (which may or may not be pre-impregnated with the polymer material) are laid up in the mould and one or more layers of the polymer material in sheet form are interposed, if needed, between adjacent ones of the sheets of fibres reinforcements.

The known methods are expensive, and in some cases - particularly when making large ^'structures - impracticable. <-.

Flat sheet material is relatively cheap and easy to produce but, to date, the manufacture of useful structures from sheet fibres reinforced material has been a problem, particularly in one respect. When a thick material such as, e.g. metal or polymer without fibres reinforcement is folded or bent, the material 'outside' the median line - the centre line of the sheet- must stretch and the material 'inside' the median line compress to allow the fold to be formed. With fibres rein¬ forced materials, however, the fibres are relatively inex- tensible and incompressible and the sheet material containing them cannot be shaped in this way - unless the fibres of the fibres reinforcement extend uni-directionally within the matrix material and the axis of the fold or bend (the axis about which the bend or fold is formed) extends in a direc¬ tion parallel to the direction in which the fibres in the fibres reinforcement extend.

The invention proposes a novel way of overcoming this problem in thermoplastics materials reinforced with non- unidirectionally arrayed fibres reinforcement and which may with advantage be used in bending or folding thermoplastics materials reinforced with a unidirectionally arrayed fibre reinforcement on an axis not parallel to the direction in which the fibres extend.

A first aspect of the invention provides a method of making a complex shaped fibre reinforced thermoplastics material structure in which: a flat sheet of fibres rein- forced thermoplastics material is locally heated to a tem¬ perature at which the polymer material therein is plasticised, the sheet thereafter being manipulated so that it is bent or folded at the area at which it was heated with ones of said fibres of said reinforcement extending about the axis of the said bend within the outermost layer of said fibres reinforcement remaining intact and forming, with said polymer material a bead extending along the length of said bend or fold.

Although the invention may be used with any thermo- plastics matrix material (e.g. low temperature thermoplastics materials such as polystyrene) we feel that the methods now proposed are of especial advantage with high temperature aromatic polymer material materials such as polysulphone, polyethersulphone, polyetheretherketone, a polyamide or the like.

The fibres reinforcement may with advantage be of glass, carbon or quartz and the fibres therein may be multi- directionally disposed or uni-directionally disposed and extending in a direction about the axis of the said bend or fold.

A second aspect of the invention provides method of making a complex shaped thermoplastics material article formed by joining pre-shaped sheets made in accordance with the above noted first aspect of the invention with other similarly pre-shaped sheets and/or flat sheets. Preferably,in accordance with the second aspect the sheets to be joined are locally heated in the areas at which they are to be joined whilst being held in abutment until those areas are plasticised and then holding those areas together as the sheets cool to a temperature below the glass 5 transition temperature of the thermoplastics matrix material,

One method in accordance with the second aspect of the invention provides that the local heating is effected by platens held in contact with one or both sides of the sheets to be conjoined.

0 An alternative method in. accordance with the second aspect of the invention provides that the local heating is effected by interposing resistive metal mesh between the areas of the sheets held in abutment and passing to that metal mesh an electric current sufficient to raise the tem- 5 perature thereof above the glass transition temperature of the thermoplastics material being used, after cooling the metal mesh being trimmed such that the portion of the metal mesh left in the complex structure becomes an integral part thereof.

- r. A third aspect of the invention provides a complex shaped fibres reinforced thermoplastics material structure made in accordance with the first and second aspects noted above.

Various other aspects, features and advantages of the invention will become apparent from the following descrip¬ tion of various methods embodying the invention now made with reference to the accompanying drawings, in which:-

Figure 1 schematically shows at A an end view, and at B a side view of apparatus used in the method of the invention,

Figure 2 illustrates schematically the bending of a fibres reinforced plastics material in accordance with the invention.

Figure 3 schematically shows an alternative form of the apparatus illustrated in Figure 1 , and

Figures 4 to 7 schematically illustrate ways of making various other complex shapes embodying the invention.

With reference now to Figures 1 and 2 of the drawings.

Figure 1 shows at 10 an electrically resistive heating element coupled via a switch 12 to a low voltage/high current source 14 (such as an arc-welding transformer) by means of which, when switch 12 is closed, element 10 may be heated to a temperature at which the polymer material in a fibres reinforced flat sheet 16 to be worked is plasticised

(e.g. for polyethersulphone fibres reinforced materials a o temperature of 270 -300 C).

One side 18 of the fibres reinforced material sheet 16 is, in accordance with the invention, brought into close proximity - but not into contact - with the element 10. After a time, dependent upon the polymer material and the ς

thickness of the sheet 6 (e.g. for a sheet of polyethersulphone glass fibres reinforced material 3mm thick - after 10 seconds) the sheet is reversed so that the side 20 thereof is brought into proximity with the element 10 and heated. During heating the sheet 16 may be supported, if desired, on a rigid platform such as shown at 22.

Subsequent reversals of the disposition of the sheet may be necessary until the thermoplastic material of sheet 16 adjacent the element 10 has been heated to a temperature at which it is plasticised. Once in this condition the material may be folded or bent about an axis C so that its inner surface, e.g. surface 20 is raised to form a bead or roll 24 on the 'inside' of the fold.

Care is taken in the heating of the sheet to ensure that the area of the sheet being heated is plasticised but the temperature of that area does not rise to a level at which the polymer material therein degrades, for that reason the sheet material must not be allowed to contact the heating element directly and its heating is, desirably, effected by a large number of reversals of its disposition relative to the element 10 so that the temperature of the sheet is slowly raised to a temperature at which it is plasticised and can be worked.

After working, the sheet 16 is removed from proximity with element 10 (if necessary being held to retain the shape that has been imparted to it) and allowed to cool to a temperature below its glass transition temperature. Further bends may be formed in the sheet material if desired.

It will be appreciated that after formation of the or each bend as described above all the fibres in the rein- forcement in sheet 16 remain intact. That is to say all of the longitudinal fibres (those extending normally of the plane of the drawing) and all of the lateral fibres (those extending in the direction of the arrow X-X) remain intact. The longitu dinal fibres are relatively unaffected by the manipulation and retain the restrictive effect they have on the lateral fibres; the outermost ones of which are merely bent and not stretched whilst those within the outermost layer are all to some extent bent in a sense opposite to that of the bend which has been formed in sheet 16 - the inner- most ones of the lateral fibres in the reinforcement forming a loop which with the polymer material forms the bead or roll 24.

In an alternative arrangement shown in figure 3 the heating element 10 is replaced with two heating elements 26 disposed on either side of the sheet 16 enabling both of its surfaces 18 and 20 to be heated at the same time. The ele¬ ments 26 may be coupled to the power supply 14 by a single switch (as described with reference to Figure 1 ) or by two switches 28 as shown in Figure 3. It is thought that such an arrangement has particular advantage when there is a need for the process to be performed relatively quickly (e.g. when making a plurality of similarly formed sheets which are to be further processed) and/or the sheets are thick.

Other forms of heating the thermoplastics material of the flat sheet in place of or in addition to the particular arrangement described above, e.g. the platform 22 may be provided at its edge with embedded heating means - electrical £5 heating elements or channels through which a heating medium (hot oil or the like) is passed.

Once the folded sheet has cooled, it may be joined to other fibres reinforced sheets which may be flat, or of similar or different shaped forms, by any suitable techni-

10 que. A plurality of flat and/or shaped sheets may be welded together by the method illustrated schematically in Figure 4.

In the arrangement of Figure 4 two pre-shaped sheets 42 (each of which has been folded twice at 44 and 46) are pos¬ itioned with their ends 48 in abutment. Heated platens 50 are

15 then brought into contact with the material of the sheets 42 as shown and after heating the two sheets forced together so that the ends 48 (plasticised by the heat from the platens 50) are welded together. A second platen 50' may be located on the other side of the abutting ends of the sheets 42 as 0 shown at the bottom of Figure 4 so that both sides 52 and 54 of the sheets 42 ar directly heated if the desired oper¬ ational speed of the process and/or the thickness of the sheets 42 makes it necessary and/or desirable.

An alternative method of bonding together flat and/or shaped sheets is shown in Figures 5,6 and 7 in each of which areas of pre-shaped sheets are joined to areas of other pre-shaped or flat fibres reinforced sheets.

In the method illustrated in Figure 5 a sheet 60 which has been bent or folded three times to the particular shape shown is fixed to a flat sheet 62 in the following way. The two sheets 60 and 62 are brought into abutment at the pos¬ ition they are to be joined with an interposed layer of a resistive metal mesh 64 (e.g. a 200-200 mesh of 0.002" Dia. Stainless Steel wire). The mesh is coupled to a power supply (e.g. the power supply described with reference to

Fig.1 ) and the heat generated in the mesh causes the hermo¬ plastics material in the. areas of the sheets contacted by the mesh to be plasticised. Pressure is then applied to the sheets 60 and 62 (e.g. a pressure of the order of 300KPa. for polyethersulphone glass fibres reinforced sheets). After sufficient time, the power supply is disconnected and the joint allowed to cool, the pressure is then released, the ends of the mesh are trimmed and a permanent joint has been formed, the remaining mesh in the joint forming an integ- ral part of it.

The method illustrated in Figure 6 shows how a complex shape such as an I-beam may be formed. In the method of Figure 6 two sheets 66 and 68 pre-formed by the method disclosed above to the 'C shape shown are positioned back- to-back with interposed metal mesh layers 69. Flat sheets 70 and 72 of thermoplastics fibres reinforced material are positioned on the top and bottom respectively of the abutting sheets 66 and 68 as shown with interposed layers of metal mesh 76 and 78 as shown. The various parts of the structure are held in a jig (not shown) and- current is passed to the metal mesh layers 69, 76 and 78. After sufficient heating the power supply to the metal mesh layers is disconnected and the structure allowed to cool. After cooling the structure is removed from the jig and the metal mesh layers trimmed and an I-beam which is in part metal mesh reinforced has been formed.

Figure 7 illustrates how complex shapes such as Box- section structures may be formed from flat sheets of thermo¬ plastics fibres reinforced materials with interposed sheets which have been pre-formed in accordance with the methods described with reference to figures 1, 2 and 3. In the arran- gement of Figure 7 flat sheets 80 of thermoplastics fibre reinforced materials are layed up in a jig as shown on top and bottom of pre-shaped sheets 82 and 84 and with interposed metal mesh layers 86 at the areas of contact. The metal mesh layers are heated by passing thereto a current for sufficient time to plasticise the thermoplastics polymer material adjacent the abutting surfaces of the sheets 80, 82 and 84. After heating the power supply is disconnected from the metal mesh and the structure allowed to cool to below its glass transition temperature. Once cool the structure is removed from the jig, the metal mesh trimmed and the complete Box- section article with integral metal mesh reinforced joints has been formed.

Other ways of joining pre-shaped sheets with other similarly pre-shaped or flat sheets may of course be used, for example the sheets may be joined by chemical/ solvent welding techniques, adhesive bonding or in any other suitable way.

The rolls or beads of material left in making a struc¬ ture embodying the invention add to the rigidity and strength of the finished product.

The above described arrangements are merely exemplary of methods embodying the invention for making fibres rein¬ forced thermoplastics material structures of complex shape.

It is for example, possible in accordance with the invention to make the noted and other complex shaped struc- tures continuously simply by providing that the various parts to be joined are brought into juxtaposition, are heated and held in desired relative positions whilst sufficient heat is applied to them to plasticise the thermoplastics matrix material in them and are then held in those relative positions whilst the materials are allowed to cool below the glass transition temperature of the thermoplastics material. It will be appreciated that this can be accomplished in a continuous process in which the various parts are carried through a plant in which the different successive operations are carried out. It will be appreciated that the use of electrically resistive metal mesh interposed between adjacent layers of fibres reinforced thermoplastics materials to to be conjoined may be used in addition to the use of heated platens should the process, requirements (e.g. the thickness of the sheets) make it desirable and/or necessary.

In the ways described above it is possible to make structurally stiff components of rib/skin box or open girder multispar construction making use of fibres reinforced thermoplastics materials more readily than has until now been possible. As a result of the methods described it is possible to make components of complex form which until now it has been possible to make only of metals (such as aluminium) or in non-reinforced thermoplastics materials.

Claims

1. A method of making a complex shaped fibre reinforced thermoplastics material structure in which: a flat sheet of fibres reinforced thermoplastics material is locally heated to a temperature at which the polymer material therein is plasticised, the sheet thereafter being manipulated so that it is bent or folded at the area at which it was heated with ones of said fibres of said reinforcement extending about the axis of the said bend within the outermost layer of said fibres reinforcement remaining intact and forming, with said polymer material a bead extending along the length of said bend or fold.

2. A method as claimed in claim 1 , wherein the thermo¬ plastics material is a high temperature aromatic polymer material.

3. A method as claimed in claim 2, wherein the thermo¬ plastics material is one of polysulphone, polyethersulphone, polyetheretherketone, and a polyamide.

4. A method as claimed in any one of the preceeding claims wherein, the fibres reinforcement is of glass, carbon or quartz.

5. A method of making a complex shaped thermoplastics material article in which the article is formed by joining pre-shaped sheets made in accordance in any one of the preceeding claims with other similarly pre-shaped sheets and/or flat sheets of fibres reinforced thermoplastics material.

6. A method as claimed in claim 5, wherein the sheets to be joined are locally heated in the areas at which they are to be joined whilst being held in abutment until those areas are plasticised those areas then being held together as the sheets cool to a temperature below the glass transition temperature of the thermoplastics matrix material.

7. A method as claimed in claim 6, wherein the local heating is effected by platens held in contact with one or both sides of the sheets to be conjoined.

8. A method as claimed in claim 6, wherein the local heating is effected by interposing electrically resistive metal mesh between the areas of the sheets held in abutment and passing to that metal mesh an electric current sufficient to raise the temperature thereof above the temperature at which the thermoplastics matrix material is plasticised, and after cooling to below the glass transition temperature of the thermoplastics material the metal mesh is trimmed such that the portion of the metal mesh left in the complex structure becomes an integral part thereof.

9. A complex shaped fibres reinforced thermoplastics material structure made in accordance with the method of any one of the preceeding claims.

10. A method of making a complex shaped fibres reinforced thermoplastics material structure as claimed in any one of the preceeding claims and substantially as herein described.

11. A complex shaped fibres reinforced thermoplastics material structure made in accordance with any one of the preceeding claims and substantially as herein described with reference to Figures 2, 4, 5, 6, and 7 of the accompanying drawings.