Method of manufacturing a composite part

Abstract

A method of preparing a stringer (101) and panel (103) lay-up comprising the steps of providing a stringer preform (303), a panel preform (508), a filler (309) and a mold (307). The mold is adapted to define an inner surface of a stringer. The method further comprises the steps of arranging the stringer preform (303) to contact the mold (307), placing filler (309) material between the mold (307) surface and stringer preform (303), and bringing the reinforcement material (303) into contact with the panel preform (508). The shape of the mold (307) is configured to control filler (309) placement and/or filler shape and/or filler volume.

Claims

1. A method of preparing a stringer or stiffener and panel lay-up comprising the steps of: a) providing a stringer preform which comprises a reinforcement material, a panel preform, a filler and a mould, the mould being adapted to define an inner surface of a stringer; b) arranging the stringer preform to contact the mould; c) placing filler material between the mould surface and stringer preform; d) bringing the reinforcement material of the stringer preform into contact with the panel preform, wherein the shape of the mould is configured to control filler placement and/or filler shape and/or filler volume, and e) additional step of removing the mould and replacing said mould with an inflatable bladder.

2. The method of claim 1, wherein the mould is removed prior to resin infusion of the panel preform and/or stringer preform or following infusion of the panel preform and/or stringer preform prior to cure.

3. The method according to claim 2 wherein the bladder is shaped to fill the same volume as the mould when inflated.

4. The method according to claim 2 comprising an additional step of placing at least one rigid or semi-rigid sheet material between the panel preform and the inflatable bladder.

5. The method of claim 4 wherein the rigid or semi-rigid sheet is removed after curing.

Description

(1) The invention will now be described by way of example only and with reference to the following Figures in which

(2) FIG. 1 is a schematic drawing of an omega stringer or stiffener mounted on a panel or skin according to an embodiment of the invention;

(3) FIG. 2 is a flowchart of a method of forming a stringer stiffened panel in accordance with another embodiment of the present invention;

(4) FIG. 3 is a schematic drawing of an assembly in accordance with step 203 of the method illustrated in FIG. 2;

(5) FIG. 4 is a schematic drawing of a mould in accordance with another embodiment of the present invention;

(6) FIG. 5A and FIG. 5B disclose a skin panel preform and stringer preform assembly inside a vacuum bag to allow resin infusion wherein the surface configuration of the skin panel has been varied; and

(7) FIG. 6 is a micrograph from A: a cured stringer and panel section without a filler, and a micrograph from B: a cured stringer stiffened panel section with a filler, made by a method in accordance with a further embodiment of the present invention.

(8) The schematic drawing of FIG. 1 illustrates an omega stringer 101 bonded to a panel 103. The stringer comprises two flanges 108, 109, a cap 111 and two webs 114, 115. The flanges provide a contact area to bond the stringer to the panel. The manufacture of stiffened panel is described with reference to FIGS. 2, 3, 4 and 5.

(9) In FIG. 2, the method comprises the step of first arranging reinforcement material against a caul plate 201 to form the stiffener preform. The caul plate is shaped to the external dimensions of the stringer. This step is optional as the material could be placed directly onto an inner mould. Preferably multiple layers of dry fibre reinforcement material are used, however at least one layer of prepreg may also be included. A mould is placed against the reinforcement material in the caul plate 202. The filler is then placed between the inner mould and reinforcement fibres into spaces formed between the mould and the stringer preform 203. The mould may then be replaced by a bladder 204 that is shaped to have the same overall shape as the mould when inflated. Laminates may be placed between the bladder and the reinforcement material to distribute pressure more evenly. It is understood that is it also an embodiment of the present invention that the mould remains in place and is not replaced with a bladder. Layers of reinforcement material are laid-up on a mould shaped to the desired external shape of the panel to form a panel preform 205. The panel preform may comprise dry fibrous reinforcement, prepreg or a combination of both.

(10) The panel and stringer preforms are then brought together to form a panel and stringer lay-up 206. The assembly can then be vacuum bagged, optionally placed in an auto-clave or oven and infused with a curable resin in one shot. Silicon inserts (intensifiers) can be placed in the corners of the caul plate to evenly distribute the consolidating force from the vacuum bag. The infused resin is cured to obtain a completed stringer stiffened panel free from defects on the panel surface.

(11) FIG. 3 illustrates an assembly following step 203 of FIG. 2. The assembly comprises a caul plate 301, layers of fibrous reinforcement material 303 a mould 307 and two fillers 309.

(12) FIG. 4 illustrates the cross section of a mould 401 having acute corners 403 of the cross section that are configured to control the placement of the filler material.

(13) In FIG. 5A, a skin and panel preform 508 assembly 500 is presented inside a vacuum bag 518. Inside the vacuum envelope 518 is provided on a mould 501 a layer of a distribution mesh or breather 510 in combination with peel ply 514 to ensure good evacuation of the surface of the panel preform to promote resin infusion and to allow the preform to be released from the mould following cure and having the desired surface properties. Within the stringer preform, a bladder 504 is located. This bladder 504 performs the function as hereinbefore described. For the sake of clarity, the filler is not shown here. Peel ply 514 is also applied over the preform 508 on the side which is not in contact with the mould 501 together with a perforated foil 512 in combination with a distribution mesh 510 to again promote air evacuation and infusion of the resin. An outer stringer mould 506 is located over the stringer preform 508. This stringer mould contains an aperture 522 to allow infusion resin to be applied within its own vacuum envelope 522. This assembly is further provided within a first envelope 516 onto which is located a further distribution mesh 510 inside the vacuum bag 518. Vacuum is applied within the vacuum bag 518 via vacuum port 502.

(14) The infusion resin is applied through inlet ports 520 and removed through outlet ports 522.

(15) In use, the assembly 500 is prepared by laying up the relevant materials as shown in FIG. 6A starting with the materials which are in contact with the mould 501 surface (so from the mould surface up). Vacuum is applied via the port 502 which allows for the removal of air from within the assembly followed by the influx of infusion resin such as RTM6 (produced by Hexcel Corporation) via the inlet port 520. Once the perform is saturated with resin and resin flows out of the outlet 522, the influx of infusion resin is stopped by closing off of the outlet 522 which may also be followed by the closing off of the inlet 520.

(16) The vacuum pressure is maintained on the part and the temperature of the infused preform is raised to promote cure of the resin. Following this, the cured preform is removed from the mould 501 and it is ready for further finishing.

(17) FIG. 5B shows a similar assembly 600. For the sake of clarity the reference numerals for identical parts in FIG. 5B are the same as in FIG. 5A. However the assembly 600 differs from the assembly 500 in that the peel ply 514 and distribution mesh 510 have been replaced by an expanded conductive foil 530 in the form of Dexmet expanded copper foil. This surface material performs in the same way as the distribution mesh 510 in allowing air removal and resin infusion of the skin panel perform, whilst obviating the need for further surface treatment of the cured preform to enable this to be conductive.

(18) In use, the assembly 600 is evacuated and infused in the same way as the assembly 500 of FIG. 5A.

EXAMPLE

(19) HiTape material (as supplied by Hexcel Reinforcements, Les Avenieres) was deposited in multiple layers on the inner surface of a caul plate shaped to the outer surface of an omega shaped stringer or stiffener to form a stringer preform. Hitape is a dry tape which comprises unidirectional carbon fibre tows having thermoplastic veils on either side of the tows to facilitate heat bonding of the tape during lay-up.

(20) An inner mould was brought into contact with the stringer preform. This inner mould has a cross section of an isosceles trapezoid with the acute angles corners removed.

(21) In one embodiment no filler material was used (Comparative Example). In the other embodiment filler material was used (Example). The filler material, also HiTape, was placed in the space between the fibrous reinforcement and the mould along the lateral edges of the mould. The filler material was fixed in place by melting the veil in spots.

(22) In both the Comparative Example and the Example, the mould was removed and replaced with an inflatable bladder which was subsequently inflated. The bladder was shaped so that when inflated it occupied the same volume as the mould.

(23) In both examples, a panel preform was prepared by laying up HiTape on the surface of a panel mould shaped to the desired shape of the panel. The panel preform and stringer preform assembly including bladder and caul plate were combined. Two pressure distributing blocks were placed against the caul plate. The assemblies were then vacuum bagged, infused with HexFlow RTM 6 and cured according to the recommended cure schedule of RTM 6.

(24) The micrograph of FIG. 6B shows a cross section of the cured stringer and panel assembly for the Example. No fibre distortion was evident on the panel where the flange transitions to the web. In contrast, for the Comparative Example of FIG. 6A which was formed without using filler, a significant distortion is evident.