The present invention relates to a method of forming an article on a tool.
The article to be formed is made of resin prepregs or plies, such as thermo setting plastic comprising fibres.
Composite articles may be produced by mechanical forming or method hot drape forming (HDF). When producing composite articles by hot drape forming, it requires the use of pressure onto stacks of prepregs or plies against a tool. A vacuum bag is used to achieve a pressure such that wrinkles and trapped air in the stack can be forced out under vacuum pressure. The vacuum bag can be used for curing the resin of the plies in an autoclave or in an oven at elevated temperature and pressure. After curing the bag is removed from the forming tool and the article is removed from the tool. By mechanical forming a roll could be used to conform a stack of prepregs or plies against a tool.
When articles are hot drape formed or mechanical formed on a tool, which has one substantially longitudinal direction and one substantially transversal direction, wrinkles are easily formed if the tool has some small curvature, bevels, any protrusion or any depression formed in the tool. It is thus desirable that formation of wrinkles at the location of bevels or other projections or depressions of the article is eliminated in the stack during the forming process.
The tool may have a pad-up area, or a depressed area in the tool. The purpose of the depressed area or the pad-up area is to make a thickening of the article. The thickening is a reinforcement in the article. It is difficult to form articles without wrinkles on a tool which has pad-up areas or depressed areas. Until today it has been impossible to hot drape form an article on such a tool, without creating wrinkles in the flanges.
US 2004/0115299 discloses a method where the vacuum bag is made thinner within the area of a forming surface, which more readily stretches and conforms the stack to the forming surface.
U.S. Pat. No. 5,129,813 describes an evacuation process which reduces the tendency of the vacuum bag to trap air. The method provides a vacuum bag having a plurality of interconnected channels.
US 2005/0163975 A1 and U.S. Pat. No. 5,984,511 relates to stacking sequences when forming articles having an uneven surface, but does not relate to the problem of wrinkles in the article.
EP 1775106 describes forming articles on tools, which may have a curvature, which relates to the orienting of fibre directions of the prepregs in the fibres stack so that none of the fibre directions of the prepres occur parallel with a curve of the moulding tool. The downforming may then be carried out in a simpler manner.
However, there is still a need to improve forming of articles when a stack it is formed over a forming tool, for eliminating the risk that wrinkles appear within the plies or in the stack at the location of a bevel or other projections of the article. Other projections can be a step wise thickening of the article wherein the steps project towards the forming surface keeping the outer surface even.
The present invention has the purpose to solve the problem above.
The present invention relates to a method of forming an article on a tool, the tool having one longitudinal direction and one transversal direction, wherein the method comprises the steps of:
arranging a stack of plies comprising fibres, wherein the stack comprises a plurality of plies having fibres substantially in the orthogonal direction to and substantially in the same direction as the longitudinally direction of the tool, so that when positioned on the tool the ply arranged closest to the tool and the ply arranged furthest away from the tool have the fibres substantially orthogonal to the longitudinal direction of the tool, and arranging at least one ply having the fibres substantially in the same direction as the longitudinal direction of the tool between plies having fibres substantially orthogonal to the longitudinal direction of the tool.
The method further comprises conforming the stack to the tool with a forming medium, and removing the article from the tool.
The present invention also relates to a composite article produced according to the method above, wherein the article has a longitudinal direction and a transversal direction, the article is made of a stack of plies wherein one ply is the bottom ply and one ply is a top ply, the plies comprises fibres, and the article comprises a plurality of plies having fibres substantially in the orthogonal direction and substantially in the same direction as the longitudinally direction of the article, characterized in that the bottom ply and the top ply have fibres in a substantially orthogonal direction to the longitudinal of the article, at least one ply has the fibres substantially in the same direction as the longitudinal direction of the article.
The article to be produced can be a beam for an air craft.
The present invention will now be described by way of example with reference to the accompanying schematic drawings, of which:
When referring to the direction of fibres in the plies, it is referred to the direction of the fibres in an angle to the longitudinal direction of the tool if nothing else is stated. The stack is transferred to the tool in such a way that the fibres are arranged in different ways on the tool as defined in the claims.
In
Further, fibres diagonal 4, 5 to the longitudinal direction L are also shown and those fibres have the angle 45° or 135° to the longitudinal direction L.
Diagonal fibres may thus have the angle 45° or 135° to the longitudinal direction L.
The present invention relates to a method of forming an article on a tool, which can be seen in
The fibre reinforced polymer plies have unidirectional fibres in the plies.
An apparatus for forming an article by conforming a stack according to the present invention is disclosed in
The stack may be arranged on a temporary support (not shown), where after the stack is transferred to the tool. The temporary support could be a plane and vertical support. The support could however have other forms. When referring to the directions of the fibres in the different plies, the direction always refer to the direction of the tool, to which the stack is transferred to. Several prepregs or tapes may first be laid in the form of a stack. This is done by hand or by an Automatic Tape Laying Machine on a temporary support. This is followed by for example a Hot drape forming, HDF, process. The stack is transferred to the tool 61, 71 in a HDF apparatus 62 and then the stack may be heated up followed by conforming the stack 66, 73 with a forming medium 65, 72, which could be a vacuum bag made of an elastic bag material.
The article to be formed could for example be a beam. It can be seen in
For easiness, the fibre direction of the plies will sometimes shortly be called orthogonal direction and the longitudinal direction, respectively.
For further simplifying the expressions, the plies having the fibres substantially orthogonal to the longitudinal direction of the tool are sometimes called 90° plies, relating to the angle 90° . In the same way, the plies having the fibres substantially in the same direction as the longitudinal direction is called 0° plies, while the plies having the fibres substantially diagonal to the longitudinal direction of the tool are called 45° and 135° plies.
When forming a stack 22 of plies on a tool 21, the force from the forming medium will generate shearing forces onto the stack 22 of plies. There will also be shearing forces between the plies. The inventors have now found that when plies having a substantially orthogonal direction 3 to the longitudinal direction L of the tool is arranged closest to the tool 1, 21, and closest to the forming medium, the shearing forces between the plies and the tool and the forming medium, respectively, decrease. This means that the plies will slide on the tool and against the forming medium. This leads to a decrease in the risk of obtaining wrinkles in the article. Further, when plies having fibres substantially in the same direction 2 as the longitudinal direction L of the tool are situated between plies having fibres substantially in an orthogonal 3 direction to the longitudinal direction L of the tool 1, 21, the plies having fibres in the same direction 2 as the longitudinal L direction will slide together with the plies having orthogonal 3 fibres. This also avoids wrinkles in the article. If wrinkles are formed in hot drape formed articles, the wrinkles are usually formed in the flanges 82, 84 of the articles. The flanges are the parts which are formed on the longitudinal sides of the tool. One longitudinal side 26 of the tool 21 can be seen in
It has now been found that plies having fibres in substantially orthogonal direction 3 have the property of being able to slide compared to the tool 1, 21 and the forming medium. The orthogonal ply slides in the orthogonal direction. Further, it may help other plies having fibres in other directions to slide between the plies having orthogonal 3 fibres, which will avoid wrinkling of the article to be formed.
The method according to the present invention further comprises arranging at least one ply having fibres substantially diagonal 4, 5 to the longitudinal direction L of the tool 1, 21, wherein such ply or plies are arranged next to each other or between plies having fibres substantially orthogonal 3 to the longitudinal direction L of the tool 1, 21. By diagonal direction is meant the direction of 45° or 135° to the longitudinal direction L of the tool. The plies having diagonal 4, 5 directions can be situated next to each other. It could be two plies having 45° angle or two plies having 135° angle to the longitudinal direction L of the tool arranged next to each other. Further, a ply having 45° fibres could be situated next to a ply having 135° . In such a sequence, the plies can also be expressed to be lying orthogonal to each other. However, on the outer side of a combination of diagonal plies, plies having orthogonal fibres should be situated. The plies having orthogonal direction will help the diagonal fibres to slide in a suitable way in order to avoid wrinkles, which could otherwise be obtained in the article. Other ply sequences may lock the plies together which may form wrinkles in the article.
The forming force generated by the forming medium can be divided in shear forces which will make the plies slide relatively each other as the forming procedure proceeds. When discussing forming force generated by the forming medium, the forming medium may be a mechanical forming medium or a hot drape forming medium. The sliding has shown to be better between 90° plies, which the method according to the present invention utilizes.
45° and 135° plies are often used in the sequence 45°/45°/135°/135°, or 45°/135° and these plies can create a Pin Jointed Net forming (PJN). When such ply sequences are arranged between 90° plies, the PJN is not locked, which could be the case if arranged between 0° plies. When 45° and 135° plies are locked between for example 0° plies, wrinkles are formed. This is thus avoided with the solution according to the present invention.
It may be possible to use plies having the fibres substantially diagonal 4, 5 to the longitudinal direction L of the tool next to plies having fibres substantially in the same direction 2 as the longitudinal direction L of the tool. However, if such an arrangement is used, those plies should be arranged close to the middle of the stack.
Further, the present invention relates to a method, wherein the tool 31, 51 has at least one depressed part 34, 52, 53 and at least one protruding part 35, 36, 54, which protruding part is protruding in relation to the depressed part 34, 52, 53, of the tool 31, 51. The tool 31, 51 has at least one narrower part and at least one thicker part in the cross-section of the tool 31, 51. The depressed areas 34, 52, 53 correspond to the narrower part of the tool 31, 51. The protruding areas 35, 36, 54 correspond to the thicker part of the tool 31, 51.
As discussed above, plies having fibres substantially diagonal 4,5 to the longitudinal direction L of the tool can be arranged next to plies having fibres substantially in the same direction 2 as the longitudinal direction L of the tool. Such plies could be arranged in the depressed part 34, 52, 53 of the tool 31, 51. However, as disclosed above, if such an arrangement is used, those plies should be arranged close to the middle of the stack.
In
The present invention also relates to a method wherein the plies 42 are arranged so that at least one of the plies 43 covers at least a part of the at least one depressed part 34, 52, 53 and not the at least one protruding part 35, 36, 54 and the other plies 45 cover both the at least one depressed parts 34, 52, 53 and the at least one protruding parts 35, 36, 54. The plies covering the depressed part 34, 52, 53, but not the protruding parts 35, 36, 54, could also be called interleaved plies. When using plies that cover the depressed part 34, 52, 53, but not the protruding part 35, 36, 54, care has to be taken regarding the sequence of plies at both the depressed part 34, 52, 53 and the protruding part 35, 36, 54.
The method also comprises arranging several plies that cover at least a part of the at least one depressed part 34, 52, 53 and not the at least one protruding part 35, 36, 54. When forming articles using such depressed 34, 52, 53 and protruding 35, 36, 54 parts, and covering the depressed parts 34, 52, 53 with plies that do not cover the protruding parts 35, 36, 54, the purpose is to obtain an article which is thickened in the area of the depressed part 34, 52, 53 of the tool. This can be seen in
The method further comprises arranging every ply 46 covering at least a part of the at least one depressed part 34, 52, 53 and not the at least one protruding part 35, 36, 54 between two plies 47 covering both the at least one depressed part 34, 52, 53 and the at least one protruding part 35, 36, 54 so that every second ply is a ply covering the at least one depressed part 34, 52, 53 and not the at least one protruding part 35, 36, 54. Sometimes, the area of the depressed part of the tool is called “pad-up” area. The plies 46 covering the depressed part 34, 44 but not the protruding parts 35, 36, 49a, 49b, could be considered to pad up the article in this area.
The plies 46 covering the at least one depressed part 34, 52, 53 and not the at least one protruding part 35, 36, 54 may also be sequenced in any other order, such as two of more such plies together between plies 47 covering both the at least one depressed part 35, 36, 54 and the at least one protruding part 35, 36, 54. The sequence could also be in any other suitable order depending on the desired properties of the article to be formed. The number of plies 46 covering the at least one depressed part 34, 52, 53 and not the at least one protruding part 35, 36, 54 arranged between plies 47 covering both the at least one depressed part 35, 36, 54 and the at least one protruding part 35, 36, 54 could for example vary.
In the field of composite articles, a thicker region 48 of the article has the purpose to form a strengthened region of the article. In such a region, fastening elements could be arranged for example. This makes it possible to have a light article, but still makes it possible to arrange fastening elements in the article. This is a desire in for example the air craft industry.
A depressed part 34 or a pad-up part of the tool 31 is intended for forming a thickened part 48 in the article, which could also be called a pad-up or build-up part of the article. Such a pad-up area in the tool is also sometimes called a ramp. The ramp is a bevel angle. The ramp can be a 1:xx ramp. The angle of the ramp depends for example on the thickness which is desired in the thickened part of the article. Ramps in the order of 1:10 to 1:200 could be used. A 1:20 ramp is sometimes used when producing composite articles in the air craft industry. The effect of the present invention has shown good effects in avoiding wrinkles when using ramps and the method according to the present invention has been used.
An article formed by the method according to the present invention is shown in
This makes the article to have an even outer surface. The article 81 has three sides 82, 83, 84, which have been conformed to the tool 31 by the method discussed above, and which will be further disclosed below. In the middle of the article is a region 85, between the sloping areas 86, 89, which show the thicker region of the article. The article has an even surface on the side which has not been directed to the tool during forming, but an uneven surface on the side directed to the tool 41, as disclosed in
A tool 51 having two depressed parts 52, 53 is disclosed in
The benefit with the gliding effect from the plies having orthogonal fibres is good when thicker regions, pad-up areas, are made in the article. The thickened region is intended for making a pad-up stack in the article for making the article stronger in this part. If for example a bolt should be attached to the beam the bolt need to be mounted on a stronger part of a beam. The stronger part is then made by the thickened region 85 in the article 81. The plies which cover at least a part of the depressed area are sometimes also called interleaved plies.
The tools 31, 41, 51 shown in
The present invention also relates to a method comprising arranging the stack 22, 42 so that when positioned on the tool 21, 41 the ply arranged closest 24, 44 to the tool 21, 41 has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41, the next four plies have the fibres substantially diagonal 4, 5 to the longitudinal direction L of the tool 21, 41, the next ply has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41, the next four plies have the fibres in substantially the same direction as the longitudinal direction L of the tool 21, 41, the next ply has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41, the four next plies have the fibres substantially diagonal 4, 5 to the longitudinal direction L of the tool 21, 41, the next ply has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41.
The method according to the present invention also comprises arranging the stack 22, 42 so that when positioned on the tool the ply arranged closest 24, 44 to the tool 21, 41 has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41, the next two plies have the fibres substantially 45° to the longitudinal direction L of the tool, the next two plies have the fibres substantially 135° to the longitudinal direction L, the next ply has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41, the next four plies have the fibres in substantially the same direction as the longitudinal direction L of the tool, the next ply has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41, the two next plies have the fibres substantially 135° to the longitudinal direction L of the tool, the two next plies have the fibres substantially 45° to the longitudinal direction L, the next ply has the fibres substantially orthogonal 3 to the longitudinal direction L of the tool 21, 41. The stack sequence could be 90°/45°/45°/135°/135°/90°/0°/0°/0°/0°/90°/135°/135°/45°/45°/90°.
The arrangement of the fibres in the order as disclosed above, gives very good mechanical properties. It is beneficial to have the same number of plies for every direction of the fibres. That means that it is an advantage to have in one stack, for example four plies having orthogonal 3 fibres, four plies having fibres in the longitudinal direction L, four fibres having 45° 4 and four fibres having 135° 5.
In order to get a simple quasi isotropic lay-up, the directions 0°, 90°, 45° and 135° are all used. The plies having fibres in different directions should be used in the same number, i.e. for example four 0° plies, four 90° plies, four 45° plies and four 135° plies. However, different lay-ups can also be used, and it depends on how the article will be used and the properties which are needed in the article. The 0° plies give the article rigidity and those plies can be arranged in about the middle of the stack.
A beam for use in an aeroplane must be very strong and stacks having plies with fibres in several directions is necessary. The lay-up of 90, 45, 45, 135, 135, 90, 0, 0, 0, 0, 90, 135, 135, 45, 45, 90 is a good lay-up, which will give a producible beam.
The method according to the present invention also comprises
The forming medium may be a mechanical forming medium, such as a roll or press forming.
The method according to the present invention can also comprise
Further, the method comprises
According to the present invention, the forming medium 65, 72 used under the forming step can be an elastic vacuum bag.
The method will now also be described with the aid of
The evacuating step may be performed in all temperature ranges. After the forming step, an elevated temperature may be used in order to obtain a faster curing of the article. The curing may also be performed at ambient temperature.
The prepregs are in the form of resin impregnated fibres. The resin could be thermosetting resins such as epoxy, polyester, cyanate ester, vinyl ester, BMI (bismaleimide), or thermoplastics such as PPS (poly(p-phenylene sulfide),
PEI (polyethylene imine), PEEK (polyetheretherketone). The fibres are for example carbon fibres, glass fibres, organic fibres and ceramic fibres.
In the method according to the present invention, the stack starts with a ply closest to the tool having the fibres substantially orthogonal to the longitudinal direction of the tool. A ply having fibres substantially orthogonal to the longitudinal direction of the tool has the ability to slide in the orthogonal direction of the tool. This is an advantage, since the mobility of the ply prevents that wrinkles are formed. The stack also ends with a ply having the fibres substantially orthogonal to the longitudinal direction of the tool. When an elastic vacuum bag is enclosing the stack and the bag stretches and conform the stack, the ply also has the mobility against the bag, which also avoids the forming of wrinkles. Further, the slip is improved by arranging substantially diagonal plies and plies having substantially the same direction as the longitudinal direction of the tool between orthogonal plies. The advantage with the mobility of the orthogonal fibre plies has solved the problem with wrinkles in composite articles according to the method according to the present invention.
With a stack sequence according to the present invention, a both intra and inter ply sliding effect can be obtained, which is advantageous when used for making articles which will result without wrinkles. It has been found that composite articles can be formed without wrinkles formed in the articles. This is especially clear when tools having depressed and protruding parts, or tools having some small curvature, bevels, any protrusion or any depression formed in the tool are used. Further, the advantage can be seen when a thicker part is formed in an article.
The present invention also relates to a composite article produced according to the method disclosed above and, wherein the article has a longitudinal direction L and a transversal direction T, the article 81 is made of a stack of plies wherein one ply is the bottom ply and one ply is a top ply, the plies comprises fibres, and the article comprises a plurality of plies having fibres substantially in the orthogonal direction 3 and substantially in the same direction 2 as the longitudinally direction L of the article 81, wherein the bottom ply and the top ply have fibres in a substantially orthogonal direction 3 to the longitudinal L of the article 81, at least one ply has the fibres substantially in the same direction 2 as the longitudinal direction L of the article 81. When referring to the different directions of the fibres, it should be understood that the same directions as referred to in
The stack may also be laid directly on the tool. This can be made by advanced fibre placement (AFP). The method would not include the hot drape forming for conforming the stack to the tool, since the plies will conform to the tool when laid on to the tool. By this method wrinkles are also avoided in the articles formed by the method which utilizes direct laying the stack onto the tool.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SE08/51304 | 11/13/2008 | WO | 00 | 6/29/2011 |