A composite article and a method of forming a composite article
TECHNICAL FIELD
The present invention relates to a composite article and a method of forming
a n article o n a tool.
The article is made of resin prepregs o r plies, such as thermo setting plastic
comprising fibres.
BACKGROUND ART
Composite articles may be produced by mechanical forming, method hot
drape forming (HDF) o r vacuum forming. When producing composite articles
by hot drape forming, i t requires the use of pressure onto stacks of prepregs
o r 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 a n
autoclave o r in a n 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 o r plies against a tool.
When articles are hot drape formed o r mechanical formed o n a tool, which
has one substantially longitudinal direction and one substantially transversal
direction, wrinkles are easily formed i f the tool has some small curvature,
bevels, any protrusion or any depression formed in the tool. I t is thus
desirable that formation of wrinkles at the location of bevels o r other
projections o r depressions of the article is eliminated i n the stack during the
forming process.
US 2004/01 15299 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.
The applicant has found a method in which i t is possible to hot drape form a n
article o n a tool without creating wrinkles in the article. This is disclosed in
WO 2010/0561 64 which relates to a method in which a certain stacking
sequence is used for avoiding wrinkling when forming a n article by hot drape
forming. Plies having fibres in the longitudinal direction of the tool, plies
having fibres in the orthogonal direction of the tool and fibres having a
diagonal direction of the tool are arranged in a specific order in the stack in
order to avoid wrinkles. In some cases, there might still be some problems
during the forming in which wrinkles are formed in the article. The inventors
of the present invention have now evaluated the stacking method.
The present invention intends to solve the problems above.
SUMMARY OF THE INVENTION
The present invention relates to a composite article, wherein the article has a
longitudinal direction and a transversal direction, the article comprises a
stack of plies wherein one ply is a bottom ply and one ply is a top ply, most of
o r all of the plies comprise fibres, and the article comprises a plurality of plies
having fibres substantially in the orthogonal direction to the longitudinal
direction of the article and a plurality of plies having fibres substantially in the
same direction as the longitudinally direction of the article, wherein at least
one of the ply/plies having fibres substantially in the orthogonal direction to
the longitudinal direction of the article comprise fibres that are stiffer than the
fibres in the other plies which have less stiff fibres.
Further, the present invention relates to a method of forming a n article o n a
tool, the tool having one longitudinal direction and one transversal direction,
wherein the method comprises the steps of:
arranging a stack of plies, wherein one ply is a bottom ply and one ply is a
top ply, and wherein most of o r all of the plies comprise fibres, wherein
the stack comprises a plurality of plies having fibres substantially in the
orthogonal direction to the longitudinally direction of the tool and a
plurality of plies having fibres substantially in the same direction as the
longitudinally direction of the tool, so that when positioned o n the tool at
least one of the ply/plies having fibres substantially in the orthogonal
direction to the longitudinal direction of the tool have fibres that are stiffer
than the fibres in the other plies which have less stiff fibres;
-conforming the stack to the tool with a forming medium; and
-removing the article from the tool.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described by way of example with
reference to the accompanying schematic drawings, of which:
Figure 1 shows a tool according to the present invention, in a view from
above, in which different fibre directions of plies are disclosed.
Figure 2 shows a cross-section in the longitudinal direction of a tool with a
stack of plies according to the present invention.
Figure 3 shows a side view of a part of a tool according to the present
invention.
Figure 4 shows a cross-section of a part of the tool shown in Figure 3 and a
stack of plies o n the tool part.
Figure 5 shows a cross-section in the transversal direction of a part of a
composite article produced according to a prior art method.
Figure 6 shows a cross-section in the transversal direction of a tool according
to the present invention, a stack of plies o n the tool and a forming medium i n
a n apparatus for forming the stack.
Figure 7 shows a cross-section in the transversal direction of a tool according
to the present invention, a stack of plies o n the tool and a forming medium.
Figure 8 shows a n article according to the present invention.
Figure 9 shows a n article according to the present invention.
DEFINITIONS
When referring to the direction of fibres in the plies, i t is referred to the
direction of the fibres in a n angle to the longitudinal direction of the article o r
of the tool i f nothing else is stated. The stack is transferred to the tool in such
a way that the fibres are arranged i n different ways o n the tool as defined i n
the claims.
In Figure 1, a tool 1 is shown i n a view from above. The tool has a
longitudinal direction L and a transversal direction T . Different directions of
fibres are also shown in the Figure. A ply having the fibres in the same
direction 2 as the longitudinal direction L of the tool 1 is also defined to have
the fibres in a n angle of 0 ° to the longitudinal direction L of the tool 1. A ply
having the fibres orthogonal 3 to the direction of the tool is also defined to
have the fibres in a n angle of 90° to the longitudinal direction L of the tool 1.
Further, the fibre direction diagonal to the longitudinal direction L are such
fibres that have the angle of 30° 6 to 60° 7 and 120° 8 to 150° 9 to the
longitudinal direction L of the tool 1, o r to the article, shown in Figure 8 .
Diagonal fibres may thus have the angle 45° o r 135°, shown as 4 and 5 in
the Figure 1, to the longitudinal direction L . However, the diagonal direction is
extending from the angle 30° to 60° and from 120° to 150°, which is shown
as 6 , 7 , 8 and 9 in Figure 1 and 8 15 , 8 16 , 8 17 and 818 in Figure 8 . The same
applies when referring to a n article.
By intra ply sliding is meant sliding of the fibres in one ply, while inter ply
sliding is sliding between the plies.
DETAILED DESCRIPTION
The present invention relates to a composite article 801 shown in Figure 8 ,
wherein the article has a longitudinal direction L and a transversal direction T ,
the article 801 comprises a stack of plies wherein one ply is a bottom ply and
one ply is a top ply, most of o r all of the plies comprise fibres, and the stack
comprises a plurality of plies having fibres substantially in the orthogonal
direction 8 1 0 to the longitudinal direction of the article 801 and the stack
further comprises a plurality of plies having fibres substantially in the same
direction 8 1 1 as the longitudinally direction L of the article 801 and/or a
plurality of plies having fibres substantially i n the diagonal direction 8 12 , 813,
8 15 , 8 16 , 8 17 , 8 18 of the longitudinal direction L of the article 801 , wherein at
least one of the ply/plies having fibres substantially in the orthogonal direction
810 to the longitudinal direction L of the article 801 comprises fibres that are
stiffer than the fibres in the other plies which have less stiff fibres. Such a n
article has the advantage that wrinkles are avoided i n the article.
Fibres in the orthogonal direction may be compressed in the longitudinal
direction of the fibre. Observe that the longitudinal direction of the fibre is not
related to the direction of the article o r the tool. One reason for compression
i n the plies having fibres substantially in the orthogonal direction to the
longitudinal direction of the article may be a n inter ply sliding in those plies
during forming of the article and during this inter ply sliding the orthogonal ply
may be locked. When the fibres are sliding in the orthogonal direction during
forming and the ply is locked, the fibres may be compressed in the fibre
length and the fibres may then buckle. The plies may be locked by each
other during the forming and thus buckling may appear. Such buckling is
illustrated in Figure 5 , which shows a cross section in the transversal
direction of a corner 5 1 of a composite article produced according to a prior
art method. The transversal direction T , which is orthogonal to the
longitudinal direction of the article, is shown in the Figure. The plies 52
having fibres substantially in the orthogonal direction of the article are
disclosed by a lighter colour. Between the orthogonal plies 52 are other plies
53, 54, 55 arranged. Those plies 53, 54, 55 have fibres in the longitudinal
direction and/or fibres in the diagonal direction. I t can be seen that the plies
52 have been compressed i n the longitudinal direction of the fibres and
thereby buckled 54 below the corner of the article. Buckling of the orthogonal
plies 52 will affect the surrounding plies 53, 54, 55 to be buckled in the same
way. Thus, all plies will be buckled due to the buckling of the orthogonal plies
52. The buckling is a larger problem close to the tool than further away from
the tool. I f the fibre is stiffer, the compression is avoided and the fibre will
conform to the form of the tool. When producing the article, the stiffer fibres in
the plies having fibres substantially in the orthogonal direction 810 avoid
compression of the ply/plies. This avoids that the fibres are bended in the
wrong direction and thus avoids wrinkling. The plies having stiffer fibres will
cooperate with the plies having less stiff fibres in a n advantageous way and
the plies having stiffer fibres will conform easier to the tool as disclosed
above.
I t is defined that most of o r all of the plies comprise fibres. For example a ply
comprising resin o r polymer material but no fibres could be arranged
between plies comprising fibres. However, this will only concern a few plies, i f
any. The fibre reinforced polymer plies have unidirectional fibres i n the plies.
Further, the present invention relates to a composite article, wherein at least
one of the ply/plies having fibres substantially in the orthogonal direction 8 10
to the longitudinal direction L of the article 801 has a cure ply thickness which
is smaller than the cure ply thickness of the other ply/plies. I t is a common
way to use the cure ply thickness as a dimension for the thickness of plies.
Smaller cure ply thickness of the plies further avoid compression of the
ply/plies and the ply/plies will conform to the tool during forming. This in turn
avoids bending of the plies and fibres in a n incorrect way, and wrinkles are
avoided in the composite article. Plies having smaller cure ply thickness do
not need to be sheared as long distance as a ply having a thicker cure ply
thickness. Plies having a thinner cure ply thickness thus have a shorter
distance to be sheared during formation. This leads to that the ply having a
smaller cure ply thickness will be less prone to compression in the
longitudinal direction of the fibres in the ply/plies.
The ply/plies having fibres substantially i n a n orthogonal direction and a
smaller cure ply thickness may also comprise fibres which are stiffer than the
other plies which have less stiff fibres. However, one ply having fibres
substantially in a n orthogonal direction may comprise stiffer fibres than the
other plies, while another ply having fibres substantially in a n orthogonal
direction may have a smaller cure ply thickness than other plies.
The ply/plies having a smaller cure ply thickness may have a cure ply
thickness of < 0.1 5 and the cure ply thickness of the other ply/plies may >
0.1 5 . However, in order to obtain a higher effect of the thickness difference,
the ply/plies having a smaller cure ply thickness could have a cure ply
thickness of < 0.14 mm and the cure ply thickness of the other ply/plies could
> 0.1 7 mm. With the difference of the cure thickness wrinkling is avoided
since the compression is avoided of the ply/plies having a lower cure ply
thickness. Further, deformation is avoided in the ply/plies having a higher
cure ply thickness. The combination of plies having different cure ply
thickness and having fibres in different directions will also improve the
mechanical properties of the composite article.
As disclosed above, at least one of the ply/plies having fibres substantially in
the orthogonal direction T to the longitudinal direction L of the article
comprises fibres that are stiffer than the fibres in the other ply/plies. The
stiffer fibres may have a Young Modulus of at least 250 GPa and the less stiff
fibres have a Young Modulus of less than 250 GPa. However, in order to
have a quite good effect of the stiffer fibres compared to the less stiff fibres,
the stiffer fibres may have a Young Modulus of at least 20 GPa more than the
less stiff fibres. Further improved avoidance of compression could be
obtained i f the Young Modulus of the stiffer fibres are at least 30-50 GPa
more than the less stiff fibres. Stiffer fibres may have a Young Modulus of
about 280-300 GPa and less stiff fibres may have a Young Modulus of about
230-245 GPa.
According to the present invention, the bottom ply may have fibres i n the
orthogonal direction and the bottom ply can comprise fibres that are stiffer
than the fibres in the other plies which have less stiff fibres. Further, a ply
close to the bottom ply having fibres substantially in the orthogonal direction
may comprise fibres that are stiffer than the fibres in the other plies which
have less stiff fibres. The bottom ply is the ply which is applied to the tool
during forming of the article. The buckling may be most severe close to the
tool and therefore i t may be advantageous to have a ply having fibres
substantially in the orthogonal direction close to the bottom ply of the article
which comprise fibres that are stiffer than the fibres in the other plies which
have less stiff fibres. The ply o r plies close to the bottom ply may comprise
fibres in the orthogonal direction and that are stiffer than the fibres in the
other plies which have less stiff fibres.
Further, the bottom ply may have fibres in the orthogonal direction and the
bottom ply can have a cure ply thickness which is smaller than the cure ply
thickness of the other ply/plies. Further, a ply close to the bottom ply having
fibres substantially in the orthogonal direction may have a cure ply thickness
which is smaller than the cure ply thickness of the other ply/plies. The ply or
plies close to the bottom ply may compris fibres in the orthogonal direction
and have a cure ply thickness which is smaller than the cure ply thickness of
the other ply/plies.
According to the present invention, all the plies having fibres substantially i n
the orthogonal direction 8 10 may comprise fibres that are stiffer than the
fibres in the other plies. The plies in the other directions, such as in the
longitudinal direction of the article would then have fibres with less stiff fibres.
Such articles will have improved properties as avoidance of wrinkles and
improved mechanical properties are then obtained. The stiffer fibres are more
expensive than the less stiff fibres. A n improved article is obtained due to the
stiffer fibres and still all plies do not need fibres which are as stiff as the plies
having the stiffer fibres.
Further, all the plies having fibres substantially in the orthogonal direction 8 10
may have a cure ply thickness which is smaller than the cure ply thickness of
the other ply/plies. This will further avoid wrinkle formation in the composite
articles and the mechanical properties are improved. At the same time as
wrinkle is avoided i n the plies comprising stiffer fibres and plies having a
smaller cure ply thickness, the plies comprising less stiff fibres and a thicker
cure ply thickness will be less deformed.
In the composite article according to the present invention, the bottom ply
and the top ply may have fibres in a substantially orthogonal direction 8 10 to
the longitudinal L direction of the article 801 and at least one ply has the
fibres substantially in the same direction 8 1 1 as the longitudinal direction L of
the article 801 arranged between plies having fibres substantially orthogonal
810 to the longitudinal direction L of the article 801 , and at least one ply has
fibres substantially diagonal 8 12 , 8 13 , 8 1 5 , 8 16 , 8 17 , 8 18 to the longitudinal
direction L of the article 801 , wherein such ply or plies are arranged next to
each other or between plies having fibres substantially orthogonal 8 10 to the
longitudinal direction L of the article 801 . The sliding of the diagonal plies will
be improved by being arranged between orthogonal plies o r diagonal plies.
The good sliding of the orthogonal plies will reduce the risk of wrinkling of the
article during manufacturing.
I t is pointed out that the composite article may comprise at least one ply/plies
having fibres in the angle of 30° 8 15 to 60° 816 and 120° 817 to 150° 8 18 to
the longitudinal direction L of the article. Those plies are defined to be
diagonal to the longitudinal direction L of the article. Such plies are arranged
next to each other o r between plies having the fibres substantially in the
orthogonal direction.
The article may comprises a stack, wherein the bottom ply has the fibres
substantially orthogonal 8 1 0 to the longitudinal direction L of the article 801 ,
the next four plies have the fibres substantially diagonal 8 12 , 8 1 3 , 815, 8 16 ,
8 17 , 818 to the longitudinal direction L of the article 801 , the next ply has the
fibres substantially orthogonal 8 10 to the longitudinal direction L of the article
801 , the next four plies have the fibres in substantially the same direction as
the longitudinal direction L of the article 801 , the next ply has the fibres
substantially orthogonal 8 1 0 to the longitudinal direction L of the article 801 ,
the four next plies have the fibres substantially diagonal 8 12 , 8 13 , 8 15 , 8 16 ,
8 17 , 8 1 8 to the longitudinal direction L of the article 801 , the next ply has the
fibres substantially orthogonal 8 10 to the longitudinal direction L of the article
801 . Such a stacking sequence is good for composite articles, which will
have no wrinkles. At least one of the ply/plies having fibres substantially i n
the orthogonal direction 8 10 to the longitudinal direction L of the article 801
will have fibres that are stiffer than the other ply/plies as disclosed above.
Further, the ply/plies having fibres substantially in the orthogonal direction
8 10 to the longitudinal direction L of the article 801 may have a cure ply
thickness which is smaller than the cure ply thickness in the other ply/plies.
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 could 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 i t
depends o n 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. The 45° and 135° could be
exchanged with other diagonal angles according to the definition. The angles
could for example be 30° and 150° o r 60° and 1 20°.
The article 801 may also comprise at least one curved part 814. At curved
parts, such as corners, buckling is common to occur. The ply/plies having the
fibres in the orthogonal direction to the longitudinal direction of the article
may bend in the wrong way and may be wrinkled quite easily during the
forming of the article. When the fibres in the ply/plies having fibres
substantially i n the orthogonal direction to the longitudinal direction of the
article are stiffer, the buckling is avoided. The stiffer fibres are less prone to
compression and thereby buckling is avoided. This is especially useful at
curved parts of composite articles. A curved part 814 is disclosed in the
composite article 801 and may be for example a corner.
In figure 8 is further a cross section disclosed. A n upper part 803 and two
flanges 802, 804 of the article are disclosed. The article could for example be
a beam.
A corner is here a n example of a curved part. However, any other curve form
could be used. A n example of a curved form is a radius. A further example is
as shown above, a corner. I f the corner is rounded i t also may comprise a
radius. Further, several curved parts could be used, o r a double curved part.
Even i f a corner is shown in Figure 8 , several more rounded forms are
included in the present invention. The ply o r plies are formed down from one
surface to another surface in the area around the curved part.
The present invention also relates to a composite article, wherein the article
includes a thicker region or a build-up area 905. Such a n article 901 is
disclosed in Figure 9 . The article comprises at least one ply which covers
only the area of the thicker region o r the build-up area 905. Sometimes this
area is also called a pad-up area. The term pad-up area is however also
used for the area of a tool, o n which the thicker region o r build-up area is
made on. This is referred to further below. The terms "thicker region" or
"build-up area" 905 are used for a thicker area of the article, which can be
seen in Figure 9 . The same reference numbers as in Figure 8 are used,
except that the first figure "8" is exchanged with "9" i n Figure 9 . Further, two
cross sections 908 and 907 are disclosed in Figure 9 , wherein the cross
section 907 of the pad-up area 905 is larger due to the thickening of the
article 901 i n this part. Transition areas 906, 909 are disclosed showing the
transition between the thickened region 905 and the other parts at the ends
of the article. Further down, it is described how such a n area is built up by the
method. A thicker area o r a build-up area 905 is used in order to strengthen
the article in the area. I t could for example be used for the positioning of
fastening elements, which might require a stronger part of a n article.
In the field of composite articles, a thicker region 905 of the article has the
purpose to form a strengthened region of the article. A thicker region 48 is
also disclosed in Figure 4 . In such a region, fastening elements could be
arranged for example. This makes i t possible to have a light article, but still
makes i t possible to arrange fastening elements i n the article. This is a desire
in for example the air craft industry. Figure 4 discloses several plies being
applied in a stack 42 o n a tool 4 1 . Plies 43, 46 cover only a depressed part
and plies 45, 47 cover both the depressed part and the protruding part 49a,
49b of the tool 4 1 are arranged o n the tool 4 1 . This leads to a n article that will
have a thicker region 48 in the article. The plies 46 may i n this context be
expressed as interleaved plies. Figure 3 further discloses a tool 3 1 , which
have a depressed part 34 and protruding parts 35, 36. A transition area 39 is
arranged between the depressed part 34 and the protruding part 36. A
curved part 38 is also disclosed. A side part 37 of the depressed part is also
disclosed.
Further, the composite article may comprise at least one ply having fibres in
substantially diagonal to the longitudinal direction L of the tool that
comprise/s particles selected from the group of thermoplastic tougheners,
nano particles, micro particles, elastic particles, elastomer particles and
polymer particles o r a combination of them. Such a n article has the
advantages that no wrinkles are formed in the article and the thickness of
thinning of the article is avoided. The particles increase the friction between
the fibres in the ply in which the particles are comprised, preventing the fibres
from sliding away from each other during the production method. Thus, the
thinning of the ply is prevented during production of the article when the ply
comprises particles and fewer articles with defects are made. All the plies
having fibres substantially in the longitudinal direction may comprise
particles. I t may be especially advantageous to include particles in special
areas, such as in curved parts of the tool o r curved parts of the article. The
friction of the fibres is increased by the addition of the particles. The particles
are disclosed and described in PCT/SE201 0/05051 8 and those particles
disclosed in PCT/SE201 0/05051 8 can be used according to the present
invention.
The particles have improved the possibility of the plies having fibres
substantially in the diagonal direction to the longitudinal direction L to keep
the fibres in place, in order to prevent thinning of the article. When the article
contains plies having fibres substantially diagonal 812, 8 13 , 815, 8 16 , 8 1 7 ,
8 18 to the longitudinal direction L of the article, its mechanical properties are
improved. Further, the thinning of the article is avoided, which also improves
the mechanical strength of the article, and the particles may also give
additional strength to the article. Besides, the article is not wrinkled. Further,
all plies having fibres in the diagonal direction may comprise particles.
A tool for forming a n article according to the present invention is disclosed i n
for example Figures 1 and 2 . The present invention relates to a method of
forming a n article o n a tool, the tool having one longitudinal direction L and
one transversal direction T , wherein the method comprises the steps of:
arranging a stack 22 of plies 23 wherein one ply is a bottom ply and one
ply is a top ply, and wherein most of o r all of the plies comprise fibres,
wherein the stack comprises a plurality of plies having fibres substantially
in the orthogonal direction 3 to the longitudinally direction L of the tool and
the stack further comprises a plurality of plies having fibres substantially
in the same direction 2 as the longitudinally direction L of the tool 2 1
and/or a plurality of plies having fibres substantially in the diagonal
direction 4 , 5 , 6 , 7 , 8 , 9 to the longitudinally direction L of the tool 2 1 , so
that when positioned o n the tool 2 1 at least one of the ply/plies arranged
in the orthogonal direction 3 to the longitudinal direction L of the tool 2 1
have fibres that are stiffer than the fibres in the other plies which have
less stiff fibres;
-conforming the stack to the tool with a forming medium; and
-removing the article from the tool 6 1 , 7 1 . The article may be cured
before o r after removing the article from the tool.
The method further comprises the step of arranging a further stack of plies o n
the tool 2 1 after a conforming step and then conforming the further stack to
the tool with a forming medium. This can be repeated several times. A stack
of plies can be arranged o n the tool, the stack is conformed to the tool with a
forming medium, a further stack o p plies is arranged o n the tool 2 1 and the
further stack is conformed to the tool with a forming medium. The further
stack is arranged o n top of the earlier stack of plies. This can be repeated
until a desired numbers of plies are arranged o n the tool 2 1 . In addition, the
plies can be applied o r arranged o n the tool 2 1 one at a time. This is
considered to be encountered in the context of applying a stack of plies o n a
tool. I t is not necessary to have a stack of plies before adding the stack o n
the tool. The stack can be arranged o n the tool by adding a ply one at a time.
The stiffer fibres will avoid compression of those plies and thereby wrinkles
are avoided during the forming of the article. Fibres in the orthogonal
direction may be compressed in the longitudinal direction of the fibre during
forming of the article. One reason for compression in the plies having fibres
substantially in the orthogonal direction to the longitudinal direction of the
article may be inter ply sliding in those plies during forming of the article. Intra
ply sliding is sliding of the fibres in one ply, while inter ply sliding is sliding
between the plies. When the fibres are sliding in the orthogonal direction, the
fibres may be compressed in the fibre length and the fibres may then buckle.
However, i f the fibres are stiffer, the compression is avoided and the fibres
will conform to the form of the tool. When producing the article, the stiffer
fibres in the plies having fibres substantially in the orthogonal direction 810
avoid compression of the ply/plies. This avoids that the fibres are bended in
the wrong direction and thus avoids wrinkling. The plies having stiffer fibres
will cooperate with the plies having less stiff fibres in a n advantageous way.
The plies having less stiff fibres will not be deformed so easy when formed
together with plies having stiffer fibres. The plies having stiffer fibres will also
conform easier to the tool as disclosed above. A stiff fibre will not be
compressed so easy, but will be conformed to the tool.
The fibre reinforced polymer plies have unidirectional fibres i n the plies.
The method also comprises arranging at least one ply/plies with a cure ply
thickness which is smaller than the cure ply thickness of the other ply/plies,
so that the ply/plies with the smaller cure ply thickness have the fibres in the
orthogonal direction 3 to the longitudinal direction L of the tool 1. When
forming the article, compression in the fibre length direction of the plies
having smaller cure ply thickness than the other plies is avoided and thereby
is wrinkling of the plies avoided.
The method may also comprise to arrange ply/plies having fibres
substantially in a n orthogonal direction and having a smaller cure ply
thickness and wherein the ply/plies also comprise fibres which are stiffer than
the other plies which have less stiff fibres. However, i t can also comprise to
arrange one ply having fibres substantially in a n orthogonal direction wherein
the ply/plies may comprise stiffer fibres than the other plies, and arranging
another ply having fibres substantially in a n orthogonal direction that have a
smaller cure ply thickness than other plies.
The method also relates to arrange ply/plies having a smaller cure ply
thickness wherein they may have a cure ply thickness of < 0.1 5 and the cure
ply thickness of the other ply/plies may be > 0.15. The method also relates to
arrange ply/plies wherein the ply/plies having a smaller cure ply thickness
have a cure ply thickness of < 0.14 mm and the cure ply thickness of the
other ply/plies > 0.1 7 mm. With the difference of the cure thickness wrinkling
is avoided since the compression is avoided of the ply/plies having a lower
cure ply thickness.
The method also relates to arranging a bottom ply o n the tool, wherein the
bottom ply has fibres in the orthogonal direction and wherein the bottom ply
fibres are stiffer than the fibres in the other plies which have less stiff fibres.
The method may also comprise to arrange ply/plies having fibres
substantially in the orthogonal direction and having stiffer fibres close to the
tool. The effect of the stiffer fibres may be more advantageous close to the
tool, since the compression of the fibres in the longitudinal direction of the
fibres may be larger close to the tool.
The method also relates to arranging a bottom ply o n the tool, wherein the
bottom ply has a cure ply thickness which is smaller than the cure ply
thickness of the other plies. The method may also comprise to arrange
ply/plies having fibres substantially in a n orthogonal direction and having a
smaller cure ply thickness than the other plies close to the tool.
The method may also comprise arranging the ply/plies so that all ply/plies
having fibres substantially in the orthogonal direction 3 comprise fibres that
are stiffer than the other ply/plies. During forming of the article, the plies
having stiffer fibres will avoid wrinkling at the same time as plies having less
stiff fibres will avoid to be deformed. This combination will provide a n article
with very good properties, such as good mechanical properties.
Further, i t may comprise arranging the ply/plies so that all ply/plies having
fibres substantially in the orthogonal direction 3 has a cure ply thickness
which is smaller than the cure ply thickness of the other ply/plies. This further
avoids that the plies having smaller cure ply thickness will avoid wrinkling and
will thus provide a n article with very good mechanical properties.
Further, the method comprises arranging a ply 24 closest to the tool 2 1 and
arranging a ply 25 furthest away from the tool 2 1 which have fibres
substantially orthogonal 3 to the longitudinal direction L of the tool, and
arranging at least one ply having the fibres substantially i n the same direction
2 as the longitudinal direction L of the tool 2 1 between plies having fibres
substantially orthogonal 3 to the longitudinal direction L of the tool 2 1 and
arranging at least one ply having fibres substantially diagonal 4 , 5 to the
longitudinal direction L of the tool 1, 2 1 , wherein such ply o r plies are
arranged next to each other o r between plies having fibres substantially
orthogonal 3 to the longitudinal direction L of the tool 1, 2 1 .
The method further comprises arranging the stack 22, 42 so that when
positioned o n the tool 2 1 , 4 1 the ply arranged closest 24, 44 to the tool 2 1 , 4 1
has the fibres substantially orthogonal 3 to the longitudinal direction L of the
tool 2 1 , 4 1 , the next four plies have the fibres substantially diagonal 4 , 5 to
the longitudinal direction L of the tool 2 1 , 4 1 , the next ply has the fibres
substantially orthogonal 3 to the longitudinal direction L of the tool 2 1 , 4 1 , the
next four plies have the fibres i n substantially the same direction as the
longitudinal direction L of the tool 2 1 , 4 1 , the next ply has the fibres
substantially orthogonal 3 to the longitudinal direction L of the tool 2 1 , 4 1 , the
four next plies have the fibres substantially diagonal 4 , 5 to the longitudinal
direction L of the tool 2 1 , 4 1 , the next ply has the fibres substantially
orthogonal 3 to the longitudinal direction L of the tool 2 1 , 4 1 .
The tool may also comprise at least one curved part 38. At curved parts,
such as corners, buckling is common to occur. The ply/plies having the fibres
in the orthogonal direction to the longitudinal direction o n the tool may bend
in the wrong way and may be wrinkled quite easily during the forming of the
article. When the fibres i n the ply/plies having fibres substantially in the
orthogonal direction to the longitudinal direction of the tool are stiffer, the
buckling is avoided. The stiffer fibres avoids compression and thereby the
buckling. This is especially useful at curved parts of tools. A curved part 38 is
disclosed in the tool 3 1 and may be for example a corner.
Further, the present invention relates to a method, wherein the tool 3 1 has at
least one depressed part 34 and at least one protruding part 35, 36 which
protruding part is protruding in relation to the depressed part 34 of the tool
3 1 . The tool 3 1 has at least one narrower part and at least one thicker part i n
the cross-section of the tool 3 1 . The depressed areas 34 correspond to the
narrower part of the tool 3 1 . The protruding areas 35, 36 correspond to the
thicker part of the tool 3 1 .
In Figure 3 there is one depressed part 34 o n the tool 3 1 . A tool can have
several depressed parts. When forming a stack of plies o n a tool comprising
depressed and protruding parts, there is a transition area 39 between the
depressed part 34 and the protruding part 35, 36. This area may form a n
inclined surface o n the tool 3 1 . In the side parts 37 there may be difficulties
with wrinkles formed during the forming step. This problem is solved with the
present invention by arranging the plies having substantially longitudinal
direction L and plies having substantially diagonal direction 4 , 5 between
plies having orthogonal 3 fibres. The plies with longitudinal fibres L and
diagonal fibres 4 , 5 will slide between the plies having orthogonal fibres 3 ,
and thereby wrinkles are avoided. The benefit is also obtained by that the
plies arranged next to the tool and furthest away from the tool, thus next to
the forming medium, are arranged orthogonal to the longitudinal direction L .
At least one ply of the plies having the fibres in the longitudinal direction L of
the tool and one of the plies having the fibres i n the diagonal direction of the
tool may comprise particles. This will improve the method of producing the
article, since the fibres in the plies comprising particles will not move o r slide
as easily as without the particles. The particles will increase the friction
between the fibres, which makes the fibres stay in their positions. This avoids
thinning of the article, which together with the avoidance of wrinkles achieves
a good composite article. I t is also a n advantage to use particles in a curved
part of a tool, since this will avoid thinning of the article in the curved parts.
A n apparatus for forming a n article by conforming a stack according to the
present invention is disclosed in Figure 6 and in Figure 7 . A tool 6 1 , 7 1 is
disclosed with a stack 66, 73 and a forming medium 65, 72.
The stack may be arranged o n 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 i n the different plies, the direction
always refer to the direction of the tool, to which the stack is transferred to
when i t refers to the method. Several prepregs o r tapes may first be laid i n
the form of a stack. This is done by hand o r by a n Automatic Tape Laying
Machine o n a temporary support. This is followed by for example a Hot drape
forming, HDF, process. The stack is transferred to the tool 6 1 , 7 1 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 a n elastic bag material.
The article to be formed could for example be a beam. I t can be seen in
Figures 6 and 7 that the prepreg stack 66, 73 extends outside the top surface
68, 76 of the tool. When hot drape forming is performed, the outer parts of
the stack will be forced down to the side edges 69, 74, 75 of the tool 6 1 , 7 1
by a forming medium in the form of a vacuum bag and there form flanges in
the article. The stack may also be forced down by mechanical means, such
as rolls, when forming flanges in the article. Examples of flanges 802, 804 i n
a n article 801 are shown in Figure 8 .
For easiness, the fibre direction of the plies will sometimes shortly be called
orthogonal direction and the longitudinal direction, respectively. The direction
is related to the tool o r the article, depending o n what is concerned in the
circumstances.
For further simplifying the expressions, the plies having the fibres
substantially orthogonal to the longitudinal direction of the tool o r the article
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 o r the article are
called 45° and 135° plies o r any other angle which is defined to be included
in the diagonal direction, as defined to be 30° to 60° and 120° to 150°.
When forming a stack 22 of plies o n a tool 2 1 , 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. When plies having a substantially
orthogonal direction 3 to the longitudinal direction L of the tool is arranged
closest to the tool 1, 2 1 , 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 o n the tool and against the
fornning 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 i n a n orthogonal 3 direction to the longitudinal
direction L of the tool 1, 2 1 , the plies having fibres substantially 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. I f wrinkles
are formed in hot drape formed articles, the wrinkles are usually formed in
the flanges 802, 804 of the articles. The flanges are the parts which are
formed o n the longitudinal sides of the tool. One longitudinal side 26 of the
tool 2 1 can be seen in Figure 2 and longitudinal sides 69, 74, 75 are shown
in Figures 6 and 7 . When the stacks are conformed over the corners 27
(Figure 2) of the tool 2 1 , the wrinkles may be formed o n the longitudinal sides
26, close to the corners. This is also disclosed in Figure 5 . The wrinkles may
be formed due to that the plies do not slide easily between each other, but
are locked in positions forming wrinkles. When locked in the position, the
fibres may be compressed in the fibre direction in the plies having fibres in
the orthogonal direction of the longitudinal direction of the tool. The
compression is avoided due to the stiffer fibres in the plies having fibres
substantially in the orthogonal direction. The problems discussed with the
wrinkles are the same for hot drape forming and mechanical forming.
The method according to the present invention also comprises
- conforming the stack with a mechanical forming medium.
The forming medium may be a mechanical forming medium, such as a roll o r
press forming.
The method according to the present invention can also comprise
- conforming the stack by hydroforming o r vacuum forming with a n elastic
membrane.
Further, the method comprises
- enclosing the stack within a fornning medium 65, 72,
- evacuating the forming medium 65, 72 for allowing the forming
medium to stretch and conform the stack 66, 73 to the tool 6 1 , 7 1 .
According to the present invention, the forming medium 65, 72 used under
the forming step can be a n elastic vacuum bag.
The method thus relates to a method that comprises
conforming the stack with a mechanical forming medium, o r
enclosing the stack within a forming medium (65, 72),
- evacuating the forming medium (65, 72) for allowing the forming
medium to stretch and conform the stack (66, 73) to the tool (61 , 7 1 ) .
As disclosed above, the forming medium may be a hydroforming o r vacuum
forming medium o r a mechanical forming medium.
The evacuating step may be performed in all temperature ranges. After the
forming step, a n 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.
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. The plies having stiffer and
optionally smaller cure ply thickness improve the inter ply sliding during
forming in that the compression of the stiffer fibres and the plies having
smaller cure ply thickness are avoided which reduces the risk of wrinkling.
The present invention also relates to a composite article produced according
to the method disclosed above. A n article according to the present invention
has been able to produce without wrinkles.
The stack may also be laid directly o n 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 o n 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.
The description and definition of the plies applies for both the article and the
method according to the present invention.
CLAIMS
A composite article (801 ) , wherein the article has a longitudinal
direction (L) and a transversal direction (T), the article (801 ) comprises
a stack of plies wherein one ply is a bottom ply and one ply is a top
ply, most of o r all of the plies comprise fibres, and the stack
comprises a plurality of plies having fibres substantially in the
orthogonal direction (81 0) to the longitudinal direction (L) of the article
(801 ) and the stack further comprises a plurality of plies having fibres
substantially in the same direction (81 1) as the longitudinally direction
(L) of the article (801 ) and/or a plurality of plies having fibres
substantially in the diagonal direction (81 2 , 8 13 , 8 15 , 816, 8 17 , 8 1 8 ) of
the longitudinal direction (L) of the article (801 ) , characterized in that
at least one of the ply/plies having fibres substantially in the
orthogonal direction (81 0) to the longitudinal direction (L) of the article
(801 ) comprise fibres that are stiffer than the fibres in the other plies
which have less stiff fibres.
A composite article according to claim 1, characterised in that at
least one of the ply/plies having fibres substantially in the orthogonal
direction (81 0 ) to the longitudinal direction (L) of the article (801 ) has a
cure ply thickness which is smaller than the cure ply thickness of the
other ply/plies.
A composite article according to claim 2 , characterised in that the
ply/plies having a smaller cure ply thickness have a cure ply thickness
of < 0.14 mm and the cure ply thickness of the other ply/plies > 0.1 7
mm.
A composite article according to any of claims 1 to 3 , characterized in
that all the plies having fibres substantially in the orthogonal direction
(81 0 ) comprise fibres that are stiffer than the fibres i n the other plies.
A composite article according to any of claims 2 to 4 , characterized in
that all the plies having fibres substantially in the orthogonal direction
(81 0) has a cure ply thickness which is smaller than the cure ply
thickness of the other ply/plies.
6 . A composite article according to any of claims 1 to 5 , characterised
in that the bottom ply (24) and the top ply (25) have fibres i n a
substantially orthogonal direction (81 0 ) to the longitudinal (L) direction
of the article (801 ) and at least one ply has the fibres substantially in
the same direction (81 1) as the longitudinal direction (L) of the article
(801 ) arranged between plies having fibres substantially orthogonal
(810) to the longitudinal direction (L) of the article (801 ) and i t further
comprises at least one ply having fibres substantially diagonal (81 2 ,
8 13 , 8 15 , 8 16 , 8 17 , 8 18 ) to the longitudinal direction (L) of the article
(801 ) , wherein such ply o r plies are arranged next to each other o r
between plies having fibres substantially orthogonal (81 0 ) to the
longitudinal direction (L) of the article (801 ) .
7 . A composite article according to any of claims 1 to 6 , characterized in
that the article includes at least one curved part (814).
8 . A method of forming a n article o n a tool, the tool having one
longitudinal direction L and one transversal direction T , wherein the
method comprises the steps of:
arranging a stack (22) of plies (23), wherein one ply is a bottom ply (24)
and one ply is a top ply (25), and wherein most of o r all of the plies
comprise fibres, wherein the stack comprises a plurality of plies having
fibres substantially in the orthogonal direction (3) to the longitudinally
direction (L) of the tool and the stack further comprises a plurality of plies
having fibres substantially in the same direction (2) as the longitudinally
direction (L) of the tool (21 ) and/or a plurality of plies having fibres
substantially in the diagonal direction (4, 5 , 6 , 7 , 8 , 9 ) to the longitudinally
direction (L) of the tool (21 ) , so that when positioned o n the tool (21 ) at
least one of the ply/plies having fibres substantially in the orthogonal
direction (3) to the longitudinal direction (L) of the tool (21 ) have fibres
that are stiffer than the fibres in the other plies which have less stiff fibres;
-conforming the stack to the tool with a forming medium; and
-removing the article from the tool (61 , 7 1 ) .
9 . A method according to claim 8 , comprising the step of arranging a
further stack of plies o n the tool (21 ) after a conforming step and then
conforming the further stack to the tool with a forming medium.
10 . A method according to claim 8 o r 9 , comprising arranging at least one
ply/plies with a cure ply thickness which is smaller than the cure ply
thickness of the other ply/plies, so that the ply/plies with the smaller
cure ply thickness have the fibres substantially in the orthogonal
direction (3) to the longitudinal direction (L) of the tool ( 1 ) .
11.A method according to claim 10 , comprising arranging ply/plies
wherein the ply/plies a having smaller cure ply thickness have a cure
ply thickness of < 0.14 mm and the cure ply thickness of the other
ply/plies > 0.1 7 mm.
12 . A method according to any of claims 8-1 1, comprising arranging the
ply/plies so that all ply/plies having fibres substantially in the
orthogonal direction (3) comprise fibres that are stiffer than the other
ply/plies.
13 . A method according to any of claims 8-1 1, comprising arranging the
ply/plies so that all ply/plies having fibres substantially in the
orthogonal direction (3) has a cure ply thickness which is smaller than
the cure ply thickness of the other ply/plies.
14. A method according to any of claims 8 to 13 , wherein the ply (24)
arranged closest to the tool (21 ) and the ply (25) arranged furthest
away from the tool (21 ) have fibres substantially orthogonal (3) to the
longitudinal direction (L) of the tool, and arranging at least one ply
having the fibres substantially in the same direction (2) as the
longitudinal direction (L) of the tool (21 ) between plies having fibres
substantially orthogonal (3) to the longitudinal direction (L) of the tool
(21 ) and i t further comprises arranging at least one ply having fibres
substantially diagonal (4, 5 ) to the longitudinal direction (L) of the tool
( 1 , 2 1 ) , wherein such ply o r plies are arranged next to each other o r
between plies having fibres substantially orthogonal (3) to the
longitudinal direction (L) of the tool ( 1 , 2 1 ) .
15 . A method according to any of claims 8 t o 14, wherein the tool
comprises at least one curved part (38).