U.S. patent application number 13/789965 was filed with the patent office on 2014-09-11 for forming composite features using steered discontinuous fiber pre-preg.
This patent application is currently assigned to The Boeing Company. The applicant listed for this patent is The Boeing Company. Invention is credited to Michael Jeffrey Graves, Kenneth H. Griess, Derek Paul Vetter.
Application Number | 20140255646 13/789965 |
Document ID | / |
Family ID | 50190809 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140255646 |
Kind Code |
A1 |
Griess; Kenneth H. ; et
al. |
September 11, 2014 |
Forming Composite Features Using Steered Discontinuous Fiber
Pre-Preg
Abstract
Interlaminar features of a composite structure are laid up by
placing and steering individual chopped fiber pre-preg segments
onto a substrate.
Inventors: |
Griess; Kenneth H.; (Kent,
WA) ; Vetter; Derek Paul; (Olympia, WA) ;
Graves; Michael Jeffrey; (Seattle, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Boeing Company; |
|
|
US |
|
|
Assignee: |
The Boeing Company
Chicago
IL
|
Family ID: |
50190809 |
Appl. No.: |
13/789965 |
Filed: |
March 8, 2013 |
Current U.S.
Class: |
428/114 ;
156/176; 156/361; 156/517; 156/94 |
Current CPC
Class: |
B29K 2105/14 20130101;
Y10T 156/1322 20150115; B29C 70/14 20130101; B29K 2105/0872
20130101; Y10T 428/24132 20150115; B29C 70/38 20130101; B29C 70/021
20130101; B29K 2105/26 20130101; B32B 5/32 20130101 |
Class at
Publication: |
428/114 ;
156/176; 156/94; 156/517; 156/361 |
International
Class: |
B29C 70/02 20060101
B29C070/02; B32B 5/32 20060101 B32B005/32 |
Claims
1. A method of forming a composite feature having discontinuous
reinforcement fibers, comprising: producing a plurality of resin
infused fiber segments each having unidirectional reinforcing
fibers; placing the resin infused fiber segments on a substrate;
and, arranging the resin infused fiber segments such that the
reinforcing fibers of resin infused fiber segments placed on the
substrate are substantially aligned relative to a desired reference
orientation.
2. The method of claim 1, wherein producing the resin infused fiber
segments includes chopping scrap fiber pre-preg into individual
pieces.
3. The method of claim 1, wherein producing the resin infused fiber
segments is performed by splitting fiber pre-preg along and between
the reinforcing fibers into individual pieces.
4. The method of claim 1, wherein placing the resin infused fiber
segments on the substrate includes: moving a applicator over the
substrate, and dispensing the resin infused fiber segments from the
applicator onto the substrate as the applicator moves over the
substrate.
5. The method of claim 4, wherein arranging the resin infused fiber
segments includes aligning the resin infused fiber segments as they
are being dispensed from the applicator onto the substrate.
6. The method of claim 4, wherein producing the resin infused fiber
segments is performed by: drawing continuous fiber pre-preg tape
from the applicator, and chopping the pre-preg tape into the resin
infused fiber segments as the resin infused fiber segments are
being dispensed from the applicator onto the substrate.
7. The method of claim 4, wherein dispensing the resin infused
fiber segments from the applicator includes dispensing a bandwidth
of the resin infused fiber segments onto the substrate.
8. The method of claim 1, wherein placing the resin infused fiber
segments on the substrate is performed by introducing the resin
infused fiber segments into an airstream, and using the airstream
to stream the resin infused fiber segments from an applicator head
onto the substrate.
9. The method of claim 8, wherein streaming the resin infused fiber
segments is performed by: introducing the resin infused fiber
segments into an airstream, and using the airstream to project the
resin infused fiber segments onto the substrate.
10. The method of claim 1, wherein arranging the resin infused
fiber segments is performed after the resin infused fiber segments
have been placed on the substrate.
11. The method of claim 1, further comprising: applying resin to
the substrate before the resin infused fiber segments are placed on
the substrate.
12. The method of claim 1, further comprising applying a resin on
at least one end of each of the resin infused fiber segments before
they are placed on the substrate.
13. A method of laying up composite material on a substrate,
comprising: placing individual chopped fiber pre-preg segments on
the substrate; and, controlling an orientation of the pre-preg
segments on the substrate.
14. The method of claim 13, wherein placing the pre-preg segments
on the substrate is performed by: moving an applicator head over
the substrate along a desired path, and dispensing the pre-preg
segments from the applicator head onto the substrate as the
applicator moves over the substrate.
15. The method of claim 14, wherein controlling an orientation of
the pre-preg segments is performed by substantially aligning the
pre-preg segments being dispensed from the applicator head relative
to a desired orientation.
16. The method of claim 13, wherein controlling an orientation of
the pre-preg segments includes changing the orientation of the
pre-preg segments after the pre-preg segments have been placed on
the substrate.
17. A composite laminate structure layup, comprising: a plurality
of layers of composite material, each of the layers including a
plurality individual chopped fiber pre-preg segments having
substantially aligned fiber orientations.
18. The composite laminate structure layup of claim 17, wherein the
fiber orientations of the chopped fiber pre-preg segments are
substantially aligned with a non-linear load path through the
composite laminate structure.
19. The composite laminate structure layup of claim 17, wherein
each of the individual chopped fiber pre-preg segments has an
aspect ratio of approximately 6:1.
20. The composite laminate structure layup of claim 17, wherein the
plurality of layers of composite material have a tailored
cross-sectional shape and is contoured along a length of the
layup.
21. Apparatus for laying up a composite structure, comprising: an
applicator adapted to move over a substrate, and dispense at least
one stream of substantially aligned chopped, resin infused fiber
segments onto the substrate.
22. The apparatus of claim 21, further comprising a computer
controlled manipulator for moving the applicator along a
preselected path over the substrate.
23. The apparatus of claim 21, wherein the applicator includes: a
supply of continuous resin infused fiber, and a chopper for
chopping the continuous resin infused fiber into individual resin
infused fiber segments.
24. The apparatus of claim 23, wherein the applicator includes an
airstream generator for streaming the resin infused fiber segments
from the applicator onto the substrate.
25. The apparatus of claim 21, wherein the applicator is adapted to
simultaneously dispense multiple streams of substantially aligned
chopped, resin infused fiber segments onto the substrate.
Description
BACKGROUND INFORMATION
[0001] 1. Field
[0002] The present disclosure generally relates to fabrication of
composite laminate structures using fiber pre-preg, and deals more
particularly with a method and apparatus for forming composite
structural features by steering discontinuous fiber pre-preg onto a
substrate with desired fiber orientations.
[0003] 2. Background
[0004] The strength, stiffness and load transfer characteristics of
a composite laminate structure may be optimized through control of
fiber orientation during the layup process. Conventional composite
laminates may be laid up using pre-preg tapes, tows or broad goods,
employing either automated fiber placement equipment or hand
placement techniques to layup the material. Generally, the
resulting composite structure exhibits substantially consistent
structural properties throughout. In some cases, however, it may be
necessary or desirable to control the thickness and/or fiber
orientation in local areas of a composite laminate in order to
optimize its structural properties and/or account for higher local
stresses.
[0005] The ability to control local thickness/fiber orientation is
limited using current fabrication processes. For example, automated
fiber placement equipment may be used to steer continuous tows onto
the substrate, but the radius of curvature that can be achieved is
limited, thus making control of fiber orientation difficult in
local areas having tight contours. Achieving close control over
thickness and/or fiber orientation in local areas of laminate may
also be costly and time-consuming.
[0006] Accordingly, there is a need for a method and apparatus for
controlling composite laminate thickness and/or fiber orientation
in local areas of a laminate in order to optimize the laminate's
structural properties. There is also a need for a method and
apparatus of the type mentioned above which is efficient, highly
controllable and which may reduce labor and material costs.
SUMMARY
[0007] The disclosed embodiments provide a method and apparatus for
fabricating composite features of laminates which provide increased
control over feature thickness and/or fiber orientation in local
areas of a laminate structure, such as in tight contours and/or
within transitions in laminate thickness. Composite material may be
laid up such that fiber orientations are substantially continuously
aligned with load vectors in selected local areas of a laminate,
thereby optimizing the laminate's structural properties.
[0008] The amount of composite material required to provide local
areas of a laminate structure with desired structural properties
may be reduced by forming the composite features using scrap
pre-preg derived from other products/processes. Recycling of scrap
pre-preg for use in the disclosed method may reduce material costs,
thus optimizing the buy-to-fly ratio (the ratio of materials weight
procured to the weight of the finished product) for aircraft
applications of the embodiments. The embodiments allow composite
material in the form of discontinuous fiber pre-preg to be
"steered" onto a substrate in order to achieve desired fiber
orientations.
[0009] The use of discontinuous fiber pre-preg allows greater
control over laminate thickness variations in local areas of the
laminate, while allowing local tailoring of laminate thickness in
three dimensions to provide smooth transitions between differing
features of a laminate structure. Moreover, the use of
discontinuous fiber pre-preg permits the formation of doublers or
other pad-ups having tight contours and/or tapered edges to achieve
smooth load transitions within a structure. Also, the use of
discontinuous fiber pre-preg may result in composite features
having a higher fiber content.
[0010] According to one disclosed embodiment, a method is provided
of forming a composite feature having discontinuous reinforcement
fibers. The method comprises producing a plurality of resin infused
fiber segments each having unidirectional reinforcing fibers,
placing the resin infused fiber segments on a substrate, and
arranging the resin infused fiber segments such that the
reinforcing fibers of resin infused fiber segments placed on the
substrate are substantially aligned relative to a desired reference
orientation. Producing the resin infused fiber segments includes
chopping scrap fiber pre-preg into individual pieces, which may be
performed by breaking or splitting fiber pre-preg along and between
the reinforcing fibers into individual pieces. Placing the resin
infused fiber segments on the substrate includes moving an
applicator over the substrate, and dispensing the resin infused
fiber segments from the applicator onto the substrate as the
applicator moves over the substrate. Arranging the resin infused
fiber segments includes aligning the resin infused fiber segments
as they are being dispensed from the applicator onto the substrate.
Producing the resin infused fiber segments is performed by drawing
continuous fiber pre-preg tape from the applicator, and chopping
the pre-preg tape into the resin infused fiber segments as the
resin infused fiber segments are being dispensed from the
applicator onto the substrate. Dispensing the resin infused
segments from the applicator includes dispensing a bandwidth of the
resin infused fiber segments onto the substrate. Placing the resin
infused fiber segments on the substrate is formed of by streaming
the resin infused fiber segments from an applicator head onto the
substrate. Streaming the resin infused fiber segments is performed
by introducing the resin infused fiber segments into an airstream,
and using the airstream to project the resin infused fiber segments
onto the substrate. The resin infused fiber segments is performed
after the resin infused fiber segments have been placed on the
substrate. The method may further comprise applying resin to the
substrate before the resin infused segments are placed on the
substrate. The method may also comprise applying a resin on at
least one end of each of the resin infused fiber segments before
they are placed on the substrate.
[0011] According to another disclosed embodiment, a method is
provided of laying up composite material on a substrate the method
comprises placing individual chopped fiber pre-preg segments on the
substrate, and controlling the orientation of the pre-preg segments
on the substrate. Placing the pre-preg segments on the substrate is
performed by moving an applicator head over the substrate along a
desired path, and dispensing the pre-preg segments from the
applicator head onto the substrate as the applicator moves over the
substrate. Controlling the orientation of the pre-preg segments is
performed by aligning the pre-preg segments being dispensed from
the applicator head. Controlling the orientation of the pre-preg
segments includes changing the orientation of the pre-preg segments
after the pre-preg segments have been placed on the substrate.
[0012] According to still another embodiment, a composite laminate
structure layup is provided comprising a plurality of layers of
composite material, each of the layers including a plurality
individual chopped fiber pre-preg segments having aligned fiber
orientations. The fiber orientations of the chopped fiber pre-preg
segments are substantially aligned with a non-linear load path
through the composite laminate structure. Each of the individual
chopped fiber pre-preg segments may have an aspect ratio of
approximately 6:1. The plurality of layers of composite material
have a tailored cross-sectional shape and is contoured along a
length of the layup.
[0013] According to still another disclosed embodiment, apparatus
is provided for laying up a composite structure. The apparatus
comprises an applicator adapted to move over the surface of a
substrate, and dispense at least one stream of substantially
aligned chopped, resin infused fiber segments onto the surface of a
substrate. The apparatus may also comprise a computer controlled
manipulator for moving the applicator along a preselected path over
the substrate. The applicator includes a supply of continuous resin
infused fiber, and a chopper for chopping the continuous resin
infused fiber into individual resin infused fiber segments.
Applicator may further include an airstream generator for carrying
the resin infused fiber segments from the applicator onto the
substrate. The applicator may be adapted to simultaneously dispense
multiple streams of substantially aligned chopped, resin infused
fiber segments onto the substrate. The features, functions, and
advantages can be achieved independently in various embodiments of
the present disclosure or may be combined in yet other embodiments
in which further details can be seen with reference to the
following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The novel features believed characteristic of the
illustrative embodiments are set forth in the appended claims. The
illustrative embodiments, however, as well as a preferred mode of
use, further objectives and advantages thereof, will best be
understood by reference to the following detailed description of an
illustrative embodiment of the present disclosure when read in
conjunction with the accompanying drawings, wherein:
[0015] FIG. 1 is an illustration of a combined block and
diagrammatic of discontinuous fiber pre-preg being applied to a
substrate along a tight contour.
[0016] FIG. 1A is an illustration of a plan view showing one shape
of the pre-preg segments.
[0017] FIG. 1B is an illustration of a plan view showing another
shape of the pre-preg segments.
[0018] FIG. 1C is an illustration of a plan view showing a further
shape of the pre-preg segments.
[0019] FIG. 2 is an illustration of a perspective view of a barrel
section of an aircraft fuselage showing loads applied to the
fuselage.
[0020] FIG. 3 is an illustration of a diagrammatic view of one of
the window openings in the fuselage of FIG. 2, also showing load
vectors around the window opening.
[0021] FIG. 4 is an illustration of an elevational view of one of
the window openings in the fuselage shown in FIG. 2, also showing a
surrounding doubler formed of discontinuous fiber pre-preg.
[0022] FIG. 5 is an illustration of the area designated as "FIG. 5"
in FIG. 4.
[0023] FIG. 6 is an illustration of a sectional view taken along
the line 6-6 in FIG. 5.
[0024] FIG. 7 is an illustration of a cross-sectional view of a
composite structure showing a discontinuous interlaminar fiber
filler and transition in a gap within the thickness of a composite
laminate structure.
[0025] FIG. 8 is an illustration of a flow diagram of a method of
laying up interlaminar composite features using the disclosed
method.
[0026] FIG. 9 is an illustration of a perspective view of a portion
of an aircraft fuselage frame section, broken lines indicating
areas where interlaminar structural features may be formed using
the disclosed method.
[0027] FIG. 10 is an illustration of a sectional view taken along
the line 10-10 in FIG. 9 showing an interlaminar structural feature
formed using the disclosed method.
[0028] FIG. 11 is an illustration of a sectional view taken along
the line 11-11 in FIG. 9.
[0029] FIG. 12 is an illustration of a combined block and
diagrammatic view of a system for placing discontinuous fiber
pre-preg.
[0030] FIG. 13 is an illustration of a combined block and
diagrammatic view of an alternate embodiment of the system for
placing discontinuous fiber pre-preg.
[0031] FIG. 14 is an illustration of a flow diagram of a method of
laying up composite laminates using discontinuous fiber pre-preg
derived from pre-preg scrap.
[0032] FIG. 15 is an illustration of a plan view showing various
shapes of pre-preg scrap that may be used in the method shown in
FIG. 14.
[0033] FIG. 16 is an illustration of a plan view showing randomly
oriented, fiber pre-preg segments formed by chopping the scrap
shown in FIG. 15.
[0034] FIG. 17 is an illustration of a plan view similar to FIG.
16, but showing the fiber orientations of the fiber pre-preg
segments having been aligned in preparation for application to a
substrate.
[0035] FIG. 18 is an illustration of a diagrammatic view of a
method of converting fiber pre-preg scrap into segments and
readying it for application to a substrate.
[0036] FIG. 19A is an illustration of a diagrammatic side view of
an applicator applying resin onto a substrate.
[0037] FIG. 19B is an illustration of a plan view of the resin
applied to the substrate shown in FIG. 19A.
[0038] FIG. 20A is an illustration of a diagrammatic side view
showing chopped fiber pre-preg segments being applied over the
resin shown in FIG. 19B.
[0039] FIG. 20B is an illustration of a plan view of the substrate
in FIG. 20A, showing the random orientation of the chopped fiber
pre-preg segments.
[0040] FIG. 21A is an illustration of a diagrammatic side view
showing the fiber segment aligner aligning the chopped fiber
pre-preg segments.
[0041] FIG. 21B is an illustration of a plan view showing the
chopped fiber pre-preg segments of FIG. 21A having been aligned by
the fiber segment aligner.
[0042] FIG. 22A is an illustration of a side view of a chopped
fiber pre-preg segment with a drop of resin having been placed on
one end thereof.
[0043] FIG. 22B is an illustration of a bottom view of the chopped
fiber pre-preg segment shown in FIG. 22A.
[0044] FIG. 23A is an illustration of a side view of the chopped
fiber pre-preg segment of FIG. 22A having been placed on a
substrate, but prior to rotation thereof.
[0045] FIG. 23B is an illustration of a plan view of the chopped
fiber pre-preg segment shown in FIG. 23A.
[0046] FIG. 24A is an illustration of a side view, similar to FIG.
23A, but after the chopped fiber pre-preg segment has been
rotated.
[0047] FIG. 24B is an illustration similar to FIG. 23B, but showing
the fiber pre-preg segment having been rotated, the position of the
chopped fiber pre-preg segment before rotation being indicated in
the phantom.
[0048] FIG. 25 is an illustration of a flow diagram of aircraft
production and service methodology.
[0049] FIG. 26 is illustration of a block diagram of an
aircraft.
DETAILED DESCRIPTION
[0050] The disclosed embodiments provide a method and apparatus for
fabricating fiber reinforced resin laminates which provide
increased control over laminate thickness, contour, width,
cross-sectional profile and/or fiber orientation in local areas of
a laminate structure. Referring to FIG. 1, a composite feature 30
comprises discontinuous, resin infused fibers which may be in the
form of chopped fiber pre-preg segments 32 having unidirectional
reinforcing fibers 25. Each of the fiber pre-preg segments 32 is
elongate, having a length L that is greater than its width W. Each
of the fiber pre-preg segments 32 may have an aspect ratio (L/W) in
the range of approximately 6:1, however this particular ratio is
merely illustrative. The fiber pre-preg segments 32 may have other
aspect ratios that are selected and/or optimized for the
application, including structural requirements and the equipment
used to position or place the segments 32. In some embodiments, the
fiber pre-preg segments 32 may have a length that is equal to or
less than its width. For convenience and ease of description, the
illustrative examples of composite features 30 that will be
discussed below utilize unidirectional fiber pre-preg. However, it
should be noted here that the principals of the disclosed
embodiments may be employed to form composite features 30 using
other types of pre-preg segments 32, including resins that are
reinforced with fibers having multiple fiber orientations, such as,
for example and without limitation, bidirectional fibers that are
woven (cloth pre-preg) or otherwise combined in a manner to suit
the particular application.
[0051] The disclosed embodiments are particularly well-suited for
forming any of a variety of interlaminate features 30, i.e.
features 30 that are located between two continuous plies. However,
the embodiments may also be employed to form composite features 30
that are partially or fully exposed, such as external features. In
some applications, it may be useful or desirable to employ pre-preg
segments 32 having fibers of differing lengths. Differing fiber
lengths in a segment 32 may be achieved by, for example and without
limitation, shaping the segment 32, such as by chopping, in a
manner that results in some of the fibers being longer or shorter
than other fibers. Three illustrative examples of pre-preg segments
32 having shapes configured to produce reinforcing fibers of
differing lengths are respectively shown in FIGS. 1A-1C. Other
segment shapes resulting in differing fiber lengths are possible.
As previously mentioned, while the pre-preg segments 32 shown in
FIGS. 1A-1C employ unidirectional reinforcing fibers, other fiber
arrangements are possible, such as a woven fibers (not shown).
[0052] The reinforcing fibers 25 may comprise high-strength fibers,
such as glass or carbon fibers, graphite, aromatic polyamide fiber,
fiberglass, or another suitable reinforcement material. The resin
matrix in which the fibers 25 are held may comprise thermoplastic
or thermoset polymeric resins. Exemplary thermosetting resins may
include allyls, alkyd polyesters, bismaleimides (BMI), epoxies,
phenolic resins, polyesters, polyurethanes (PUR),
polyurea-formaldehyde, cyanate ester, and vinyl ester resin.
Exemplary thermoplastic resins may include liquid-crystal polymers
(LCP); fluoroplastics, including polytetrafluoroethylene (PTFE),
fluorinated ethylene propylene (FEP), perfluoroalkoxy resin (PFA),
polychlorotrifluoroethylene (PCTFE), and
polytetrafluoroethylene-perfluoromethylvinylether (MFA);
ketone-based resins, including polyetheretherketone; polyamides
such as nylon-6/6, 30% glass fiber; polyethersulfones (PES);
polyamideimides (PAIS), polyethylenes (PE); polyester
thermoplastics, including polybutylene terephthalate (PBT),
polyethylene terephthalate (PET), and poly(phenylene
terephthalates); polysulfones (PSU); or poly(phenylene sulfides)
(PPS).
[0053] As used herein, "pre-preg" means fibers that have been
impregnated with an uncured or partially cured resin which acts as
a matrix to hold the fibers and which is flexible enough to be
formed into a desired shape. The resin is then "cured," e.g., by
the application of heat in an oven or an autoclave, to harden the
resin into a strong, rigid, fiber-reinforced structure. In the case
of pre-preg segments 32 having unidirectional fibers, the fibers
extend substantially parallel to each other and, for purposes of
this description, have a 0.degree. axial orientation, referred to
hereinafter as the fiber direction or orientation of the pre-preg
segments 32. Where pre-preg segments 32 are used that have multiple
sets of fiber orientations, typically the fiber orientations one or
more of these sets will be used in aligning and orienting the
segments 32 as they are being placed on a substrate 34 during the
layup process.
[0054] The fiber pre-preg segments 32 may be laid up on a substrate
34 that may comprise a tool or an underlying continuous composite
ply, using a suitable applicator system 38 which "steers" the fiber
pre-preg segments 32 onto the substrate 34. The applicator system
dispenses, places and aligns the fiber pre-preg segments 32 on the
substrate 34 such that the direction of the fibers 25 in each of
the fiber pre-preg segments 32 is substantially aligned in a
desired orientation. For example, in the example shown in FIG. 1,
the fiber orientations of the fiber pre-preg segments 32 are
substantially aligned with a curved center axis 36 forming a
relatively tight contour 35, with the fiber orientations of the
segments 32 changing in direction along the contour 35 to remain
substantially aligned in a desired orientation relative to the
center axis 36. The degree to which a chosen set of the fiber
orientations of the pre-preg segments 32 are aligned with respect
to a desired orientation, direction, or axis will depend upon the
application. In some applications, the orientations of the pre-preg
segments 32 may vary to some extent at one or more locations of a
composite feature 30. In fact, in some applications, some degree of
variation of pre-preg segment orientation relative to a desired,
reference orientation may be useful or desirable within a specified
tolerance of variation.
[0055] In one embodiment, the applicator system 38 dispenses a
serial stream 40 of pre-aligned fiber pre-preg segments 32, which
are then steered and placed onto substrate 34 by moving an
applicator head (not shown) forming part of the applicator system
38 in a desired path over the substrate 34, which in the
illustrated example, is along, or parallel to the center axis 36.
Repeated passes of the applicator head over the substrate result in
successive layers or plies being laid up, each comprising aligned
fiber pre-preg segments 32. Thus, the composite feature 30
comprises multiple layers or plies of discontinuous fibers infused
with resin.
[0056] Although not shown in FIG. 1, as will become apparent later
in the description, the disclosed embodiments may also be employed
to fill voids or gaps (not shown) in composite structures as well
as to form transitions (not shown) in laminate thicknesses by
steering resin infused, discontinuous fibers such as chopped fiber
pre-preg onto a substrate. By continuously steering the orientation
of the fiber pre-preg segments 32 as they are being placed,
structural properties of the laminate may be closely controlled on
a local basis and therefore optimized. These void or gap fillers,
as well as features such as bulk doubler areas that include
transitions in laminate thicknesses will typically be interlaminar
features (located between continuous plies), however in some
applications as previously mentioned, it is possible that they may
be exposed, external features.
[0057] Attention is now directed to FIGS. 2-6 which illustrate use
of the disclosed method and apparatus in connection with the
fabrication of an aircraft fuselage (FIG. 2). The fuselage 44
comprises an outer skin 46 supported on internal framework 45 which
includes barrel shaped frames 65 and longitudinally extending
stringers 47. The skin 46 may include one or more discontinuities,
such as window openings 42, cargo doors (not shown), etc. Fuselage
pressure 49 results in a hoop load 50 being applied to the
circumference 55 of the fuselage 44, passing through the windows 48
or other openings in the skin 46. Further, during flight, the crown
54 of the fuselage 44 is placed under tension 75, while the belly
of the fuselage 44 is placed under compression 77, resulting in
shear loads 52 (FIG. 3) that must traverse the window openings 42.
As shown in FIG. 3, the hoop loads 50 and shear loads 52 are
transferred around the perimeter of the window openings 42.
Consequently, the corners 58 around the window openings 42 are more
highly stressed 59 because they must transfer both the hoop loads
50 and the shear loads 52. As will be discussed below, the
disclosed method and apparatus may be employed to layup composite
doublers forming an interlaminar pad-up feature 30 around the
window openings 42 that stiffens and strengthens the fuselage 44
around the window opening 42, enabling the skin 46 to transfer the
required loads through the corners 58.
[0058] Referring particularly to FIG. 5, the pad-up feature 30 is
formed of a discontinuous fiber pre-preg comprising a plurality of
steered fiber pre-preg segments 32 similar to the fiber pre-preg
segments 32 previously discussed in connection with FIG. 1. The
fiber pre-preg segments 32 are steered as they are being placed on
a tool (not shown) or underlying ply (not shown) so that their
respective fiber orientations are substantially aligned with
structural load paths, which in this example, is along or parallel
to a contoured axis 36 at the corners 58. The number of layers or
plies of fiber pre-preg segments 32 that are steered onto the
substrate will vary with the application, and the desired thickness
of the pad-up feature 30. In some applications, it may be desirable
to tailor the cross-sectional area of the pad-up feature 30 formed
by steering the fiber pre-preg segments 30 onto the substrate 34.
For example, referring to FIG. 6, the pad-up feature 30 shown in
FIGS. 4 and 5 may be laid up on one or more underlying full plies
60 and may be covered by one or more overlying full plies 62. The
pad-up feature 30 comprises a double taper 64 that is formed by
laying down layers of the fiber pre-preg segments 32 that are
successively narrower in width "W". Tapering of the pad-up feature
30 allows the resulting doubler to better conform to the full plies
60, 62.
[0059] For example, referring to FIG. 7, the fiber pre-preg
segments 32 may be steered and layered to form cross-sectional
shapes that are suitable for filling gaps or voids 82 in a
composite laminate, such as gaps 82 that may be formed in
transitions in the thickness of a laminate structure 85. In the
example shown in FIG. 7, the composite sandwich laminate structure
85 comprises a core 86 sandwiched between two composite plies 60,
62. A gap 82 is formed as the laminate structure 85 as it
transitions from the core 86 to a solid laminate 87. The gap 82
forms a structural discontinuity that may require strengthening and
reinforcement in order to carry the required loads. The gap 82 may
be filled with layers of the fiber pre-preg segments 32 to form a
discontinuous fiber pre-preg filler feature 30, which in this
example, has a single taper 84.
[0060] FIG. 8 illustrates the overall steps of a method of making a
discontinuous fiber composite feature by steering fiber pre-preg
segments 32 onto a substrate 34. Beginning at 66, fiber pre-preg
segments 32 are produced, as by, for example, chopping the fiber
pre-preg to a desired dimensions and a desired aspect ratio. At 68,
discontinuous fiber plies are laid up by placing the fiber pre-preg
segments 32 on a substrate 34 at step 70, and at 72, arranging the
fiber pre-preg segments 32 such that the fiber orientations of the
reinforcing fibers are aligned in a desired direction. As will be
discussed below in more detail, the fiber pre-preg segments 32 may
be placed on the substrate 34 using an applicator head which may
also be used to steer the fiber pre-preg segments 32 and align them
along load paths through a structure.
[0061] Attention is now directed to FIGS. 9-11 which illustrate a
portion of a frame section 74 having a generally Z-shaped
cross-section. The frame section 74 may form a portion of a barrel
shaped frame 65 such that used in the fuselage 44 shown in FIG. 1.
The frame section 74 includes upper and lower, oppositely extending
flanges 76, 78 connected by a web 80. "Mousehole" openings 82 may
be provided in the web 80 and flange 76 in order to provide
clearance for longitudinally extending stringers 47 (FIG. 2) in the
fuselage 44. The disclosed method and apparatus may be employed to
form discontinuous resin infused fiber features 30 selectively
reinforce portions of the frame section 74, particularly in local
areas that may experience higher stresses. Thus, one side of a
central portion of the web 80 may be provided with a longitudinally
extending, contoured, pad-up feature 30a formed by multiple layers
of discontinuous fiber pre-preg comprising fiber pre-preg segments
32 that are steered onto the web 80 as the frame section 74 is
being laid up.
[0062] In the illustrated embodiment, as is apparent from FIGS. 10
and 11, the pad-up feature 30a varies in cross-sectional shape
along its length, however in other embodiments the cross-sectional
shape of the pad-up feature 30a may be constant along its length.
Similarly, pad-up features 30b, 30c comprising layers of fiber
pre-preg segments 32, such as chopped pre-preg, may be steered onto
the web 80 in contoured patterns surrounding the mouseholes 82. The
pad-up features 30a, 30b, 30c may have any desired cross-sectional
geometry selected to optimize local structural properties of the
frame section 74. Any of the pad-up features 30b, 30c may vary in
cross-sectional size and/or shape along its length.
[0063] Attention is now directed to FIG. 12 which illustrates one
embodiment of a system 88 that may be employed to form
discontinuous, resin infused fiber features 30 of the type
previously described, including local features of a structure that
may require strengthening, stiffening and/or reinforcement. The
system 88 broadly comprises an applicator head 90 that is adapted
to place fiber pre-preg segments 32, such as chopped pre-preg 32,
onto a substrate 34, forming multiple layers or plies 96.
Applicator head 90 is displaced in X, Y and Z directions over the
substrate 34 by an automated manipulator 92 which may comprise, for
example and without limitation, a robot.
[0064] The manipulator 92 as well as the applicator head 90 are
operated by a programmed CNC (computer numerically controlled)
controller 94. The applicator head 90 includes a pre-preg tape
supply 98 which supplies unidirectional fiber pre-preg tape 100
through guides 102 to a chopper 103. The chopper 103 may comprise a
conventional cutter mechanism (not shown) operated in
synchronization with the movement the applicator head 90 to chop
the pre-preg fiber tape 100 into fiber pre-preg segments of the
desired size and shape. The chopped fiber pre-preg segments 32 are
fed 40 into an airstream 104 generated by airstream generators 106
on the applicator head 90. The airstream 104 propels and places the
pre-aligned fiber pre-preg segments 32 through a nozzle 108 onto
the substrate 34 as the applicator head 90 over the substrate 34.
The pre-preg segments 32 are applied to the substrate 34 in the
desired orientation as they contact and adhere to the substrate 34.
Orienting the segments 32 as they are being placed on the substrate
34 may eliminate the need to subsequently adjust the orientation of
the segments 32. A heater 105 may be provided on the applicator
head 90 in order to heat the pre-preg fiber segments 32 and thereby
increase their tackiness. This increased tack may assist in
adhering and holding the pre-preg fiber segments 32 in a desired
orientation on the substrate 34. The heater 105 may comprise any of
a variety of devices suitable for the application, including but
not limited to a hot air blower, a conduction rod, a focused
infrared heater or a laser, to name only a few. The heater 105 may
generally heat the entire area of the segments 32, or may produce a
focused beam (not shown), such as a laser beam, that heats only a
portion of a segment 32 until it is "sticky" enough to adhere to
the substrate when it is placed.
[0065] The applicator head 90 may move from side-to-side (in the Y
direction) in order to apply a width of the chopped pre-preg
segments 32 in a desired orientation, while in other embodiments,
the applicator head 90 may be used to make multiple linear passes
over the substrate 34 in the X direction, in order to cover a
desired width of the substrate 34 with the chopped fiber pre-preg
segments 32 for each layer or ply 96. While the applicator head 90
has been illustrated with airstream generators 106 to place the
fiber pre-preg segments 32, other means such as mechanical
mechanisms may be employed to dispense, place and align the fiber
pre-preg segments 32, as the applicator head 90 moves across, and
steers the fiber pre-preg segments 32 onto the substrate 34. It
should be particularly noted here that the system 88, including the
applicator head 90 discussed above are merely illustrative of a
wide variety of equipment may be used to place and position the
pre-preg segments 32. The particular form of the system 88 that is
used will depend upon the application, including specific
structural requirements and the layup techniques that are employed.
Moreover, the fabrication of the pre-preg segments 32 and equipment
used to place and position the segments 32 on a substrate 34 may be
implemented using a single machine, or several different
machines.
[0066] FIG. 13 illustrates an alternate embodiment of the
applicator head 90 shown in FIG. 12, in which multiple rows of
individual chopped fiber pre-preg segments 32 may be simultaneously
dispensed, aligned in a desired orientation and placed by the
applicator head 90 to form a bandwidth 110 of segments 32 with each
pass of the applicator head 90 across the substrate 34.
[0067] Referring now to FIGS. of 14-17, the disclosed embodiments
may be employed to layup layers or plies of discontinuous fiber
pre-preg using scrap pre-preg 124 (FIG. 15). Referring to FIG. 14,
as shown at step 112, the scrap pre-preg 124 may be obtained from
non-conforming/scrap parts or from scrap pre-preg resulting from
other production processes. The scrap pre-preg 124 may have any of
various shapes, as shown in FIG. 15. At step 116 shown in FIG. 14,
the scrap pre-preg 124 is chopped into individual fiber pre-preg
segments 32, and following this chopping process, the segments 32
may have a random fiber orientation 126, as shown in FIG. 16 and/or
may have fibers of differing lengths. At step 118, the chopped
fiber pre-preg segments are substantially aligned 128 with a
desired fiber orientation as shown in FIG. 17. At step 120, the
aligned fiber pre-preg segments 32 are fed to an applicator. At
step 122 the applicator is used to dispense, steer and place the
fiber pre-preg segments 32 on the substrate 34, such that fiber
orientations of the fiber pre-preg segments 32 are aligned in a
desired direction.
[0068] The chopped fiber pre-preg 32 derived from scrap that is
used in the disclosed method may be produced using any of several
processes. For example, referring to FIG. 18, scrap pre-preg 124
may be introduced into a chopper device 130 which may be similar to
a blender, having rotating blades 132 inside an open vessel 135.
The blades 132 chop and break the scrap fiber pre-preg 124 into
individual fiber pre-preg segments 32, breaking or splitting the
pre-preg along the lines of, and between the reinforcing fibers,
resulting in the fiber pre-preg segments that have a random
orientation 126. With the scrap pre-preg having been chopped into
individual fiber pre-preg segments 32, the randomly oriented 126
fiber pre-preg segments 32 are aligned, for example by placing them
in a shaker tray 134 having a series of parallel channels 136. The
shaker tray 134 is vibrated side-to-side 138, causing the randomly
oriented 126 fiber pre-preg segments 32 that have been loaded onto
the tray 134 to fall into and align themselves within the channels
136, resulting in rows 140 of aligned, fiber pre-preg segments 32.
The aligned rows 140 of the fiber pre-preg segments 32 may be fed
to an applicator head 90 which dispenses, places and steers the
fiber pre-preg segments 32 on the substrate 34 with desired fiber
orientations.
[0069] FIGS. 19A-21B illustrate another embodiment of a method of
steering chopped fiber pre-preg segments 32 onto a substrate 34. As
shown in FIGS. 19A-19B, an applicator 140 is used to apply 142 a
suitable resin 144 onto the substrate 34, as the applicator 140
moves 150 across the substrate 34. The resin 144 may be applied by
spraying the resin 144 onto the substrate 34, rolling the resin 144
onto the substrate 34 or using other application techniques. Next,
as shown in FIGS. 20A-20B, chopped fiber pre-preg segments 32 are
applied to the substrate 34 by a suitable applicator 146 that moves
150 over the substrate 34. When initially applied in this manner,
the fiber pre-preg segments 32 may have random orientations, as
shown in FIG. 20B. Then, as shown in FIGS. 21A and 21B, a fiber
segment aligner 148 is moved 150 over the substrate 34 to align the
fiber pre-preg segments 32 in a desired direction, which in this
case, is along axis 36. The fiber segment aligner 148 may use one
or more mechanical devices to contact and realign the fiber
pre-preg segments 32, or alternatively may use noncontact
techniques, such as an airstream (not shown) to achieve the desired
segment alignment. As previously discussed, however, orienting the
segments 32 as they are being initially placed on the substrate 34
may be desirable in some applications, since this technique may
eliminate the need for the additional step of repositioning the
segments 32 to the desired fiber orientations.
[0070] FIGS. 22A-24B illustrate an alternate technique for placing
and aligning the fiber pre-preg segments 32 on the substrate 34.
Referring to FIGS. 22A and 22B, a small quantity, such as a drop,
of resin 152 is placed on one end 154 of each of the fiber pre-preg
segments 32. Then, as shown in FIGS. 23A-23B, the fiber segment 32
is placed on the substrate 34. At this point, the fibers of the
fiber segment 32 may not be aligned with the desired orientation,
such as axis 36. As shown in FIGS. 24A-24B, the fiber segment 32 is
then rotated 156 so that the fiber orientation of the fiber segment
32 is aligned with the axis 36. The orientation process may be
performed using mechanical devices 49, or using noncontact
techniques such as streaming air over the substrate 34.
[0071] Embodiments of the disclosure may find use in a variety of
potential applications, particularly in the transportation
industry, including for example, aerospace, marine, automotive
applications and other application where composite structures may
require local features requiring tight contours, thickness control
and/or cross-sectional tailoring. Thus, referring now to FIGS. 25
and 26, embodiments of the disclosure may be used in the context of
an aircraft manufacturing and service method 158 as shown in FIG.
25 and an aircraft 160 as shown in FIG. 26. Aircraft applications
of the disclosed embodiments may include, for example, without
limitation, various parts of the airframe 176 such as frames,
beams, spars, and stringers to name only a few. During
pre-production, exemplary method 158 may include specification and
design 162 of the aircraft 160 and material procurement 164. During
production, component and subassembly manufacturing 166 and system
integration 168 of the aircraft 160 takes place. Thereafter, the
aircraft 160 may go through certification and delivery 170 in order
to be placed in service 172. While in service by a customer, the
aircraft 160 is scheduled for routine maintenance and service 174,
which may also include modification, reconfiguration,
refurbishment, repair and so on.
[0072] Each of the processes of method 158 may be performed or
carried out by a system integrator, a third party, and/or an
operator (e.g., a customer). For the purposes of this description,
a system integrator may include without limitation any number of
aircraft manufacturers and major-system subcontractors; a third
party may include without limitation any number of vendors,
subcontractors, and suppliers; and an operator may be an airline,
leasing company, military entity, service organization, and so
on.
[0073] As shown in FIG. 26, the aircraft 160 produced by exemplary
method 158 may include an airframe 176 with a plurality of systems
178 and an interior 180. Examples of high-level systems 178 include
one or more of a propulsion system 182, an electrical system 184, a
hydraulic system 188, and an environmental system 190. Any number
of other systems may be included. Although an aerospace example is
shown, the principles of the disclosure may be applied to other
industries, such as the marine and automotive industries.
[0074] Systems and methods embodied herein may be employed during
any one or more of the stages of the production and service method
158. For example, components or subassemblies corresponding to
production process 166 may be fabricated or manufactured in a
manner similar to components or subassemblies produced while the
aircraft 160 is in service. Also, one or more apparatus
embodiments, method embodiments, or a combination thereof may be
utilized during the production stages 166 and 168, for example, by
substantially expediting assembly of or reducing the cost of an
aircraft 160. Similarly, one or more of apparatus embodiments,
method embodiments, or a combination thereof may be utilized while
the aircraft 160 is in service, for example and without limitation,
to perform maintenance and service 174, or to carry out repair or
refurbishment of structures at any time during the service life of
the aircraft 160.
[0075] As used herein, the phrase "at least one of", when used with
a list of items, means different combinations of one or more of the
listed items may be used and only one of each item in the list may
be needed. For example, "at least one of item A, item B, and item
C" may include, without limitation, item A, item A and item B, or
item B. This example also may include item A, item B, and item C or
item B and item C. The item may be a particular object, thing, or a
category. In other words, at least one of means any combination of
items and number of items may be used from the list but not all of
the items in the list are required.
[0076] The description of the different illustrative embodiments
has been presented for purposes of illustration and description,
and is not intended to be exhaustive or limited to the embodiments
in the form disclosed. Many modifications and variations will be
apparent to those of ordinary skill in the art. Further, different
illustrative embodiments may provide different advantages as
compared to other illustrative embodiments. The embodiment or
embodiments selected are chosen and described in order to best
explain the principles of the embodiments, the practical
application, and to enable others of ordinary skill in the art to
understand the disclosure for various embodiments with various
modifications as are suited to the particular use contemplated.
* * * * *