U.S. patent application number 10/662743 was filed with the patent office on 2004-03-25 for unitized fastenerless composite structure.
This patent application is currently assigned to Lockheed Martin Corporation. Invention is credited to Black, Marvin D., McKague, Elbert L. JR..
Application Number | 20040058108 10/662743 |
Document ID | / |
Family ID | 22868376 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040058108 |
Kind Code |
A1 |
McKague, Elbert L. JR. ; et
al. |
March 25, 2004 |
Unitized fastenerless composite structure
Abstract
Plies of continuous fiber material are oriented and cut to the
intended shape of a structural component, such as the vertical tail
of an aircraft. Two skins or laminates are created by laying the
cut-to-shape plies into a matched mold, with over-woven or
over-braided mandrels or similar tooling details placed between the
skins. The mold is closed and a thermosetting resin is injected
into the mold to fully impregnate any fibers that were
unimpregnated at the time of mold closure and to fully fill all
void areas inside the mold. The mold is held closed with pressure,
such as by a press, and heated to cure the resin while the resin in
the mold is subjected to a hydrostatic pressure sufficient to
constrain growth of voids. The contiguous faces of the impregnated
braid or weave covering the mandrels are united by the resin,
forming vertical or angular laminate between the inner faces of the
skins. The resin similarly unites the portions of the braids or
weaves that are contiguous with the inner surfaces of the skins,
bonding the braids or weaves to the skins to create a unitized
structure. The resulting structure is capable of functioning
without addition of mechanical fasteners that are required in
conventional structures to join skins to understructure.
Inventors: |
McKague, Elbert L. JR.;
(Fort Worth, TX) ; Black, Marvin D.; (Fort Worth,
TX) |
Correspondence
Address: |
BRACEWELL & PATTERSON, L.L.P.
P. O. Box 61389
Houston
TX
77208-1389
US
|
Assignee: |
Lockheed Martin Corporation
|
Family ID: |
22868376 |
Appl. No.: |
10/662743 |
Filed: |
September 15, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10662743 |
Sep 15, 2003 |
|
|
|
09755221 |
Jan 5, 2001 |
|
|
|
60231245 |
Sep 8, 2000 |
|
|
|
Current U.S.
Class: |
428/36.3 ;
442/304; 442/64 |
Current CPC
Class: |
B64C 3/20 20130101; Y10T
442/3813 20150401; B29C 70/48 20130101; Y10T 442/3789 20150401;
B64C 3/24 20130101; Y02T 50/43 20130101; Y10T 442/3764 20150401;
Y10T 428/1369 20150115; Y10T 428/24995 20150401; B29C 70/086
20130101; Y02T 50/40 20130101; B29L 2031/3085 20130101; Y10T
442/2041 20150401; Y10T 442/40 20150401 |
Class at
Publication: |
428/036.3 ;
442/304; 442/064 |
International
Class: |
D04B 009/00 |
Claims
What is claimed is:
1. A structural assembly on or component comprising: a pair of
outer skins or laminates, each formed from layers or plies of
continuous fiber-reinforced composite; an inner structure located
between the outer laminates such that the outer laminates are
coupled together; a series of understructure details consisting of
unimpregnated or partially impregnated woven material; and a series
of understructure details which are tapered taped and each of which
is supported by a suitable mandrel during handling and prior to
cure of a thermosetting resin that is infused.
2. The structural assembly or component of claim 1 wherein the
understructure is formed from braided fibers.
3. The structural assembly or component of claim 1 wherein the
understructure is formed from woven fibers.
4. The structural assembly or component of claim 1 wherein the
understructure is formed by braiding "socks" or "sleeves" over
mandrels that define the internal geometry of the finished
substructure.
5. The structural assembly or component of claim 1 wherein the
outer skins or laminates are composed of layers of unimpregnated
continuous fiber materials.
6. The structural assembly or component of claim 1 wherein the
outer skins or laminates are composed of layers of unimpregnated
continuous fiber materials intermixed with layers of fully
impregnated continuous fiber materials.
7. The structural assembly or component of claim 1 wherein the
outer skins or laminates are composed of some layers of
unimpregnated continuous fiber materials intermixed with some
layers of fully impregnated continuous fiber materials and some
layers of partially impregnated continuous fiber materials.
8. The structural assembly or component of claim 1 wherein the
outer skins or laminates are composed completely of layers of fully
impregnated continuous fiber materials.
9. The structural assembly or component of claim 8 wherein a layer
of uncured film adhesive is placed on the inner surface or each
skin to toughen the cured interface between the skins and the
understructure.
10. A structural assembly or component comprising: external skins
or laminates joined to a series of contiguous structural channels
or tubes or beams; and unitized by composite structural details
joined by cured thermosetting resin that provides mechanical
integrity without use of mechanical fasteners.
11. The structural assembly or component of claim 10 wherein the
resin permeates the structure leaving few or no voids.
12. The structural assembly or component of claim 10 wherein the
resin is injected or transferred into the structure.
13. The structural assembly or component of claim 10 wherein the
inner and outer mold lines of each skin are accurately defined and
held to close dimensional tolerances defined by a matched mold.
14. The structural assembly or component of claim 10 wherein the
internal structural details are dimensionally accurate and defined
by dimensions and geometry of mandrels or similar tooling
details.
15. A method for fabricating a structure or component comprising
the steps of: (a) creating skins or laminates by laying layers of
plies of continuous fiber materials containing a low resin content
of less than 20% by weight; (b) braiding or weaving unimpregnated
fibers to conform to the external shape of mandrels; (c) placing
one skin onto the inner face of one half of a matched mold; (d)
placing the over-braided or over-woven mandrels onto the skin so
that they are contiguous with one another; (e) placing the other
skin onto the top of the over-braided or over-woven mandrels; (f)
placing the other half of the matched mold over the skin of step
(e) so that the inner face of the mold half is against the skin;
(g) placing the resulting tooling/component assembly into a
hydraulic press and applying a compacting force that results in
mold closure; (h) sealing the mold and drawing a vacuum inside the
closed mold; (i) heating the mold, injecting resin into the mold to
completely fill void areas, and pressurizing the resin to a level
sufficient to suppress formation of voids that could be caused by
moisture, solvents, or volatile reaction products; and (j) heating
the mold to a temperature for a period sufficient to cause cure of
the thermosetting resin, removing the top half of the mold,
withdrawing the internal mandrels or similar tooling details, and
removing the part from the mold.
16. The method of claim 15 wherein the skins are formed by laying
fully impregnated strips of continuous fiber material using
automated machine methods.
17. The method of claim 15 wherein the skins are formed by laying
fully impregnated layers of continuous fiber material.
18. The method of claim 15 wherein the skins or laminates are
formed by intermixing layers of low resin content layers and
unimpregnated layers.
19. The method of claim 15 wherein the skins are formed by
intermixing layers of partially impregnated and fully impregnated
continuous fiber materials.
20. The method of claim 15 wherein the skins are formed by
intermixing layers of partially impregnated and unimpregnated
continuous fiber materials.
21. The method of claim 15 wherein the skins are formed by
intermixing layers of fully impregnated and unimpregnated
continuous fiber materials.
22. The method of claim 15 wherein the skins are formed by
intermixing partially, fully, and unimpregnated layers of
continuous fiber materials.
23. The method of claim 15 wherein the skins are formed from
material selected from the group consisting unimpregnated
continuous fibers, partially unimpregnated continuous fibers, fully
unimpregnated continuous fibers, and unidirectional fabric and
woven fabric.
24. The methods of claim 15-23 wherein the layers formed the skins
are not debulked prior to closing the mold in the press.
25. The methods of claim 15-23 wherein the layers forming the skins
are debulked prior to closing the mold in the press.
Description
[0001] This application claims the benefit of a copending U.S.
provisional application, Serial No. 60/231,245, filed on Sep. 8,
2000, by Applicant.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates in general to an improved
structural design, and in particular to an improved structure
composed of skins and understructure. Still more particularly, the
present invention relates to a unitized structure concurrently
fabricated from composite materials in such a way that mechanical
fasteners are not required.
[0004] 2. Description of the Prior Art
[0005] In the prior art, structural components such as aircraft
empennage members are fabricated by individually making skins and
understructure elements and then assembling them into the final
component using mechanical fasteners. This requires drilling and
countersinking holes, reaming and cleaning holes, buying and
installing mechanical fasteners, and in some cases applying a
fairing material to the fastener heads. Together, these processes
cause high costs for building such components.
[0006] In some more advanced methods, one composite skin is
fabricated with composite understructure co-cured to it and then a
separately fabricated skin is mechanically fastened to finish the
assembly. This approach typically has required hand-lay of prepreg
materials to create the understructure details, and usually has
required relatively complex tooling to locate and provide pressure
to all of the material during cure. This hand-lay and use of the
mechanical fasteners to attach the separately processed skin have
driven costs to levels higher than desired.
SUMMARY OF THE INVENTION
[0007] A laminate or skin is formed from composite material. This
skin may be formed using prepreg material, unimpregnated fibrous
material, or combinations of these two. The material for this skin
is laid onto one half of a matched die mold or onto an
appropriately shaped tool from which it is transferred to the
matched die tool half. A series of tooling mandrels, each wrapped
with unimpregnated reinforcing fibers, are placed onto the skins so
that they are precisely located with respect to prescribed datum
dimensions. A second skin is formed from the same materials as the
first skin and in the same manner, being either laid directly over
the wrapped mandrels and lower skin or transferred to it. Then the
mating half of the matched die is placed over the resulting
assembly, and then sealed to the lower die half. This tooling
assembly then is placed into an appropriate restraint device, such
as a press or clamping fixture, and resin is injected into the mold
to completely fill all void spaces between fibers within the mold.
The resin is heated to cure, and then the mold is opened, mandrels
are removed, and the unitized composite component is removed.
[0008] The cured component conforms to the exact geometric shape
required for the intended structure, such as an aircraft vertical
tail. Both inside and outside dimensions of the component are
accurately rendered by cure of the injected resin inside the tool
that has the required shape. Both skins are integrally connected to
the understructure material between them as a result of a common
matrix of cured resin.
[0009] Accordingly, it is an object of the present invention to
provide a unitized structural component.
[0010] It is an additional object of the present invention to
provide an improved structural component that is unitized without
mechanical fasteners or secondary adhesive bonding.
[0011] Another object of the present invention is to provide a
unitized, fastenerless structural composite assembly that conforms
to a required geometric shape with closely held dimensional
accuracy.
[0012] Still another object of the present invention is to provide
a low cost method of fabricating a composite assembly.
[0013] The foregoing and other objects and advantages of the
present invention will be apparent to those skilled in the art, in
view of the following detailed description of the preferred
embodiment of the present invention, taken in conjunction with the
appended claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the features, advantages and
objects of the invention, as well as others which will become
apparent, are attained and can be understood in more detail, more
particular description of the invention briefly summarized above
may be had by reference to the embodiment thereof which is
illustrated in the appended drawings, which drawings form a part of
this specification. It is to be noted, however, that the drawings
illustrate only a preferred embodiment of the invention and is
therefore not to be considered limiting of its scope as the
invention may admit to other equally effective embodiments.
[0015] FIG. 1 is a schematic, isometric drawing of a laminate or
skin representing one side of an intended structural component.
[0016] FIG. 2 is a view showing a laminate or skin resting on one
half of a matched die or mold.
[0017] FIG. 3 is an illustration of a series of mandrels that
define the internal substructure configuration of an intended
structural assembly.
[0018] FIG. 4 is an illustration showing unimpregnated graphite
reinforcing fibers braided to form a tightly conforming sock or
sleeve over a mandrel of FIG. 3.
[0019] FIG. 5 is an isometric illustration showing a series of
over-braided mandrels placed on top of a laminate or skin that
rests on one half of a matched die or mold.
[0020] FIG. 6 is an isometric illustration showing a second
laminate or skin placed on top of the over-braided mandrels of FIG.
5.
[0021] FIG. 7 is a section view of the assembled tool containing
the upper and lower skins and the over-braided mandrels of FIG.
6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring to FIG. 1, a skin or laminate 12 is formed by
stacking layers or plies 11 of fibrous reinforcing material onto a
suitable tool or surface. Long, continuous fibers in each ply are
oriented in specific directions to provide subsequent strength and
stiffness in directions subject to loading during use. In the
preferred embodiment, the layers or plies 11 are not impregnated
with resin. However, acceptable results also can be obtained when
the layers or plies 11 are partially or fully impregnated with
resin, or when some of the layers are unimpregnated and some are
either partially or fully impregnated with resin. Acceptability of
both the latter combinatorial case and of the preferred embodiment
has been demonstrated. To more fully explain, the layers or plies
11, whether impregnated or unimpregnated, may be provided in
several different material forms. In one form, they may be composed
of unidirectional "fabrics", i.e., layers of collimated fibers held
together by a sparse number of transverse thread or fibers. In
another form, the layers may be of a woven fabric such as 5-harness
satin weave fabric. In both of these forms, the layers or plies 11
may be either unimpregnated, fully impregnated, or partially
impregnated with resin. In still another form, the layers or plies
11 consist of collimated or unidirectional fibers that are
partially or fully impregnated with resin.
[0023] As shown in FIG. 2, the skin or laminate 12 of FIG. 1 is
created by laying layers or plies 11 onto the surface of a tool 21
that represents half of a matched die. Alternatively the skin or
laminate 21 can be created and then transferred to the tool half
21.
[0024] Referring now to FIG. 3, a series of mandrels are created,
typically by NC Machining, each with a general configuration
determined according to structural requirements for the internal
structure of a unified structure such as a vertical tail for an
aircraft.
[0025] As illustrated by FIG. 4, unimpregnated tows or bundles of
continuous fibers are braided over each mandrel 5 to form a "sock"
or "sleeve" 41. Together, these "socks" or "sleeves" will form the
internal structure of the unitized composite component.
[0026] FIG. 5 is an isometric illustration showing a series of
mandrels 51 placed on top of a skin or laminate 12 that rests on
one half of the matched die tool 21. The braided "sock" or "sleeve"
41 on the side of a given mandrel mates against the side of the
"sock" or "sleeve" covering the adjacent mandrel. These "socks" or
"sleeves" will be filled by injecting with resin, pressed against
each other, and made rigid by curing resin. Together these mating
faces will form a structural web of members that will connect the
first skin or laminate 12 to a second skin or laminate that will be
applied prior to such resin injection and cure.
[0027] FIG. 6 is an isometric illustration showing the second skin
or laminate 22 resting on the over-braided mandrels of FIG. 5.
Again, this skin can be formed by stacking suitable layers or plies
11 directly onto the socked mandrels or in a separate location and
then transferred to and placed onto the socked mandrels.
[0028] At this point, as shown in FIG. 7, the other half of the
matched die or mold is placed on top of the assembly. Then the
assembled component and matched die are placed into a suitable
hydraulic press or equivalent restraining device. The mold may be
sealed to sufficiently hold a vacuum either before or after being
placed in a hydraulic press or restraining device.
[0029] A suitable thermosetting resin is selected that has low
viscosity at some temperature allowing an adequately long injection
life. This resin is injected into the mold, creating an internal
pressure that is resisted by the press or restraining device. This
resin is injected into the mold through injection ports arranged at
various locations around the matched mold. These ports are located
in such a way that the flowing resin completely fills the mold,
wetting any unimpregnated or partially impregnated layers or plies
in the skins and all of the unimpregnated braided "socks" or
"sleeves" surrounding each of the internal mandrels. After filling
the dry or void areas of the mold with resin, the mold is heated to
and held at a temperature sufficient to cause curing of the
injected resin. After cure, the mold is removed from the press or
restraining fixture, the top half of the mold is removed, any side
plates that were installed are removed, and then the completed
component is removed from the mold. With appropriate handling
procedures and protective devices, removal can be accomplished hot,
before the mold cools appreciably.
[0030] The invention has several advantages as it provides a
completely assembled, low-cost, weight efficient structure
consisting of two skins or laminates structurally connected by the
co-cured, braided "socks" or "sleeves". Just as the mating braids
on the sides of adjacent mandrels were pressed together, infused
with resin, and cured into one member, so too are the portions of
the "socks" or "sleeves" at the top and bottom of each mandrel
joined to the mating surfaces of the skins or laminates. Being
commonly infused with the same resin and cured together, the
braided "socks" or "sleeves" are bonded to the skins with the same
efficiency as each layer or ply of the skin or laminate is bonded
to the layer or ply above and below it.
[0031] While the invention has been shown or described in only some
of its forms, it should be apparent to those skilled in the art
that it is not so limited, but is susceptible to various changes
without departing from the scope of the invention. For example, a
series of appropriately shaped "C" channels made of low resin
content fabric could be used instead of the braided "socks" or
"sleeves". In another variation, all of the layers or plies of each
skin could be composed of narrow strips of fully impregnated
unidirectional fibers that are "fiber placed", i.e., laid into the
laminate using an NC machine. If all of the layers or plies are
fully impregnated with resin, then the resin in the skins could be
different than the one used to inject and impregnate the braided
"socks" or "sleeves"--provided that the two resins are compatible
with curing together and yielding a strong interface layer. In
another variant, the skins or laminates could be partially or fully
cured so that the resin injected into the internal structural
members creates an interface bond between the skins and
understructure. In a case like this, the cured skins might be
placed into the mold with a layer of film adhesive applied to the
faces to toughen the bonds with the understructure.
* * * * *