Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR RESIN CURING
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
resin curing, and more specifically to an improved system for curing
resin in a composite structure.
BACKGROUND OF THE INVENTION
[0002] Composite materials exhibit high strength and stiffness, as
well as corrosion resistant properties. In addition, their light
weight is particularly advantageous when compared to similar
components constructed from metals. As such, there has been
increasing interest in recent years in the use of parts and
assemblies constructed from fiber reinforced composite materials in
industries such as, for example, the aerospace industry, where parts
and assemblies having high strength to weight ratios are desired.
[0003] Whether the resin has been infused between reinforcing
fibres, or sheets are provided which have been pre-impregnated with
resin (commonly and hereinafter referred to as "pre-preg" sheets),
the manufacturing of composite structures requires that resins be
cured in situ with layered reinforcing fibres. To produce a part or
assembly exhibiting the above-described advantageous properties,
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cu'ring must result in low porosity (i.e., a low number of voids
within the composite structure) and a high and substantially uniform
degree of cure throughout the entire composite structure.
[0004] Curing of resin in a composite structure commonly involves
heating the structure so as to induce a cross-linking reaction
between molecules of the resin, and a resulting increase in resin
viscosity. Ideally, heating is continued until the increase in
viscosity of the resin reaches a point whereat gelation occurs, such
that the structure has solidified.
[0005] Prior art processes used to cure resin in composite
structures are not adapted to adequately control the heating of the
structure to achieve an optimal uniform level of cure throughout
most composite structures, particularly those having more complex
cross-sectional shapes. Further, prior art processes yielding
products with consistently high quality and strength have required
lengthy cure cycles, often in excess of 150 minutes per part. Thus,
the inability to provide a cure system capable of quickly and
uniformly heating the composite structure so as to achieve a uniform
level of cure throughout has been a limiting factor in the use of
composite structures in, for example, the aerospace industry.
[0006] Prior art curing processes have exhibited the additional
disadvantage of being accompanied by high costs, due in large part
to the fact that their use necessitates consumption of relatively
large quantities of energy.
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[0007] Moreover, the curing of resin in composite structures
having cross-sectional thicknesses greater than about 1.0 inch in
any cross-sectional plane (hereinafter referenced in this
specification as "thicker cross-sections") has heretofore been
particularly problematic, since a specific and controlled rate of
heat is required to cure each such thicker cross-sections to achieve
the same degree of cure therein as in other areas of the composite
structure at the end of the cure cycle.
[00081 It is well known in the art to cure resin in composite
structures using an autoclave. Traditionally, curing systems
including autoclaves have been the most common means of producing
high strength and high quality composite parts. In such processes,
a resin impregnated structure is placed in the autoclave, then
heated gas at a raised temperature and pressure flows from an inlet
end to an outlet end, to thereby heat the composite structure by
convective currents circulating within the autoclave. Temperature
can vary greatly from one location to another within the autoclave,
and no control is typically provided over this variation. For
example, the side areas of an autoclave tend to be cooler than the
middle areas of an autoclave. As such, the temperature cannot be
precisely controlled in all areas of an autoclave and, more
importantly, at specific locations throughout the composite
structures produced using such systems. This is particularly
problematic with respect to composite structures having multiple
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cross-sectional thicknesses throughout, which ideally require
differing rates of heat to be applied at different locations in
order to each reach a high and uniform degree of cure. Thus, such
controlled differential heating cannot be effectively carried out in
prior art autoclave-based systems.
[0009] In addition, the use of convective heating means, such as
autoclaves, is inefficient in terms of production cycle times, and
in terms of energy consumption. This is so for several reasons,
including but not limited to the following: i) a long warm-up
period is required to bring the autoclave up to its critical
operating temperature (at which cross-linking of the resin occurs);
ii) a large quantity of energy must be expended to maintain the
large volume of the autoclave at temperatures suitable for use in a
curing system; iii) a long cure period is required to ensure that
the cross-linking is complete throughout all locations of the
composite structure; again, for composite structures having thicker
cross-sections this is particularly troublesome, and process
engineers will typically err on the side of caution in this regard
by increasing the cure period; and, iv) a long cool down period is
required before the cured composite structures can be safely removed
from the autoclave for further production processing. Of course, a
long warm up period is again required for the next part or batch of
parts to be cured. Thus, in autoclave-based systems, curing times in
excess of 150 minutes (exclusive of any necessary cooling time) are
relatively common. This, of course, limits the number of composite
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parts or assemblies that can be produced in any given period of
time.
[0010] Moreover, given the broad disparity between the volume of
the composite structure (and that of any tooling which may be
provided thereabouts) and that of the autoclave, the inefficiency of
an autoclave from the standpoint of energy consumption per curing
cycle is staggering.
[0011] It should further be noted that autoclave-based curing
systems exhibit yet a further disadvantage, in that they require a
very large initial capital investment to build and install. This
cost, coupled with high ongoing operating costs, including
increasing energy costs, represent a significant barrier to the more
widespread use of composite parts and assemblies. Moreover, in an
age of perhaps diminishing natural resources, any means of reducing
energy consumption is advantageous; quite apart from monetary
concerns.
[0012] It is desirable, from both quality control and safety
standpoints, that all of the resin in the curing of composite
structures, whether cured in an autoclave or otherwise, be cured to
a substantially uniform level throughout, regardless of the
variations in cross-sectional thickness and geometry throughout such
structures. Thus, one further significant limitation of prior art
curing processes, including those using autoclaves, is the
difficulty of consistently achieving the aforesaid uniform level of
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cure throughout the structure, which is required in order for the
final product to have the aforesaid quality and safety. As
previously stated, complete and consistent curing of the resin in
the structure becomes increasingly difficult as the cross-sectional
thickness of the structure varies as between regions of the part.
Ideally, thicker cross-sections, and indeed portions having
different magnitudes of cross-sectional thickness, require the
application of different and controlled rates of heating during the
curing process, in order to uniformly cure all portions of the
structure to substantially the same degree within a given cure
cycle.
[0013] Attempts have been made in the prior art to develop curing
systems which mitigate the disadvantages of using only an autoclave
as their heat source. For example, U.S. Patent No. 4,828,472 (Itoh
et al.), issued May 9, 1989, discloses the use of elemental heaters
positioned throughout a mould, which mould is placed in an autoclave
environment; however, the elemental heaters of Itoh et al. are
merely a supplemental source of heat for curing the workpiece.
Thus, the aforementioned disadvantages inherent to autoclave-based
curing systems, particularly the high costs (i.e., energy and
otherwise) of using same and slow process times, are still
experienced with the Itoh et al. system. Moreover, U.S. Patent No.
4,828,472 does not disclose variable heating and control of the
elemental heaters, which variation and control is necessary to
achieve high, uniform levels of cure in composite structures having
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thicker cross-sections, or multiple varying cross-sectional
thicknesses.
[0014] In addition, the use of elemental heaters such as those
discussed in U.S. Patent No. 4,828,472 (or other conductive heating
means) as the primary heat source for a curing system does not
substantially mitigate the aforementioned disadvantages of the prior
art as related to energy consumption.
[0015] Thus, for the reasons mentioned above, amongst others, it
has not been practical or economical (for reasons of, among other
things, high energy consumption, as discussed above) using known
prior art systems or techniques to cure resin in composite
structures having thicker cross-sections and/or large thickness
variations. There thus continues to exist in the prior art, amongst
other things, a need to address these and other limitations, which
need is increasing over time as, for example, the aerospace industry
looks to increase the variety, complexity and size of composite
parts and assemblies used in the construction of airplanes and
spacecraft to, amongst other things, reduce weight 62, fuel
consumption and cost.
[0016] it is thus an object of this invention to obviate or
mitigate at least one of the above mentioned disadvantages of the
prior art.
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SUMMARY OF THE INVENTION
[0017] In accordance with the present invention there is
disclosed a system for curing a resin in a composite structure.
The composite structure has one or more interconnected cure volumes.
The cure volumes have one or more heatable surface zones. The system
comprises a mould, having a mould base portion and a mould closure
portion. The mould base portion is adapted to support the composite
structure, and the mould closure portion is adapted to overlie the
mould base portion in sealable relation to define a mould chamber
containing the composite structure. The system further comprises a
plurality of heating units each selectively positionable about the
mould. The heating units transmit heat to the mould by radiation
and the mould heats one or more of the surface zones of the
composite structure.
[0018] Other advantages, features and characteristics of the
present invention, as well as methods of operation and functions of
the related elements of the structure, and the combination of parts
and economies of manufacture, will become more apparent upon
consideration of the following detailed description and the appended
claims with reference to the accompanying drawings, the latter of
which is briefly described hereinbelow.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The novel features which are believed to be characteristic
of the according to the present invention, as to its structure,
organization, use and method of operation, together with further
objectives and advantages thereof, will be better understood from
the following drawings in which a presently preferred embodiment of
the invention will now be illustrated by way of example. it is
expressly understood, however, that the drawings are for the purpose
of illustration and description only, and are not intended as a
definition of the limits of the invention. In the accompanying
drawings:
[0020] Figure 1 is a right side perspective view, from above, of
a system according to the present invention, shown in a semi-
exploded configuration, with the housing shown in the open
configuration, with the temperature sensing means, programmable
control means, and cure sensing means removed for clarity of
illustration;
[0021] Figure 2 is a view similar to Figure 1, with the
temperature sensing means, programmable control means, and cure
sensing means shown therein;
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[04 022] Figure 3 is a view similar to Figure 1, with the housing
in a closed configuration;
[0023] Figure 3A is a sectional view along sight line 3A-3A of
Figure 3;
[0024] Figure 4 is a sectional view along sight line 4-4 of
Figure 1.
[0025] Figure 4A is an enlarged view of the encircled area 4A of
Figure 4;
[0026] Figure 5 is a front right perspective view, from below, of
the upper housing portion of the system of Figure 1;
[0027] Figure 6 is a top plan view of the lower housing portion
of the system of Figure 1; and
[0028] Figure 7 is a bottom plan view of the composite structure
of Figure 1, with all other structures removed for clarity of
illustration, and showing, in phantom outline, the heatable surface
zones on the underside of the composite structure
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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0029] Referring now to the Figures, there will be seen a system
20 for curing a resin 10 in a composite structure 12 in accordance
with but one non-limiting embodiment of the present invention. The
composite structure 12 has one or more interconnected cure volumes 14
exhibiting a variety of cross-sectional thicknesses of the composite
structure 12, with each separated from one or more others by
notionally defined boundaries (indicated by dotted lines), as seen in
Figures 3A, and 4. The cure volumes 14 have heatable surface zones
16, as will be appreciated from a consideration of Figures 3A, 4, and
7. As will be appreciated by one skilled in the art, the composite
structure 12 is comprised of a plurality of layers of a fiber
containing textile roving material, which layers are typically pre-
adhered to one-another and pre-formed into a desired shape, as is
known in the art, so as to form a core for the particular composite
part or assembly being manufactured. As well known in the art, the
fibers which make up the layers may be chosen from a group
comprising, but not limited to, KevlarTM woven fiber, KevlarTM
unidirectional fiber, woven glass fiber, unidirectional glass fiber,
woven carbon fiber and unidirectional carbon fiber. As is well known
in the art, the resin 10 is impregnated between the layers prior to
curing. Further, the composite structure 12 to be cured could be made
up of what are referred to in the art as "pre-preg" sheets, or could,
as in the composite structure 12 shown in the Figures, be produced
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using for example, vacuum-assisted resin transfer moulding (VARTM),
or analogous processes. The list of resins that can be used with the
present system 20 includes, but is not limited to, epoxy, cyanate
ester, polyester and phenolic resins.
[0030] The shapes and dimensions of the cure volumes 14 are
selected based on, inter alia, the various cross-sectional
thicknesses of the composite structure 12. Cure volumes 14 having
different cross-sectional thicknesses as shown, necessitate
application of heat to the heatable surface zones 16 thereof at
different watt densities, in order to achieve substantially the same
degree of cure throughout all the resin 10 in the composite structure
12 at the same time. Thicker cross-sections generally require the
application of heat at higher watt densities than do thinner cross-
sections (though that is not necessarily the case in all instances -
in some instances the curing reaction is exothermic and application
of less heat to thicker cross-sections may be necessary), at least
where the total cure cycle is to be kept as short as practicable. As
such, and where practicable, each cure volume 14 will be selected to
have a substantially uniform cross-sectional thickness. As stated
above, the cure volumes 14 each have one or more heatable surface
zones 16. The heatable surface zones 16 together comprise
substantially the entire surface of the composite structure 12, as
will be appreciated from a consideration of Figure 1. There may, but
need not necessarily, only be one heatable surface zone 16 per cure
volume 14; however, in many instances, the cure volume 14 will span
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the entirety of the cross-sectional thickness of the composite
structure 12, as will be appreciated from a consideration of Figures
3A and 4, necessitating the cure volume 14 to have at least a second
heatable surface zone 16, as shown in Figures 3A and 4. The selection
of the number and dimensions of the heatable surface zones 16 may
vary greatly, and will be based upon the overall geometry of the
composite structure 12; that is, the dimensions of the cure volumes
14, and the geometry of the surface of the particular composite
structure 12, among other things. The selections of the dimensions
and arrangements of cure volumes 14 and their associated heatable
surface zones 16 are matters of routine design choice for one skilled
in the art, which selections may be assisted by the use of computer
simulation of curing, using software such as, for example, MSC
NastranTM (available from MSC Software Corporation, Santa Ana,
California, U.S.A.).
[0031] As seen in Figure 4, the system 20 also includes a mould
base portion 24 adapted to support the composite structure 12. The
mould base portion 24 may be constructed of wood, steel, aluminum, or
plastic materials, but is preferably constructed from a composite
material or a metallic alloy having a low coefficient of thermal
expansion, and may advantageously be substantially formed, as shown
in the Figures, to correspond in shape to substantially the entire
overlying portion of the composite structure 12. As seen in Figure 4,
the mould base portion 24 typically includes (but need not
necessarily include) a central body portion 26 and a peripheral
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flange portion 28. In many applications, the portion of the composite
structure 12 contacting the peripheral flange portion 28 would be a
distinct cure volume 14, as will be appreciated from a consideration
of Figures 3A, 4, and 7.
[0032] The system 20 also includes a mould closure portion 30
adapted to overlie the mould base portion 24, in sealable relation
therewith, as seen in Figure 4, so as to define a mould chamber 32.
In a similar manner to the mould base portion 24, the mould closure
portion 30 may also be constructed of wood, steel, aluminum, plastic,
metallic alloy, or composite materials; however, and as is shown the
Figures, the mould closure portion 30 may be a known form of vacuum
bag 30, which vacuum bag 30 may be composed of such commercially
available materials as nylon, polypropylene, silicon rubber, and the
like. Furthermore, the vacuum bag 30 needs to be composed of a
material capable of withstanding temperatures in the approximate
range of about 200-450 F for periods as long as approximately 300
minutes, in order to cure substantially all the resin 10 in the
composite structure 12, depending on the type of resin 10 being cured
and the geometry of the particular composite structure 12. The
selection of the material to be used for construction of the mould
closure portion 30 is a matter of routine design choice to be made by
those skilled in the art, which choice may be influenced by, for
example, the means of impregnation of resin 10 into the layers of the
composite structure 12. For example, in applications according to
the present invention involving the aforementioned "pre-preg" sheets
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(not shown), it may be advantageous to employ more rigid materials in
the construction of the mould closure portion 30, such as the
composite materials discussed hereinabove.
[0033] As best shown in Figure 4, a seal 34 joins the vacuum bag
30 and the mould base portion 24 in sealed relation to one another.
For ease of illustration, the seal 34 is shown as located on the
peripheral flange portion 28; however, it could be located at
different positions between the mould base portion 24 and the vacuum
bag 30, depending upon the shape of the particular composite
structure 12 and the materials used to construct the mould base
portion 24 and mould closure portion 30. Again, routine design choice
plays a role in the shape and position of the seal 34 as between
particular workpiece applications. The seal 34 may be constructed
from an adhesive material, a rubber material, a liquid material, a
putty, or, as shown, a semi-liquid sealant such as, but not limited
to, epoxy and the like. The seal 34 is preferably releasable and
resealable, but need not be so. One skilled in the art will recognize
that the seal 34 may be any seal 34 means, including self-adhesive
gasketing material, capable of maintaining a sealed bond between the
mould base portion 24 and the mould closure portion 30 at the above-
mentioned temperature levels. The seal 34 may also be a mechanical
device such as, for example, a gasket with suitable clamps depending
upon, again, the materials used to construct the mould base portion
24 and mould closure portion 30, as well as the suitability of such
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materials for use at the elevated temperature levels mentioned
hereinabove.
[0034] The system 20 also includes a plurality of heating units 40
that are each selectively positionable about the mould 22. The
heating units 40 transmit heat to the mould 22 by radiation. In this
specification and the appended claims the term "by radiation" is
hereby defined to mean substantially all transmission of heat is by
way of radiation, without any significant transfer of heat by way of
conduction from the heating units 40 to the mould 22, or by way of
convective transfer of heat from the heating units 40 to the mould 22
via any medium, or media, therebetween. The heating units 40 need
not all be heating at the same time. Those heating units 40 actually
transmitting at any particular time are referred to herein as
"energized".
[0035] The mould 22 (i.e., at least a portion thereof) receives
the heat transmitted by radiation from the heating units 40 and is
heated thereby. The mould 22 transfers a portion of the received
heat to one or more of the heatable surface zones 16 of the composite
structure 12. One skilled in the art will recognize that the
presence of the mould 22 between the heating units 40 and the
composite structure 12 may introduce some inefficiency in terms of
heat transfer; however, such a skilled person will further recognize
that the mould 22 (or an analog thereof) is necessary for retention
of the composite structure 12 in the desired post-curing shape, and
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that such inefficiency will be minimal through use of materials well
known in the art.
[0036] The heating of the heatable surface zones 16 by transfer of
heat from the mould 22 may occur by, for example, convection of heat
within any gaps that may exist between the mould 22 and the composite
structure 12; however, it may also, or alternatively, occur via
conduction from the mould 22 to the composite structure 12.
[0037] The heating units 40 are adapted to transmit heat to the
mould 22 at one or more respective variable heating unit levels. In
this specification and the appended claims, the term "variable
heating unit level" means a level, wherein a target quantity of
energy in the form of heat is transmitted by one or more of the
heating units 40 by radiation, to the mould 22, and therefrom to one
or more of the cure volumes 14 via the heatable surface zones 16,
thereby providing the ability to heat the composite structure 12 to
temperatures necessary for the curing reaction to occur, and the
ability to closely vary the temperature of each cure volume of the
composite structure 12 as per unit time. By way of comparison,
heating each cure volume at a respective variable heating unit 40
level contrasts with the prior art practice of heating composite
structure 12 in autoclaves wherein temperature variations, as between
areas of the structure having different cross-sectional thicknesses,
are largely un-variable and uncontrollable, and require the
expenditure of very high quantities of energy in order to heat the
17
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autoclave chamber. Further, heating each cure volume at a respective
variable heating unit level also contrasts with the prior art
practice of heating the entire composite structure 12 to a uniform
temperature throughout regardless of variations in the cross-
sectional thickness thereof. Moreover, it has not been prior art
practice to provide a means of heating areas of the structure having
different cross-sectional thicknesses, or which are otherwise
distinguishable in terms of the quantity of energy in the form of
heat that needs to be applied to each of them in order to
substantially cure all the resin 10 therein. Heating by radiation
serves to greatly increase efficiency of energy consumption as it
allows for the use of heating means (i.e., the heating units 40) that
consume smaller quantities of energy per unit time. That is, heating
each cure volume 14 at a respective variable heating unit level is
also different from prior art methods and apparatuses which specify a
set temperature throughout an autoclave, and hence, the mould chamber
32. In the present invention, the quantity of heat applied to
particular cure volumes of the composite structure 12 (which is
critical to more consistent and heightened product quality) can be
closely controlled and varied. Moreover, in applying such heat by
radiation from the heating units 40 to the mould 22, the quantity of
energy (e.g., electricity) required to complete the curing cycle can
be minimized.
[0038] The variable heating unit level at which heat is provided
to each heatable surface zone 16 may, of course, be altered over time
18
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throughout the curing process. As such, an additional parameter over
which control can be exercised in a curing process exists as a result
of providing heat to the cure volumes 14 at a respective variable
heating unit 40 level.
[0039] In some embodiments of the present invention, arrays 42
comprised of one or more heating units 40, as seen in Figure 5, will
preferably each be arranged in operative heating relation (as will be
appreciated from a consideration of Figures 3, 3A and 5) to a single
heatable surface zone 16, with the mould 22 interposed therebetween.
Thus, the variable heating unit level at which heat is provided to
each heatable surface zone 16 need not be unique, as compared to the
variable heating unit levels of the other heatable surface zones 16.
[0040] As described above, the plurality of heating units 40
comprises one or more arrays 42 of the heating units 40, each of the
arrays 42 comprising one or more of the heating units 40, as will be
appreciated from a consideration of Figure 5. Each of the arrays 42
is preferably positionable in operative heating relation to a
corresponding one of the heatable surface zones 16, with the mould 22
interposed therebetween, as will be appreciated from a consideration
of Figures 3, 3A, 5 and 6.
[0041] Providing an appropriate number of heating units 40 in each
array 42 - e.g., for each heatable surface zone 16 - may serve to
better tailor the system 20 to the properties of the particular
composite structure 12. Such optimization contributes to the high
19
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level of control during and efficiency of the curing process offered
by the system 20 of the present invention.
[0042] The number of heating units 40 used in any particular
application can and will vary significantly depending on factors
including, but not limited to, the variations in and magnitude of
cross-sectional thicknesses of the composite structure 12 and the
heat-providing capacity of each heating unit 40. In this regard, one
skilled in the art will recognize that the power of each heating unit
40 must be balanced against energy requirements for the operation of
same. As noted above, heating by radiation is advantageous in this
regard. The precise placement of the heating units 40, as well as the
number to be used in any particular application and their density of
placement per unit area, is a matter of routine design choice for one
skilled in the art, which choice may be assisted by computer
simulation of the curing process, as otherwise described herein.
[0043] Each of the heating units 40 may preferably be a commonly
available type of halogen light bulb 40 of a Wattage in the order of
approximately 25 to 100 Watts, though all of the heatings units 40
employed in a particular embodiment of the present invention need not
all be the same wattage. Low voltage halogen light bulbs are
particularly preferred. Moreover, it may be preferable, and helpful
in tailoring the system 20 to the particular composite structure 12,
to employ multiple different bulbs.
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[0044] Each such halogen light bulb 40 preferably includes a
reflector means 46, as seen in Figure 4A, that serves to reflect
light when energized toward the mould 22 when the system 20 is in
operation, with the reflected light otherwise not having been
directed toward the mould 22.
[0045] The system 20 preferably also includes a housing 50
comprised of two or more matable housing portions, preferably being
an upper housing portion 52 and a lower housing portion 54, as shown
in Figures 1, 2, 3, 3A and 4. As will be appreciated from a
consideration of Figures 3 and 3A, the housing 50 is shaped,
configured and otherwise adapted to selectively enclose the mould 22.
[0046] One or more of the housing 50 portions are movable so as to
allow for transition of the housing 50 between an open configuration
of the housing 50, as shown in Figures 1, 2 and 4, and a closed
configuration of the housing 50, as shown in Figures 3 and 3A. In
the closed configuration, the housing portions 52 and 54 are mated in
close fitting relation about the mould 22. In the open
configuration, the housing portions 52 and 54 are unmated and
positioned sufficiently remotely from one another to allow for
removal of the mould 22 from therebetween, as will be appreciated
from a consideration of Figure 1. In order to facilitate mating of
the housing portions 52 and 54, the upper housing may preferably have
an optional tongue 53 projecting downwardly from the periphery of the
bottom surface thereof, as shown in Figure 5. The lower housing
21
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portion 54 may have an optional complimentary groove 55 defined in
the periphery of the upper surface thereof, as shown in Figure 6.
The tongue 53 and groove 55 mate when the housing 50 is in the closed
configuration, as shown in Figure 3A. In the embodiment shown in the
Figures, the lower housing portion 54 is fixed and the upper housing
portion 52 is vertically movable; however, alternate configurations
may be employed where any one or more of the housing portions 52 and
54 may be movable so as to transition the entirety of the housing 50
between the aforesaid open and closed configurations thereof. To
facilitate movement between the open and closed configurations of the
housing 50, the system 20 may preferably further comprise a mechanism
60, shown in Figures 3 and 3A, for moving the housing portions 52 and
54 so as to move the housing 50 between its open and closed
configurations. While this mechanism 60 is shown in the Figures as
including two pulleys 66, a cord 64, guide slots 68 and a
counterweight 62, one skilled in the art will recognize that this
mechanism 60 could be any other means of facilitating movement
between the open configuration and the closed configuration of the
housing 50, e.g., gas struts, and could be, for example, motorized.
[0047] The system 20 may additionally comprise a frame 56
surrounding the housing portions 52 and 54. The frame 56 includes a
plurality of metal rails 58 mechanically bonded or welded to one
another to form an open rectangle. The lower housing portion 54 may
be fixed to the frame 56. The frame 56 serves to guide the housing
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portions 52 and 54 between their respective positions in each of the
open and closed configurations of the housing 50.
[0048] The frame 56 may additionally comprise an inverted U-shaped
beam 69 spanning the top of the frame 56, and having the pulleys 66
rotatably mounted therein to guide the cord 64 that joins the
counterweight 62 to the upper housing portion 52 along its path. The
beam 69 is shown in phantom outline to better illustrate the pulleys
66 therein. As will be appreciated from a comparison of Figures 1
and 3, the counterweight 62 will serve to counterbalance the mass of
the upper housing portion 52 and will thus obviate the requirement
for lifting or supporting of the entire weight thereof during
movement of the upper housing portion 52, thereby facilitating
movement between the open and closed configurations of the housing
50. The frame 56 may additionally comprise casters 59 as shown in
the Figures.
[0049] As described above, each of the housing portions 52 and 54
is preferably shaped to substantially match the shaping of a portion
of the mould 22. In this regard, one skilled in the art will
recognize that the housing portions 52 and 54 could be constructed
and shaped as necessary to conform to the geometry of the particular
mould 22 to be housed therebetween. Such shaping facilitates
operative positioning of the heating units 40 adjacent the mould 22
as shown in Figure 3A for heating efficiency.
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[0050] The housing portions 52 and 54 may preferably each be
comprised of any material or combination of materials having a high
thermal resistance, so as to minimize transfer of heat therethrough
in directions other than towards the mould 22. The material or
materials making up the housing 50 must also be able to withstand
exposure to temperatures of the magnitude and for the duration
mentioned hereinabove.
[0051] As shown in Figures 5 and 6, the heating units 40 are
preferably movably mounted on the housing 50 so as to allow for
manual or mechanical manipulation or positioning, so as to most
accurately conform to a particular mould 22 and provide for efficient
heating thereof by accurate direction of the reflector means 46 of
the heating units 40. In this regard, the system 20 may preferably,
but need not necessarily, further comprise means 48 for adjusting the
distance between each of the heating units 40 and the mould 22.
These means 48 could include, among other things, pivot means (not
shown) or the tracks 48 shown in Figures 1, 2, 3A, 4, 5, and 6. As
will be appreciated by one skilled in the art, these tracks 48
facilitate both lateral translation, which may or may not be effected
manually, of the heating units 40 with respect to the mould 22, and
projection and/or retraction of the heating units 40 (i.e., by way of
adjustment of the depth of the heating unit 40 in the track 48) with
respect to the mould 22.
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[0'052] One or more temperature sensing means 72, shown in Figure
2, are preferably further included as part of the system 20 of the
present invention, for monitoring one or more temperatures within the
one or more cure volumes 14. Each temperature sensing means 72
includes temperature sensors 73 and one or more temperature sensing
lines 74 operatively connecting each temperature sensor 73 to a
programmable control means 80, as seen in Figure 2. For ease of
illustration, the temperature sensing lines 74 are shown in Figure 2
as being bundled into a harness and converging at point "B". One
skilled in the art will appreciate that these temperature sensing
lines 74 connect to the programmable control means 80 at point "BB"
in Figure 2. As is well known in the art, the temperature sensors 73
may be, for example, thermocouples, infrared-based sensors, or the
like.
[0053] One or more cure sensing means 76, seen in Figure 2, may
further preferably be included as part of the system 20 of the
present invention, for monitoring one or more cure parameters within
the one or more cure volumes 14. The cure parameters monitored
include one or more of degree of cure of the resin 10, and viscosity
of the resin 10. Each cure sensing means 76 includes a cure sensor 77
together with one or more cure sensing lines 78 operatively
connecting each cure sensor 77 to the programmable control means 80.
For ease of illustration, the cure sensing lines 78 are shown in
Figure 2 as being bundled into a harness and converging at point "A".
One skilled in the art will recognized that these cure sensing lines
CA 02593163 2007-07-06
78 connect to the programmable control means 80 at point "AA" in
Figure 2. The cure sensors 77 may preferably be known types of
ultrasonic transducers, and may also be, but are not limited to,
resistance, capacitance, electrically and dielectrically based
sensors.
[0054] The cure sensing lines 78 and the temperature sensing lines
74 may preferably be insulated copper wires. Each may also be
composed of any material capable of acting as a conduit for
transmission of one or more electronic signals. In some embodiments
of the present invention, and as is well known in the art, the
temperature lines and cure lines may each be multiplexed, as
suggested by Figure 2.
[0055] Temperature sensors 73 and/or cure sensors 77 may be
positioned on one or more of the mould closure portion 30 and the
mould base portion 24, as will be appreciated from a consideration of
Figure 2. One skilled in the art will recognize that the total
numbers of temperature sensors 73 and/or cure sensors 77 used in any
particular production application can and will vary significantly as
between different applications. The number and placement of the
temperature sensors 73 and/or the cure sensors 77 is a matter of
routine design choice for one skilled in the art, which choice may be
based on, for example, the shape and configuration of the composite
structure 12; however, the temperature sensors 73 and cure sensors 77
are preferably positioned such that at least one of each is located
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so as to monitor temperatures and cure parameters, respectively,
within each cure volume 14.
[0056] The programmable control means 80, shown in Figure 2, is
preferably responsive to the temperature sensing means 72 and to the
cure sensing means 76 and operatively connected, as described
hereinbelow, to the heating units 40 by unit supply lines 41. For
ease of illustration, but one unit supply line 41 is shown in Figure
2, connected to each of the housing portions 52 and 54 through a
conduit 51. One skilled in the art will recognize that the conduits
51 will be shaped so as to allow for passage of the unit supply lines
41 into the housing portions 52 and 54, whilst minimizing loss of
heat therethrough. One skilled in the art will further recognize that
each of the unit supply lines 41 may be bundled from the control
means to the housing portions 52 and 54, and separate with the
housing portions 52 and 54 so as to operatively connect each heating
unit 40 to the programmable control means.
[0057] The unit supply lines 41 may be composed of any material
capable of acting as a conduit for transmission of electricity at the
levels described herein, and may preferably be known types of power
transmission cables, such as, for example copper wire.
[0058] The programmable control means 80 may, but need not,
further comprise a relay means 84, interconnected between the
programmable control means 80 and the heating units 40 by the unit
supply lines 41, for supplying variable levels of electrical current
27
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to the heating units 40, under control of the programmable control
means 80. The relay means 84 may preferably comprise solid-state
relays. Routine design choice again plays a role in the selection of
the specific type or types of relays, if any, employed in particular
embodiments, which choice is influenced by the power loads required
to operate the heating units 40 employed in the particular system 20.
[0059] The programmable control means 80 is preferably a digital
signal processor 82, which may comprise any processor programmed to
and otherwise capable of rapidly manipulating large quantities of
data and of performing large numbers of calculations and analyses.
(i.e., in some embodiments, the programmable control means 80 may
comprise a known type of programmable logic controller, or PLC). Such
manipulations, calculations and analyses may include, but are not
necessarily limited to, digitizing signals received in analog form,
and comparing the digitized signals with stored sets of reference
data. The digital signal processor 82 must also be capable of
generating and transmitting signals based on the manipulations,
calculations and analyses described herein. The relay means 84 is
adapted to receive signals from the digital signal processor and
respond to same by supplying respective levels of electrical current
to each of the heating units, which quantities are specified by the
received signals, and which quantities are in proportion with values
indicated by the signals received from the digital signal processor.
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[0060] In use, the composite structure 12 (in the mould 22, as
described above) is positioned between the housing portions 52 and
54, as shown in Figure 1, and then rested on the lower housing
portion 54. The upper housing portion 52 is then lowered until the
housing 50 is in its closed configuration, as shown in Figure 3.
Curing of the resin 10 in the composite structure 12 is commenced
when heat is applied to the mould 22 by radiation from the heating
units 40, which are energized as per an initial state specific to the
particular cure cycle, and thereby to one or more of the heatable
surface zones 16 as described above. Each of the heatable surface
zones 16 is heated at a respective variable heating unit level by the
one or more heating units 40 in the particular one or more arrays 42
relating to that heatable surface zone 16. Each of the heatable
surface zones 16 is preferably heated at a respective variable
heating unit level by a respective array 42 of the heating units
through the mould 22. Thus, each cure volume 14 is heated
substantially independently of all other cure volumes 14. The
selection of initial values of the variable heating unit levels is a
matter of routine design choice for one skilled in the art, which
choice may be influenced by, among other things, the properties of
the particular type of resin 10 being cured, and may advantageously
be assisted by the use of computer simulation of curing, using
software such as the aforementioned MSC NastranTM.
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[0061] In use, reference signals representative of respective
target ranges of the cure parameters at locations within one or more
of the cure volumes may be externally predetermined and input to the
programmable control means 80 prior to commencement of the cure
cycle. These predeterminations may be assisted by computer simulation
of the curing process, or may occur by empirical testing. The
reference signals will be predetermined for various locations
throughout the one or more cure volumes 14. Further, these locations
will preferably substantially correspond to the locations monitored
by the cure sensors 77 and temperature sensors 73, and will be
predetermined for substantially all times at these locations, from
the beginning to the end of the cure cycle of the resin 10 in the
particular composite structure 12 being produced by the system 20.
The cure parameters include those discussed above, but may also
include pre-stored temperature values throughout the composite
structure 12 throughout the cure cycle, in addition to other
properties relevant to characterizing behaviour of the resin 10
within the composite structure 12 during a cure cycle.
[0062] The temperature sensors 73 and cure sensors 77 may
preferably be employed to monitor the cure parameters and
temperatures within the cure volumes 14 in real, or near real time.
More specifically, as the present invention allows for curing of
resin 10 in composite structures with a number of cross-sectional
thicknesses and variations between same, data with respect to the
cure parameters and temperatures may be collected in three
CA 02593163 2007-07-06
dimensional terms, though in some embodiments only temperatures at
the surface of the mould 22 will be monitored. The temperature
sensors 73 and cure sensors 77 each monitor such data, taking samples
on a substantially contemporaneous basis, at a sampling rate
generally in the range of about one sample per ten seconds. As curing
all of the resin 10 in the composite structure 12 using the present
invention can typically require in the approximate range of 60 to 300
minutes to be substantially completed, such a sampling rate
facilitates a high level of real time or near real time control of
curing of the resin 10 in each cure volume 14 of the composite
structure 12. Based on the monitored cure parameters and
temperatures, the temperature sensors 73 and cure sensors 77 generate
signals indicative of the temperatures and cure parameters,
respectively. The temperature sensors 73 and cure sensors each convey
their respectively produced signals, typically in analog form, to the
programmable control means 80 via the temperature lines 74 and the
cure lines 80, respectively. The programmable control means receives
the signals from the temperature sensors and cure sensors, and
preferably, but not necessarily, converts any analog signals to
digital format. The generation and conveyance by each of the
temperature sensors 73 and the cure sensors 77 of their respective
signals relating to a common location occurs in such close
chronological proximity as to be substantially contemporaneous.
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[0063] The digital signal processor 82 then compares the signals
indicative of the cure parameters and/or temperatures as monitored
within respective ones of the one or more cure volumes 14 and, more
specifically as monitored at one or more particular locations within
said cure volumes 14, with respective ones of the one or more
reference signals representing respective target ranges of same
within those same one or more cure volumes 14 (i.e., specific to a
particular location therewithin). The digital signal processor 82
analyses the results of the comparison and correlates the results of
the comparison with the temperatures monitored within respective ones
of the one or more cure volumes 14 (by comparing the pre-stored
temperatures to the monitored temperatures), so as to generate a
first set of delta signals in relation to the temperatures and a
second set of delta signals in relation to the cure parameters as
appropriate. The first set of delta signals are thereafter sent by
the control means to the relay means 84 to thereby proportionally
vary the level of electrical current respectively supplied by the
relay means 84, if employed, and via the particular corresponding
relay, to each of the heating units 40 and its respective unit supply
line 41. As stated above, the comparison may also result in a second
set of delta signals, which are sent by the programmable control
means 80 to the relay means 84 to influence the aforesaid variation
of the level of electrical current respectively supplied by the relay
means 84 (via the particular corresponding relay) to each of the
heating units 40.
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[0064] As a result, the respective variable heating unit level
associated with the respective one of the one or more heating units
40 to which the level of electrical current supplied was varied may
be varied in a manner conducive to achieving subsequently monitored
temperatures and/or cure parameters closer to the target values
thereof for the particular location in the respective cure volume 14.
[0065] Alterations in variable heating unit levels are localized
to correct irregularities in the curing process at the specific
locations in particular cure volumes 14 where such irregularities are
sensed. The delta signals may be indicative of raising, lowering, or
maintaining the respective levels of electrical current supplied to
the heating units 40, and thus may result in like changes in variable
heating unit 40 levels applied to the composite structure 12 at
particular heatable surface zones 16.
[0066] By way of example, the signals indicative of temperatures
could be such that, the comparison results in a finding that the
resin 10 in a particular cure volume has been under heated. A risk
could therefore exist of the remaining cure volumes 14 prematurely
fully curing, or the composite structure 12 otherwise not curing to
an optimal degree. This may produce lines of weakness, and cracks
caused by off-gassing or other undesirable by-products, with an
accompanying lack of strength and rigidity in any end-product
composite part or assembly. In such instances, the first set of delta
signals may be generated by the digital signal processor, and
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ttansmitted to the heating units 40, such that, subsequent to the
transfer, greater watt densities of heat are applied through the
heating units 40 to the mould 22 and, as a result, to the composite
structure 12. The number of energized heating units 40 in the
relevant array 42, and/or the proximity of one or more of the
energized heating units 40 in said array 42 could alternatively or in
tandem be adjusted (e.g., by translation or vertical movement thereof
via the tracks 48). More specifically, such changes would be
directed to the particular cure volume 14 where curing was sensed to
have been occurring out of step as compared to desired parameters.
In the described instance, the real time, or near real time feedback
loop control offered by the system 20 of the present invention would
allow for complete curing of the resin 10 in the composite structure
12 to be achieved at the appropriate time in the curing cycle (and
not before), thereby maintaining the overall strength, rigidity, and
quality of the end-product. The composite structure 12 would thus not
be spoiled and thereby rendered useless by inconsistent degrees of
cure as between different portions of the composite structure 12.
This level of control and efficiency is particularly significant in
aerospace applications, which demand high strengths and, in many
instances, large quantities, and, as such, greater quality control as
between one composite part or assembly and the next. This type of
real time or near real time continuous corrective action, as
facilitated by the ability to closely control the watt density of
heat applied to each of the heatable surface zone(s) 16, of the cure
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volumes 14 of the composite structure 12, and to do so in a highly
energy-efficient manner by way of heating units 40 supplying heat by
radiation. Moreover, obviating the need to use an autoclave results
in significant savings in time, capital, and operating costs.
[0067] Other modifications and alterations may be used in the
design and manufacture of other embodiments according to the present
invention without departing from the spirit and scope of the
invention, which is limited only by the accompanying claims. For
example, multiple signals are described hereinabove as being
transmitted via various lines. One skilled in the art would recognize
that these signals could alternatively each be conveyed wirelessly
from their sources to their destinations.
[0068] Numerous determinations including, among others, the
locations and numbers of the heating units, as well as initial levels
of the variable heating unit levels are described hereinabove as
being assisted by computer simulation using prior art modeling
software such as the aforementioned MSC NastranTM. One skilled in the
art would recognize that each of these determinations could also be
made by, for example, empirical testing. Such empirical testing could
include, for example, iteratively curing resin 10 in composite
structure 12 while each time using different locations and numbers
of, for example, heating units. All other system 20 parameters would
be maintained at constant levels, in order to determine an optimum
level of the varied parameter, among those values attempted. Similar
CA 02593163 2007-07-06
iterations could, of course, be performed with respect to all other
parameters in regard to which computer simulation was discussed. It
is noted that, in some instances, the use of computer simulation may
be a more cost-effective and less laborious means of making the
determinations discussed hereinabove.
[0069] The system 20 is shown as including only one programmable
control means controlling the curing of resin 10 in but one composite
structure 12. One skilled in the art would readily recognize that
some embodiments of the present invention could be adapted to perform
substantially simultaneous curing of multiple composite structures
12, controlled by one or more programmable control means, still
maintaining real time, or near real time control.
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