Title: Heating apparatus for in-situ de-bulking composite parts during layup
Abstract: The invention is an apparatus for de-bulking a composite material preform laid up in a mold. In detail, the apparatus includes a flexible cover adapted to fit over the mold and preform and attach to the sides of the mold. The cover includes an inlet port located in the cover such that when the cover is fit over the mold and preform, the inlet port positioned over the preform. A stretchable cord seals the peripheral portions of the cover to the sides of the mold forming a chamber over the preform. A hot air pump is coupled to the inlet port of the cover for pumping hot air into the chamber.
Patent Number: 6,991,449 Issued on 01/31/2006 to Mead, et al.
| Inventors:
|
Mead; William T. (Long Beach, CA);
Potter; John (Camaarillo, CA);
Hurka; Tom (Whittier, CA)
|
| Assignee:
|
Northrop Grumman Corporation (Los Angeles, CA)
|
| Appl. No.:
|
412375 |
| Filed:
|
April 11, 2003 |
| Current U.S. Class: |
425/389; 425/405.1; 425/504; 156/382; 156/286 |
| Current Intern'l Class: |
B29C 43/56 (20060101) |
| Field of Search: |
425/389,405.1
156/382
|
References Cited [Referenced By]
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| 5702663 | Dec., 1997 | Seemann.
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| 5814175 | Sep., 1998 | Rau et al.
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| 5863452 | Jan., 1999 | Harshberger et al.
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| 6017484 | Jan., 2000 | Hale.
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| 6018614 | Jan., 2000 | Garcia et al.
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| 6159414 | Dec., 2000 | Tunis et al.
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| 6406659 | Jun., 2002 | Lang et al.
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| |
| 2003/0025231 | Feb., 2003 | Slaughter et al.
| |
Primary Examiner: Davis; Robert
Assistant Examiner: Rao; G. Nagesh
Attorney, Agent or Firm: Dachs; Louis L.
Claims
What is claimed is:
1. An apparatus for de-bulking a composite material preform laid up in a mold,
the apparatus comprising:
a vacuum bag adapted to seal said perform to said mold, said vacuum bag having
means for drawing a vacuum from between said vacuum bag and the mold;
a flexible cover adapted to fit over the mold, vacuum bag and preform and attach
to the sides of mold, said cover having an inlet port located in the cover such
that when the cover is fitted over the mold, and said vacuum bag and preform, said
inlet port is positioned over the preform;
sealing means for sealing the peripheral portions of said cover to the sides
of the mold forming a chamber over the preform and vacuum bag; and
pump means having an inlet and an outlet coupled to the inlet port of said cover,
said pump means for pumping heated air into said chamber, said pump means including:
a pump; and
a heater coupled to said pump.
2. The apparatus as set forth in claim 1 wherein said sealing means is a stretchable
cord tied about said peripheral edge of said cover securing said cover to the sides
of the mold.
3. The apparatus as set forth in claim 2 wherein:
said pump means is adapted to provide heated air at a specific pressure to cause
said flexible cover to inflate; and
said stretchable cord adapted to stretch sufficiently to allow heated air to
escape from said chamber when said pump means provides the heated air at the specific pressure.
4. The apparatus as set forth in claim 3 wherein:
said stretchable cord secures said peripheral side portion of said cover to the
mold at a specific distance from the edge of said peripheral side portion and said
edge is secured to the mold forming a plenum chamber about the periphery of the mold;
an tubular member having a first end in communication with said plenum and a
second end in communication with said inlet of said pump means;
such that heated air pumped into said cover and flowing passed said stretchable
cord into said plenum is recirculated to said pump means.
5. An apparatus for de-bulking a vacuum-bagged composite material preform laid
up on an upper surface of a mold, the apparatus comprising:
a flexible cover having a center portion having an inlet port and a peripheral
side portion terminating in a peripheral edge, said center portion of said cover
adapted to fit over the upper surface of the mold and vacuum bagged preform, said
peripheral side portion adapted to fit about the sides of the mold;
first sealing means for sealing the peripheral portion at a point between said
center portion and said peripheral edge of said cover to the sides of the mold
forming a chamber over the upper surface with the vacuum bagged preform thereon;
second sealing means for sealing said peripheral edge to the sides of the mold
or the floor forming a plenum about the side of the mold; and
an air pump having an inlet port and an outlet port;
a heater having an inlet coupled to said outlet of said air pump, said heater
having an outlet coupled to said inlet of said cover;
a duct having a first end coupled to said plenum and a second end coupled to
said outlet port of said air pump; and
a valve mounted in said second end of said duct for modulating the flow of air
from said plenum to said inlet port of said air pump.
6. The apparatus as set forth in claim 5 wherein said first sealing means is
a stretchable cord tied about said peripheral portion said cover.
7. The apparatus as set forth in claim 6 wherein:
said pump means is adapted to provide heated air at a specific pressure to cause
said flexible cover to inflate; and
said stretchable cord adapted to stretch sufficiently to allow heated air to
escape from said chamber when said pump means provides the heated air at the specific pressure.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of composite structure fabrication, in particular,
to an improved system for de-bulking the uncured composite sheets as they are laid
up in a mold at the workstation.
2. Description of Related Art
Typically, composite structures are formed by a process that involves
the following steps:
1. Sheets of filamentary material impregnated with uncured resin are laid
up in a mold having the contour of the completed part.
2. After the lay-up is complete, the lay-up is vacuum bagged.
3. Thereafter a vacuum is pulled between the lay-up and mold.
4. The vacuum-bagged lay-up is then placed in an autoclave wherein the temperature
is increased to the curing temperature of the resin and the autoclave is pressured
until the resin is cured.
5. Thereafter, the cured lay-up and mold are removed from the oven or autoclave
and the now cured part is removed from the mold.
However, often the number of plies in the lay-up requires multiple de-bulks
during the lay-up process that a de-bulking procedure is required. Typically, the
lay-up process requires a de-bulk after a certain number of plies of resin impregnated
filamentary material have been laid up in the mold. The partially completed lay-up
has to be vacuum bagged and a vacuum pulled in order to de-gas and consolidate
it if this is not done, there is a high probability that the completed part will
have unacceptable voids caused by air pockets. It is preferred that this de-bulking
process take place at a temperature at which the resin will flow but not readily
cure. Thus the mold with vacuum-bagged partially completed lay-up must be moved
into the autoclave. If the part is vary large, thus requiring a large and heavy
mold, the process and be difficult and time consuming.
Portable oven and autoclave type devices are available. For example, U.S.
Pat. No. 5,116,216 "Apparatus For Preparing Thermoplastic Composites" by R. C.
Cochran, et al. discloses an apparatus for fabricating composites using thermoplastic
matrix materials. A blanket heater is placed over the lay-up is used to supply
the necessary heating. An inner flexible vacuum bag is placed over the lay-up and
sealed to the mold surface and a ridged outer chamber is placed over the flexible
vacuum bag and also sealed to the mold surface. A differential vacuum is drawn
from between the flexible vacuum bag and lay-up and between the vacuum bag and
ridged outer chamber, with the higher vacuum drawn from under the flexible vacuum
bag. The blanket heater is turned on and the lay-up heated until the thermoplastic
material has melted. Thereafter, the lay-up is allowed to cool to ambient conditions.
The problem with this apparatus is that, its advantage of portability is diminished
if the part being formed is large. Secondly, if high compaction pressures were
required, an autoclave would still be necessary, even if the apparatus was used
for de-bulking. Further the heater system and rigid chamber is part specific and
must be fabricated for each tool and lay-up.
Thus, it is a primary object of the invention to provide to provide a de-bulking
system for the manufacture of composite parts that does not require the partially
completed lay-up and mold to be placed in an autoclave.
It is another primary object of the invention to provide a de-bulking system
for
the manufacture of composite parts that is easily transportable.
It is a further object of the invention to provide a de-bulking system for the
manufacture of composite parts that is inexpensive to manufacture and is can be
easily adapted to various size parts.
SUMMARY OF THE INVENTION
The invention is an apparatus for de-bulking a composite material preform laid
up in a mold. In detail, the apparatus includes a flexible cover having a center
portion to fit over the mold and preform and a peripheral portion for attaching
to the sides of mold. The cover has an inlet port located in the cover such that
when the cover is fit over the mold and preform, the inlet is positioned over the
preform. Preferably, the cover includes a perforated sheet such that when the cover
is installed, the sheet separates the inlet port from the preform. This perforated
sheet insures that the hot air is distributed uniformly over the preform.
A sealing assembly is provided for sealing the peripheral portion of the cover
to the sides of the mold forming a chamber over the preform. The sealing assembly
is preferably a stretchable cord tied about the peripheral edge of the cover securing
the cover to the sides of the mold. A hot air pump has its output port coupled
to the inlet port of the cover. Preferably, the pump produces heated air a sufficient
pressure to cause the stretchable cord to expand allowing heated air to escape
from the chamber.
In another embodiment, the peripheral side portion extends beyond the sealing
assembly and the edge of peripheral side portion is secured to the mold to form
a second chamber extending about the mold. Alternately, the edge extends to the
floor upon which the mold rests also forming a second chamber about the mold. In
either instance the second chamber includes an outlet port which is coupled to
the inlet port of the pump. Thus hot air can be re-circulated improving heating efficiency.
During lay-up of the preform, the process is periodically stopped and the
partially completed preform is vacuum bagged and the apparatus installed. A vacuum
is pulled from between the vacuum bag and mold, in-situ heated air is applied causing
the preform to heat of a temperature that drives off any entrapped gases. After
a sufficient time has passed insuring that all entrapped gases have been removed,
the apparatus is removed and along with the vacuum bag and the lay-up process continues.
The novel features which are believed to be characteristic of the invention,
both as to its organization and method of operation, together with further objects
and advantages thereof, will be better understood from the following description
in connection with the accompanying drawings in which the presently preferred embodiments
of the invention are illustrated by way of example. It is to be expressly understood,
however, that the drawings are for purposes of illustration and description only
and are not intended as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a molding apparatus for the manufacture
of composite parts.
FIG. 2 is a cross-sectional view of the molding apparatus shown in FIG. 1 with
a first embodiment of the invention installed there on.
FIG. 3 is a cross-sectional view of the molding apparatus shown in FIG. 1 with
a second embodiment of the invention installed there on.
FIG. 4 is a perspective view of the molding apparatus and second embodiment
of the invention shown in FIG. 3
DESCRIPTION OF THE PREFERRED EMBODIMENT
A typical composite fabrication tool is illustrated in FIG. 1 and generally indicated
by numeral
10, resting on the floor
12. It includes a mold
14
having a mold surface
16 and side surfaces
18. The molding surface
16 for purposes of illustration is flat, however, it could, and in most
cases would have a complex contour. A release agent
20 is first positioned
on the surface
16. Thereafter, individual plies of pre-impregnated cloth
and resin, for example and epoxy impregnated filamentary material is laid up over
the release agent
20 on mold surface
16 to form preform
22.
The individual plies could comprise woven material or could be unidirectional plies
laid up at plus and minus 90 degrees as well as plus or minus 45 degrees. For purposes
of illustration the preform
22 is laid up in three sections
22A,
22B and
22C. After the preform
22 is complete, a release film
24 is placed there over. Finally, an impervious flexible vacuum bag
28,
typically made of nylon or a Silicone based material is placed over the release
agent
20 and release film
24 and preform
22 and sealed to
the molding surface
16 by means of sealant tape
30 forming a chamber
32. A vacuum line
34 is provided for drawing a vacuum from the chamber
32.
A vacuum is applied to consolidate and remove entrapped gases from preform
22.
The completed assembly is then moved into an autoclave (not shown) wherein the
temperature and pressure are raised, while a vacuum is drawn from the chamber
32.
This will cause the resin within the preform
22 to melt and cure, while
consolidating the preform into its final shape. The temperature and pressure are
then reduced to ambient and the mold
14 is removed from the autoclave and
the now finished part removed therefrom. While the above process has been simplified
for purposes of illustration, it does present the basics of composite manufacture.
One of the problems that may occur, especially if the preform
22 is made
up of a large number of plies, is entrapped gases that will expand during heating
may cause voids to be formed in the completed part, greatly reducing its strength.
To eliminate this possibility, the prior art method of de-bulking was to only partially
complete the preform
22 on the molding surface
16 of the mold
14
and place the assembly in the autoclave. For example section
22A. The temperature
was raised, to a temperature well below the curing temperature of the resin, while
vacuum was drawn from the chamber
32. This allowed any entrapped gases to
be removed. This process would be repeated several times, depending upon the complexity
of the preform. If the part being formed was large, requiring a corresponding large
and heavy tool, the process of de-bulking was time consuming and expensive. The
subject invention eliminated this problem.
Referring to FIG. 2, the subject invention is a portable in-situ heating
apparatus, generally designated by numeral
36, to accomplish de-bulking
of the preform as it is assembled. After preform section
22A has been assembled
on the mold surface
16, the apparatus
36 bought to the mold
14.
The apparatus
36 includes a flexible cover
38, preferably made of
a lightweight Nylon cloth, comprising a center portion
40 for extending
over the mold surface
16 and preform section
22A. The cover
38
also includes a peripheral side portion
42 having an peripheral edge
44,
which is configured to fit about the side surfaces
18. The cover
38
further includes and inlet port
46 positioned in the center portion
40.
The cover is secured to the mold
12 by means of a stretchable cord (bungee
cord)
48 that secures the peripheral side portion
42 of the cover
38 to the side surfaces
18 of the mold
14. Thus a chamber
50 is created over the mold surface
16. A suitable cover material
is NYLON®, manufactured by the E. I. duPont de Nemours & Company, Delaware.
Preferably, Diamond Rip Stop Fabric using Type 6,6 NYLON®, coated with urethane
manufactured by Astrostar International Incorporated, Sioux Falls, S. Dak. I
The apparatus
36 further includes a portable platform
52 containing
a control panel
54. The platform
52 includes an air pump
56,
having an inlet port
58 and outlet port
60. The outlet port
60
is coupled to a heater assembly
61. The heater assembly
61 includes
an outlet port
62 that is coupled to inlet port
46 in the cover
38
via a tube
63. The tube
63 is supported by an over head support beam
assembly
64. Thus in operation, after preform section
22A of the
preform
22 has been assembled and vacuum bagged and the cover
38
installed as illustrated, the pump
56 is turned on. Heated air enters the
chamber
50 and heats the partially assembled preform
22A, to cause
any entrapped gases to be expelled and drawn off therefrom.
The temperature of the heated air is maintained at a level well below the curing
temperature of the resin. The heated air passes over the mold surface
16
and around the side surfaces
18. Note that the pump
56 is designed
to produce sufficient pressure to inflate the flexible cover
38 and forces
air pass the bungee cord
48. This insures that hot air at the required temperature
is maintained over the preform section
22A. Additionally, the center portion
40 includes a perforated partition
65, which will further insure
that hot air is evenly distributed over preform section
22A. After de-bulking
of preform section
22A has been accomplished the pump
56 is turned
off, the cover
38 removed as well as the vacuum bag
28. Thereafter
addition layers of filamentary material is added to the partially assembled preform
and the de-bulking process is repeated.
In FIGS. 3 and 4 a second embodiment of the apparatus is illustrated. In this
embodiment the peripheral side portion
42 extends passed the stretchable
cord
48 and the peripheral edge
44 is either sealed to the floor
12 or the side portion
18 of the mold
14 forming a peripheral
plenum
70. Sealing can be accomplished by a second stretchable cord (not
shown) or weights
71, which seal the plenum
70 to the floor
12.
An outlet port
72 is provided in the plenum
70 that is coupled to
the inlet port
58 of the pump
56 via a duct
74. A Valve
76,
preferably a butterfly valve, is mounted in the duct
74 in proximity to
the inlet port
58 of the pump
56. Thus heated air, now at a reduced
temperature, that is expelled passed the stretchable cord
48 is recycled,
improving efficiency. The valve
76 is adjusted to insure that the cover
38 is fully inflated and that heated air is circulated over the preform
section
22A.
Thus it can be seen that the portable apparatus
36 can be used in place
of an oven or autoclave for de-bulking of the preform, thus eliminating the time
consuming task of moving a large mold and the expense of operating a large oven
and resetting of the ply locater. The de-bulking process is used as many times
as necessary. In the example provided this would include a de-bulking step after
preform section
22B of the preform
22 was assembled. A cost benefit
analysis has indicated that a significant cost saving is achieved.
While the invention has been described with reference to particular embodiments,
it should be understood that the embodiments of merely illustrative as there are
numerous variations and modifications, which may be made by those skilled in the
art. Thus, the invention is to be construed as being limited only by the spirit
and scope of the appended claims.
INDUSTRIAL APPLICABILITY
The invention has applicability to industries manufacturing composite structures.
*
