Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present invention relates -to methods of repro-
ducing complicated shapes and finishes; and more particularly,
is useful in the art of filamen-t winding, and the molding of
plastic materials generally.
Filamen-t winding of complicated shap.es is carried
out by deposi-ting a strand under tension in the cavi-ties of
a mold designed to hold the deposi.ted strand in the desired
shape. The strand is wrapped around and around the same
cavities of the mold until the desired thickness of strand
is deposited. Usually the strand is completely wetted ou-t
with a binder before it is wound into the cavi-ties of the mold,
but the invention is not limited in this respect. As the binder
wetted strand is pulled down in-to the mold, excess binder
exudes into the spaces between the wrappings of the strand
and also into contact with the surEaces of the mold. The binder
i.s then caused to harden in the mold to bind the fibers to-
gether and hold them in the desired shape. Binders will usually
sti.ck to the surface of the moldl and the art has long mi-ti-
cJated the mold sticking problem by incorporating mold release
agen-ts into the binders. The mold release agents appear to
function by rising to -the external surfaces of the binder as
it agglomerates, to -thereby coat the surface of the mold.
Another problem which occurs in the filament winding
art, is that it is impractical for the mos-t part, to incor-
porate fibers crosswise -to the windings for the purpose of
binding the windings -together. Separation of the windings
therefore is prevented almost entirely by the binder, and its
attachment to -the filamen-ts of the strand. For this reason,
the strength of the binder may be rnore critical in filament
wound parts than in other types of fiber reinforced par-ts.
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A still fur-ther problem exists in the process of
filamen-t winding in that the molds are-usually ro-tated while
a "finger" positions the strand in the proper location rela-
tive to the mold's cavities. The tension on the binder wetted
strand, in conjunction with the ro-ta-tion of the mold, causes
excess binder to flow out of the mold cavities over other sur-
faces of the mo]d, including its separating and clamping sur~
faces. This excess resin has proved costly -to remove.
Also in the commercial production of fi]ament wound
parts, a considerable time period is spent winding the strand
in~o the cavities oE the mold. To achieve volume production,
therefore, it is necessary to have a large number of such molds,
not only for the winding operation, but to support the wound
part during the time that the binder is hardening. In the
case where the binder is a thermoset-ting resin, the mold with
a wound par~ therein is moved to an oven and heated to approxi-
ma-te:Ly 350F -to cause the binder to harden. During this time,
anothex mold will have been placed in the winding machine and
another part formed. The molds are usually made of a cast
aluminum, or o-ther me-tal, to wi-thstand the temperature and
handling; and the cost of produciny and machining the com~
plicated shapes of -the mold is appreciable.
The present invention provides a method of duplicating
shapes which comprises producing a master pa-ttern, producing a
sand mold negative of the mas-ter pattern, casting a replica of
the master pattern from the sand mold, producing a vacuum form-
ing pat-tern from the replica, producing a vacuum formed separa-
tion sheet o~ the vacuum forming pa-ttern, coveriny surfaces of
the replica with the vacuum formed separation sheet, packing a
plastic material against -the vacuum formed separa-tion sheet
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in the moldr and causing the plas-tic ma-terial to harden.
The present invention fur-ther provides a me-thod of
producing paralle] fiber reinforced ar-tlcles which comprises
producing a vacuum formed separa-tion sheet -to fi-t a mold for
confining the parallel fibers, fitting the separa-tion sheet
over surfaces of the mold, placing binder incorporated parallelly
laid fibers over -the surfaces of the separation shee-t and
hardening the binder against the separation shee-t.
The present invention still further provides a method
of producing a molded part from a plastic ma-terial which re-
quires a mold release to prevent -the parts from sticking -to
-the mold, which comprises vacuum :Eorming a sheet of mold release
agent to conform to the shape of the mold, fitting -the vacuum
:Eormed sheet onto molding surfaces of the mold, molding the
plastic material agains-t the separation sheet, and hardening
-the plastic ma-terial.
Figure 1 is a block diagram indicating s-teps involved
:in a preferred embodiment of -the inven-tion for producing and
using filament winding molds.
Figure 2 is an exploded view showing a release sheet
of the present inven-tion as positioned for ma-ting with a mo].d
constructed according to other aspects of the present invention.
Figure 3 is an oblique exploded view of the assembly
made as indicated by Figure 2 with cer-tain hold down segmen-ts
positioned for installation to comple-te -the filament winding
mold.
Figuxe 4 i~s a fragmentary sec-tional view taken ap-
pro~imately on the line 4 - 4 of Figure 3.
Figure 5 is a fragmen-tary sectional view taken ap-
proximate].y on the line 5 ~ 5 of Figure 3.
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According -to some of the aspects of the pr~sent in-
vention, the mold release ayent in the binder can be reduced
or eliminated by placing a sheet of mold release agent over
the surfaces of the mold. The sheet of release agent may be
formed in situ, but this is time consuming, and is preferably
made of a sufficiently thick sheet that it can be formed in
a separate operation and be placed in -the mold. It has been
found that not only is this practical, but that it can be made
to provide a smoother finish -to the par-ts made therefrom than
is obtained if the parts are made directly on the mold sur-
faces. This in turn can be utilized to effect certain economies
in the making of molds, provided steps are taken to correc-t
for size variations that occur during the process of making
the sheet of release agent. Certain broad steps in ~pplicant's
process are depicted diagramatically in Figure 1, and some
of these steps, are shown more fully in Figures 2 through 5
as they relate to the filament winding of a s-teering wheel
for an automotive vehicle.
In -the em~odimen-t of Applicant's process depic-ted
in Figure 1, polypropylene is used as the mold release separa-
tion sheet, and cast aluminum is used ~or the production molds.
Polypropylene shee-ts after being removed from the vacuum forming
mold shrink by 0.020 inch per inch. Cast aluminum, during
cooling from the molten casting temperature, shrinks approxi-
mately one eighth of an inch per foot. The precise amount
of shrinkage of the cast aluminum can be con-trolled -to some
degree by the particular alloy used, -the CaStincJ temperature,
etc. The polypropylene sheet -tha-t is to be used is 0.025 inch
thick, and it has been determined -that it stretches to a -thick-
ness of 0.015 inch during vacuum ~orming. With -this in mind,
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a master pattern 10 is made of wood, or other easily shaped
material, with i-ts filament winding cavities being 0.030 inch
wider, and 0.015 inch deeper than the part desired. The
overall dimensions of the filament winding cavl-ties are 1/~
inch per foot ]arger than the desired production part, since
it turns out that the polypropylene shrinks, or can be made
to shrink by this amount.
A vacuum forming mold 12 can be made in any one of
a number of differen-t ways. In the process diagrammed in
Figure 1, an accurate sand mold 14 is made of the mas-ter pat-
tern 10. Vacuum tubes are laid into the cavity of a sand mo:Ld,
and the cavity is filled with a me-tal powder - filled plastic
which has a very small shrinkage during solidification. ~he
vacuum forming mold 12 will only be very slightly smaller than
the master pattern 10. Holes are drilled from -the appropriate
surfaces of the plastic to the vacuum tubes, and the surfaces
are given a high polish. The vacuum forming mold 12 is then
utilized to form separation sheets 24.
The master pattern 10 is also used -to make the pro-
duction molds. In the process diagrammed, an accura-te sand
mold 16 is first made and molten aluminum is cast -therein to
produce a cast aluminum pattern 18. A~ter cooling the aluminum
pattern 1~ will have shrunk by approxima-tely 1/2 of -the desired
amount necessary to match -the shrinkage of polypropylene. The
aluminum pattern 18 is checked for surface and size. If ac-
ceptable, an accurate sand mold 20 is made from it, and cast
aluminum is poured into it - this time under condition~ in-
tended to give the remaining necessary shrinkage -to end up
with a mold on which a vacuum forming separation sheet will
fit. For any large scale production of filament wound parts~
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a large number of productlon molds 22 are necessary; and i-t
is intended that a large number of sand molds 20 will firs-t
be made from the cast metal pattern 18, and tha-t the necessary
productionmolds 22 will be ob-tained therefrom.
An advan-tage of Applicant's me-thod of moldin~ is
that the separation sheeks 24 will retain the high finish of
the vacuum forming mold 12. The metal production molds 22,
when removed from the sand molds 20, will have surface irregu-
larities arising fxom the depressions be-tween sand grains.
It has been found that in filamen-t winding, the separation
sheets 24 are not forced down into these surface irregularities
and -therefore, no expensive machining or polishing operation
need be performed on the production molds 22.
Filament wound parts are made by placing a vacuum
formed separation sheet 2~ on a production mold 22 as shown
at 26 and installing the necessary filament re-taining plates
on the top side edge of the mold's filamen-t retaining cavi-ties.
A strand we-tted out wi-th catalyzed polyester prepolymer, or
other sui-table prepolymer, is positioned by a finger opposite
-the mold's filament re-taining cavities; and ei-ther the mold
is rotated to lay -the strand into the cavlty, or the finger
is moved to lay the s-trand into -the cavity. This operation
is depicted at 28 and is explained in de-tail in prior art
patents so that it need not be explained further here, excep-t
as such a process coacts with Applicant's shee-t of mold release
2~. The mold with the filament windings therein is placed
in an oven at approxima-tely 350F to harden the binder as
depicted at 30; and thereaf-ter, the mold is opened to release
the production part~ as deplc-ted at 32.
Referrlng to Figures 2 through 5, -there is shown
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therein a sheet of mold release and ma-tching mold parts for
producing a filarnent wound steering wheel of an automotive
vehicle. Figure 2 shows a filament winding mold 22 having
an annular rim forming groove 34 opening ou-twardly oE its
periphery. Four pairs of vertlcal guides 36, 38, 40 and 42
extend generally radially from a hub supporting pLa-teau 44
to the rim groove 34 to provide respective channels for build-
ing the rim supporting arms of -the steering wheel. Six studs
46 project vertically from -the base of the mold just radially
inwardly oE the groove 34 for retaining the segmental plates
48, 50, 52 and 54 which provide the top wall of the rim groove
34. Suitable wing nu-ts 56 are -threaded on-to the studs 46 to
clamp the segmental cover plates 48 through 54 in place. Be-
foxe the segmental cover plates are slipped into position,
however, a mold release sheet 24 of vacuum formed polypropylene
is slipped down over the studs 46 and ma-ted with the surfaces
of the mold 22. Referring to sections 4 and 5, it will be
seen that the release sheet 24 is retained by the segmental
cover plates 48 through 54, and that it lays down tightly on
the surfaces of the mold 22. Also it will be seen that the
release sheet 24 has a peripheral resin retaining groove 34
to catch any excess resin that may be thrown ~rom the rim groove
34 during rotation of the mold 22.
The resin retaining groove 58 is made durlny vacuum
forming by an appropriate por-tion of the vacuum forming mold
12 which was added to the basic shape produced by -the sand
mold 14 from which the vacuum forming mold 12 was made. A
peripheral space 60 exists between the surface of the mold
~2 and the segmental cover pla-tes 48 through 54 to receive
resin soaked glass s-trand from a finger, not shown, positioned
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outwardly of the resin re-taining groove 58 as the mold 22 is
rotated. Rotation of the mold 2~ stops at appropriate times
wlth the finger, not shown, opposite the ~roove between one
of the pairs of vertical guides 36 through ~2, following which
the finger moves inwardly be-tween the guides to the center.
Upon reaching the center, -the mold 22 rotates again -to wrap
the strand around a hub, not shown, following which -the finger
moves radially outwardly between ano-ther pair of vertical
guides. This operation is continued until -the rim cavity 34
and the arm cavities between the vertical guide plates, shown
in sections 4 and 5 are filled with strand. The mold with
the resin saturated wound filaments is then moved to an oven
held at approximately 350F for twenty minutes to harden the
binder into the steering wheel armature 32. The hot mold is
opened, and the release sheet with the armature 32 is pulled
from the surfaces of the heated mold 22, and is allowed to cool.
While Figure l depic-ts a preerred sequence oE steps
which will produce release sheets that mate wi-th a produc-tion
mold, other sequences of steps can be utilized. For those
~0 instances where the release sheets shrink at twice the rate
of the production molds during cooling, it is possible to build
a to-tally independent vacuum fo~ming mold from scratch which
is appropriately larger than the master pattern from which
the production molds are made. In the case of polypropylene
release sheets, the vacuum forming mold could be made lar~er
than the desired production part by l/4 inch per foot, while
the pattern for the produc-tion molds is only made l/8 inch
per foot larger than the desired production part. Instead
of laying each ou-t independently of each other, however, a
production mold can be cut into a number of pieces, say 16,
which are then arranged with spaces in between to give overall
dimensions whlch are 1/4 inch per foot larger than the pro~
duction mold. The pieces can be doweled together using powdered
metal filled plastic to fill the spaces, and the mold cavlties
can then be worked -to the proper dimensions.
In ano-ther embodiment of the invention, the material
from which the vacuum sheets are made is compounded or selected
to have the same shrinkage as has the material from which the
produc-tion mold is made. In this case, only one master pa-ttern
need be made, and the production molds can be made from sand
molds whose cavities are made by the master pattern itse]f.
While the invention has been described as having
special advantages in making filament winding molds, it is
not so limited ~ nor is it limited to the use of a single re-
lease sheet.
We do no-t wish to be limited to the particular embodi-
ments shown or described, and it is our intention hereby to
cover all novel adaptations, modifications, and arranyements
thereof which come within the practice of those skilled in
the art -to which the invention relates and which fall within
the purview of the following claims.
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