Note: Descriptions are shown in the official language in which they were submitted.
CA 02389872 2002-03-27
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Iv~THOD FOR MDLD~TG URETHANE FOAM WITH COZJN?FR-PRESSURE
Find of the Invention
The present invention relates to a method for manufacturing vehicle trim
panels.
Specifically, the subject invention relatrs to a method of molding a trim
panel using
urethane foam that eliminates costly void defects that are inherent in molding
of urethane
foams.
Description of the Related Art
Urethane foam molding processes for manufacturing vehicle trim panels such as
headliners and vehicle door panels are generally known to those skilled in the
art. For
example, a vehicle headliner is typically manufactured with a forming tool or
die wherein
top and boctom layers arc inserted into the forming cool and a uredtane matrix
is sprayed
between the layers to form a core. Examples of urothane foam molding processes
are
I 5 illustrated is WO 89/08547 and United Scales Patent No. 5,841,449.
A conventional urethane foam molding process for manufacturing vehicle a'un
panels is generally disclosed in Figures 1 and I_ ,As shown L~ert is Figure 1,
a conventional
urethane foam nwldine process is accomplished in two steps. The first step
begins by
inserting an anti-squeak foam backing 10 into a lower molding tool (not shown
in Fins. 1-
2). Next, a porous filaerglass mat 12 is placed on the foam backing 10.
Coatinuitig,
urethane matrix is sprayed on the foam backing 10 and fiberglass mat 12
positioned in the
lower molding tool and is dispersed within and throughout the fiberglass mat
1Z. Afrer the
urethane is sprayed, the urethane foams, rises, sad hardens, and a urethane
foam 16 is
established. During the foaming and rising of the urethane, air bubbles 19
inherent to the
process migrate toward a top surface 18 of the foam 16. Often, as the urethane
hardens
into the foam 16, the migrating air bubbles 19 are trapped within the urethane
arid the
fiberglass mat 1Z. However, as the urethane foam hardens, the air bubbles 19
may be
trapped at the top surface 18 of the foam 16.
Refertiuig now to Figure Z, as a result of the air bubbles being trapped at
the tap
1
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CA 02389872 2002-03-27
WO 01/26932 PCT/CA00/01213
layer 24 and a foam layer 26. The cloth layer 24 is the outer layer that forms
the exterior or
viewable surface of the trim panel. In order to apply the foam backed cloth 22
to the urethane
foam 16, an adhesive/barrier layer 28 must be included between the foam layer
26 of the
foam backed cloth 22 and the urethane foam 16. As shown in Figure 2, if the
top surface 18
of the urethane foam 16 includes a void defect 20, then ultimately the cloth
layer 24 of the
foam backed cloth 22 also realizes the same void defect 20.
Attempts to offset this realization of the void defect 20 at the cloth layer
24 where
such a defect would be noticeable to occupants of a vehicle have proven to be
costly. For
example, one such attempt inserts a structural film to structurally mask the
void defect 20
before adding the foam backed cloth 22 in the second step, which is costly and
labor
intensive.
Accordingly, there remains a need in the art for a method of manufacturing a
trim
panel that eliminates void defects resulting from air bubbles occurnng in the
urethane foam
during the foaming of the urethane matrix.
Summary of the Invention
Accordingly, the present invention is a method for molding a vehicle trim
panel
having an exterior or outer layer and a urethane core. The method includes the
steps of
providing a forming tool having a core portion and a cavity portion that
cooperate to form
a die cavity complementary with the trim panel. The exterior or outer layer is
placed in the
forming tool adjacent to the mold surface of the cavity portion and a vacuum
is drawn on the
cavity portion to hold the exterior layer against the mold surface of the
cavity portion. The
method also includes the steps of providing a foamable material and applying
the foamable
material to the core portion of the molding tool. The forming tool is closed
and the foamable
material expands. The method further includes the step of applying pressure
against the
exterior or outer layer while the foamable material is expanding to inhibit
bubbles from
forming at the surface of the foamable material. Finally, the pressure is
released and the
forming tool is opened to remove the trim panel from the forming tool.
One advantage of the method for molding a trim panel according to the present
invention is that adding pressure to the forming tool during expansion of the
foamable
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material controls the formation of air bubbles on the surface of the foamable
material and
prevents the urethane foam from penetrating the exterior or outer layer.
Further advantages of the present invention will be readily appreciated as the
same
becomes understood by reference to the following detailed description when
considered in
connection with the accompanying drawings.
Brief Description of the Drawings
Fig. 1 is a cross sectional side view of a conventional two-step urethane foam
molding process according to the prior art;
Fig. 2 is a cross sectional side view of the conventional two-step urethane
foam
molding process according to the prior art illustrating the effect of a void
defect formed
initially at a top surface of a urethane foam;
Fig. 3 is a schematic side view showing a molding apparatus for use in forming
a trim
panel according to the one-step urethane foam molding process of the present
invention with
the mold open;
Fig. 4 is a schematic side view showing the molding apparatus of Fig. 3 for
use in
forming the trim panel according to the one-step urethane foam molding process
of the
present invention with the mold closed;
Fig. 5 is a cross sectional side view of a trim panel formed according to the
one-step
urethane foam molding process of the subject invention; and
Fig. 6 is a fragmentary cross sectional side view taken in the circle 6-6 of
Fig. 4,
showing a trim panel formed according to the one-step urethane foam molding
process of the
present invention and illustrating a cavity and the application of pressure
being applied
through the cavity to counteract formation of void defects at the top surface
of the urethane
foam.
Detailed Description of the Preferred Embodiment
Referring to the Figs. 3-6, wherein like numerals indicate like or
corresponding parts
throughout the several views, an apparatus for performing a one-step urethane
foam molding
process is shown. The one-step urethane foam molding process of the subject
invention
applies to both rigid and semi-rigid polyurethanes. For example, a rigid
polyurethane can
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be incorporated into the one-step urethane foam molding process of the subject
invention to
manufacture vehicle door panels. Also for example, a semi-rigid polyurethane
can be
incorporated into the one-step urethane foam molding process of the subject
invention to
manufacture vehicle headliners. For descriptivepurposes,althoughthe subject
invention will
be described hereinbelow only in terms of the semi-rigid polyurethaneand
vehicle headliners,
the subject invention is not limited to such.
As shown in Figs. 3-4, the molding apparatus 30 includes a frame 32 that
supports
an upper mold assembly or cavity 34 of a forming tool 36. The cavity 34 has a
mold surface
38 which is shaped in a configuration corresponding to that of the desired
shape of the
headliner. Vertical or reciprocal movement of the cavity 34 may be
accomplished in a
number of ways. In the present embodiment, the cavity 34 is supported on
columns 40 having
a rack portion. Each column is slidably secured in a housing 42. Pinion gears
(not shown)
engage the rack portion and are driven by a drive rod 44, which is rotated by
a motor 46, to
lift and lower the cavity 34.
The molding apparatus 30 ftwther includes a fixed track 48 that extends
through the
frame 32, below the cavity 34. Wheel members 52 support a lower mold assembly
or core
50 for movement on the track 48. Known to those skilled in the art are a
number of ways to
drive of the core 50 on the track 48. Secured beneath the core 50 is a steel
platen 54. A
plurality of tubular airbags 56 extend transversely to the track 48. In Figs.
3-4, the airbags
56 are shown inflated such that they engage the steel platen 54 and raise the
wheel members
52 of the core 50 above the track 48. In this manner, see Fig. 4, the
compressive load
occurring during the molding process is borne by the airbags 56.
The molding apparatus 30 is shown here utilizing a core 50 movable on a fixed
track
48, this is for illustration purposes only. In this embodiment, the molding
apparatus 30 is
provided with additional cores 50 that can be alternately moved on the track
48 under the
cavity 34 during the molding operation. In such fashion, the core 50 not being
used is set up
or prepared for the next molding operation. It should be appreciated that the
molding
assembly 30 could be a single, stationary forming tool 36 having a cavity 34
and core 50.
In accordance with the present invention, as shown in Fig. 3, an anti-squeak
foam
backing 60 is placed on the mold surface 58 of the core 50. A porous
fiberglass mat 62 is
then placed over the anti-squeak foam backing 60. As part of the molding
process, as outer
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or exterior layer 64 placed on the cavity 34 and maintained against the mold
surface 38 of
the cavity 34 by a vacuum assembly 66 such that the outer or exterior layer
backed cloth 64
conforms to the mold surface 38. In the preferred embodiment, the outer or
exterior layer is
a foam backed cloth 64. The foam backed cloth 64 includes a cloth layer 68 and
an open-cell
foam layer 70. As shown in Figs. 3-4, the cavity 34 contains a plurality of
vacuum ports 72
extending through the cavity 34 to the mold surface 38. A vacuum channel or
plenum 74
connects the vacuum ports 72 through vacuum hose 76 to a pump 78. As set forth
in greater
detail below, the pump 78 is capable of both generating a vacuum or negative
pressure, i.e.
a pressure less than atmospheric and a pressure, i.e. a positive pressure or
pressure greater
than atmospheric.
Concurrent with the placement of the foam backed cloth layer 64 on the cavity
34,
the semi-rigid polyurethane is sprayed on and dispersed within and throughout
the fiberglass
mat 62 placed in the core S0. As shown in Fig. 4, the forming tool 36 is
closed by lowering
the cavity 34 downward into engagement with the core 50 after which the semi-
rigid
1 S polyurethane begins to foam, rise, and harden. Ultimately, a semi-rigid
polyurethane foam
80 is established. The foam 80 comprises a mixture of the fiberglass mat 62
and the semi-
rigid polyurethane. During the foaming and rising of the semi-rigid
polyurethane, air bubbles
such as those shown in the prior art, Figs. 1-2, and inherent to the urethane
foaming process
migrate toward a top surface 82 of the foam 80. As discussed above in the
Background of the
Invention, if the air bubbles become trapped at the top surface 82 of the foam
80 while the
semi-rigid polyurethane rises and hardens, then the air bubbles form permanent
void defects
in the top surface 82 of the now hardened foam 80.
As shown in Fig. 6, the one-step urethane foam molding process of the subject
invention directly counteracts the migration of air bubbles to the top surface
82 of the foam
80 by applying pressure (represented by Arrows B,, B2, B3, B4, and BS) to the
top surface 82.
As a result, the formation of permanent void defects at the top surface 82 is
minimized, if not
entirely eliminated. The pressure application will be discussed further
hereinbelow.
As shown specifically in Fig. 5, an advantage of the one-step urethane foam
molding
process is realized by the elimination of an adhesive/barrier layer adjacent
to the foam layer
70 of the foam backed cloth 64. Instead, the foam backed cloth 64 is directly
adhered to the
top surface 82 of the foam 80 by a chemical bond established between the foam
layer 70 of
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the foam backed cloth 64 and the semi-rigid polyurethane as it foams, rises,
and hardens.
Eliminatingthe adhesive/barner layer obviously incorporates advantageous cost
savings into
the one-step urethane foam molding process.
Although not shown in the Figures, it is understood by those skilled in the
art that
mold release films may be incorporated at critical interfaces between the
various components
of the subject invention to permissibly release the completed vehicle
headliner from the
cavity 34 and core 50 of the forming tool 36.
As discussed above, in order to effectively counteract the formation of void
defects
at the top surface 82 of the foam, a gas under pressure B I - BS is applied
through passageways
72. More specifically, as the semi-rigid polyurethane foams, rises, and
hardens, and as the
air bubbles migrate toward the top surface 82 of the rising semi-rigid
polyurethane, the
vacuum, originally established to maintain the foam backed cloth 36 layer in
the upper
molding tool 34, is reversed to now input a preferably inert gas to create a
positive pressure
(as shown in Figure 6) into the cavity 34 of the forming tool 36. As such, the
gas under
positive pressure permeates through the cloth layer 68 and the foam layer 70
of the foam
backed cloth 64 to the top surface 82 of the foam 80 to discourage the air
bubbles from
reaching the top surface 82 and ultimately forming void defects in the foam
80. As a result,
an insertion of a structural film to structurally mask any void defects is not
required as the
void defects are not at the top surface 82 of the foam 80. Instead, the void
defects, if any, are
dispersed below the top surface 82.
As appreciated, introduction of positive pressure to counteract the formation
of void
defects at the top surface 82 of the foam 80 preferably utilizes existing
molding equipment.
That is, the same ports or passageways 72 utilized to maintain the foam backed
cloth 64 in
the cavity 34 are the same ports 72 that are subsequently utilized to
introduce a gas under a
positive pressure to counter the formation of void defects.
As understood by those in the art, the relation between the cavity 34 and core
50
portions of the forming tool 36 is not critical. As a result, the one-step
urethane foam
molding process may interchange the operation of the cavity 34 and core 50 so
long as the
positive pressure introduced to counteract the formation of void defects is
correspondingly
interchanged.
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tr.. r l
surface I8 of the foam 16, a permanent void defect 20 is formed at a top
surface 1 B of the
now hardened urethane foam 16.
Next, the second step of the conventional urethane foam molding process
applies
a foam backed cloth Z2 to the urethane foam 16. The foam hacked cloth 22
includes a
cloth
The time interval where the vacuum maintaining the foam backed cloth 64 in the
cavity 34 is changed over to positive pressure introduced into the closed
cavity 34 and core
50 is important. For instance, a short rime interval prior to changing from
the vacuum to
a positive pressure could introduce an excessive amount of air bubbles into
the foaming and
rising semi-rigid polyurethane and could patenaally create more void defects
in the foam
80. on the ocher hand, if the time interval is tvo long, then the vacuum may
permit the
semi-rigid polyurethane to excessively foam and rise thereby pe~netraring
through the foam
layor 7o and isito the cloth layer 68 of the foam backed cloth 64.
Accordingly, it is desirable
to apply a positive or counter-pressure during expansion of the foam at a
prrssura level
necessary to prevent the foam 80 from expanding into the open-cell foam lsyer
70 of the
foam backed cloth 64.
By way of example, a headliner cart be manufactured utilizing the present
irwenaon
with a 125 second cycle time. Unce the mold is closed, the foam 80 is allowed
to expand
for a period of 25 seconds. The expanding foam will create a pressure in the
mold of about
32 psi. Far the next 100 seconds, air is infected into the mold throuEh
passageways 7Z to
achieve a pressure in the closed cavity 34 of about 45 psi (4_310264 MPa or
3.IOZ64bar).
The invention has been described in an illustrative manner, and it i,s to be
understood that the terminology which has been used is intended to be in the
nature of
words of description rather than of limitation. Many modifiications and
variations of the
present invention are possible in light of the above teachings. It is,
therefore, to be
understood that the invention may be practiced otherwise as specifically
described.
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