  Shape
Memory
Polymer
Bladders
for
Composites
Manufacturing
Conventional
silicone
or
latex
bladders
are
not
rigid
enough
to
support
composite
lay-up
before
custom
molding.
Often
material
must
be
applied
to
the
inside
of
a
female
mold
first,
an
inflatable
bladder
inserted,
the
mold
closed,
and
the
bladder
pressurized
and
inflated
to
consolidate
the
material
against
the
mold
surface.
This
process
is
labor
intensive,
can
produce
seams,
wrinkles
and
bridging,
and
often
results
in
inaccurate
part
shapes.
These
drawbacks
have
led
to
the
theory
of
an
inflatable
bladder
core
used
as
the
mandrel,
but
conventional
bladder
cores
lack
the
structure
required
for
the
composite
lay-up
process.
SMP
bladders
operate
first
as
mandrels
and
later
as
inflatable
bladder
cores.
First
providing
a
rigid,
durable
surface
for
composite
layup,
SMP
bladders
then
provide
flexibility
and
inflatability
when
the
part
is
formed
against
the
interior
of
the
final
mold.
When heated above their activation temperature,
SMP bladders become flexible and can be molded into a near-net
bladder shape. When cooled while still under pressure in the
near-net mold, they become rigid in the new shape. The resulting
rigid bladder is used as a mandrel for lay-up or filament
winding of a composite part.
The
composite
lay-up
on
the
SMP
bladder
is
then
inserted
into
a
clamshell
mold
and
subjected
to
air
pressure
and
heat.
The
heat
softens
the
SMP
bladder,
so
it
becomes
flexible
and
inflates,
consolidating
the
composite
material
against
the
mold,
ensuring
even
expansion
and
precise
outer
surface
dimensions
on
the
part.The
part
is
then
cured
while
pressurized.
Since
the
cure
temperature
of
the
composite
is
higher
than
the
rigid-to-flexible
transition
temperature
of
the
bladder,
the
bladder
remains
flexible
and
provides
consistent
pressure
on
the
interior
of
the
part.
Once
the
part
is
cured,
the
flexible
SMP
bladder
is
depressurized
and
contracts
from
the
inner
surface
of
the
part.
Because
of
its
flexibility
when
heated,
it
can
be
removed
easily
and
reused.
Since
the
mold
was
completely
closed
when
forming
the
part,
wrinkling,
bridging
and
pinching
are
less
likely.
The
resulting
precision
part
is
seamless
and
requires
no
taping,
sealing
or
pleating.
Benefits:
•
Suitable
for
hand
and
mechanical
lay-up,
filament
winding,
fiber
placement,
over-braiding
and
more
•
No
waste,
no
EPA
restrictions,
clean
process
•
Eliminates
the
need
for
part-specific
tool
retention
and
storage
•
Easily
extracted
•
Reusable
•
Reduces
cycle
time
|
