  Leave-In
Mandrels
Rotomolding
Rotational
molding,
or
rotomolding,
is
an
innovative
process
used
in
manufacturing
composite
solid
rocket
motors
(SRMs)
and
other
tank-like
vessels.
A
rotomolding
technique
developed
by
CRG
eliminates
mandrel
removal
from
the
manufacturing
process
of
SRMs.
The
process
involves
using
unique
leave-in
mandrels
structural
enough
for
filament
winding
and
also
suitable
to
remain
in
place
and
be
used
as
insulation
material
in
the
SRM
itself.
Originally
funded
by
the
Missile
Defense
Agency
(MDA),
this
SRM
manufacturing
is
compatible
with
a
variety
of
materials,
resulting
in
low-cost,
insulating,
leave-in
mandrels.
Leave-in
Mandrels
Leave-in
mandrels
can
be
inserted
into
the
traditional
filament
winding
process
used
to
manufacture
SRMs.
Conventional
methods
involve
fabricating
SRMs
on
multi-piece
metal
mandrels,
a
process
which
is
both
expensive
and
labor-intensive.
In
the
conventional
scenario,
the
mandrel
is
assembled,
the
insulation
is
applied,
and
the
part
is
filament
wound.
The
composite
is
then
cured,
and
the
metal
mandrel
is
disassembled
and
removed.
CRG’s
rotomolding
technique
uses
the
mandrel
as
the
insulation.
Since
there
is
no
need
to
remove
the
mandrel
after
fabrication,
this
novel
process
eliminates
more
than
50%
of
the
manufacturing
labor,
with
the
added
benefit
of
customizing
insulation
designs
tailored
to
specific
applications.
Benefits
Future
tactical
SRMs
may
have
to
operate
at
pressures
nearly
twice
those
of
current
designs
for
improved
performance
requirements.
They
will
require
greater
maneuverability
and
longer
burn
times
and
will
need
the
ability
to
withstand
higher
G-forces
and
carry
additional
propellant
loading.
CRG’s
rotomolding
process
provides
these
properties
with
the
capability
of
high
specific
strength
composite
parts
made
from
high-temperature
materials
and
high-performance
insulation.
This
technology
supports
missile
systems
with
enhanced
multi-layer
composite
cases,
providing
improved
performance
with
significantly
reduced
unit
cost.
Leave-in
mandrels
improve
on
conventional
rotational
molding
processes
by
using
a
new
approach
to
mold
design,
dynamic
loading,
and
heat
transfer
to
accommodate
a
wider
variety
of
component
configurations,
materials,
and
cure
processes.
CRG’s
rotomolding
is
designed
to
allow
for
several
processing
variables
including
spin
rate,
angle
of
spin,
and
heating
capability,
resulting
in
leave-in
mandrels
with
properties
tailored
to
fit
customers’
needs.
Additional
details
on
leave-in
mandrels
can
be
found
in
the
published
article:
Stahl,
J.,
Pora,
E.,
and
Freeman,
P.
“Innovative
Manufacturing
for
Solid
Rocket
Motors,”
SAMPE
Journal,
Vol.
42.
No.
6.
November/December
2006.
pp.
21-27.
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