Extrusion
Injection Moulding
Resin Transfer Moulding
John Summerscales
Extrusion
• normally a screw in a “barrel”
pushes a stream of material through a die
to produce a constant cross-section.
• confined to use with discontinuous fibre
as the action of the screw breaks fibres
• not a significant technique in the production of
composite components
• finds use in compounding (mixing) to provide
pellets for injection moulding.
Injection Moulding (IM)
• closed cavity mould tool
placed at the output end of an extruder
• discrete charges of material are delivered,
to "injection mould" components
• normally thermoplastic matrix, but
RIM = reaction IM for thermosets
o RRIM = reinforced RIM
o

o
for short fibre thermoset composite
SRIM = structural RIM

for pre-loaded continuous fibre composites
Injection Moulding (IM)
• image from http://www.rutlandplastics.co.uk/
Injection Moulding (IM)
Close
Open & Eject
Inject
Hold
• images from http://www.rutlandplastics.co.uk/
Injection Moulding (IM)
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2 3
9
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8
4
5
1.
2.
3.
4.
5.
6.
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8.
9.
Guide Pins
Runner
Gate
Sprue Bush
Locating Ring
Mould Cavity
Ejector Pins
The Shot
Sprue
• image from http://www.rutlandplastics.co.uk/
Case study:
injection-moulded beamless
passenger terminal
seating component
Knowledge Transfer Partnership with Zoeftig in Bude
- winner of UoP Enterprise Award for KTP of the Year 2009
- images from http://www.zoeftig.com/products.aspx#furniture
KTP in Bude
• “inFINITE” injection-moulded passenger terminal seating
• easily reconfigurable component
• PU VC’s KTP of the Year Award 2009
• Best KTP South West England 2010
Kunming Changshui installed in just 16 weeks
 Shenzhen Bao’an International Airport Terminal 3

17,000 seats
10,700 seats
Shear controlled technologies
• Wolfson Centre for Materials Processing
developed Shear Controlled Technologies
to improve orientation in short fibre composites
SCOREX: shear controlled orientation in extrusion
o SCORIM: s’c’o’ in injection moulding
o
•
•
Images from http://www.brunel.ac.uk/about/acad/wolfson/cmp/technology
•
<< SCOREX
•
SCORIM >>
RTM:
Resin
Transfer
Moulding
Resin Transfer Moulding
Resin Transfer Moulding (RTM)
for most thermoset resins and fabrics
• two moulded surfaces
• inserts, fixing points and lightweight core materials
incorporated at moulding stage.
• place dry fibre (preform) in mould cavity
• close mould, then inject resin to fill porespace.
• cure (thermoset) resin, then remove component from mould.
• net-shape, so requires only minimal trimming.
• superior dimensional tolerances to hand-lay/autoclave products
• reduced worker and environmental hazards
o
Elimination of uncontrolled emissions of VOCs.
Magnum Venus Plastech
RTM Division schematic
SRIM .. vs .. RTM
SRIM
RTM
Resin
polyurethane
epoxy or polyester
Injection
Pressure (kPa)
Mould fill time
10000-40000
100-1000
< 1 min
>> 1 min
Steel
Steel or FRP
Mould tool
Resin Transfer Moulding (RTM)
• most composite manufacturing process
involve only short range flow of the resin
through the laminate thickness
• RTM involves long-range flow of resin
parallel to the laminae, through the porespace
between the reinforcement fibres
Resin Transfer Moulding (RTM)
• Darcy equation (1856):
Q = K A ΔP / μ L
• where
Q = volumetric flow rate
o K = constant of proportionality (permeability)
o A = cross section normal to the flow direction
o ΔP = pressure differential driving the flow
o μ = fluid viscosity
o L = length of mould.
NB: tensor form for anisotropic reinforcements
o
Resin Transfer Moulding (RTM)
not in the
examination
• Kozeny (1927) - Carman (1937)
Q = ε A m2 ΔP / k μ L
• where
ε is the porosity (1-Vf)
o m is the hydraulic radius (Blake 1922),
o k is the Kozeny constant,
o other parameters as previously described.
o
RTM: fabric compressibility
• Quinn and Randall
Vf = K1 + K2 √P
• Toll and Månson
P = k E (Vfn - Vfon)
• where
P = applied pressure
o K1 and K2 are constants
o k = power-law coefficient
o E = through-plane modulus of fabric
o Vf = fibre volume fraction,
o Vfo = limiting fibre volume fraction (P = 0)
o n = power-law exponent.
o
RTM: viscosity
•
•
•
•
initial resin viscosity ~200 mPa.s
Becker: upper limit for viscosity = 800 mPa.s
non-injection point (NIP) = 1000 mPa.s
The flow front is effectively stationary at
this viscosity, and
o low pressure used in the process
o
• 1 mPa.s (SI units) = 1 centipoise (cp: industry cgs units).
RTM: thermoplastics
• molten thermoplastic polymers too viscous
• in-situ polymerisation possible with:
caprolactam (e.g. DSM) to produce polyamide 6,
laurolactam (e.g. EMS) to produce polyamide 12
o cyclic butylene terephthalate oligomers
(e.g. Cyclics) to produce PBT polyester
o acrylics (e.g. Arkema Elium®)
o
… but generally require
high-temperature (~80ºC) processing.
RTM: resin delivery
• mixing:
i.
mixing by static mixers
– in a pumped resin feed line
ii.
pre-mixed and fed from a pressure pot
– compressed air above resin drives it to mould
• flow
i.
constant flow rate with variable pressure
usually via pumps, or
ii.
constant pressure with variable flow rate
pressure pot
• introduce the initial resin at low pressure
/flow rate to minimise "fibre wash“.
RTM: flow strategies
• uniaxial (slow)
• radial
• convergent (fast)
o inlet
o vent
RTM: mould tools
• positive pressure:
the mould edges may “leak” resin
o reinforcement may be placed over the seals
to provide a path for air to escape
o
• vacuum:
requires the tool has vacuum integrity
o no air ingress paths through the tool
o some vacuum systems use peripheral channel
at higher vacuum than the cavity
to clamp the mould halves together.
• pressure driven flow + vacuum for low void content
o
RTM: flow problems and solutions
• reinforcement pack incompletely fills mould
o
=> "race tracking“
• mould deflection
o
=> "easy flow paths"
• both may produce dry spots in the component.
• these feature may be used
to generate "galleries" which feed the resin
to specific positions in the mould.
RTM: flow processes/voids
• at low pressure,
flow primarily in tow by capillary effect
• at high pressure,
flow primarily between tows
• if flow not balanced
then air can be trapped leading to voids
• voids are slowly dissipated
by continued resin flow over their surfaces
RTM: typical applications
• marine propeller
• hull of Advanced
Composite Armoured
Vehicle Platform (ACAVP)
RTM: typical applications
• Lotus car bodies
• Beneteau yachts
• British Rail (now First Great Western)
High Speed Train cabs
• Chelton radomes
• Dowty aircraft propellers
• jet engine blocker doors
RTM: process simulation
•
•
•
•
•
CRIMSON (NIST)
LIMS (Delaware)
PAM RTM (ESI-Group)
RTMFLOT (Montreal) … discontinued
RTMWorx (NL)
o
•
developed from pi-7/SEPRAN (TNO Delft)
RTMworx simulation of
Kok en van Engelen
Den Haag (NL) bus seat
RTM: process simulation
• other modelling techniques include:
computational fluid dynamics (CFD)
o Pore-Cor
o Pore-Flow©
o
• mesh-less methods
smoothed particle hydrodynamics (SPH)
o finite pointset method (FPM)
o natural element method (NEM)
o discrete element method (DEM)
o