ExtrusionInjection 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 toolplaced at the output end of an extruder

• discrete charges of material are delivered,to "injection mould" components

• normally thermoplastic matrix, buto RIM = reaction IM for thermosetso RRIM = reinforced RIM

for short fibre thermoset compositeo SRIM = Structural RIM

for pre-loaded continuous fibre composites

Injection Moulding (IM)

• Image from http://www.rutlandplastics.co.uk/

Injection Moulding (IM)

• Images from http://www.rutlandplastics.co.uk/

Close Inject

HoldOpen & Eject

Injection Moulding (IM)

• Image from http://www.rutlandplastics.co.uk/

1. Guide Pins2. Runner3. Gate4. Sprue Bush5. Locating Ring6. Mould Cavity7. Ejector Pins8. The Shot9. Sprue

1 2 3 4 5

6

7

8

9

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

•“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 17,000 seats Shenzhen Bao’an International Airport Terminal 3 10,700 seats

KTP in Bude

Shear controlled technologies• Wolfson Centre for Materials Processing

developed Shear Controlled Technologies to improve orientation in short fibre compositeso SCOREX: shear controlled orientation in extrusion o SCORIM: s’c’o’ in injection moulding

• Images from http://www.brunel.ac.uk/about/acad/wolfson/cmp/technology•

• << SCOREX

• SCORIM >>

Resin Transfer Moulding

• image from http://www.netcomposites.com/education.asp?sequence=59

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 PlastechRTM Division schematic

SRIM .. vs .. RTM

SRIM RTM

Resin polyurethane epoxy or polyester

InjectionPressure (kPa)

10000-40000 100-1000

Mould fill time

< 1 min >> 1 min

Mould tool Steel Steel or FRP

Resin Transfer Moulding (RTM)

• most composite manufacturing processinvolve only short range flow of the resinthrough the laminate thickness

• RTM involves long-range flow of resinparallel to the laminae, through the porespace between the reinforcement fibres

Resin Transfer Moulding (RTM)

• Darcy equation (1856):• Q = K.A.ΔP/μ.L• where

o Q = volumetric flow rateo K = constant of proportionality (permeability)o A = cross section normal to the flow directiono ΔP = pressure differential driving the flowo μ = fluid viscosityo L = length of mould.

Resin Transfer Moulding (RTM)

• Kozeny (1927) - Carman (1937)• Q = ε .A.m2.ΔP/k.μ.L• where

o ε is the porosity (1-Vf)o m is the hydraulic radius,o k is the Kozeny constant.

not in the examination

RTM: fabric compressibility• Quinn and Randall

o Vf = K1 + K2.√P

• Toll and Månsono P = kE(Vf

n - Vfon)

• whereo P = applied pressureo K1 and K2 are constantso k = power-law coefficiento E = through-plane modulus of fabrico Vf = fibre volume fraction,

o Vfo = limiting fibre volume fraction (P = 0)

o n = power-law exponent.

RTM: viscosity

• initial resin viscosity ~200 mPa.so 1 mPa.s = 1 centipoise.

• Becker: upper limit for viscosity = 800 mPa.s

• non-injection point (NIP) = 1000 mPa.s• The flow front is effectively stationary at

o this viscosity, ando low pressure used in the process

RTM: thermoplastics

• molten thermoplastic polymers too viscous

• in-situ polymerisation possible with:o 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

but generally a high-temperature process.

RTM: resin delivery

• mixing by static mixers in the resin feed line• premixed and fed from a pressure pot

o compressed air above resin drives it to mould

• two basic approaches: o constant flow rate with variable pressure

(usually via pumps), or o constant pressure with variable flow rate

(pressure pot).

• introduce the initial resin at low pressure /flow rate in order to minimise "fibre wash":

RTM: flow strategies

• uniaxial (slow)

• radial

• convergent (fast)

o inleto vent

RTM: mould tools• with only positive pressure,

the mould edges may “leak” resin.• reinforcement can be placed over the

seals to provide a path for air to escape

• with vacuum, it is important that thetool has vacuum integrity o no paths for air ingress through the tools

itself.

• some vacuum systems use peripheral channel at higher vacuum than the cavityto clamp the mould halves together.

RTM: flow problems and solutions

• reinforcement pack incompletely fills mouldo => "race tracking“

• mould deflectiono => "easy flow paths"

• both may produce dry spots in the component. 

• these feature can 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 balancedthen air can be trapped leading to voids

• voids are slowly dissipatedby 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:o computational fluid dynamics (CFD)o Pore-Coro Pore-Flow©

• mesh-less methodso smoothed particle hydrodynamics (SPH)o finite pointset method (FPM)o natural element method (NEM)o discrete element method (DEM)