MATS324C6 RTM

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ExtrusionInjection Moulding

Resin Transfer Moulding

John Summerscales

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Extrusion

normally a screw in a barrelpushes a stream of material through a die

to produce a constant cross-section.

confined to use with discontinuous fibreas 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.

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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, but

o RIM = reaction IM for thermosets

o RRIM = reinforced RIMfor short fibre thermoset composite

o SRIM = Structural RIM

for pre-loaded continuous fibre composites

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Image from

http://www.rutlandplastics.co.uk/

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

Close Inject

HoldOpen & Eject

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Image from

http://www.rutlandplastics.co.uk/

1. Guide Pins2. Runner3. Gate4. Sprue Bush

5. Locating Ring6. Mould Cavity7. Ejector Pins8. The Shot9. Sprue

1 2 3 4 5

6

7

8

9

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Case study:injection-moulded beamless

passenger terminalseating 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
http://www.zoeftig.com/products.aspxhttp://www.zoeftig.com/products.aspx

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Shear controlled technologies

Wolfson Centre for Materials Processingdeveloped Shear Controlled Technologiesto improve orientation in short fibre composites

o SCOREX: shear controlled orientation in extrusiono SCORIM: sco in injection moulding

Images fromhttp://www.brunel.ac.uk/about/acad/wolfson/cmp/technology

>
http://www.brunel.ac.uk/about/acad/wolfson/cmp/technologyhttp://www.brunel.ac.uk/about/acad/wolfson/cmp/technology

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Resin Transfer Moulding

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

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Resin Transfer Moulding (RTM)for most thermoset resins and fabrics two moulded surfaces

inserts, fixing points and lightweight core materialsincorporated 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 hazardso Elimination of uncontrolled emissions of VOCs.

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Magnum Venus Plastech

RTM Division schematic

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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

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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 porespacebetween the reinforcement fibres

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Darcy equation (1856): Q = K.A.P/.L

whereo Q = volumetric flow rate

o K = constant of proportionality (permeability)

oA = cross section normal to the flow direction

oP = pressure differential driving the flow

o = fluid viscosity

o L = length of mould.

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Kozeny (1927) - Carman (1937)

Q = .A.m2.P/k..L

whereo is the porosity (1-Vf)

o m is the hydraulic radius,

o k is the Kozeny constant.

not in the

examination

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RTM: fabric compressibility Quinn and Randall

oVf= K1 + K2.P Toll and Mnson

o P = kE(Vfn - Vfo

n)

whereo P = applied pressure

o K1 and K2 are constants

ok = 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.

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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 ato this viscosity, and

o low pressure used in the process

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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 12o cyclic butylene terephthalate oligomers

(e.g. Cyclics) to produce PBT polyester

but generally a high-temperature process.

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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":

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RTM: flow strategies

uniaxial (slow)

radial

convergent (fast)

o inlet

o vent

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RTM: mould tools with only positive pressure,

the mould edges may leak resin.

reinforcement can be placed over the sealsto 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 peripheralchannel at higher vacuum than the cavity

to clamp the mould halves together.

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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 specificpositions in the mould.

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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 dissipatedby continued resin flow over their surfaces

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RTM: typical applications

marine propeller

hull of AdvancedComposite Armoured

Vehicle Platform (ACAVP)

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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

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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 ofKok en van EngelenDen Haag (NL) bus seat
http://www.polyworx.com/apz/kveng/http://www.polyworx.com/apz/kveng/

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RTM: process simulation

other modelling techniques include:o computational fluid dynamics (CFD)

o Pore-Cor

o Pore-Flow

mesh-less methodso smoothed particle hydrodynamics (SPH)

o finite pointset method (FPM)o natural element method (NEM)

o discrete element method (DEM)

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MATS324C6 RTM