Extrusion Injection Moulding Resin Transfer Moulding John Summerscales

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 • RRIM = reinforced RIM • • • 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) 1 2 3 9 7 6 8 4 5 1. 2. 3. 4. 5. 6. 7. 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 Uo. P Enterprise Award for KTP of the Year 2009 - images from http: //www. zoeftig. com/products. aspx#furniture

KTP in Bude • “in. FINITE” injection-moulded passenger terminal seating • easily reconfigurable component • PU VC’s KTP of the Year Award 2009 • Best KTP South West England 2010 • • Shenzhen Bao’an International Airport Terminal 3 Kunming Changshui installed in just 16 weeks 10, 700 seats 17, 000 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 • SCORIM: s’c’o’ in injection moulding • 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 • Elimination of uncontrolled emissions of VOCs.

Magnum Venus Plastech RTM Division schematic

Rheology. . and. . Viscosity • rheology is a branch of physics that deals with deformation and flow of matter, especially non-Newtonian flow of liquids and plastic flow of solids. • viscosity of a fluid is a measure of resistance to gradual deformation by shear stress or tensile stress.

Viscosity • dynamic viscosity: μ (used in Darcy’s Law) force required to overcome internal friction • SI units are Pascal-seconds • • • Pa·s: identical to 1 kg·m− 1·s− 1 1 m. Pa·s = 1 centipoise (c. P: cgs units) • kinematic viscosity: η = μ/ρ ratio of viscous force to inertial force • the latter is a function of the fluid density ρ • SI units are m 2·s− 1 • • centi. Stokes (cgs units): 1 c. St = 1 mm 2 s-1

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 • K = constant of proportionality (permeability) • A = cross section normal to the flow direction • ΔP = pressure differential driving the flow • μ = fluid viscosity • L = length of mould. NB: tensor form for anisotropic reinforcements •

Resin Transfer Moulding (RTM) • Kozeny (1927) - Carman (1937) Q = ε A m 2 ΔP / k μ L • where ε is the porosity (1 -Vf) • m is the hydraulic radius (Blake 1922), • k is the Kozeny constant, • other parameters as previously described. •

RTM: viscosity • • initial resin viscosity ~200 m. Pa. s Becker: upper limit for viscosity = 800 m. Pa. s non-injection point (NIP) = 1000 m. Pa. s The flow front is effectively stationary at this viscosity, and • low pressure used in the process • 1 m. Pa. s (SI units) = 1 centipoise (cp: industry cgs units).

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“.

SRIM. . vs. . RTM SRIM RTM Resin polyurethane epoxy or polyester Injection Pressure (k. Pa) Mould fill time 10000 -40000 100 -1000 < 1 min >> 1 min Steel or FRP Mould tool High-Pressure RTM (HPRTM) closing the technology gap

RTM: thermoplastics • molten thermoplastic polymers too viscous • in-situ polymerisation (ISP) possible with: caprolactam (e. g. Fibrant) to produce polyamide 6, laurolactam (e. g. EMS) to produce polyamide 12, • cyclic butylene terephthalate oligomers (e. g. Cyclics) to produce PBT polyester, • acrylics (e. g. Arkema Elium®), • … but ISP generally requires high-temperature (~80ºC) processing. • Connora Recyclamine thermoplastic epoxy polymers, where Tg is 40 -60°C and Tm is 120 -140°C.

RTM: flow strategies • uniaxial (slow) • radial • convergent (fast) o inlet o vent

RTM: mould tools • positive pressure: the mould edges may “leak” resin • reinforcement may be placed over the seals to provide a path for air to escape • • vacuum: requires the tool has vacuum integrity • no air ingress paths through the tool • 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 •

RTM: flow problems and solutions • reinforcement pack incompletely fills mould • => "race tracking“ • mould deflection • => "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: fabric compressibility • Quinn and Randall Vf = K 1 + K 2 √P • Toll and Månson P = k E (Vfn - Vfon) where • • P = applied pressure K 1 and K 2 are constants k = power-law coefficient E = through-plane modulus of fabric Vf = fibre volume fraction, Vfo = limiting fibre volume fraction (P = 0) n = power-law exponent.

RTM: typical applications • marine propeller • ACMC test panels (1 m square x 35 -60 mm thick) to inform the design of Advanced Composite Armoured Vehicle Platform (ACAVP) hull.

RTM: typical applications • • • Lotus car bodies Beneteau yachts British Rail (now GWR) high-speed train cabs GWR <200 kph Eurostar 300 kph Chelton radomes CRH >300 kph Dowty aircraft propellers jet engine blocker doors

RTM: process simulation • • • CRIMSON (NIST) LIMS (Delaware) PAM RTM (ESI-Group) RTMFLOT (Montreal) … discontinued RTMWorx (NL) • 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) • Pore-Cor • Pore-Flow© • • mesh-less methods smoothed particle hydrodynamics (SPH) • finite pointset method (FPM) • natural element method (NEM) • discrete element method (DEM) •

Lecture summary • short fibres extrusion: constant x-section • injection moulding: 3 D components • • rheology and viscosity • Resin Transfer Moulding (RTM) permeability: Darcy. . and. . Kozeny-Carman • compressibility: Toll and Månson • applications • simulation •