Presentation on theme: "Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm moulding Compression moulding. John Summerscales."— Presentation transcript:
1 Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm moulding Compression moulding. John Summerscales
2 Pre-preg (usually epoxy matrix) Reinforcement is pre-impregnatedwith B-staged resinA-stage: soluble and fusibleB-stage: swollen but not dissolved by a variety of solventsC-stage: rigid, hard, insoluble, infusiblesafer than liquid resinsmixing done by suppliers > better qualityexpensive relative to dry reinforcements
3 Pre-preg finite life: there will be a use before date out-life: if out-of-date should not be used for applications which may result in injury, loss or damage.out-life:time outside cold storage will reduce its useful lifenormal to allow the material to warm to ambient temperature before use as condensation may form on cold material
4 Pre-preg systems cold-cure (not normally prepreg) cure at ambient temperaturelow temperature systems:cure at ~60ºC, out-life typically 3 monthsmedium temperature systems:cure at ~120ºC, out life typically 6 months,high temperature systems:cure at ~180ºC, out-life typically one year.Out-life increases with cure temperatureNB: the above times are indicative, check the manufacturers’ recommendation
5 Pre-preg key considerations include: drape formability to complex curvaturestack stickinessdebulk every few layers subject the stack to vacuum in temporary bag or a vacuum table.
6 Moulding compounds normally unsaturated polyester resin matrix normally short fibre reinforcementnormally supplied "just in time" for the production of composite components usually by compression mouldingCompounds marketed in three major forms:bulk moulding compound (BMC)dough moulding compound (DMC)sheet moulding compound (SMC)
7 Vacuum bag (VB)VB procedures as in lecture C5, but reinforcement now pre-impregnated
8 Compressibility of fabrics Quinn and Randall:Vf = a + b √P i.e. P Vf2Toll and MånsonP = kE(Vfn – Vfon)k = power-law coefficientE = elastic modulus of fibres (normal to plane!)Vf = fibre volume fractionVfo = limiting fibre volume fraction, below which P=0n = power-law exponentalso Freundlich equation (see C8 webpage)
9 Toll and Månson exponents Fibre kE Vfo % n ReferenceWool J Schofield, J Textile Institute, 1938 Wool CM van Wyk, J Textile Institute, 1946 Planar S Toll et al, ICCM-9, 1993 spun glass roving YR Kim et al, Polymer Composites, 1991 fluffy glass roving YR Kim et al, Polymer Composites, 1991 straight glass roving YR Kim et al, Polymer Composites, 1991 graphite roving YR Kim et al, Polymer Composites, 1991 Mat R Gauvin & Chibani, SPI-43, 1988 Mat JA Quinn and Randall, FRC-4, 1990 Weave YR Kim et al, Polymer Composites, 1991Weave R Gauvin & Chibani, SPI-43, 1988 Weave JA Quinn and Randall, FRC-4, 1990 
10 Autoclave only possible to apply ~1000 mbar pressure with a vacuum bag to achieve greater levels of consolidation, use an autoclave: advanced pressure cookerautoclave is a pressure vessel with pipework to allow a vacuum to be maintained in the bagged work-piece.temperature control is normally bygas- or electric-heatingproportional-integral-derivative (PID) controller
11 Autoclaves images from Google search “autoclave + image”
14 Autoclave dwell to get correct resin viscosity cure to achieve optimum propertieshigh capital cost equipmentlong cycle timeseconomics demands high autoclave loadingmould tools designed to permit circulation of heated airVB consumables may be a thermal barrier
15 Pressclave pressclave: alternative relatively inexpensive technology normally a hinged frame with an elastomeric membrane so vacuum can be drawn under the membrane via perforations in the pressclave base and external pressure is applied outside the membrane.
16 Diaphragm forming (DF) autoclave technique used solely for thermoplastic matrix compositeslaminate laid up flat between 2 diaphragmssuperplastic aluminium sheets, orhigh-temperature polymeric filmsdiaphragms are clamped in a framethe laminate is not clampedlaminate is formed over mould tool using heat, vacuum and pressure in the autoclave.
17 Diaphragm forming (DF) disadvantagesdiaphragms are normally a disposable itemrubber membranes can be used for limited production runsconsiderable literature on (avoiding) wrinkling of the reinforcement
18 Compression mouldingtwo matched (usually steel) mould halves mounted in a (normally hydraulic) pressmovement limited to one axis normal to the plane of the mould
19 Compression mouldingunlike VB/autoclave processes, no consolidation pressure on vertical surfacesnear vertical surfaces subject to wrinklingmay be resolved by the use ofrubber-block moulding, orhydroforming (pressurised liquid)substituting the male mould halfmouldingX
20 Compression moulding: materials Several materials suitable:prepreg continuous fibres in epoxy resinprepreg short fibres in polyester resinsheet moulding compound (SMC)dough moulding compound (DMC)bulk moulding compound (BMC)prepreg short fibre in a thermoplastic matrixcontinuous random orientation filament glass mat thermoplastics (GMT)