Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm moulding Compression moulding.

1. Pre-preg/moulding compoundsVacuum bagAutoclaveDiaphragm moulding Compression moulding. John Summerscales

2. Pre-preg ..usually epoxy matrix Reinforcement is pre-impregnated with B-staged resin A-stage: soluble and fusible B-stage: swollen but not dissolved by a variety of solvents C-stage:rigid, hard, insoluble, infusible safer than liquid resins mixing done by suppliers > better quality expensive relative to dry reinforcements

3. Pre-preg • use before date: there will be a finite life • if out-of-date should not be used for applicationswhich may result in injury, loss or damage. • out-life: • time outside cold storagewill reduce its useful life • normal to allow the material to warmto ambient temperature before use as condensation may form on cold material 

4. Pre-preg systems • (not ambient cure) (not normally prepreg) • low temperature systems: • cure at ~60ºC, out-life ~3 months • medium temperature systems: • cure at ~120ºC, out life ~6 months, • high temperature systems: • cure at ~180ºC, out-life ~12 months. … above temperatures may be ±20ºC Out-life increases with cure temperature NB: the above times are indicative,check the manufacturers’ recommendation

5. Pre-preg • key considerations include: • drape • natural ability to follow complex curvature • … and conformability • ability to be (manually) formed to complex curvature • tack • stickiness • debulk • the laminate stack is subject to vacuum every few layers in temporary bag or vacuum table.

6. Tube rolling (mandrel wrapping) • a technique where pre-preg isformed onto a tapered mandreland consolidated using shrink-wrap. • most often used to make fishing rod blanks • Kilwell Fibretube (NZ) technical information • YouTube video (Mister Ataraxia)

7. Tube rolling ~ micrographs Courtesy of Gregory Benson, 2016 solid unidirectional tip inserted in rolled blank evidence of voids

8. Vacuum bag (VB) • VB procedures as in lecture C5 (hand-lay),but reinforcement now pre-impregnated

9. Pearce compressibility curves • 625 gsm plain weave E-glass • one (black) or five (red) layers http://dx.doi.org/10.1016/0956-7143(95)93709-S

10. Compressibility of fabrics • Quinn and Randall: • Vf = a + b √P i.e. P Vf2 • Toll and Månson • P = kE(Vfn – Vfon) • k = power-law coefficient • E = elastic modulus of fibres (normal to plane!) • Vf = fibre volume fraction • Vfo = limiting fibre volume fraction, below which P=0 • n = power-law exponent • also Freundlich equation (see C8 webpage)

11. Toll and Månson exponents • Fibre kE Vfo % n Reference • Wool 13 1.45 3 J Schofield, J Textile Institute, 1938 [3] • Wool 420 2 3CM van Wyk, J Textile Institute, 1946 [4] • Planar 4500 3 5S Toll et al, ICCM-9, 1993 [5] • spun glass roving 820 8.5YR Kim et al, Polymer Composites, 1991 [6] • fluffy glass roving 260 7YR Kim et al, Polymer Composites, 1991 [6] • straight glass roving 700 15.5YR Kim et al, Polymer Composites, 1991 [6] • graphite roving 500 14.5YR Kim et al, Polymer Composites, 1991 [6] • Mat 115 3.5R Gauvin & Chibani, SPI-43, 1988 [7] • Mat 100 4.5 JA Quinn and Randall, FRC-4, 1990 [1] • Weave 500 11YR Kim et al, Polymer Composites, 1991 • Weave 8 7R Gauvin & Chibani, SPI-43, 1988 [7] • Weave 15 9 JA Quinn and Randall, FRC-4, 1990 [1]

12. Autoclave • only possible to apply~1000 mbar pressure with vacuum bag • greater levels of consolidation requirean autoclave: advanced pressure cooker • autoclave is a pressure vessel withpipework to allow a vacuumto be maintained in the bagged work-piece. • temperature control is normally by • gas- or electric-heating, • proportional-integral-derivative (PID) controller

13. Autoclavesimages from Google search “autoclave + image”

14. Autoclave

15. Autoclave temp./pressure cycle

16. Autoclave • dwell to get correct resin viscosity • cure to achieve optimum properties • high capital cost equipment • long cycle times • economics demands high autoclave loading • mould tools must be designedto permit circulation of heated air • VB consumables may be a thermal barrier

17. 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 baseand external pressure applied outside membrane. Hydroclave • extremely high costs and elevated risk • pressurized with liquid water at high temperature • only for exceptional requirements • curing of ablative compositerocket engine nozzles and missile nosecones

18. Diaphragm forming (DF) • autoclave technique used solely for thermoplastic matrix composites • laminate laid up flat between 2 diaphragms • superplastic aluminium sheets, or • high-temperature polymeric films • diaphragms are clamped in a frame • the laminate is not clamped • laminate is formed over mould tool usingheat, vacuum and pressure in the autoclave. 

19. Diaphragm forming (DF) • disadvantages • diaphragms are normally a disposable item • rubber membranes can be used for limited production runs • considerable literature on(avoiding) wrinkling of the reinforcement

20. Diaphragm forming (DF) • Solvay Applications Centre are developingrobotic pick-and-place of dry fibre, or prepregs,combined with diaphragm formingand use of matched press toolingto produce complex 3D componentsat rates required by the automotive industry. • the polymeric diaphragms serve a secondary roleas post-production protection/delivery packaging

21. Compression moulding • two matched (usually steel) mould halvesmounted in a (normally hydraulic) press • movement limited to one axisnormal to the plane of the mould

22. Compression moulding: materials Several materials suitable: • prepreg continuous fibres in epoxy resin • prepreg short fibres in polyester resin • sheet moulding compound (SMC) • dough moulding compound (DMC) • bulk moulding compound (BMC) • prepreg short fibre in a thermoplastic matrix • continuous random orientation filamentglass mat thermoplastics (GMT)

23. Compression:moulding compounds • normally unsaturated polyester resin matrix • normally short fibre reinforcement • normally supplied "just in time" for production of composite componentsusually by compression moulding • Compounds marketed in three major forms: • bulk moulding compound (BMC) • dough moulding compound (DMC) • sheet moulding compound (SMC)

24. Compression moulding X X X X  moulding  • unlike VB/autoclave processes,no consolidation pressure on vertical surfaces • near vertical surfaces subject to wrinkling • may be resolved by the use of • rubber-block moulding, or • hydroforming (pressurised liquid) substituting the male mould half

25. Any questions ? Summary of lecture • pre-preg/moulding compounds • vacuum bag • autoclave .. pressclave/hydroclave • diaphragm moulding • compression moulding