1. Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm 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 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if out-of-date should not be used for applications which may result in injury, loss or damage.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 life
normal 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 temperature
low temperature systems:
cure at ~60ºC, out-life typically 3 months
medium 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 temperature
NB: the above times are indicative, check the manufacturers’ recommendation

5. Pre-preg key considerations include:
drape formability to complex curvatures
tack stickiness
debulk 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 reinforcement
normally supplied "just in time" for the production of composite components usually by compression moulding
Compounds 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  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)

9. Toll and Månson exponents
Fibre kE Vfo % n Reference
Wool J Schofield, J Textile Institute, 1938 [3]
Wool CM van Wyk, J Textile Institute, 1946 [4]
Planar S Toll et al, ICCM-9, 1993 [5]
spun glass roving YR Kim et al, Polymer Composites, 1991 [6]
fluffy glass roving YR Kim et al, Polymer Composites, 1991 [6]
straight glass roving YR Kim et al, Polymer Composites, 1991 [6]
graphite roving YR Kim et al, Polymer Composites, 1991 [6]
Mat R Gauvin & Chibani, SPI-43, 1988 [7]
Mat JA Quinn and Randall, FRC-4, 1990 [1]
Weave YR Kim et al, Polymer Composites, 1991
Weave R Gauvin & Chibani, SPI-43, 1988 [7]
Weave JA Quinn and Randall, FRC-4, 1990 [1]

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

11. Autoclaves images from Google search “autoclave + image”

12. Autoclave

13. Autoclave temp./pressure cycle

14. 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 designed to permit circulation of heated air
VB 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 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 using heat, vacuum and pressure in the autoclave. 

17. 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

18. Compression moulding
two matched (usually steel) mould halves mounted in a (normally hydraulic) press
movement limited to one axis normal to the plane of the mould

19. Compression 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
moulding X 

20. 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 filament glass mat thermoplastics (GMT)