On Tuesday, 6 December 2016 08:45:13 UTC+1, Fraser Wilson wrote:
Three further points with pre preg;-
1-Uni directional (UD) pre-preg, which is extensively used in wings, is
difficult
to form into compound curves;- it wrinkles
2-stray fibres, with pre-preg stray fibres can puncture the vac bag. The
wing
skins don't come out of the moulds until after the wings have been fully
glued
together. It's a bad day to discover a single stray fibre has killed the
vacuum
during the cure of a skin and you've just glued it to a good
spar/skin/installed
controls etc
3 - wet lay up wings post cure at 60C, normally out of mould. Pre-Preg
cures
at least 80C maybe hotter but this must be done in the mould. This means
the part and mould thermal expansion must be closely matched and the
longer the part , the more compound curves, the more difficult this
becomes.

Dry fibre resin infusion probably offers the best way forward as it can
provide
similar fibre fractions to pre preg but without the above and earlier
mention
drawbacks.

Fraser


I tend to disagree with most of that.
UD is difficult on complex shapes yes, but what is complex about a wing? It is basically straight. If you can laminate it with wet laminate, you can do it with prepreg.

You would cure the skins then glue the rest in. Well, this would be my approach. The spar can be co-cured in there if you like. Makes for easy small steps in manufacturing.
Similar way to the concept behind a F1 car. Outersking, honeycomb and inserts, innerskin.

Don't see the issue with postcure. No need for it to be done in the mold with Prepreg. We were postcuring suspension to 180-220 deg C out of the mold and had no issues. They were cured at 130 to start with.
As far as thermal expansion goes, why not make your molds out of tooling prepreg? Works like a charm, and if you have a decent glider you will make plenty of gliders out of the mold and you will always have the same shape. Beats having to rework your molds every couple of years