Delinquent
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| posted on 7/10/07 at 10:34 AM |
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Advanced composite moulding
Anyone have any good sources of info / forums on advanced composite moulding?
In designing my moncoque I obviously need to take into account exactly how I'm going to mould the thing, and am constantly coming up against the
same problem, time and time again - large undercuts that really necessitate a join made after moulding - which I'm not happy about.
Looking at "production" carbon monocoques they seem to get away with it, so really I need info on the moulding techniques, joining
techniques etc employed. I've got plenty of info and reasonable experience of straight forward moulding - either single or multi piece moulds,
but some of what I need is well past that!
A good example is the Carrera GT passenger cell - which can be seen here...
http://www.auto-power-girl.com/pics/photo-gallery/_porsche_carrera_gt__end_of_production-11863
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Mal
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| posted on 7/10/07 at 11:05 AM |
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Removal from Mould
My knowledge of mding is limited to simple forms of GRP so these ides might be flawed.
I wonder if the answer to your problem is to think in terms of making the mould in several slideable sections and remove the mould from the moulding
instead of the moulding from the mould. By this thinking it may be possible to extract the portion of the mould with re-entrant angles, after first
taking away an 'easy section.
The other approach may be a sacraficial
mould in say, a skinned polyeuthethane ,which you extract in little pieces and then bin.
Mal.
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Syd Bridge
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| posted on 7/10/07 at 11:18 AM |
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That Porsche pic is a cad model. I'd like to see what they actually built. I would suspect something with a few alterations.
If you haven't got a big oven, or better still an autoclave, then restrict yourself to what you know and can do. Keep things simple. Sometimes
a simple moulding glued on is much more cost effective than to try and 'mould it in' on a single large moulding.
Trying to explain what you are asking is not in any books, and would take far too long , if at all, in writing.
Cheers,
Syd. 
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Delinquent
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| posted on 7/10/07 at 11:57 AM |
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I agree Syd, I suspect alterations as well and would like to see how it ended up!
No autoclave, the oven is going to be nothing more fancy than a large heater, some circulation fans and a shed load of insulation sectioning off an
area of the workshop with some feeds for the vacuum - have some advice from a boat builder to get that bit together, unfortunately his work was all
fairly simple (if rather substantial!) so that's as far as his advice can take me.
Mal - it's going to be a mulitpart mould anyway, it's just that because of all the returns to give structural stiffness, plus the
requirements for the finished face, I can't see a way to mould the top overhang of the footwell (compounded on mine by the fact that it's
3 seater driver mid mounted, so this bit is very long!)
Looks like it's going to be easiest to modify to include a large lip for the top of the footwell to be bonded on to then - shame as obviously
less aesthetically pleasing, but guess that's the life of the shed builder!
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Dantheman
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| posted on 7/10/07 at 12:10 PM |
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I'm interested to hear more about turning ones shed into an autoclave! I work as a composite technician and have often looked at the mountain of
scrap carbon that gets binned and wondered what I could make out of it all. I'd be happy to offer any advice I could throw your way.
Danny.
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Delinquent
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| posted on 7/10/07 at 02:04 PM |
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quote:
Originally posted by Dantheman
I'm interested to hear more about turning ones shed into an autoclave! I work as a composite technician and have often looked at the mountain of
scrap carbon that gets binned and wondered what I could make out of it all. I'd be happy to offer any advice I could throw your way.
Danny.
sent you a U2U
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Werner Van Loock
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| posted on 7/10/07 at 03:16 PM |
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If I understand you correctly you need a inner and outer mould, and it's the inner mould that's the problem (outer mold can be
sectionised)
What you could do is work with throw away moulds (PU foam) but first make one and before making a monocoque out of it make a negative FiberGlass mould
of it in wich you can pour/spray future positive PU moulds in wich will be used for making the monocoque. It's not very enviromentally sane, but
it's a way to make the same complex structures over and over again in low volume.
This is off course thinking out loud of me, but it's a possibility.
The outside mould can be made afterwards off course adding the required monocoque thickness to the positive foam mould and taking a second negative
mould wich will be the pressing mould.
This way you will have 2 negative mould, one a little smaller then the other.
So when making the monocoque you first make a foam positive, prepare it so you can laminate it. Then laminate and then put the negative mould over it
to press your lamination between the positive and negative mould.
When cured you take away the negative mould and burn away the PU with acetone.
http://www.clubstylus.be
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Hammerhead
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| posted on 7/10/07 at 05:13 PM |
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Radical did a lmp car with a carbon monocoque, check out their website for the build pics, if you have trouble finding it let me know cos I think I
downliaded all the images for reasearch purposes 
Steve.
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Delinquent
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| posted on 7/10/07 at 06:52 PM |
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Thanks for all the help guys
The "lost foam" method was one that I had considered, but to be frank, I don't like the process - it's not one I've got
on well with in the past, and being in such a structurally essential position something I'm a bit loathed to play with.
I think I might actually have worked it to my advantage, putting a 2 inch wide lip on the sides of the footwell to form a bonding platform, then a
much more sculpted top piece for extra strength - the wishbone mounts will now sit right up into the newly created recess, which will be twice as
thick as elsewhere plus have strength through the shape. I hope.
Hammerhead - Found a few pics - nice one, some handy idea's flowing from there 
Edited to add some words so it reads proper ingeesh like. innit.
[Edited on 7/10/07 by Delinquent]
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tuffnut
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| posted on 8/10/07 at 06:18 PM |
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composites
Have been chatting to Gary at east coast fibreglass.......really helpful guy , been in the business 20 yrs , give him or martin a ring on 01914975134
as they could probably tell you the best way to go about it
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