Front Wing Cores

[marcush.]

sure this is funny but a bit too expensive just to see it blow up like a baloon...

so you produce an oversize core and manage to get it inside the mold.Hey..thats not going to work...Make it just right to size and lay up your laminate and still you will have no chance to close the mold,let alone have plies overlap from one mold half to the other.This is just not going to work out if you ask me...then what for is the autoclave in this? or the vaccum bagging -just to close the mold? or is the mold so weak it needs the support of the vaccum?
I always thought the vac was used to really push the fibre layup to the moldsurface.
don´t get me wrong I do believe it is done like that ...sort of ..but to me some key elements are missing to make it feasible.

[conni]

when i say its oversize its not really oversize

the rohacel would be a loose fit in a empty mould but would be a perfect fit if you laid up each half and cured them individually at 90psi as the cured thickness is less than the uncured due to the consolidation of the plies so when i do it i always put the rohacel in the half with the overhanging plies then vac it down so it crushes/consolidates then put the top on bolt it up job done
the reason for bagging is that it is such a tight fit that you would stretch the bolts trying to fully close the mould if it was a metal mould or damage it if it was carbon but once its warmed up the resin flows and the plies consolidate and it all sqaushes together

conni

[marcush.]

now we are getting closer to the core.
But hows the top half of the wing attached to the core?
you remove the peeloff fabric after vaccum and simply layup the plies in the upper half and close the mold?where is the pressure coming from to bond the core to the upper half? you use a resin film ?
I somehow get the idea now ..

[polarboy]

You use a film glue,unless you have a resin system that is core bondable like 28b
closed mould wind/flap moulds are a pain to close an get right(but once you work out how they are easy as anything) an the core might be just under,to size or over size depending on the part being made an the layup being used .As conni said there are tricks of the trade to get round it and a average size wing mould will have about 40/45 tons applied to the top surface in a clave at 90psi,more than enough to give it than final squeeze
Well known phrase both conni an i know "the clave will sort it out"

[conni]

lol the clave will get it and living the dream

conni

[marcush.]

tbh ..are those parts dimensionally accurate coming out of the mold? I don´t think it is possible.And for me ..working in an automotive environment it is pure
horror to hear about your degree of freedom in having reproduceability or traveability..it is more of a experience and finesse thing (which I really like ,by the way..!!)
To me it seems almost impossible to produce two exactly same parts.

[polarboy]

Parts are all cut on a computer controlled cutting table so all of the kits of carbon you get will be exactly the same,if your doing foam cores they will be CNC machined an will all be the same and when you come to do the layup you will be using the layup books so all parts will be done the same
If your doing internal bagging or foam cores all the forces are exerted pushing the laminates to the mould surface so all parts will come out the size of your mould every time
You can read a lot of books on composites an how its done/how to do it but when your actually at the coal face doing the job its a bit diffrent an there is an awful lot they dont mention in books or material spec sheets
Then again dont think that any of the obove has ever been written by someone who has actually done the job

[marcush.]

polarboy...I do understand what you say and I can follow your lines still the bit putting the top half onto the bottom remains a mystery to me .

You have bagged the lower half with resin core and laid up the upper half all plys and put the two halfs together ,bagging the whole lot and putting it in an
Autoclave building up the pressure and heat.
But hows the alignment of the bottom and top molding halfs ensured? I would put pins trough the top and bottom half of the mold ...but with the tho halfs not closing before the heat is applied ..as soon as you apply the vaccum the bag will get trapped sucked between the two halfs and gets ripped or acts as a spacer preventing fuly closing of the mold.
I´m pretty sure I´m missing something there.

the rest is pretty clear though.

[conni]

we bolt the 2 halves together then wrap it in release film and breather and put it in the bag

conni

[conni]

its unlikely that any 2 parts will be EXACTLY the same but they will be close enough to do the job

conni

[marcush.]

conni that was my damn point excatly.i feel those parts will have some -lets say personal cue -to them ...a degree of ,ahem, freedom.Wonder if those wing sections go through a cmm and just how much tolerance in F1 one would allow.

[sticky667]

hey conni and polarboy. maybe a few pix of the process if possible to follow a little better.

thanks!

[polarboy]

As conni said the moulds are bolted together,if your doing a part with a solid foam core if your using Rohacell 51 it wont take pressure (if you use 71 you can stick 90psi on it and it wont affect it)but it wont collapse in a closed mould situation but it is soft enough that even if its 1/2 mm over size it will compress down when bolted together.
On a wing on the trailing edge the top an bottom skins join to form a solid section so even if your wing is 90mm deep your foam will be 75mm long to allow for where the skins join on the trailing edge.So taking a cross section of your wing if its 20mm an your foams 21 it will compress an your foams 76 it will only be 1mm into the no core section al that 1mm will easily compress
Your moulds will be ali or carbon,the ali will be drilled an tapped for bolting fixings and there will be dowling pins to jig the mould together as you join it.the carbon moulds have the joining/location pointd bonded in when you 1st make them.With hollow wings the moulds are joined in the same way buy if you push the laminate down when you place the top section of the mould it dosent matter as when you vac the mould down the internal bags will push the laminate back out to the surface when the internal bags expand out
Sticky I will see what i can do RE photos but never posted any before but im away for another week

[polarboy]

When parts are designed the inspection details are on the drawing for the component,the patterns will have full CMM,not normally done with the mould as the mould should be exactlly the same as the pattern (not totally true thou as if your using painted patterns they will be machined 20 thou under size to allow for the paint finnish)
When you have a finnished part it will norally be checked for x,y,z dimensions that are relavant,fixings,holes,thread depths etc not full CMM as part should be the same as the mould

[Mystery Steve]

Polarboy,

That would be great if you could post pictures of the overall process of the layup of a wing. I know I would personally like to see a better method than simply wrapping carbon cloth around a foam core then slapping resin on it and calling it a day.

Or if anyone can recommend any books that actually go into technical details of advanced layup methods (not just wings, but in general) and composite design from a design-for-manufacturing perspective, that would be appreciated. I already have some experience with the materials and tools, and I've taken classes dealing with the structural mechanics of composites, but I'm looking for something that would help in the design process from a practical point of view. I've found a dozen or so books online, but I haven't been able to find a bookstore in my area that carries books on this topic, so I'd be buying them blindly.