High Temp (Carbon) Mold Making?

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#1

Hi Folks,
Having a difficult time finding the answers to my questions. I want to make a High Temp 2 part female split (clamshell) mold for carbon bicycle chainstays and seatstays. Parts will be made from Prepreg 275F cure. I can’t seem to find any reference materials or info on how best to do this(make high temp carbon molds that is), and wondering if anyone has any suggestions. I’ll be inserting a bladder for pressure.

I plan to make the plug out of wood and layup the carbon over that at room temp using ez lam High Temp epoxy and gel coat from acp composites in CA.(then post cure). I read somewhere that my mold should be 3 times my part thickness. SO. . . this means that I would have molds approx. 3/8" thick or 20 layers of 2x2 twill (.019). Can I just use twill for a mold, or should I be using uni as well? Any stiffeners, or “bulking agents” that are used in instances such as this to reduce the layering and build a stronger/thicker mold? Anyone tried this, and how many layers at a time, 10 and 10?(if just carbon alone).

All the molds I’ve made have been milled from aluminum and very small. So this is a new endeavor for me. Appreciate any help. Thanks.
-M

#2

I would use 3k for surface layers and 12k carbon to bulk up the thickness. This will save lots of money. As far as how thick, that will depend on geometry, mould structure (if has) and bladder pressure that you will be applying. Best way to find out is to run FEA. If possible I recommend that you infuse the moulds as the quality will be much better than wet/vacuum mould.

#3

3/8 is too thin and unstable for high pressure bladder work. The mold will bulge at the seams.

I would make the mold to around 1" thick by creating a fiber/tooling dough/fiber sandwich. This will be much stiffer to handle the bladder.

Putting 3k carbon against the tooling will create some print-thru issues to the mold surface.

#4

Why not go with CNC Aluminium?, I have been using this system for 10yrs. now with terrific results and constant quality.



John Hayes
www.bladerunneroutriggers.com

#5

If this is a production bike part, go with the metallic tooling, aluminium if handier and dimensions are not highly critical (or CTE is accounted for) or steel tooling if you can get it machined cheaply enough.
Im guessing you arent overly worried about tolerances given that you want to lay-up initially on timber and post cure things, so perhaps aluminium is the way to go?