flanges for autoclave prepreg tooling

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#1

Hi everyone,

OK ive been doing composites for 7-8 years now and i have a small company making automotive and motorsport products. When we make moulds we normally cut patterns from cnc/tooling block but i have a few products that i need to make moulds directly of the pattern from in prepreg. Ive done wetlay glass/ carbon which is fine but as the pattern and flanges will be under vacuum (envelope bagging) the flanges need to be very strong and not come away from the pattern when under pressure/heat.

What im struggling with is what is the best thing to stick the flanges (and what material to use for prepreg flanges) to the pattern and as the patterns can be quite complex shapes, the flanges may only be edge-edge bonded in some areas with very minimal bonding footprint…

Any help would be much appreciated here guys as its one thing im struggling to solve!

thanks in advance and i look to hear from you soon

#2

So…you are making a mold, off an original part, using prepreg as the mold material? And you need to figure out how to model in flanges?
I would try epoxy adhseive and sheet aluminum. Not knowing the part, it is hard to make many guesses. Tooling foam can go high temp, so you might try to use that as a part-to-tooling flange.

#3

Hi Riff42,

Yeah we need to mould a motorcycle fairings (various models), and i know where the split lines will need to be but the issue is getting a flange/split lines to stick to a surface without damaging the part ( as i need to be able to remove flanges during mould process) metal or carbon sheet im guessing will be fine as its only going to 60 degrees but whats the best material to stick the flanges to a part that is strong enough not to bend or snap off the part under load?

basically i think i need to find a very good adhesive that can be removed, like a very strong tape or adhesive that can hold flanges with minimal footprint, or techniques with taps possibly? But any experience or ideas would be much appreciated.

#4

Do you really need to vacuum bag the mold making process? You can often use hot glue to the hold flanges in place. The hot glue typically will not permanently stick to the master.

If you are determined to vacuum bag the mold then you are going to need to build a parting tray. This is wood or composite structure the master mounts into that follows the parting contour. If the parting line is complex then they can be difficult to make. It is possible though. There can still be issues with vacuum bagging these. The vacuum bagging can displace the master in the tray, break the seal between the master and the tray, damage the surface coat in the seal location, and force resin through the seal.

#5

Hi Wyowindworks,

Thanks for your response, yes the idea for the bag is that the material is prepreg but i understand what you mean. It will be alot of work and i think we may need a “scaffolding” style flange arrangement so it has structure on the underside.This will be difficult to do on a bike kit. UNLESS… i could make good strong (extra wide) flanges with a 3m style adhesiveand single side bag the part. That way as long as we seal the flange correctly ( epoxy spray coat the part and flanges to seal air paths) the bag wouldnt pull the flanges downwards? any thoughts here?

But it may just be easier scanning the part and cutting it from block! :slight_smile:

#6

I use Axson SC258 with great success for doing this job.

#7

Axson sc258? What is this? An adhesive?

#8

It’s a modelingpaste.

http://www.axson.com/sites/default/files/sc258-gb.pdf

#9

Can the axson handle autoclave temps? The stated Tg is only 53*C.