Mould Build

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#21

Indeed first layer must have torn edges, or you risk line bubbles which are not nice. I would not risk the second layer either. After that, the problem is not so severe.

About ordinary polyester: This usually has a Tg of 50-60 degrees C or so.
I would recommend a high-Tg polyester or vinylester. What I recommend is a vinylester that has a Tg of some 110 degrees C. Also transparent, so you can chase bubbles. This will survive the high curing temperatures that might be achieved, especially when using infusion.

Oh, and there are also tooling resins which do not need the thickness to cure properly (free of shrinkage). Nord Composites RM3000 is one of them.

#22

Ok thanks for the advice. I will remember ut for the future.

Like I said im just following the manufactures recomendations for the resin. Its a scott bader resin, I have been using this in this way for about two and a half years now and not had any problems.

#23

Check the technical data of the resin. Perhaps it IS a high Tg resin.

If you never let sometyhing heat up considerably in the mould, there should be no problem anyhow.

#24

Great write up. Thanks for the details and pictures. It’s great to see that some of us know each other in real life! The composites world sure is small.

#25

edges for edges! is what i was taught. straight edges on mold edges make it easier for green trimming of parts :slight_smile:
but yeah, anything inside the mold was torn for blending.
i understand about the tooling resin now, but for a hand layup mold that would only have parts in it that wouldn’t heat up THAT much [comparativly], mold made from poly resin and tolling gel would be allright for a while wouldnt it?

#26

Yes, that mould will stay alive for a while.

It is when people change from hand layup to infusion (where you load the complete stack of materials at once) that can give problems due to heat build-up. It sometimes also has to do with poor initiator choice (to much heat generated during cure) as some companies insist on using standard MEKP. They usually learn the hard way.

One of my next projects is infusing a structure with 35mm (1"-3/8) skins. That will be a high temp cure. Luckily fiber/resin ratio is very high, I can use slow and low-temp initiator (Syrgis Andonox MCP) and the part is not visually critical. (industrial stuff).

#27

Well Im finally back in the country and back at the workshop after two weeks in Portugal and spain doing some work.
Anyway havnt got that much work on for the rest of this week so im going to crack on with this mould a bit more.

I have just flanged the returns for the lower side of this nose, In the morning I just need to plastercine the edges and then I can wax, pva and gelcoat. Ill try and get some more pics up tomorrow.

#28

Well I have flanged up the lower side of the pattern for this mould after removing the damns from the upper side.

Note that the mould Is NOT pulled off the pattern untill all mould sections are completed.

IMG_3832 by dobsonm, on Flickr
Yhis is the underside of the part, the two areas in the middle where you can see the board are cut-outs in the final piece.


IMG_3835 by dobsonm, on Flickr


IMG_3837 by dobsonm, on Flickr
I used aluminium for these curved flanges as the board wouldnot bend this far. the aluminium bends and conforms to 2d curves very nicely and is very easy to polish.

This is then given 6 coats of wax.

IMG_3841 by dobsonm, on Flickr

After the wax it is then sprayed with PVA, to do this I use an old paint spray gun with a 1.5mm nozzle. the air regulator is turned down to 40psi. Sprayed on in thin coats to avoid runs on the surface. 5-6 coats is usually sufficient. I find that this gives a smooth glossy surface that is far superior to hand application using a cloth. I generally only use PVA on patterns when mould making.

#29

This is then given 2 coats of Tooling gelcoat once dry.

IMG_3851 by dobsonm, on Flickr

Then a skin coat of 300gsm Chopped strand mat is applied, aloud to cure, lightly sanded, wiped with acetone.

IMG_3866 by dobsonm, on Flickr

#30

The subsequent layers of CSM are then cut and placed on the rack in order. This was the same as on the top side of the mould, all where then applied in one session using polyester tooling resin as before. This is what I have done this afternoon/evening. This will now be left for at least 24hours before removing the flanges and preparing for the next mould stage.

#31


IMG_3869 by dobsonm, on Flickr
Paddle roller to elininate any trapped air


IMG_3871 by dobsonm, on Flickr


IMG_3873 by dobsonm, on Flickr
After 2 layers of the CSM

#32

awesome!! i love that you’ve kept up with the pics and details…
its looking good - are you still on the 2 layers or have you progressed further?
the aluminum flange is a good idea, waxed up it should be relatively easy to pull from that right?
cant wait to see it finished and your first part from it!!

#33

the CSM for the bulking layers, these were 1 x 300g, 3x 450g and 2x600g csm. this is now done on the lower side shown in these most recent pictures.

The aluminium works well in the past I have used it a lot, I switch between the aluminium and the hardboard for the flanges dependant upon where it needs to be fitted, the hardboard is far far cheaper than the aluminium. both pull off with ease once waxed.

#34


IMG_3873 by dobsonm, on Flickr
after two layers applied


IMG_3873 by dobsonm, on Flickr
After 3 layers applied


IMG_3880 by dobsonm, on Flickr
after all the layers applied

It has started to cure by this stage whick=h is why the colour is not totaly even, once fully cured this resin turns to a pale white colour.


IMG_3885 by dobsonm, on Flickr

#35

Excellent and very informative thread - thanks.

A couple of questions to help my learning;

obviously you are making a two part mould which will allow you to make 2 pieces in CF and then bond together to make the complete whole part.

In the images here you have presumably already removed the ‘formers’ that were used to create the flanging alignment spigots - thus leaving the recesses formed from the moulding process.

When you form the bottom half of the mold are you then putting fibreglass and resin into these apertures to create a ‘positive’ project on the bottom half of the mold? Will this positive (or male) piece of the mold release ok from the top half of the mold once it is cured or will this have a tendency to snap off when trying to separate the mold halves?

#36

yes, there is a good draft angle on the allignment pegs. they wont break off because they are almost solid once all the layers are on the mould full of glass strands that spread out in the mould!

Yes the part will be laminated in two seporate pieces (Top and Bottom) then bonded together. There will be a bolt on extra piece to the mould that will give a joggle join line between the two halfs to make a surface that the bonding can takeplace on.

#37

I don’t mean to pull a somewhat old thread back, but are there new developments in this where you attach the pieces together?

#38

Yes I need to add some more photos… Ill try and get some more up over then next couple of days. Im glad that you have brought this up it just reminded me that I havnt put any more on this for some time.

#39

Great thanks. So far it’s great to see in detail the work you have done.