Hi guys,

Because I don't see on the forum this technic of moulding, I think it will be interesting to show you how it work !! I use this technic at work for hollow parts or with small radius.

Let me explain you through a piece for my motorbike :




First step : Machining the model :

With my CNC, I machined the model into PU tooling board (prolab65).

http://uprapide.com/images/invite/img-4495.png (During machining)

http://uprapide.com/image/929238-img-4496_2 (During machining)

http://uprapide.com/image/929239-img-3840 (At the end of machining)




Step 2 : Sand the model

Then I sand the model until the machining traces disappear.(No photo)




Step 3 : Paint the model

To allow molding on the model, I paint it with PU coating.

http://uprapide.com/image/929240-img-3842




Step 4 : Realised the mold :

With unimould product from easy composite, I realised the mold with a little support made of wood.

http://uprapide.com/image/929242-img-3940

Products are easy to work, and the finish was shiny as I wanted.




Step 5 : Realise the mold for silicone intensifier :

The silicone intensifier has the same design as the part. But it's dimensioned just a little bit smaller to be able to get in the mold with prepreg.

I've machined it into the easy composite tooling board :

http://uprapide.com/image/929251-img-3953




Step 6 : Sand the silicone intensifier mold :

Just to have a better finish inside the pièce, sand the silicone mold to make it smooth ! (No photo)




Step 7 : Cast the silicone :

It's time to cast the silicone in the mold ! To avoid air bubble, you must degas it with a vaccum pump. I done this operation a first time after mixed it, and a second time in the mold. No need to prepare the mold with release agent !

http://uprapide.com/image/929259-img-3957 (system)

http://uprapide.com/image/929266-img-3972

http://uprapide.com/image/929260-img-3960 (bubble !)

http://uprapide.com/image/929262-img-3964_1 (unmoulding)




Step 8 : Molding preparation :

With the CAO, I've print out templates to cut the prepreg.

http://uprapide.com/image/929263-fullsizerender_51




Step 9 : Wrapping :

http://uprapide.com/image/929264-img-3970

http://uprapide.com/image/929265-img-3971




Step 10 : Place the silicone :

Use non perforated film to protect him from the resin. In this way, it will be able to do a lot of moulding !

http://uprapide.com/image/929267-img-3974 (No exact photo with the prepreg, but it looks like that)




Step 11 : Close the mold and cure !

I close the mold with a plate and clamp it very strong.

HOW IT WORKS : Silicone has a very high coefficient of thermal expansion. When you cure the prepreg (at 100°C in my case, because unimould tooling system cannot up more), silicone expand because of its CTE and it presses the prepreg on the mold.

This is why you have to close very strong the mold. (In some of our project, silicone is so strong that it opened our press (100T) !!)

Then cure the prepreg !




Step 12 : Demoulding !

Some pics just after demoulding :

http://uprapide.com/image/929268-img-3991

The pièce is very beautiful, even without polishing or clear coat it ! All the little corners are well compacted. I think (I don't try) that just a vacuum bagging cannot do the same thing...




Step 13 : Finish the part :

Deflashing and clear coat it :

http://uprapide.com/image/929269-fullsizerender2_3







Hope you enjoy and help you for your project !! Feel free to ask your question and correct my English mistakes !!!

(I've not been able to directly insert my photos, so if admin can ?)




Julien

Very nice end product.  It is interesting how much force the expanding silicone can apply to the mould. 

It really could be a useful technique for complicated or awkward parts to bag.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

You can buy heat cure silicone sheet and make your former in the part when you do your 1st cure

NO need for another pattern/mould or having to mix/pour silicone

might save you a bit of time and effort

try vac innovations or synflex

Hi,

I know silicone sheet (mosit/fenform) because I work with at work for vaccum prepreg.

But for this part, two reason why it doesn't work :

- Edges are too small (maybe you cannot see on pics),

- It's an autoclave prepreg must have more than 1 bar of pressure.

Moreover, this technic works well for part that you cannot have vaccum bagging (frame, extruded shape...).




But silicone sheet works well to help the vaccum bagging !!




Thanks,

Julien

I don't mean cured silicone sheet

What I am talking about is raw silicone that is a heat cure system that is similar to putty/plasticine and once your part has the release on it can be pushed into your mould,even the tightest knife edge corner and you make your silicone intensifier as small or as large as you want

when you cook your part that also cures the silicone and when you strip the part you have your silicone part just like the one you cast that can be used again an again

Yes I'm talking about the same thing. It's call "Mosite" but we buy the same product called Fenform (Axson). I've already realized intensifier for my company with this raw silicone that becomes stiff after curing.

But it's just an help for the vacuum bag and it's always the vacuum bag that press on the Mosite and prepreg. You cannot have more than 1 bar (-0.95b...) without autoclave.

Massive silicone, like I present, can replace autoclave : When it expands, it press so hard that you have a lot of pressure on your prepreg...

To help you to understand the real utility of massive silicone, have a look to the pictures :

http://uprapide.com/image/929818-frame_4

This is a frame with U section. Mold and counter mold with silicone intensifier. Impossible to realise with vacuum bag...

And this is a silicone intensifier in fenform that I realised :

http://uprapide.com/image/929820-fenform 

thanks for sharing! small question, how much space did you calculated between your outer mould and inner silicone core (the place for you prepreg) 

Hi Matt,

I've create an Excel sheet that gives me the exactly thickness of prepreg. So for this project, I calculated 1.47mm BEFORE curing.

In this way you have to create the silicone mould minimum 1.5mm smaller.

Now, let's calculate how much the silicone expands with temperature:

For a 100mm silicone (this is approximately the size (width and length) of mine), for 20°C to 100°C, the silicone will expand of 1.7mm. This is your margin !

In this way, you know that you can create your mould between 1.5mm and 3.2mm smaller in width and length ! I think I had chosen 2mm.




But for the thickness (topplate), silicone will expand a little less because it's smaller. Silicone thickness is about 20mm, for 20 to 100°C, it just expands of 0.3mm. So I've created my silicone mould just 1.5mm smaller (prepreg thinkness). When I close the mould, the plate comes touch the silicone.

I hope I was clear, otherwise, don't hesitate to ask for more details !

Julien

great, thanks for the great and clear information!

Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com