Hi guys,

I am almost finished with my pattern and I have ordered materials for high temperature mould that will be used for pre preg. I cannot find some answers so I hope you can help me.

First thing is, since I still don't have oven and won't finish it in next 1 or 1 and a half month, can I make mould and post cure it when I finish oven, or I need to post cure it as soon as possible?

My plan was to brush approx. 1mm of gelcoat, brush some resin afterwards and add chopped carbon on sharp angles and reinforce everything with 12 layers of 200g black stuff twill. In total, mould should have thickness around 4-5mm for each part of mould. Is that enough? I am not comfortable using thicker fabrics due to complexity of pattern.

Also, is it maybe possible to "level" some curves with mix of high temp epoxy and milled carbon fiber and pour it as next layer after gelcoat and before fabric? That would greatly reduce amount of work needed for laying fabric reinforcements.

You can sort of consider a mould uncured at any temperature it hasn't previously been exposed to. So it doesn't really matter how long a mould sits at room temperature, the cross-linking can't progress until it is exposed to heat to excite the molecules. You could lay up a mould and put it into use at room temperature for 5 years, and then one day decide you want to use it for pre-preg and give it a post-cure and that would be fine. The one consideration is that it is always best to post-cure as high as your pattern materials will allow while the mould is still supported by the pattern, and in a lot of cases with high temperature resins you can't demould until it has been post-cured at a certain minimum temperature. However if you can resist the temptation to demould before your oven is finished, then this isn't a concern for you.

I would consider anything under 1sqm to be pretty small. At 130cm long, you will want to be thinking about the torsional rigidity of your mould, but 4-5mm thick carbon is going to be pretty rigid, and hopefully your part has some geometry there that will help.

You've somewhat touched on the critical aspect of making wet-laid carbon/epoxy moulds - those air voids can be quite difficult to get rid of, and they will ruin your day like nothing else. It is only that first layer behind the gelcoat that is a major concern, and from there any voids shouldn't affect the surface of the mould unless they are very large. Unfortunately using a torch or a heat gun isn't likely to get rid of voids on the other side of the reinforcement, which is what you are concerned about. A combination of good layup technique, a finned consolidation roller and a bristle roller are the best methods to get rid of them.