If a large mold is going to be hand lay up with epoxy resin, how many layers should be laminated in order to get the mold airtight and appropiate to produce parts with resin infusion?
Typically I try to make my molds 3/8ths or so thick. For molds in my opinion it’s the thickness you need since you are trying to build up for it to not flex. Unsure on epoxy molds since I’ve never used one but probably will be doing it sooner or later when I have tight tolerances.
Its better that you infuse the laminate, it will be less permeable than hand laminated. What level of vacuum integrity are you looking to achieve?
And what means large for you? 2m or 80m?
6m x 1,5m. I was looking at an alternative to poliester molds. I thought i could achieve rigidity by using 3d core or lantor sandwich. However i am not sure if it will be airtight. Due to how the falnges are setup i cannot vaccuum bag or infuse the mold.
I can’t even imagine how you could possibly build a mold that is not airtight , the first surface coat alone has to be airtight.
I can tell you one thing, you are building your project starting with zero experience but yet you are building the biggest pieces first ,
That means you are doing all your learning and the typical mistakes on a giant scale, making it much harder on yourself.
You should have learned and tested your tool building process all the way trough finished parts on much smaller pieces first, then apply what you learned that works or doesn’t to the big ones.
The stabilator mold is a bit smaller but really doesnt make a big diference 4m x 1m. I will start with that smaller mold but in poliester, as handling wont be a problem. However the wingmold will be huge and handling becomes an issue. Once finished i will need to get the mold out of the basement. Therefor i am asking, if i do it out of epoxy, could i save one third of the weight by using sandwich and stringers and still have a tight mold. Are all epoxy resins shrink free?. For poliester molds i got from the provider precise instructions on layups and all the steps. For epoxy molds i lack that information and dont know where to start.
We often have made mould by infusion and epoxy with core material. Also I often used 3D core. The moulds have nearly shrinkage, maybe a few 1/10mm on 1m, but nothing critical.
For a tool that size I would definitely do infusion over hand lamination. It will be faster, likely cheaper, but more importantly the quality and tolerance will be much better. Key is to have a nice strong, stiff baking structure for your mould surface. Since your mould is likely static, I don’t think you will need a super thick laminate. 10-15mm of fiberglass (much less if its carbon) is more than enough assuming your backing structure is suffice. If you plan to have these moulds for a production run of many parts, I would go to the thicker side, if only a few sets, thinner. As far as vacuum, even 5mm infused laminate is sufficient (Assuming successful infusion). How are you planning to cure your parts in mould? Whats the process for your parts?
Thanks for the reply. I wish i could infuse the mold laminate, but I really think it would be imposible to fit the bag. The support structure is sturdy and the flanges are supported by a wood structure that is impossible to bag.Between the wing and the flanges there will always be leaks.
It wont be a production mold, just a few sets.
The parts will be infused.
I would like to cure the parts in the mold. 70ºC is the minimum cure temperature as parts heat to over 70ºC exposed to the sun. I would use a curing tent.
So you state that 10mm glass epoxy laminate would be the minimum if hand layuped? What cloth would you recommend? What resin fraction would you recommend? The resin to fiber ratio in poliester systems is 4:1. Thats an absurd amount of weight.
How would things change in case of carbon fiber? What type of cloth?
Do you disregard a sandwich?
I have hand layup moulds in production made with Optimould II Polyester resin. That one is quite good, no shrinkage and it is easy to laminate with CSM. 10mm will be about ~8-10 layers of 400g CSM.
Somehow it is easier to get a tight hamd layup mould made by PE than wuth EP.
I think 10mm is ok, but of course it depends on your supporting structure. I think if hand laminating, then go with a PE, or VE tooling system as DD has already suggested. Scott Bader has some nice systems. Epoxy is tough to hand laminate unless using vacuum. If youre going to use carbon, then I would only suggest infusing. And I think in your case just cheap 3K and 12K is suffice. Sandwich laminate is ok, but for tooling its better to do that in multiple stages, depending on the type of core, of course.
It is only a mould, and will not see a lot of stress. I would make the mould out of polyester tooling resin. It can be fairly thin / lightweight.
I am not familiar with your project (just jumping in from a 2 year detour) but if a bit of sanding and a coat of paint are acceptable, I would not worry too much about surface quality.