Materials for making moulds

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#1

Hi all!
I´m producing some carbon fiber automotive body panels using infusion.
I´ve been using the uni mould system from easy composites UK that consists in a vinylester gel coat, coupling coat, and poliester resin to back up.
They claim their poliester resin is filled and suitable to use with post cure with temperatures to about 90 degrees. But they don´t give any datasheet on the resin.
Problem is that i´m experiencing some issues with this system beeing:

  • gelcoat is not sprayable (or at least i cant find any info were they say it can be done) and i prefer to spray over brush.
  • i´m getting voids under the gelcoat no matter how hard i press the fibers
  • i´m getting lots of print through on the gelcoat
  • it distorts quite a bit and the maximum temperature i use in post cure is 60º
  • it´s from UK so price is in Pounds and makes it very expensive to buy since my country has Euros as main currency

Can you recommend a mould making system that is suitable to use with resin infusion and oven post cure?
I would prefer a poliester/fiberglass based one has i only produce maximum 20 parts from a mould and want to keep my costs low on that. But if you use any other option i can also go for it as i prefer to spend all the time at once in the mould and not beeing always repairing/fixing it

Thanks in advance for any help.

#2

Hi Wochi,
I utilize tooling system resins from NORD COMPOSITES:

  • Vinylester tooling gel coat NORESTER GC 207 (spray application)
  • Skin coat NORESTER 842 TPA
  • Mould resin RM3000
    Hope it will help you.
#3

The unimould tooling gelcoat can be sprayed no problem.

Voids under the gelcoat sounds like you haven’t quite got the technique right. However if it is unavoidable and you do trap some air, I simply allow the skin coat to cure to a green stage and then cut the voids out with a sharp Stanley knife. Then you can either fill them with a bit of skin coat, or I just carry on with the backing layers and let the tooling resin fill the voids. This has worked well for me so far, despite the tooling resin being mineral filled.

#4

what type of gun could i use to spray it?
As for the voids, they are not visible. i can´t spot a dry area in the coupling coat. Usually when i demould everything looks fine, after one or two infusions all ok. But then at some point the gelcoat goes down and i get a bump in my part.
Another problem is the amount of resin. They say that (rough estimate) if i use 1kg of gelcoat and 1kg of coupling coat i should use 4 kg of tooling resin with the 4 layers os 450g matt. but i can only full wet the mat with much more resin. at least 8 or 9kg , almost the double. And even so i get dry spots.

#5

thanks. I will contact their reseller here to see what i can get to try that system.

#6

Best way to make a mould is to infuse it (in my opinion). This eliminates voids/blistering. The quality is superior to hand lamination, and depending on the size, it can be faster. Depending on your out of mould finish requirements, you can skip the gelcoat. Gelcoat is the weak link to a mould. Better without it unless you require a very high gloss. Thats my two cents. Good luck

#7

infusing a part seems a very good idea but how do you do it?? how can you get vaccum when all you have is a part with some fillet wax and flanges that most often can barely take the strikes of the brush so wouldn´t take the “force” that vaccum makes for sure.
Not using gel coat, never heard of such technique but i need my moulds to be as perfect as possible as most of the time they are for cosmetic carbon parts

#8

You need solid flanges to infuse a mould. Works well if you are building a pattern from scratch and can build flanges on.

The voids in the skin coat are caused by trapped air bubbles, not dry spots. They can be difficult to spot sometimes, you need to look closely.

As for the amount of resin you are using, I think you are reading that wrong. You need a 4:1 ratio of tooling resin to fabric. So for a 1 square meter mould with 5 layers of 450gsm csm, then you will need 9kg of resin.

#9

I usually take moulds from auto parts that already exist so i think it´s not an option to infuse :frowning:

As for the tooling resin you are correct but even so why do they sell packs of 1kg gel 1kg coupling and 5kg tooling? it should be 1:1:5 and not 1:1:9…

I´m not unhappy with the system but i always look for other options that may suit better my workflow and skills :slight_smile:

#10

Yea, of course thats the catch 22. You can take the time to make solid flanges using a material like MDF and then seal to your master part using something like epoxy/cabosil. You will need to leak check before starting lamination. If you do choose to use a gel coat/surface coat this will also seal any potential leaks.

Last option is to splash a VE/PE/Epoxy mould by hand lamination, splash a plug of the splash mould, infuse your final mould off the splah plug. Its time consuming but if your looking to make a high quality mould then this is a good way to go.

#11

Because that’s the sizes that the packaging comes in. I buy epoxy that has a 100:30 mix ratio, and that comes in a 4kg kit with 3kg of resin and 1kg of hardener. That inevitably leads to me ending up with excess resin and not enough hardener.

It’s not convenient, but that’s the way it is. The guys like EC that are distributing the material are not making the containers to store the resin in. And yes they could probably sell the kits in 1kg/1kg/10kg containers, but that likely doesn’t suit their majority market. Most people are probably doing small projects and are happy buying the 5kg kits.

#12

that should leave you with excess hardener and not excess resin… Even the packs from EC come with exact amount of resins and hardener so i don´s see why the toling resin is different.

#13

Yeh my bad, meant 70:30 ratio. Every 3 or 4 kits I need to buy an extra 1kg bottle of hardener to make up the difference. Annoying as hell, but that’s how it is.

I understand your frustration, I don’t like things being ‘messy’ like that. End of the day, despite the efforts of companies like EC, composites isn’t really an industry geared towards supplying the average hobbiest, so small quantities are always going to be a compromise.

#14

Thats exactly why i´m asking this questions because i want to place a “big” order like 100 or 200kg. Ordering 25kg and waiting a week to get them is a bit anoying and i can spend that on a simple hood mould. My next project will be a pair of doors so at least 50kg i would need just for that.