What method for Carbon Fiber Moncoque, and mould building

[CSUNFormulaOne]

Hey guys,
the last two years we have used prepreg carbon fiber for our front monocoque. We have two freezer and plenty of prepreg. We have free autoclave access but its is a 2hr drive each way.

The entire process just takes too long. We want our car to touch ground earlier this year.

We are building experimental Vacuum Infusion Test Panels. We have experience with this and have had success with small parts.

What I want to know is: How many Moncoques are using Vacuum Infusion? Why did you NOT go with it?

My Mould building question is this:
Assuming we want to machine our female mould and use the prepreg we have, which cures at 350degrees. What options for mould material do we have?

The foams we have melt at 300 degrees, or their density is 15lb/sqft which would not stand up to the autoclave pressures.

What do you think we should look into for mould materials? This is really our backup plan.

[CSUNFormulaOne]

Hey guys,
the last two years we have used prepreg carbon fiber for our front monocoque. We have two freezer and plenty of prepreg. We have free autoclave access but its is a 2hr drive each way.

The entire process just takes too long. We want our car to touch ground earlier this year.

We are building experimental Vacuum Infusion Test Panels. We have experience with this and have had success with small parts.

What I want to know is: How many Moncoques are using Vacuum Infusion? Why did you NOT go with it?

My Mould building question is this:
Assuming we want to machine our female mould and use the prepreg we have, which cures at 350degrees. What options for mould material do we have?

The foams we have melt at 300 degrees, or their density is 15lb/sqft which would not stand up to the autoclave pressures.

What do you think we should look into for mould materials? This is really our backup plan.

[DART-CG]

Hi,

we used the prepreg technology for our monocoque the last two year and were really satisfied with it.
We first milled a positive mould from BM5055 eopxy resin, afterwards we laminated a negative CFRP-mould from tooling prepregs.

We did so because the prepreg technology guarantees the best and the most consistent results.
I would not recommend to use the vacuum infusion if your design is near the physical limit. Even a small air bubble embedded in the cured matrix system in a zone which is stressed in bending may lead to delamination.

You seem to have a very very good access to the machinery necessary for prepreg technology and the pregpregs themselves. I would suggest to use it!
BM5055 is quite expensive as a mould material, think about Uriol or an aluminium mould. Our prepregs were cured at 120?C, those mould materials will withstand this thermal exposure without problems.

[Moke]

We infused our first attempt at a monocoque. We had mixed results, there were no dry spots but we did have some resin rich areas, so it was a little heavier than planned. After the experience I would warn people away from it IF they have access to pre-preg, if you don't but want to try a monocoque I'd say be careful but it does work. If you have a good vacuum and wait long enough you can get nearly all the air out (we archived 1mbar after 12hrs)

As for moulds we start with a machined UDF (uniform density fibre, kinda like MDF but without the hard skins) male plug of the chassis, this year the plug was made in a left and right side. These were Duratec'ed and then we set them up on a large aluminium plate. We made female composite tools off these using a high temp tooling epoxy gel coat. then 1200gsm quad axial glass was infused onto the gel coat using a high temp epoxy. The epoxy is produced in NZ so I doubt you'd be able to get the exact same stuff we use but there would be something similar around. This method produced very stable moulds cheaply and quickly.

[RiNaZ]

The disadvantage that you have with infusion is that, once you start the infusion, there is no turning back. If you didnt get a good suction, or there is air or leak in your lamination, it's going to be hard to fix it. I agree that infusion can be a lot faster than hand lay up, but in your case, with zero experience, i personally think you should stick with hand lay up.

What you can do, is test whatever materials that you have for your mold in an oven or something. Get a high density foam, and heat it up till 300 and see if it can take the heat. Or test with MDF or something. You just have to find a solution for this, but opting for infusion when you have stacks of pre-pregs available to you is not one of them.

when you have free access to the autoclave, does that include the operator? You're probably gonna spend the whole day trying to cure the chassis.