Use of VE resins for large pre-preg female mould

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#1

Some advice please!
I am currently working on a project that needs a large female tool.
The tool will be 20m x 6m and is for a race yacht prepreg hull in Gurit SE70
Target temp 80-85 Celsius. Minimum 3x cure cycles.

Female tool laminate thickness will be 9mm for all options.

The options on the table are:

  1. To build a CNC male plug and make a carbon/epoxy wet lay & Vacuum female tool.
  2. Build a direct to female mould in carbon/epoxy, epoxy tooling paste & CNC’d.
  3. Build a direct to female mould in carbon /Vinylester, epoxy tooling paste & CNC’d.

My preferred option is either 1 or 2… I have used these methods before.

The CNC facility would like option 3.

I did some homework and the VE resin that the supplier will use has 8% shrinkage on the data sheet… Which makes me very nervous!

My priority is Dimensional accuracy as this is not your typical yacht.
Can anyone with direct experience of large VE & Carbon female tools give me some pros and cons?
Is 8% in the normal range for VE resins.
The resin in question here is “Distitron” VE 100 ST

Thanks.

#2

Why using carbon for your mold ?

I whould go for option 4. Build a direct to female mould in glas with the first layer vinylester and the backing layers with a polyester tooling resin. Almost no shrinkage, but that depends with resins you use.

Some resins I use are: Derakane, Norester, RM 3000 and Optimold 2.

#3

The CTE of glass is too high which is why ideally you use carbon tooling for carbon parts on large structures. Pre-release would cause big problems.

#4

Or you could do option 4… Have Gurit Tooling make it for you;)

As for option 1, I would suggest you infuse rather than wet layup. It will probably be easy for you, cleaner, and better quality.

Option 2 is viable, but you will need to check the ability/limitations of the CNC . You probably need to do many sections of DM and connect after CNC. Then you have an issue possibly with vacuum integrity. Also, make sure your tooling paste has a Tg high enough to account for your cure cycle. If its not high enough, it will crack and probably cannot be able to use a second time if you ever needed to.

Good luck!

#5

Thanks Hojo…

Any experience or comments about the VE and carbon?..

#6

And you are right, the DM is in four sections to facilitate machining and transportation.

Two main parts with a centreline join that is bolted and then taped over with carbon to connect the halves permanently, the other two parts are within the Vacuum envelope and a non issue.

The tooling paste has a Tg 80-85. Checked that and we have done test panels as well.

The biggest problem is that it’s CTE above that temp is too high.

The perimeter for sealing the bag on too- will be the laminate face and there will be no bagging to the paste! I am hoping that it will keep the paste in check and prevent it cracking.

#7

I have never used VE with carbon for tooling basically because the reason I use epoxy with carbon is for its strength, tolerances, and combined CTE which maybe in some cases you could reach with a really good VE, but then, why not just use epoxy. If youre concerned with accuracy, then I would suggest you use epoxy/infuse the mould. If not, then you can probably just get away with a VE laminated carbon mould for one or two parts. Just be sure the HDT/Tg is greater than your curing temp

#8

My are for concern is that if the VE is used, and the carbon laminate isn’t perfectly balanced (9mm is a lot) that it will twist on the weakest plane…

Due to the shape of the hull - even with the use of epoxy you will see this happen on a small scale, but this particular VE has four times the shrinkage of most epoxies.

#9

I’ve worked on cnc’d moulds for prepreg production, and distitron gives some shrinkage. I’m sorry I can’t tell how we solved the problem, but it can be done. Epoxy geve less shrinkage, but the framework and foam(?)support will have influence too. Can’t the facility give any insurance? tho what kind of stability are you looking, within 0,5 mm?
Anyway, Mouldcam (europe) has done it before for Rondal, Mouldcam UK has close ties to the facility here. If you aren’t a client, I would suggest to get in contact to them. But I’m saying that as an ex- employee :stuck_out_tongue:

#10

Things that can be calculated and fixed, but I understand your point of view. If accuracy and quality are your priority I whouldn’t even think about wet layup or VE and go for epoxy and infusion.

Why does the CNC facility prefer the VE ?

#11

Thanks for the info Susho,

I will call the people I know At Rondal and see what their experience was with the VE tooling.

Was it a large structure, and for more than one cycle?

Most of the Parts that they produce are for Superyachts and get 10mm of filler on them so dimensional stability is not quite as big of an issue. I would like no filling on the hull, just primer and paint!

0.5-1.0mm would be my tolerance for accuracy.

#12

Price and their workforce knows VE and polyester.

#13

The people at rondal aren’t very informative abouth their production techniques probably. parts around 20 metres in length, for parts of the rig. can’t tell a lot more than that. After I left mouldcam europe they did a hullmould for multiple cycles. Those tolerances are quite hard for a CNC that can handle those kinds of moulds, let alone at those temperatures…

Anyway, the best option is probably 2. Less shrinkage: easier to control. If you have a cnc facility who knows what they’re doing, it shouldn’t be a big problem to manufacture close to their machinespecs. wet laying/vacbagging your own mould gives a bit of shrinkage too, and is more work. The CNC facility should be able to cope with the shrinkage.
But costs, the VE option is cheaper?

#14

Thanks for the input everyone!

The decision has now been made above me to use the VE… So let’s see.
Odd how people who don’t use the materials, understand their unique characteristics or believe in testing - ultimately decide!
I am hoping for the best, and preparing for the worst…

#15

Good luck with the moulding.

With the SE70 curing at low temperatures could you have used it to make a female tool from a male plug made of cheap materials?

You could then have postcured the prepreg tool and generated the required end use temperature with little shrinkage.

#16

If there was the budget for a prepreg female tool, then this thread wouldn’t exist!

I have been on a build team that has the budget to do just that and without hesitation, I would do it again. The difference is incredible.

That boat still holds the 24hr monohull record ( for six years)
But, with the new breed of 100’ super maxi’s being launched, I doubt it will hold for much longer.

So, I have been trying to predict the areas that may cause issue and I have worked out a build process that involves a procedure to reduce the risks as much as possible.

Even with these steps, after discussing at length with a colleague with direct experience in this style of mould- A carbon VE tool will expand a predicted 5-10mm over 20m.
Managing the pre-release is going to be tough,and I can forget dimensional accuracy of >1mm