Mold Layup Schedule?

Hi Guys,

I’ve learned allot from your forum; spent a bunch of time going through posts related to my current project. This is my first post. I’m getting ready to pull the trigger on mold materials and I wanted to see what you thought before I proceed. I’ve done many smaller molds (8-10 CSM layers thick) using tooling resins for RD projects but this one is quiet a bit larger so I’m proceeding cautiously.

My project consists of a male EPS plug that’s been faired and ultimately coated with Duratec high gloss coating and wet sanded to 1500 grit and fully polished. The shape is some what like a canoe hull 20 feet long with 3 feet of maximum draft. I’m going to use Nord RM 3000 (VE tooling) due to its lower peak exotherm properties – I’m concerned about the plug suffering during the molding process, after all its a combination of several different coatings all with different expansion coefficients.

Here’s what I’m thinking for layup schedule:

Tooling Gelcoat
¾ oz surfacing veil or CSM – let cure
1 x 1.5 oz CSM – let cure
3 x 1.5 oz CSM – let cure
3mm coremat with 1 x 1.5 oz CSM on top – let cure
4 x 1.5 oz CSM – let cure

I’m debating about using surfacing veil or light CSM as the first layer after gelcoat. I’m leaning towards the veil so print-through is less of a concern. The first layer after is a single layer of 1.5 oz CSM just so I keep the thermal load down, then I really start building thickness after that.

Any additional direction you guys can lend would be appreciated.

Thanks!

 

Wild guess! If it is like a canoe hull it is not a canoe so it must be for a cat?

So you don't want to mess up the plug as you would be switching parts of it around to make a mold for the other side? Anyway, none of my business just curious.

I would use veil and then a thinner first layer of csm and then keep building up allowing enough time to cool in between so heat doesn't build up.

Once done measure your symmetry and form a jig out of welding pipes ending in really flat pieces against the mold and I use mixing PU foam for attachment points with a film around it so once you unmold the flexxy mold from the plug you can attach it to the jig in all the right spots so you have dimensional stability.

You don't want to have anything hard or in concentrated small areas in uneven thickness in the flat areas of the mold or it will come through and distort the surface on the other side. So make your jig attachment areas large flat and with materials that will allow some movement to the mold. Big flat areas with PU has worked for me, I just put some resin on the outside of it and paint to protect it from UV.

 

Hey, thanks for the reply, I really appreciate it!

Na, not cat... It's actually not marine craft related but you guys have a great deal of knowledge when it comes to these types of molds so I wanted to ask the group. I'm sorry that I can't provide greater detail; maybe after its released later this year I can post some pictures.

It's not that I'm too concerned about re-use of the plug I just don't want to stress it out if possible, which could be an issue for the mold surface. Although, it would be nice to be able to re-use the plug in the future. I agree that the trick is being careful with the heat but I also need to balance this with the requirements of the RM 3000 – the thinnest layer that they want beyond the skim layer is 1 oz CSM. So I could do:

Tooling Gelcoat
¾ oz surfacing veil or CSM – let cure
1 x 1 oz CSM – let cure
3 x 1.5 oz CSM – let cure
3mm coremat with 1 x 1.5 oz CSM on top – let cure
4 x 1.5 oz CSM – let cure

Do you see any issue with using the coremat in this fashion? I’d like to use this as strategically as possible to reduce the weight and simplify the layup schedule, so I’m totally open to suggestions. I was actually hoping to use more of it.

Does the thickness of the mold seem reasonable? It seems a tad overkill but I want it stable because I may need to do some post heat-treatment on the parts. The mold will be used for a hand full of parts – less then 10. The parts will be vacuum bagged with epoxy.

Thanks for the advice on the support. I hadn’t really thought about it much till now. So much to do so little time…

 

It depends on the shape. If you have large really flat surfaces a flexy mold will create uneven parts and you really need something to stiffen it up. If it is all curves you are fine probably attaching the whole thing in a cradle at the edges. Make sure coremat is really saturated and use some film to hold it tight to make sure it sticks, vacuum if possible.
Why should the mold be light? For picking it up and storing it?
Coremat, even at 3mm, due to it involving a large quantity of resin, will be your heat source. What if you were to add a layer of fabric in there between CSM for stiffness?
Once you go past the first couple of layers of CSM with hand lay-up you really can't go wrong. You see if you have airpockets while it's still soft and you slit them out, slosh some resin on the cut and you'll be ok.
Make sure you get top quality tooling gel coat and after you finish it overdo the waxing routine before your first epoxy run.

 

I get what you’re saying about geometry, unfortunately its not all curves so I have to build the thickness to the flattest section. The cross section is kind of a 'U' shape.

Maybe I should have been more concise about the core - weight and stiffness primarily. I use allot of core materials in the parts I build so its kind of a habit... It would also be nice to make this thing movable with just a couple guys, but it is what it is.

I specifically put the coremat further out in the layup to avoid unnecessary heating that could affect the surface. I also thought about fabric but felt the coremat probably provides more relative stiffness. Would you agree?

It could also be safer to add the coremat after a single wet layer of CSM.

I’m trying to buy the best of everything so I do this once. This is very helpful – thank you!

 

Check this core. I have used it in flat panels and it comes out lighter and stronger than regular coremat.

http://www.spheretex.com/en/
http://www.spheretex.com/en/videolounge.html

 

zerogara - thanks for the link. That's some cool stuff, I like the fact that it easily conforms to the surface because once wetted it becomes more like a marshmallow consistency. I've been testing with Soric and 3D-core but these are really intended for vacum and infusion applications. Where this stuff lends it self more to my mold building, even more then coremat. Its offered at 6, 8, and 10 mm which is quiet thick so it would be very easy to achieve the thickness I’m looking for, but I’d likely drop some outer CSM layers out of the mix. I would be a little leery about using a new product (to me...) but as you said earlier once you have some thickness in the mold it pretty hard to screw up. The only other issue would be how I handle the flange – the cross section with the flange is like ¯U¯. So from the flat vertical of the U to the flange is 90 degrees, with the coremat I was going lay this into the corner but not add coremat to the flange, just add some additional CSM for thickness. Do you think handling the flange in fashion would cause any distortion? Could this be more of an issue with the thicker sphere core?

 

They have thinner ones in other varieties the one you are referring to is for balsa substitute. They have fabrics/csm that have those bubbles in them, which is structurally superior to coremat as it has fibers in it.
What I do is cut the edge at as small of an angle as I can to the surface. Maybe if you are too concerned use a little filler at the edge to make a curve so the next layer of csm will not meet the next layer of csm in a an angle but kind of blend with the bottom csm. Much of this is related to the thickness of your layers, and how much your resin shrinks. By using a layer of cloth in there close to the gel you add resistance to warping and print through of core or mounting points.

2nd guess You are making a 200ft (10x20') water slide for kids or a 100' tunnel! (just kidding).

U flanges are very common on dinghy hulls as long as the two sides of the U are not parallel or you have a hard time releasing the piece.

 

Damn ya got me... ok,ok - its somewhere between that and a spaceX project.

I have to take some time to have a look at their products in greater detail but the concept seems cool. It could be a bit of an issue getting it here in the US. Some filler between the core and the corner may be in order to ease the transition, good idea. The tooling resin I'm using should provide some protection from shrinkage but (as you implied) I should be careful about the thickness or vary thicknesses that is... This could cause greater localized areas of shrinkage. I have read of people using 10oz cloth just after the skim layer as you’re describing, the guy that first showed me how to make molds used to alternate 2 CSM layers then 1 fabric layer which seemed to work quiet well for smaller molds.

 

They produce it right in the US and when I had first inquired for a sapmle kit they sent me a whole bunch of it to make trials. It was enough I used it to make small motorcycle parts with it. The parent company is in Germany I think but they have a US subsidiary.

The difference with other cores is that you have different materials trying to bond with each other. Here, other than the bubbles you have the same material so it acts as a uniform piece.

 

Ok, I finally talked with Spheretex and they seemed to think the other fabric/csm mats wouldn’t really gain me much. They did have some customers using the SBC product in mold making with good success. I have a chunk on the way that I can play with, we’ll see…

If I don’t end up using this stuff I’ll go coremat in the very outer layers and this will be done in between two wet layers of CSM to insure proper bonding. Something like this:

Tooling Gelcoat
¾ oz surfacing veil – let cure
1 x 1 oz CSM – let cure
3 x 1.5 oz CSM – let cure
3 x 1.5 oz CSM – let cure
1 x 1.5 oz CSM then 3mm coremat with 1 x 1.5 oz CSM on top – let cure

On another note I’ve been having some difficulties sourcing the gelcoat for this project. The RM 3000 system specifies vinyl ester tooling gelcoat but the stuff they make isn’t available in the US so I’ve been looking into using HK Research’s vinyl ester tooling gelcoat instead. If anyone here has specific experience with these guys I’d like to hear about it.

I’ve also found some comments regarding poor UV resistance of the RM 3000 tooling system. It sounds like this is overcome with an outer layer of epoxy which is simple enough. Is this really something I should really be concerned about?

 

You know, we do molds completely different.

Tooling Gel
1oz mat - wet
1700 biax - wet

Then..

1700 biax x 4 - dry
1/2 or 3/4" core balsa or what ever's handy.
1700 biax x 4 - dry
Framework, usually sawn balsa boards.
1700 biax over framework.
peel ply

Vacuum bag and shoot the entire thing all at once.

This makes a very rigid and actually quite light mold. You may not want to go in a direction like this, but it might be something different to think about.

Good luck.

-jim lee

 

Hey Jim,

Thanks for sharing that. I wasn't aware that boat builders would use infusion for molds, really cool. What are you using for resin? I've always known that you guys tend to use more biax I just don't have any experience with it. This is still really helpful to see a different perspective; I'm actually surprised to see how (relatively) close your core is to the gelcoat.

The issue that I’m running into with this project is that it bridges multiple specialties. I’m trying to pull the best methods/technology from each. The plug materials along with the need for some post curing makes things interesting…