Styrene Plug - Surface Coat & Longevity Help

General Composites Discussions Composites Talk
#1

Hello Ladies and Gentlemen,

Been reading alot on this site, and tried to take in as much info as possible. What a great site with a ton of info, thank you. Hopefully you guys can direct me in the right direction…

I designed a panel from 3d data and am having difficulties determining whats the best method of making the plug. The panel is about 20" x 38" with a lot of contour and will be made by infusion. Keep in mind, I only need to make 3 panels. Below is an image of the panel on top of the mold I designed:

(orange is the mold, grey is the panel)

First, the mold will be cut in a CNC so any material is okay, but I figured glueing styrene panels together would be the most cost effective. Will this be a good option or would I be better off using MDF boards? The only reason why I am avoiding the MDF is because the price would be almost twice as much. Trying to keep this project cost at a minimum (wedding around the corner).

Second, what is the recommended surface coating for the styrene? Should I use the products from Duratec or would a couple layers of fiberglass & tooling gel be better? Also, what can I expect for life of the plug? Will I only be able to get one part from the mold.

If I am way off on this one, please let me know. First project from scratch and a little nervous I’m going down the wrong road. Thanks for your time reading this and your responses are greatly appreciated.

Thanks,
Jason

#2

For the mold, closed cell foam works great. Just cover it with bondo, sand, and paint.

Congratulations on the marriage!

#3

Guys, just a reminder EPS will dissolve when polyester products (bondo, Duratec) are applied. Your choice is to either seal the EPS with epoxy then you can use polyester products, or start with a foam that can already work with the polyester.

A properly finished plug would be good for 3 parts as long as you don’t have any release issues along the way.

#4

Bondo, sand and paint won’t allways be the best method. styrene based products eat away the polystyrene, epoxy filler is expensive. when you apply filler, you’ll need a thick coat, otherwise you’ll sand trough it, and you will keep yourself busy with filling and sanding a long time. Cover it up with some epoxy/glass or polyester/glass(when using Foams like PU) and you’ll have a nice and hard surface to fair.

#5

Thanks guys,

What a big help, didn’t know that the EPS dissolves from polyester! I’ll go ahead with the epoxy/glass. How many layers of glass do you recommend? I image only a couple layers are needed, as it would be hard to sand through…

Any recommendations on tooling gel/supplier? See a lot of products out there, but don’t know what necessarily works best for this application. Also, it looks like Soller Composites is a reasonably priced retailer for fabric & epoxies. Any other suggestions for small orders in the USA?

Thanks Again,
Jason

#6

I should have mentioned what Susho and Shoe said. When making the car we used two types of foam, one was styrofoam with melted and fell apart easy if you so much as looked at it. That one I had to cover with two layers medium weight glass and epoxy. The other was this much denser closed cell foam which sanded easily. That second one I could easily sand to my desired shape, then bondo over it with no issues. I know it’s closed cell foam but I don’t know what the name is.

#7

MDF is going to be the cheapest way to get this mold done. You may think EPS is cheaper, but by the time you add fiberglass, resin, and two gallons of bondo, chances are the EPS will be more expensive. Both will need to be sealed which can range from clear tape to a nice mold primer (duratec is good). With the MDF mold you will probably want to envelope bag it due to porosity. With the EPS you’ll want to make sure the mold surface is vacuum tight as envelope bagging usually brings bad results. Of course if there is no vacuum step, omit the previous. Either mold will be sufficient for 3 parts and more, assuming temperatures don’t reach higher than 140F or so. At 160F EPS starts to do bad things. MDF will take limited oven cycling to 250F.

Cheers,
Mike

#8

Is there anyway to garentee that the molding surface will be air tight with either the mdf or EPS? I assumed this would be given by adding the glass/epoxy and tooling gel coat. It sounds as if this is easier said than done.

Also, anyone have luck with this duratec product made for EPS? Its pricy but most likely cheaper than what fiberglast offers it at:

http://www.fibreglast.com/product/3128/Duratec

Sorry for so many questions, just want to make sure Im not going into this blind.

Thank you all again,
Jason

#9

don’t wanna upset the low cost options here, but tooling board is easily machined to a good surface finish, and accepts coating spray for polishing. core foam can work as well, but you will need to seal it well.
other foams can be eaten by resins like VER/PER.

#10

After reading a lot over the last couple of days, the less appealing MDF & EPS is to me. I know I stated I was looking to get into this cheap, but I don’t want to sacrifice the quality & accuracy of the mold because of it. Since the panel is both visual, mating to adjacent panels, & structural. I would prefer to avoid any hand worked details if possible. So as usual, it’s probably going to cost more in the end to get a better product.

Riff,

Any recommended sources for the closed cell tooling boards or foam for a reasonable price? Also, I noticed that mixes (polyurethane & epoxy) are available for pouring into forms. Will this work in the same method as the closed cell tooling boards? Back when CNC’s weren’t as prevalent, our company use to pour similar mixtures into die cast casting so we could have a plug to make tooling from. Some of which I believe we still have around…… This might be my best option

Thanks,
Jason

#11

If it is for a low amount of parts, why not machine the female mould, instead of male. Vacuum a high stretch bag in it, and laminate on that. This is done many times by the student challenges such as Solar race, hydrocruisers, etc. Very cheap, very fast. There are limitations on what you can make, but the above part is well within limits.

Use a slightly higer density EPS though.

#12

And for CNC-ing look into a product called “Masterworks M2” which is cheap, cures fast (machining within the hour after application) and has a high heat resistance.

#13

Herman,

Thanks for the suggestion!  I'll check into the Masterworks stuff as it seems like a good solution for what i'm after.  Read a little into the website, and it looks promising.

More on the bagged plug though.  Why does it have to be a femal mold?  Because it garuntees that the bag will be sucked down without any slack?  Also, what recommendations do you make for a barrier between the fiber/epoxy and the bag?  Just prep it as a regular mold or add peel-ply?

Thanks,
Jason

#14

Positive can be done as well. You can apply release on the vacuum bag, or do a test to see if the bag sticks. (some don’t)

Peelply is not a mould release. It just provides you with a rough layer, nothing more. It is not easy to peel either.