Multi Part Mold

General Composites Discussions Composites Talk
#1

I’m planning on fabricating a CF airbox for my track bike. I’ve picked up a spare original part from which I hope to form a mold (or series of molds) from which I can ultimately fabricate a composite part.

The original part is a 2 piece plastic airbox comprising lid and main body.

I’ve been staring at it for months trying to decide the best approach and before I start cutting up the original part to prepare molds I thought I’d seek any views.

The ultimate CF composite part need not be too pretty as it will be hidden below the tank on the bike. That said, a reasonable finish would be preferred.

Heres the original part assembled…

and here it is with the lid off

The lid will be made as one mold, the base is the tricky part I’m planning to make in 4 (or more) separate molds and then resin together.

So, comments please on the proposed mold ‘pieces’ I envisage as follows:

I will carefully cut off the 2 x air ducts that are the oval pieces exiting the main assembly on the top left and bottom left of this picture. I propose to fabricate each of these as separate composite pieces (each piece in a 2 part mold) which will later be fitted (using resin bond) back into the final assembly. Longer pieces will be made as I envisage the oval tube to protrude inside the finished assembly so that there is good overlap to resin bond, with any final material trimmed back inside the finished part to suit.

Next piece; I plan to remove the ‘ribbed’ section of ‘tray’ shown in the photo above and in the photo below. Again, I envisage forming a new composite ‘tray’ with large overlaps so that it can be dropped into the final piece and resin bonded in place. Again trimming back any surplus material. Heres the ‘tray’ piece viewed from inside the airbox and also showing the 2 x oval ducts which will be fabricated separately.

That should leave me with one final piece which is a reasonably straightforward (!) larger main body into which the above component parts can be fitted once prepared.

I’m about to start cutting up the original piece and wanted to get some feedback before doing so!!

I’ve also got to cut off a number of small protrusions for breather hoses and the like. I envisage these can be added into the final part at the end of the process using soem pre formed CF tube or similar.

Last question, flanges? Not flanges on the mold, but flanges between the top and bottom final pieces. As you may see from the above images the original part uses a raised profile in the bottom piece around the edge, and a ‘slot’ in the lid piece around the edge. One ‘slots’ into the other to achieve a seal once the airbox is together. I’m not sure how to achieve an alternative method for this, other than to form a rolled edge thatreturns inside the finished part to form a wider flat edge on both top and bottom parts, which can then be gasketed together during final assembly.

Any thoughts or tips???

PS -just thought I’d add that my latest thoughts are to form a male mold, since I want the smooth finish on the inside of sirbox for maximum airflow, thus the ‘raw’ carbon finish on the outside. This will probably simplify slightly some of the molding process; particularly the oval air intakes

#2

That is a serious project :slight_smile: Complicated.

I had a guy ask us if we could make an RC51 airbox… think we quoted him $1200. We are leaning away from bike parts now… too complicated to justify making them. But I do always love to see others cf bike projects :slight_smile:

I will have to reread your post, but the more air you can get into the airbox the better for performance. The sealing edges you mold seperately. This is how you do the female seal side of the airbox… mold the outside edge of the sealing area all as one piece with your airbox. The inside seal edges are a seperate mold… make that part then bond it in around the inside perimeter. As for the other male sealing edge make a mold then bond that in after the part is made. You may think of another way now that you are thinking about it :wink:

The inside “guts” if you can make them yourself out of carbon or fiberglass and that box could sell for 1200usd to more than one guy. I would say this project is even more complicated than making a cf fuel tank for say a CBR.

Also if you have any negative draft angles you will need to do a multi piece mold for each section of the airbox that requires it. Always be thinking how you will pull the part from the mold and have it not be trapped in the mold.

#3

I think Fastrr has summed it up pritty well there, I agree with him regarding making the ‘sealing flanges(edges)’ seporate then bonding them in after. Other than that what you have said sounds good and sounds like you have already been thinking about it quite a lot already.

For the inlet tubes you could do it in a 2 piece mould that you lay-up inside of it, or you could create a mandril that you lay-up over the outside of it. Depends which surface that you want the smooth side.

It is very inportant to remember to pay plenty of attention to draft angles on things like this or you wont be able to get parts out of the moulds.

How are you planning to make the actual part? wet lay and vac bag? infusion, prepreg?

Great project.

#4

Wow, I’m about to start the same project, CF airbox for a gsxr .As soon as I get my hands dirty I’ll post photos…

#5

I would recommend simplifying the curvatures of the lower half and reshaping to make a corners larger radius. Then throw the top half in the garbage and make it so that the bottom of the gas tank is your top half of the airbox and it seals down on the bottom half. This is taking after the durbahn rc51 airbox as inspiration. not only will you have a much simpler project on hand parhaps but also likely a considerably larger airbox!

#6

I agree, get rid of the ribs in the top and bottom. it will be easier to lay up without them. As for the vacuum hose connection to the airbox or air hose fitting buy some made out of plastic, drill a hole in the cf airbox, and bond it in place with the proper glue/epoxy. Much easier and then you can buy actuall hose fittings. We are having some made out of delrin and bonding them on after. bond from the inside of the airbox.

#7

Very useful; I hadnt considered moulding the sealing edges separately, I’ll give it some more thought. NOt sure where to start with this and will have to stare at it some more!! My initial thoughts are that the separately formed edges could be quite intricate and tricky to mold and form. Good advice though, thanks.

#8

Ha ha, I havent thought that far ahead yet!!! Probably wet lay and vac bag though.

So far I’ve just been trying to think about the molding process. I plan to try and form some trial parts using fibre glass for practice and to refine the mold, before getting anywhere near any CF.

#9

Good point

I had given this some thought and the Durbahn projects are a regular source of inspiration (particularly as I’m an ex RC51 owner).

At the moment, the existing lid seems to be the easier part to mold and fabricate (famous last words!) so I’m going to start there. I think a larger capacity air box and sealed using the fuel tank is more likely a ‘mark II’ or maybe even a ‘mark III’ project for the future. I’ll see how everything unfolds!

#10

You will need to think a head a little bit as if your ever going to want to do/try this as an infusion you will need to have large flanges onto which you can use as sealing surfaces and places to put vac/resin lines ect. the flanges would also be good if you are doing a wetlay and vac bag as this would give you a surface to attach your vac bag to rather than needing to do an envelope bag.

Good idea to lay a GRP item up ion the mould first aswell, alows you to check all is good with the mould before wasting really expensive materials. Also gives a chance to break-in the mould, atfer the first pull parts generally release slightly easier from the mould.