I want to make this prop in carbon fibre , Has anyone seen any videos or threads covering the best way to make a mould and the part?
I 3d printed this one and will smooth it up and paint it before making the mould off it.
It is from a jet pump for a powered surf board.
There are plenty of videos on YouTube demonstrating how to make a mold for composite part making.
Easy Composites in the UK has a fairly detailed tutorial.
If you haven’t worked with carbon fiber before, be prepared to go through an expensive learning process before you can make a part like that. You picked a very difficult pattern for your first part.
From the look of it, it will require at least a three part mold if you have any hope of releasing the part cleanly due to the under-cuts.
If it doesn’t have to be carbon fiber, you’ll have a much easier time casting a part like that in a silicone mold. Flexible silicone in a hard shell mold would work well.
If you have access to a 3D printer, then why don’t you print the mold to make it easier on yourself? You can use the free month trial of Autodesk mold designer if you don’t have access to other software.
The mould is not your biggest problem. I think you have never made a prop from composites.
The problem is the layup to get the fluid dynamics you want and need. Wrong layup and you have 50% less efficiency. Depending on how it bends under load you have to design your prop, layup and shape.
For your prop you need a split mould to get a double sided smoth surface. I would reccomend wet press or LRTM.
The easiest way would be to make the mould in CAD and mill the moulds. It is no fun to create the mould splits.
Look at the angle of the propellers. There would be a mechanical lock that would prevent the part releasing if the mold was in just two parts. Each propeller undercuts the next.
Tricky design but I am sure there could probably be a way?? Probably cnc metal multiple piece mould.
I just question the idea of having a carbon water jet prop? I did a few repairs on the jetsurf boards which also had carbon props. I was just repairing the internal bulkheads as they would breakaway from the hull bottoms with jumping impacts.
Composites just will not have the durability of steel or other metals as usually used. So easy for any debris to sucked in and damage the carbon blades, then you have a damaged and inefficient prop. Just not practical or sensible to me.
You could make this as a composite part but, not gonna be easy.
If you have the cad files, throw it in cad, and you should be able to create the mold fairly easily… It’ll be many pieces, and the hard part with these types of molds is that you need either a bladder, silicone, or vacuum to get compaction, which isn’t going to be easy to do. I’ve made propellers in this fashion but, they’re laid up in multiple pieces and then bonded together. For the amount of work, I don’t really see the benefit of a laid up piece in carbon. Is the weight really an issue? A SMC made part would probably be easier in some way, if you have a way to use that process? Or else, why not a machined aluminium or metal prop?
I have come to believe that with carbon fiber parts, the process starts at the pattern design stage. Designing for the material makes life a lot easier. Does it have to be that specific shape or could you use another design without the undercuts?
When I have problems making a cf part, 95% of the time, the problem is that I just took a part made in another material and thought “that would be great in carbon fiber” without redesigning it first.
There are certain design features that make parts extra difficult to make in carbon fiber and are best avoided if they aren’t absolutely necessary. These include: small fine details, sharp tight corners, long flat sides, overall complex shapes and undercuts.
Sometimes the answer is to go back to design and remove these features so you can make a better-looking stronger part that is more efficient to produce.
If redesign is not possible, another option is to use the material in a different way. I have had success making complex shapes using carbon fiber sheet molding compound. It can me made with more of a casting process and, if needed, it can use a flexible mold (to handle the undercuts).
To see what I am talking about, Google the Steyr SSG carbon. Steyr sells a carbon fiber rifle stock that uses cf sheet molding compound. It’s not as pretty as woven fabric but does that matter for this part?
Some companies have also started milling carbon fiber parts from solid blocks. It’s hideously expensive but it would work for this part.
The pump is 100mm diameter so not easy to find stainless props of various pitch. for sure the composite prop will not have the durability of aluminium or stainless.
From my experience with jet skis the main debris floating is plastic bags ,rope etc ( Ice is not an issue here in thailand lol)
If ridden on to a shingle beach will destroy even a metal pump!
I have made a six part test mould and a prop in carbon , First tests in the tank have been very encouraging ! I will post pics later.
Here are some pictures of the first try, the prop seems to work perfectly in static tank tests , no cavitation and massive thrust !
after post curing i don’t think the blades are flexing at all under load.
I can improve on the layup a little for more strength ( precut the carbon pieces slightly different.)
problem uploading several pics !
That was fast, nice.
What is that tube made from?
The pump is 3d printed and carbon wrapped
the pump is 3d printed and carbon covered
Fairly simple part to make
9 part Ali mould an foam filled blades with oven cooked pre preg you wouldn’t even need a autoclave.
3 split moulds (2part) for each blade
2 assembly plates that are for the top and bottom of the blade moulds when they are together to hold them together and locate a central spigot
1 central spigot that goes through the blade assembly
Layup
Without fe its hard to say but I made a lot of scaled turbine blades for the new Rolls Royce Trent engine an they were spinning at 50,000 rpm an ran within a fraction of the compressor housing without deflection.
They were 4 plies of T300 200g,due to the blade profile the plies were staggered back from the tip of the blade so there were only 2 plies either side at the very edge
So if you fancy a bit of trial an error start at 4 ply an see how you go
Without seeing the cross sections of the blade its hard to say but depending on the edge profiles you maybe able to be able to cut your foam from the sheet an rely on compression .
Presume your blade profile has a"thicker" leading edge ? An the trailing edge tapers out to nothing ?
Get one pair of your blade moulds
One part is the “base” where I would leave the plies long,hard to say without knowing the size of your part but lets say 10,15,20 an 25 mm.
Obviously on the trailing edge it depends on the thickness,8 plies of 200. Will give you 1.6-1.8 mm so if your edge thickness is that sort of dimension there’s no need to leave long
Rohacell foam is the only one o would recommend,can get it in whatever thickness you want so no problem there
Would debulk eack laminate in the mould before adding foam,even if your resin system is a core bondable one I would film glue the foam before putting it in the mould. Would also debulk the film glue onto the foam.
Place the foam in your bottom mould an fold your long joining plies onto the foam.
On your “top” mould you need to stagger your plies back to allow for your joining plies.
First ply is to the split line obviously for cosmetic reasons
Unless I’m doing a critical component like a wishbone and it has to be mm perfect I like to play it safe. So if my second ply for example has been left long by 10mm I would stagger my second ply on the top mould back 5mm from the mould edge so I have a 5mm margin of error
This is obviously done with the other plies as well
Once the tops laid up place on the bottom mould/foam and bolt up
Repeat 2 more times !
When you laminate your blades and the 2 parts are bolted together you have the faces where one assembly joins another ( this is going to be a rather staggered split line) you could use joining strips but I prefer to do it all in one so would do a staggered join just like when you join the moulds.
Leave either the front or rear face long and stagger the other back,doesn’t matter which just that you do all three the same !!!.
That way when you slot blade one to blade two the join should be seamless
You have a thick laminate where your blade fixes to the drive shaft. I would have a shaft machine for the size you want and roll/wrap with material till its up to the correct thickness
Would have the shaft drilled and tapped and corresponding holes drilled into the top an bottom plates that hold your blade moulds in place.
Assembly might be a bit of a jigsaw.
Probaly bolting your shaft to an assembly plate,then adding your blades one at a time then adding your top assembly plate an bolting that to the shaft an blade moulds
Also might want on invest in some redux 204
Very handy to fill any gaps an give it a little more “juice” during the cook
Yes Rob, that is the simplest way to do the job, as long as you work in a F1 workshop or a high end composite company, have a millimg machine and a professional CAD system where you can design the mould.
He did say " the best way to…"
Could just as easily laminate the prop moulds in polyester,vinylester,or epoxy
Two Ali or steel plates for top an bottom
Only “difficult” part would be getting your hole an tapping it central in your mandrel
Can easily be done at home without going near a F1 clean room/cad/cnc etc