how can I do this mold?

General Composites Discussions Composites Talk
#1

I want to make the mold of this piece, is the internal ventilation of the car.
It’s made of abs, I want to make other with casting polyurethane resin.
I tried to do the mold with silicone rubber paste, but it’s too thin.
How can I do it? With an external mold made with paste of epoxy resin with chopped glass? and the internal with a casting silicone rubber?

#2

I think this is the only way:

[ame=“http://www.youtube.com/watch?v=oabCofuknbc”]Updated - Moldmaking With Clear Silicone Rubber - YouTube[/ame]

#3

thanx Roberto, very interesting video. But a question…why curing with pressure? I have always hear curing with vacuum

#4

I was thinking also like this for the external, and inside with silicone rubber.
Yesterday I did some tests for make a epoxy paste, with epoxy, chopped glass and iron powder…I don’t have experience with paste, so I try

[ame=“http://www.youtube.com/watch?v=lRdi1dSQI9g&feature=colike”]http://www.youtube.com/watch?v=lRdi1dSQI9g&feature=colike[/ame]

#5

That appears to be quite an intricate part, would that not need a mould that would have a multitude of split lines so that the finished item can be easily removed…especially if you are wanting to make a number of parts?

#6

Aye, there is no way to accurately make this part with carbon fiber, and still have all the correct attachment points. You have several options:

1: Plastic extrusion. Use a highly CF filled plastic, and injection mold it.
2: Filled-resin casting. Do a silicon mold as above (i guess, did not watch), and fill the mold with a short milled CF, carbon dust, or even a microballoon filled resin with low shrinkage.
3: Remake the entire system, from the part, to the car itself, to be able to make a normal composite duct work. That would of course, need remodeling of the entire part, and car, heavy modifications, and a loss of mind…

There is just NO way to get fabric to lay in any right spot. You might try a casting, but use fabric in the large areas, and inject it with a filled resin for the rest. While this will not do what you want, it MIGHT lighten it up, and still show some carbon fiber in the flat spots in the ducts.

#7

That is odd. I can only think that the pressure will even out any irregularities in the pour, and dissolve any bubbles that were left in the resin, and near the vent holes.

#8

Hi Riff, I’m not interested to do this piece with CF…too difficult and pointless.
1: Yes, it can be, but for the moment this is a hobby for me, so I haven’t the possibility for this. Plastic injection intrigues me, but for now I can’t do it at home…I should make a small injection machine, and a problem is the high pressure of injection (I found on wikipedia about 100 bar), so the mold resistance is a problem, because I do it with fiberglass or CF, not in aluminum
2: this is the way I want to follow. I have polyurethane casting resin ebalta SG130, I can use it with or without fillers. I think this is the only way to do it, expecially for the attachment points. Maybe I can do the structure with CF and RTML process, but then I have then problem for make the attachment.
3: not applicable this, it’s a modify for a fiat grande punto, I take off a ventilation openings and insert a gauge. There isn’t support for gauges like this, so I want to do a piece that can be installed without modification in all same model car.

Now I’m trying to do the mold with casting silicon rubber and the external structure with polyurethane casting resin.
I will put some photos as soon as I did the mold

#9

Can be that with pressure the bubbles in the resin decrease in size? With vacuum bubbles expand, with pressure maybe decrease

#10

That’s the point: for the vacuum to be effective, you need low viscosity, long pot life and a mold that can assure the air vent throughout.
With pressure you don’t need all of that. Just a pressure resistant vessel, like an autoclave.

#11

yes, I agree. Polyurethane casting resin ebalta SG130 is very low viscosity, it seems water.
a doubt that came to me, it’s if this resin is enough strong and flexible in small thickness for make the attachment points. Next week I prove this, if is ok I proceed with the mold, else I study a new attachment points.

#12

at the end, I’m trying with a gap of putty for glass, outside polyester resin with sand, the in place of putty, I put casting silicon rubber.

#13

It need some changes, but it can be done