how would you make a mold for this part

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#1

Hi guys,
I had designed a brake duct funnel and had a fiberglass shop make them for me however he is having problem with molds breaking after 10 pulls or so. not sure how he made the mold but i would appreciate if anyone can help and i might make the mold and produce them myself. here are couple of pics

#2

Hi
Looking at the images I would use a two piece split mould, it may be easier to make a new mould instead of re working you current one.
Regards Chris
www.carbonfibreworks.co.uk

#3

I assume the goal here is to mold the INSIDE of the brake duct rather than the OUTSIDE. Or am I misunderstanding??

Seems like it would be extremely difficult to make the flanges for the inside of the bowl of the brake duct…

Can you comment on how you would approach creation of the flanges? How would you get the proper profile given the limited space within the brake duct?

#4

Before I start this guys videos are pretty grim but it will show you the basic idea, I would use 3-4 mm corex sign board to create the flange on the part and hold in place with hot melt glue. [ame=“http://www.youtube.com/watch?v=--tSlGyASPU”]How to Make Fibreglass Split Moulds - YouTube[/ame] remember I do not endorse this chaps methods but you will pick up the basics and have a giggle at the same time .
Regards Chris
Also have a look at easy composites carbon bonnet (hood) build tutorial on youtube.

#5

If you can get away with a single piece mould great…There has to be a draught on the part to allow it out of the mould without it getting bound up or breaking the mould. If it would come out in one piece then I would look at having a more defined 90 degree flange on the outer edge of the mould… That would allow you to pry out the part slowly working round the flange. It would also give you a defined edge to cut and trim up to. I have some early moulds that have an angled flange which will come out but are a little tight in a few places… I have seen the edges chip the gel coat or parts get a crack in the gel coat because the part has to flex to come out of the mould. Now I know my errors but as the moulds still produce good saleable parts I keep using them. But the replacement moulds will be changed or fine tuned… It may only need a little change to the new mould but look where the moulds fail and see if it is th same place each time… That may give you the answer you are looking for…

#6

The goal is to make a mold of the INSIDE the duct. 2 piece mold with flanges would work perfect for outside but it is the inside that needs to have a smooth finish.
Is it possible to apply gelcoat on the inside and then fill up the whole inside of the duct with resin?

#7

You can use this with a tooling gel coat… It has metal powder inside it and it can be used to make wet lay or pre-preg parts… I have a mould that was made using this material and it is very strong… but I would suggest you make some nice wide flanges on the outside edge to allow you to pry the part up gently away from the edges of the actual part.

http://www.alchemie.com/wp-content/uploads/2011/05/TDS-EP-4350.pdf

#8

Hard to tell if the cone would cause make it difficult, but from what I see I would create flanges on the outside, prep the inside, put on a few coats of tooling gelcoat and lay SEVERAL layers of fiberglass mat on the inside.

Wet the fiberglass mat out on a piece of glass and give the resin a few minutes to do it’s job and make the mat maleable/formable. Should give you a nice mold that will hold up to a lot of pulls once it’s polished up.

#9

You could use a one piece flexible silicone mold to be able to pull the part out thru the curvature

#10

That is my idea as well. Silicone (shore 22 or so) should be able to be pulled out. When using epoxy, make sure you use a parting agent, or the silicone will stick after some pulls.

#11

thanks herman and berridos, i also came out with the same conclusion and ordered Bluestar V-340, formerly Rhodia/Rhodorsil V-340 silicone rubber. never used it before, and I will post my progress for everyone.
thanks

#12

Rhodia is a quite good brand. Make sure you mix well, use a 2 pot mixing system (measure and mix in 1 pot, then pour into second pot, and mix again). And mix the silicone even before using it. It settles somewhat. This solves 99% of the problems I see with silicones.