RTM mold and other thingieS

General Composites Discussions Composites Talk
#1

Dear inmates,

A sort introduction is that I am mechanical engineer who has a little knowledge as far as composites is concerned but I am a quick learner and I can add to the other thread’s knowledge pool :smiley:

Off to the main topic… :smiley:
I am trying to make a mold similar to that that you see on the two pics. One male and one female part. I have only worked with vacuum bag systems before but very very briefly so this process with the mold is completely new to me. Excuse my ignorance… :eek:

Try as I might I could not find enough information for the RTM method. There is info in RTM light but it is not the same…

The part will be like an open box so I would like to ask all the people here if you could help me with the following.

  1. I have seen that I need to put the inlet in the middle of the part in order to help with the air moving toward the highest point (the sides). But what about the vacuum line? Where does it need to be ?

  2. The other thing that I would like to ask is about the edges of the box. I would like of be able to create them in the compression mold (made of Aluminium) so I avoid the trimming. Would that be possible ?

  3. I need to bolt the box on to a steel structure. I have seen metal rivets, sandwich plates… the lot. Which one in your opinion would be the best? Would it be better to embed aluminium into the CF matrix or make a mechanical connection afterwards?

Many thanks,
D.

#2

Vacuum around the perimeter. You could design a resin gutter around the part, which catches excess resin, and acts as vacuum channel. (if you like to use vacuum)

The vacuum channel should be connected to the part by a thin channel. This also creates a “break off” point for the part. This minimises trimming.

Too many options for question 3. Totally depends on part, metal structure, etc.

Embedding aluminium into carbon is not a good idea. (galvanic corrosion)

#3

Many thanks for the reply.

I understand the principles.

I had a part which was made by 6 layers. Outer 2x2, next a Carbon Kevlar weave and then 4 layers of unidirectional carbon to reach a thickness of 2mm.
Three powerful hammer hits and the hammer penetrated the thing completely.
I know that probably Kevlar or Vectran will outperform CF in this application but is there any specific type of resin to increase the toughness of the final part?

Will post pics of the broken part tomorrow… :frowning:

#4

Carbon is of no use for impact strength. You only have have a minimal amount of aramides to withstand impact strength. What other design considerations went into the part? Stiffness? (that is what carbon is good for)

On resins: find a rubber toughened epoxy resin.

And one more thing: fill out your location in your profile, does not need to be very specific, but helps to recommend stuff. Different continents, different suppliers…

#5

The part is broke :frowning: I see. Unfortunately, even you made it in 4mm you will have the same results.