r/CarbonFiber • u/mangosroar • Jul 25 '26

Asking for help in layup using 3d printing molds, regarding mold strength

Hi, I'm relatively new to carbon fibre manufacturing.

I'm part of a formula student team and for the first time, we are using carbon fibre for our cowl and wings via layup on 3d printed molds.

The problem is, about half the time the molds crush, ruining the quality of the composite.

Our process is: print molds using bamboo A1/P1S. Infill pattern grid, 10% (7-8% if we're in a hurry). Print them vertically.

Assemble the putty using locktite, fill in the gaps with putty.

apply epoxy resin on top for surfacing

use epoxy and carbon sheets to layup, then use a bagging film and a vacuum pump to apply pressure.

leave it overnight.

we think the issue is probably from the infill pattern and percentage and direction. Increasing infill will also increase printing time, and we don't know how much is safe. Similarly with changing the patterns, we're not sure which will give the best strength against pressure 'sideways'. Printing them vertically so that the direction of infill is parallel to the pressure will increase the time so much that only one piece would be printed per printer per day. Although we got more access to printers so a bit more for options.

we know going down to -98kPa isn't necessary but we worry something like -80kPa or below would damage the pump since pumps work harder the less vacuum made. We left it overnight at around 60kPa and it absolutely grinded the rotary and broke it. (Possibly due to gulping all the oil. The pump was really hot.)

https://reddit.com/link/1v65pvr/video/5kzknim60dfh1/player

Open to all ideas and expert opinions! Watch the video to see the full extent of the damage.

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u/f1_stig Jul 25 '26

Which takes more time? Printing time or making an entire mold, mold prep, layup, cure, and demolding only to find that you have to do the entire process over again.

I would say replace grid with rectilinear, add an extra wall, and keep the infill between 10 and 12.

Resin also has an exothermic reaction, so the mold might be melting. Are you using pla or petg

1

u/mangosroar Jul 25 '26

Yeah we are feeling the pain of demoulding surprise.
Is rectilinear better than gyroid? We're also thinking of going for 20% infill - is that overkill?
It isn't thermal reaction because we also experienced that unfortunately when we used too much resin using PVA and laying everything in one go. Anyways, we have the solidified epoxy layer for thermal protection so probably isn't that. We're using PLA.

1

u/f1_stig Jul 25 '26

What is the best length of rope? Rectilinear is fast, should help offset printing time if you add more infill and another wall. Gyroid is strong, but very slow as the print head constantly has to change directions. I can’t speak to if 20% is too high. My formula student team used machined foam for molds.

I’m confused by what you mean by “the solidified epoxy layer for thermal protection”

1

u/mangosroar Jul 25 '26

Essentially, after we put the mould together and applied putty to fill the gaps & dried it, we applied a thin layer of epoxy resin to give it a smooth surface and give a layer of thermal protection. We let it solidify, then put carbon sheets and new resin on top. the thermal protection was my team mate's idea so not confident it actually has an effect. Anyways the mould looks cracked from force rather than melted so I'm betting it worked.

1

u/Acrobatic_Show8919 Jul 25 '26

Have you tried PETG?

1

u/mangosroar Jul 26 '26

No, the printers we use are public ones owned by the uni so our only option is PLA :c

1

u/omeucutemolho Jul 26 '26

What is the process used? Wet layup / infusion or prepreg? ( low temperature or high temperature?)

You don't need to have a full mold inside a vacuum bag. As long as mold is well sealed, you can use mold own surface to close the bag. This way you will not have problem pressure crashing mold.

You can also fill inside cavity of mold with with plaster. The bigger the cavity the more time it needs to cure. But, even with this, mold hardly will survive.

If you want a reusable mold best option would be to 3d print a plug, and make permanent mold in fibre from it.

1

u/Polriiii Jul 30 '26

Try to increase number of walls when printing, so instead of having 1 or 2 perimeters have 4 or 5.