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Using PVA or Breakaway as a mold for silicon

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Posted · Using PVA or Breakaway as a mold for silicon

Dear all,


Do any of you have experience with using PVA or Breakaway material to print molds for injecting silicone?


I need to generate quite intricate silicone parts by injecting silicon in a mold, and there are 2 options to make the unmolding possible:

  1. Split the mold into separate "unmoldable" parts, then assemble the complete mold, inject, wait, unmold in the correct order.
  2. Print the mold in one shot, inject, wait, break away mold.


Any advice, comments or sharing of experience would be of great help!

Thank you all in advance :-)


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Posted · Using PVA or Breakaway as a mold for silicon

I do have experience with moulds for silicone printed in PLA, but not in PVA or breakaway.


The biggest problem, even with "correct" moulds with slanted sidewalls and no undercuts, are the layer lines. The silicone gets stuck into these, causing a very firm grip, which makes it hard to remove the model from the mould. You might also have this problem with breakaway.

Most silicone can withstand 250°C for a while, so another option would be to use PLA, and then heat it up and peel away or melt away the PLA at around 100...150°C?


If you would use PLA, "smoothing" is highly recommended. This reduces the undercuts in the layer lines, and tends to fill and close tiny gaps. See the thread of user cloakfiend on this forum, where he has done an enormous amount of tests, with excellent results.


I don't know if breakaway can be smoothed. If using PVA, smoothing should be possible with water, so you might want to try that on a test piece: it will probably be required to close the gaps and remove irregularities, because PVA seems to print less smooth than PLA.


Further, there do exist dedicated mould-making filaments, but I have no experience with them.


This you will already know, but I add it for other people not familiar with mould making or silicones: if you make a mould from multiple parts (the A and B side of the mould), make sure to seal all gaps, because the silicone will leak away through the tiniest openings, even if only microns. And provide a way to let air escape while pouring or injecting the silicone. Entrapped bubbles are another common problem.


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Posted · Using PVA or Breakaway as a mold for silicon

Dear Geert,


Thanks a million for your comprehensive answer!! I will look into the leads that you mention.


The topic looks tricky... I will post here once I have some results! Wish me luck.


Cheers 😉


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