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Using PVA or Breakaway as a mold for silicon


MarBuc

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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 :-)

Marek

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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 😉

    M
     

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    • 1 month later...
    Posted · Using PVA or Breakaway as a mold for silicon

    One of my customer did it: he asked me to print the mould in PVA then he poured silicon in it. It worked like a charm. It was a small thing, a few centimetres of diameter. You can see the two parts of the mould in the picture below. I sent it with a silica gel packet to try and prevent damage by humidity during transport, some postal services can be rough and uncaring with packages, I had packages arrive with water damage due to rain or such.

     

     

    DSC_0248.JPG

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    Posted · Using PVA or Breakaway as a mold for silicon

    Dear wuzley and Brulti,

    Thank you very much for your input. I still haven't had the opportunity to try this technique... We should receive our printer in a couple of weeks and I will keep the community posted on our progress.

    Cheers

     

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    Posted · Using PVA or Breakaway as a mold for silicon

    You're welcome, looking forward to see the results of your experiments in printing moulds!

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    Posted · Using PVA or Breakaway as a mold for silicon

    Ok :-) One more thing. Do you happen to have a picture of the silicone part that was produced by your client? Just to have an idea of the level of detail. Thanks!

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    Posted · Using PVA or Breakaway as a mold for silicon

    Unfortunately I don't have the picture of the end result anymore, sorry.

    Though, I can tell you, as was pointed out, that the silicon will show the layers and every surface imperfection. There was a clear 'stairs' effect on the picture of the silicon part that my client made. But that was ok for him since it was some kind of proof of concept. You'll want to use a very fine resolution for parts that will be used. I would advise against trying to smooth the surface of a PVA mould with water, as it risk softening the whole mould.

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    Posted · Using PVA or Breakaway as a mold for silicon

    We will be using an Ultimaker S5 with a 20 micron resolution so hopefully the finish will be clean. I'll let you know how this molding strategy works out...

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    Posted · Using PVA or Breakaway as a mold for silicon

    Thanks Marbuc, also looking fwd to seeing some of your results. I'm going to keep the idea in mind for some experiments myself as well.

    Woah! 20 Micron, is that with the .25mm nozzle? Must be printing something small? Please give us print times as well, curious to know how long it will take. 

    My finest print settings are at 60 Micron on .4mm nozzle.  

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    Posted · Using PVA or Breakaway as a mold for silicon

    Yes, the piece will be quite small (10x10x10 cm max). I have no idea which nozzle will be used... We are experimenting a lot of things at this point, (resolution, molding, medical grade silicon, ...) and we are quite new to 3D printing! So please expect lots of trials and errors. :-) I'll keep the community posted.

     

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    Posted · Using PVA or Breakaway as a mold for silicon

    I've done silicone molds where you print the PLA mold and pour in the silicone.  This works very well.  The silicone is flexible (like soft rubber) and so it can be pulled out of most crevices.  You need some mold release on the mold so the silicone doesn't get into the layer line cracks.  Google "mold release".

     

    This process works extremely well and you can make high precision, very useful parts and once you have a mold you can go wild and make lots of parts.

     

    PVA is a difficult material to print.  You can do it but you won't get the same nice surface finish and accuracy.  It's also more expensive.  But it's still a cool material to work with.

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    Posted (edited) · Using PVA or Breakaway as a mold for silicon

    Hi gr5,

    Thanks for the mold release tip, as well as your feedback regarding PLA. The part we want to print is quite intricate and I still need to figure out how to unmold it.

     

    • Option 1 = unmolding by disassembly of the mold. This raises a few geometric issues regarding the design of the mold. Also, a mold split into pieces can lead to silicon leakage at junctions (according to previous posts in this thread)... So this looks a bit tricky.

     

    • Option 2 = unmolding by destruction of the mold. Mold destruction should not harm the part so "breakaway" might not be well suited. Soluble PVA looks like a good candidate, however the question of resolution must be clarified...

     

    As I understand (I have 0 hands on experience so far) : PVA is water soluble, while PLA is not... which would require me to solve the issues in option 1.

    Edited by MarBuc
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    Posted · Using PVA or Breakaway as a mold for silicon

    Just thought of a 3rd option where a PLA mold is split into parts not printed separately but held together by thin PVA layers. Unmolding = 1) dissolve PVA "seals" between PLA parts; 2) carefully remove the PLA mold pieces.

     

    Does this sound doable? Regarding e.g. adherence of PVA on PLA?

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    Posted · Using PVA or Breakaway as a mold for silicon

    Using two-part moulds will for sure cause the silicone to leak, if it is a slow curing one (>10min). A very fast curing one (<5 minutes) might not leak too much. Unless you fill the seams. Silicone leaks through microscopic pores.

     

    A common method to seal the seams, is to use plasticine or wax. But it has to be a plasticine that is compatible with silicone, it should not contain any sulphur (plus a lot of other stuff) which inhibits curing. Do a compatibility test before with a little bit of silicone and the plasticine or wax. You can find good tutorials on Youtube. Search for: silicone mould making and casting.

     

    Concerning details: if you use good silicone, *everything* that is visible in the mould, will be visible and mirrored in the casting, just everything. Silicone reproduces up to microns. So: all layer lines, underextrusion gaps, blobs, strings, fingerprints in plasticine parts, nail marks, hairs, dust, any defects,..., all will be horribly visible.

     

    And you may have entrapped bubbles if you don't remove them by vacuum after mixing both parts of the silicone. Another way to reduce bubbles, is pouring the silicone in from very high in a very thin stream. And gently (!) blow on bubbles, or prick them with a needle. If you have a shaker while pouring in the silicone, that also reduces bubbles: maybe try an electric tooth brush, or your girl friend's pleasure toys.  :-)

     

    Do a lot of small test prints, before doing a big one, just to get familiar with the materials.

     

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    Posted · Using PVA or Breakaway as a mold for silicon

    Thanks Geert,

     

    That's a lot of interesting info!! Thanks a million. As soon as I get any result (good or bad :-)) I will post it here. I think end of September or October, as soon as the lab is set-up.

     

    Now, the part about the use of a sex toy to remove the bubbles will definitely be a topic of conversation at tonight's family dinner. 😄

     

    Cheers!

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