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MarBuc

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 :-)

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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Posted · Using PVA or Breakaway as a mold for silicon

I like the idea of printing a  PVA mould, then dissolving it after. has anyone tried this? 

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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...

  • Thanks 1

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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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