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Objet 3D Printed Molds (Vero materials) for Silicone Injection Help/Best Practices

Hi All,

For some time I have been 3D printing molds for injecting silicone rubber (Namely smooth-on platinum rtv materials). This is a great way to prototype silicone parts. Here is a link showing what I mean.

However, some 3D printed materials (Vero family from Stratasys) can show some cure inhibition on silicone parts. In the past, we have attributed this to the UV light weakening with time. The remedy has been to increase the UV light settings which gives us favorable results.

Another solution is to use Acura Xtreme White (SLA Tech.) but this printer requires a magnitude higher of money than Objet. When Objet works, its amazing… when it doesn’t many :sob: given.

Does anyone have the same experience?

Does anyone have good material compatibility recommendations? (other Silicones that cure better with Vero printed molds, rumor is some LSR are better, but I don’t have experience with them, literature suggests you need higher curing temperatures but one article suggests curing at 60C is possible)

*Update
I found an article from Cornell Nanoscience and Technology who talk about this!!! here is the relevant info… albeit, I am not sure on all the terms they use, but still, they highlight this curing inhibition issue

Can printed devices be used for casting PDMS (silicone)?

Yes, with antistiction and/or parylene coating, the devices can be used as molds. There is a tendency for vertical sidewalls to be rough and to continue to outgas during the molding process, so some post-printing treatments will be required. See the next question.

What are some common post-printing treatments for the devices?

The following procedures can be performed at the CNF. These are typically done by the user (not staff).

· High-temperature RGD 525 can be baked to make to resist low heat (75-80°C).

· Devices can be put in a vacuum for outgassing. This is useful (and sometimes necessary) for coating devices with parylene, silanes and/or preparing for cell culture.

· Devices that will be used as molds will likely require antistiction treatment. FOTS ((1H,1H,2H,2H-Perfluorooctyl) trichlorosilane) is an excellent antistiction coating and can be used as a release layer for molds.

· Some materials withstand low-temperature metal deposition such as sputtering of a seed layer followed by electroplating.

**END of update

Thanks for reading and hope to hear back from all of you!

PS Here is another user injecting real abs plastic

[AMENDED] PS Here is a very nice article about silicone RTV cure Inhibition
http://www.kitpackers.com/images/resources/Silicone_cure_inhibition_tagged.pdf

UPDATE 2018-08-20
Below is a silcone part (Smoothsil 940) made with Verowhite (Objet 24) using EaseRelease200 as the mold release . I was able to make this part with two different molds, one was waterjet cleaned and the other waterbath. Both molds were demolded at 24 hours (as per datasheet). The extra material was well cured at 16 hours for handling. The parts were like 90-95% cured which had a wall thickness varying from 1 to 2mm. The film between the mold halves was still sticky :sob::sob: But after a couple of hours, I felt comfortable to remove from the mold. After three days I went to clean the molds. I noticed that the waterbath mold was all cured while the waterjet mold film was still tacky.

Conclusion, there is something going on that inhibits the curing process. This process can work on large parts, but care and patience must be employed and for larger wall thicknesses. If done right, this is a fastest way I know how to prototype. If anyone else has some insight, I would love to hear back!

UPDATE 2018-08-31
**Today I molded with a new material, Troll Factory 35 Durometer. This had a listed 90 min cure time. I used the same mold making procedure as I did in my previous silicone casting. **

I am happy to report 100% success!!!

Further inspection of the original mold, by way of the sniff test, the mold has a much more neutral odor than when I last casted (about 2 weeks ago). I stored the molds on a desk, which was exposed to the light half the day (this was unintentional).

Next… I will try the smooth on material and see what results I can get.


Some sticky silicone after 24 hours from mixing

20180820_waterbath_cured_silicone_film_closeup
dried film from objet 24 after 3 days of curing, this was sticky when demolded.

2 Likes

Hey @Taltos cool that you’re using 3D Printed molds for injecting silicone rubber, do you have any pictures of the good and bad results? I’m sure there will be people on the forum who have a solution for your issue :slight_smile: !

Thanks, right now I don’t have photos… but I will get some new prints made and will cast next week. Then there will be lots of photos of the good or bad. Thanks for getting back! :+1:

1 Like

Awesome, looking forward to the photo’s!

I have updated the thread, feel free to take a look. I kept the silicone parts hidden for now, just illustrating the process is my goal.

Interesting issue, I hope someone can come up with a solution on the forum here. @MaddieG do you know anyone with deep knowledge on this matter that we can ask?

1 Like

Thanks for tagging me in here @Brian

@Taltos, this is very interesting. I definitely agree that something in the resin mold seems to be inhibiting the silicone from curing… I don’t know of anyone else doing work like this, but I have some theories.

Have you tried a mold release agent between the silicone and the mold? I believe this could create a silicone-compatible barrier between the materials, so that whatever is in the resin causing this issue wouldn’t be able to contact the silicone. Just an idea though, I’m not sure how this would work in practice.

Hi @MaddieG, Thanks for replying. I have been using Ease Release 200 with a variety of materials. With other materials (PLA and Accura Xtreme White) no issues. One theory is that Ease Release and Verowhite might not be compatible, this is an interesting idea.

I have used a coating to create a barrier as you suggest using Inhibit X, with mixed success. Sometimes it works, sometimes it doesn’t. It is labeled to have a short shelf life and is very expensive. Here is a link to it. https://www.smooth-on.com/products/inhibit-x/ On my last project I had trouble because I could no longer demold the part (even with three cost of mold release) or it just didn’t block the silicone inhibitors.

I have recently seen SLS nylon and would be curious to know if this is compatible with silicone. But its layer resolution is .080 to .100 mm verses the Objet’s .028 layer height. For my work, this is important.

The search goes on!

Hm maybe try without the mold release like you’ve said?

Have you tried curing the mold more, maybe even to the point of being overcured?

Hum good questions @MaddieG. I will update when I have tried these, although I wont be able to back anything that high as I dont have a good oven.

I found a couple of research papers that hint that cleaning with Oil (vegatable oil) might help remove wax and then to clean with soap and wax. Oils help soften the wax from my understanding.

Will update as I learn something

Looking forward to hearing how this works out!

May even consider a small cross-post to the Injection Molding category if you want to?

1 Like

UPDATE 2018-08-31
**Today I molded with a new material, Troll Factory 35 Durometer. This had a listed 90 min cure time. I used the same mold making procedure as I did in my previous silicone casting. **

I am happy to report 100% success!!!

Further inspection of the original mold, by way of the sniff test, the mold has a much more neutral odor than when I last casted (about 2 weeks ago). I stored the molds on a desk, which was exposed to the light half the day (this was unintentional).

Next… I will try the smooth on material and see what results I can get.

(if this part degassed because the mold cured extra in the sun, then maybe there is a way to speed up this process??!!!)

Awesome! Thanks for the update.

What method do you currently use to cure the parts, is there any sort of post-cure after the print completes?

If not, using a UV-light container (cheaply, a container filled with reflective foil with a UV light on the top, and the part is placed on a rotating table) would help to overcure the part.

Finally found some answers, which I updated in the body but I also add here.

Currently, I was the parts to remove the support material and scrub with dishsoap and rinse with water afterwards.

I wonder if a UV container will do the trick (Or if a reptilian UVA and UVB light bulb would do the trick).

The cornell article talks about “degassing” which, if true, may not be solved with UV light… wont know until I try!

*Update
I found an article from Cornell Nanoscience and Technology who talk about this!!! here is the relevant info… albeit, I am not sure on all the terms they use, but still, they highlight this curing inhibition issue

Can printed devices be used for casting PDMS (silicone)?

Yes, with antistiction and/or parylene coating, the devices can be used as molds. There is a tendency for vertical sidewalls to be rough and to continue to outgas during the molding process, so some post-printing treatments will be required. See the next question.

What are some common post-printing treatments for the devices?

The following procedures can be performed at the CNF. These are typically done by the user (not staff).

· High-temperature RGD 525 can be baked to make to resist low heat (75-80°C).

· Devices can be put in a vacuum for outgassing. This is useful (and sometimes necessary) for coating devices with parylene, silanes and/or preparing for cell culture.

· Devices that will be used as molds will likely require antistiction treatment. FOTS ((1H,1H,2H,2H-Perfluorooctyl) trichlorosilane) is an excellent antistiction coating and can be used as a release layer for molds.

· Some materials withstand low-temperature metal deposition such as sputtering of a seed layer followed by electroplating.

**END of update

This is some great information, do you mind if I move this topic to our Injection Molding category instead? It may be more appropriate there.

Hi Taltos,

I’ve had a bit of trouble with cure inhibition while using Smooth-on’s Platinum cure products in the past. Especially when trying to duplicate surface finishes of post-processed 3D printed parts.

Have you tried any of their Tin cure products? I’ve had great success with MoldMax 30. I particularly like to use it with Fast Cat 30 which can drastically decrease the silicone cure times.

-Joe

Hi @MaddieG if you think this is helpful, then please!

Hi @eckerj,

THanks for the feedback. No I haven’t tried this before. I will give this a try and let you know how it goes.

Cheers, Arpad