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 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)
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!
[AMENDED] PS Here is a very nice article about silicone RTV cure Inhibition
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 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!
**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
dried film from objet 24 after 3 days of curing, this was sticky when demolded.