Thank you for that. My work around has been to print in the castable resin and let the caster made a mold from that. It works quite well. I just get a little annoyed sometimes at having to design around supports and sprues.
my feeling would be that ALL rubber molds are sacrificial.
That is- they wear out with use and must be replaced.
A Poured silicone mold is always going to be significantly less costly than a printed rubber mold in terms of materials cost, and time, and a poured mold will always capture a molecular level of detail- whereas any printed rubber mold will be limited by layer artifacting.
what’s the best way to color this resin? Food Color? Also, how do i prevent over-shrinkage?
With no warranty expressed or implied, the methods that others have used to color clear resin should work with Elastic.
I’m not sure I know what you mean by over-shrinkage, though. Elastic resin will reversibly swell when exposed to IPA, so it’s a good idea not to wash it for too long, especially when the part has thin features, or the distortion introduced by that swelling could be permanent.
Printing in Elastic is so much faster and easier than casting silicone rubber from 3D printed molds. I printed a 2mm thick wrist strap using Elastic but even with direct rubbing off of resin in an IPA bath for 10 minutes and curing 20 minutes at 60C, the surfaces remains very tacky (as if resin residue remains). The IPA is 95% and new. I am concerned about too much IPA exposure (is 10 minutes the maximum exposure time?). I am planning to print for user testing prior to committing to tooling, but need non-tacky parts. Any suggestions?
Get 99% IPA. I had tackiness with any lower concentration of IPA.
99% IPA will help, and there are a few other techniques you can try to get towards a tack-free part, all based around reducing oxygen transport at the surface:
- Put your part inside a clear plastic jar or plastic bag full of water inside your curing machine, or a bowl of water with something to hold the part down. This is what I mostly do, and I’ve got a lot of tack-free Elastic parts on my desk.
- Coat or submerge your part in glycerine/glycol during curing.
I’m getting some amazing parts from Elastic. I design medical devices that are often made in TPEs or silicones and this is giving us a way to prototype like we have never been able to do before without a slow expensive messy casting processes. Getting a functional soft rubber model in a few hours is awesome.
Some questions though.
Any way to make it slightly softer? like 30 or 40 Shore(A)?
Any way to nicely remove the supports? The remaining pips are really tricky to remove, and you can’t really sand the material well. We have best results scraping the surface with a sharp blade, but it’s not ideal. They work great as functional test parts, but not as cosmetic ones.
We’re glad to hear you like what you can do with Elastic!
It can be slow, but one way for a better appearance and feel can be to use flush cutters to cut the support while you’re pulling it away from the surface. Then, the cut area pulls back into the surface of the part, leaving a more subtle mark than just cutting it without tension.
You may also want to play around with whether you remove supports when the part is freshly printed (soft, some risks of tearing part while removing supports), after rinsing (very soft, easier to remove supports but a higher risk of tearing), or after post-curing (stiffer part, lower risk of tearing, but more difficult to remove supports).
In any state, I like to use scissors to cut away most of the supports before going in with flush cutters to try and get a good finish.
There may also be more techniques for finishing Elastic that haven’t been figured out yet. I don’t personally know of any way to make it softer than it already is. It might be close to that soft when soaked in IPA long enough, but I don’t think those parts would be very usable, and they’d gradually dry out and harden somewhat even if they retained that IPA-swelled softness for a few hours.
I have yet to play with Elastic, but some tricks from Flexible may help.
After finishing your cleaning and curing procedure (I also use a mechanical means to assure a clean surface (brush with IPA)… freeze the part, and file and sand. You may need a couple of times in and out of the freezer. Granted not all parts are sandable because of geometry, this works WONDERFULLY for Flexible to remove and tackyness and give it a beautiful satin (to the touch) finish. If you have a media blaster the freezing forks for it too.
Just wanted to add something that Ike didn’t mentioned, don’t know if it will work though I as I don’t (yet) print with Elastic :
Flexible parts could be put in the freezer after post-curing and support removal was cleaner and it was possible to sand the parts.
Interesting idea with freezing. Thank you. I will give this a go.
I have been printing some small parts that contains 2mm diameter tubes, this goes well for small tubes but as the tubes get longer i noticed that the tubes get clogged. I suspect that the uncured resin that is stuck inside the tubes cures as it is exposed to the light of the laser while it is printing successive layers.
Is there a way of fixing this ?
I have been thinking about colouring the resin with a dye that blocks the laser light. But i do not know if this will be possible ? And what kind of dye (or powders) can be recommended to experiment with ?
True, but if the elastic resin could capture fine detail better, it could print a flawless bubble free mold every time (other than the occasional print failure, which hardly ever happens with my Form 2). And the extra time would be machine time and not human time, freeing up the user to do other things. So yeah, pros and cons…
I can’t remember the last time I saw a bubble in a poured silicone mold… but then, I am a moldmaker and I have a vacuum pump.
You CAN use this to produce printed molds- but the resin costs 8 times as much as tin cured silicones.
The the cost of one liter- I can buy 2 gallons of silicone.
I advise using the form 2 to print a CASING that accurately maintains a 3/16" gap between your master and the inner wall of the casing… ( no counting undercut areas where the rubber will be thicker for draft ) and then Pouring silicone into the gap.
You may be able to use a syringe or other pumping method to flush your small tubes before postcuring; I’ve done some experiments with long tubes and I find it works best for me to do this washing before I do general washing. Because the uncured elastic resin is so thick and viscous, the longer a tube gets the harder it is to purge out after printing. I wouldn’t rule it out, but it may not be an effect of laser light scattering into the part and curing the resin inside the tubes.
Depending on your exact dimensions, it may be tricky to avoid tearing the tube you’re trying to flush, and if you can align the length of the tubes with the peel/wipe direction, that may also help slightly.
Coloring the resin with a pigment or dye is possible, but not officially supported, and if you block too much of the light that’s curing the resin, then it just won’t print period. It’s possible that there’s a sweet spot that doesn’t inhibit layer-by-layer curing too much but does block light scattering into the already-cured part.
Though a little expensive, an ultrasonic knife such as this can work well for removing supports. It requires less force than even a sharp blade so the resulting surface finish is better.
Considering the comment regarding minimizing oxygen transport, does that imply not leaving a finished part on the build plate for a long period of time. This would make runs that do not finish during working hours difficult since they may be exposed to air for many hours (or days if over the weekend) before being able to cure.
So far have only made a couple of parts with the elastic material and they have been very tacky. I have not yet tried curing in a clear bag with water yet. I assume this will need a longer cure time since the water will need to come up to temperature. Any recommendations for that?
I’m pretty sure Ike’s comment on creating an oxygen barrier is only relevant to when you are actually post-curing the part, not before. Oxygen prevent proper reticulation of the resin by UV light.
@ralfieri JohnHue is correct - oxygen inhibiting the cure isn’t relevant to printed parts hanging out on the build platform for hours, or days after printing.
Anecdotally and unofficially, I’m not sure a heated post-cure is as important for Elastic resin as it is for other resins. That said, to get a heated, underwater cure with Elastic, I fill a plastic jar with hot tap water, and then run the cure with No Heat. I know that the water won’t cool off too much during the cure time. I find that about 10 minutes cure time is good at eliminating surface tack, and giving good enough tear strength. The officially-recommended 20 minutes should be good too, but beyond 20 minutes, you may see some yellowing.