These button pads I are made for a GPS faceplate. I’m very pleased with the bubble-free result. I will post more pics after they are painted and laser etched.
If you have a moment I would like to hear more about this.
Is that a mold printed on the Form, what material?
How did you inject the silicone?
Was it just vented on the one side?
Yes the mold was printed from form 2 with clear resin.
I can do a tutorial how I made these parts but also please check out this link where I got my inspiration from. http://www.stratasys.com/solutions/additive-manufacturing/tooling/liquid-silicone-rubber
Are you planning to do a similar project?
Very interesting… A tutorial would be awesome!
I wonder how the success rate is with getting two mold halfs to to align exactly on the Form2.
I did do some experimenting once using vacuum and pressure to cast silicone, the project was stopped, but I remember venting was an issue thats why I asked about that.
Looks great! I’ve some experience myself with casting silicone in standard clear resins molds but always have some airbubbles trapped inside the cast model. The air bubbles are introduced into the silicone when I mix the two components. What did you do to prevent this? Also, did you use some mold release spray to create a “skin” inside the mold to protect the silicone? The kind of silicone I use gets contaminated when it comes in direct contact with the SLA material.
Ideally you place your mixed silicone in a vacuum chamber for a few minutes before injecting. Or if you dont have one you can pour the silicone after it is mixed from one container to another, having the two containers separated by 18" so a fine steam is created when you pour slowly, this will release most of the trapped air bubbles they will pop in the thin stream.
In order to get rid of the bubbles I usually mix the two part silicone in a container pour it in a syringe then degas in a vacuum chamber. After injecting it in a mold I then place it inside a compression chamber for however long the cure time is.
This is my my result =)
Also I don’t use mold release. Just inject the silicone directly in to the mold.
You will notice the part feel sticky after demolding it as if it didn’t cure properly this is actually normal. Use a blow dryer or a heat gun for a couple of minutes and your part will feel smooth and dry.
There are also two common types of silicone used on molding - platinum cure and tin cure. The tin cure is usually less affected by contamination. The downside is that you have to measure the ratio carefully (and it is usually something like 10:1). Platinum cure is usually equal parts mixed and if you are off a bit it doesn’t matter.
If you have having sticky castings you could switch to tin cure and will probably have better luck. You could also post-cure your mold - that would probably help.
I have been try to make a mold of a part printed in black resin and having no luck. The Platinum silicone will not cure. I’ve tried to seal the parts with clear spray paint and that doesn’t even work. I may have to try Tin Cure silicone. Do you have tips on post-curing the parts or what silicone brand to use?
I’m curious which platinum silicone did you use?
Smooth on Rebound 25
I may try a tin-cure silicone next, but hate spending money on one failed experiment after another.
Another option which works very well to get rid of bubbles is centrifuging. If the volume isn’t too large and you have access to a centrifuge, I run 2 minutes at 3200rpm (or 1315 × g relative centrifugal force), this removes all bubbles. Remember to balance the centrifuge.
Those button pads look great!