So I said I post more of the process. This will show making the silicone mold. Here we go:
1. Grab your mold
20121014_153156.jpg [ 2.87 MiB | Viewed 360 times ]
2. I use my CAD software to figure out the volume of the mold cavity, then subtract the volume of the part from that to find how much empty space needs to be filled. I do a little math to figure out how much silicone I need, by weight, and add a little extra to be sure it overflows the mold just a bit. Then I weigh out the components.
20121017_204922.jpg [ 2.95 MiB | Viewed 360 times ]
20121017_205109.jpg [ 2.99 MiB | Viewed 360 times ]
3. Then mix it well and place it in the vacuum chamber to degas. The container you mix in should be at least 3 times the volume of the silicone. That allows space for the silicone to expand as the bubbles grow. After a short amount of time the silicone collapses and it's ready to pour into the mold.
You might be able to see that my container wasn't three times the volume of the silicone in it. In this case, I let the silicone rise to the top, release vacuum, let it rise again, release vacuum, and continue to do this until it collapses.
20121017_205843.jpg [ 2.52 MiB | Viewed 360 times ]
4. Pour silicone into the mold to fill it only part way, making sure that every surface is covered by at least a little silicone. This is important for degassing a second time, allowing the silicone to get into every tiny detail. In this pic you can see the chamber extension I had to make. Just a tube with a similar diameter that I made a gasket for with silicone window sealant.
20121017_210955.jpg [ 2.45 MiB | Viewed 360 times ]
5. Fill the mold with the remainder of the silicone and leave it alone for several minutes to allow any bubbles to rise to the surface. Give them a gentle blast with canned air and they'll pop quite easily.
20121017_211604.jpg [ 2.79 MiB | Viewed 360 times ]
6. Take a sheet of hdpe large enough to cover the entire block and place it on gently, starting from one side and lying it down slowly so that no air gets trapped underneath. Then put the classiest (yeah, beer bottles. That's classy) weight you can find on top to clamp the sheet down. This will push extra silicone out and give the mold a flat bottom.
The size of the mold will dictate how much weight you'll need. I've got 6lbs on this one. Just be careful not to weight the middle too much or you'll have a depression in the middle of your mold from the sheet's deflection.
20121017_212238.jpg [ 2.27 MiB | Viewed 360 times ]
7. Next you'll remove the mold. This involves cussing, sweating, bleeding, more cussing, sawing, wondering if it's worth it and finally getting it removed. Ha, this was actually an isolated case, usually it's pretty easy if the mold isn't deeper than 7mm. This one was 23mm deep so it was very difficult. Needed more draft angles.
20121018_180440.jpg [ 3.51 MiB | Viewed 360 times ]
20121018_180451.jpg [ 2.16 MiB | Viewed 360 times ]
8. Now you just cast your part. It's pretty much the same exact process just using polyurethane. You'll also probably need to do it faster since the curing time is usually shorter.
20121023_185422.jpg [ 1.91 MiB | Viewed 360 times ]
So that's pretty much it. I'm sure there are details I missed so if you have questions let me know.