We're looking at prototyping some parts out of compression molded silicone. I'm having trouble finding a good reference on the actual molding process: mold design, tonnage, etc. Pretty much all of the compression molding resources I've found are geared towards bulk molding compound, so they are running high tonnage (3-4 tons / in2) and needing to close rapidly. My understanding with silicone is that we can put it in a cold mold, clamp it down, and then put it in the oven to cure. Does anyone have any good resources (either online or a book) for compression molding silicone?
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Compression molding silicone
- Thread starter DanielG
- Start date
- Replies 5
- Views 708
Scottl
Diamond
- Joined
- Nov 3, 2013
- Location
- Eastern Massachusetts, USA
No personal experience but this looks like a pretty good writeup.
Guide to Compression Molding From Prototyping to Mass Production
Learn how anyone can use compression molding to create prototypes, mass produce parts, and everything in between.
formlabs.com
implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi Daniel G:
My experience with compression molding silicone is pretty limited but there are a couple of things I remember.
(I did a project involving escape respirator exhaust valves back around 2005 or so.)
So the things:
1) The project was far more successful when we went to a transfer mold compared to a bog standard compression mold that you pack from the parting surface.
We were molding low durometer flurosilicone and it was a bitch to cryo deflash, so transfer molding helped a lot. (less flash to start with)
2) Our first prototype mold was aluminum, and as I recall, the silicone stuck to it badly; I believe we ended up going to NAK 80 and that was fine.
You can crowd a lot of cavities together with a transfer mold...ours was about 6" x 6" and had 9 cavities in it each about 3/4" diameter if I recall right.
The tonnage on a transfer mold is not that high but I can't recall what it was.
You still have to get the uncured silicone from the transfer pot through the gates into the cavities (0.025" round gates for my parts, I believe) so you do have to give it a bit of grunt but nothing like injection molding.
I believe the gates were about 0.025" tall too, and nothing bent when the mold was squeezed in the press, so not much tonnage.
I want to say the transfer pot was about 4" x 4" but I really can't remember if that is true and the files are long gone so I can't look it up.
So that's it for what it's worth.
Hopefully that is of some use to you.
I gotta ask though, why are you planning to prototype using this process?...there are several others available to you including gravity pour urethanes and 3D printed flexible plastics too.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
My experience with compression molding silicone is pretty limited but there are a couple of things I remember.
(I did a project involving escape respirator exhaust valves back around 2005 or so.)
So the things:
1) The project was far more successful when we went to a transfer mold compared to a bog standard compression mold that you pack from the parting surface.
We were molding low durometer flurosilicone and it was a bitch to cryo deflash, so transfer molding helped a lot. (less flash to start with)
2) Our first prototype mold was aluminum, and as I recall, the silicone stuck to it badly; I believe we ended up going to NAK 80 and that was fine.
You can crowd a lot of cavities together with a transfer mold...ours was about 6" x 6" and had 9 cavities in it each about 3/4" diameter if I recall right.
The tonnage on a transfer mold is not that high but I can't recall what it was.
You still have to get the uncured silicone from the transfer pot through the gates into the cavities (0.025" round gates for my parts, I believe) so you do have to give it a bit of grunt but nothing like injection molding.
I believe the gates were about 0.025" tall too, and nothing bent when the mold was squeezed in the press, so not much tonnage.
I want to say the transfer pot was about 4" x 4" but I really can't remember if that is true and the files are long gone so I can't look it up.
So that's it for what it's worth.
Hopefully that is of some use to you.
I gotta ask though, why are you planning to prototype using this process?...there are several others available to you including gravity pour urethanes and 3D printed flexible plastics too.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
Last edited:
BoxcarPete
Stainless
- Joined
- Nov 30, 2018
- Location
- Michigan, USA
I'm not surprised that you're only finding sources for big boy presses. For most people invested in the rubber molding industry, there are usually only two differences between a prototype tool and a production tool: the number of cavities (1 or 4 vs 16, 64, or 400+), and hardness of steel.
Marcus, I'm impressed that you were able to cryo deflash fluorosilicone at all.
Marcus, I'm impressed that you were able to cryo deflash fluorosilicone at all.
implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi Boxcar Pete:
You wrote: "Marcus, I'm impressed that you were able to cryo deflash fluorosilicone at all."
It wasn't me...it was a company in Texas whose name now escapes me.
They did swear a lot.
But they did it eventually.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
You wrote: "Marcus, I'm impressed that you were able to cryo deflash fluorosilicone at all."
It wasn't me...it was a company in Texas whose name now escapes me.
They did swear a lot.
But they did it eventually.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
Thanks for the advice. This is a low-rate part that may make more sense to farm out to a compression molding shop. At this point I'm trying to see if doing it in-house is feasible. We're more set up for metals and composites, so silicone is new to us. Part of the part is a weird EMI shielding silicone, so we have to do it in silicone.
