Liquid Silicone Rubber Molds

[seanathan]

I have needed to make latches for a portable kegerator project me and a buddy have been working on...and i figured i might as well get experimenting. This first pass was mostly a feasibility study, but it worked pretty well.



I used o flutes for the bulk of the pocketing, a ball nose to round the interior corners, and a 20deg .2mm tip engraving bit for the letter details. Material is hdpe, buts that was just for the first test. I would probably go with aluminum or acetal in the future.



The silicone is 2 part platinum cure with black pigment. It was pressure cast at 45psi. While this worked well, i really need a 60psi pop off for slightly higher pressure as there was 1 small bubble. Also, it needs better clamping, but i couldn't wait for the clamps to come in to test...patience isnt always a virtue.


The injection was done with a large dispensing syringe, so it was obviously low pressure. The injection port is on the back of the top mold half....and you can see the tiny vent port on the other end. 


Here are the molds after the first part was made:





Here's the First Part:

[buildswithbrian]

Very Cool
nice to see some innovative uses for the CNC other than nice woodworking projects
I have been wanting to try making a mold for some castable urethane.

[savannahdan]

Glad you posted this. My wife has been asking whether the CNC can be used to make jewelry molds. I've been thinking a 3d printer would be my best bet because I could print the jewelry piece on it and then make a silicone mold for casting. Did you have to plug the vent plug and then apply more silicone to the pressure you wanted?

[Deleted]

Reynolds Advanced Materials -

www.reynoldsam.com

has recently introduced their Dragon Skin 10 NV -

www.reynoldsam.com/product/dragon-skin/

It doesn't require vacuum degassing and they have great tech support for telling you how to do everything. They also have a variety of silicone molding materials to choose from -

www.reynoldsam.com/product-category/tin-silicone/
www.reynoldsam.com/product-category/platinum-silicone/

[seanathan]

Oct 25, 2018 11:30:45 GMT -5 savannahdan said:

Glad you posted this. My wife has been asking whether the CNC can be used to make jewelry molds. I've been thinking a 3d printer would be my best bet because I could print the jewelry piece on it and then make a silicone mold for casting. Did you have to plug the vent plug and then apply more silicone to the pressure you wanted?

I was actually using a technique called pressure casting where I slightly over filled the mold and then put it in a pressure pot to cure.

I'm actually going to try a similar process with hard urethane soon on some airfoils. I think I will have to vacuum degas and not use the pressure pot in this case due to mold size.

[Deleted]

A common technique for good casting is to paint a first layer directly on your model so that there will be no bubbles on its surface. Then degassing isn't as much of an issue as bubbles in the body of the mold affect your casting little.