If you’ve tried to mold resin 3dprinted parts before and got a goopy mess, here’s some tips on how to get a successful silicone mold from a resin 3dprint. When silicone rubber doesn’t harden out all the way after the cure time and you’re sure you mixed the rubber properly, it is called cure inhibition. Cure inhibition is caused by incompatible chemicals in the part you’re trying to mold.
Method 1: Use tin silicone. Tin silicone is not affected by chemicals that cause cure inhibition as much as platinum silicone. However, most tin silicone has a lower tear strength and a high viscosity (it is thick, doesn’t flow as easily), which doesn’t always work well for every project, especially a complex one. This method is recommended for simple 1 part box molds, and is usually pretty cheap and easy to get.
Recommended products: Mold Max series by Smooth-On, Amazing Mold Rubber by Aluminite
The lower the Shore A number, the softer the silicone rubber. Softer silicone is easier to demold complex parts with undercuts or concave areas, and harder silicone rubber maintains shape better for parts with less complex surfaces, so the resulting cast has less opportunity to warp or expand. Harder rubber will also last longer if you need to make many copies.
Method 2: Use a special platinum silicone developed to resist cure inhibition. You should still wash, dry and cure your resin 3dprint about 2 or 3x longer than normal or do it multiple times. 20 to 30 minutes of UV curing works well in my experience. Make sure you don’t see any glossy wet-looking areas on the resin print after the curing. If you do, wash and cure it again. This method has no need for primers or sealers.
Platinum silicone designed for resin 3dprints by SirayaTech.
Method 3: Use standard platinum silicone. This method is the most risky, especially for big projects. You wash and cure the resin print extra just like in method 2. It is highly recommended to let your resin part dry out on the shelf for a week.
You have to seal your resin print after, preferably using a coat of a very hardy 2K clearcoat or multiple coats of acrylic varnish, then let your resin print cure again for a couple days. Before you mold your entire part, test for cure inhibition by mixing up a tiny bit of platinum silicone and applying it into a concave or deepest area of your resin print. Those areas are the dodgy risky bits that would receive less UV light and a thinner coat of your sealer. If it’s not sticky after the rubber cure time elapsed, you should be safe to mold the entire part.
You could also try products to help prevent cure inhibition, but I haven’t tried those myself. Such as Inhibit X by Smooth-on.
Common platinum silicone mold rubbers are Mold Star series by Smooth-On, Amazing Mold Maker Silicone by Aluminite, or Plat-Sil by Aluminite