Silicone Rubber
RTV Molding

Silicone is cast around an SLA master pattern creating a repeatable mold. After curing, the mold is used to create cast urethane prototypes of your design. This process is also called “soft tooling” and is often used as a cost-effective method to create low-run length prototype parts.

The process begins with a 3D printed stereolithography (SLA) rapid prototype master pattern. Machined and/or fabricated master patterns can also be used for tighter tolerances. The SLA RP model is inspected for accuracy, then the “appearance” surfaces are bead-blasted, sanded smooth, and a primer coat is applied to achieve the surface finish required to meet your application requirements. If the parts are to be polished or cast in clear resin, then the surface will be polished to a gloss finish in preparation for making the silicone rubber mold.

Bastech RTV Molding #3.jpg

Next, the mold is created. The silicone rubber uses a room temperature vulcanization process typically referred to as RTV. The part is scrutinized by one of our technicians to determine the best molding setup to achieve the highest quality urethane casting reproduction. Parting lines are selected to assure the best location thus avoiding flash on appearance surfaces. Rubber mold runners, gates, sprues, and vents are located in areas to support mold fill, isolating and minimizing air bubbles to non-critical areas, while optimizing appearance surface quality.

The SLA rapid prototype master is set-up on a parting block to make a two- (or many) part mold or suspended in a frame to make a one-part cut mold. Silicone is poured around the SLA master pattern to create the mold. After the silicone is fully cured (approximately one day), the master pattern is removed and the mold is reassembled, whereupon the urethane material is poured into the mold to create the cast urethane part.