Plastic or Polymer Parts

Silicone tools can typically be used to mold several parts before it becomes necessary to replace them. The number depends on accuracy and finish requirements and the specific geometry of the item produced. It may be possible to make many dozens of simple, or non-critical parts from a single silicone rubber mold, but ten to twenty is typical if the parts are more complex. Wear of the mold occurs due to the exothermic and reactive nature of the polymers, and because of the necessity to mechanically deform the mold to remove the part. It may often be necessary to replace the RP-generated pattern as well, depending on the number of molds to be made and similar accuracy and geometric considerations.

The process is carried out by placing the RP-generated pattern in a frame, usually made of wood. The pattern itself usually must undergo secondary operations to bring it to the desired state of accuracy and finish before it can be used. See the section on RP-generated patterns. Silicone rubber room temperature vulcanizing (RTV) molding compound is then poured around the pattern. It may be necessary to apply a vacuum to the assembly to pull air bubbles out of the rubber and insure fidelity to the pattern. Once the rubber has solidified, the pattern is removed and the mold is ready to be used.

Silicone rubber tooling is most often used in manual casting processes, but in recent years more automated technologies have appeared. So-called reaction injection molding (RIM) systems can produce several parts per hour from rubber molds. Molds also last longer because of the lower exposure time to chemical processes. A number of other variants of the process are also available from particular vendors, such as rubber plaster molding. RPM allows the technique to be extended to other materials, such as metals.