Silicone rubber parts are used in virtually every product market from infant care, medical, dental applications to beauty and cosmetics. The term silicone prototyping more commonly refers to the process of using RTV silicone molds for making cast urethane prototype parts (discussed further in the next section). Silicone rubber prototyping as discussed in this section refers to actual silicone rubber prototype parts. There are two primary methods used in making these parts. One process utilizes machined molds made from either aluminum, acrylic or Renshape. The second utilizes an RTV mold made from a "master" pattern which is discussed in further detail below. The latter is not commonly done, is very difficult and one of the main reasons why most prototypers do not offer silicone prototype services. Silicone is a material that takes feature detail very well and can be held to tight dimensional tolerances. The silicones used to produce prototype parts come as two part mixtures (base and catalyst) and are selected based upon the desired mechanical properties of the finished parts. Once the two part mixtures are combined and cast into the mold cavity there is a curing (hardening) process which occurs. Depending upon the selected mixture, the curing process may occur at room temperature (room temperature vulcanizing or RTV) or with the use of an oven curing process and possibly both in some cases.
These are the prototype silicone rubber parts we had made from the Edelhoff face seal design. Again, silicone takes feature detail with a high degree of accuracy and the final product in many cases is a very near to production quality part. These parts were used to test and validate a final production molding design:
The images below were taken from a (3) part RTV silicone mold that we had constructed for Edelhoff Technologies'rubber face seal project. These molds are constructed by pouring and immersing the two part silicone mixture over the pre-treated SLA master pattern. After the silicone cures, the master pattern is removed and the resultant mold may be further treated to increase it's operational longevity and liklihood of producing high quality parts. Process times for making parts by this method are longer with respect to rapid prototyping but in many cases the need for production quality part for testing and validating designs justifies it's use. Normal curing time for most silicones is between 18 and 24 hours, but cure times may be greatly reduced by using fast-acting catalysts: