Silicone Design Limitations: Is there a minimum/maximum dimension that is achievable or surface finish that is unattainable?

Silicone, especially liquid silicone will conform well to just about any mold shape that can be dreamed up, the difficulty is typically in the mold making process. In the prototyping sector, we see a lot of cutting edge design concepts that push the envelope with features that are very small and precise. Every molder has their own specialty and also their own limitations. At Albright we specialize in quick-turn micro medical device parts molded in liquid silicone rubber. One design limitation that we frequently contend with is the size and geometry of micro features, we like to use “The 3X Rule”, which basically means that if you have a microscopic opening in your part design (which would be reflective of a raised boss in the mold) the overall height of that feature shouldn’t exceed three times the diameter (or side length) of the feature. That would mean that if you wanted to form a 0.005″ diameter hole in your molded part, you wouldn’t want to go much more than 0.015″ deep into the part, from a tool making standpoint.

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