Definition: A thermoplastic is a plastic polymer material that becomes pliable or moldable above a specific temperature and solidifies upon cooling.
Definition: A thermosetting plastic is a polymer that irreversibly crosslinks and cures when heated due to internal catalyst or external heat source. Thermosets cannot be heated and reformed once cured.
Over the past 30 years of owning and operating my Product Model Shop, the majority of Solid Models I received were designed for the process of injection molding using thermoplastics for high volume production. Most plastic parts are designed for the injection molding process using thermoplastics, facilitating long term production of parts.
If you are planning to make visual models, functional prototypes, or short-run production parts utilizing silicone molds and castable polyurethane materials, it may be a good idea to look over the Solid Model before having it fabricated (machined or 3D printed), molded and cast.
Here is a list of things you can do to produce stronger cast parts while increasing your silicone mold life.
Parts designed for the injection molding process generally have thin wall sections. The part walls are kept thin to keep the material and production costs down. For thermoplastics, thinner walls mean faster demold times. Unlike thermoplastics, thermo-set plastics (like castable polyurethane) can be demolded quicker with thicker walls. Thin wall sections will limit your polyurethane casting material selection requiring lower viscosity material options only. Suffice to say, adding wall thickness where possible in polyurethane cast parts will help strengthen your part and decrease your demold time.
Try to eliminate undercuts where possible. Stretching and distorting the mold in order to remove parts with an undercut can be hard on molds and reduce the life of the mold. Where possible, fill in the small voids of the part between bosses, ribs, and part walls to eliminate thin silicone sections. Finally, eliminate sharp corners where possible by creating a fillet or radius in those areas.
As always, should you have additional questions on this topic, feel free to contact our knowledgable & helpful Tech Department.