Bastech, Inc. Rapid Prototyping • Rapid Manufacturing

RTV/Urethane Molds

Bastech, Inc.'s model shop has the capability to provide services from custom finishing, painting and assembly of SLA and SLS models to RTV silicone molding.

  • RTV Molding
  • Urethane Reproductions
  • Custom Finishing & Painting
  • Machined Patterns

RTV Silicone Molding

RTV (Room Temperature Vulcanization) silicone molding is a well-recognized rapid tooling method for producing small quantities of production-like prototypes of plastic injection molded parts. Short mold lead times are coupled with exceptional detail and surface finish. Complex parts with undercuts can be produced using this process. RTV molding is very cost effective at low quantities while maintaining good accuracy and excellent detail. Prototype parts can be color matched and textured with a variety of material characteristics. Durometers range from very soft foams or rubbers through very rigid nylon-like materials. Some functional testing can be performed.

Use RTV Silicone Molds when your project requires short lead times, low volumes, production-like characteristics, and fine detail and surface finish.

Understanding Urethane Molding

Urethane molding is a process where a master pattern, typically created by stereolithography, is used to cast a silicone mold that can then be injected with various urethane materials.

Step-by-step Process

1. Create and prepare master pattern. Usually the best choice for master pattern is a SLA model. However, existing parts or machined parts can also be used with success. If an SLA model is used, it can be polished for a smooth finish or textured for a custom look. The finish of the pattern will transfer to the mold and cast urethane pieces.

2. Create the silicone mold. The mold parting line and vent and fill holes are determined based upon the part geometry. There are various methods for creating a parting line; two of the methods used by Bastech are clay for a two pour mold or tape for a single-pour mold. To create a two-part mold, the parting line is clayed and the part is enclosed in a box. Silicone is poured around the model to create its negative. The part is then flipped, the clay is removed and the second half of the mold is poured. Once the silicone has cured, the master is removed and the mold is cleaned and prepared for injection.

3. Inject and pressurize mold. Urethane material is mixed and/or colorized and injected into the mold through fill holes using low-pressure pneumatic gun injection method. The mold is placed into a pressure pot to compress air bubbles that may have been trapped during injection.

4. Remove parts from mold. After the allotted cure time has passed, the molds are removed from the pressure pot, opened, and the part is then carefully removed.

5. Post-finish urethane reproductions. Gates and flashing are removed from urethane parts. Straightening is sometimes required. The parts may also be painted, polished, or functionally assembled. Threaded inserts, if not added during molding, can be added at this time.

Material Description Advantages Considerations Applications

Urethanes, a wide variety of material characteristics

A rubber mold is created from an SLA model.  Urethane material is then filled into the void and a duplicate part is created.

  • Excellent detail and surface finish
  • Quick turn-around
  • Simulate some production material properties
  • Mold typically lasts for 25 - 30 shots
  • Low temp. heat deflection
  • Tolerances +/- 0.010
  • Plastic parts in quantities of 15 –25
  • Excellent for display or field test models