Cast Urethane Models & Low Volume Production

RTV silicone molds are the fastest, most accurate, and least expensive way to create duplicates of a prototype part in quantities from one up to hundreds of pieces. RTV molds can faithfully duplicate details and textures present on the original part, and can be very forgiving of part geometry when it comes time to remove it from the mold.

After the RTV molds are completed, they are then typically used to produce limited quantity polyurethane castings with a wide variety of material properties. Urethane casting material can be formulated to imitate elastomers, high-impact materials, and glass filled materials. It can mimic production parts in material and thermal properties, color, and surface texture. It can also be machined, sanded, glued, and painted readily or have color cast into the part.

Urethane Casting Applications

With the RTV molding and casting process, low volumes of prototype parts can be produced quickly and without hard tooling. These parts may serve a variety of purposes, such as:

• Sales and marketing demos
• Conceptual models
• Pre-production parts
• Low volume production
• Durable representative and functional models
• Rapid and inexpensive test assemblies, etc.
• Insert molding capabilities

Urethane Casting Materials

• Flexible (25 Shore A) materials to hard durable urethanes (90 Shore D)
• Cast-in custom coloring
• Materials with UL 94V0 ratings
• Glass filled materials
• Simulate injection molded properties
• Finishing techniques include painting, plating and texturing

Urethane Casting Production Rates and Accuracy

From RTV mold to first part: 3-7 days after customer approval of the RP master pattern. Typically a mold can be shot 1-3 times per day. A typical mold will yield from 10-20 parts before breakdown of the RTV material. The rubber molds are as accurate as the RP model (+/-0.005 – 0.010") on critical to function features; however, tolerances of +/-0.002" have been achieved.

Process Description

A rapid prototype (RP) model is used as a master pattern to form the RTV rubber mold. This RP model can be made via any RP technology (i.e. FDM, SLA, SLS, CNC, etc.).

After customer approval of the RP model, the model is hand-finished to a high level on all required surfaces with texturing if required. If inserts are going to be cast into the parts, the RP model would be made with these inserts in the CAD data so that the insert is represented in the RP model or the insert can be added after the RP model is completed. In either event, the insert is added to the master model prior to casting the RTV rubber mold. In the case of large sized parts and particular casting materials, the master pattern may be made oversized to compensate for shrinkage.

The master pattern is then surrounded by a parting surface that establishes the parting line of the mold. The liquid RTV rubber is poured over the pattern and parting surface combination. Once the rubber has solidified, the parting block is removed. Then rubber is poured over the pattern and first mold half combination to complete the second mold half. The pattern is removed to yield the mold halves of a rubber tool.

Complicated geometries may require more than two pours to form cores or cavities to encapsulate all the geometry. Curing time for the mold is dependent on the product and curing agent but is usually 24 hours per pour. Liquid urethanes, thermoset materials, are then poured or injected into the rubber mold and left to solidify. The RTV tool is then separated to remove the cast urethane prototype.

Urethane castings from PERIDOT, Inc. can be further categorized into standard castings, flame retardant castings, or food and medical grade castings. Contact us today for a custom quotation on a cast urethane manufacturing solution that will meet your exact needs.