Cast Urethane Process
The cast urethane molding process has been around for years. In addition to rapid prototyping, urethane molding can serve as a bridge for injection molding, as well as a low volume molding option when injection molding is cost prohibitive.
Cast urethane parts are strong and have similar properties to that of thermo plastics. These parts can capture remarkable details due to the flexibility of silicone tooling. Additionally, they have the look and feel of an injection molded part and can be crafted from several material options, including both rigid and flexible durometers.
Cast urethane tooling has a limited life, but generally yields from one to 25 parts. Tools can then be refurbished at a cost less than the original tool, and multiple molds can be utilized where volumes and speed are needed. The typical lead-time from start to finish is one to three weeks depending on the requirements.
Options to Consider
There are many cast urethane options to consider, such as materials, color, texture, inserts and over-molding.
- Materials: There are over 40 urethane resins to choose from when designing your part. Most of them are able to meet the demands of several industries, including defense, aerospace, medical and consumer. Resin selections range from 10 shore A to 85 shore D and other available properties include FDA, UL-94VO and fire rated.
- Color: Parts can be painted to your exact specifications and matched to a pantone number or chip. Molded in color is another option for cast urethane parts. Like any paint project, preparation and understanding the properties of the surface are key components of achieving high-quality results.
- Texture: Cast urethane parts can pick up the texture of specific molds. However, different textures can be added to enhance the appearance of the final product. Light Matte and Matte are two of our most popular textures.
- Inserts: Inserts can be molded directly into cast urethane parts, as well as pins, wires and electronics.
- Create master pattern: In this step, a master pattern for your CAD file is created. Once the part is produced at a SLA or CNC machining center, the pattern is then finished to customer specifications, which might include inserts or a surface finish.
- Make the mold: Afterwards, the master pattern is suspended in a frame and silicone is poured around it. Once set, the pattern is removed and the mold is ready for making parts.
- Urethane casting parts: Once a specific urethane material is chosen, it is then injected into the mold. After the urethane hardens, the part is removed.
- Final finishing: Once the part is molded, it is then cleaned and painted before shipment.
Basic Design Tips
Wall thickness – Minimum wall thickness for parts should be no less than .050” with the maximum being .187’. Of course, these are not hard rules and variations are acceptable. Uniform wall thickness is preferred, but variations can be processed without impacting part results.
Drafts – The process for this option is very flexible and engineering-friendly. Unlike injection molded parts, the cast urethane process doesn’t require a draft, which saves valuable design time.
Undercuts – This option is not a concern and can be accommodated for within the cast urethane tooling process.
Ribs – The general rule of thumb is that ribs should not exceed 60% of the nominal thickness. This will help prevent sink effects in the part.
Bosses – These can be easily molded in to accommodate molding in fasteners or inserts.
EMI/RFI shielding – Enclosures designed to house electrical components may require EMI or RFI shielding. PDS offers both processes with copper shielding methods.
Cast Urethane Benefits
- Low tooling investment
- Design freedom
- Ease of design change
- Lower risk
- Fast to market
The cast urethane process is an inexpensive and accurate way to produce parts. Additionally, it can accommodate short lead times and create a variety of low volume production parts.
If time or money is a concern, urethane molding is an excellent alternative to steel tooling. Overall, cast urethane molding is a practical process to produce high-quality prototypes in a fast and efficient manner. Contact PDS today to learn more.