OVERVIEW

Urethane Castings are ideal when you need parts that have properties similar to production parts and need to look production quality. It is a cost-effective method to reproduce a small quantity of prototypes for sales and marketing, early customer samples, focus groups, or design verification.

Urethane Castings typically fit in the development process between prototype and production. Urethane is used because it is cost effective for low quantity and urethane materials can be chosen to match specific mechanical properties of the production material.

The casting process is capable of reproducing small details. Due to the flexibility of the molds, draft angles and undercuts are not as critical as in other molding processes. Urethane Castings are produced using low-cost silicone molds, sometimes called RTV (Room Temperature Vulcanization) molds.

Urethanes can be used for functional testing depending on the objective of the testing. For example, when performing life testing or failure mode testing, urethanes are typically not a good substitute for the production material parts unless the urethane part is not the part under failure mode test. However when a specific test parameter can be isolated (deformation, mechanical operation under load, impact, etc.) a urethane with material properties that closely match the specific production material property can often be used for testing. A lower material property value may be adequate since the part is being testing in a typical environment, which requires no safety margin.

 

PROCESS

Step 1 — The Pattern

The process begins by first building an SLA master pattern. In most cases, draft is not an issue and small undercuts are not a problem because the silicone mold is flexible. Large undercuts are accommodated using hand loaded tooling.

Step 2 — The Tool

The master pattern is finished to a pattern level finish. A gate assembly is attached to the master pattern and the master pattern is suspended in a frame or box. Silicone is poured around the master pattern and is allowed to cure. Once the silicone is cured, one or more cuts are made in the mold to remove the master pattern.

Step 3 — The Parts

The mold is then reassembled and the urethane material is poured into the mold to create the urethane casting. Once the urethane has hardened, it is removed and the mold can be used to cast additional parts. These molds can produce up to 20 parts per mold, and they can be made as family or multi-cavity molds. Depending on the material selected, one to four parts per day can be produced from a tool. When more parts per day are required, a multicavity tool can be made to meet the requirements.

Rubber tools yield between 8 and 20 parts in Shore D materials and between 50 and 75 parts in Shore A materials.

To prevent colors from chipping, parts are cast in color instead of painted. DPT can custom color match using a Pantone or color sample. Texture is added to the SLA patterns by transferring the texture directly to the mold when it is created. Different textures are available and multiple textures can be placed on the same part for cosmetic purposes.

 

ADDITIONAL USES

Urethane casting can also be used to create two-shot production.

Step 1

Two patterns are produced:
Rubber Mold A: With the over mold
Rubber Mold B: Without the over mold

Step 2

Two rubber molds are produced and the urethane is cast.

Step 3

The first part is cast into Rubber Mold B. That part is then pulled from the mold and inserted into Rubber Mold A.

Step 4

The over mold is cast around the existing cast part. Once that part is pulled, it has both materials cast to complete the two-part over mold.

Existing parts can also be cast into a urethane casting, such as embedded pins and wiring.

 

APPLICATIONS

• Intermediate number of prototypes needed (5 - 100)
• Form and fit testing
• Functional testing
• Field testing
• Focus group and presentation models