Urethane Casting Design Guidelines

Urethane Casting Design Guidelines

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Urethane castings offer a practical solution for producing production-grade plastic parts without the drawbacks associated with costly hard tooling, complicated designs, and extended lead times. When creating cast urethane components, adhering to fundamental design guidelines is crucial. Following these rules will help maintain your part's functionality and ensure timely production. To assist you in developing master patterns that meet your specifications, Premium Part Manufacturing Solutions has compiled a set of actionable tips for designing high-quality urethane cast parts.

1. Maintain Uniform Wall Thickness

Consistency in wall thickness is vital for ensuring the dimensional stability of urethane cast parts. The wall thickness should be uniform throughout the part, allowing the molten urethane to flow into the mold and cure evenly. Variability in wall thickness can lead to failure, impact functionality, and even result in product defects during production. Ideally, wall thickness should fall within the range of 0.020" to 0.050", with recommendations of at least 0.20" for smaller parts and 0.40" for larger ones. Keep in mind that wall thickness must provide the necessary support based on product size, with average thickness ranging from 0.80" to 1.50".

2. Incorporate Draft Angles and Undercuts

Unlike injection molding, the design of urethane castings does not require significant emphasis on drafts, as liquid urethane is inherently fluid and conforms to any mold shape. However, to avoid issues such as breakage and warping, it's advisable to include a draft angle of at least one degree in your design. This practice aids in the easy extraction of the finished part from the mold.

3. Account for Shrinkage

Shrinkage is a normal aspect of both urethane casting and metal die-casting processes. It occurs due to the density change between the liquid urethane and the solidified part. Therefore, the final dimensions of your cast urethane part will largely depend on the precision and allowances built into your master pattern design. For optimal results, factor in a shrinkage rate typically ranging from 0.10% to 0.20%.

4. Evaluate Accessibility and Manufacturing Feasibility

Having a thorough understanding of your design, paying close attention to both functional and purely aesthetic features, greatly contributes to creating an effective master model. Before introducing specific features, assess their importance and how they can influence the part’s functionality and moldability. For corners, utilize radii of at least 0.125" to ensure strength and facilitate seamless mold flow. Boss corners should have radii of around 0.060" to maintain part strength, even with slightly reduced wall thickness. Keep your urethane casting design tolerances within +/- 0.010" for the first inch and half that for every additional inch. It is crucial to eliminate any design features that may complicate mold flow or inflate overall production costs.

5. Finishing Considerations

Finishing aspects are also important when creating urethane cast parts, as they can be produced with various finishes including matte, sanded, and polished surfaces, as well as options for lettering, embossing, or engraving at an additional cost. If your cast parts require lettering, ensure that the logo or marking is at least 0.040 inches thick, either raised to this thickness for an elevated effect or recessed to achieve a sunk-in effect.

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