Design Rules for Draft Angles in Injection Molded Products
A draft angle refers to the angle between the mold cavity surface and the mold’s parting line. The presence of this angle allows injection-molded parts to be smoothly ejected from the mold after cooling and shrinkage.
1. Design Principles
Based on Product Shape and Size
Shape Complexity: The more complex the shape, especially with recessed or protruding features, the greater the draft angle required.
Size: Larger products generally require larger draft angles.
Considering Material Properties
Shrinkage Rate: Materials with higher shrinkage rates require larger draft angles.
Flowability: Materials with poor flowability need larger draft angles.
Mold Structure
Mold Opening Direction: Draft angles vary depending on the mold opening direction.
Demolding Aids: Features like sliders or angled ejector pins may influence the draft angle design.
2. Typical Draft Angle Ranges
In general, draft angles range from 1° to 5°, but specific values should be adjusted based on product characteristics:
Small or Thin-Walled Products: 0.5°–1°
Standard Products: 1°–2°
Large or Complex Products: 2°–5°
3. Influencing Factors
Wall Thickness: Thicker walls require larger draft angles.
Surface Finish: Smoother surfaces need smaller draft angles.
Functional Requirements: Products with specific functional needs may require tailored draft angles.
4. Design Considerations
Uniform Draft Angles: Ensure the draft angles are consistent to avoid excessively large or small areas.
Alignment with Mold Opening Direction: Draft angles must align with the demolding direction.
Accounting for Shrinkage: Consider the material’s shrinkage rate when determining the draft angle.
Maximizing Without Compromise: The draft angle should be as large as possible without affecting the appearance or performance of the product.
