Designing Undercuts: Techniques and Tooling Considerations
Designing Undercuts: Techniques and Tooling Considerations
Pioneer Plastech
written by Joyce W.
edited by Joyce W.
In the world of injection molding, undercuts present unique design and tooling challenges. Whether you're creating snap fits, holes perpendicular to the mold opening direction, or complex part geometries, undercuts require specialized solutions to ensure manufacturability without compromising function or quality.
What is an Undercut?
An undercut refers to any recessed or protruding feature that prevents the mold from opening or ejecting the part in a straight line. Common examples include internal threads, side holes, and latches. These features often add value to the product’s functionality but complicate the mold design and manufacturing process.
Techniques for Managing Undercuts
There are several ways to address undercuts in injection molding, depending on part geometry, material, and production volume:
- Side Actions (Slides):
The most common solution for undercuts. Slides move perpendicular to the mold opening direction and retract during part ejection. Ideal for large-scale production with consistent geometry.
- Lifters:
These angled components rise during ejection to clear internal undercuts, such as snap features. Lifters are excellent for designs that require internal release but have limited access from the mold's exterior.
- Collapsible Cores & Unscrewing Mechanisms:
Used for internal threads or circular undercuts, these systems allow complex internal features to be formed and released. They are typically reserved for high-precision or high-volume production due to cost.
- Part Redesign or Assembly Split:
In some cases, it's more cost-effective to redesign the part to eliminate the undercut or split it into multiple components for later assembly. This approach balances cost, performance, and tooling complexity.
Tooling Considerations
Undercuts inevitably lead to more complex mold construction. Here are key tooling factors to consider:
1) Mold Cost & Lead Time: More moving components mean higher tooling costs and longer build times.
2) Tolerance Control: Slides and lifters introduce tolerance challenges, especially in multi-cavity tools.
3) Maintenance Requirements: Moving parts like slides and lifters require regular maintenance to ensure mold longevity and consistent part quality.
4) Ejection Force & Parting Lines: Designing smooth ejection paths and minimizing cosmetic impact at parting lines is critical for high-appearance parts.
Conclusion
Designing undercuts is a balancing act between function, manufacturability, and cost. A close collaboration between product designers and mold makers during the early design stages can prevent costly iterations later. By understanding the available techniques and tooling implications, manufacturers can make informed decisions that optimize both product performance and production efficiency.
