Complex Undercuts and Hooks: How to Design the Mold?

In consumer products, functional requirements often necessitate the inclusion of hooks and undercuts in product design. Some products feature undercuts on both exterior and interior surfaces, along with specialized internal undercuts, deep reinforcing ribs, and a highly complex front mold cavity. Additionally, the external structure may involve numerous undercuts. How should the mold structure be designed for such challenging products? This article shares insights through an automotive cover mold design case study, aiming to provide practical guidance.

Table of contents：
Product Gating Method
Critical Design Challenges
Key Structural Details

Product Gating Method

Common gating methods include edge gating, submarine gating, direct sprue, horn-shaped gates, and pinpoint gates. For this automotive cover, strict aesthetic requirements and high production efficiency dictated the use of a large sprue direct gating system, as shown below:

Critical Design Challenges

Front Mold Complexity

• Slope analysis revealed deep reinforcing ribs (80mm depth) and a cylindrical feature in the front mold cavity.
• Design Solutions:
  • The cylindrical feature was split into a front mold insert to prevent sticking.
  • For deep ribs, a front mold ejection system (actuated by a latch mechanism during mold opening) was added to ensure smooth demolding.
• The circular product geometry includes undercuts around its perimeter, some facing opposing directions (see diagram).

Rear Mold Undercuts

• The rear mold contains five undercuts:
• First Undercut: A long-travel slide requiring a hydraulic cylinder for core pulling.
• Second and Fifth Undercuts: Identical angled slides. Due to limited space adjacent to the first slide, the second slide uses single-sided guide rails. Thick A-plate design allows angled guide pins for smaller slides to be secured with clamping blocks.
• Third and Fourth Undercuts: Long-travel angled slides with embedded cores. These require hydraulic cylinder actuation and modular core inserts for manufacturability.

Key Structural Details

Front Mold Ejection System. A latch mechanism synchronizes ejection with mold opening to release the product from deep ribs and inserts.

Hydraulic Slide Design. Long-travel slides integrate modular core inserts to simplify machining and maintenance. Hydraulic cylinders connect to slide inserts via robust linkages to withstand high pulling forces.

Space Optimization. Single-sided guide rails and compact clamping blocks address spatial constraints near adjacent slides.

Conclusion

This case demonstrates strategies for complex molds:

• Modular inserts for deep features and undercuts.
• Hydraulic actuation for long-travel slides.
• Front mold ejection to address sticking risks.
• Space-efficient guidance systems (e.g., single-sided rails).

By balancing structural robustness, manufacturability, and demolding reliability, such designs meet both functional and production demands.