Collapsible core moulds are specialized tooling components used in injection moulding to produce undercuts or complex internal features in plastic parts, which cannot be demoulded using traditional straight-pull moulds. These cores collapse inward after moulding to allow easy ejection of the part.
Purpose and Application:
In plastic part design, internal features such as threads, grooves, or reentrant geometries often pose a challenge for demoulding. Collapsible core moulds enable the creation of such features without needing side actions or unscrewing mechanisms, making them ideal for:
Threaded caps and closures
Medical and consumer products
Automotive components
Parts with internal snap-fits or retaining rings
How It Works:
Injection Phase:
The collapsible core is in an expanded (open) state.
Molten plastic is injected into the cavity around the core.
Cooling Phase:
The plastic part solidifies around the core, forming the internal undercut features.
Core Collapse:
Once moulding is complete, the core collapses inward via mechanical or hydraulic action.
The core segments move toward the center, reducing the diameter or profile of the core.
Part Ejection:
The part is now free from undercut constraints and can be ejected smoothly without damage.
Core Reset:
After part removal, the core expands back to its original shape for the next cycle.
Advantages:
Enables moulding of complex internal geometries in a single shot
Reduces or eliminates the need for secondary machining or assembly
Saves space compared to side-action moulds
Increases moulding efficiency and cycle time
Enhances part design flexibility
Limitations:
Higher initial mould cost and complexity
More maintenance due to moving segments
Not ideal for very large parts or extremely high-volume production without careful engineering
Precision required for consistent collapse/expansion cycles
Types of Collapsible Cores:
Mechanically Collapsing Cores:
Use linkages or cam-driven systems to collapse the core segments during ejection.Hydraulic or Pneumatic Collapsing Cores:
Utilize fluid pressure to drive core collapse and reset.Spring-Loaded Collapsing Cores:
Rely on internal spring mechanisms to control the collapsing action.
Conclusion:
Collapsible core moulds are a valuable solution in modern injection moulding, particularly when manufacturing parts with intricate internal details that would otherwise require costly and complex secondary operations. They offer design freedom, reduce assembly steps, and improve part functionality — making them an essential option in high-precision plastic part production.
