Preform Mold Stack With Retractable Neck Rings and Cam Actuation
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Solution Overview
Problem
Current preform injection molding systems face challenges in efficiently ejecting preforms with complex geometries, such as bell-mouth or reverse-taper designs, due to limitations in mold design and ejection mechanisms, which can lead to preform distortion and increased friction during the ejection process.
Innovation Solution
A preform molding system with a mold stack assembly featuring a core insert with an undercut to create an annular protrusion, paired with a stripper ring and neck rings that retract to allow radial expansion of the preform's open end, facilitating smooth ejection and minimizing distortion, using a cam plate and cam follower mechanism to manage the lateral displacement of neck rings and stripper plate for precise alignment and ejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional mold design without undercut is used, then the ejection process is simple, but preforms with complex geometries (bell-mouth or reverse-taper) cannot be properly formed or ejected without distortion
Solution Approach 1:
The mold core is segmented into multiple components: a core insert with undercut features, neck rings, and a stripper ring. This segmentation allows each component to perform a specific function - the core insert forms the complex geometry, the neck rings maintain neck dimensions, and the stripper ring facilitates ejection - while collectively enabling precise formation of bell-mouth or reverse-taper preforms without excessive overall mold complexity
Solution Approach 2:
The mold design incorporates dynamic elements including the retractable neck rings that move axially to accommodate preform expansion, and the stripper ring that applies ejection force. These dynamic components allow the mold to adapt during the ejection process, maintaining precision for complex geometries while managing the complexity through controlled movement rather than fixed complex structures
2Ease of operation
If a standard ejection mechanism is used, then the ejection process is straightforward, but friction during ejection increases causing preform distortion
Solution Approach 1:
The ejection function is extracted and dedicated to a separate stripper ring component that is axially displaceable relative to the core insert. This dedicated ejection mechanism applies force uniformly to the preform's outer surface, reducing friction and distortion during ejection while keeping the core insert focused on forming the complex geometry, thus maintaining both operational simplicity and reducing harmful friction effects
Solution Approach 2:
The stripper ring acts as an intermediary between the ejection system and the preform. It transfers ejection force uniformly across the preform's outer surface, mediating the interaction to minimize localized stress and friction that would cause distortion, while the neck rings serve as intermediaries to maintain neck dimensions during the process
3Stability of the object's composition
If neck rings remain fixed during ejection, then alignment is maintained, but preform radial expansion is restricted causing ejection difficulties
Solution Approach 1:
The neck rings are designed with axial mobility while maintaining radial positioning. During ejection, they can move axially to accommodate the preform's radial expansion at the open end, preventing ejection difficulties. The cam plate mechanism provides dynamic control, allowing the neck rings to retract when needed while maintaining alignment stability through their guided movement paths
Data Source
AI summary
A preform molding system is disclosed that includes a cavity half that is mountable to a stationary platen of an injection molding machine and a core half that is mountable to a moving platen of the injection molding machine. The preform molding system includes a mold stack assembly having a cavity portion and a core portion. The cavity portion is coupled to the cavity half and includes a cavity insert, and the core portion is coupled to the core half and includes a core insert, a pair of neck rings, and a stripper ring. The core insert has an undercut that defines an annular protrusion on an internal surface of a preform that is created in the mold stack assembly. The preform molding system is configured to permit in sequence, retraction of the pair of neck rings away from the core insert and ejection of the preform from the core insert via the stripper ring.