Movable Core Press Molding Apparatus Hard Stop Prevention
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Solution Overview
Problem
In press molding processes, the occurrence of a 'hard stop' due to excess thermoplastic resin causing internal die pressure to exceed the pressing force, leading to incomplete molding and reduced mechanical properties of the final product, is a persistent issue, especially when using stampable sheets with varying basis weights or featuring protuberances and depressions in the dies.
Innovation Solution
Incorporating a movable core within the dies that activates when internal die pressure reaches a predetermined value, allowing the cavity to increase in volume and redirecting excess resin, thereby maintaining pressure within safe limits and preventing the hard stop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a stampable sheet with greater thickness is used to prevent insufficient resin volume, then the volume of thermoplastic resin increases, but excess portions of resin may remain at sites near protuberances and depressions causing hard stop
Solution Approach 1:
The invention extracts the harmful excess portions of resin from the molding cavity by providing overflow channels that guide the surplus resin to designated overflow outlets. This prevents the excess resin from causing hard stop while maintaining sufficient resin volume for proper molding.
Solution Approach 2:
The overflow channels act as intermediary pathways that mediate between the excess resin and the molding cavity. These channels provide a controlled route for surplus resin to exit, preventing direct interference with the molding process while allowing pressure equalization.
2Strength
If the stampable sheet is pressed to original thickness to recover mechanical characteristics, then the physical property is recovered, but insufficient basis weight and voids remain due to material flowage
Solution Approach 1:
The invention changes the pressure distribution parameters during molding by introducing overflow channels at strategic locations. This allows different regions of the molding cavity to experience optimized pressure conditions, ensuring both mechanical property recovery and uniform basis weight distribution.
3Manufacturing precision
If internal die pressure is increased to ensure complete molding, then the molding completeness improves, but hard stop occurs when pressure exceeds pressing force
Solution Approach 1:
The overflow channels provide beforehand cushioning by preparing a pressure relief pathway before hard stop can occur. When internal die pressure approaches dangerous levels, the excess resin automatically flows through the overflow channels, cushioning against pressure buildup that would cause hard stop.
4Shape
If protuberances and depressions are added to dies for shaping, then the molded product shape is improved, but material flow resistance increases causing excess portions to reside
Solution Approach 1:
The invention segments the molding cavity into regions with different flow characteristics by strategically placing overflow channels near protuberances and depressions. This segmentation allows each region to be optimized independently, maintaining shape complexity while managing flow resistance through localized pressure equalization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents the hard stop phenomenon, ensuring the internal die pressure remains manageable, allowing for complete mold closure and maintaining the desired mechanical characteristics of the stampable sheet in the molded product.
Implementation Method 1
when receiving a pressure greater than or equal to a predetermined value, moves in such a direction that the cavity increases in volume
Data Source
AI summary
A press molding apparatus includes two dies and press-molds a heated stampable sheet into a predetermined shape by using the two dies. The press molding apparatus includes a movable core provided in at least one of the two dies. The movable core is disposed at an inward side of an edge portion of a cavity. When receiving a pressure greater than or equal to a predetermined value, the movable core moves in such a direction that the cavity increases in volume.