Foamed Preform Injection Molding with Expandable Cavity
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Solution Overview
Problem
Current methods for injection molding of polymeric foamed materials, particularly in the footwear industry, lack efficiency and precision in producing foamed parts with varying thickness and complex shapes, such as midsoles, which require improved processes for achieving desired structural and performance characteristics.
Innovation Solution
The method involves using an injection molding system with a heated barrel and controlled blowing agent delivery to create a foamed preform, which is then processed in an expandable mold cavity with temperature-controlled and surface-feature-equipped press mold cavities to form multi-element unitary parts with specific thickness and structural properties, allowing for the integration of different materials and surface features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional injection molding methods are used to produce foamed parts, then the process is simpler, but the manufacturing precision and control over varying thickness are insufficient
Solution Approach 1:
The mold cavity is designed to be expandable rather than static, allowing the cavity volume to dynamically increase during the foaming process. This dynamic expansion accommodates the foam material's expansion while maintaining precise control over the final part thickness and shape, resolving the contradiction between manufacturing precision and process simplicity.
Solution Approach 2:
The process utilizes controlled parameter changes including temperature gradients (heated barrel for melting, cooled mold for setting), pressure variations (injection pressure, holding pressure), and blowing agent delivery timing. These parameter changes enable precise control over foam expansion and final part geometry, achieving varying thickness control without overly complicating the process.
2Reliability
If complex shapes with varying thickness are produced, then the performance characteristics are improved, but the process control difficulty increases
Solution Approach 1:
The process incorporates preliminary actions including pre-heating the polymeric material to melting temperature before injection, pre-cooling the mold cavity to the setting temperature range (155-160°C), and pre-delivering the blowing agent to the molten material. These preliminary actions ensure that when the foaming process begins, all parameters are optimally positioned to achieve complex shapes with consistent performance characteristics.
Solution Approach 2:
The process implements feedback control through monitoring injection pressure, mold cavity pressure, and temperature at various stages. This feedback enables real-time adjustments to maintain process control difficulty at acceptable levels while producing reliable complex-shaped foamed parts with varying thickness.
3Adaptability or versatility
If multiple materials are integrated in the finished part, then the functional performance is enhanced, but the manufacturing process complexity increases
Solution Approach 1:
The manufacturing process is segmented into distinct phases: injection of first polymeric material, delivery of blowing agent, injection of second polymeric material. This segmentation allows different materials to be introduced at optimal times and conditions, enabling multi-material integration while keeping each individual step relatively simple and controllable.
Solution Approach 2:
The process merges multiple functions into a single integrated injection molding cycle: foam formation, multi-material layering, and complex shape formation all occur simultaneously within the expandable mold cavity. This merging reduces the need for separate manufacturing steps, thereby limiting the increase in overall process complexity despite achieving multi-material integration.
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 approach enables the production of foamed parts with controlled thickness, density, and performance characteristics, such as improved cushioning and durability, while allowing for complex shapes and integrated structural elements, enhancing the quality and efficiency of footwear components like midsoles.
Implementation Method 1
a mixture of polymeric material and blowing agent is injected through a nozzle and into an expandable mold cavity. The mold cavity is then expanded to form the foamed part.
Implementation Method 2
An aspect of the present disclosure includes a method of forming a foamed part by injecting a mixture of polymeric material and blowing agent into an expandable mold cavity
Data Source
Figure 1
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Figure 3A~3B
AI summary
The invention relates to systems and methods for creating a foamed part. An example method includes providing a polymer processing system (100), providing a mold (150) having at least one expandable mold cavity (152) in fluid communication with the polymer processing system (100), mixing polymeric material and blowing agent within the polymer processing system (100) to produce a unfoamed mixture, injecting a volume of the mixture of polymeric material and blowing agent from the polymer processing system (100) and into the expandable mold cavity (152), and expanding the mold cavity (152) to expand the unfoamed mixture within the mold cavity (152) and form a foamed preform. Thereafter, the foamed preform may be inserted into a compression mold to press-form the foamed preform into a finished part.