Foamed Molded Part with Local Density Control for Load Stability
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Solution Overview
Problem
Existing methods for producing foamed polymer parts, such as shoe soles, face challenges in achieving a gradual transition between flexible and rigid sections, require complex molds, and result in unstable parts that break under peak loads, leading to high production costs.
Innovation Solution
A method involving a polymer melt with high molecular mass is injected into a mold, where certain portions solidify without foaming, while others form a micro-cellular foam structure, using supercritical gas as a foaming agent and controlling pressure or mold volume to achieve precise foaming, allowing a single molding process to create parts with varying mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gradual transition between flexible and rigid sections is implemented using complex molds with reinforcing ribs, then the functional properties are improved, but the device complexity and production costs increase
Solution Approach 1:
The patent applies local quality by creating different foam densities in different regions of the molded part. The mold includes a first region with restricted volume expansion that forms a first foam density, and a second region with less restriction that forms a second foam density. This allows different sections of the same molded part to have different mechanical properties (flexible vs rigid) without requiring complex molds with reinforcing ribs, thus resolving the contradiction between functional properties and device complexity.
2Reliability
If multiple subcomponents are assembled from different materials and manufacturing methods, then the functional properties are improved, but the productivity and production costs worsen
Solution Approach 1:
The patent merges multiple manufacturing operations into a single injection molding process. By incorporating a foaming agent into the polymer melt and using a mold with regions of different volume expansion restrictions, the process simultaneously produces a molded part with multiple foam densities and different mechanical properties in one step. This eliminates the need to assemble multiple subcomponents produced by different methods, thereby improving productivity while maintaining functional properties.
3Ease of manufacture
If conventional foaming methods are used, then the production process is simple, but the resulting parts are not sufficiently stable and break under peak loads
Solution Approach 1:
The patent uses local quality to create regions of different foam densities within the molded part. The first region with restricted volume expansion produces a higher foam density that provides structural stability and load-bearing capacity, while the second region with less restriction produces a lower foam density that provides flexibility. This local differentiation allows the part to withstand peak loads without breaking while maintaining production simplicity through a single injection molding process.
Solution Approach 2:
The patent creates a composite structure within a single molded part by forming regions with different foam densities. The first foam density region acts as a structurally stable component that resists breaking under peak loads, while the second foam density region provides complementary properties. This internal composite structure achieves both production simplicity and structural stability without requiring separate components or complex assembly.
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 method produces lightweight parts with superior mechanical and structural properties, enabling a single molding process to create parts with varying degrees of foaming, reducing manufacturing costs and improving stability.
Implementation Method 1
solidifying at least a first portion of the molded part without foaming
Implementation Method 2
at least a second portion of the molded part after foaming inside the mold
Implementation Method 3
solidifying at least a second portion of the molded part after foaming
Implementation Method 4
using supercritical gas as a foaming agent and controlling pressure or mold volume to achieve precise foaming
Data Source
AI summary
A method for producing a molded part, in particular a component of a sporting good, includes providing a mixture of a polymer melt and a foaming agent and injecting the mixture into a mold. The method includes solidifying at least a first portion of the molded part without foaming and at least a second portion of the molded part after foaming inside the mold, wherein the mixture includes a polymer having an average molecular mass corresponding to a viscosity number ≥130 ml/g, preferably ≥170 ml/g, more preferably ≥190 ml/g and most preferably ≥225 ml/g, wherein the viscosity number is determined via solution viscometry according to the ISO 307 standard.