Knitted Dry Preform for Composite Materials
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Solution Overview
Problem
The manufacturing of complex composite materials with non-continuous fibers requires intricate cutting and layering of parts to achieve mechanical resistance, which complicates the process and results in imperfect mechanical recovery due to trapped air bubbles and non-uniform resin distribution.
Innovation Solution
A dry, convertible knitted preform is produced through simultaneous weft/column knitting of mesh yarns and unidirectional reinforcement yarns, where thermoplastic materials melt to form the matrix and reinforce fibers are embedded, allowing for direct shaping and impregnation without additional resin injection, enabling continuous yarns and precise control over material distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If traditional cutting and layering methods are used to manufacture complex composite materials, then the desired geometric conformation can be achieved, but the manufacturing process becomes complicated and mechanical recovery is imperfect due to trapped air bubbles and non-uniform resin distribution
Solution Approach 1:
The manufacturing process is segmented into distinct phases: knitting the preform with embedded thermoplastic material, heating to melt the thermoplastic, and cooling to form the final composite. This segmentation simplifies the overall process by eliminating complex cutting and layering operations while maintaining geometric flexibility through the knitted preform structure.
Solution Approach 2:
The thermoplastic material undergoes parameter changes through phase transition from solid to liquid during heating, enabling it to flow and impregnate the reinforcement uniformly. This parameter change eliminates the need for complex resin injection systems while ensuring uniform distribution without trapped air bubbles.
2Shape
If traditional cutting and layering methods are used, then complex shapes can be formed, but mechanical strength is reduced due to non-continuous fibers and imperfect mechanical recovery
Solution Approach 1:
The knitted preform provides continuous reinforcement fibers throughout the entire structure, eliminating the discontinuities introduced by cutting and layering. The continuous fibers maintain mechanical integrity while the thermoplastic material flows to fill all voids, ensuring perfect mechanical recovery and uniform strength distribution.
Solution Approach 2:
The invention creates a composite material system where continuous reinforcement fibers are embedded in a thermoplastic matrix that is formed in-situ during the knitting process. This composite structure combines the high strength of continuous fibers with the uniform distribution capability of melted thermoplastic, achieving both complex shapes and high mechanical strength.
3Shape
If resin injection is used to manufacture composite materials, then complex shapes can be achieved, but the process complexity increases and uniform resin distribution is difficult to achieve
Solution Approach 1:
The thermoplastic material embedded in the knitted preform performs the function of resin injection automatically during the heating phase. The material melts and flows to impregnate the reinforcement structure itself, eliminating the need for external resin injection systems while ensuring uniform distribution through the self-contained preform structure.
Solution Approach 2:
The thermoplastic material is pre-positioned within the knitted preform structure before heating. This preliminary placement ensures that the material is already in the correct position and configuration to flow uniformly during heating, eliminating the need for complex injection systems and ensuring complete impregnation without trapped air bubbles.
4Shape
If multiple cutting and layering operations are performed to achieve complex shapes, then geometric conformation is achieved, but production time increases
Solution Approach 1:
Multiple operations that would traditionally be performed separately (knitting, shaping, and resin impregnation) are merged into a single integrated process. The knitted preform is formed and shaped simultaneously, then heated to melt the embedded thermoplastic material which automatically impregnates the structure, eliminating the need for separate cutting and layering operations and significantly reducing production time.
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 enables the production of complex 3D composite materials with improved mechanical strength and reduced complexity by ensuring continuous yarns and uniform resin distribution, eliminating the need for resin injection and simplifying the manufacturing process.
Implementation Method 1
heating to reach at least the temperature of the lowest melting point, in order to impregnate and/or coat the reinforcing material with the at least one thermoplastic material transformed by melting
Data Source
AI summary
The invention relates to a method for manufacturing a transformable dry preform, in particular for manufacturing a product made of composite materials, characterised in that it comprises the consecutive steps of simultaneous weft/column knitting of at least one mesh thread and at least one unidirectional reinforcement thread, at least one mesh thread comprising a material of a different nature to a material contained in at least one unidirectional reinforcement thread, at least one of said materials being thermoplastic and having a melting point lower than the melting point of at least one other material, referred to as reinforcement material, and production of a three-dimensional knit fabric constituting a dry preform in the shape of the product to be obtained.