Thermoplastic Prepreg Press Molding for Fiber Isotropy
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Solution Overview
Problem
Existing methods for manufacturing fiber-reinforced composite materials often result in shaped products with reduced isotropy and require trimming, leading to material waste and increased costs, especially when the charge ratio of prepreg to mold is low.
Innovation Solution
A method involving the preparation of a prepreg with randomly oriented reinforcing fibers and a thermoplastic resin, where the prepreg is heated and arranged in a mold under specific temperature conditions to maintain isotropy, allowing for press-molding with a charge ratio of 50% or less without the need for trimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the charge ratio of prepreg to mold is reduced to 50% or less, then material waste is reduced and productivity is improved, but manufacturing precision deteriorates due to difficulty in maintaining isotropy
Solution Approach 1:
The prepreg is pre-heated to a temperature between the glass transition temperature and melting point of the thermoplastic resin before being placed in the mold. This preliminary heating action causes the resin to become viscous and flowable in advance, enabling the prepreg to automatically spread and fill the mold cavity uniformly even when the charge ratio is low (50% or less). As a result, isotropy is maintained throughout the molded product without requiring excessive material or complex arrangement procedures.
Solution Approach 2:
The invention changes the temperature parameter of the prepreg from ambient temperature to a controlled range between the glass transition temperature and melting point of the thermoplastic resin. This parameter change transforms the resin from a rigid state to a viscous flowable state, allowing the prepreg to self-adjust and distribute uniformly in the mold cavity. This enables achieving both low charge ratio (high productivity) and uniform fiber distribution (high isotropy).
2Manufacturing precision
If symmetric layering is enforced to maintain isotropy, then manufacturing precision is improved, but device complexity and time for preparing perform increase
Solution Approach 1:
The prepreg, when pre-heated to the appropriate temperature range, possesses self-service capability to automatically spread and fill the mold cavity uniformly without requiring complex external arrangement procedures. The viscous resin naturally flows to distribute fibers evenly throughout the mold, eliminating the need for manual symmetric layering or complex positioning mechanisms. This self-adjusting property simplifies the preparation process while maintaining high isotropy.
3Ease of manufacture
If long fiber composite pellets are used for injection molding, then ease of manufacture is improved, but the length of reinforcing fibers is largely reduced in the shaped product
Solution Approach 1:
The invention replaces the injection molding process with a preheating and press-molding process. Instead of injecting molten resin that mechanically shears and shortens fibers, the prepreg is simply heated to activate resin flow and then pressed into the mold. This substitution of the molding mechanism eliminates the fiber-shortening effect of injection while maintaining ease of manufacture, preserving the long fiber length (5-100 mm) in the final product.
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 lightweight, rigid, and isotropic shaped products with reduced material waste and production time, suitable for complex shapes without the need for trimming, while maintaining high productivity and surface quality.
Implementation Method 1
a prepreg preparation step of obtaining a prepreg in which a random mat including reinforcing fibers with an average fiber length of 5 mm to 100 mm and a thermoplastic resin is heated up to a temperature of a melting point or more and less than a thermal decomposition temperature
Implementation Method 2
up to a temperature of a glass transition temperature or more and less than a thermal decomposition temperature in a case where the thermoplastic resin is amorphous
Implementation Method 3
a molding step in which the prepreg is pressurized within the mold and at the same time, the molding is completed at a temperature less than the melting point
Data Source
AI summary
The present invention provides a method for manufacturing a shaped product constituted by a fiber-reinforced composite material including reinforcing fibers and a thermoplastic resin, the shaped product with maintained isotropy of the fibers to the end thereof even if press-molded under conditions in which charge ratio of a prepreg to a die is low. Specifically, the method includes using a specific prepreg obtained by impregnating the reinforcing fibers with thermoplastic resin, and molding-processing the prepreg under specific conditions.