Vacuum Compression Molding of Fiber Reinforced Composites
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Solution Overview
Problem
Current processes for manufacturing fibre-reinforced composite articles face challenges in achieving high fibre content, low void content, and excellent mechanical properties while maintaining short cycle times, particularly in the production of lightweight composite parts for the automotive and aerospace industries.
Innovation Solution
A process involving a mold with an upper and lower die, where a thermosetting resin composition is applied to fibre reinforcement, the mold is partially closed, evacuated, and then fully closed under hydraulic pressure to ensure complete impregnation and curing, allowing for high fibre volume fractions and rapid production cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If compression molding of SMC/BMC is used to achieve short cycle times, then productivity is improved, but fibre volume content is limited to less than 50% and mechanical performance is reduced
Solution Approach 1:
The patent changes the viscosity parameter of the resin composition by using a low viscosity thermosetting resin that remains liquid at molding temperature, eliminating the need for high viscosity modifiers like mineral fillers. This allows achieving high fibre volume content (60-70%) while maintaining short cycle times, as the low viscosity resin can be injected and distributed quickly without compromising productivity
2Ease of manufacture
If mineral fillers are added to increase viscosity for molding process, then ease of manufacture is improved, but weight of parts increases and fibre volume content is reduced
Solution Approach 1:
The patent changes the rheological parameters of the resin system by selecting a low viscosity thermosetting resin that inherently provides suitable flow characteristics for compression molding. This eliminates the need to add mineral fillers like magnesium oxide or calcium carbonate, resulting in lighter parts with higher fibre content while maintaining ease of manufacture through the resin's natural low viscosity properties
3Strength
If high fibre volume content is achieved by removing mineral fillers, then mechanical performance is improved, but viscosity control becomes difficult for molding process
Solution Approach 1:
The patent changes the temperature parameter by conducting the molding process at elevated temperatures (typically 100-200°C) where the low viscosity thermosetting resin maintains optimal flow characteristics. The heat softens the resin further, ensuring it remains liquid and easily penetrates the fibre reinforcement, providing excellent impregnation and mechanical performance without requiring high fibre volume content to achieve proper viscosity control
4Manufacturing precision
If liquid resin is used to achieve high fibre volume fraction, then manufacturing precision is improved, but cycle time increases due to longer curing time
Solution Approach 1:
The patent changes the chemical reactivity parameter by selecting a thermosetting resin with high reactivity that can cure rapidly at molding temperature. This allows the liquid resin to be applied, impregnate the fibres, and cure within a short cycle time (typically 1-5 minutes), achieving both high fibre volume fraction (60-70%) and short cycle times without the long curing times associated with less reactive resin systems
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 process enables the production of composite articles with fibre volume fractions of 50-70% and excellent mechanical properties, such as high tensile strength and modulus, while significantly reducing cycle times to less than 10 minutes, and improving visual quality by eliminating fibre movement and voids.
Implementation Method 1
evacuating the mold in the partially closed position by means of a vacuum outlet to a pressure of from 0.1 to 100 mbar
Implementation Method 2
completely closing the mold and exerting a hydraulic pressure of from 2 to 100 bar onto the resin treated reinforcement to complete impregnation of the fibre reinforcement
Implementation Method 3
curing the resin impregnated reinforcement
Data Source
Figure 1~2
Figure 3a~4
AI summary
A process for the preparation of a fiber reinforced composite article comprising the steps of a) providing a mold, comprising an upper die (11) and a lower die (12), the lower die (12) having a molding surface and vertically extending side walls (14), the upper die (11) having a complementary molding surface and vertically extending side walls (13) substantially aligned with the side walls of the lower die, so that the upper die vertically moves into the lower die to form a cavity (17) in a partially and completely closed position of the mold, wherein the cavity (17) in a partially closed position is sealed vacuum-tight by at least one seal (15) placed around the vertically extending walls of the upper die (11), or the lower die (12), horizontally to the moving direction of the upper die (11), and wherein the at least one seal (15) also works as a resin retention seal which prevents the resin from leaking, b) applying a thermosetting resin composition onto a fibre reinforcement, and placing the thus treated fibre reinforcement into the lower die of the mold (12), or c) placing a fibre reinforcement into the lower die of the mold (12), and applying a thermosetting resin composition onto the fibre reinforcement d) moving the upper die (11) into the lower die (12) and partially closing the mold, e) evacuating the mold in the partially closed position by means of a vacuum outlet to a pressure of from 0.1 to 100 mbar, f) completely closing the mold and exerting an hydraulic pressure of from 2 to 100 bar onto the resin treated reinforcement to complete impregnation of the fibre reinforcement, g) curing the resin impregnated reinforcement, h) demolding the cured composite article, facilitates manufacturing of composite articles with reduced cycle times, said composite articles exhibit high fibre content, low void content and excellent visual and mechanical properties, and can be used for the construction of mass transportation vehicles, in particular, in automotive and aerospace industry.