Out-of-Autoclave Composite Curing with Sequential Vacuum
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Solution Overview
Problem
Existing methods for producing composite moulded parts from fibre-reinforced plastics outside an autoclave result in lower mechanical strength and porosity compared to those cured in an autoclave, making them unsuitable for high mechanical loading applications, such as in situ repairs.
Innovation Solution
A method involving a prepreg semi-finished product encased with a flexible sheet material containing a gas-permeable membrane and an inner planar gas-conducting element, subjected to sequential negative pressures and temperatures, ensuring low porosity and high fibre content, allowing for in situ repairs with mechanical properties comparable to autoclave-cured parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If out-of-autoclave processes are used to produce composite moulded parts, then the processing complexity and equipment requirements are reduced, but the mechanical strength and porosity of the resulting parts deteriorate
Solution Approach 1:
The curing process is divided into multiple stages with different pressure conditions. The method uses sequential negative pressure application in different chambers (first gas-tight casing and second gas-tight casing) to achieve progressive consolidation and curing, allowing out-of-autoclave processing while achieving autoclave-quality mechanical properties
Solution Approach 2:
The process employs periodic application of negative pressure and heating cycles. Multiple heating steps at different temperatures are applied sequentially, with negative pressure applied during specific phases to remove volatiles and consolidate the prepreg, creating a periodic action pattern that achieves high-quality curing without autoclave equipment
2Productivity
If out-of-autoclave processes are used to produce composite moulded parts, then the processing time and energy consumption are reduced, but the porosity of the resulting parts increases
Solution Approach 1:
A first negative pressure is applied before the main curing process to remove air and volatiles from the prepreg structure. This preliminary action prevents entrapment of gases during subsequent heating and consolidation, achieving low porosity without requiring extended processing times or autoclave equipment
Solution Approach 2:
Multiple heating steps with intermediate negative pressure applications are used to progressively remove volatiles and consolidate the material. This periodic action pattern achieves thorough degassing and consolidation while maintaining reasonable processing time and without autoclave equipment
3Manufacturing precision
If low-viscosity matrix material is used in out-of-autoclave prepreg systems to achieve low porosity, then the fibre content by volume increases, but the mechanical strength of the products decreases
Solution Approach 1:
The process controls the viscosity and flow characteristics of the matrix material through temperature management and pressure application timing. By applying negative pressure at specific stages and using controlled heating ramps, the process achieves proper impregnation and consolidation without requiring permanently low-viscosity resins, thereby maintaining both low porosity and high mechanical strength
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
The method achieves high-quality composite moulded parts with reduced processing time and energy consumption, comparable to autoclave-cured parts, while simplifying the construction and enabling the production of complex shapes, suitable for in situ repairs.
Implementation Method 1
The flexible sheet material comprises a membrane, which is gas-permeable but holds back the matrix material
Implementation Method 2
A first negative pressure is applied to the inner planar gas-conducting means and the inside of the first gas-tight casing
Implementation Method 3
A second negative pressure is applied to the inside of the second gas-tight casing
Implementation Method 4
the entire arrangement is heated for a first time at a first temperature; A second negative pressure is applied to an inside of the second gas-tight casing and the entire arrangement is heated for a second time at a second temperature
Implementation Method 5
the matrix material of a formed prepreg semi-finished product undergoing a curing process under the influence of negative pressure and temperature
Data Source
AI summary
A method for producing a composite molded part from fiber-reinforced plastics material includes providing a prepreg semi-finished product including fibers that are pre-impregnated with a matrix material and encasing the semi-finished product with a flexible sheet material to form an inner arrangement. The flexible sheet material includes a gas-permeable membrane and an inner planar gas-conducting element. The inner arrangement is encased with a first gas-tight casing and positioned on a molding surface of a mold. The inner arrangement and molding surface is encased with a second gas-tight casing. A first negative pressure is applied to the inner planar gas-conducting element and the inside of the first gas-tight casing, and the entire arrangement is heated for a first time at a first temperature. A second negative pressure is applied to an inside of the second gas-tight casing and the entire arrangement is heated for a second time at a second temperature.