Induction Heating Cell Caul for Composite Layup Thermal Isolation
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Solution Overview
Problem
Processing parts with complex shapes is challenging due to CTE mismatches between mandrels and composite layups, leading to non-uniform heating and pressure application, especially in non-planar portions, which can result in thermal expansion issues and shear forces.
Innovation Solution
An induction heating cell comprising a caul with a CTE closer to the composite layup than the mandrel, positioned between the mandrel and the composite layup, to isolate thermal expansions and contractions of the mandrel while providing localized heating and pressure transfer, using a bladder for uniform pressure application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a mandrel is used to shape complex portions of the composite layup, then the composite part can achieve complex geometries, but the CTE mismatch between the mandrel and composite layup causes thermal expansion issues and shear forces during heating-cooling cycles
Solution Approach 1:
A caul made of Invar alloy is introduced as an intermediary layer between the mandrel and the composite layup. The Invar caul has a CTE that matches both the aluminum mandrel and the carbon fiber reinforced polymer composite, serving as a thermal expansion mediator that eliminates shear forces and wrinkling during heating and cooling cycles while allowing the mandrel to define the complex geometry
2Manufacturing precision
If uniform pressure is applied to consolidate the composite layup, then consolidation quality improves, but non-planar portions experience non-uniform pressure distribution
Solution Approach 1:
The system employs locally-adapted pressure application through a flexible bladder that can conform to the complex geometry of the molded part. The bladder applies pressure through multiple contact points that adapt to the local surface topology, ensuring uniform pressure distribution across both planar and non-planar portions of the composite layup during consolidation
3Force
If the mandrel directly contacts the composite layup to transfer pressure, then pressure application is efficient, but the mandrel's thermal expansion directly affects the composite part causing distortion
Solution Approach 1:
The Invar caul acts as a pressure transfer intermediary that decouples the mechanical pressure transfer function from the thermal expansion effect. It efficiently transfers pressure from the mandrel to the composite layup through its rigid structure, while its matched CTE properties prevent thermal expansion-induced distortion of the composite part
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 solution ensures uniform heating and pressure distribution on complex shapes, minimizing shear forces and wrinkling, and allowing for the formation of composite parts with complex geometries like wing components and fuselage doors.
Implementation Method 1
heating the composite layup using an induction heater
Implementation Method 2
The induction heater is configured to inductively heat the composite layup
Implementation Method 3
The CTE of the caul may be closer to the CTE of the composite layup than to the CTE of the mandrel. As such, the caul isolates the composite layup from the dimensional changes of the mandrel, driven by temperature fluctuations
Data Source
Figure 1A
Figure 1B~2C
Figure 3
AI summary
An induction heating cell (100) is used for processing (e.g., consolidating and/or curing) a composite layup (190) having a non-planar portion (194). The induction heating cell comprises a caul (170), configured to position over and conform to this non-planar portion. Furthermore, the cell comprises a mandrel (160), configured to position over the caul and force the caul again the surface of the layup. The CTE of the caul is closer to the CTE of the composite layup than to the CTE of the mandrel. As such, the caul isolates the composite layup from the dimensional changes of the mandrel, driven by temperature fluctuations. At the same time, the caul may conform to the surface of the mandrel, which can be used to define the shape and transfer pressure to the non-planar portion.