Thermally Expansive Composite Forming Tool for Hat Stiffener Accuracy
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Solution Overview
Problem
Conventional rigid forming tools fail to produce hat stiffened composite parts with the required accuracy due to differential thermal expansion between the tooling mandrel and the forming tool, leading to part porosity, material movement, and bonding flaws, resulting in scrapped composite material.
Innovation Solution
A composite forming tool and method using a stretchable tooling caul and mandrel with differential thermal expansion properties, where the first and second leg portions are made of less thermally expansive fluoroelastomer and the third and fourth leg portions, along with the interconnect portion, are made of more thermally expansive silicone rubber, allowing controlled expansion and contraction to maintain critical shape tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid forming tool is used, then the tool structure is simple and stable, but the tool cannot accommodate differential thermal expansion, resulting in part porosity, material movement, and bonding flaws
Solution Approach 1:
The forming tool material is changed from rigid to thermally expansive material, fundamentally altering the physical parameter of thermal expansion capability. This allows the tool to expand and contract with temperature changes, accommodating the tooling mandrel's expansion and preventing differential expansion issues that cause porosity and bonding flaws.
Solution Approach 2:
The forming tool is constructed using composite material structure with thermally expansive material as the base and reinforcement elements (rigid reinforcement inserts) embedded within. This composite structure combines the thermal expansion capability of the base material with the structural stability and pressure distribution capability of the reinforcement inserts, resolving the contradiction between reliability and device complexity.
2Device complexity
If a less thermally expansive forming tool is used, then the tool structure is simple, but the differential expansion with the tooling mandrel causes high and low pressure areas, resulting in part porosity and unwanted composite material movement
Solution Approach 1:
The forming tool is specifically designed using thermally expansive material that expands and contracts in sync with the tooling mandrel during the curing process. This matched thermal expansion behavior eliminates the differential expansion between tool and mandrel, preventing the formation of high and low pressure areas that would compromise manufacturing precision and critical dimensions accuracy.
3Reliability
If a more thermally expansive forming tool is used, then the tool can accommodate mandrel expansion better, but the corner radius of the finished part is out of tolerance
Solution Approach 1:
The forming tool employs local quality by positioning rigid reinforcement inserts at specific locations (such as corner regions) within the thermally expansive material. These localized reinforcement elements provide precise geometric control and dimensional accuracy for critical features like corner radius, while the surrounding thermally expansive material continues to provide overall accommodation of mandrel expansion, thus maintaining both bonding quality and manufacturing precision.
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 approach enhances the accuracy and quality of composite part formation by reducing flaws and material scrap, ensuring precise control over critical dimensions like the corner radius at the intersection of hat stiffener legs and planar structures.
Implementation Method 1
the tooling mandrel expands while the less thermally expansive composite forming tool, which covers at least a portion of the composite material, expands to a lesser degree
Implementation Method 2
The composite material may then be subjected to a curing process, such as debulking and heating, to further adhere and bond the composite layers
Data Source
Figure 1~3
Figure 4~5
AI summary
An apparatus and methods for forming a composite part are provided. A method for forming a composite part may include placing initial composite material on a base tool (40), placing a tooling mandrel (30) on the composite material (51), placing additional composite material over the tooling mandrel, covering at least a portion of the composite material that overlays the tooling mandrel with a composite forming tool (20), heating the composite material to at least partially cure the composite material, and permitting a first portion (24,25) of the composite forming tool to change size during the heating of the composite material to a greater degree than a second portion (22,23) of the composite forming tool. In this regard, the second portion of the composite forming tool is closer to the base tool than the first portion of the composite forming tool. A composite forming tool is also provided that permits differential expansion of different portions of the tool.