Vacuum Bag Pleats for Composite Laminate Thickness Control
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Solution Overview
Problem
Vacuum bagging machines face challenges in contouring accurately to complex surfaces of composite laminates with stringers, leading to variations in consolidation pressure and laminate thickness due to material deformation and resin flow, resulting in inconsistent thickness of the cured composite laminate.
Innovation Solution
A method and apparatus that involve applying a vacuum bag with digital indicia to monitor and manipulate stress levels within the bag, using techniques like digital image correlation or shearography to ensure uniform strain, thereby maintaining consistent cure pressure and thickness during the vacuum bagging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If pressure is used to deform the vacuum bag to contour to the complex inner surface, then the bag can better fit the skin panel with stringers, but laminate consolidation pressure is reduced causing variations in thickness
Solution Approach 1:
Pleats are formed in the vacuum bag material before the bag is applied to the skin panel. These pre-formed pleats are positioned to correspond with the stringers, allowing the bag to contour to the complex surface without requiring additional pressure-induced deformation during curing, thus maintaining consistent consolidation pressure
Solution Approach 2:
The vacuum bag has non-uniform material properties through the strategic placement of pleats in specific locations corresponding to stringers. This local modification of the bag structure allows differential deformation only where needed, maintaining uniform pressure in the critical consolidation zones
2Shape
If the vacuum bag material deforms to contour to stringers, then the bag can accommodate the complex surface, but resin flows from higher pressure areas to lower pressure areas causing thickness variations
Solution Approach 1:
Pleats are pre-formed in the vacuum bag material before application, positioning the material to accommodate stringers in advance. This preliminary structuring prevents unwanted resin flow by maintaining uniform consolidation pressure while still allowing necessary contouring
Solution Approach 2:
The physical structure of the vacuum bag is modified by introducing pleats that change the material's deformation characteristics. This alters how the bag responds to vacuum pressure, enabling contouring without creating harmful pressure differentials that would cause resin flow and thickness variations
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 solution reduces cure pressure and thickness variations in the composite laminate, minimizing the need for shimming and reducing production costs by ensuring consistent thickness and reducing resin flow issues during autoclaving.
Implementation Method 1
When a vacuum is drawn in the vacuum bag, the material of the bag deforms (i.e., stretches) in the vicinity of each stringer due to contour
Implementation Method 2
Pressure on the vacuum bag during cure removes air (i.e. porosity) in the curing laminates
Implementation Method 3
These laminate thickness variations occur because resin in the vacuum bag flows from higher pressure areas to lower pressure areas
Data Source
AI summary
A method is provided for facilitating a vacuum bagging operation during fabrication of a composite laminate. The method comprises applying a vacuum bag over a composite part to fabricate the composite laminate from the composite part. The method also comprises drawing a vacuum in the vacuum bag, and monitoring one or more portions of the vacuum bag for strain within the vacuum bag when the vacuum is drawn. The method further comprises manipulating the vacuum bag to even out strain within the vacuum bag.