Mold Insert with Tapered Thickness for Composite Flatness
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Solution Overview
Problem
The formation of elongated composite components on a mandrel often results in surface waviness due to the flexible inflatable bladder, leading to non-compliance with flatness tolerances, necessitating rework and post-cure adjustments.
Innovation Solution
A mold insert with tapering thickness and recessed ramps is used in conjunction with a mandrel, where the mold insert is attached with indexing lugs and positioned over bladders to maintain flatness, allowing for the application and curing of composite material while minimizing contact undulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flexible inflatable bladder is used on the mandrel, then the mandrel can be simplified and easier to manufacture, but the composite structure develops surface waviness and fails to meet flatness tolerances
Solution Approach 1:
A rigid plate is introduced as an intermediary component between the flexible bladder and the composite material. The plate has a flat inner surface that contacts the composite material, while its outer surface contacts the bladder. This mediator transfers the forming pressure from the bladder to the composite material without allowing the flexibility of the bladder to manifest as surface waviness in the final product.
Solution Approach 2:
The plate is designed with varying thickness - thinner at the edges and thicker toward the center - to locally compensate for the bladder's flexibility. This non-uniform thickness distribution allows the plate to maintain contact with the bladder while providing a consistently flat surface for composite material formation, addressing the flatness issue locally across different regions of the mandrel.
2Manufacturing precision
If a rigid tool surface is used instead of a flexible bladder, then flatness tolerances can be maintained, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of making the entire mandrel rigid and complex, only a localized plate component is made rigid with specific thickness variations. The rest of the mandrel can remain simple and flexible. This localized application of rigidity provides the necessary flatness control only where the composite material is formed, without increasing overall device complexity.
Solution Approach 2:
The plate's thickness parameter is varied systematically - thinner at edges, thicker at center - to create the desired mechanical behavior. This parameter change allows the plate to flex slightly at the edges to accommodate the bladder while maintaining a flat contact surface in the center where the composite material is laid up, achieving precision without full rigidity.
3Ease of manufacture
If the plate thickness is uniform, then manufacturing is simpler, but the plate cannot compensate for bladder depression and surface waviness occurs
Solution Approach 1:
The plate is designed with non-uniform thickness - thinner at the edges and thicker toward the center - to locally compensate for the bladder's flexibility. This non-uniform thickness distribution allows the plate to maintain contact with the bladder while providing a consistently flat surface for composite material formation, addressing the flatness issue locally across different regions of the mandrel.
Solution Approach 2:
The thickness parameter of the plate is varied systematically to change its mechanical properties in different regions. The tapered thickness creates a stiffness gradient that allows the plate to resist deformation in the center (maintaining flatness) while being more compliant at the edges (accommodating bladder flexibility), thus achieving precision through parameter modification.
Data Source
AI summary
A mold insert and method of using a mold insert to make a composite part. The mold insert is configured to make a composite part from composite material. The mold insert is configured to be attached to a mandrel. Once attached, the composite material is applied to the mandrel over the mold insert, stringers, and bladders. The composite material is then cured on the mandrel. The mold insert can then be removed from the mandrel.