Split Sleeve Cold Working for Composite-Metal Stacks
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Solution Overview
Problem
Cold working holes in a stack of metal and composite layers often results in undesirable deformation of the composite layers and composite residue buildup, requiring disassembly for processing, which is time-consuming and impractical in many applications.
Innovation Solution
A method and tool for cold working holes in a composite and metal stack without disassembly, where a split sleeve is inserted into the hole and expanded only into contact with the metal layers, maintaining a gap between the composite layers and the sleeve by interposing material, allowing for radial expansion and residual compressive stress creation in the metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a split sleeve is expanded during cold working to create residual compressive stresses in metal layers, then fatigue resistance is improved, but composite layers deform undesirably and composite residue builds up on the tool
Solution Approach 1:
A gap material is introduced as an intermediary between the expandable split sleeve tool and the composite layers. This gap material allows the sleeve to expand and contact only the metal layers for cold working, while preventing direct contact with composite layers that would cause deformation and residue buildup. The gap material effectively mediates the interaction between the tool and different material layers.
Solution Approach 2:
The hole through the stack is segmented into different zones: a first portion through the composite layer, a second portion through the metal layer, and a third portion through the composite layer. The gap material is positioned to create a gap only in the region where the sleeve contacts the composite layers, allowing selective cold working of metal layers while protecting composite layers from direct tool contact.
2Object-generated harmful factors
If the stack is disassembled to cold work holes in metal layers separately, then composite deformation and residue issues are eliminated, but processing time and labor intensity increase significantly
Solution Approach 1:
The gap material is pre-positioned between the split sleeve and the composite layers before the cold working operation begins. This preliminary action ensures that when the sleeve is expanded, the protective gap is already in place, preventing composite deformation and residue buildup from the outset, thereby eliminating the need for disassembly and reassembly operations.
3Ease of operation
If the split sleeve contacts both metal and composite layers during expansion, then one-sided processing is enabled, but the composite layers suffer deformation and residue buildup
Solution Approach 1:
The gap material is positioned selectively to create a gap only in the regions where the split sleeve would contact the composite layers during expansion. This local modification allows the sleeve to maintain contact with metal layers for effective cold working while creating protective gaps only where needed to prevent composite layer deformation and residue buildup.
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
Enables cold working of holes in a composite and metal stack from one side, reducing deformation and residue issues, thus improving efficiency and practicality by maintaining a gap between the composite layers and the tool, allowing for effective stress creation in the metal layers without deforming the composite layers.
Implementation Method 1
Drawing the mandrel through the sleeve expands and causes a radial plastic flow of material in the metal structure surrounding the hole, placing the material in tension. After the mandrel is removed, an annular zone of residual compressive stresses is present in the structure surrounding the hole
Implementation Method 2
maintaining a gap between the composite layers and the sleeve by interposing material
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A hole (40) in a metal (24) and composite (26) stack (22) is cold worked. An interference is formed between a cold working tool and the metal layers results in a radial force that is applied only to the metal layers (24).