Interlocking Friction Stir Butt Joints for Thermoplastic Composites
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Solution Overview
Problem
Existing methods for joining fibre reinforced composite parts, such as adhesive bonding, riveting, and welding, result in added weight, complex preparation processes, and weak joints due to discontinuity in load carrying from one part to another, particularly for continuous fibre reinforced polymers.
Innovation Solution
A method using friction stir welding with interlocking protrusions and grooves on the joining surfaces of fibre reinforced thermoplastic parts, allowing for a butt joint without pre-treatment, cleaning, or additional weight, and creating a strong joint resistant to high loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive bonding is used to join fibre reinforced composite parts, then the joint strength is improved, but additional weight is added and surface preparation is required
Solution Approach 1:
The invention extracts and removes the adhesive layer from the joining system, replacing it with a direct mechanical interlocking mechanism through protrusions and grooves. This eliminates the additional weight of adhesive material while maintaining joint strength through the interlocking geometry that transfers loads directly between parts.
Solution Approach 2:
The invention replaces the chemical bonding mechanism of adhesive bonding with a mechanical interlocking system. The protrusions on one part fit into grooves on the other part, creating a mechanical connection that transfers loads through direct contact and geometric constraint rather than through adhesive chemistry.
2Strength
If riveting is used to join fibre reinforced composite parts, then the joint strength is improved, but additional weight is added and the process becomes more complex
Solution Approach 1:
The invention merges the joining function and the structural function into a single integrated feature. The protrusions and grooves serve both as the joining mechanism and as part of the structural design, eliminating the need for separate rivets or fasteners and simplifying the overall assembly process while maintaining strength.
Solution Approach 2:
The invention extracts the rivet or fastener element from the joining system and replaces it with the integrated protrusion-groove geometry. This removes the additional components and simplifies the process by eliminating drilling, rivet installation, and associated tooling requirements.
3Ease of manufacture
If conventional welding is used to join fibre reinforced composite parts, then the joining process is simplified, but the joint strength is reduced due to discontinuity in load carrying
Solution Approach 1:
The invention uses a composite joining approach combining mechanical interlocking (protrusions and grooves) with localized thermoplastic material flow. The thermoplastic material acts as a matrix that binds the interlocking features together, creating a composite joint structure that maintains continuous fibre load paths while enabling simplified welding processing.
4Strength
If overlap geometry is used for joining composite parts, then the joint strength is improved, but additional weight is added and complex secondary loads are created
Solution Approach 1:
The invention inverts the traditional overlap joint geometry and replaces it with a butt joint configuration. Instead of one part overlapping another, the parts are joined end-to-end with protrusions on one part fitting into grooves on the other, eliminating the additional weight of overlap while maintaining strength through the interlocking mechanism.
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 method achieves a robust, low-effort joint with improved load transfer and reduced complexity, maintaining continuous fibres integrity and avoiding additional weight, while utilizing the cost advantages of friction stir welding.
Implementation Method 1
Friction Stir Welding (FSW) is frequently used for metal joining. This process employs a rotating pin to generate heat to induce a welding and mixing of material between two parts.
Implementation Method 2
welding the parts by friction stir welding along a welding path which follows the geometry of the one or more protrusions and/or grooves to locally melt the material of both parts in a contact area
Data Source
Figure 1
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AI summary
A method for joining fibre reinforced composite parts using friction stir welding comprises providing at least a first and a second part (11, 12), both made of fibre reinforced thermoplastic material and both having a joining surface (13, 14) for forming a butt joint (17) between both parts (11, 12). The joining surface (13) of the first part (11) comprises one or more protrusions (15) which fit into one or more grooves (16) of the second part (12) when forming the butt joint (17). Both parts (11, 12) are positioned thereby forming the butt joint (17). Then, the parts (11, 12) are welded by friction stir welding along a welding path (19) which follows the geometry of the one or more protrusions (15) and/or grooves (16) to locally melt the material of both parts (11, 12) in a contact area (27) defined by that geometry.