Semi-Hollow F-SPR Rivet Geometry for Stable High-Speed Alignment
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Solution Overview
Problem
Existing vehicle sheet metal joining technologies face challenges with high strength steels and lightweight alloys due to oxide films, low heat conduction, and non-conductive properties, leading to poor mechanical interlocking and joint strength issues, particularly with semi-hollow rivets experiencing spinning instability and axis misalignment in friction self-piercing riveting (F-SPR) processes.
Innovation Solution
A rivet with wedge-shaped cone angles and a chamfered rivet head, combined with a driving spindle featuring matching wedge-shaped projections, ensures stable rotation and positioning, reducing the likelihood of joint failure by aligning the rivet's rotation axis with its geometric axis and minimizing gaps between the rivet shank and sheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a semi-hollow rivet is used in F-SPR process, then the ductility of lightweight materials can be improved through frictional heat, but the rivet is prone to spin instability and axis misalignment resulting in joint failure
Solution Approach 1:
The rivet head is provided with a positioning structure (cross flower-shaped groove) before the riveting process begins. This positioning structure engages with the driving spindle's boss to pre-establish accurate rotational alignment, preventing spin instability and axis misalignment during the high-speed rotation phase of F-SPR joining
Solution Approach 2:
The cross flower-shaped groove in the rivet head creates an asymmetric engagement pattern with the driving spindle's boss. This asymmetric design provides multiple positioning points that constrain the rivet's rotational movement, ensuring stable rotation and preventing spin instability during the F-SPR process
2Ease of manufacture
If traditional resistance spot welding is used, then the process is simple, but it cannot join aluminum and magnesium alloys due to oxide film and material properties
Solution Approach 1:
The invention transitions from resistance spot welding (thermal process) to friction self-piercing riveting (mechanical-thermal-solid state process). This parameter change enables joining of aluminum and magnesium alloys by using frictional heat to improve ductility while maintaining solid-state bonding, overcoming the limitations of oxide films and material properties that prevent traditional welding
3Object-affected harmful factors
If SPR process is used, then fusion welding problems are avoided, but rivet upsetting or fracture occurs due to large deformation resistance of high strength steels
Solution Approach 1:
The invention introduces frictional heating as an additional parameter to the SPR process, creating F-SPR. The frictional heat softens high strength steel sheets, reducing their deformation resistance and allowing the rivet to form proper mechanical interlocking without upsetting or fracture, while still avoiding fusion welding defects
4Strength
If FSSW process is used, then solid state joining is achieved, but a key hole is left in the joint significantly affecting joint strength
Solution Approach 1:
Instead of using a rotating pin that leaves a key hole (FSSW), the invention uses a solid rigid rivet that is driven to spin and then locked in place (FBJ). This inverted approach replaces the pin with a rivet structure that can be securely anchored, eliminating the key hole defect while maintaining solid state bonding advantages
5Manufacturing precision
If FBJ process is used, then the key hole problem is avoided, but larger riveting force and longer process time are required raising equipment cost and lowering efficiency
Solution Approach 1:
The invention combines the solid rivet approach of FBJ with frictional heating to create F-SPR. The frictional heat softens the materials, reducing the riveting force required and shortening the process time, thereby maintaining joint integrity while improving riveting efficiency and reducing equipment cost
6Strength
If FBJ process is used, then solid rivet penetration is achieved, but larger amount of frictional heat causes overheating and strength degradation of the joint
Solution Approach 1:
The invention uses a semi-hollow rivet instead of a solid rivet, which reduces the mass and therefore the total frictional heat generated during rotation. This partial action approach provides sufficient frictional heat to soften materials and create solid state bonding, while avoiding excessive heat that would cause overheating and strength degradation
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 proposed solution enhances the stability and accuracy of rivet rotation, improving the mechanical properties and reliability of F-SPR joints by increasing tensile-shear strength and reducing gaps, thereby enhancing the fatigue performance of the joints.
Implementation Method 1
the nonferrous alloys and/or high strength steels are therefore softened by the generated frictional heat and the ductility of materials can be improved
Implementation Method 2
A hybrid solid state-mechanical joining joint is then formed by deforming the rivet into the sheet materials to form mechanical interlock
Implementation Method 3
the formation of solid state bonding between the rivet and sheets under the generated frictional heat and the applied riveting pressure at the rivet/sheets interfaces
Data Source
Figure 1~3
Figure 4(a)~5(e)
Figure 6(a)~7(e)
AI summary
A rivet rotational feeding method for friction self-piercing riveting (F-SPR) system, comprising: a semi-hollow rivet, a driving spindle and a die. The bottom surface of the rivet head is connected to the semi-hollow rivet shank. The semi-hollow rivet shank has a wedge-shaped end. The rivet head has rotation driving structures and positioning structure on the top end. The rotation driving structures are central symmetric concave or convex surfaces. The positioning structure is a central symmetric and mirror symmetric concave or convex surface. The matching between the driving spindle and the rivet can improve the rotation reliability and positioning accuracy of the riveting at a high rotational speed during F-SPR process, which is beneficial to solve the problems of poor stability and non-coincidence between the geometry axis and the rotation axis of the rivet. This invention is also helpful to reduce the failure rate of the F-SPR joint and avoid the formation of gap between the rivet shank and the sheets in the joint. This invention can provide a high reliability of the F-SPR process in joining steels, aluminum alloys, magnesium alloys, composites and other dissimilar materials.