Self-Piercing Rivet Geometry for High-Strength Steel Joining
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Solution Overview
Problem
Existing self-piercing rivets, such as the C rivet, face limitations in achieving high joint quality and load-bearing capacity, particularly with high-strength sheet steel, due to stress during joining, gap formation, and deformation issues.
Innovation Solution
A self-piercing rivet with a specialized geometry featuring a conical underhead chamfer and shank face design, which reduces joining forces, minimizes deformation, and ensures uniform stress distribution, allowing for optimized joint quality and load-bearing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional C rivet geometry is used, then the rivet can be manufactured with simple production engineering possibilities, but the achievable joint quality and load bearing capacity are limited when joining high strength sheet steel
Solution Approach 1:
The patent applies local quality by providing different geometric features at different locations of the rivet. The underhead region has a specific chamfer angle (20°+5°/-5°) and radius configuration, while the foot region has a different geometry with a conical shank inside chamfer (45°+10°/-5°) and plane shank face. This localized geometric optimization addresses the specific stress and deformation requirements at each region during the self-piercing riveting process, thereby improving joint quality and load bearing capacity without compromising manufacturability.
2Ease of manufacture
If the underhead radius is made larger to reduce stress concentration, then manufacturing becomes easier, but gap formation between the rivet and metal sheets increases
Solution Approach 1:
The patent applies parameter changes by precisely defining the underhead radius as less than 0.30, in particular 0.15 times the diameter of the cylindrical shank exterior, and the underhead chamfer angle as 20°+5°/-5°. These optimized parameters balance the competing requirements: the radius is sufficiently large to reduce stress concentration and facilitate manufacturing, yet small enough to minimize gap formation between the rivet and metal sheets during the joining process.
3Strength
If the joining forces are reduced to minimize damage and cracking, then the rivet geometry must be optimized, but this increases the complexity of the rivet design
Solution Approach 1:
The patent reduces joining forces and minimizes damage and cracking by implementing local geometric optimizations rather than overall complexity increases. Specifically, the underhead region features a controlled radius (less than 0.30, in particular 0.15 times the shank diameter) and chamfer angle (20°+5°/-5°), while the foot region has a conical shank inside chamfer (45°+10°/-5°) and plane shank face. These localized features distribute stresses more effectively during piercing and setting, reducing peak forces without requiring complex overall rivet design.
4Stress or pressure
If the conical underhead chamfer angle is optimized to reduce tensile forces in the rivet shank, then the stress distribution becomes more homogeneous, but the manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the conical underhead chamfer angle to 20°+5°/-5° and the conical shank inside chamfer to 45°+10°/-5°. These parameter changes create a more homogeneous stress distribution in the rivet shank during the joining process. The tolerance ranges (+5°/-5° and +10°/-5°) are specified to balance manufacturing precision requirements with the need for optimized stress distribution, making the design both performant and manufacturable.
Data Source
AI summary
A self-piercing rivet of a special rivet geometry is described, which in particular is suitable for joining high strength steel sheets, but can also be used for other metal sheets. The self-piercing rivet is in particular characterized by a special underhead geometry as well as a special geometry of the rivet foot (cutting region). Thus the self-piercing rivet has an underhead chamfer which with a radial plane of the self-piercing rivet encloses an angle of 20°+5°/−5° and merges tangentially into the cylindrical outer surface of the rivet shank via a radius. In the region of the rivet foot the self-piercing rivet has a plane shank face, which extends essentially at a right angle to the rivet axis and which merges “smoothly” into the cylindrical inner surface via a shank inner surface and a radius. In comparison to conventional self-piercing rivets the special rivet geometry enables lower joining forces and tensile forces in the joining operation, an optimized load bearing performance and an optimum joint quality of the self-piercing rivet joint as well as minimum gap formation between the rivet and the metal sheet.