Self-Piercing Rivet Geometry for Stable Joining of High-Strength Steel
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Solution Overview
Problem
Existing self-piercing riveted joints for high-strength and super-high-strength steels face issues with asymmetrical expansion, shank compression, twisting, and potential fracturing, making it difficult to achieve reliable connections with sufficient strength.
Innovation Solution
A self-piercing rivet design with a reduced axial recess depth ratio to shank diameter, a flat surface section at the foot end, and a frustoconical recess to promote upsetting rather than expansion, ensuring stability and sufficient connection strength through counter-pressure from high-strength steels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the axial depth of the shank cavity is increased to reduce expansion, then the rivet shank becomes less stable and more prone to asymmetrical deformation and fracturing
Solution Approach 1:
The patent optimizes the axial depth of the shank cavity within a specific range (0.2-0.5 times the shank diameter) rather than maximizing it. This parameter optimization balances the reduction of expansion with maintaining rivet stability, preventing asymmetrical deformation and fracturing while ensuring adequate connection strength.
Solution Approach 2:
The patent specifies that the rivet shall be produced from steel with a hardness of greater than 500 HV, creating a composite structure where the high-hardness material compensates for the moderate cavity depth, providing both the needed expansion control and structural stability against asymmetrical deformation.
2Strength
If the rivet shank is designed to expand during piercing, then the rivet can form a secure connection, but the expansion becomes asymmetrical causing shank compression and twisting
Solution Approach 1:
The patent controls the expansion symmetry by optimizing the axial depth of the shank cavity to 0.2-0.5 times the shank diameter. This parameter control ensures that the rivet expands sufficiently to form a secure connection while maintaining symmetrical deformation characteristics that prevent shank compression and twisting.
Solution Approach 2:
The patent creates local quality differences by specifying a frustoconical recess shape with specific dimensional relationships. This localized geometric feature at the foot end of the rivet promotes uniform radial expansion while the overall rivet geometry maintains symmetrical deformation characteristics.
3Stability of the object's composition
If the axial depth of the shank cavity is decreased to improve stability, then the rivet shank expands excessively and fails to achieve sufficient connection strength
Solution Approach 1:
The patent establishes a minimum axial depth of 0.2 times the shank diameter to ensure adequate expansion control for achieving sufficient connection strength, while simultaneously setting a maximum of 0.5 times the shank diameter to maintain rivet stability. This parameter range resolves the contradiction between stability and strength.
Solution Approach 2:
The patent uses high-hardness steel (greater than 500 HV) as the rivet material, which compensates for the moderate axial cavity depth. The high-strength material enables the rivet to achieve sufficient connection strength even with limited expansion, while maintaining stability.
4Ease of manufacture
If a pointed rivet foot is used to pierce high-strength steel, then piercing is easier, but the rivet shank expands excessively and becomes unstable
Solution Approach 1:
The patent employs a frustoconical recess shape at the foot end of the rivet, creating an asymmetric geometry that concentrates stress during piercing to facilitate penetration of high-strength steel. Simultaneously, the overall symmetric configuration and controlled cavity depth prevent excessive expansion and maintain shank stability.
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 design achieves symmetrical deformation, increased stability, and effective connection strength in high-strength steels, allowing for reliable piercing and upset formation without excessive expansion or fracturing, suitable for high-strength and super-high-strength steel applications.
Implementation Method 1
a deformation of the self-piercing rivet that is less focussed on an expansion of the rivet shank is produced during the self-piercing riveting method. Rather, the effect achieved by the relatively short axial depth of the recess is that the connection is formed by an upsetting operation of the rivet
Data Source
Figure 1~2
Figure 3
AI summary
Self-piercing rivet (10) for connecting high-strength steels, with a head (12) which has a head diameter (DH), and with a shank (14) which has a shank diameter (DS), wherein, at the foot end (18) opposite the head (12), the shank (14) has an axial recess (22) which has an axial depth (LB), and wherein, at the foot end (18), the shank has a flat surface section (20). The ratio of axial depth (LB) of the recess (22) to shank diameter (DS) is in this case smaller than 0.3.