Self-Piercing Rivet Geometry for Stable High-Strength Steel Joints
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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.
Innovation Solution
A self-piercing rivet design with a reduced axial recess depth ratio (less than 0.3) and a flat surface section at the foot end, which focuses on an upsetting operation rather than expansion, enhancing stability and connection strength by using a semi-tubular design with a frustoconical recess and specific dimensions to accommodate high-strength materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the axial depth of the shank cavity is increased to achieve sufficient expansion after piercing, then the expansion behaviour is improved, but the rivet shank becomes more prone to compression and twisting, and may fracture
Solution Approach 1:
The patent changes the geometric parameters of the shank cavity, specifically reducing the axial depth ratio to less than 0.3 (preferably 0.25 or less), and modifies the cavity shape to frustoconical with a flat surface section at the foot end. These parameter changes optimize the balance between expansion capability and structural stability, preventing shank compression and twisting while ensuring adequate connection strength.
Solution Approach 2:
The patent introduces asymmetry in the shank cavity design by creating a frustoconical shape with a flat surface section at the foot end, rather than a symmetric cylindrical or uniformly tapered cavity. This asymmetric geometry directs the deformation more uniformly and prevents twisting of the shank during the piercing and expansion process.
2Strength
If the rivet shank is designed to expand significantly after piercing, then the connection strength is improved, but the punching force required increases and the rivet may fracture
Solution Approach 1:
The patent optimizes the geometric parameters of the shank cavity, reducing the axial depth ratio to less than 0.3 and designing a frustoconical shape with a flat surface section. These parameter changes enable the rivet to achieve sufficient connection strength through controlled deformation while reducing the peak punching force required during installation.
3Ease of operation
If the self-piercing rivet is designed with a pointed foot end to facilitate piercing, then the piercing ability is improved, but the expansion behaviour becomes unstable and the rivet may twist or fracture
Solution Approach 1:
The patent replaces the symmetric pointed foot end with an asymmetric frustoconical cavity design that has a flat surface section at the foot end. This asymmetric geometry provides stable piercing capability while ensuring uniform expansion behaviour and preventing twisting during the deformation process.
Solution Approach 2:
Instead of using a pointed foot end that concentrates stress and causes unstable expansion, the patent inverts the approach by using a frustoconical cavity with a flat surface section at the foot end. This inverted geometry distributes the deformation more evenly and achieves stable piercing and expansion.
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 solution provides a stable and strong connection by minimizing undercut and maximizing deformation within a die, allowing for effective piercing through high-strength steels with reduced punching forces, ensuring connection strength and stability.
Implementation Method 1
a deformation of the self-piercing rivet that is less focused 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.