Self-Piercing Rivet Die Geometry to Prevent Cracks and Buckling
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Solution Overview
Problem
Joining methods using self-piercing rivets often result in crack development in die-cast materials with reduced extensibility due to increased stress concentrations and lack of extensibility, leading to potential buckling and interlock deficiencies.
Innovation Solution
A joining device and method featuring a die with specific concave portions and a self-piercing rivet design, including a first concave portion, a second concave portion, and a terrace portion, which disperses stress and prevents crack formation by allowing the foot portion to spread outward, reducing the risk of buckling and ensuring interlock strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a self-piercing rivet is driven into die-cast members with reduced extensibility, then joining strength is achieved, but stress concentration causes crack development
Solution Approach 1:
The die cavity is segmented into multiple functional zones: a first cavity for initial rivet deformation, a second cavity for further deformation control, and a terrace portion for stress distribution. This segmentation allows progressive deformation that reduces stress concentration and prevents crack development in low-extensibility materials while maintaining joining strength.
Solution Approach 2:
Different regions of the die cavity are designed with different geometries and depths to create localized deformation zones. The first cavity, second cavity, and terrace portion each provide specific local conditions for rivet deformation, allowing controlled stress distribution that accommodates the reduced extensibility of die-cast materials while achieving strong joints.
2Strength
If the rivet foot portion is constrained during deformation, then interlock strength is improved, but buckling risk increases in low-extensibility materials
Solution Approach 1:
The die cavity is divided into a first cavity and a second cavity with different geometries. The first cavity provides initial deformation space while the second cavity provides additional constraint. This segmented approach allows the rivet to deform progressively, achieving interlock strength while the distributed constraints prevent buckling in low-extensibility materials.
Solution Approach 2:
The terraced structure introduces a vertical dimension to the die cavity design, creating stepped levels that provide both deformation space and constraint. This three-dimensional configuration allows the rivet to deform in a controlled manner, achieving interlock while preventing buckling through multi-level geometric constraints.
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 effectively suppresses crack development and ensures strong interlocks in members with varying hardness and extensibility, preventing buckling and interlock deficiencies while maintaining joint strength.
Implementation Method 1
the foot portion of the self-piercing rivet is spread outward by the terrace portion
Implementation Method 2
a first concave portion recessed in a substantially cylindrical shape in a direction of driving the self-piercing rivet is formed on the die, a second concave portion recessed in the direction of driving the self-piercing rivet is formed in a central portion on a bottom face of the first concave portion
Data Source
AI summary
A joining device comprises a die and driving means. A first concave portion is recessed in a substantially cylindrical shape in a driving direction on the die, and a second concave portion is recessed in the driving direction in a central portion on a bottom face of the first concave portion. A portion on an external side of the second concave portion on the bottom face of the first concave portion forms a terrace portion that is shallower than the second concave portion, and a diameter of the foot portion of the self-piercing rivet corresponds to a diameter of the terrace portion. In driving the foot portion of the self-piercing rivet toward the terrace portion of the first concave portion, the foot portion of the self-piercing rivet is spread outward by the terrace portion and a part of the members to be joined runs into the second concave portion.