Self-Piercing Rivet Insert Structure for AHSS Flaring
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Solution Overview
Problem
Self-piercing rivets face challenges when joining high-strength and low-ductility materials like advanced high-strength steel (AHSS) and ultra-high strength steel (UHSS), as they result in limited flaring, high stresses, and potential cracking, leading to weakened structural stability and vulnerability to corrosion.
Innovation Solution
A method involving a rivet with a hollow shank and an insert, where the insert is received within the rivet interior, driven into the workpiece to cause flaring and interlock, reducing internal stresses and requiring standard tooling, thus avoiding specialized tooling and promoting flaring even in high-strength materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a stronger rivet is used to penetrate AHSS or UHSS, then the rivet can penetrate the high-strength material, but the reduced ductility of the rivet results in limited flaring and high stresses
Solution Approach 1:
The rivet system is segmented into two functional components: a strong insert for penetrating the high-strength material and a more ductile rivet body for flaring and creating the mechanical interlock. This segmentation allows each component to be optimized for its specific function, resolving the contradiction between penetration strength and flaring ductility
Solution Approach 2:
The insert is nested within the rivet interior, with the insert serving as an internal reinforcement. This nested configuration allows the strong insert to provide penetration capability while the outer rivet structure maintains ductility for flaring, effectively combining the advantages of both strong and ductile materials
2Strength
If a stronger rivet is used to penetrate AHSS or UHSS, then the rivet can penetrate the high-strength material, but extremely high stresses are generated resulting in cracking
Solution Approach 1:
By segmenting the rivet system into a strong insert and a ductile rivet body, the stress distribution is improved. The ductile rivet body can undergo plastic deformation to accommodate stress, preventing crack initiation and propagation that would occur in a fully high-strength rivet
Solution Approach 2:
The material parameters of the rivet system are changed by combining materials with different mechanical properties. The insert uses high-strength material for penetration while the rivet body uses material with higher ductility, creating a composite structure that reduces peak stresses and prevents cracking
3Strength
If a stronger rivet is used to penetrate AHSS or UHSS, then the rivet can penetrate the high-strength material, but the limited flaring weakens the structural stability
Solution Approach 1:
The segmentation of the rivet system allows the rivet body to be made from material with superior ductility, enabling adequate flaring and mechanical interlock formation. This resolves the contradiction by decoupling the penetration function (handled by the strong insert) from the interlock function (handled by the ductile rivet body)
Solution Approach 2:
The rivet system functions as a composite structure combining high-strength material in the insert with high-ductility material in the rivet body. This composite configuration enables both penetration of high-strength workpieces and adequate flaring for structural 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
This method effectively reduces residual stresses, prevents cracking, and enhances the mechanical interlock between the rivet and workpiece, improving the structural integrity and corrosion resistance of the joint.
Implementation Method 1
the geometry of the die is such that it is able to resist the force of the setting apparatus in a direction normal to the layers of material whilst encouraging outward flaring of the rivet shank
Data Source
AI summary
A method of riveting comprising providing a rivet having a head and a shank depending downwardly therefrom, the shank terminating in a tip and being hollow so as to define a rivet interior, receiving an insert at least partially within the rivet interior, placing the rivet and insert on the opposite side of a workpiece from a die, driving the rivet and the insert towards the die and into the workpiece under the action of a force using a punch along a central axis, and reacting the force using the die so as to cause the rivet to flare outwardly and interlock the workpiece.