Self-Piercing Rivet Geometry for Joining UHSS to Dissimilar Sheet
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Solution Overview
Problem
Self-piercing rivets face challenges when joining Ultra High Strength Steel (UHSS) due to its high tensile strength, leading to shank collapse and insufficient engagement, and using high-hardness rivets results in brittle joints prone to failure under dynamic loads.
Innovation Solution
A method involving a self-piercing rivet with a shank having a larger outer diameter at the top than the bottom, which flares outwardly to cut a slug from the UHSS and then pushes into a non-UHSS layer, allowing the non-UHSS layer to deform around the flared shank, forming a strong joint without relying on shank flaring in the lower layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the shank wall thickness is increased to prevent collapse when penetrating UHSS, then the column strength of the shank is improved, but the flaring capability is reduced resulting in insufficient engagement with the lower sheet
Solution Approach 1:
The shank is designed with non-uniform wall thickness, having a first wall thickness in a first region and a second wall thickness in a second region. This local variation allows the shank to have sufficient column strength in certain regions while maintaining flaring capability in other regions, resolving the contradiction between preventing collapse and enabling engagement.
Solution Approach 2:
The invention changes the geometric parameters of the shank by varying the wall thickness along its length. This parameter modification enables the shank to exhibit different mechanical behaviors in different regions - sufficient rigidity to prevent collapse during penetration while maintaining the ability to flare for engagement with the lower sheet.
2Strength
If a rivet with very high hardness is used to penetrate UHSS without collapsing, then the penetration capability is improved, but the rivet becomes brittle and prone to cracking under dynamic loads
Solution Approach 1:
The shank incorporates different hardness values in different regions - a first hardness in a first region and a second hardness in a second region. This local differentiation allows the shank to have high hardness for penetration capability in certain regions while maintaining lower hardness and better toughness in other regions to resist cracking under dynamic loads.
Solution Approach 2:
The invention creates a composite structure within the rivet shank by combining materials or heat treatment zones with different hardness properties. This internal composite approach allows the rivet to exhibit both high penetration capability and resistance to dynamic loading without requiring uniform high hardness throughout.
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 creates a strong and corrosion-resistant joint by ensuring contact between the rivet shank and UHSS around the circumference, preventing moisture ingress and improving fatigue life, while reducing the need for excessive force and minimizing the risk of joint failure.
Implementation Method 1
the lower portion of the shank flares outwards and cuts a slug from the UHSS
Implementation Method 2
pushing the flared shank of the self-piercing rivet and the slug into the non-UHSS layer such that the non-UHSS layer deforms into a die recess and flows around an outer surface of the flared shank
Data Source
AI summary
According to a first aspect of the invention there as provided a method of forming a riveted joint comprising a UHSS layer and a non-UHSS layer using a self-piercing rivet comprising a head and a shank, an outer diameter of a top of the shank being greater than an outer diameter of a bottom of the shank before insertion of the rivet, the method comprising pushing the self-piercing rivet into the UHSS layer such that the lower portion of the shank flares outwards and cuts a slug from the UHSS, and pushing the flared shank of the self-piercing rivet and the slug into the non-UHSS layer such that the non-UHSS layer deforms into a die recess and flows around an outer surface of the flared shank.