Self-Piercing Rivet Recess Geometry for Stable High-Strength Steel Joining

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Solution Overview

Problem

Self-piercing rivets used for joining high tensile and super high tensile steels often face issues with asymmetrical spreading, shank bending, and high setting forces, which can lead to rivet fracture and damage during the joining process.

Innovation Solution

The introduction of an axial circular recess at the transition between the head and shank of the self-piercing rivet reduces setting forces by allowing the head protrusion to stand out radially, preventing cracks and maintaining stability, with a preferred ratio of axial recess depth to shank diameter optimized for high tensile steels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If self-piercing rivets are used for joining high tensile steels, then joint strength is achieved, but asymmetrical spreading and shank bending occur leading to rivet fracture

Engineering Contradiction:

Improvejoint tensile strengthVSAvoidrivet stability during setting

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention introduces an asymmetrical axial recess in the rivet shank that is offset from the central axis. This asymmetrical geometry creates a counterbalancing effect during the setting process, preventing the shank from bending asymmetrically and ensuring stable rivet formation when joining high tensile steels

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The axial recess creates a localized region with different mechanical properties in the shank. This local modification allows the rivet to accommodate high setting forces without fracturing, while maintaining overall structural integrity and joint strength

Inventive Principle:

Principle #3Local quality

2Strength

If high setting forces are applied to join high tensile steels, then joint strength is achieved, but rivet damage and workpiece damage occur

Engineering Contradiction:

Improvejoint tensile strengthVSAvoidrivet and workpiece damage

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The axial recess acts as a cushioning feature that absorbs and distributes the high setting forces before they reach critical stress concentrations. This pre-cushioning effect prevents damage to both the rivet and the workpiece during the joining process while still achieving the required joint strength

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If the axial recess depth is increased to reduce setting forces, then rivet stability improves, but undercut size increases requiring larger rivet dimensions

Engineering Contradiction:

Improverivet stability during settingVSAvoidrivet shank volume

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The invention optimizes the parameters of the axial recess, specifically maintaining a depth-to-diameter ratio between 0.1 and 0.3. This parameter optimization achieves the necessary rivet stability and reduces setting forces without creating excessive undercut that would require larger rivet dimensions

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11408457B2Self-piercing rivet and self-piercing riveted joint

Publication Date: 2022.08.09 NEWFREY LLC

AI summary

A self-piercing rivet for joining workpieces comprises: a head defining a head diameter, and a shank which defining a shank diameter. The shank on a foot end opposite to the head, partially defines an axial recess which has an axial depth. The shank further includes a flat surface portion or a circular cutter on the foot end. And an axial circular recess is partially defined in a transition portion between the head and the shank.